draft-ietf-ippm-twamp-session-cntrl-05.txt   draft-ietf-ippm-twamp-session-cntrl-06.txt 
Network Working Group A. Morton Network Working Group A. Morton
Internet-Draft AT&T Labs Internet-Draft AT&T Labs
Updates: 5357 (if approved) M. Chiba Updates: 5357 (if approved) M. Chiba
Intended status: Standards Track Cisco Systems Intended status: Standards Track Cisco Systems
Expires: October 2, 2010 March 31, 2010 Expires: October 10, 2010 April 8, 2010
Individual Session Control Feature for TWAMP Individual Session Control Feature for TWAMP
draft-ietf-ippm-twamp-session-cntrl-05 draft-ietf-ippm-twamp-session-cntrl-06
Abstract Abstract
The IETF has completed its work on the core specification of TWAMP - The IETF has completed its work on the core specification of TWAMP -
the Two-Way Active Measurement Protocol. This memo describes an the Two-Way Active Measurement Protocol. This memo describes an
OPTIONAL feature for TWAMP, that gives the controlling host the OPTIONAL feature for TWAMP, that gives the controlling host the
ability to start and stop one or more individual test sessions using ability to start and stop one or more individual test sessions using
Session Identifiers. The base capability of the TWAMP protocol Session Identifiers. The base capability of the TWAMP protocol
requires all test sessions previously requested and accepted to start requires all test sessions previously requested and accepted to start
and stop at the same time. and stop at the same time.
Requirements Language Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
Status of this Memo Status of this Memo
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provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . 3 2. Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . 5
3. TWAMP Control Extensions . . . . . . . . . . . . . . . . . . . 4 3. TWAMP Control Extensions . . . . . . . . . . . . . . . . . . . 5
3.1. Connection Setup with Individual Session Control . . . . . 4 3.1. Connection Setup with Individual Session Control . . . . . 5
3.2. Start-N-Sessions Command with Individual Session 3.2. Start-N-Sessions Command with Individual Session
Control . . . . . . . . . . . . . . . . . . . . . . . . . 5 Control . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.3. Start-N-Ack Command with Individual Session Control . . . 7 3.3. Start-N-Ack Command with Individual Session Control . . . 8
3.4. Stop-N-Sessions Command with Individual Session Control . 9 3.4. Stop-N-Sessions Command with Individual Session Control . 10
3.5. Stop-N-Ack Command with Individual Session Control . . . . 10 3.5. Stop-N-Ack Command with Individual Session Control . . . . 11
3.6. SERVWAIT Timeout Operation . . . . . . . . . . . . . . . . 12 3.6. SERVWAIT Timeout Operation . . . . . . . . . . . . . . . . 13
3.7. Additional considerations . . . . . . . . . . . . . . . . 12 3.7. Additional considerations . . . . . . . . . . . . . . . . 13
4. TWAMP Test with Individual Session Control . . . . . . . . . . 13 4. TWAMP Test with Individual Session Control . . . . . . . . . . 14
4.1. Sender Behavior . . . . . . . . . . . . . . . . . . . . . 13 4.1. Sender Behavior . . . . . . . . . . . . . . . . . . . . . 14
4.2. Reflector Behavior . . . . . . . . . . . . . . . . . . . . 13 4.2. Reflector Behavior . . . . . . . . . . . . . . . . . . . . 14
5. Security Considerations . . . . . . . . . . . . . . . . . . . 14 5. Security Considerations . . . . . . . . . . . . . . . . . . . 14
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
6.1. Registry Specification . . . . . . . . . . . . . . . . . . 14 6.1. Registry Specification . . . . . . . . . . . . . . . . . . 15
6.2. Registry Management . . . . . . . . . . . . . . . . . . . 14 6.2. Registry Management . . . . . . . . . . . . . . . . . . . 15
6.3. Experimental Numbers . . . . . . . . . . . . . . . . . . . 15 6.3. Experimental Numbers . . . . . . . . . . . . . . . . . . . 16
6.4. Registry Contents . . . . . . . . . . . . . . . . . . . . 15 6.4. Registry Contents . . . . . . . . . . . . . . . . . . . . 16
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
8.1. Normative References . . . . . . . . . . . . . . . . . . . 16 8.1. Normative References . . . . . . . . . . . . . . . . . . . 17
8.2. Informative References . . . . . . . . . . . . . . . . . . 16 8.2. Informative References . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction 1. Introduction
The IETF has completed its work on the core specification of TWAMP - The IETF has completed its work on the core specification of TWAMP -
the Two-Way Active Measurement Protocol [RFC5357]. TWAMP is an the Two-Way Active Measurement Protocol [RFC5357]. TWAMP is an
extension of the One-way Active Measurement Protocol, OWAMP extension of the One-way Active Measurement Protocol, OWAMP
[RFC4656]. The TWAMP specification gathered wide review as it [RFC4656]. The TWAMP specification gathered wide review as it
approached completion, and the by-products were several approached completion, and the by-products were several
recommendations for new features in TWAMP. There are a growing recommendations for new features in TWAMP. There are a growing
number of TWAMP implementations at present, and wide-spread usage is number of TWAMP implementations at present, and wide-spread usage is
expected. There are even devices that are designed to test expected. There are even devices that are designed to test
implementations for protocol compliance. implementations for protocol compliance.
