Test Protocol for One-way IP Capacity Measurement

The performance community has seen development of Informative Bulk Transport Capacity definitions in for Framework for Bulk Transport Capacity (BTC) for Network Capacity and Maximum IP-layer Capacity, and the Experimental metric definitions and methods in , Model-Based Metrics for BTC. This document specifies the UDP Speed Test Protocol (UDPSTP) enabling the measurement of Network Capacity metrics as defined by . The Method of Measurement discussed there deploys a feedback channel from the receiver to control the sender's transmission rate in near-real-time. This protocol supports measurement features which weren't available by TCP based speed tests and standard measurement protocols like One Way Active Measurement Protocol (OWAMP) , Two-Way Active Measurement Protocol (TWAMP) and Simple Two-Way Active Measurement Protocol (STAMP) prior to this work. The controlled Bulk Capacity measurement or Speed Test, respectively, is based on UDP rather than TCP. The bulk measurement load is unidirectional. Apart from measurement functionality, the UDPSTP security features have been developed following guidance given by the IETF Security Area and the resulting specification is compliant with state of the art security implementations. This is a secondary improvement reached by the UDPST Protocol and may simplify its reuse for other measurement purposes.

Downstream UDP Speed Test: a client initiated Network Capacity measurement between a server acting as sender and a client acting as receiver. Upstream UDP Speed Test: a client initiated measurement of Network Capacity measurement between a client acting as a sender and a server acting as receiver.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 , when, and only when, they appear in all capitals, as shown here.

The scope of this document is to define a protocol to measure the Maximum IP-Layer Capacity metric according to the Method of Measurement standardized by Section 8 of . Some aspects of this protocol and end-host configuration can lead to support of additional forms of measurement, such as application emulation enabled by creative use of the load rate adjustment algorithm. The goal is to harmonize the specified IP-Layer Capacity metric and method across the industry, and this protocol supports the specifications of IETF and other Standards Development Organizations (SDO's; see, e.g., ). The primary application of the protocol described here is the same as in Section 2 of where: The access portion of the network is the focus of this problem statement. The user typically subscribes to a service with bidirectional access partly described by rates in bits per second.

All messages defined by this document SHALL use UDP transport. The remainder of this section gives an informative overview of the communication protocol between two test endpoints (without expressing requirements or elaborating on the authentication and encryption aspects). One endpoint takes the role of server, listening for connection requests on a standard UDP Speed Test Protocol port number from the other endpoint, the client. The client requires configuration of a test direction parameter (upstream or downstream test, where the client performs the role of sender or receiver, respectively) as well as the hostname or IP address(es) of the server(s) in order to begin the setup and configuration exchanges with the server(s). By default, the client uses the single, standard UDPSTP port number per connection (see ). If the default port number is not used, the client may require configuration of the control port number used by each server. This would be the case, if multiple server instances (processes) operate on one or more machines. Additionally, multi-connection (multi-flow) testing is supported by the protocol. Each connection is independent and attempts to maximize its own individual traffic rate. For multi-connection tests, a single client process would replicate the connection setup and test procedure multiple times (once for each flow) to one or more server instances. The server instance(s) would process each connection independently, as if they were coming from separate clients. It shall be the responsibility of the client process to manage the inter-related connections: handling the individual connection setup successes and failures, cleaning up connections during a test (should some fail) as well as aggregate the individual test results into an overall set of performance statistics. Fields in the Setup Request (mcIndex, mcCount, and mcIdent, see ) are used to both differentiate and associate the multiple connections that comprise a single test. The protocol uses UDP transport with two connection phases (Control and Data). The exchanges 1 and 2 (see below) constitute the Control phase, while exchanges 3 and 4 constitute the Data phase. In this document, the term message and the term Protocol Data Unit, or PDU () are used exchangeable. If a server instance is identified with a host name that resolves to both IPv4/IPv6 addresses, it is recommended to use the first address returned in the name resolution response - regardless, whether it's IPv4 or IPv6. Thus the decision on the preferred IP address family is left to the DNS operator. Support for separate IPv4 and IPv6 measurements or an IPv4 and IPv6 multi connection setup are left for future improvement. The client then requests to begin a test by communicating its protocol version, intended security mode, and datagram size support. The server either confirms matching a configuration or rejects the connection request. If the request is accepted, the server provides a unique ephemeral port number for each test connection, allowing further communication. In a multi-connection setup, distinct UDP port numbers may be assigned with each Setup Response from a server instance. Distinct UDP port numbers are assigned, if all Setup Response messages originate from the same server in that case. Test Activation Request and Response: after having received a confirmation of the configuration by a server, the client composes a request conveying parameters such as the testing direction, the duration of the test interval and test sub-intervals, and various thresholds (for a detailed discussion, see and ). The server then chooses to accept, ignore or modify any of the test parameters, and communicates the set that will be used unless the client rejects the modifications. Note that the client assumes that the Test Activation exchange has opened any co-located firewalls and network address/port translators for the test connection (in response to the Request packet on the ephemeral port number) and the traffic that follows. See for a more detailed discussion of firewall and NAT related features. If the Test Activation Request is rejected or fails, the client assumes that the firewall will close the address/port number pinhole entry after the firewall's configured idle traffic timeout. Test Stream Transmission and Measurement Feedback Messages: Testing proceeds with one endpoint sending Load PDUs and the other endpoint receiving the Load PDUs and sending frequent status messages to communicate status and transmission conditions there. The data in the feedback messages, whether received from the client or when being sent to the client, is input to a load rate adjustment algorithm at the server which controls future sending rates at either end. The choice to locate the load rate adjustment algorithm at the server, regardless of transmission direction, means that the algorithm can be updated more easily at a host within the network, and at a fewer number of hosts than the number of clients. Note, that this mode of operation also keeps the keep the pinhole (or mapping, resepcitvely) active at on-path stateful devices. UDPSTP is at least partially compliant to section 3.1 of : the bottleneck is congested, but pending congestion is avoided by limiting the duration of that congestion to the minimum required to determine the bottleneck capacity. Stopping the Test: When the specified test duration has been reached, the server initiates the exchange to stop the test by setting a STOP indication in its outgoing Load PDUs or Status Feedback messages. After being received, the client acknowledges it by also setting a STOP indication in its outgoing Load PDUs or Status Feedback messages. A graceful connection termination at each end then follows. Since the Load PDUs and Status Feedback messages are used, this exchange is considered a sub-exchange of 3. If the Test traffic stops or the communication path fails, the client assumes that the firewall will close the address/port number combination after the firewall's configured idle traffic timeout. Both the client and server react to unexpected interruptions in the Control or Data phase, respectively. Watchdog timers limit the time a server or client will wait before stopping all traffic and terminating a test. Figure 1 provides an example exchange of control and measurement PDUs for both a downstream and upstream UDP Speed Tests (always client initiated):

=========== Downstream Test =========== +---------+ +---------+ | Client | Test Setup Request -----> | Server | +---------+ +---------+ <----- Test Setup Response (Accept) <----- Null Request PDU Test Activation Request -----> <----- Test Activation Response (Accept) <----- Load PDUs Status Feedback PDUs -----> After expiry of server's test duration timer... <----- Load PDU (TEST_ACT_STOP) Status Feedback PDU (TEST_ACT_STOP) -----> ============ Upstream Test ============ +---------+ +---------+ | Client | Test Setup Request -----> | Server | +---------+ +---------+ <----- Test Setup Response (Accept) <----- Null Request PDU Test Activation Request -----> <----- Test Activation Response (Accept) Load PDUs -----> <----- Status Feedback PDUs After expiry of server's test duration timer... <----- Status Feedback PDU (TEST_ACT_STOP) Load PDU (TEST_ACT_STOP) -----> Figure 1: Successful UDPSTP Message Exchanges

Security and checksum operation aren't covered by , which only defines the Method of Measurement. This section adds the operational specification related to security and optional checksum. Due to the additional complexities, and loss of the direct Layer 3 to Layer 4 mapping of packets to datagrams, it is recommended that Layer 3 fragmentation be avoided. A simplified approach is to choose the default datagram size small enough to prevent fragmentation. MTU size detection prior to a test is out of scope of this document. A method to detect the path MTU size are proposed by .

Please refer to Section 4 of for an overview of Parameters related to the Maximum IP-Layer Capacity Metric and Method. A set of error-codes to support debugging are provided in .

There are four security modes of operation, one unauthenticated mode, two authenticated modes and a fourth adding encryption. Operational support of unauthenticated and authenticated modes MUST be mutually exclusive. Once the modes requiring or optionally adding authentication or encryption are implemented and configured locally, the unauthenticated mode must be disabled. The four modes are: An OPTIONAL Unauthenticated mode for all messages shall only be allowed when all other modes requiring authentication (or Partial Encryption) are blocked or unavailable for use. This mode is intended for a lab or limited domain . A REQUIRED mode with authentication during the Control phase (Test Setup and Test Activation exchanges). An OPTIONAL mode with the additional authentication of the Status Feedback messages during the Data phase. An OPTIONAL mode that adds encryption, prior to authentication, of the Control phase exchanges and the Status Feedback messages. This mode is optional, as Performance measurements don't transport application data and encryption has impact on or at least may impact performance measurements (especially on very low-end devices). The requirements discussed hereafter refer to the PDUs in sections 5 and 6 below, primarily the authMode, keyId, authUnixTime, initVector, and authDigest fields. The roles in this section have been generalized so that the requirements for the PDU sender and receiver can be re-used and referred to by other sections within this document. Each successive mode increases security, but comes with additional performance impacts and complexity. The protocol is used with unsubstantial payload and it may operate on very low-end devices. Offering the flexibility of various security operation modes allows for adoption of available end-device resources. In general, an active measurement technique as the one defined by this document is better suited to protect the privacy of those involved in measurement .

