Network Working Group A. Morton
Internet-Draft AT&T Labs
Intended status: Standards Track M. Chiba
Expires: April 29, 2009 Cisco Systems
October 26, 2008
Individual Session Control Feature for TWAMP
draft-ietf-ippm-twamp-session-cntrl-00
Status of this Memo
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Abstract
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.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
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"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . 3
3. TWAMP Control Extensions . . . . . . . . . . . . . . . . . . . 4
3.1. Connection Setup with Individual Session Control . . . . . 4
3.2. Start-Sessions Command with Session Control . . . . . . . 5
3.3. Stop-Sessions Command with Session Control . . . . . . . . 6
3.4. SERVWAIT Timeout Operation . . . . . . . . . . . . . . . . 7
3.5. Additional considerations . . . . . . . . . . . . . . . . 8
4. TWAMP Test with Individual Session Control . . . . . . . . . . 8
4.1. Sender Behavior . . . . . . . . . . . . . . . . . . . . . 9
4.2. Reflector Behavior . . . . . . . . . . . . . . . . . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6.1. Registry Specification . . . . . . . . . . . . . . . . . . 9
6.2. Registry Management . . . . . . . . . . . . . . . . . . . 10
6.3. Experimental Numbers . . . . . . . . . . . . . . . . . . . 10
6.4. Registry Contents . . . . . . . . . . . . . . . . . . . . 10
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Normative References . . . . . . . . . . . . . . . . . . . 11
8.2. Informative References . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
Intellectual Property and Copyright Statements . . . . . . . . . . 13
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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 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.
2. Purpose and Scope
The purpose of this memo is to describe an additional function and
feature for TWAMP [RFC5357]. 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:
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1. Extension of the modes of operation through assignment of a new
value in the Mode field to communicate feature capability and
use,
2. the definition of augmented Start Session and Stop Session
commands, and
3. the definition of related procedures for TWAMP entities.
The motivation for this added feature is the ability to start and
stop individual test sessions at will, using a single TWAMP-control
connection.
3. TWAMP Control Extensions
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.
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 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]). In
the [I-D.ietf-ippm-more-twamp] memo, bit position (3) allows a
different security mode in the Test protocol and uses the
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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.
3.2. Start-Sessions Command with Session Control
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:
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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].
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].
The Control Client MUST NOT send a subsequent Start Sessions command
until an outstanding message is acknowledged with a Start-Ack
message.
3.3. Stop-Sessions Command with Session Control
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:
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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].
3.4. 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-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.
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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 >>>>>
3.5. 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.
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].
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 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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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 describe 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 Packets for a specific session/SID not received within the Timeout
(following the Stop-Session command) MUST be ignored by the
Session-Reflector. The Session-Reflector MUST NOT generate a test
packet to the Session-Sender for packets that are ignored.
o If the RECOMMENDED REFWAIT timer is implemented, it SHOULD be
enforced when any test session is in-progress (started and not
stopped).
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
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.
6.1. Registry Specification
IANA has created a TWAMP-Modes registry (as requested in
[I-D.ietf-ippm-more-twamp]). TWAMP-Modes are specified in TWAMP
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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. 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], and
augmented by this memo. This registry may contain sixteen possible
values.
6.2. Registry Management
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](an RFC documenting
registry use that is approved by the IESG). Management of these
registries is described in section 8.2 of [RFC5357] and
[I-D.ietf-ippm-more-twamp].
This memo proposes assignment of values 7 and 8.
6.3. Experimental Numbers
One experimental value has been assigned in the TWAMP-Control Command
Number registry.
No additional experimental values are assigned in the TWAMP-Modes
registry.
6.4. Registry Contents
TWAMP-Control Command Number Registry
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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)
7. Acknowledgements
The author would like to thank anyone who provides valuable comments
on this feature.
8. References
8.1. Normative References
[I-D.ietf-ippm-more-twamp]
Morton, A. and K. Hedayat, "More Features for TWAMP",
draft-ietf-ippm-more-twamp-00 (work in progress),
October 2008.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
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IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[RFC4656] Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
Zekauskas, "A One-way Active Measurement Protocol
(OWAMP)", RFC 4656, September 2006.
[RFC5357] Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
RFC 5357, October 2008.
8.2. Informative References
[x] "".
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
USA
Phone: +1
Fax: +1
Email: mchiba@cisco.com
URI:
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