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The IETF has completed its work on the core specification of TWAMP - the Two-Way Active Measurement Protocol. This memo describes a new feature for TWAMP, that gives the controlling host the ability to start and stop one or more individual test sessions using their Session Identifiers. The base capability of the TWAMP protocol requires all test sessions previously requested and accepted to start and stop at the same time.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.) [RFC2119].
1.
Introduction
2.
Purpose and Scope
3.
TWAMP Control Extensions
3.1.
Connection Setup with Individual Session Control
3.2.
Start-Sessions Command with Session Control
3.3.
Stop-Sessions Command with Session Control
3.4.
SERVWAIT Timeout Operation
3.5.
Additional considerations
4.
TWAMP Test with Individual Session Control
4.1.
Sender Behavior
4.2.
Reflector Behavior
5.
Security Considerations
6.
IANA Considerations
6.1.
Registry Specification
6.2.
Registry Management
6.3.
Experimental Numbers
6.4.
Registry Contents
7.
Acknowledgements
8.
References
8.1.
Normative References
8.2.
Informative References
§
Authors' Addresses
§
Intellectual Property and Copyright Statements
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The IETF has completed its work on the core specification of TWAMP - the Two-Way Active Measurement Protocol [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.). TWAMP is an extension of the One-way Active Measurement Protocol, OWAMP [RFC4656] (Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M. Zekauskas, “A One-way Active Measurement Protocol (OWAMP),” September 2006.). The TWAMP specification gathered wide review as it approached completion, and the by-products were several recommendations for new features in TWAMP. There are a growing number TWAMP implementations at present, and wide-spread usage is expected. There are even devices that are designed to test implementations for protocol compliance.
This memo describes a new feature for TWAMP. TWAMP (and OWAMP) start all previously requested and accepted test sessions at once. This feature allows the Control-Client to control individual test sessions on the basis of their Session Identifier (SID). The feature permits a short duration TWAMP test to start (and/or stop) during a longer test. This feature permits a specific diagnostic test to begin if intermediate results indicate that the test is warranted, for example.
This feature requires a Mode bit position assignment and the assignment of two new TWAMP command numbers (for the augmented Start and Stop commands). This feature also specifies a new Stop-ACK Server response, to complete the symmetry of the session stopping process in the same way as the Start-ACK response.
Implementers of this feature may also wish to implement the "Reflect Octets" feature, described in [draft-ietf-ippm-twamp-reflect-octets, work in progress]. This feature allows a Control-Client to insert a locally-specified request number into the Request-TW-Session command (in octets originally designated MBZ=Must Be Zero), and a compliant Server will return the request number in its reply (Accept message).
This memo is intended to be an update to the TWAMP RFC.
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The purpose of this memo is to describe an additional function and feature for TWAMP [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.). The feature needs a clear description so it can be discussed and (hopefully) adopted in the IP Performance Metrics Charter.
The scope of the memo is currently limited to specifications of the following features:
The motivation for this added feature is the ability to start and stop individual test sessions at will, using a single TWAMP-control connection.
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TWAMP-Control protocol is a derivative of the OWAMP-Control protocol, and provides two-way measurement capability. TWAMP [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.) uses the Modes Field to identify and select specific communication capabilities, and this field is a recognized extension mechanism. The following sections describe one such extension.
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TWAMP-Control connection establishment follows the procedure defined in section 3.1 of [RFC4656] (Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M. Zekauskas, “A One-way Active Measurement Protocol (OWAMP),” September 2006.) OWAMP. The Individual Session Control mode requires one new bit position (and value) to identify the ability of the Server/Session-Reflector to start and stop specific sessions (according to their Session Identifier, or SID). This new feature requires an additional TWAMP mode bit assignment as follows:
Value Description Reference/Explanation
0 Reserved
1 Unauthenticated RFC4656, Section 3.1
2 Authenticated RFC4656, Section 3.1
4 Encrypted RFC4656, Section 3.1
8 Unauth. TEST protocol, draft-...-more-twamp (3)
Auth. CONTROL
--------------------------------------------------------
zzz Individual Session this memo, bit position (Z)
Control
In the original OWAMP mode field, setting bit positions 0, 1 or 2 indicated the security mode of the Control protocol, and the Test protocol inherited the same mode (see section 4 of [RFC4656] (Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M. Zekauskas, “A One-way Active Measurement Protocol (OWAMP),” September 2006.)). In the [I‑D.ietf‑ippm‑more‑twamp] (Morton, A. and K. Hedayat, “More Features for the Two-Way Active Measurement Protocol - TWAMP,” May 2009.) memo, bit position (3) allows a different security mode in the Test protocol and uses the unauthenticated test packet format.
