Individual Session Control Feature for the Two-Way Active Measurement Protocol (TWAMP)
RFC 5938
| Document | Type |
RFC - Proposed Standard
(August 2010; Errata)
Updates RFC 5357
|
|
|---|---|---|---|
| Authors | Al Morton , Murtaza Chiba | ||
| Last updated | 2020-01-21 | ||
| Replaces | draft-morton-ippm-twamp-session-cntrl | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Formats | plain text html pdf htmlized with errata bibtex | ||
| Reviews | |||
| Stream | WG state | (None) | |
| Document shepherd | No shepherd assigned | ||
| IESG | IESG state | RFC 5938 (Proposed Standard) | |
| Action Holders |
(None)
|
||
| Consensus Boilerplate | Unknown | ||
| Telechat date | |||
| Responsible AD | Lars Eggert | ||
| Send notices to | (None) | ||
Internet Engineering Task Force (IETF) A. Morton
Request for Comments: 5938 AT&T Labs
Updates: 5357 M. Chiba
Category: Standards Track Cisco Systems
ISSN: 2070-1721 August 2010
Individual Session Control Feature
for the Two-Way Active Measurement Protocol (TWAMP)
Abstract
The IETF has completed its work on the core specification of TWAMP --
the Two-Way Active Measurement Protocol. This memo describes an
OPTIONAL feature for TWAMP, that gives the controlling host the
ability to start and stop one or more individual test sessions using
Session Identifiers. The base capability of the TWAMP protocol
requires all test sessions that were previously requested and
accepted to start and stop at the same time.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc5938.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Morton & Chiba Standards Track [Page 1]
RFC 5938 TWAMP Session Control August 2010
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . 4
3. TWAMP Control Extensions . . . . . . . . . . . . . . . . . . . 4
3.1. Connection Setup with Individual Session Control . . . . . 5
3.2. Start-N-Sessions Command with Individual Session
Control . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.3. Start-N-Ack Command with Individual Session Control . . . 7
3.4. Stop-N-Sessions Command with Individual Session Control . 9
3.5. Stop-N-Ack Command with Individual Session Control . . . . 10
3.6. SERVWAIT Timeout Operation . . . . . . . . . . . . . . . . 12
3.7. Additional Considerations . . . . . . . . . . . . . . . . 12
4. TWAMP Test with Individual Session Control . . . . . . . . . . 13
4.1. Sender Behavior . . . . . . . . . . . . . . . . . . . . . 13
4.2. Reflector Behavior . . . . . . . . . . . . . . . . . . . . 13
5. Security Considerations . . . . . . . . . . . . . . . . . . . 14
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
6.1. Registry Specification . . . . . . . . . . . . . . . . . . 14
6.2. Registry Management . . . . . . . . . . . . . . . . . . . 14
6.3. Experimental Numbers . . . . . . . . . . . . . . . . . . . 15
6.4. Registry Contents . . . . . . . . . . . . . . . . . . . . 15
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
8.1. Normative References . . . . . . . . . . . . . . . . . . . 16
8.2. Informative References . . . . . . . . . . . . . . . . . . 16
Morton & Chiba Standards Track [Page 2]
RFC 5938 TWAMP Session Control August 2010
1. Introduction
The IETF has completed its work on the core specification of TWAMP --
the Two-Way Active Measurement Protocol [RFC5357]. TWAMP is an
extension of the One-way Active Measurement Protocol, OWAMP
[RFC4656]. 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 of TWAMP implementations at present, and widespread usage is
expected. There are even devices that are designed to test
implementations for protocol compliance.
This memo describes an OPTIONAL feature for TWAMP. [RFC5357] 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). This 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 Modes field bit position assignment and the
use of two new TWAMP command numbers (for the augmented Start and
Stop commands). This feature also specifies the use of a new Stop-N-
ACK Server response, to complete the symmetry of the session-stopping
process in the same way as the Start-ACK (Start-N-ACK when used with
this feature) response.
