Network Working Group S. Baillargeon
INTERNET-DRAFT C. Flinta
Intended Status: Standards Track A. Johnsson
Expires: September 5, 2011 S. Ekelin
Ericsson
March 4, 2011
TWAMP Value-Added Octets
draft-baillargeon-ippm-twamp-value-added-octets-01.txt
Abstract
This memo describes the optional extensions to the standard TWAMP
test protocol for identifying test sessions and packet trains, and
for measuring capacity metrics like the available path capacity,
tight section capacity and UDP throughput in the forward and reverse
path directions.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
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The list of current Internet-Drafts can be accessed at
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Copyright and License Notice
Copyright (c) 2011 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
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(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.
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Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Requirements Language . . . . . . . . . . . . . . . . . . . 4
2 Purpose and scope . . . . . . . . . . . . . . . . . . . . . . . 5
3 Capacity Measurement Principles . . . . . . . . . . . . . . . . 6
4 Test packet Demultiplexing Principles . . . . . . . . . . . . . 7
5 TWAMP Control Extensions . . . . . . . . . . . . . . . . . . . . 8
6 Extended TWAMP Test . . . . . . . . . . . . . . . . . . . . . . 9
6.1 Sender Behavior . . . . . . . . . . . . . . . . . . . . . . 9
6.1.1 Packet Timings . . . . . . . . . . . . . . . . . . . . 9
6.1.2 Session-Sender Packet Format . . . . . . . . . . . . . 9
6.2 Reflector behavior . . . . . . . . . . . . . . . . . . . 17
6.2.1 Session-Reflector Packet Format . . . . . . . . . . 19
6.3 Additional Considerations . . . . . . . . . . . . . . . . 19
7 Security Considerations . . . . . . . . . . . . . . . . . . . 20
8 IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
8.1. Registry Specification . . . . . . . . . . . . . . . . . 20
8.2. Registry Contents . . . . . . . . . . . . . . . . . . . 20
9 References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
9.1 Normative References . . . . . . . . . . . . . . . . . . 20
9.2 Informative References . . . . . . . . . . . . . . . . . 21
Author's Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
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1 Introduction
The notion of embedding a number of meaningful fields in the padding
octets has been established as a viable methodology for carrying
additional information within the TWAMP-Test protocol running between
a Session-Sender and a Session-Reflector [RFC5357] [RFC6038].
This memo describes an OPTIONAL feature for the Two-Way Active
Measurement Protocol [RFC5357]. It is called the Value-Added Octets
feature.
This feature enables the controller host to measure capacity metrics
like the IP-type-P available path capacity (APC) [RFC5136], IP-layer
tight section capacity (TSC) [Y1540] and UDP throughput [RFC1242] on
both forward and reverse paths. With this feature, it is also
possible to improve the demultiplexing of test packets to the correct
test sessions running on the controller and responder hosts when
methods solely based on IP and UDP header information is not
desirable or insufficient.
The Valued-Added Octets feature consists of new behaviors for the
Session-Sender and Session-Reflector, and a set of value-added octets
of information that are placed at the beginning of the Packet Padding
field [RFC5357] or at the beginning of the Packet Padding (to be
reflected) field [RFC6038] by the Session-Sender, and are reflected
or returned by the Session-Reflector. The length of the value-added
octets varies in size between 6, 10 and 14 octets depending on the
setting of the flag bits specified at the beginning of the value-
added octets.
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].
UDP throughput is defined in the Benchmarking Terminology for Network
Interconnection Devices [RFC1242]. IP-Type-P APC metric is defined in
Defining Network Capacity [RFC5136]. IP-layer TSC metric is defined
in IP Packet Transfer and Availability Performance Parameters
[Y1540]. The actual method to calculate the available path capacity,
the tight section capacity or the UDP throughput from packet-level
data performance data is not discussed in this memo.
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].
