K. Hedayat
Internet Draft Brix Networks
Expires: September 2007 R. Krzanowski
Verizon
K. Yum
Juniper Networks
A. Morton
AT&T Labs
J. Babiarz
Nortel Networks
March 2007
A Two-way Active Measurement Protocol (TWAMP)
draft-ietf-ippm-twamp-03
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Copyright Notice
Copyright (C) The IETF Trust (2007).
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Abstract
The IPPM One-way Active Measurement Protocol [RFC4656] (OWAMP)
provides a common protocol for measuring one-way metrics between
network devices. OWAMP can be used bi-directionally to measure
one-way metrics in both directions between two network elements.
However, it does not accommodate round-trip or two-way
measurements. This memo specifies a Two-way Active Measurement
Protocol (TWAMP), based on the OWAMP, that adds two-way or
round-trip measurement capabilities. The TWAMP measurement
architecture is usually comprised of two hosts with specific roles,
and this allows for some protocol simplifications, making it an
attractive alternative in some circumstances.
Table of Contents
1. Introduction..................................................3
1.1 Relationship of Test and Control Protocols................3
1.2 Logical Model.............................................3
2. Protocol Overview.............................................5
3. TWAMP Control.................................................5
3.1 Connection Setup..........................................5
3.2 Integrity Protection......................................6
3.3 Value of the Accept Fields................................6
3.4 TWAMP Control Commands....................................6
3.5 Creating Test Sessions....................................6
3.6 Send Schedules............................................8
3.7 Starting Test Sessions....................................8
3.8 Stop-Sessions.............................................8
3.9 Fetch-Session.............................................8
4. TWAMP Test....................................................8
4.1 Sender Behavior...........................................9
4.2 Reflector Behavior........................................9
5. Implementers Guide...........................................15
5.1 Complete TWAMP...........................................15
5.2 TWAMP Light..............................................16
6. Security Considerations......................................17
7. Acknowledgements.............................................17
8. IANA Considerations..........................................17
9. Internationalization Considerations..........................17
10. References..................................................18
10.1 Normative References....................................18
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1. Introduction
The IETF IP Performance Metrics (IPPM) working group has completed
a draft standard for the round-trip delay [RFC2681] metric. IPPM
has also completed a protocol for the control and collection of
one-way measurements, the One-way Active Measurement Protocol
(OWAMP) [RFC4656]. However, OWAMP does not accommodate round-trip
or two-way measurements.
Two-way measurements are common in IP networks, primarily because
time accuracy is less demanding for round-trip delay, and
measurement support at the remote end may be limited to a simple
echo function. This memo specifies the Two-way Active Measurement
Protocol, or TWAMP. TWAMP uses the methodology and architecture of
OWAMP [RFC4656] to define an open protocol for measurement of
two-way or round-trip metrics (henceforth in this document the term
two-way also signifies round-trip). The TWAMP measurement
architecture is usually comprised of only two hosts with specific
roles, and this allows for some protocol simplifications, making it
an attractive alternative in some circumstances.
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].
1.1 Relationship of Test and Control Protocols
Similar to OWAMP [RFC4656], TWAMP consists of two inter-related
protocols: TWAMP-Control and TWAMP-Test. The relationship of these
protocols is as defined in section 1.1 of OWAMP [RFC4656].
1.2 Logical Model
The role and definition of the logical entities are as defined in
section 1.2 of OWAMP [RFC4656] with the following exceptions:
- The Session-Receiver is called the Session-Reflector in the
TWAMP architecture. The Session-Reflector has the capability
to create and send a measurement packet when it receives a
measurement packet. Unlike the Session-Receiver, the
Session-Reflector does not collect any packet information.
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- The Server is an end system that manages one or more TWAMP
sessions, and is capable of configuring per-session state in
the end-points. However, a Server associated with a
Session-Reflector would not have the capability to return the
results of a test session, and this is a difference from OWAMP.
- The Fetch-Client entity does not exist in the TWAMP
architecture, as the Session-Reflector does not collect any
packet information to be fetched. Consequently there is no
need for the Fetch-Client.