In this mode, all PDU senders SHALL set the keyId, authUnixTime, the initVector, and the authDigest fields of all related packets to zero. Any errors (configuration miss-match between client and server) found in the Test Setup exchange or the Test Activation exchange SHOULD result in silent rejection (no further packets sent on the address/port pairs). The exception is when the testing hosts have been configured for troubleshooting control phase failures and rejection messages will aid in the process.

In this mode, the client and the server SHALL be configured to use one of a number of shared secret keys, designated via the numeric keyId field (see ). During the Control phase, the sender SHALL read the current system (wall-clock) time and populate the authUnixTime field, then calculate the authDigest field of the entire PDU according to section 6 of (with initVector and authDigest preset to all zeroes) and send the packet to the receiver. The value in the authUnixTime field is a 32-bit time stamp and a 10-second tolerance window (+/- 5 seconds) SHALL be used by the receiver to distinguish a subsequent replay of a PDU. See Table 2 of for a recommended timestamp resolution. Upon reception, the receiver SHALL validate the message PDU for correct length, validity of authDigest, immediacy of authUnixTime, and expected formatting (PDU-specific fields are also checked, such as protocol version). Validation of the authDigest requires that it will be extracted from the PDU and the field zeroed prior to the HMAC calculation used for comparison (see section 7.2 of ). If the validation fails, the receiver SHOULD NOT continue with the Control phase and implement silent rejection (no further packets sent on the address/port pairs). The exception is when the testing hosts have been configured for troubleshooting Control phase failures and rejection messages will aid in the process. If the validation succeeds, the receiver SHALL continue with the Control phase and compose a successful response or a response indicating the error conditions identified (if any). This process SHALL be executed for the request and response in the Test Setup exchange, including the Null Request () and the Test Activation exchange ().

This mode incorporates Authenticated mode 1. When using the optional authentication during the Data phase, authentication SHALL also be applied to the Status Feedback PDU (see ). The client sends the Status PDU in a downstream test, and the server sends it in an upstream test. The Status PDU sender SHALL read the current system (wall-clock) time and populate the authUnixTime field, then calculate the authDigest field of the entire Status PDU (with the initVector and authDigest field set to all zeroes) and send the packet to the receiver. Upon reception, the receiver SHALL validate the message PDU for correct length, validity of authDigest, immediacy of authUnixTime, and expected formatting (PDU-specific fields are also checked, such as protocol version). Validation of the authDigest will require that it be extracted from the PDU and the field zeroed prior to the HMAC calculation used for comparison. If the authentication validation fails, the receiver SHALL ignore the message. If the watchdog timer expires (due to successive failed validations), the test session will prematurely terminate (no further load traffic SHALL be transmitted). If this optional mode has not been selected, then the keyId, authUnixTime, initVector, and authDigest fields of the Status PDU (see ) SHALL be set to all zeroes.

This mode incorporates authentication mode 2 after encryption of all fields prior to the authMode field. This is done for all Control and Status Feedback messages. The encryption algorithm only provides encryption and relies on the existing authentication mechanism to provide integrity protection. Adding encryption to prior authentication allows to re-use code of optional authentication mode, and additionally allows to re-use several protocol fields. Still, both authentication and encryption are provided. See sections to for the field format. When using the optional Partial Encryption, the process SHALL be applied to the Test Setup Request, the Test Setup Response, the Null Request (if applicable), the Test Activation Request, the Test Activation Response, and the Status PDU. The client sends the Status PDU in a downstream test, and the server sends it in an upstream test. In the OPTIONAL Partial Encryption mode, the client and the server SHALL be configured to use one of a number of shared secret keys (see keyId). The following encryption specifications SHALL be used for this : Advanced Encryption Standard, AES, according to Federal Information Processing Standards Publication 197 Cipher Block Chaining (CBC) Key size of 128 bits (fixed block size of 128 bits) The encrypted portion of each PDU SHALL contain the padding required to maintain a multiple of the AES CBC block size of 16 octets. As such, any library functions used for encryption and decryption SHALL have padding disabled (to maintain an equal encrypted and unencrypted length). In OpenSSL for example, this can be accomplished via "EVP_CIPHER_CTX_set_padding(ctx,0)". The sender SHALL populate the initVector field with a random 16-octet Initialization Vector (IV). The IV, in conjunction with the shared secret key, SHALL be used to encrypt the header up to, but not including, the authMode field. The shared secret key is designated via the keyId field. The sender SHALL then read the current system (wall-clock) time and populate the authUnixTime field and then calculate (and populate) the authDigest, for the entire PDU, in the same manner as specified with Authentication modes 1 and 2. Finally, the sender SHALL send the packet with partially encrypted PDU to the receiver. Upon reception, the receiver SHALL validate the message PDU for correct length, validity of authDigest, and immediacy of authUnixTime. Validation of the authDigest will require that it be extracted from the PDU and the field zeroed prior to the HMAC calculation used for comparison. If the PDU validation succeeds, the receiver SHALL then decrypt the initial portion of the PDU using the included IV and shared key designated by the keyId. Finally, the PDU-specific fields that control the test are validated and processed. If the PDU validation fails in the Control phase, the receiver SHOULD NOT continue with current exchange and implement silent rejection (no further packets sent on the address/port pairs). The exception is when the testing hosts have been configured for troubleshooting Control phase failures and rejection messages will aid in the process. If the validation succeeds in the Control phase, the receiver SHALL continue with the current exchange and compose a successful response or a response indicating the error conditions identified. The response PDU SHALL be encrypted and authenticated as described above using a new random 16-octet IV. The packet with partially encrypted PDU SHALL be sent back to the originator. This process SHALL be executed for the request and response in the Test Setup exchange, including the Null Request () and the Test Activation exchange (). If the PDU validation fails for a Status PDU, the receiver SHALL ignore the message. If the watchdog timer expires (due to successive failed validations), the test session will prematurely terminate (no further load traffic SHALL be transmitted).

Section 2 of specifies a conceptual database for long-lived cryptographic keys. The key table SHALL be used with the REQUIRED authentication mode and the OPTIONAL authentication mode (using the same key). The same key table and key SHALL also be used with the OPTIONAL Partial Encryption mode, when utilized. The lifetime of the long-lived keys deployed is expected be on the order of double digit seconds to avoid pending congestion of the measured bottleneck. Key rotation and related management specifics are beyond the scope of this document. The key table SHALL have (at least) the following fields, referring to Section 2 of : AdminKeyName LocalKeyName AlgID Key SendLifetimeStart SendLifetimeEnd AcceptLifetimeStart AcceptLifetimeEnd The LocalKeyName SHALL be determined from the corresponding keyId field in the PDUs that follow.

Successful interaction with a local firewall assumes the firewall to be configured allowing a host to open a bidirectional connection using unique source and destination addresses as well as port numbers by sending a packet using that 4-tuple for a given transport protocol. The client's interaction with its firewall depends on this configuration. The firewall at the server MUST be configured with an open pinhole for the server IP address and standard UDP port of the server. Assuming that the firewall administration at the server does not allow an open UDP ephemeral port range, then the server MUST send a Null Request to the client from the ephemeral port communicated to the client in the Test Setup Response. The Null Request may not reach the client: it may be discarded by the client's firewall. If the server firewall administration allows an open UDP ephemeral port range, then the Null Request is not strictly necessary. However, the availability of an open port range policy cannot be assumed. Network Address Translators are expected to offer support of a wider set of operational configurations as compared to Firewalls. Specifications covering NAT behaviour apart from the above are out of scope of this document.

All of the PDUs exchanged between the client and server support a header checksum that covers the various fields in the UDPST PDU (excluding the Payload Content of the Load PDU and, to be clear, also the IP header). This checksum is intended for environments where UDP data integrity may be uncertain. This includes situations where the standard UDP checksum is disabled or a nonstandard network API is in use (things typically done to improve performance on low-end devices). The calculation is the same as the 16-bit one's complement Internet checksum used in the IPv4 packet header (see section 3.1 of . If a PDU sender is populating the checkSum field, it SHALL do so after the PDU is built but prior to any authentication or encryption processing (i.e., all fields starting with authMode are zeroed). The PDU receiver SHALL subsequently verify the PDU checksum whenever checksum processing has been configured. Verification requires that all fields starting with authMode are zeroed prior to the checksum calculation used to verify the PDU. Because of its redundancy when authentication is being used, it is OPTIONAL for a PDU sender to utilize the checkSum field whenever the authDigest field is also utilized. However, because authentication is not applicable to the Load PDU, the checkSum field SHALL be utilized by the sender whenever UDP data integrity may be uncertain (as outlined above).

