Network Working Group S. Shalunov Request for Comments: 4656 B. Teitelbaum Category: Standards Track A. Karp J. Boote M. Zekauskas Internet2 September 2006 A One-way Active Measurement Protocol (OWAMP) Status of This Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2006).
AbstractThe One-Way Active Measurement Protocol (OWAMP) measures unidirectional characteristics such as one-way delay and one-way loss. High-precision measurement of these one-way IP performance metrics became possible with wider availability of good time sources (such as GPS and CDMA). OWAMP enables the interoperability of these measurements. 1. Introduction ....................................................2 1.1. Relationship of Test and Control Protocols .................3 1.2. Logical Model ..............................................4 2. Protocol Overview ...............................................5 3. OWAMP-Control ...................................................6 3.1. Connection Setup ...........................................6 3.2. Integrity Protection (HMAC) ...............................11 3.3. Values of the Accept Field ................................11 3.4. OWAMP-Control Commands ....................................12 3.5. Creating Test Sessions ....................................13 3.6. Send Schedules ............................................18 3.7. Starting Test Sessions ....................................19 3.8. Stop-Sessions .............................................20 3.9. Fetch-Session .............................................24
4. OWAMP-Test .....................................................27 4.1. Sender Behavior ...........................................28 4.1.1. Packet Timings .....................................28 4.1.2. OWAMP-Test Packet Format and Content ...............29 4.2. Receiver Behavior .........................................33 5. Computing Exponentially Distributed Pseudo-Random Numbers ......35 5.1. High-Level Description of the Algorithm ...................35 5.2. Data Types, Representation, and Arithmetic ................36 5.3. Uniform Random Quantities .................................37 6. Security Considerations ........................................38 6.1. Introduction ..............................................38 6.2. Preventing Third-Party Denial of Service ..................38 6.3. Covert Information Channels ...............................39 6.4. Requirement to Include AES in Implementations .............39 6.5. Resource Use Limitations ..................................39 6.6. Use of Cryptographic Primitives in OWAMP ..................40 6.7. Cryptographic Primitive Replacement .......................42 6.8. Long-term Manually Managed Keys ...........................43 6.9. (Not) Using Time as Salt ..................................44 6.10. The Use of AES-CBC and HMAC ..............................44 7. Acknowledgements ...............................................45 8. IANA Considerations ............................................45 9. Internationalization Considerations ............................46 10. References ....................................................46 10.1. Normative References .....................................46 10.2. Informative References ...................................47 Appendix A: Sample C Code for Exponential Deviates ................49 Appendix B: Test Vectors for Exponential Deviates .................54 RFC2679] and loss [RFC2680] across Internet paths. Although there are now several measurement platforms that implement collection of these metrics [SURVEYOR] [SURVEYOR-INET] [RIPE] [BRIX], there is not currently a standard that would permit initiation of test streams or exchange of packets to collect singleton metrics in an interoperable manner. With the increasingly wide availability of affordable global positioning systems (GPS) and CDMA-based time sources, hosts increasingly have available to them very accurate time sources, either directly or through their proximity to Network Time Protocol (NTP) primary (stratum 1) time servers. By standardizing a technique for collecting IPPM one-way active measurements, we hope to create an environment where IPPM metrics may be collected across a far broader mesh of Internet paths than is currently possible. One particularly compelling vision is of widespread deployment of open OWAMP servers
that would make measurement of one-way delay as commonplace as measurement of round-trip time using an ICMP-based tool like ping. Additional design goals of OWAMP include: being hard to detect and manipulate, security, logical separation of control and test functionality, and support for small test packets. (Being hard to detect makes interference with measurements more difficult for intermediaries in the middle of the network.) OWAMP test traffic is hard to detect because it is simply a stream of UDP packets from and to negotiated port numbers, with potentially nothing static in the packets (size is negotiated, as well). OWAMP also supports an encrypted mode that further obscures the traffic and makes it impossible to alter timestamps undetectably. Security features include optional authentication and/or encryption of control and test messages. These features may be useful to prevent unauthorized access to results or man-in-the-middle attacks that attempt to provide special treatment to OWAMP test streams or that attempt to modify sender-generated timestamps to falsify test results. In this document, the key words "MUST", "REQUIRED", "SHOULD", "RECOMMENDED", and "MAY" are to be interpreted as described in [RFC2119].