An example of possible relationship scenarios between these roles
are presented below. In this example different logical roles are
played on different hosts. Unlabeled links in the figure are
unspecified by this document and may be proprietary protocols.
+----------------+ +-------------------+
| Session-Sender |<-TWAMP-Test-->| Session-Reflector |
+----------------+ +-------------------+
^ ^
| |
| |
| |
| +----------------+<----------------+
| | Server |
| +----------------+
| ^
| |
| TWAMP-Control
| |
v v
+----------------+
| Control-Client |
+----------------+
As in OWAMP [RFC4656], different logical roles can be played by the
same host. For example, in the figure above, there could be
actually two hosts: one playing the roles of Control-Client and
Session-Sender, and the other playing the roles of Server and
Session-Reflector. This example is shown below.
+-----------------+ +-------------------+
| Control-Client |<--TWAMP Control-->| Server |
| | | |
| Session-Sender |<--TWAMP-Test----->| Session-Reflector |
+-----------------+ +-------------------+
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Additionally, following the guidelines of OWAMP [RFC4656], TWAMP
has been defined to allow for small test packets that would fit
inside the payload of a single ATM cell (only in unauthenticated
mode).
2. Protocol Overview
The Two-way Active Measurement Protocol is an open protocol for
measurement of two-way metrics. It is based on OWAMP [RFC4656] and
adheres to its overall architecture and design. The protocol
defined in this document extends and changes OWAMP [RFC4656] as
follows:
- Define a new logical entity, Session-Reflector, in place of the
Session-Receiver.
- Define the Session-Reflector behavior in place of the
Session-Receiver behavior of OWAMP [RFC4656].
- Define a new test packet format for packets transmitted from the
Session-Reflector to Session-Sender.
- Fetch client does not exist in the TWAMP architecture.
3. TWAMP Control
All TWAMP Control messages are similar in format and follow similar
guidelines to those defined in section 3 of OWAMP [RFC4656] with
the exceptions outlined in the following sections. All OWAMP
[RFC4656] Control messages except for the Fetch-Session command
apply to TWAMP.
3.1 Connection Setup
Connection establishment of TWAMP follows the same procedure
defined in section 3.1 of OWAMP [RFC4656]. The host that initiates
the TCP connection takes the roles of Control-Client and (in the
two-host implementation) the Session-Sender. The host that
acknowledges the TCP connection accepts the roles of Server and (in
the two-host implementation) the Session Reflector.
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3.2 Integrity Protection
Integrity protection of TWAMP follows the same procedure defined in
section 3.2 of OWAMP [RFC4656].
3.3 Value of the Accept Fields
Accept values used in TWAMP are the same as the values defined in
section 3.3 of OWAMP [RFC4656].
3.4 TWAMP Control Commands
TWAMP control commands are as defined in section 3.4 of OWAMP
[RFC4656] except that the Fetch-Session command does not apply to
TWAMP.
3.5 Creating Test Sessions
Test sessions creation follows the same procedure as defined in
section 3.5 of OWAMP [RFC4656].
In order to distinguish the session as a two-way versus a one-way
measurement session the first octet of the Request-Session command
MUST be set to 5. Value of 5 indicates that this is a
Request-Session for a two-way metrics measurement session.
In OWAMP, the Conf-Sender field is set to 1 when the
Request-Session message describes a task where the Server will
configure a one-way test packet sender. Likewise, the
Conf-Receiver field is set to 1 when the message describes the
configuration for a Session-Receiver. In TWAMP, both endpoints
perform in these roles, with the Session-Sender first sending and
then receiving test packets. The Session-Reflector first receives
the test packets, and returns each test packet to the
Session-Sender as fast as possible.
Both Conf-Sender and Conf-Receiver MUST be set to 0 since the
Session-Reflector will both receive and send packets, and the roles
are established according to which host initiates the TCP
connection for control. The server MUST interpret any non-zero
value as zero.
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The Session-Reflector in TWAMP does not process incoming test
packets for performance metrics and consequently does not need to
know the number of incoming packets and their timing schedule.
Consequently the Number of Scheduled Slots and Number of Packets
MUST be set to 0.