The Individual Session Control feature gives the Control-Client new
flexibility to manage any number of test sessions once they are
established. However, [RFC5357] test sessions are established in
serial order and the total establishment time grows with the number
of sessions and the round-trip time. Therefore, implementers of this
feature may also wish to implement the "Reflect Octets" feature,
described in [REFLECT]. This feature allows a Control-Client to
distinguish between parallel Request-TW-Session commands because a
participating Server can return octets (e.g., the Control-Client's
local index) in its reply to the request. Thus, the Reflect Octets
feature supports the efficient establishment of many simultaneous
test sessions that the Individual Session Control feature can then
manage (start/stop).
This memo is an update to the TWAMP core protocol specified in
[RFC5357]. Measurement systems are not required to implement the
feature described in this memo to claim compliance with [RFC5357].
Morton & Chiba Standards Track [Page 3]
RFC 5938 TWAMP Session Control August 2010
Throughout this memo, the bits marked MBZ (Must Be Zero) MUST be set
to zero by senders and MUST be ignored by receivers. Also, the HMAC
(Hashed Message Authentication Code) MUST be calculated as defined in
Section 3.2 of [RFC4656].
1.1. Requirements Language
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 [RFC2119].
2. Purpose and Scope
The purpose of this memo is to describe an additional OPTIONAL
function and feature for TWAMP [RFC5357].
The scope of the memo is limited to specifications of the following
features:
1. extension of the modes of operation through assignment of a new
value in the Modes field to communicate feature capability and
use,
2. the definitions of augmented start session and stop session
commands (with corresponding acknowledgements), and
3. the definition of related procedures for TWAMP entities.
The motivation for this feature is the ability to start and stop
individual test sessions at will, using a single TWAMP-Control
connection.
When the Server and Control-Client have agreed to use the Individual
Session Control mode during control connection setup, then the
Control-Client, the Server, the Session-Sender, and the Session-
Reflector MUST all conform to the requirements of that mode, as
identified below. The original TWAMP-Control Start and Stop commands
MUST NOT be used.
3. TWAMP Control Extensions
The TWAMP-Control protocol is a derivative of the OWAMP-Control
protocol, and provides two-way measurement capability. TWAMP
[RFC5357] 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.
Morton & Chiba Standards Track [Page 4]
RFC 5938 TWAMP Session Control August 2010
3.1. Connection Setup with Individual Session Control
TWAMP-Control connection establishment follows the procedure defined
in Section 3.1 of [RFC4656] 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 RFC 4656, Section 3.1
2 Authenticated RFC 4656, Section 3.1
4 Encrypted RFC 4656, Section 3.1
8 Unauth. TEST protocol, RFC 5618, Section 3.1
Encrypted CONTROL
--------------------------------------------------------
16 Individual Session RFC 5938, bit position 4
Control
In the original OWAMP Modes 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]). In
the [RFC5618] 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 4) 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 (4, corresponding to the new mode) in the Setup Response
message. This means that:
1. The Control-Client and the Server MUST use the start and stop
commands intended for individual session control and the
corresponding acknowledgements, as defined in the sections that
follow.
2. The Control-Client and the Server MUST NOT use the start and stop
commands (2 and 3) and the acknowledgement defined in [RFC5357].
The Control-Client MUST also set one mode bit to indicate the chosen
security mode (currently bits 0, 1, 2, or 3), consistent with the
modes offered by the Server. The Control-Client MAY also set Modes
Morton & Chiba Standards Track [Page 5]
RFC 5938 TWAMP Session Control August 2010
field bit 4 with other features and bit positions (such as the
reflect octets feature).
3.2. Start-N-Sessions Command with Individual Session Control
Having
o initiated Individual Session Control mode in the Setup Response,
o requested one or more test sessions, and
o received affirmative Accept-Session response(s),
a TWAMP Client MAY start the execution of one or more test sessions
by sending a Start-N-Sessions message to the Server (note that "N"
indicates that this command is applicable to one or more sessions,
and does not change with the number of sessions identified in the
command).
The format of the Start-N-Sessions 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
Note: In figures, "B" indicates the boundary of a 16-octet word.
Morton & Chiba Standards Track [Page 6]
RFC 5938 TWAMP Session Control August 2010
The Command Number value of 7 indicates that this is a Start-N-
Sessions command. The Control-Client MUST compose this command, and
the Server MUST interpret this command, according to the field
descriptions below.