negotiation of sender and receiver addresses and port numbers, session start time, session length, test packet size, the mean Poisson sampling interval for the test stream, and some attributes of the very general [RFC 2330] notion of packet type, including packet size and per-hop behavior (PHB) [RFC2474], which could be used to support the measurement of one-way network characteristics across differentiated services networks. Additionally, OWAMP-Control supports per-session encryption and authentication for both test and control traffic, measurement servers that can act as proxies for test stream endpoints, and the exchange of a seed value for the pseudo- random Poisson process that describes the test stream generated by the sender. We believe that OWAMP-Control can effectively support one-way active measurement in a variety of environments, from publicly accessible measurement beacons running on arbitrary hosts to network monitoring deployments within private corporate networks. If integration with Simple Network Management Protocol (SNMP) or proprietary network management protocols is required, gateways may be created.
One possible scenario of relationships between these roles is shown below. +----------------+ +------------------+ | Session-Sender |--OWAMP-Test-->| Session-Receiver | +----------------+ +------------------+ ^ ^ | | | | | | | +----------------+<----------------+ | | Server |<-------+ | +----------------+ | | ^ | | | | | OWAMP-Control OWAMP-Control | | | v v v +----------------+ +-----------------+ | Control-Client | | Fetch-Client | +----------------+ +-----------------+ (Unlabeled links in the figure are unspecified by this document and may be proprietary protocols.) Different logical roles can be played by the same host. For example, in the figure above, there could actually be only two hosts: one playing the roles of Control-Client, Fetch-Client, and Session- Sender, and the other playing the roles of Server and Session- Receiver. This is shown below. +-----------------+ +------------------+ | Control-Client |<--OWAMP-Control-->| Server | | Fetch-Client | | | | Session-Sender |---OWAMP-Test----->| Session-Receiver | +-----------------+ +------------------+ Finally, because many Internet paths include segments that transport IP over ATM, delay and loss measurements can include the effects of ATM segmentation and reassembly (SAR). Consequently, OWAMP has been designed to allow for small test packets that would fit inside the payload of a single ATM cell (this is only achieved in unauthenticated mode).
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Unused (12 octets) | | | |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Modes | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Challenge (16 octets) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Salt (16 octets) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Count (4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | MBZ (12 octets) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The following Mode values are meaningful: 1 for unauthenticated, 2 for authenticated, and 4 for encrypted. The value of the Modes field sent by the server is the bit-wise OR of the mode values that it is willing to support during this session. Thus, the last three bits of the Modes 32-bit value are used. The first 29 bits MUST be zero. A client MUST ignore the values in the first 29 bits of the Modes value. (This way, the bits are available for future protocol extensions. This is the only intended extension mechanism.) Challenge is a random sequence of octets generated by the server; it is used subsequently by the client to prove possession of a shared secret in a manner prescribed below. Salt and Count are parameters used in deriving a key from a shared secret as described below. Salt MUST be generated pseudo-randomly (independently of anything else in this document). Count MUST be a power of 2. Count MUST be at least 1024. Count SHOULD be increased as more computing power becomes common.
If the Modes value is zero, the server does not wish to communicate with the client and MAY close the connection immediately. The client SHOULD close the connection if it receives a greeting with Modes equal to zero. The client MAY close the connection if the client's desired mode is unavailable. Otherwise, the client MUST respond with the following Set-Up-Response message: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Mode | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . . . KeyID (80 octets) . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . . . Token (64 octets) . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . . . Client-IV (16 octets) . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Here Mode is the mode that the client chooses to use during this OWAMP-Control session. It will also be used for all OWAMP-Test sessions started under control of this OWAMP-Control session. In Mode, one or zero bits MUST be set within last three bits. If it is one bit that is set within the last three bits, this bit MUST indicate a mode that the server agreed to use (i.e., the same bit MUST have been set by the server in the server greeting). The first 29 bits of Mode MUST be zero. A server MUST ignore the values of the first 29 bits. If zero Mode bits are set by the client, the client indicates that it will not continue with the session; in this case, the client and the server SHOULD close the TCP connection associated with the OWAMP-Control session.