The client SHALL begin the Control phase exchanges by sending a Test Setup Request message to the server's (standard) control port. This standard UDPSTP port number is utilized for each connection of a multi-connection test (assuming each server to have a distinct IP address and / or a client to have one or more distinct IP adresseses, respectively). The client SHALL simultaneously start a test initiation timer so that if the Control phase fails to complete Test Setup and Test Activation exchanges in the allocated time, the client software SHALL exit (close the UDP socket and indicate an error message to the user). Lost messages result in a Test Setup and Test Activation failure. The test initiation timer MAY reuse the test termination timeout value. The watchdog timeout is configured as a 1 second interval to trigger a warning message that the received traffic has stopped. The test termination timeout is based on the watchdog interval, and implements a wait time of 2 additional seconds before triggering a non-graceful termination. The UDP PDU format layout SHALL be as follows (big-endian AB, most significant to least significant byte):

0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | pduId | protocolVer | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | mcIndex | mcCount | mcIdent | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | cmdRequest | cmdResponse | maxBandwidth | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | testPort |modifierBitmap | reserved1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | checkSum | reserved2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | padding (12 octets) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | authMode | keyId | reserved1a | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | authUnixTime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . initVector (16-octet) . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . authDigest (32-octet) . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: Test Setup PDU Layout Additional details regarding the Setup Request and Response fields are as follows: pduId: A two-octet field. IANA is asked to assign the value hex 0xACE1 (). protocolVer: A two-octet field, identifying the actual protocol version. IANA is asked to assign only one initial value, 20 (). mcIndex: The index of a connection relative to all connections that make up a single test (starting at 0, incremented by 1 per connection). It is used to differentiate separate connections within a multi-connection test. An implementation may restrict the number of connections supported for a single test to a value smaller or equal to 255. mcCount: The total count of attempted connections. mcIdent: A pseudorandom non-zero identifier (via a Random Number Generator, source port number,...) that is common to all connections of a single test. It is used by clients/servers to associate separate connections within a multi-connection test. cmdRequest: Is set to CHSR_CREQ_SETUPREQ to indicate a Setup request message. Note that CHSR_CREQ_NONE remains unused. cmdResponse: All Request PDUs always have a Command Response of XXXX_CRSP_NONE. maxBandwith: When this field is non-zero, it is a specification of the maximum bit rate the client expects to send or receive during the requested test. The server compares this value to its currently available configured limit for test admission control. This field MAY be used for rate-limiting the maximum rate the server should attempt. The maxBandwidth field's most significant bit, the CHSR_USDIR_BIT, is set to 0 by default to indicate "downstream" and has to be set to 1 to indicate "upstream". testPort: The UDP ephemeral port number on the server that the client has to use for the Test Activation Request and subsequent Load or Status PDUs. modifierBitmap: this document only assigns two bits in this bitmap, see : Above a sending rate of 1Gbps, allow datagram sizes that result in Jumbo Frames (with a max IP packet size of 9000 bytes). Up to a sending rate of 1Gbps, or for all sending rates if CHSR_JUMBO_STATUS is not set, datagram sizes SHALL NOT produce an IP packet size greater than 1250 bytes (unless CHSR_TRADITIONAL_MTU is also set). Allow datagram sizes, at any sending rate, that can result in a Traditional IP packet size of 1500 bytes. Effectively increasing the default non-Jumbo maximum from 1250 bytes to 1500 bytes. Other bit positions are left unassigned by this document. checkSum: An optional checksum of the entire PDU. The calculation is done with the fields checksum, authMode and those following after authMode set to zero. authMode: The authMode field currently has four values assigned (see ). One of these has to be set (see for requirements and details of operation): Optional Unauthenticated mode Required Authentication for Control phase Optional Authentication for Control and Data phase (Status Feedback PDU only) Optional Partial Encrypted mode A range of 60 through 63 is reserved for experimentation. A IANA is asked to create a registry for the assigned values; see the IANA Considerations Section. keyId: This is a localKeyName, the numeric key identifier for a key in the shared key table. authUnixTime: A 32-bit time stamp of the current system (wall-clock) time since the Unix Epoch on January 1st, 1970 at UTC. initVector: This field contains the 16-octet random IV used for Partial Encryption mode. A new random 16-octet IV SHALL be used each time encryption is performed. authDigest: This field contains the 32-octet HMAC-SHA256 hash that covers the entire PDU.

This section describes the processes at the server to evaluate the Test Setup Request and determine the next steps.

When the server receives the Setup Request, it SHALL: verify the size of the Setup Request message and if correct evaluate the authMode field, if operating in one of the Authenticated modes, validate the Setup Request message by checking the authDigest as prescribed in , and if operating in the Partial Encryption mode, use the available keyId and IV to decrypt the Setup Request message up to the authMode field using the method prescribed in Then, the server evaluates the other fields in the protocol header, such as the protocol version, the PDU ID (to validate the type of message), the maximum Bandwidth requested for the test, and the modifierBitmap for use of options such as Jumbo datagram status and Traditional MTU (1500 bytes). If the client has selected options for: Jumbo datagram support (modifierBitmap), Traditional MTU (modifierBitmap), Authentication mode (authMode) that do not match the server configuration, the server MUST reject the Setup Request. If the Setup Request must be rejected, the conditions below determine whether the server sends a response: In Authenticated modes, if the authDigest is valid, a Test Setup Response SHALL be sent back to the client with a corresponding command response value indicating the reason for the rejection. If operating in the Partial Encryption mode, the server SHALL proceed per , else the server SHALL proceed per . In Authenticated modes, if the authDigest is invalid, then the Test Setup Request SHOULD fail silently. The exception is for operations support: server administrators using authentication are permitted to send a Setup Response to support operations and troubleshooting. If Unauthenticated mode is selected, the Test Setup Request SHALL fail silently. The additional, non-authentication circumstances when a server SHALL NOT communicate the appropriate Command Response code for an error condition (fail silently) are when: the Setup Request PDU size is not equal to the 'struct controlHdrSR' size shown in figure 3, the PDU ID is not 0xACE1 (Test Setup PDU), or a directed attack has been detected, in which case the server will allow setup attempts to terminate silently. Attack detection is beyond the scope of this specification. When the server replies to a Test Setup Request message, the Test Setup Response PDU is structured identically to the Request PDU and SHALL retain the original values received in it, with the following exceptions: The cmdRequest field is set to CHSR_CREQ_SETUPRSP, indicating a response. The cmdResponse field is set to an error code (starting at cmdResponse 2, Bad Protocol Version, see ), indicating the reason for rejection. If cmdResponse indicates a bad protocol version (CHSR_CRSP_BADVER), the protocolVer field is also updated to indicate the current expected version. The PDU is encrypted up to the authMode field using a new random IV, if doing encryption. The authUnixTime field is updated to the current system (wall-clock) time and the authDigest is recalculated, if doing authentication. The Setup Request/Response message PDU SHALL be organized as follows:

<CODE BEGINS> // // Control header for UDP payload of Setup Request/Response PDUs // struct controlHdrSR { #define CHSR_ID 0xACE1 uint16_t pduId; // PDU ID #define PROTOCOL_VER 20 uint16_t protocolVer; // Protocol version uint8_t mcIndex; // Multi-connection index uint8_t mcCount; // Multi-connection count uint16_t mcIdent; // Multi-connection identifier #define CHSR_CREQ_NONE 0 #define CHSR_CREQ_SETUPREQ 1 // Setup request #define CHSR_CREQ_SETUPRSP 2 // Setup response uint8_t cmdRequest; // Command request #define CHSR_CRSP_NONE 0 // (used with request) #define CHSR_CRSP_ACKOK 1 // Acknowledgment #define CHSR_CRSP_BADVER 2 // Bad version #define CHSR_CRSP_BADJS 3 // Jumbo setting mismatch #define CHSR_CRSP_AUTHNC 4 // Auth. not configured #define CHSR_CRSP_AUTHREQ 5 // Auth. required #define CHSR_CRSP_AUTHINV 6 // Auth. (mode) invalid #define CHSR_CRSP_AUTHFAIL 7 // Auth. failure #define CHSR_CRSP_AUTHTIME 8 // Auth. time invalid #define CHSR_CRSP_NOMAXBW 9 // Max bandwidth required #define CHSR_CRSP_CAPEXC 10 // Capacity exceeded #define CHSR_CRSP_BADTMTU 11 // Trad. MTU mismatch #define CHSR_CRSP_MCINVPAR 12 // Multi-conn. invalid params #define CHSR_CRSP_CONNFAIL 13 // Conn. allocation failure uint8_t cmdResponse; // Command response #define CHSR_USDIR_BIT 0x8000 // Upstream direction bit uint16_t maxBandwidth; // Required bandwidth in Mbps uint16_t testPort; // Test port on server #define CHSR_JUMBO_STATUS 0x01 #define CHSR_TRADITIONAL_MTU 0x02 uint8_t modifierBitmap; // Modifier bitmap uint8_t reserved1; // (reserved for alignment) uint16_t checkSum; // Header checksum uint16_t reserved2; // (reserved for alignment) // uint8_t padding[12]; // Padding for encryption // ========== Encryption ends here ========== #define AUTHMODE_0 0 // Mode 0: Unauthenticated #define AUTHMODE_1 1 // Mode 1: Authenticated Control #define AUTHMODE_2 2 // Mode 2: Authenticated Control+Status #define AUTHMODE_3 3 // Mode 3: Encrypted+Auth Control+Status uint8_t authMode; // Authentication mode uint8_t keyId; // Key ID in shared table uint16_t reserved1a; // (reserved for alignment) uint32_t authUnixTime; // Authentication time stamp #define AUTH_IV_LENGTH 16 // Initialization Vector length uint8_t initVector[AUTH_IV_LENGTH] // IV #define AUTH_DIGEST_LENGTH 32 // SHA-256 digest length uint8_t authDigest[AUTH_DIGEST_LENGTH] // HMAC }; <CODE ENDS> Figure 3: Test Setup PDU