The Number of Sessions field indicates the count of sessions that
this Start command applies to, and MUST be one or greater. The
number of SID fields that follow MUST be equal to the value in the
Number of Sessions field (otherwise, the command MUST NOT be affirmed
with a zero Accept field in the Start-N-Ack response).
All SID fields are constructed as defined in the last paragraph of
Section 3.5 of OWAMP [RFC4656] (and referenced in TWAMP). Note that
the SID is assigned by the Server during the session request
exchange.
The message is terminated with a single block HMAC, as illustrated
above.
The Server MUST respond with one or more Start-N-Ack messages (which
SHOULD be sent as quickly as possible). Start-N-Ack messages SHALL
have the format defined in the next session.
When using Individual Session Control mode and its Start-N-Ack
command as described in the next section, multiple Start-N-Sessions
commands MAY be sent without waiting for acknowledgement, and the
Start-N-sessions commands MAY arrive in any order.
3.3. Start-N-Ack Command with Individual Session Control
The Server responds to the Start-N-Sessions command (for one or more
specific sessions referenced by their SIDs) with one or more Start-N-
Ack commands with Accept fields corresponding to one or more of the
SIDs. This allows for the possibility that a Server cannot
immediately start one or more of the sessions referenced in a
particular Start-N-Sessions command, but can start one or more of the
sessions.
Morton & Chiba Standards Track [Page 7]
RFC 5938 TWAMP Session Control August 2010
The format of the 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
| 8 | Accept | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ (8 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Sessions |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
| |
| First SID (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
| |
. remaining SIDs (16 octets each) .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
| |
| HMAC (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Command Number value of 8 indicates that this is a Start-N-Ack
message. The Server MUST compose this command, and the Control-
Client MUST interpret this command, according to the field
descriptions below.
The Accept field values are defined in Section 3.3 of OWAMP
[RFC4656].
The Number of Sessions field indicates the count of sessions that
this Start-N-Ack command applies to, and MUST be one or greater. The
number of SID fields that follow MUST be equal to the value in the
Number of Sessions field.
All SID fields are constructed as defined in the last paragraph of
Section 3.5 of OWAMP [RFC4656] (and referenced in TWAMP). Note that
the SID is assigned by the Server during the session request
exchange.
The message is terminated with a single block HMAC, as illustrated
above.
Morton & Chiba Standards Track [Page 8]
RFC 5938 TWAMP Session Control August 2010
Note that the SIDs for all Sessions with the same 'Accept' code can
be acknowledged using the same Start-N-Ack message.
For example, say that the Server receives a Start-N-Sessions command
for SIDs 1, 2, 3, and 4. The Server determines that the resources
for SID=3 are temporarily unavailable. The Server responds with two
Start-N-Ack commands with fields as follows:
Accept = 0 Number of Sessions = 3 SIDs 1, 2, 4
Accept = 5 Number of Sessions = 1 SID 3
3.4. Stop-N-Sessions Command with Individual Session Control
The Stop-N-Sessions command can only be issued by the Control-Client.
The command MUST contain at least one SID.
The TWAMP Stop-N-Sessions command for use in Individual Session
Control mode is formatted 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
| 9 | |
+-+-+-+-+-+-+-+-+ +
| MBZ (11 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Sessions |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
| |
| First SID (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
| |
. remaining SIDs (16 octets each) .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
| |
| HMAC (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
Morton & Chiba Standards Track [Page 9]
RFC 5938 TWAMP Session Control August 2010
The Command Number value of 9 indicates that this is a Stop-N-
Sessions command. The Control-Client MUST compose this command, and
the Server MUST interpret this command, according to the field
descriptions below.
The Number of Sessions field indicates the count of sessions to which
this Stop-N-Sessions command applies. The SID is as defined in
Section 3.5 of OWAMP [RFC4656] (and TWAMP), and the value MUST be one
or greater. The number of SID fields that follow MUST be equal to
the value in the Number of Sessions field.
The message is terminated with a single block HMAC, as illustrated
above.
The Server MUST respond with one or more Stop-N-Ack messages (which
SHOULD be sent as quickly as possible). Stop-N-Ack messages SHALL
have the format defined in the next session.