In unauthenticated mode, KeyID, Token, and Client-IV are unused. Otherwise, KeyID is a UTF-8 string, up to 80 octets in length (if the string is shorter, it is padded with zero octets), that tells the server which shared secret the client wishes to use to authenticate or encrypt, while Token is the concatenation of a 16-octet challenge, a 16-octet AES Session-key used for encryption, and a 32-octet HMAC- SHA1 Session-key used for authentication. The token itself is encrypted using the AES (Advanced Encryption Standard) [AES] in Cipher Block Chaining (CBC). Encryption MUST be performed using an Initialization Vector (IV) of zero and a key derived from the shared secret associated with KeyID. (Both the server and the client use the same mappings from KeyIDs to shared secrets. The server, being prepared to conduct sessions with more than one client, uses KeyIDs to choose the appropriate secret key; a client would typically have different secret keys for different servers. The situation is analogous to that with passwords.) The shared secret is a passphrase; it MUST not contain newlines. The secret key is derived from the passphrase using a password-based key derivation function PBKDF2 (PKCS #5) [RFC2898]. The PBKDF2 function requires several parameters: the PRF is HMAC-SHA1 [RFC2104]; the salt and count are as transmitted by the server. AES Session-key, HMAC Session-key and Client-IV are generated randomly by the client. AES Session-key and HMAC Session-key MUST be generated with sufficient entropy not to reduce the security of the underlying cipher [RFC4086]. Client-IV merely needs to be unique (i.e., it MUST never be repeated for different sessions using the same secret key; a simple way to achieve that without the use of cumbersome state is to generate the Client-IV values using a cryptographically secure pseudo-random number source: if this is done, the first repetition is unlikely to occur before 2^64 sessions with the same secret key are conducted).
The server MUST respond with the following Server-Start message: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | MBZ (15 octets) | | | | +-+-+-+-+-+-+-+-+ | | Accept | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Server-IV (16 octets) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Start-Time (Timestamp) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MBZ (8 octets) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The MBZ parts MUST be zero. The client MUST ignore their value. MBZ (MUST be zero) fields here and after have the same semantics: the party that sends the message MUST set the field so that all bits are equal to zero; the party that interprets the message MUST ignore the value. (This way, the field could be used for future extensions.) Server-IV is generated randomly by the server. In unauthenticated mode, Server-IV is unused. The Accept field indicates the server's willingness to continue communication. A zero value in the Accept field means that the server accepts the authentication and is willing to conduct further transactions. Non-zero values indicate that the server does not accept the authentication or, for some other reason, is not willing to conduct further transactions in this OWAMP-Control session. The full list of available Accept values is described in Section 3.3, "Values of the Accept Field". If a negative (non-zero) response is sent, the server MAY (and the client SHOULD) close the connection after this message. Start-Time is a timestamp representing the time when the current instantiation of the server started operating. (For example, in a multi-user general purpose operating system, it could be the time when the server process was started.) If Accept is non-zero, Start-
Time SHOULD be set so that all of its bits are zeros. In authenticated and encrypted modes, Start-Time is encrypted as described in Section 3.4, "OWAMP-Control Commands", unless Accept is non-zero. (Authenticated and encrypted mode cannot be entered unless the control connection can be initialized.) Timestamp format is described in Section 4.1.2. The same instantiation of the server SHOULD report the same exact Start-Time value to each client in each session. The previous transactions constitute connection setup.
2 Internal error. 3 Some aspect of request is not supported. 4 Cannot perform request due to permanent resource limitations. 5 Cannot perform request due to temporary resource limitations. All other values are reserved. The sender of the message MAY use the value of 1 for all non-zero Accept values. A message sender SHOULD use the correct Accept value if it is going to use other values. The message receiver MUST interpret all values of Accept other than these reserved values as 1. This way, other values are available for future extensions.
The format of Request-Session message is as follows: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 1 | MBZ | IPVN | Conf-Sender | Conf-Receiver | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Number of Schedule Slots | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Number of Packets | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sender Port | Receiver Port | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sender Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Sender Address (cont.) or MBZ (12 octets) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Receiver Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Receiver Address (cont.) or MBZ (12 octets) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | SID (16 octets) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Padding Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Start Time | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Timeout, (8 octets) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type-P Descriptor | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MBZ (8 octets) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | HMAC (16 octets) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This is immediately followed by one or more schedule slot descriptions (the number of schedule slots is specified in the "Number of Schedule Slots" field above): 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Slot Type | | +-+-+-+-+-+-+-+-+ MBZ (7 octets) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Slot Parameter (Timestamp) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ These are immediately followed by HMAC: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | HMAC (16 octets) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ All these messages constitute one logical message: the Request- Session command. Above, the first octet (1) indicates that this is the Request-Session command. IPVN is the IP version numbers for Sender and Receiver. When the IP version number is 4, 12 octets follow the 4-octet IPv4 address stored in Sender Address and Receiver Address. These octets MUST be set to zero by the client and MUST be ignored by the server. Currently meaningful IPVN values are 4 and 6. Conf-Sender and Conf-Receiver MUST be set to 0 or 1 by the client. The server MUST interpret any non-zero value as 1. If the value is 1, the server is being asked to configure the corresponding agent (sender or receiver). In this case, the corresponding Port value SHOULD be disregarded by the server. At least one of Conf-Sender and Conf-Receiver MUST be 1. (Both can be set, in which case the server is being asked to perform a session between two hosts it can configure.)