If the server finds that the Setup Request matches its configuration and is otherwise acceptable, the server SHALL initiate a new connection to receive the Test Activation Request from the client, using a new UDP socket allocated from the UDP ephemeral port range. This new socket will also be used for the subsequent Load and Status PDUs that are part of testing (with the port number communicated back to the client in the Test Setup Response). Then, the server SHALL start a watchdog timer (to terminate the new connection if the client goes silent) and SHALL send the Test Setup Response back to the client. The watchdog timer is set to the same values as on the Client side (see ) When the server replies to the Test Setup Request message, the Test Setup Response PDU is structured identically to the Request PDU and SHALL retain the original values received in it, with the following exceptions: The cmdRequest field is set to CHSR_CREQ_SETUPRSP, indicating a response. The cmdResponse field is set to CHSR_CRSP_ACKOK, indicating an acknowledgment. The testPort field is set to the ephemeral port number to be used for the client's Test Activation Request and all subsequent communication. The PDU is encrypted up to the authMode field using a new random IV, if doing encryption. The authUnixTime field is updated to the current system (wall-clock) time and the authDigest is recalculated, if doing authentication. Finally, the new UDP connection associated with the new socket and port are made ready, and the server awaits further communication there. To ensure that a server's local firewall will successfully allow packets received for the new ephemeral port, the server SHALL immediately send a Null Request with the corresponding values including the source and destination IP addresses and port numbers. The source port SHALL be the new ephemeral port. This operation allows communication to the server even when the server's local firewall prohibits open ranges of ephemeral ports. The packet is not expected to arrive successfully at the client if the client-side firewall blocks unexpected traffic. If the Null Request arrives at the client, it is a confirmation that further exchanges are possible on the new port-pair (but this is not strictly necessary). Note that there is no response to a Null Request. The UDP PDU format layout SHALL be as follows (big-endian AB):

<CODE BEGINS> // // Control header for UDP payload of Null Request PDU // struct controlHdrNR { #define CHNR_ID 0xDEAD uint16_t pduId; // PDU ID uint16_t protocolVer; // Protocol version #define CHNR_CREQ_NONE 0 #define CHNR_CREQ_NULLREQ 1 // Null request uint8_t cmdRequest; // Command request #define CHNR_CRSP_NONE 0 // (used with request) uint8_t cmdResponse; // Command response uint16_t checkSum; // Header checksum // uint8_t padding[8]; // Padding for encryption // ========== Encryption ends here ========== uint8_t authMode; // Authentication mode uint8_t keyId; // Key ID in shared table uint16_t reserved1a; // (reserved for alignment) uint32_t authUnixTime; // Authentication time stamp uint8_t initVector[AUTH_IV_LENGTH] // IV uint8_t authDigest[AUTH_DIGEST_LENGTH] // HMAC }; <CODE ENDS> Figure 5: Null Request PDU

When the client receives the Test Setup Response message, it SHALL: verify the size of the Setup Response message and if correct interrogate the authMode field, if operating in one of the Authenticated modes, validate the Setup Response message by checking the authDigest as prescribed in , if operating in the Partial Encryption mode, use the available keyId and IV to decrypt the Setup Response message up to the authMode using the method prescribed in , and then proceed to evaluate the other fields in the protocol, beginning with the protocol version, PDU ID (to validate the type of message), and cmdRequest for the role of the message, which MUST be Test Setup Response, CHSR_CREQ_SETUPRSP, as indicated by figure 3. If the cmdResponse value indicates an error (values greater than CHSR_CRSP_ACKOK) the client SHALL display/report a relevant message to the user or management process and exit. If the client receives a Command Response code that is not equal to one of the codes defined, the client MUST terminate the connection and terminate operation of the current Setup Request. If the Command Server Response code value indicates success (CHSR_CRSP_ACKOK), the client SHALL compose a Test Activation Request with all the test parameters it desires, such as the test direction, the test duration, etc., as described below.

This section is divided according to the sending and processing of the client, server, and again at the client.

Upon a successful setup exchange, the client SHALL compose and send the Test Activation Request to the UDP port number the server communicated in the Test Setup Response (the new ephemeral port, and not the standard UDPSTP port). The UDP PDU format layout is as follows (big-endian AB):

0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | txInterval1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | udpPayload1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | burstSize1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | txInterval2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | udpPayload2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | burstSize2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | udpAddon2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | pduId | protocolVer | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | cmdRequest | cmdResponse | lowThresh | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | upperThresh | trialInt | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | testIntTime | subIntPeriod | ipTosByte | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | srIndexConf | useOwDelVar |highSpeedDelta | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | slowAdjThresh | seqErrThresh | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ignoreOooDup |modifierBitmap | rateAdjAlgo | reserved1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . srStruct (28 octets) . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | reserved2 | checkSum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | padding (4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | authMode | keyId | reserved1a | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | authUnixTime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . initVector (16-octet) . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . authDigest (32-octet) . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 6: Test Activation PDU Layout Fields are populated based on default values or command-line options. Authentication and encryption modes follow the same methodology as with the Setup Request and Response. pduId: A two-octet field. IANA is asked to assign the value hex 0xACE2 (). cmdRequest: Is set to CHTA_CREQ_TESTACTUS to indicate an upstream test activation or alternatively to CHTA_CREQ_TESTACTDS to indicate a downstream test activation. Note that CHTA_CREQ_NONE remains unused. See The content of many of the unique fields in Figures 6 and 7 are defined in Section 4 of and Appendix A of . Additional details are given below. srIndexConf: The requested Configured Sending Rate Table index, used in a Test Activation Request, of the desired fixed or starting sending rate (depending on whether CHTA_SRIDX_ISSTART is cleared or set respectively). Because a value of zero is a valid fixed or starting sending rate index, the field SHALL be set to its maximum (CHTA_SRIDX_DEF) when requesting the default behavior of the server (starting the selected load rate adjustment algorithm at its minimum/zero index). This SHALL be equivalent to setting srIndexConf to zero and setting the CHTA_SRIDX_ISSTART bit. rateAdjAlgo: The applied Load Rate Adjustment Algorithm, see . modifierBitmap: this document only assigns two bits in this bitmap, see : Treat srIndexConf as the starting sending rate to be used by the load rate adjustment algorithm Randomize the Payload Content beyond the Load PDU header Other bit positions are left unassigned by this document. srStruct: Sending Rate structure, used by the server in a Test Activation Response for an upstream test, to communicate the (initial) Load PDU transmission parameters the client SHALL use. For a Test Activation Request or a downstream test, this structure SHALL be zeroed. Two sets of periodic transmission parameters are available, allowing for dual independent transmitters (to support a high degree of rate granularity). The udpAddon2 field specifies the size of a single Load PDU to be sent at the end of the txInterval2 send sequence, even when udpPayload2 or burstSize2 are zero and result in no transmission of their own. checkSum: An optional checksum of the entire PDU. The calculation is done with the checkSum field, and all fields starting with authMode, set to zero. The Test Activation Request/Response message PDU (as well as the included Sending Rate structure) SHALL be organized as follows:

<CODE BEGINS> // // Sending rate structure for a single row of transmission parameters // struct sendingRate { uint32_t txInterval1; // Transmit interval (us) uint32_t udpPayload1; // UDP payload (bytes) uint32_t burstSize1; // UDP burst size per interval uint32_t txInterval2; // Transmit interval (us) uint32_t udpPayload2; // UDP payload (bytes) uint32_t burstSize2; // UDP burst size per interval uint32_t udpAddon2; // UDP add-on (bytes) }; // // Control header for UDP payload of Test Act. Request/Response PDUs // struct controlHdrTA { #define CHTA_ID 0xACE2 uint16_t pduId; // PDU ID uint16_t protocolVer; // Protocol version #define CHTA_CREQ_NONE 0 #define CHTA_CREQ_TESTACTUS 1 // Test activation upstream #define CHTA_CREQ_TESTACTDS 2 // Test activation downstream uint8_t cmdRequest; // Command request #define CHTA_CRSP_NONE 0 // (used with request) #define CHTA_CRSP_ACKOK 1 // Acknowledgment #define CHTA_CRSP_BADPARAM 2 // Bad/invalid test params uint8_t cmdResponse; // Command response uint16_t lowThresh; // Low delay variation threshold (ms) uint16_t upperThresh; // Upper delay variation threshold (ms) uint16_t trialInt; // Status Feedback/trial interval (ms) uint16_t testIntTime; // Test interval time (sec) uint8_t subIntPeriod; // Sub-interval period (sec) uint8_t ipTosByte; // IP ToS byte for testing #define CHTA_SRIDX_DEF UINT16_MAX // Request default server rate search uint16_t srIndexConf; // Configured Sending Rate Table index uint8_t useOwDelVar; // Use one-way delay, not RTT (BOOL) uint8_t highSpeedDelta; // High-speed row adjustment delta uint16_t slowAdjThresh; // Slow rate adjustment threshold uint16_t seqErrThresh; // Sequence error threshold uint8_t ignoreOooDup; // Ignore Out-of-Order/Duplicates (BOOL) #define CHTA_SRIDX_ISSTART 0x01 // Use srIndexConf as starting index #define CHTA_RAND_PAYLOAD 0x02 // Randomize payload uint8_t modifierBitmap; // Modifier bitmap #define CHTA_RA_ALGO_B 0 // Algorithm B #define CHTA_RA_ALGO_C 1 // Algorithm C uint8_t rateAdjAlgo; // Rate adjust. algorithm uint8_t reserved1; // (reserved for alignment) struct sendingRate srStruct; // Sending rate structure uint16_t reserved2; // (reserved for alignment) uint16_t checkSum; // Header checksum // uint8_t padding[4]; // Padding for encryption // ========== Encryption ends here ========== uint8_t authMode; // Authentication mode uint8_t keyId; // Key ID in shared table uint16_t reserved1a; // (reserved for alignment) uint32_t authUnixTime; // Authentication time stamp uint8_t initVector[AUTH_IV_LENGTH] // IV uint8_t authDigest[AUTH_DIGEST_LENGTH] // HMAC }; <CODE ENDS> Figure 7: Test Activation PDU

After the server receives the Test Activation Request on the new connection, it MUST choose to accept, ignore or modify any of the test parameters. When the server replies to the Test Activation Request message, the Test Activation Response PDU is structured identically to the Request PDU and SHALL retain the original values received in it unless they are explicitly coerced to a server acceptable value.