The Sender Port is the UDP port from which TWAMP-Test packets will
be sent. Receiver Port is the UDP port to which TWAMP test packets
are reflected by the Session-Reflector (the port where the
Session-Sender wants to receive test packets).
The Sender Address and Receiver Address fields contain,
respectively, the sender and receiver addresses of the endpoints of
the Internet path over which a TWAMP test session is requested.
They MAY be set to 0, in which case the IP addresses used for the
Session-Sender to Session-Reflector Control Message exchange MUST
be used in the test packets.
The SID is as defined in OWAMP [RFC4656]. Since the SID is always
generated by the receiving side, the Session-Reflector determines
the SID, and the SID in the Request-Session message MUST be set to
0.
The Start Time is as as defined in OWAMP [RFC4656].
The Timeout is interpreted differently from the definition in OWAMP
[RFC4656]. In TWAMP, Timeout is the interval that the
Session-Reflector MUST wait after receiving a Stop-Sessions
message. In case there are test packets still in transit, the
Session Reflector MUST reflect them if they arrive within the
timeout interval following the reception of the Stop-Sessions
message. The Session-Reflector MUST NOT reflect packets that are
received beyond the timeout.
Type-P descriptor is as defined in OWAMP [RFC4656]. The only
capability of this field is to set the Differentiated Services Code
Point (DSCP) as defined in [RFC2474]. The same value of DCSP MUST
be used in test packets reflected by the Session-Reflector.
Since there are no Schedule Slot Descriptions, the Request-Session
Message is completed by MBZ and HMAC fields. This completes one
logical message, referred to as the Request-Session Command.
The Session-Reflector MUST respond to each Request-Session Command
with an Accept-Message as defined in OWAMP [RFC4656]. The Port is
the port to which TWAMP test packets are sent by the Session-Sender
toward the Session-Reflector. In other words, the Port field
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indicates the port number where the Session-Reflector expects to
receive packets from the Session-Sender.
3.6 Send Schedules
The Send Schedule for test packets defined in section 3.6 of OWAMP
[RFC4656] is not used in TWAMP. The Control-Client and
Session-Sender MAY autonomously decide the Send Schedule. The
Session-Reflector SHOULD return each test packet to the
Session-Sender as quickly as possible.
3.7 Starting Test Sessions
The procedure and guidelines for Starting test sessions is the same
as defined in section 3.7 of OWAMP [RFC4656].
3.8 Stop-Sessions
The procedure and guidelines for Stopping test sessions is the same
as defined in section 3.8 of OWAMP [RFC4656]. The Stop-Session
command can only be issued by the Session-Sender. The Next SeqNo
and Number of Skip Ranges MUST be set to 0 and the message MUST NOT
contain any session description records or skip ranges. The
message is terminated with a single block HMAC, to complete the
Stop-Sessions Command.
3.9 Fetch-Session
The purpose of TWAMP is measurement of two-way metrics. Two-way
measurements do not rely on packet level data collected by the
Session-Reflector such as sequence number, timestamp, and TTL. As
such the protocol does not require the retrieval of packet level
data from the Server and the Fetch-Session command is not defined
in TWAMP.
4. TWAMP Test
The TWAMP test protocol is similar to the OWAMP [RFC4656] test
protocol with the exception that the Session-Reflector transmits
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test packets to the Session-Sender in response to each test packet
it receives. TWAMP 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 [RFC4656] test
protocol there are three modes: unauthenticated, authenticated, and
encrypted.
4.1 Sender Behavior
The sender behavior is determined by the configuration of the
Session-Sender and is not defined in this standard. Further, the
Session-Reflector does not need to know the Session-Sender
behaviour to the degree of detail as needed in OWAMP [RFC4656].
Additionally the Session-Sender collects and records the necessary
information provided from the packets transmitted by the
Session-Reflector for measuring two-way metrics. The information
recording based on the received packet by the Session-Sender is
implementation dependent.
4.1.1 Packet Timings
Since the Send Schedule is not communicated to the
Session-Reflector, there is no need for a standardized computation
of packet timing.
Regardless of any scheduling delays, each packet that is actually
sent MUST have the best possible approximation of its real time of
departure as its timestamp (in the packet).