If the Server sets the new bit position (bit position Z) in the Server Greeting message to indicate its capabilities, then the Server and Session-Reflector MUST comply with the requirements of this memo to control sessions on an individual basis if desired.
If the Control-Client intends to control sessions on an individual basis (according to the requirements in this memo), it MUST set the mode bit (Z, corresponding to the new mode) in the Setup Response message.
IF the Control-Client has selected the Reflect Octets feature [draft-ietf-ippm-twamp-reflect-octets, work in progress] in combination with the Individual Session Control feature (after the Server identified its capability), AND utilizes the feature to insert a locally-specified request number in the Request-TW-Session command, THEN the Control Client MAY send more than one Request-TW-Session command to a given Server without waiting for the corresponding Accept-Session message.
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Having requested one or more test sessions and received affirmative Accept-Session responses, a TWAMP Client MAY start the execution of the requested test sessions by sending a Start-Sessions message to the server.
The format of this 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B | 7 | | +-+-+-+-+-+-+-+-+ + | MBZ (11 octets) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Number of Sessions | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B | | | First SID (16 octets) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B | | . remaining SIDs (16 octets each) . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B | | | HMAC (16 octets) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
The Number of sessions field indicates the count of sessions that this Start command applies to. The SID is as defined in OWAMP (and TWAMP) section 3.5 [RFC4656] (Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M. Zekauskas, “A One-way Active Measurement Protocol (OWAMP),” September 2006.).
The Server MUST respond with a Start-Ack message (which SHOULD be sent as quickly as possible). Start-Ack messages have the format defined in section 3.7 of [RFC4656] (Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M. Zekauskas, “A One-way Active Measurement Protocol (OWAMP),” September 2006.).
The Control Client MUST NOT send a subsequent Start Sessions command until an outstanding message is acknowledged with a Start-Ack message.
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The Stop-Sessions command can only be issued by the Control-Client. The message MUST contain at least one SID. The message is terminated with a single block HMAC, to complete the Stop-Sessions Command.
Thus, the TWAMP Stop-Sessions command for individual session control is constructed 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B | 8 | Accept | MBZ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Number of Sessions | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MBZ (8 octets) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B | | | First SID (16 octets) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B | | . remaining SIDs (16 octets each) . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B | | | HMAC (16 octets) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
The Number of sessions field indicates the count of sessions that this Stop command applies to. The SID is as defined in OWAMP (and TWAMP) section 3.5 [RFC4656] (Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M. Zekauskas, “A One-way Active Measurement Protocol (OWAMP),” September 2006.).
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Section 3.1 of [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.) describes the operation of the optional SERVWAIT timer. In normal TWAMP operation, the Server suspends monitoring the SERVWAIT timer while test sessions are in progress. When the Individual Session Control feature is utilized, this suspension is extended to cover the time when ANY test session is in progress.
Thus, the Server SHALL suspend monitoring control connection activity after receiving any Start-Sessions command, and after receiving a Stop-Sessions command for all corresponding SIDs (and no test sessions are in-progress), OR when REFWAIT expires on ALL test sessions initiated by a TWAMP-Control connection, then the SERVWAIT monitoring SHALL resume (as though a Stop-Sessions command had been received). An implementation which supports the SERVWAIT timeout option SHOULD also implement the REFWAIT timeout option.
The diagram below illustrates the operation of timers SERVWAIT and REFWAIT.
SERVWAIT REFWAIT SERVWAIT
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+
(no sessions
in-progress)
+-+-+-+-+-+-+-+-+-+-+-+
SID="1"
+-+-+-+-+
SID="2"
+-+-+-+-+-+-+-+-+
SID="3"
>>>>>>>>>> Time >>>>>>>>>>>>>>>>>>> Time >>>>>>>>>>>>>>>> Time >>>>>
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The value of the Modes field sent by the Server (in the Server Greeting message) is the bit-wise OR of the mode values that it is willing to support during this session.
If this feature is adopted, the last ???? bits of the Modes 32-bit field are used. A Control-Client MAY ignore other bit positions greater than 2 in the Modes Field, or it MAY support other features that are communicated in these bit positions. (The unassigned bits are available for future protocol extensions.)
Other ways in which TWAMP extends OWAMP are described in [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.).
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The TWAMP test protocol is similar to the OWAMP [RFC4656] (Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M. Zekauskas, “A One-way Active Measurement Protocol (OWAMP),” September 2006.) test protocol with the exception that the Session-Reflector transmits test packets to the Session-Sender in response to each test packet it receives. TWAMP [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.) defines two different test packet formats, one for packets transmitted by the Session-Sender and one for packets transmitted by the Session-Reflector. As with OWAMP-Test protocol there are three security modes: unauthenticated, authenticated, and encrypted. Unauthenticated mode has one test packet format, while authenticated and encrypted modes use another (common) format.