Number of Schedule Slots, as mentioned before, specifies the number of slot records that go between the two blocks of HMAC. It is used by the sender to determine when to send test packets (see next section). Number of Packets is the number of active measurement packets to be sent during this OWAMP-Test session (note that either the server or the client can abort the session early). If Conf-Sender is not set, Sender Port is the UDP port from which OWAMP-Test packets will be sent. If Conf-Receiver is not set, Receiver Port is the UDP port OWAMP-Test to which packets are requested to be sent. The Sender Address and Receiver Address fields contain, respectively, the sender and receiver addresses of the end points of the Internet path over which an OWAMP test session is requested. SID is the session identifier. It can be used in later sessions as an argument for the Fetch-Session command. It is meaningful only if Conf-Receiver is 0. This way, the SID is always generated by the receiving side. See the end of the section for information on how the SID is generated. Padding length is the number of octets to be appended to the normal OWAMP-Test packet (see more on padding in discussion of OWAMP-Test). Start Time is the time when the session is to be started (but not before Start-Sessions command is issued). This timestamp is in the same format as OWAMP-Test timestamps. Timeout (or a loss threshold) is an interval of time (expressed as a timestamp). A packet belonging to the test session that is being set up by the current Request-Session command will be considered lost if it is not received during Timeout seconds after it is sent. Type-P Descriptor covers only a subset of (very large) Type-P space. If the first two bits of the Type-P Descriptor are 00, then the subsequent six bits specify the requested Differentiated Services Codepoint (DSCP) value of sent OWAMP-Test packets, as defined in [RFC2474]. If the first two bits of Type-P descriptor are 01, then the subsequent 16 bits specify the requested PHB Identification Code (PHB ID), as defined in [RFC2836]. Therefore, the value of all zeros specifies the default best-effort service.
If Conf-Sender is set, the Type-P Descriptor is to be used to configure the sender to send packets according to its value. If Conf-Sender is not set, the Type-P Descriptor is a declaration of how the sender will be configured. If Conf-Sender is set and the server does not recognize the Type-P Descriptor, or it cannot or does not wish to set the corresponding attributes on OWAMP-Test packets, it SHOULD reject the session request. If Conf-Sender is not set, the server SHOULD accept or reject the session, paying no attention to the value of the Type-P Descriptor. To each Request-Session message, an OWAMP server MUST respond with an Accept-Session message: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Accept | MBZ | Port | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| | | | SID (16 octets) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | MBZ (12 octets) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | HMAC (16 octets) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ In this message, zero in the Accept field means that the server is willing to conduct the session. A non-zero value indicates rejection of the request. The full list of available Accept values is described in Section 3.3, "Values of the Accept Field". If the server rejects a Request-Session message, it SHOULD not close the TCP connection. The client MAY close it if it receives a negative response to the Request-Session message. The meaning of Port in the response depends on the values of Conf- Sender and Conf-Receiver in the query that solicited the response. If both were set, the Port field is unused. If only Conf-Sender was set, Port is the port from which to expect OWAMP-Test packets. If
only Conf-Receiver was set, Port is the port to which OWAMP-Test packets are sent. If only Conf-Sender was set, the SID field in the response is unused. Otherwise, SID is a unique server-generated session identifier. It can be used later as handle to fetch the results of a session. SIDs SHOULD be constructed by concatenation of the 4-octet IPv4 IP number belonging to the generating machine, an 8-octet timestamp, and a 4-octet random value. To reduce the probability of collisions, if the generating machine has any IPv4 addresses (with the exception of loopback), one of them SHOULD be used for SID generation, even if all communication is IPv6-based. If it has no IPv4 addresses at all, the last four octets of an IPv6 address MAY be used instead. Note that SID is always chosen by the receiver. If truly random values are not available, it is important that the SID be made unpredictable, as knowledge of the SID might be used for access control.
reproducibly execute. To reproducibly execute slots of type 0, we need to be able to generate pseudo-random exponentially distributed quantities in a reproducible manner. The way this is accomplished is discussed later in Section 5, "Computing Exponentially Distributed Pseudo-Random Numbers". Using this mechanism, one can easily specify common testing scenarios. The following are some examples: + Poisson stream: a single slot of type 0. + Periodic stream: a single slot of type 1. + Poisson stream of back-to-back packet pairs: two slots, type 0 with a non-zero parameter and type 1 with a zero parameter. Further, a completely arbitrary schedule can be specified (albeit inefficiently) by making the number of test packets equal to the number of schedule slots. In this case, the complete schedule is transmitted in advance of an OWAMP-Test session.