4.1.2 Packet Format and Content
The Session-Sender packet format and content follow the same
procedure and guidelines as defined in section 4.1.2 of OWAMP
[RFC4656] (with the exception of the reference to the Send
Schedule).
4.2 Reflector Behavior
TWAMP requires the Session-Reflector to transmit a packet to the
Session-Sender in response to each packet it receives.
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As packets are received the Session-Reflector will,
- Timestamp the received packet. Each packet that is actually
received MUST have the best possible approximation of its real
time of arrival entered as its timestamp (in the packet).
- In authenticated or encrypted mode, decrypt the first block (16
octets) of the packet body.
- Copy the packet sequence number into the corresponding reflected
packet to the Session-Sender.
- Transmit a test packet to the Session-Sender in response to
every received packet. The response MUST be generated as
immediately as possible. The format and content of the test
packet is defined in section 5.2.1. Prior to the transmission
of the test packet, the Session-Reflector MUST enter the best
possible approximation of its actual sending time of as its
Timestamp (in the packet). This permits the determination of the
elapsed time between the reception of the packet and its
transmission.
- Packets not received within the Timeout are ignored by the
Reflector. The Session-Reflector MUST NOT generate a test
packet to the Session-Sender for packets that are ignored.
4.2.1 TWAMP-Test Packet Format and Content
The Session-Reflector MUST transmit a packet to the Session-Sender
in response to each packet received. The Session-Reflector SHOULD
transmit the packets as immediately as possible. The
Session-Reflector SHOULD set the TTL in IPV4 (or Hop Limit in IPv6)
in the UDP packet to 255.
The test packet will have the necessary information for calculating
two-way metrics by the Session-Sender. The format of the test
packet depends on the mode being used. The various formats of the
packet are presented below.
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For unauthenticated mode:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Estimate | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receive Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Error Estimate | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Packet Padding .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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For authenticated and encrypted modes:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ (12 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Estimate | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| MBZ (6 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receive Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ (8 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| Sender Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ (12 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Error Estimate | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| MBZ (6 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HMAC (16 octets) |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| |
. .
. Packet Padding .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Sequence Number is the sequence number of the test packet according
to its arrival at the Session-Reflector. It starts with zero and
is incremented by one for each subsequent packet. The Sequence
Number generated by the Session-Reflector is independent from the
sequence number of the arriving packets.
Timestamp and Error Estimate are the Session-Reflector's transmit
timestamp and error estimate for the reflected test packet,
respectively. The format of all timestamp and error estimate
fields follow the definition and formats defined by OWAMP[RFC4656].
Sender Timestamp and Sender Error Estimate are exact copies of the
timestamp and error estimate from the Session-Sender test packet
that corresponds to this test packet.
Receive Timestamp is the time the test packet was received by the
reflector. The difference between Timestamp and Receive Timestamp
is the amount of time the packet was in transition in the
Session-Reflector. The Error Estimate associated with the
Timestamp field also applies to the Receive Timestamp.
Sender Sequence Number is a copy of the Sequence Number of the
packet transmitted by the Session-Sender that caused the
Session-Reflector to generate and send this test packet.
Similar to OWAMP [RFC4656] the TWAMP packet layout is the same in
authenticated and encrypted modes. The encryption operation of
Session-Sender packet follow the same rules of Session-Sender
packets as defined in OWAMP [RFC4656].
The minimum data segment length is, therefore, 40 octets in
unauthenticated mode, and 80 octets in both authenticated mode and
encrypted modes (with the implication that the later two modes will
not fit in a single ATM cell).
The Session-Reflector TWAMP-Test packet layout is the same in
authenticated and encrypted modes. The encryption operations are,
however, different. The difference is that in encrypted mode both
the sequence numbers and timestamps are encrypted to provide
maximum data integrity protection while in authenticated mode the
sequence numbers are encrypted and the timestamps are sent in clear
text. Sending the timestamp in clear text in authenticated mode
allows one to reduce the time between when a timestamp is obtained
by a reflector and when the packet is reflected out. In encrypted
mode, both the sender and reflector have to fetch the timestamp,
encrypt it, and send it; in authenticated mode, the middle step is
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removed, potentially improving accuracy (the sequence number can be
encrypted before the timestamp is fetched).