When evaluating the Test Activation Request, the server MAY allow the client to specify its own fixed or starting send rate via srIndexConf. Alternatively, the server MAY enforce a maximum limit of the fixed or starting send rate which the client can successfully request. If the client's Test Activation Request exceeds the server's configured maximum, the server MUST either reject the request or coerce the value to the configured maximum bit rate, and communicate that maximum to the client in the Test Activation Response. The client can of course choose to end the test, as appropriate. Other parameters where the server has the OPTION to coerce the client to use values other than those in the Test Activation Request are (grouped by role): Load rate adjustment algorithm: lowThresh, upperThresh, useOwDelayVar, highSpeedDelta, slowAdjThresh, seqErrThresh, highSpeedDelta, ignoreOooDup, rateAdjAlgo. Test duration/intervals: trialInt, testIntTime, subIntPeriod Packet marking: ipTosByte Coercion is a step towards performing a test with the server-configured values; even though the client might prefer certain values, the server gives the client an opportunity to run a test with different values than the preferred set. In these cases, the Command Response value SHALL be CHTA_CRSP_ACKOK. Note that the server also has the option of completely rejecting the request and sending back an appropriate cmdResponse field value (currently only CHTA_CRSP_BADPARAM, see ). Whether this error response is sent or not depends on the Security mode of operation and the outcome of authDigest validation. If the Test Activation Request must be rejected (due to the Command Response value being CHTA_CRSP_BADPARAM), and In Authenticated modes, if the authDigest is valid, a Test Activation Response SHALL be sent back to the client with a corresponding command response value indicating the reason for the rejection. If operating in the Partial Encryption mode, the server SHALL follow the requirements of , else the server SHALL follow the requirements of . In Authenticated modes, if the authDigest is invalid, then the Test Activation Request SHOULD fail silently. The exception is for operations support: server administrators using Authentication are permitted to send a Setup Response to support operations and troubleshooting. If Unauthenticated mode is selected, the Test Activation Request SHALL fail silently. The additional, non-authentication circumstances when a server SHALL NOT communicate the appropriate Command Response code for an error condition (fail silently) are when: the Test Activation Request PDU size is not equal to the 'struct controlHdrTA' size shown in figure 7, the PDU ID is not 0xACE2 (Test Activation PDU), or a directed attack has been detected, in which case the server will allow Test Activation Requests to terminate silently. Attack detection is beyond the scope of this specification.

When the server sends the Test Activation Response, it SHALL set the cmdResponse field to CHTA_CRSP_ACKOK (see ) If the client has requested an upstream test, the server SHALL: include the transmission parameters from the first row of the Sending Rate Table in the Sending Rate structure (if requested by srIndexConf having been set to CHTA_SRIDX_DEF), or include the transmission parameters from the designated Configured Sending Rate Table index (srIndexConf) of the Sending Rate Table where, if CHTA_SRIDX_ISSTART is set in modifierBitmap, this will be used as the starting rate for the load rate adjustment algorithm, else it will be considered a fixed rate test. When generating the Test Activation Response (acceptance) for a downstream test, the server SHALL set all octets of the Sending Rate structure to zero. If activation continues, the server prepares the new connection for an upstream OR downstream test. In the case of an upstream test, the server SHALL prepare to use a single timer to send Status PDUs at the specified interval. For a downstream test, the server SHALL prepare to utilize dual timers to send Load PDUs based on the transmission parameters directly from the first row of the Sending Rate Table (if requested by srIndexConf having been set to CHTA_SRIDX_DEF), or the transmission parameters from the designated Configured Sending Rate Table index (srIndexConf) of the Sending Rate Table where, if CHTA_SRIDX_ISSTART is set in modifierBitmap, this will be used as the starting rate for the load rate adjustment algorithm, else it will be considered a fixed rate test. The server SHALL then send the Test Activation Response back to the client, update the watchdog timer with a new timeout value, and set a test duration timer to eventually stop the test.

When the client receives the Test Activation Response, it SHALL: If operating in an Authenticated mode, check the message PDU for validity via the authDigest field and acceptable immediacy via the authUnixTime field. If validated, and if operating in Partial Encryption mode, decrypt the PDU using the included IV and shared key designated via keyId. Finally, check the PDU for general formatting, such as protocol version, and any PDU-specific fields that control the test. When the client receives the (vetted) Test Activation Response, it first checks the command response value. If the client receives a Test Activation cmdResponse field value that indicates an error, the client SHALL display/report a relevant message to the user or management process and exit. If the client receives a Test Activation cmdResponse field value that is not equal to one of the codes defined in , the client MUST terminate the connection and terminate operation of the current setup procedure. If the client receives a Test Activation Command Response value that indicates success (CHTA_CRSP_ACKOK, see ), the client SHALL update its configuration to use any test parameters modified by the server. Next, the client SHALL prepare its connection for either an upstream test with dual timers set to send Load PDUs (based on the starting transmission parameters sent by the server), OR a downstream test with a single timer to send Status PDUs at the specified interval. Then, the client SHALL stop the test initiation timer and start a watchdog timer to detect if the server goes quiet. The connection is now ready for testing.

This section describes the data phase of the protocol. The roles of sender and receiver vary depending whether the direction of testing is from server to client, or the reverse.

Testing proceeds with one endpoint sending Load PDUs, based on transmission parameters from the Sending Rate Table, and the other endpoint sending Status Feedback messages to communicate the traffic conditions at the receiver. When the server is sending Status Feedback messages, they will also contain the latest transmission parameters from the Sending Rate Table that the client SHALL use. The watchdog timer at the receiver SHALL be reset each time a PDU is received. See non-graceful test stop in for handling the watchdog timeout expiration at each endpoint. When the server is sending Load PDUs in the role of sender, it SHALL use the transmission parameters directly from the Sending Rate Table via the index that is currently selected (which was indirectly based on the feedback in its received Status Feedback messages). However, when the client is sending Load PDUs in the role of sender, it SHALL use the discreet transmission parameters that were communicated by the server in its periodic Status Feedback messages (and not referencing a Sending Rate Table directly). This approach allows the server to control the individual sending rates as well as the algorithm used to decide when and how to adjust the rate. The server uses a load rate adjustment algorithm which evaluates measurements taken locally at the Load PDU receiver. When the client is the receiver, the information is communicated to the server via the periodic Status Feedback messages. When the server is the receiver, the information is used directly (although it is also communicated to the client via its periodic Status Feedback messages). This approach is unique to this protocol; it provides the ability to search for the Maximum IP Capacity and specify specific sender behaviors that is absent from other testing tools. Although the algorithm depends on the protocol, it is not part of the protocol per se. The default algorithm (B) has three paths to its decision on the next sending rate: When there are no impairments present (no sequence errors and low delay variation), resulting in a sending rate increase. When there are low impairments present (no sequence errors but higher levels of delay variation), the same sending rate is maintained. When the impairment levels are above the thresholds set for this purpose and "congestion" is inferred, resulting in a sending rate decrease. Algorithm B also has two modes for increasing/decreasing the sending rate: A high-speed mode (fast) to achieve high sending rates quickly, but also back-off quickly when "congestion" is inferred from the measurements. Consecutive feedback intervals that have a supra-threshold count of sequence number anomalies and/or contain an upper delay variation threshold exception in all of the consecutive intervals are sufficient to declare "congestion" within a test. The threshold of consecutive feedback intervals SHALL be configurable with a default of 3 intervals. A single-step (slow) mode where all rate adjustments use the minimum increase or decrease of one step in the sending rate table. The single step mode continues after the first inference of "congestion" from measured impairments. An OPTIONAL load rate adjustment algorithm (designated C) has been defined in . Algorithm C operation and modes are similar to B, but C uses multiplicative increases in the fast mode to reach the Gigabit range quickly and adds the possibility to re-try the fast mode during a test (which improves the measurement accuracy in dynamic or error-prone access, such as radio access). On the other hand, the test configuration MAY use a fixed sending rate requested by the client, using the field srIndexConf. The client MAY communicate the desired fixed rate in its test activation request. The reasons to conduct a fixed-rate test include stable measurement at the maximum determined by the load rate adjustment algorithm, or the desire to test at a known subscribed rate without searching. The UDP PDU format layout SHALL be as follows (big-endian AB):