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Accept | | +-+-+-+-+-+-+-+-+ | | MBZ (15 octets) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | HMAC (16 octets) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ If Accept is non-zero, the Start-Sessions request was rejected; zero means that the command was accepted. The full list of available Accept values is described in Section 3.3, "Values of the Accept Field". The server MAY, and the client SHOULD, close the connection in the case of a rejection. The server SHOULD start all OWAMP-Test streams immediately after it sends the response or immediately after their specified start times, whichever is later. If the client represents a Sender, the client SHOULD start its OWAMP-Test streams immediately after it sees the Start-Ack response from the Server (if the Start-Sessions command was accepted) or immediately after their specified start times, whichever is later. See more on OWAMP-Test sender behavior in a separate section below.
the "Number of Sessions" field above). The session description record is used to indicate which packets were actually sent by the sender process (rather than skipped). The header of the session description record is as follows: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| | | | SID (16 octets) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Seqno | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Number of Skip Ranges | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ This is immediately followed by zero or more Skip Range descriptions as specified by the "Number of Skip Ranges" field above. Skip Ranges are simply two sequence numbers that, together, indicate a range of packets that were not sent: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| | First Seqno Skipped | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Last Seqno Skipped | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Skip Ranges MUST be in order. The last (possibly full, possibly incomplete) block (16 octets) of data MUST be padded with zeros, if necessary. This ensures that the next session description record starts on a block boundary. Finally, a single block (16 octets) of HMAC is concatenated on the end to complete the Stop-Sessions message. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | HMAC (16 octets) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ All these records comprise one logical message: the Stop-Sessions command.
Above, the first octet (3) indicates that this is the Stop-Sessions command. Non-zero Accept values indicate a failure of some sort. Zero values indicate normal (but possibly premature) completion. The full list of available Accept values is described in Section 3.3, "Values of the Accept Field". If Accept had a non-zero value (from either party), results of all OWAMP-Test sessions spawned by this OWAMP-Control session SHOULD be considered invalid, even if a Fetch-Session with SID from this session works for a different OWAMP-Control session. If Accept was not transmitted at all (for whatever reason, including the TCP connection used for OWAMP-Control breaking), the results of all OWAMP-Test sessions spawned by this OWAMP-control session MAY be considered invalid. Number of Sessions indicates the number of session description records that immediately follow the Stop-Sessions header. Number of Sessions MUST contain the number of send sessions started by the local side of the control connection that have not been previously terminated by a Stop-Sessions command (i.e., the Control- Client MUST account for each accepted Request-Session where Conf- Receiver was set; the Control-Server MUST account for each accepted Request-Session where Conf-Sender was set). If the Stop-Sessions message does not account for exactly the send sessions controlled by that side, then it is to be considered invalid and the connection SHOULD be closed and any results obtained considered invalid. Each session description record represents one OWAMP-Test session. SID is the session identifier (SID) used to indicate which send session is being described. Next Seqno indicates the next sequence number that would have been sent from this send session. For completed sessions, this will equal NumPackets from the Request-Session. Number of Skip Ranges indicates the number of holes that actually occurred in the sending process. This is a range of packets that were never actually sent by the sending process. For example, if a send session is started too late for the first 10 packets to be sent and this is the only hole in the schedule, then "Number of Skip Ranges" would be 1. The single Skip Range description will have First Seqno Skipped equal to 0 and Last Seqno Skipped equal to 9. This is described further in the "Sender Behavior" section.