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2 Purpose and scope
The purpose of this memo is to define the OPTIONAL Valued-Added
Octets feature for TWAMP [RFC5357].
The scope of the memo is limited to specifications of the following
enhancements:
o The extension of the modes of operation through assignment of a
new value in the Mode field to communicate feature capability
and use,
o The definition of a structure for embedding a sequence of
value-added fields at the beginning of the Packet Padding field
[RFC5037] or Packet Padding (to be reflected) field [RFC6038]
in the TWAMP test packets and,
o The definition of new Session-Sender and Session-Reflector
behaviors
The motivation for this feature is to enable the measurements of
capacity metrics on both the forward and reverse paths, and to
improve the demultiplexing of test packets to the correct test
session at both endpoints.
This memo extends the modes of operation through assignment one new
value in the Modes field (see Section 3.1 of [RFC4656] for the format
of the Server Greeting message), while retaining backward
compatibility with the core TWAMP [RFC5357] implementations. The new
value correspond to the Valued-Added Octets Version 1 feature defined
in this memo.
When the Server and Control-Client have agreed to use the Value-Added
Octets Version 1 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 OPTIONAL packet padding octets are designed to retain backward
compatibility with the original TWAMP test protocol [RFC5357].
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3 Capacity Measurement Principles
Most capacity estimation methods for available path capacity
[RRBNC][PDM][ENHJMMB][SBW] and for UDP throughput [RFC2544] need to
send and receive packets in groups, called packet trains or simply
trains. Each train is sent at a specific transmission rate in a given
direction. These trains must be identified within each bi-directional
test session stream.
The first measurement principle is to send multiple trains within a
test session stream from one IP node to another IP node in order to
estimate the available path capacity, tight section capacity or UDP
throughput in the forward direction. Each train consists of a group
of test packets which are separated from each other by a packet
interval, as shown in the picture below.
tt tt tt
|<---------->| |<---------->| |<---------->|
| | | | | |
+------------+ +------------+ +------------+
| Packet 1 | | Packet 2 | | Packet 3 |
+------------+ +------------+ +------------+
| | |
|<--------------------->|<--------------------->|
packet interval 1 packet interval 2
The packet interval between consecutive packets for each train sent
by the Session-Sender and reflected by the Session-Reflector MUST be
calculated and determined by the controller or an application or
entity communicating with the controller. The packet interval MAY be
constant within a train. Determination of the packet interval within
a train as well as for consecutive trains for a given test session is
implementation-specific.
The transmission time tt to send one packet (i.e. determined by the
interface speed and the IP packet size) is also shown in the picture.
Observe that the packet interval MUST be larger than or equal to tt.
At the Session-Reflector, each received test packet within a forward
train is time stamped. This provides a second set of packet interval
values. Methods for measuring the available path capacity, tight
section capacity and UDP throughput use the packet intervals obtained
from both end points in the estimation process. The method to
measuring the UDP throughput may also require the packet loss at the
receiving end. The estimation process itself as well as any
requirements on software or hardware is implementation-specific.
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The second measurement principle is referred to as self-induced
congestion. According to this principle, in order to measure the
available path capacity, tight section capacity and UDP throughput,
some trains MUST cause momentary congestion on the network path. In
essence this means that some trains MUST be sent at a higher rate
than what is available on the network path. The congestion is only
transient, for the duration of the train which is typically short.
In order to fulfill the above measurement principles and to measure
the available path capacity, tight section capacity and UDP
throughput in the reverse direction, the reflected test packets MUST
be re-grouped into trains at the Session-Reflector.
4 Test packet Demultiplexing Principles
The controller (or the Session-Sender) requires a method for
demultiplexing the received test packets to the correct test session
especially when it manages multiple active test sessions. The
responder also requires a method for demultiplexing the received test
packets from multiple active test sessions originating from the same
controller or from different controllers.