0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | pduId | testAction | rxStopped | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | lpduSeqNo | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | udpPayload | spduSeqErr | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | spduTime_sec | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | spduTime_nsec | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | lpduTime_sec | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | lpduTime_nsec | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | rttRespDelay | checkSum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . Payload Content... . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 8: Load PDU Layout Specific details regarding Load PDU fields are as follows: pduId: A two-octet field. IANA is asked to assign the value hex 0xBEEF (). testAction: Designates the current test action as either TEST_ACT_TEST (testing in progress), TEST_ACT_STOP1 (first phase of graceful termination, used locally by server), or TEST_ACT_STOP2 (second phase of graceful termination, sent by server and reciprocated by client). See for additional information on test termination. rxStopped: A boolean (0 or 1) used to indicate to the remote endpoint that local receive traffic (either Load or Status PDUs) has stopped. All outgoing Load or Status PDUs SHALL continue to assert this indication until traffic is received again, or the test is terminated. The time threshold to trigger this condition is expected to be a reasonable fraction of the watchdog timeout (a default of one second is recommended). lpduSeqNo: Load PDU sequence number (starting at 1). Used to determine loss, out-of-order, and duplicates. udpPayload: The total payload size of the UDP datagram including the Load PDU message header and Payload Content (i.e., what the UDP socket read function would return). This field allows the Load PDU receiver to maintain accurate receive statistics if utilizing receive truncation (only requesting the Load PDU message header octets from the protocol stack). spduSeqErr: Status PDU loss count, as seen by the Load PDU sender. This is determined by the Status PDU sequence number (spduSeqNo) in the most recently received Status PDU. Used to communicate to the Load PDU receiver that return traffic (in the unloaded direction) is being lost. spduTime_sec/spduTime_nsec: A copy of the most recent spduTime_sec/spduTime_nsec from the last Status PDU received. Used for RTT measurements made by the Load PDU receiver. lpduTime_sec/lpduTime_nsec: The local send time of the Load PDU. Used for one-way delay variation measurements made by the Load PDU receiver. rttRespDelay: RTT response delay, used to "adjust" raw RTT. On the Load PDU sender, it is the number of milliseconds from reception of the most recent Status PDU (when the latest spduTime_sec/spduTime_nsec was obtained) to the transmission of the Load PDU (where the previously obtained spduTime_sec/spduTime_nsec is returned). When the Load PDU receiver is calculating RTT, by subtracting the copied Status PDU send time (in the Load PDU) from the local Load PDU receive time, this value is subtracted from the raw RTT to correct for any response delay due to Load PDU scheduling. checkSum: An OPTIONAL checksum of only the Load PDU header. The checksum does not cover the Payload Content. The calculation is done with the checkSum field set to zero. Payload Content: All zeroes, all ones, or a pseudorandom binary sequence. The Load PDU SHALL be organized as follows (followed by any payload content):

<CODE BEGINS> // // Load header for UDP payload of Load PDUs // struct loadHdr { #define LOAD_ID 0xBEEF uint16_t pduId; // PDU ID #define TEST_ACT_TEST 0 // Test active #define TEST_ACT_STOP1 1 // Stop indication used locally by server #define TEST_ACT_STOP2 2 // Stop indication exchanged with client uint8_t testAction; // Test action uint8_t rxStopped; // Receive traffic stopped indicator (BOOL) uint32_t lpduSeqNo; // Load PDU sequence number uint16_t udpPayload; // UDP payload (bytes) uint16_t spduSeqErr; // Status PDU sequence error count uint32_t spduTime_sec; // Send time in last received status PDU uint32_t spduTime_nsec; // Send time in last received status PDU uint32_t lpduTime_sec; // Send time of this load PDU uint32_t lpduTime_nsec; // Send time of this load PDU uint16_t rttRespDelay; // Response delay for RTT (ms) uint16_t checkSum; // Header checksum }; <CODE ENDS> Figure 9: Load PDU

The Load PDU receiver SHALL send a Status PDU to the sender during a test at the configured feedback interval, after at least one Load PDU has been received (when there is something to provide status on). In test scenarios with long delays between client and server, it is possible for the Status PDU send timer to fire before the first Load PDU arrives. In these cases, the Status PDU SHALL NOT be sent. The watchdog timer at the Load PDU sender SHALL be reset each time a Status PDU is received. See non-graceful test stop in for handling the watchdog timeout expiration at each endpoint. The UDP PDU format layout SHALL be as follows (big-endian AB):

0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | rxDatagrams | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | rxBytes | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | deltaTime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | seqErrLoss | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | seqErrOoo | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | seqErrDup | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | delayVarMin | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | delayVarMax | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | delayVarSum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | delayVarCnt | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | rttVarMinimum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | rttVarMaximum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | accumTime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | pduId | testAction | rxStopped | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | spduSeqNo | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . srStruct (28 octets) . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | subIntSeqNo | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . sisSav (56 octets) . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | seqErrLoss | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | seqErrOoo | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | seqErrDup | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | clockDeltaMin | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | delayVarMin | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | delayVarMax | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | delayVarSum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | delayVarCnt | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | rttMinimum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | rttVarSample | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | delayMinUpd | reserved1 | checkSum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | tiDeltaTime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | tiRxDatagrams | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | tiRxBytes | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | spduTime_sec | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | spduTime_nsec | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | authMode | keyId | reserved1a | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | authUnixTime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . initVector (16-octet) . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . authDigest (32-octet) . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 10: Status PDU Layout Note that the Sending Rate structure is defined in . The primary role of the Status Feedback message is to communicate to the Load PDU sender the traffic conditions at the Load PDU receiver. While the Sub-Interval Statistics structure (sisSav) covers the most recently saved (completed) sub-interval, similar fields directly in the Status PDU itself cover the most recent trial interval (the time period between Status Feedback messages, completed by this Status PDU). Both sets of statistics SHALL always be populated by the Load PDU receiver, regardless of role (client or server). Details on the Status PDU measurement fields are provided in . Additional information regarding fields not defined previously are as follows: pduId: A two-octet field. IANA is asked to assign the value hex 0xFEED (). rxDatagrams/rxBytes/deltaTime: Sub-interval received datagram and byte counts as well as the exact duration of the sub-interval in microseconds. Used to calculate the received traffic rate for the sub-interval. The rxBytes field is a 64-bit value to prevent overflow at high speeds. seqErrLoss/seqErrOoo/seqErrDup: Loss, out-of-order, and duplicate totals. Available for both the sub-interval and trial interval. seqErrOoo and seqErrDup are realized by comparing sequence numbers. A lookback list of the last n sequence numbers received is used as the basis. Each Load PDU sequence number is checked against this lookback. The number n may depend on the implementation and on typical characteristics of environments, where UDPST is deployed (like mobile networks or Wi-Fi). Currently, a default sequence number interval of n=32 has been chosen. Specifically for seqErrOoo, each successively received higher seqno sets the next-expected-seqno to seqno+1 and anything below that is considered out-of-order (i.e., delayed). For example, given the sequence 93, 94, 95, 100, 96, 97, 101, 98, 99, 102, 103, ... reception of 96, 97, 98, and 99 would not increment the next-expected-seqno and would all be considered out-of-order. delayVarMin/delayVarMax/delayVarSum/delayVarCnt: The one-way delay variation measurements of all received Load PDUs (where avg = sum/cnt). For each Load PDU received, the send time (lpduTime_sec/lpduTime_nsec) is subtracted from the local receive time, which is then normalized by subtracting the current clockDeltaMin. Available for both the sub-interval and trial interval. rttVarMinimum/rttVarMaximum (in sisSav): The minimum and maximum RTT delay variation (rttVarSample) in the sub-interval designated by the subIntSeqNo. accumTime: The accumulated time of the test in milliseconds, based on the duration of each sub-interval. Equivalent to the sum of each deltaTime (although in ms) sent in each Status PDU during the test. spduSeqNo: Status PDU sequence number (starting at 1). Used by the Load PDU sender to detect Status PDU loss (in the unloaded direction). The loss count is communicated back to the Load PDU receiver via spduSeqErr in subsequent Load PDUs. subIntSeqNo: Sub-interval sequence number (starting at 1) that corresponds to the statistics provided in sisSav, for the last saved (completed) sub-interval. sisSav: Sub-interval statistics saved (completed) for the most recent sub-interval (as designated by the subIntSeqNo). clockDeltaMin: The minimum clock delta (difference) since the beginning of the test. Obtained by subtracting the send time of each Load PDU (lpduTime_sec/lpduTime_nsec) from the local time that it was received. This value is initialized with the first Load PDU received and is updated with each subsequent one to maintain a current (and continuously updated) minimum. If the endpoint clocks are sufficiently synchronized, this will be the minimum one-way delay in milliseconds. Otherwise, this value may be negative, but still valid for one-way delay variation measurements for the default test duration (default is 10 [s]). If the test duration is extended to a range of minutes, where significant clock drift can occur, synchronized (or at least well disciplined) clocks may be required. rttMinimum (in Status PDU): The minimum "adjusted" RTT measured since the beginning of the test. See rttRespDelay regarding "adjusted" measurements. RTT is obtained by subtracting the copied spduTime_sec/spduTime_nsec in the received Load PDU from the local time at which it was received. This minimum SHALL be kept current (and continuously updated) via each Load PDU received with an updated spduTime_sec/spduTime_nsec. This value MUST be positive. Before an initial value can be established, and because zero is itself valid, it SHALL be set to STATUS_NORTT when communicated in the Status PDU. rttVarSample: The most recent "adjusted" RTT delay variation measurement. See rttRespDelay regarding "adjusted" measurements. RTT delay variation is obtained by subtracting the current (and continuously updated) "adjusted" RTT minimum, communicated as rttMinimum (in Status PDU), from each "adjusted" RTT measurement (which is itself obtained by subtracting the copied spduTime_sec/spduTime_nsec in the received Load PDU from the local time at which it was received). Note that while one-way delay variation is measured for every Load PDU received, RTT delay variation is only sampled via the Status PDU sent and the very next Load PDU received with the corresponding updated spduTime_sec/spduTime_nsec. When a new value is unavailable (possibly due to packet loss), and because zero is itself valid, it SHALL be set to STATUS_NORTT when communicated in the Status PDU. delayMinUpd: Boolean (0 or 1) indicating that the clockDeltaMin and/or rttMinimum (in Status PDU), as measured by the Load PDU receiver, has been updated. checkSum: An OPTIONAL checksum of the entire PDU. The calculation is done with the checkSum field, and all fields starting with authMode, set to zero. tiDeltaTime/tiRxDatagrams/tiRxBytes: The trial interval time in microseconds, along with the received datagram and byte counts. Used to calculate the received traffic rate for the trial interval. spduTime_sec/spduTime_nsec: The local transmit time of the Status PDU. Expected to be copied into spduTime_sec/spduTime_nsec in subsequent Load PDUs after being received by the Load PDU sender. Used for RTT measurements. The authentication, encryption, and checksum fields and their operation are as defined previously in . The Status Feedback message PDU (as well as the included Sub-Interval Statistics structure) SHALL be organized as follows:

<CODE BEGINS> // // Sub-interval statistics structure for received traffic information // struct subIntStats { uint32_t rxDatagrams; // Received datagrams uint64_t rxBytes; // Received bytes (64 bits) uint32_t deltaTime; // Time delta (us) uint32_t seqErrLoss; // Loss sum uint32_t seqErrOoo; // Out-of-Order sum uint32_t seqErrDup; // Duplicate sum uint32_t delayVarMin; // Delay variation minimum (ms) uint32_t delayVarMax; // Delay variation maximum (ms) uint32_t delayVarSum; // Delay variation sum (ms) uint32_t delayVarCnt; // Delay variation count uint32_t rttMinimum; // Minimum round-trip time (ms) uint32_t rttMaximum; // Maximum round-trip time (ms) uint32_t accumTime; // Accumulated time (ms) }; // // Status feedback header for UDP payload of status PDUs // struct statusHdr { #define STATUS_ID 0xFEED uint16_t pduId; // PDU ID uint8_t testAction; // Test action uint8_t rxStopped; // Receive traffic stopped indicator (BOOL) uint32_t spduSeqNo; // Status PDU sequence number struct sendingRate srStruct; // Sending rate structure uint32_t subIntSeqNo; // Sub-interval sequence number struct subIntStats sisSav; // Sub-interval saved stats uint32_t seqErrLoss; // Loss sum uint32_t seqErrOoo; // Out-of-Order sum uint32_t seqErrDup; // Duplicate sum uint32_t clockDeltaMin; // Clock delta minimum (ms) uint32_t delayVarMin; // Delay variation minimum (ms) uint32_t delayVarMax; // Delay variation maximum (ms) uint32_t delayVarSum; // Delay variation sum (ms) uint32_t delayVarCnt; // Delay variation count #define STATUS_NORTT UINT32_MAX // No RTT data/value uint32_t rttMinimum; // Minimum round-trip time sampled (ms) uint32_t rttVarSample; // Last round-trip time sample (ms) uint8_t delayMinUpd; // Delay minimum(s) updated (BOOL) uint8_t reserved1; // (reserved for alignment) uint16_t checkSum; // Header checksum uint32_t tiDeltaTime; // Trial interval delta time (us) uint32_t tiRxDatagrams; // Trial interval receive datagrams uint32_t tiRxBytes; // Trial interval receive bytes uint32_t spduTime_sec; // Send time of this status PDU uint32_t spduTime_nsec; // Send time of this status PDU // // ========== Encryption ends here ========== uint8_t authMode; // Authentication mode uint8_t keyId; // Key ID in shared table uint16_t reserved1a; // (reserved for alignment) uint32_t authUnixTime; // Authentication time stamp uint8_t initVector[AUTH_IV_LENGTH] // IV uint8_t authDigest[AUTH_DIGEST_LENGTH] // HMAC }; <CODE ENDS> Figure 11: Status PDU

When the test duration timer (testIntTime) on the server expires, it SHALL set the local connection test action to TEST_ACT_STOP1 (phase 1 of graceful termination). This is simply a non-reversible state awaiting the next message(s) to be sent from the server. During this time, any received Load or Status PDUs are processed normally. Upon transmission of the next Load or Status PDUs, the server SHALL set the local connection test action to TEST_ACT_STOP2 (phase 2 of graceful termination) and mark any outgoing PDUs with a testAction value of TEST_ACT_STOP2. While in this state, the server MAY reduce any Load PDU bursts to a size of one. When the client receives a Load or Status PDU with the TEST_ACT_STOP2 indication, it SHALL finalize testing, display the test results, and also mark its local connection with a test action of TEST_ACT_STOP2 (so that any PDUs subsequently received can be ignored). With the test action of the client's connection set to TEST_ACT_STOP2, the very next expiry of a send timer, for either a Load or Status PDU, SHALL result in it and any subsequent PDUs to be sent with a testAction value of TEST_ACT_STOP2 (as confirmation to the server). While in this state, the client MAY reduce any Load PDU bursts to a size of one. The client SHALL then schedule an immediate end time for the connection. When the server receives the TEST_ACT_STOP2 confirmation in the Load or Status PDU, the server SHALL schedule an immediate end time for the connection which closes the socket and deallocates the associated resources. The TEST_ACT_STOP2 exchange constitutes a graceful termination of the test. In a non-graceful test stop due to path failure, the watchdog timeouts at each endpoint will expire (sometimes at one endpoint first), notifications in logs, STDOUT, and/or formatted output SHALL be made, and the endpoint SHALL schedule an immediate end time for the connection. If an attacker clears the TEST_ACT_STOP2 indication, then the configured test duration timer (testIntTime) at the server and client SHALL take precedence and the endpoint SHALL schedule an immediate end time for the connection.

The architecture of the method requires two cooperating hosts operating in the roles of Src (test packet sender) and Dst (receiver), with a measured path and return path between them. The duration of a test, parameter I, MUST be constrained in a production network, since this is an active test method and it will likely cause congestion on the Src to Dst host path during a test.

Additional measurements may be useful in specific circumstances. For example, interface byte counters measured by a client at a residential gateway are possible when the client application has access to an interface that sees all traffic to/from a service subscriber's location. Adding a byte counter at the client for download or upload directions could be used to measure total traffic and possibly detect when non-test traffic is present (and using capacity). The client may not have the CPU cycles available to count both the interface traffic and IP-layer Capacity simultaneously, so this form of diagnostic measurement may not be possible.

Active metrics and measurements have a long history of security considerations. The security considerations that apply to any active measurement of live paths are relevant here. See and . When considering privacy of those involved in measurement or those whose traffic is measured, the sensitive information available to potential observers is greatly reduced when using active techniques which are within this scope of work. Passive observations of user traffic for measurement purposes raise many privacy issues. We refer the reader to the privacy considerations described in the Large Scale Measurement of Broadband Performance (LMAP) Framework , which covers active and passive techniques. There are some new considerations for Capacity measurement as described in this document. Cooperating client and server hosts and agreements to test the path between the hosts are REQUIRED. Hosts perform in either the server or client roles. One way to assure a cooperative agreement employs the optional Authorization mode through the use of the authDigest field and the known identity associated with the key used to create the authDigest field. Other means are also possible, such as access control lists at the server. It is REQUIRED to have a user client-initiated setup handshake between cooperating hosts that allows firewalls to control inbound unsolicited UDP traffic which either goes to a control port or to ephemeral ports that are only created as needed. Firewalls protecting each host can both continue to do their job normally. Client-server authentication and integrity protection for feedback messages conveying measurements is RECOMMENDED. To accommodate different host limitations and testing circumstances, different modes of operation are available, as described in above. Hosts MUST limit the number of simultaneous tests to avoid resource exhaustion and inaccurate results. Senders MUST be rate-limited. This can be accomplished using a pre-built table defining all the offered sending rates that will be supported. The default and optional load rate adjustment algorithm results in "ramp up" from the lowest rate in the table. Optionally, the server could utilize the maxBandwidth field (and CHSR_USDIR_BIT bit) in the Setup Request from the client to limit the maximum that it will attempt to achieve. Service subscribers with limited data volumes who conduct extensive capacity testing might experience the effects of Service Provider controls on their service. Testing with the Service Provider's measurement hosts SHOULD be limited in frequency and/or overall volume of test traffic (for example, the range of test interval duration values should be limited). One specific attack that has been recognized is an on-path attack on the testAction field where the attacker would set or clear the STOP indication. Setting the indication in successive packets terminates the test prematurely, with no threat to the Internet but annoyance for the testers. If an attacker clears the STOP indication, the mitigation relies on knowledge of the test duration at the client and server, where these hosts cease all traffic when the specified test duration is complete.

This document requests IANA to assign a User/Registered UDP port for the Test Setup exchange in the Control phase of protocol operation, and to create a new registry group for the UDP Speed Test Protocol (UDPSTP).

IANA will allocate the following service name to the "Service Name and Transport Protocol Port Number Registry" registry: udpst-control UDP IESG <iesg@ietf.org> IETF Chair <chair@ietf.org> UDP-based IP-Layer Capacity and performance measurement protocol This RFC, RFCYYYY. The protocol uses IP-Layer Unicast. The assignment of a single port number is requested to help configuring firewalls and other port-based systems for access control prior to negotiating dynamic ports between client and server. <PORTNUM> of the IANA User Port range (1024-49151)

IANA will create the following registry in a new registry group called "UDP Speed Test Protocol (UDPSTP)": Registration Procedure: see below Reference: <This RFC> Experts: Performance Metrics Experts Note: TBD

IANA will create the "PDU Identifier" registry under the "UDP Speed Test Protocol (UDPSTP)" registry group. Every UDPSTP PDU contains a two octet pduId field identifying the role and format of the PDU that follows. The code points in this registry are allocated according to the registration procedures described in Table 1.