This memo describes an OPTIONAL feature for TWAMP. TWAMP (and OWAMP) This memo describes an OPTIONAL feature for TWAMP. [RFC5357] TWAMP
start all previously requested and accepted test sessions at once. (and OWAMP) start all previously requested and accepted test sessions
This feature allows the Control-Client to control individual test at once. This feature allows the Control-Client to control
sessions on the basis of their Session Identifier (SID). This individual test sessions on the basis of their Session Identifier
feature permits a short duration TWAMP test to start (and/or stop) (SID). This feature permits a short duration TWAMP test to start
during a longer test. This feature permits a specific diagnostic (and/or stop) during a longer test. This feature permits a specific
test to begin if intermediate results indicate that the test is diagnostic test to begin if intermediate results indicate that the
warranted, for example. test is warranted, for example.
This feature requires a Mode bit position assignment and the This feature requires a Mode bit position assignment and the
assignment of two new TWAMP command numbers (for the augmented Start assignment of two new TWAMP command numbers (for the augmented Start
and Stop commands). This feature also specifies a new Stop-ACK and Stop commands). This feature also specifies a new Stop-ACK
Server response, to complete the symmetry of the session stopping Server response, to complete the symmetry of the session stopping
process in the same way as the Start-ACK response. process in the same way as the Start-ACK response.
Implementers of this feature may also wish to implement the "Reflect The Individual Session Control feature gives the Control-Client new
Octets" feature, described in [I-D.ietf-ippm-twamp-reflect-octets], flexibility to manage any number of test sessions once they are
once it has been published as an RFC. This feature allows a Control- established. However, [RFC5357] test sessions are established in
Client to insert a locally-specified request number into the Request- serial order and the total establishment time grows with the number
TW-Session command (in octets originally designated MBZ=Must Be of sessions and the round-trip time. Therefore, implementers of this
Zero), and a compliant Server will return the request number in its feature may also wish to implement the "Reflect Octets" feature,
reply (Accept message). The Reflect Octets feature makes multiple described in [I-D.ietf-ippm-twamp-reflect-octets], once it has been
simultaneous session requests possible, and supports the operation of published as an RFC. This feature allows a Control-Client to
many simultaneous test sessions (similar to the goal of this memo). 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 which the Individual Session Control feature can then
manage (start/stop).
This memo is intended to be an update to the TWAMP core protocol This memo is an update to the TWAMP core protocol specified in
specified in [RFC5357]. It is not required to implement the feature [RFC5357]. Measurement systems are not required to implement the
described in this memo to claim compliance with [RFC5357]. feature described in this memo to claim compliance with [RFC5357].
Throughout this memo, the bits marked MBZ (Must Be Zero) MUST be set Throughout this memo, the bits marked MBZ (Must Be Zero) MUST be set
to zero by senders and MUST be ignored by receivers. to zero by senders and MUST be ignored by receivers. Also, the HMAC
(Hashed Message Authentication Code) is calculated as defined in
Section 3.2 [RFC4656].
2. Purpose and Scope 2. Purpose and Scope
The purpose of this memo is to describe an additional OPTIONAL The purpose of this memo is to describe an additional OPTIONAL
function and feature for TWAMP [RFC5357]. function and feature for TWAMP [RFC5357].
The scope of the memo is currently limited to specifications of the The scope of the memo is limited to specifications of the following
following features: features:
1. Extension of the modes of operation through assignment of a new 1. Extension of the modes of operation through assignment of a new
value in the Mode field to communicate feature capability and value in the Mode field to communicate feature capability and
use, use,
2. the definitions of augmented start session and stop session 2. the definitions of augmented start session and stop session
commands (with corresponding acknowledgements), and commands (with corresponding acknowledgements), and
3. the definition of related procedures for TWAMP entities. 3. the definition of related procedures for TWAMP entities.
skipping to change at page 7, line 50 skipping to change at page 7, line 50
| | | |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
The Command Number value of 7 indicates that this is a Start-N- The Command Number value of 7 indicates that this is a Start-N-
Sessions command. The Control-Client MUST compose this command, and Sessions command. The Control-Client MUST compose this command, and
the Server MUST interpret this command, according to the field the Server MUST interpret this command, according to the field
descriptions below. descriptions below.