3.5. Stop-N-Ack Command with Individual Session Control
In response to the Stop-N-Sessions command (for one or more specific
sessions referenced by their SIDs), the Server MUST reply with one or
more Stop-N-Ack commands with Accept fields corresponding to one or
more of the SIDs. This allows for the possibility that a Server
cannot immediately stop one or more of the sessions referenced in a
particular Stop-N-Sessions command, but can stop one or more of the
sessions.
Morton & Chiba Standards Track [Page 10]
RFC 5938 TWAMP Session Control August 2010
The format for the Stop-N-Ack command 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
| 10 | Accept | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ (8 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Sessions |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
| |
| First SID (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
| |
. remaining SIDs (16 octets each) .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
| |
| HMAC (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Command Number value of 10 indicates that this is a Stop-N-Ack
message. The Server MUST compose this command, and the Control-
Client MUST interpret this command, according to the field
descriptions below.
The Accept Field values are defined in Section 3.3 of OWAMP
[RFC4656].
The Number of Sessions field indicates the count of sessions that
this Stop-N-Ack command applies to, and MUST be one or greater. The
number of SID fields that follow MUST be equal to the value in the
Number of Sessions field.
All SID fields are constructed as defined in the last paragraph of
Section 3.5 of OWAMP [RFC4656] (and referenced in TWAMP). Note that
the SID is assigned by the Server during the session request
exchange.
The message is terminated with a single block HMAC, as illustrated
above.
Morton & Chiba Standards Track [Page 11]
RFC 5938 TWAMP Session Control August 2010
Note that the SIDs for all Sessions with the same 'Accept' code can
be acknowledged using the same Stop-N-Ack message.
3.6. SERVWAIT Timeout Operation
Section 3.1 of [RFC5357] 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-N-Sessions command, and after receiving a
Stop-N-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-N-Sessions command had been
received). An implementation that 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 >>>>>
3.7. Additional Considerations
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.
With the publication of this feature, bit positions 0 through 4 of
the 32-bit Modes field are used. A Control-Client MAY ignore bit
positions greater than 2 in the Modes field, or it MAY support
Morton & Chiba Standards Track [Page 12]
RFC 5938 TWAMP Session Control August 2010
OPTIONAL features that are communicated in bit positions 3 and
higher. (The unassigned bits are available for future protocol
extensions.)
Other ways in which TWAMP extends OWAMP are described in [RFC5357].
4. TWAMP Test with Individual Session Control
The TWAMP test protocol is similar to the OWAMP [RFC4656] 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] 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 the OWAMP-Test
protocol, there are three security modes: unauthenticated,
authenticated, and encrypted. The unauthenticated mode has one test
packet format, while the authenticated and encrypted modes use
another (common) format.
4.1. Sender Behavior
The individual session control feature requires that the sender MUST
manage test sessions according to their SID. Otherwise, the sender
behavior is as described in Section 4.1 of [RFC5357].
4.2. Reflector Behavior
The TWAMP Reflector follows the procedures and guidelines in Section
4.2 of [RFC5357], with the following additional functions required by
this feature:
o The Session-Reflector MUST manage all test sessions accepted
according to their SID.
o Upon receipt of a TWAMP-Control Stop-N-Sessions command
referencing a specific session/SID, the Session-Reflector MUST
ignore TWAMP-Test packets (in the same session/SID) that arrive at
the current time plus the Timeout (in the Request-TW-Session
command and assuming subsequent acknowledgement). The Session-
Reflector MUST NOT generate a test packet to the Session-Sender
for packets that are ignored. (Note: The Request-TW-Session
command includes sender address + port and receiver address +
port, and this is usually sufficient to distinguish sessions.)
o If the REFWAIT timer is implemented, it SHOULD be enforced when
any test session is in progress (started and not stopped).
Morton & Chiba Standards Track [Page 13]
RFC 5938 TWAMP Session Control August 2010
5. Security Considerations
The security considerations that apply to any active measurement of
live networks are relevant here as well. See the security
considerations in [RFC4656] and [RFC5357].
6. IANA Considerations
As a result of this document, IANA has assigned one mode bit
position/value for a mode in the IANA registry for the TWAMP Modes
field, and this memo describes the behavior when the new mode is
used. This field is a recognized extension mechanism for TWAMP.