If the OWAMP-Control connection breaks when the Stop-Sessions command is sent, the receiver MAY not completely invalidate the session results. It MUST discard all record of packets that follow (in other words, that have greater sequence number than) the last packet that was actually received before any lost packet records. This will help differentiate between packet losses that occurred in the network and packets the sending process may have never sent. If a receiver of an OWAMP-Test session learns, through an OWAMP- Control Stop-Sessions message, that the OWAMP-Test sender's last sequence number is lower than any sequence number actually received, the results of the complete OWAMP-Test session MUST be invalidated. A receiver of an OWAMP-Test session, upon receipt of an OWAMP-Control Stop-Sessions command, MUST discard any packet records -- including lost packet records -- with a (computed) send time that falls between the current time minus Timeout and the current time. This ensures statistical consistency for the measurement of loss and duplicates in the event that the Timeout is greater than the time it takes for the Stop-Sessions command to take place. To effect complete sessions, each side of the control connection SHOULD wait until all sessions are complete before sending the Stop- Sessions message. The completed time of each session is determined as Timeout after the scheduled time for the last sequence number. Endpoints MAY add a small increment to the computed completed time for send endpoints to ensure that the Stop-Sessions message reaches the receiver endpoint after Timeout. To effect a premature stop of sessions, the party that initiates this command MUST stop its OWAMP-Test send streams to send the Session Packets Sent values before sending this command. That party SHOULD wait until receiving the response Stop-Sessions message before stopping the receiver streams so that it can use the values from the received Stop-Sessions message to validate the data.
The server MUST respond with a Fetch-Ack message. The format of this server response is as follows: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Accept | Finished | MBZ (2 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Seqno | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Number of Skip Ranges | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Number of Records | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | HMAC (16 octets) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Again, non-zero in the Accept field means a rejection of command. The server MUST specify zero for all remaining fields if Accept is non-zero. The client MUST ignore all remaining fields (except for the HMAC) if Accept is non-zero. The full list of available Accept values is described in Section 3.3, "Values of the Accept Field". Finished is non-zero if the OWAMP-Test session has terminated. Next Seqno indicates the next sequence number that would have been sent from this send session. For completed sessions, this will equal NumPackets from the Request-Session. This information is only available if the session has terminated. If Finished is zero, then Next Seqno MUST be set to zero by the server. Number of Skip Ranges indicates the number of holes that actually occurred in the sending process. This information is only available if the session has terminated. If Finished is zero, then Skip Ranges MUST be set to zero by the server. Number of Records is the number of packet records that fall within the requested range. This number might be less than the Number of Packets in the reproduction of the Request-Session command because of a session that ended prematurely, or it might be greater because of duplicates. If Accept was non-zero, this concludes the response to the Fetch- Session message. If Accept was 0, the server then MUST immediately send the OWAMP-Test session data in question.
The OWAMP-Test session data consists of the following (concatenated): + A reproduction of the Request-Session command that was used to start the session; it is modified so that actual sender and receiver port numbers that were used by the OWAMP-Test session always appear in the reproduction. + Zero or more (as specified) Skip Range descriptions. The last (possibly full, possibly incomplete) block (16 octets) of Skip Range descriptions is padded with zeros, if necessary. + 16 octets of HMAC. + Zero or more (as specified) packet records. The last (possibly full, possibly incomplete) block (16 octets) of data is padded with zeros, if necessary. + 16 octets of HMAC. Skip Range descriptions are simply two sequence numbers that, together, indicate a range of packets that were not sent: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| | First Seqno Skipped | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Last Seqno Skipped | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Skip Range descriptions should be sent out in order, as sorted by First Seqno. If any Skip Ranges overlap or are out of order, the session data is to be considered invalid and the connection SHOULD be closed and any results obtained considered invalid. Each packet record is 25 octets and includes 4 octets of sequence number, 8 octets of send timestamp, 2 octets of send timestamp error estimate, 8 octets of receive timestamp, 2 octets of receive timestamp error estimate, and 1 octet of Time To Live (TTL), or Hop Limit in IPv6:
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 00| Seq Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 04| Send Error Estimate | Receive Error Estimate | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 08| Send Timestamp | 12| | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 16| Receive Timestamp | 20| | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 24| TTL | +-+-+-+-+-+-+-+-+ Packet records are sent out in the same order the actual packets were received. Therefore, the data is in arrival order. Note that lost packets (if any losses were detected during the OWAMP-Test session) MUST appear in the sequence of packets. They can appear either at the point when the loss was detected or at any later point. Lost packet records are distinguished as follows: + A send timestamp filled with the presumed send time (as computed by the send schedule). + A send error estimate filled with Multiplier=1, Scale=64, and S=0 (see the OWAMP-Test description for definition of these quantities and explanation of timestamp format and error estimate format). + A normal receive error estimate as determined by the error of the clock being used to declare the packet lost. (It is declared lost if it is not received by the Timeout after the presumed send time, as determined by the receiver's clock.) + A receive timestamp consisting of all zero bits. + A TTL value of 255.