The purpose of this section is to provide some basic principles for
identifying the test packets and to clarify the optional usage of the
Sender Discriminator (SD) field described in this memo. It is
important to note the actual method for identifying a test packet and
the process for mapping it to the correct test session are
implementation-specific. They may differ between various controllers
and responders.
In general, the methods are based on fields available in the various
headers of the TWAMP test packet (e.g. Ethernet, IP, UDP and TWAMP
headers). Note the SID [RFC4656] is generally not used for
identification purpose since it does not normally appear in the TWAMP
test packets. As an example, a measurement system (controller or
responder) may use the source IP address of the incoming test packet
in order to associate it to the correct test session. This method is
valid but has a number of limitations. It is simple and effective
when each measurement system only requires a single test session for
each peer but fails when multiple test sessions (with different
characteristics) are running between the same pair of controller and
responder.
Another approach is to use a combination of the source IP address,
destination IP address, source UDP port and destination UDP port.
This method is also valid but to work effectively, it requires that
the controller allocates multiple UDP ports (one for each test
session for instance) and/or the responder listens on multiple ports.
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Ideally, a measurement system should limit the number of UDP ports
for sending and receiving test packets. This approach may be improved
by using a combination of the IP addresses, UDP ports and DSCP
codepoint. This method also has its limitations. For instance, it
cannot identify test packets from different test sessions running
between the same pair of controller and responder if they are using
the same UDP endpoints and the same DSCP codepoint.
This memo introduces a new field, the Sender Discriminator (SD) field
intended to simplify the identification of the test packets at the
controller and responder. It is especially useful when multiple test
sessions with different DSCP codepoints and/or test packet sizes are
expected to be running between the same pair of UDP endpoints. As
described in 6.1.2, the SD is a number generated by the Session-
Sender that uniquely identifies a test session on its system. With
this field, the controller can explicitly identify the test packets
belonging to a test session. When provided, the responder MAY use the
SD field in combination of the source IP address for instance to
identify the test packets belonging to a test session.
5 TWAMP Control Extensions
TWAMP-Control protocol [RFC5357] uses the Modes field to identify and
select specific communication capabilities, and this field is a
recognized extension mechanism.
TWAMP connection establishment follows the procedure defined in
Section 3.1 of [RFC4656] and Section 3.1 of [RFC5357]. The new
feature require one new bit position (and value) to identify the
ability of the Server/Session-Reflector to read and act upon the new
fields in the value-added octets. See the IANA section for details on
the assigned value and bit position.
The Server sets the new bit position in the Modes field of the Server
Greeting message to indicate its capability to operate in this new
mode.
Both the Reflect Octets mode and Symmetrical Size mode SHOULD be
selected to ensure the reflection of the value-added padding octets
by the Session-Reflector and symmetrical size TWAMP-Test packets in
the forward and reverse directions of transmission.
The forward and reverse APC, TSC and UDP throughput measurement
characteristics depend on the size of the test packets. All test
packets (forward and reverse test packets) belonging to a specific
test session responsible to measure the available path capacity,
tight section capacity and/or UDP throughput MUST have the same IP
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packet size.
6 Extended TWAMP Test
The TWAMP-test protocol carrying the value-added padding octets is
identical to TWAMP [RFC5357] except for the definition of first 6, 10
or 14 octets in the Padding Octet field that the Session-Sender
expects to be reflected.
The Session-Sender and Session-Reflector behaviors are also modified.
6.1 Sender Behavior
This section describes the extensions to the behavior of the TWAMP
Session-Sender.
When the Value-Added Octets Version 1 mode is selected, the Session-
Sender MAY set the Sender Discriminator Present bit to 1. If it is
set to 1, the Session-Sender MUST generate and transmit a unique
nonzero discriminator value in the Sender Discriminator field.
When the Value-Added Octets Version 1 mode is selected, the Session-
Sender MAY set the Last Seqno in Train Present bit to 1. If it is set
to 1, the Session-Sender MUST generate and transmit a valid sequence
number in the Last Seqno in Train field. The Session-Sender MUST also
group the test packets in trains and send the trains towards the
Session-Reflector at the desired forward packet intervals.