As a result of this document, IANA has assigned four command numbers
in the "TWAMP-Control Command Numbers" registry, and this memo
describes the use of the new commands. The command number field is a
recognized extension mechanism for TWAMP.
6.1. Registry Specification
IANA has created a "TWAMP-Modes" registry (as requested in
[RFC5618]). TWAMP-Modes are specified in TWAMP Server Greeting
messages and Set-Up-Response messages, as described in Section 3.1 of
[RFC5357], consistent with Section 3.1 of [RFC4656], and extended by
this memo. Modes are indicated by setting bits in the 32-bit Modes
field that correspond to values in the "TWAMP-Modes" registry. For
the "TWAMP-Modes" registry, we expect that new features will be
assigned increasing registry values that correspond to single bit
positions, unless there is a good reason to do otherwise (more
complex encoding than single bit positions may be used in the future
to access the 2^32 value space).
IANA has also created the "TWAMP-Control Command Numbers" registry.
TWAMP-Control commands are specified by the first octet in TWAMP-
Control messages as specified in Section 3.5 of [RFC5357], and
augmented by this memo. This registry may contain 256 possible
values.
6.2. Registry Management
Because the "TWAMP-Control Command Numbers" registry can contain only
256 values and "TWAMP-Modes" are based on only 32 bit positions with
a maximum of 2^32 values, and because TWAMP is an IETF protocol,
these registries must be updated only by "IETF Consensus" as
specified in [RFC5226] (an RFC that documents registry use and is
approved by the IESG). Management of these registries is described
in Section 8.2 of [RFC5357] and [RFC5618].
Morton & Chiba Standards Track [Page 14]
RFC 5938 TWAMP Session Control August 2010
The values 7, 8, 9, and 10 have been assigned in the "TWAMP-Control
Command Numbers" Registry. The value 16 corresponding to the next
available bit position (4) (as described in Sections 3.1 and 3.7) has
been assigned in the "TWAMP-Modes" registry.
6.3. Experimental Numbers
One experimental value has been assigned in the "TWAMP-Control
Command Numbers" registry.
No additional experimental values are assigned in the TWAMP-Modes
registry.
6.4. Registry Contents
TWAMP-Control Command Numbers Registry
Value Description Semantics Definition
0 Reserved
1 Forbidden
2 Start-Sessions RFC 4656, Section 3.7
3 Stop-Sessions RFC 4656, Section 3.8
4 Reserved
5 Request-TW-Session RFC 5357, Section 3.5
6 Experimentation RFC 5357, Section 8.3
------------------------------------------------------------------
7 Start-N-Sessions RFC 5938, Section 3.2
8 Start-N-Ack RFC 5938, Section 3.3
9 Stop-N-Sessions RFC 5938, Section 3.4
10 Stop-N-Ack RFC 5938, Section 3.5
TWAMP-Modes Registry
Value Description Reference/Explanation
0 Reserved
1 Unauthenticated RFC 4656, Section 3.1
2 Authenticated RFC 4656, Section 3.1
4 Encrypted RFC 4656, Section 3.1
8 Unauth. TEST protocol, RFC 5618, Section 3.1
Encrypted CONTROL
--------------------------------------------------------
16 Individual Session RFC 5938, Section 3.1
Control bit position 4
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7. Acknowledgements
The authors thank everyone who provided comments on this feature,
especially Lars Eggert, Adrian Farrel, and Alexey Melnikov.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4656] Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
Zekauskas, "A One-way Active Measurement Protocol
(OWAMP)", RFC 4656, September 2006.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5357] Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
RFC 5357, October 2008.
[RFC5618] Morton, A. and K. Hedayat, "Mixed Security Mode for the
Two-Way Active Measurement Protocol (TWAMP)", RFC 5618,
August 2009.
8.2. Informative References
[REFLECT] Morton, A. and L. Ciavattone, "TWAMP Reflect Octets and
Symmetrical Size Features", Work in Progress, June 2010.
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RFC 5938 TWAMP Session Control August 2010
Authors' Addresses
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
170 W. Tasman Drive
San Jose, CA 95134
USA
Phone: +1 800 553 NETS
EMail: mchiba@cisco.com
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