Range(Hex) Registration Procedures =============================================================== 0xFFFF and 0x0000 Reserved 0x8000-0xFFFE Expert Review 0x0001-0x7F00 First Come, First Served 0x7F01-0x7FE0 Experimental 0x7FE1-0x7FFF Private Use Table 1: Registration procedures for the PDU Identifier registry Initially, IANA will assign the "PDU Identifier" registry with the values in Table 2:

Value Description Reference =================================================== 0xACE1 Test Setup PDU <this RFC> 0xACE2 Test Activation PDU <this RFC> 0xDEAD Null PDU <this RFC> 0xBEEF Load PDU <this RFC> 0xFEED Status Feedback PDU <this RFC> Table 2: Initial PDU Identifier Values

IANA will create the "Protocol Version" registry under the "UDP Speed Test Protocol (UDPSTP)" registry group. UDPST Protocol Test Setup Request, Test Setup Response and Test Activation Request PDUs contain a two octet protocolVer field, identifying the version of the protocol in use. The code points in this registry are allocated according to the registration procedures described in Table 3.

Range(Decimal) Registration Procedures =============================================================== 0-19 Reserved 20-40960 IETF Review 40961-53248 First Come, First Served 53249-65534 Experimental 65535 Reserved Table 3: Registration procedures for the Protocol Version registry Initially, IANA will assign the decimal value 20 listed in Table 4 in the "Protocol Number" registry:

Value Description Reference ================================================ 20 Protocol version 20 <this RFC> Table 4: Initial Protocol Version value

IANA will create the "Test Setup PDU Modifier Bitmap" registry under the "UDP Speed Test Protocol (UDPSTP)" registry group. The Test Setup PDU layout contains a modifierBitmap field. The bitmaps in this registry are allocated according to the registration procedures described in Table 5.

Range(Bitmap) Registration Procedures =============================================================== 00000000-01111111 IETF Review 10000000 Reserved Table 5: Registration procedures for the Test Setup PDU Modifier Bitmap Registry Initially, IANA will assign the bitmap values defined by Table 6 in the "Test Setup PDU Modifier Bitmap" registry.

Value Description Reference =============================================================== 0x00 No modifications <this RFC> 0x01 Allow Jumbo datagram <this RFC> sizes above sending rates of 1Gbps 0x02 Use Traditional MTU <this RFC> (1500 bytes with IP-header) Table 6: Initial Test Setup PDU Modifier Bitmap values

IANA will create the "Test Setup PDU Authentication Mode" registry under the "UDP Speed Test Protocol (UDPSTP)" registry group. The Test Setup PDU layout contains an authMode field. The code points in this registry are allocated according to the registration procedures described in Table 7.

Range(Decimal) Registration Procedures =============================================================== 0-59 IETF Review 60-63 Experimental 64-255 Reserved Table 7: Registration procedures for the Test Setup PDU Authentication Mode registry Initially, IANA will assign the decimal values defined by Table 8 in the "Test Setup PDU Authentication Mode" registry.

Value Description Reference =============================================================== 0 Optional Unauthenticated mode <this RFC> 1 Required authentication <this RFC> for the Control phase 2 Optional authentication for <this RFC> the Data phase, in addition to the Control phase 3 Optional partial encrypted <this RFC> mode Table 8: Initial Test Setup PDU Authentication Mode values

IANA will create the "Test Setup PDU Command Response Field" registry" under the "UDP Speed Test Protocol (UDPSTP)" registry group. The Test Setup PDU layout contains a cmdResponse field. The code points in this registry are allocated according to the registration procedures described in Table 9.

Range(Decimal) Registration Procedures =============================================================== 0-127 IETF Review 128-239 First Come, First Served 240-249 Experimental 250-254 Private Use 255 Reserved Table 9: Registration procedures for the Test Setup PDU Command Response Field Registry Initially, IANA will assign the decimal values defined by Table 10 in the "Test Setup PDU Command Response Field" registry.

Value Description Reference =============================================================== 0 None (used by <this RFC> client in Request) 1 Acknowledgment <this RFC> 2 Bad Protocol Version <this RFC> 3 Invalid Jumbo datagram <this RFC> option 4 Unexpected Authentication <this RFC> in Setup Request 5 Authentication missing <this RFC> in Setup Request 6 Invalid authentication <this RFC> method 7 Authentication failure <this RFC> 8 Authentication time is <this RFC> invalid in Setup Request 9 No Maximum test Bit rate <this RFC> specified 10 Server Maximum Bit rate <this RFC> exceeded 11 MTU option does not match <this RFC> server 12 Multi-connection parameters <this RFC> rejected by server 13 Connection allocation <this RFC> failure on server Table 10: Initial Test Setup PDU Command Response Field values

IANA will create the "Test Activation PDU Command Request" registry under the "UDP Speed Test Protocol (UDPSTP)" registry group. The Test Setup PDU layout contains a cmdRequest field. The code points in this registry are allocated according to the registration procedures described in Table 11.

Range(Decimal) Registration Procedures =============================================================== 0-127 IETF Review 128-239 First Come, First Served 240-249 Experimental 250-254 Private Use 255 Reserved Table 11: Registration procedures for the Test Activation PDU Command Request registry Initially, IANA will assign the decimal values defined by Table 12 in the "Test Activation PDU Command Request" registry.

Value Description Reference =============================================================== 0 No Request <this RFC> 1 Request test in Upstream <this RFC> direction (client to server) 2 Request test in Downstream <this RFC> direction (server to client) Table 12: Initial Test Activation PDU Command Request values

IANA will create the "Test Activation PDU Modifier Bitmap" registry under the "UDP Speed Test Protocol (UDPSTP)" registry group. The Test Activation PDU layout (also) contains a modifierBitmap field. The bitmaps in this registry are allocated according to the registration procedures described in Table 13.

Range(Bitmap) Registration Procedures =============================================================== 00000000-01111111 IETF Review 10000000 Reserved Table 13: Registration procedures for the Test Activation PDU Modifier Bitmap registry Initially, IANA will assign the bitmap values defined by Table 14 in the "Test Activation PDU Modifier Bitmap" registry.

Value Description Reference =============================================================== 0x00 No modifications <this RFC> 0x01 Set when srIndexConf is <this RFC> start rate for search 0x02 Set for randomized <this RFC> UDP payload Table 14: Initial Test Activation PDU Modifier Bitmap values

The Test Activation PDU layout contains a rateAdjAlgo field. The table below defines the assigned Capitalized alphabetic UTF-8 values in the registry. IANA will create the "Test Activation PDU Rate Adjustment Algo." registry under the "UDP Speed Test Protocol (UDPSTP)" registry group. The Test Activation PDU layout contains a rateAdjAlgo field. The code points in this registry are allocated according to the registration procedures described in Table 15.

Range(Capital alphabet. UTF-8) Registration Procedures =============================================================== A-Q IETF Review R-V Experimental W-Y Private Use Z Reserved Table 15: Registration procedures for the Test Activation PDU Rate Adjustment Algo. registry Initially, IANA will assign the Capitalized alphabetic UTF-8 values, as well as the corresponding incremental numeric, defined by Table 16 in the "Test Activation PDU Rate Adjustment Algo." registry.

Value Description Reference (Numeric) =================================================== A(n/a) Not used <this RFC> B(0) Rate algorithm Type B <this RFC> C(1) Rate algorithm Type C <this RFC> Table 16: Initial Test Activation PDU Rate Adjustment Algo. values

IANA will create the "Test Activation PDU Command Response Field" registry under the "UDP Speed Test Protocol (UDPSTP)" registry group. The Test Activation PDU layout (also) contains a cmdResponse field. The code points in this registry are allocated according to the registration procedures described in Table 17.

Range(Decimal) Registration Procedures =============================================================== 0-127 IETF Review 128-239 First Come, First Served 240-249 Experimental 250-254 Private Use 255 Reserved Table 17: Registration procedures for the Test Activation PDU Command Response Field registry Initially, IANA will assign the decimal values defined by Table 18 in the "Test Activation PDU Command Response Field" registry.

Value Description Reference =============================================================== 0 None (used by <this RFC> client in Request) 1 Server Acknowledgment <this RFC> 2 Server indicates an error <this RFC> Table 18: Initial Test Activation PDU Command Response Field values

It is suggested that multiple designated experts be appointed for registry change requests. Criteria that should be applied by the designated experts include determining whether the proposed registration duplicates existing entries and whether the registration description is clear and fits the purpose of this registry. Registration requests are evaluated within a two-week review period on the advice of one or more designated experts. Within the review period, the designated experts will either approve or deny the registration request, communicating this decision to IANA. Denials should include an explanation and, if applicable, suggestions as to how to make the request successful.

This document was edited by Al Morton, who passed away before being able to finalize this work. Ruediger Geib only joined later to help finalizing this draft. Thanks to Lincoln Lavoie, Can Desem, Greg Mirsky, Bjoern Ivar Teigen, Ken Kerpez and Chen Li for reviewing this draft and providing helpful suggestions and areas for further development. Mohamed Boucadair's AD review improved comprehensability of the document. David Dong and Amanda Baber provided early reviews of the IANA Considerations section. Brian Weis provided an early SEC-DIR review; version 02 captures clarifications and version 03-09 took up on the protocol changes which Brian suggested. Tommy Pauly sheperded this document.