When the Value-Added Octets Version 1 mode is selected, the Session-
Sender MAY set the the Desired Reverse Packet Interval Present bit to
1. If it is set to 1, the Session-Sender MUST generate and transmit a
valid inter-packet time interval in the Desired Reverse Packet
Interval field.
The desired forward and reverse rate interval parameters are usually
provided by a measurement method, tool or algorithm. This measurement
algorithm is outside the scope of this specification.
6.1.1 Packet Timings
The Send Schedule is not utilized in TWAMP and this is unchanged in
this memo.
6.1.2 Session-Sender Packet Format
The Session-Sender packet format follows the same procedure and
guidelines as defined in TWAMP [RFC5357] and TWAMP Reflect Octets and
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Symmetrical Size Features [RFC6038].
This feature allows the Session-Sender to set the first few octets in
the TWAMP-Test Packet Padding field with information to communicate
value-added padding version number, flag bits, sender discriminator,
sequence number of the last packet in a train and desired inter-
packet time interval (or per-packet waiting time) for the reverse
path direction of transmission.
A version number and a sequence of flag bits are defined at the very
beginning of the value-added padding octets. The version number
identifies the version of the value-added padding octets and meaning
of the flag bits. Each flag bit indicates if a specific field of a
specific size is present in the valued-added padding octets. The flag
bits are designed to accommodate different combinations of fields
while reducing padding overhead when certain fields are not needed.
The version number and flag bits also provide an effective method for
parsing information at Session-Reflector and Session-Sender. This
document defines version 1 with three flag bits: S, L and D.
The format of the test packet depends on the TWAMP mode and flag bits
being used. The Value-Added Octets Version 1 mode is intended to work
with any TWAMP modes.
When the Value-Added Octets Version 1 is selected with S=1, L=0 and
D=0, the Session-Sender SHALL use the following TWAMP test packet
format in unauthenticated mode:
0 1 2 3
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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 | Ver |S|L|D| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Discriminator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Additional Packet Padding |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
When the Value-Added Octets Version 1 is selected with S=0, L=1 and
D=0, the Session-Sender SHALL use the following TWAMP test packet
format in 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 | Ver |S|L|D| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Last Seqno in Train |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Additional Packet Padding |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
When the Value-Added Octets Version 1 is selected with S=1, L=1 and
D=0, the Session-Sender SHALL use the following TWAMP test packet
format in unauthenticated mode:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Estimate | Ver |S|L|D| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Discriminator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Last Seqno in Train |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Additional Packet Padding |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
When the Value-Added Octets Version 1 is selected with S=0, L=1 and
D=1, the Session-Sender SHALL use the following TWAMP test packet
format in 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 | Ver |S|L|D| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Last Seqno In Train |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Desired Reverse Packet Interval |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Additional Packet Padding |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
When the Value-Added Octets Version 1 is selected with S=1, L=1 and
D=1, the Session-Sender SHALL use the following TWAMP test packet
format in unauthenticated mode:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Estimate | Ver |S|L|D| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Discriminator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Last Seqno In Train |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Desired Reverse Packet Interval |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Additional Packet Padding |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
When the Value-Added Octets Version 1 is selected with S=1, L=1 and
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D=1, the Session-Sender SHALL use the following TWAMP test packet
format in conjunction with the unauthenticated mode, Symmetrical Size
mode and Reflect Octets 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 (27 octets) |
| |
| |
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Ver |S|L|D| Reserved | Sender... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Discriminator | Last... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Seqno in Train | Desired... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reverse Packet Interval | Additional... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Packet Padding |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
When the Value-Added Octets Version 1 is selected with S=1, L=1 and
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D=1, the Session-Sender SHALL use the following TWAMP test packet
format in conjunction with the unauthenticated mode, Symmetrical Size
mode and Reflect Octets mode with a non-zero value in the Server
octets field:
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 (27 octets) |
| |
| |
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Server octets | Ver |S|L|D| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Sender Discriminator... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Last Seqno... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| In Train | Desired Reverse Packet... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interval | Additional Packet... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Padding |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
In the combined mode including Reflect Octets, the value-added
padding octets are embedded in the Packet Padding (to be reflected)
field.