The Number of Sessions field indicates the count of sessions that The Number of Sessions field indicates the count of sessions that
this Start command applies to, and must be one or greater. The 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 SID fields that follow MUST be equal to the value in the
Number of Sessions field (otherwise, the command MUST NOT be affirmed Number of Sessions field (otherwise, the command MUST NOT be affirmed
with a zero Accept field in the Start-N-Ack response). with a zero Accept field in the Start-N-Ack response).
All SID fields are constructed as defined in the last paragraph of All SID fields are constructed as defined in the last paragraph of
OWAMP section 3.5 [RFC4656] (and referenced in TWAMP). Note that the OWAMP section 3.5 [RFC4656] (and referenced in TWAMP). Note that the
SID is assigned by the Server during the session request exchange. SID is assigned by the Server during the session request exchange.
The message is terminated with a single block HMAC, as illustrated The message is terminated with a single block HMAC, as illustrated
above. above.
skipping to change at page 8, line 29 skipping to change at page 8, line 29
command as described in the next section, multiple Start-N-Sessions command as described in the next section, multiple Start-N-Sessions
commands MAY be sent without waiting for acknowledgement, and the commands MAY be sent without waiting for acknowledgement, and the
Start-N-sessions commands MAY arrive in any order. Start-N-sessions commands MAY arrive in any order.
3.3. Start-N-Ack Command with Individual Session Control 3.3. Start-N-Ack Command with Individual Session Control
The Server responds to the Start-N-Sessions command (for one or more 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- specific sessions referenced by their SIDs) with one or more Start-N-
Ack commands with Accept fields corresponding to one or more of the Ack commands with Accept fields corresponding to one or more of the
SIDs. This allows for the possibility that a Server cannot SIDs. This allows for the possibility that a Server cannot
immediately start one or more the sessions referenced in a particular immediately start one or more of the sessions referenced in a
Start-N-Sessions command, but can start one or more of the sessions. particular Start-N-Sessions command, but can start one or more of the
sessions.
The format of the message is as follows. The format of the message is as follows.
0 1 2 3 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 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
| 8 | Accept | MBZ | | 8 | Accept | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ (8 octets) | | MBZ (8 octets) |
| | | |
skipping to change at page 9, line 39 skipping to change at page 9, line 39
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Command Number value of 8 indicates that this is a Start-N-Ack The Command Number value of 8 indicates that this is a Start-N-Ack
message. The Server MUST compose this command, and the Control- message. The Server MUST compose this command, and the Control-
Client MUST interpret this command, according to the field Client MUST interpret this command, according to the field
descriptions below. descriptions below.
The Accept Field values are defined in OWAMP section 3.3 [RFC4656]. The Accept Field values are defined in OWAMP section 3.3 [RFC4656].
The Number of Sessions field indicates the count of sessions that 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 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 SID fields that follow MUST be equal to the value in the
Number of Sessions field. Number of Sessions field.
All SID fields are constructed as defined in the last paragraph of All SID fields are constructed as defined in the last paragraph of
OWAMP section 3.5 [RFC4656] (and referenced in TWAMP). Note that the OWAMP section 3.5 [RFC4656] (and referenced in TWAMP). Note that the
SID is assigned by the Server during the session request exchange. SID is assigned by the Server during the session request exchange.
The message is terminated with a single block HMAC, as illustrated The message is terminated with a single block HMAC, as illustrated
above. above.
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| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
The Command Number value of 9 indicates that this is a Stop-N- The Command Number value of 9 indicates that this is a Stop-N-
Sessions command. The Control-Client MUST compose this command, and Sessions command. The Control-Client MUST compose this command, and
the Server MUST interpret this command, according to the field the Server MUST interpret this command, according to the field
descriptions below. descriptions below.
The Number of sessions field indicates the count of sessions that The Number of sessions field indicates the count of sessions that
this Stop-N-Sessions command applies to. The SID is as defined in this Stop-N-Sessions command applies to. The SID is as defined in
OWAMP (and TWAMP) section 3.5 [RFC4656] and the value must be one or OWAMP (and TWAMP) section 3.5 [RFC4656] and the value MUST be one or
greater. The number of SID fields that follow MUST be equal to the greater. The number of SID fields that follow MUST be equal to the
value in the Number of Sessions field. value in the Number of Sessions field.
The message is terminated with a single block HMAC, as illustrated The message is terminated with a single block HMAC, as illustrated
above. above.
The Server MUST respond with one or more Stop-N-Ack messages (which 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 SHOULD be sent as quickly as possible). Stop-N-Ack messages SHALL
have the format defined in the next session. have the format defined in the next session.