In authenticated mode, the first block (16 octets) of each packet
is encrypted using AES Electronic Cookbook (ECB) mode.
Obtaining the key, encryption method, and packet padding follows
the same procedure as OWAMP as described below.
Similarly to each TWAMP-Control session, each TWAMP-Test session
has two keys: an AES Session-key and an HMAC Session-key. However,
there is a difference in how the keys are obtained: in the case of
TWAMP-Control, the keys are generated by the client and
communicated (as part of the Token) during connection setup as part
of Set-Up-Response message; in the case of TWAMP-Test, described
here, the keys are derived from the TWAMP-Control keys and the SID.
The TWAMP-Test AES Session-key is obtained as follows: the
TWAMP-Control AES Session-key (the same AES Session-key as is used
for the corresponding TWAMP-Control session, where it is used in a
different chaining mode) is encrypted, using AES, with the 16-octet
session identifier (SID) as the key; this is a single-block ECB
encryption; its result is the TWAMP-Test AES Session-key to use in
encrypting (and decrypting) the packets of the particular
TWAMP-Test session. Note that all of TWAMP-Test AES Session-key,
TWAMP-Control AES Session-key, and the SID are comprised of 16
octets.
The TWAMP-Test HMAC Session-key is obtained as follows: the
TWAMP-Control HMAC Session-key (the same HMAC Session-key as is
used for the corresponding TWAMP-Control session) is encrypted,
using AES, with the 16-octet session identifier (SID) as the key;
this is a two-block CBC encryption, always performed with IV=0; its
result is the TWAMP-Test HMAC Session-key to use in authenticating
the packets of the particular TWAMP-Test session. Note that all of
TWAMP-Test HMAC Session-key and TWAMP-Control HMAC Session-key are
comprised of 32 octets, while the SID is 16 octets.
ECB mode used for encrypting the first block of TWAMP-Test packets
in authenticated mode does not involve any actual chaining; this
way, lost, duplicated, or reordered packets do not cause problems
with deciphering any packet in an TWAMP-Test session.
In encrypted mode, the first two blocks (32 octets) are encrypted
using AES CBC mode. The AES Session-key to use is obtained in the
same way as the key for authenticated mode. Each TWAMP-Test packet
is encrypted as a separate stream, with just one chaining
operation; chaining does not span multiple packets so that lost,
duplicated, or reordered packets do not cause problems. The
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initialization vector for the CBC encryption is a value with all
bits equal to zero.
Implementation note: Naturally, the key schedule for each
TWAMP-Test session MAY be set up only once per session, not once
per packet.
HMAC in TWAMP-Test only covers the part of the packet that is also
encrypted. So, in authenticated mode, HMAC covers the first block
(16 octets); in encrypted mode, HMAC covers two first blocks (32
octets). In TWAMP-Test HMAC is not encrypted (note that this is
different from TWAMP-Control, where encryption in stream mode is
used, so everything including the HMAC blocks ends up being
encrypted).
In unauthenticated mode, no encryption or authentication is
applied.
Packet Padding in TWAMP-Test SHOULD be pseudo-random (it MUST be
generated independently of any other pseudo-random numbers
mentioned in this document). However, implementations MUST provide
a configuration parameter, an option, or a different means of
making Packet Padding consist of all zeros.
5. Implementers Guide
This section serves as guidance to implementers of TWAMP. Two
architectures are presented in this section for implementations
where two hosts play the subsystem roles of TWAMP. Although only
two architectures are presented here the protocol does not require
their use. Similar to OWAMP [RFC4656] TWAMP is designed with
complete flexibility to allow different architectures that suite
multiple system requirements.
5.1 Complete TWAMP
In this example the roles of Control-Client and Session-Sender are
implemented in one host referred to as the controller and the roles
of Server and Session-Reflector are implemented in another host
referred to as the responder.
controller responder
+-----------------+ +-------------------+
| Control-Client |<--TWAMP-Control-->| Server |
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| | | |
| Session-Sender |<--TWAMP-Test----->| Session-Reflector |
+-----------------+ +-------------------+
This example provides an architecture that supports the full TWAMP
standard. The controller establishes the test session with the
responder through the TWAMP-Control protocol. After the session is
established the controller transmits test packets to the responder.