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The Version (Ver) field MUST be encoded in the first 4 bits. It
identifies the version number of the value-added padding octets and
meaning of the flag bits. This document defines version 1.
The Sender Discriminator Present bit (S) MUST be the first flag. If
the Sender Discriminator Present bit is set to 1, then a Sender
Discriminator field MUST be present and MUST contain valid
information.
The Last Seqno in Train Present bit (L) MUST be the second flag. If
the Last Seqno in Train Present bit is set to 1, then the Last Seqno
in Train field MUST be present and MUST contain valid information.
The Desired Reverse Packet Interval Present bit (D) MUST be the third
flag. If the Desired Reverse Packet Interval Present bit is set to 1,
then Desired Reverse Packet Interval Present field MUST be present
and MUST contain valid information.
The Reserved field is reserved for future use. All 9 bits of the
Reserved field MUST be transmitted as zero by the Session-Sender.
The Sender Discriminator (SD) field MUST contain an unsigned 32 bit
integer generated by the Session-Sender. It is used by the Session-
Reflector and/or Session-Sender to identify packets belonging to a
test session. The Session-Sender MUST choose a nonzero discriminator
value that is unique among all test sessions on its system. This
field is present only if the Sender Discriminator Present bit is set
to one.
The Last Seqno in Train MUST contain an unsigned 32 bit integer
generated by the Session-Sender. It MUST indicate the expected
sequence number of the last packet in the train. It SHOULD be used
by the Session-Sender and Session-reflector to identify the train a
test packet belongs to. The packets belonging to a train are
determined by observing the test packet sequence number in relation
to the Last Seqno for a train. The sequence number of a packet in a
train MUST be lower than or equal to the Last Seqno for that train.
The sequence number MUST also be larger than the Last Seqno for the
previous train. This field is present only if the Last Seqno in Train
Present bit is set to one.
The Desired Reverse Packet Interval (DRPI) MUST contain an unsigned
32 bit integer generated by the Session-Sender. It MUST indicate the
desired inter-packet time interval (or the waiting time) that the
Session-Reflector SHOULD use when transmitting the reflected test
packets towards the Session-Sender. The value 0 means the The
Session-Reflector SHOULD return the test packet to the Session-Sender
as quickly as possible. The format of this field MUST be a fractional
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part of a second as defined in OWAMP [RFC4656]. This field is present
only if the Desired Reverse Packet Interval Present bit is set to
one.
The method by which the Sender Discriminator and Desired Reverse
Packet Interval values are obtained is outside of the scope of this
document.
6.2 Reflector behavior
The TWAMP Session-Reflector follows the procedures and guidelines in
Section 4.2 of [RFC5357], with some changes and additional functions.
When the Value-Added Octets Version 1 is selected, the behavior of
the Session-Reflector SHALL be as follows:
o The Session-Reflector MUST read the Version field. If Ver=1,
the Session-Reflector MUST read the S, L and D flag bits. If
Ver is not equal 1, the Session-Reflector MUST ignore the rest
of the value-added padding octets and MUST follow the
procedures and guidelines described in section 4.2 of
[RFC5357]. The Session-Reflector SHOULD transmit the packet as
quickly as possible including the test packets that are
currently stored for the test session.
o If S=0, L=0 and D=0, the Session-Reflector MUST ignore the rest
of the value-added padding octets and MUST follow the
procedures and guidelines described in section 4.2 of
[RFC5357]. The Session-Reflector SHOULD transmit the packet as
quickly as possible including the test packets that are
currently stored for the test session.
o If S=1, the Session-Reflector MUST continue reading and
extracting the information from the Sender Discriminator field
in the value-added padding octets.
o After reading and extracting the information from the Sender
Discriminator field, the Session-Reflector SHOULD associate the
test packets to the correct test session based on the value
specified in the Sender Discriminator field and the source IP
address specified in the IP header of the test packet. The
actual method for demultiplexing the received test packets to
the correct test session based on the Sender Discriminator and
source IP address is outside the scope of this specification.