3.5. Stop-N-Ack Command with Individual Session Control 3.5. Stop-N-Ack Command with Individual Session Control
In response to the Stop-N-Sessions command (for one or more specific 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 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 Stop-N-Ack commands with Accept fields corresponding to one or
more of the SIDs. This allows for the possibility that a Server more of the SIDs. This allows for the possibility that a Server
cannot immediately stop one or more the sessions referenced in a 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 particular Stop-N-Sessions command, but can stop one or more of the
sessions. sessions.
The format for the Stop-N-Ack command is as follows: The format for the Stop-N-Ack command is as follows:
0 1 2 3 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 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+B
| 10 | Accept | MBZ | | 10 | Accept | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 12, line 39 skipping to change at page 12, line 39
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Command Number value of 10 indicates that this is a Stop-N-Ack The Command Number value of 10 indicates that this is a Stop-N-Ack
message. The Server MUST compose this command, and the Control- message. The Server MUST compose this command, and the Control-
Client MUST interpret this command, according to the field Client MUST interpret this command, according to the field
descriptions below. descriptions below.
The Accept Field values are defined in OWAMP section 3.3 [RFC4656]. The Accept Field values are defined in OWAMP section 3.3 [RFC4656].
The Number of Sessions field indicates the count of sessions that 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 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 SID fields that follow MUST be equal to the value in the
Number of Sessions field. Number of Sessions field.
All SID fields are constructed as defined in the last paragraph of All SID fields are constructed as defined in the last paragraph of
OWAMP section 3.5 [RFC4656] (and referenced in TWAMP). Note that the OWAMP section 3.5 [RFC4656] (and referenced in TWAMP). Note that the
SID is assigned by the Server during the session request exchange. SID is assigned by the Server during the session request exchange.
The message is terminated with a single block HMAC, as illustrated The message is terminated with a single block HMAC, as illustrated
above. above.
skipping to change at page 14, line 43 skipping to change at page 14, line 43
o Upon receipt of a TWAMP-Control Stop-N-Sessions command o Upon receipt of a TWAMP-Control Stop-N-Sessions command
referencing a specific session/SID, the Session-Reflector MUST referencing a specific session/SID, the Session-Reflector MUST
ignore TWAMP-Test packets (in the same session/SID) that arrive at ignore TWAMP-Test packets (in the same session/SID) that arrive at
the current time plus the Timeout (in the Request-TW-Session the current time plus the Timeout (in the Request-TW-Session
command and assuming subsequent acknowledgement). The Session- command and assuming subsequent acknowledgement). The Session-
Reflector MUST NOT generate a test packet to the Session-Sender Reflector MUST NOT generate a test packet to the Session-Sender
for packets that are ignored. (Note: The Request-TW-Session for packets that are ignored. (Note: The Request-TW-Session
command includes sender address + port and receiver address + command includes sender address + port and receiver address +
port, and this is usually sufficient to distinguish sessions.) port, and this is usually sufficient to distinguish sessions.)
o If the RECOMMENDED REFWAIT timer is implemented, it SHOULD be o If the REFWAIT timer is implemented, it SHOULD be enforced when
enforced when any test session is in-progress (started and not any test session is in-progress (started and not stopped).
stopped).
5. Security Considerations 5. Security Considerations
The security considerations that apply to any active measurement of The security considerations that apply to any active measurement of
live networks are relevant here as well. See the security live networks are relevant here as well. See the security
considerations in[RFC4656] and [RFC5357]. considerations in[RFC4656] and [RFC5357].
6. IANA Considerations 6. IANA Considerations
This memo requests assignment of one mode bit position/value to the This memo requests assignment of one mode bit position/value to the
skipping to change at page 17, line 20 skipping to change at page 17, line 7
Auth. CONTROL Auth. CONTROL
-------------------------------------------------------- --------------------------------------------------------
zzz Individual Session this memo, Section 3.1 zzz Individual Session this memo, Section 3.1
Control bit position (Z) Control bit position (Z)
The suggested values are: The suggested values are:
The next value corresponding to an unused bit is zzz=16, with Z=4. The next value corresponding to an unused bit is zzz=16, with Z=4.
7. Acknowledgements 7. Acknowledgements
The authors thank everyone who provided comments on this feature. The authors thank everyone who provided comments on this feature,
especially Lars Eggert, Adrian Farrel, and Alexey Melnikov.
8. References 8. References
8.1. Normative References 8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4656] Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M. [RFC4656] Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
Zekauskas, "A One-way Active Measurement Protocol Zekauskas, "A One-way Active Measurement Protocol
 End of changes. 22 change blocks. 
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