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The individual session control feature requires that the sender MUST manage test sessions according to their SID. Otherwise, the sender behavior is as describe in section 4.1 of [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.).
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The TWAMP Reflector follows the procedures and guidelines in section 4.2 of [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.), with the following additional functions required by this feature:
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The security considerations that apply to any active measurement of live networks are relevant here as well. See the security considerations in[RFC4656] (Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M. Zekauskas, “A One-way Active Measurement Protocol (OWAMP),” September 2006.) and [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.).
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This memo requests assignment of one mode bit position/value to the IANA registry for the TWAMP Mode field, and describes behavior when the new mode is used. This field is a recognized extension mechanism for TWAMP.
This memo also requests assignment of two command numbers in the TWAMP-Control Command Number registry, and describes the use of the new commands. The command number field is a recognized extension mechanism for TWAMP.
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IANA has created a TWAMP-Modes registry (as requested in [I‑D.ietf‑ippm‑more‑twamp] (Morton, A. and K. Hedayat, “More Features for the Two-Way Active Measurement Protocol - TWAMP,” May 2009.)). TWAMP-Modes are specified in TWAMP Server Greeting messages and Set-up Response messages, as described in section 3.1 of [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.), consistent with section 3.1 of [RFC4656] (Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M. Zekauskas, “A One-way Active Measurement Protocol (OWAMP),” September 2006.), and extended by this memo. Modes are indicated by setting bits in the 32-bit Modes field. Thus, this registry can contain a total of 32 possible values.
IANA has also created a TWAMP-Control Command Number registry. TWAMP-Control commands are specified by the first octet in TWAMP-Control messages as specified in section 3.5 of [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.), and augmented by this memo. This registry may contain sixteen possible values.
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Because the TWAMP-Control Command Number registry can contain only sixteen values, TWAMP-Modes can only contain thirty-two values, and because TWAMP is an IETF protocol, these registries must be updated only by "IETF Consensus" as specified in [RFC2434] (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” October 1998.)(an RFC documenting registry use that is approved by the IESG). Management of these registries is described in section 8.2 of [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.) and [I‑D.ietf‑ippm‑more‑twamp] (Morton, A. and K. Hedayat, “More Features for the Two-Way Active Measurement Protocol - TWAMP,” May 2009.).
This memo proposes assignment of values 7 and 8.
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One experimental value has been assigned in the TWAMP-Control Command Number registry.
No additional experimental values are assigned in the TWAMP-Modes registry.
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TWAMP-Control Command Number Registry
Value Description Semantics Definition
0 Reserved
1 Forbidden
2 Start-Sessions RFC4656, Section 3.7
3 Stop-Sessions RFC4656, Section 3.8
4 Reserved
5 Request-TW-Session draft-ietf-ippm-twamp, Section 3.5
6 Experimentation draft-ietf-ippm-twamp, Section 8.3
------------------------------------------------------------------
7 Start-Sessions with this memo, Section 3.2
Individ. Session Cntrl.
8 Stop-Sessions with this memo, Section 3.3
Individ. Session Cntrl.
TWAMP-Modes Registry
Value Description Reference/Explanation
0 Reserved
1 Unauthenticated RFC4656, Section 3.1
2 Authenticated RFC4656, Section 3.1
4 Encrypted RFC4656, Section 3.1
8 Unauth. TEST protocol, draft-...-more-twamp (3)
Auth. CONTROL
--------------------------------------------------------
zzz Individual Session this memo, Section 3.1
Control bit position (Z)
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The author would like to thank anyone who provides valuable comments on this feature.
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| [I-D.ietf-ippm-more-twamp] | Morton, A. and K. Hedayat, “More Features for the Two-Way Active Measurement Protocol - TWAMP,” draft-ietf-ippm-more-twamp-02 (work in progress), May 2009 (TXT). |
| [RFC2119] | Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” BCP 14, RFC 2119, March 1997 (TXT, HTML, XML). |
| [RFC2434] | Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” BCP 26, RFC 2434, October 1998 (TXT, HTML, XML). |
| [RFC4656] | Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M. Zekauskas, “A One-way Active Measurement Protocol (OWAMP),” RFC 4656, September 2006 (TXT). |
| [RFC5357] | Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” RFC 5357, October 2008 (TXT). |
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| [x] | “.” |
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| Al Morton | |
| AT&T Labs | |
| 200 Laurel Avenue South | |
| Middletown,, NJ 07748 | |
| USA | |
| Phone: | +1 732 420 1571 |
| Fax: | +1 732 368 1192 |
| Email: | acmorton@att.com |
| URI: | http://home.comcast.net/~acmacm/ |
| Murtaza Chiba | |
| Cisco Systems | |
| USA | |
| Phone: | +1 |
| Fax: | +1 |
| Email: | mchiba@cisco.com |
| URI: |
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