The responder follows the Session-Reflctor behavior of TWAMP as
described in section 4.2.
5.2 TWAMP Light
In this example the roles of Control-Client, Server, and
Session-Sender are implemented in one host referred to as the
controller and the role of Session-Reflector is implemented in
another host referred to as the responder.
controller responder
+-----------------+ +-------------------+
| Server |<----------------->| |
| Control-Client | | Session-Reflector |
| Session-Sender |<--TWAMP-Test----->| |
+-----------------+ +-------------------+
This example provides a simple architecture for responders where
their role will be to simply act as light test points in the
network. The controller establishes the test session with the
Server through non-standard means. After the session is
established the controller transmits test packets to the responder.
The responder follows the Session-Reflector behavior of TWAMP as
described in section 4.2 with the following exceptions. The
Session-Reflector SHOULD copy the sequence number of the received
packet to the Sequence Number field of the reflected packet. This
is necessary since in case of TWAMP Light the Session-Reflector
does not have knowledge of the session state. The controller
receives the reflected test packets and collects two-way metrics.
This architecture allows for collection of two-way metrics.
This example eliminates the need for the TWAMP-Control protocol and
assumes that the Session-Reflector is configured and communicates
its configuration with the Server through non-standard means. The
Session-Reflector simply reflects the incoming packets back to the
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controller while copying the necessary information and generating
sequence number and timestamp values per section 5.2.1.
6. Security Considerations
Fundamentally TWAMP and OWAMP use the same protocol for
establishment of Control and Test procedures. The main difference
between TWAMP and OWAMP is the Session-Reflector behavior in TWAMP
vs. the Session-Receiver behavior in OWAMP. This difference in
behavior does not introduce any known security vulnerabilities that
are not already addressed by the security features of OWAMP. The
entire security considerations of OWAMP [RFC4656] applies to TWAMP.
7. Acknowledgements
We would like to thank Nagarjuna Venna, Sharee McNab, Nick Kinraid,
and Stanislav Shalunov for their comments, suggestions, reviews,
helpful discussion and proof-reading.
8. IANA Considerations
IANA has allocated a well-known TCP port number (861) for the
OWAMP-Control part of the OWAMP [RFC4656] protocol which also
applies to the TWAMP-Control part of the TWAMP protocol.
9. Internationalization Considerations
The protocol does not carry any information in a natural language,
with the possible exception of the KeyID in TWAMP-Control, which is
encoded in UTF-8.
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10. References
10.1 Normative References
[RFC4656] Shalunov, S., Teitelbaum, B., Karp, A., Boote, J.,
Zekauskas, M., "A One-way Active Measurement Protocol
(OWAMP)", draft-ietf-ippm-owdp-11.txt, October 2004.
[RFC2681] Almes, G., Kalidindi, S., Zekauskas, M., "A
Round-Trip Delay Metric for IPPM". RFC 2681, STD 1,
September 1999.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
December 1998.
Authors' Addresses
Kaynam Hedayat
Brix Networks
285 Mill Road
Chelmsford, MA 01824
USA
EMail: khedayat@brixnet.com
URI: http://www.brixnet.com/
Roman M. Krzanowski, Ph.D.
Verizon
500 Westchester Ave.
White Plains, NY
USA
EMail: roman.krzanowski@verizon.com
URI: http://www.verizon.com/
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Al Morton
AT&T Labs
Room D3 - 3C06
200 Laurel Ave. South
Middletown, NJ 07748
USA
Phone +1 732 420 1571
EMail: acmorton@att.com
URI: http://home.comcast.net/~acmacm/
Kiho Yum
Juniper Networks
1194 Mathilda Ave.
Sunnyvale, CA
USA
EMail: kyum@juniper.net
URI: http://www.juniper.com/
Jozef Z. Babiarz
Nortel Networks
3500 Carling Avenue
Ottawa, Ont K2H 8E9
Canada
Email: babiarz@nortel.com
URI: http://www.nortel.com/
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