The Session-Reflector MAY also use additional packet fields to
demultiplex test packets to a test session.
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o If L=1, the Session-Reflector MUST continue reading and
extracting the information from the Last Seqno in Train field
in the value-added padding octets.
o After reading and extracting the information from the Last
Seqno in Train field, Last Seqno in Train field MUST be
compared to Sequence number in the same packet in order to
determine when a complete train has been collected. The
Session-Reflector SHOULD buffer the packets belonging to the
current train (or store the packet-level performance data) and
SHOULD transmit them as immediately as possible after the last
packet of the train has been received. The last packet within a
train has Sender Sequence Number = Last Seqno in Train.
o The Last Seqno in Train of a packet MUST also be compared to
the Last Seqno in Train of the previous packet in order to
determine if a new train needs to be collected. In case of
packet loss, the Session-Reflector MUST transmit the incomplete
train when it receives a packet with a Last SeqNo in Train
belonging to the another train (e.g. next train) of the test
session, or after a timeout. The timeout MAY be the REFWAIT
timer specified in section 4.2 of [RFC5357].
o Packets arriving out-of-order within a train MUST be buffered
at the Session-Reflector if the train is not yet transmitted to
the Session-Sender. If the train is already transmitted, the
test packet SHOULD be returned to the Session-Sender as quickly
as possible. The Session-Reflector MUST not reorder the test
packets if they happen to arrive out-of-sequence.
o Duplicate packets within a train MUST be buffered at the
Session-Reflector if the train is not yet transmitted to the
Session-Sender. If the train is already transmitted, the
duplicate test packet SHOULD be returned to the Session-Sender
as quickly as possible. The Session-Reflector MUST not discard
duplicate test packets.
o If D=1, the Session-Reflector MUST continue reading and
extracting the information from the Desired Reverse Packet
Interval field in the value-added padding octets.
o After reading and extracting the information from the Desired
Reverse Packet Interval field, the Session-Reflector SHOULD
transmit the packets belonging to a reverse train with a
waiting time (packet interval) for each packet indicated in the
Desired Reverse Packet Interval field. If the Desired Reverse
Packet Interval field is set to zero, then the Session-
Reflector SHOULD transmit the packets as quickly as possible.
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The Session-Reflector MUST implement the changes described above when
the Value-Added Octets Version 1 mode is selected.
6.2.1 Session-Reflector Packet Format
The Session-Reflector packet format follows the same procedure and
guidelines as defined in TWAMP [RFC5357] and TWAMP Reflect Octets and
Symmetrical Size Features [RFC6038], with the following changes:
o The Session-Reflector MUST re-use (reflect) the value-added
padding octets (6, 10 or 14 octets) provided in the Sender's
Packet Padding.
o The Session-Reflector MAY re-use the rest of the padding octets
in the Sender's Packet Padding.
When using the recommended truncation process [RFC5357], the Session-
Reflector MUST truncate exactly 27 octets of padding in
Unauthenticated mode,and exactly 56 octets in Authenticated and
Encrypted modes.
6.3 Additional Considerations
It is not required to use the Sender Discriminator field for
calculating the capacity metrics. The Sender Discriminator Present
bit can be set to zero. However, the Session-Sender and Session-
Reflector MUST implement a local policy to identify the test packets
belonging to a specific test session. The method for demultiplexing
the received test packets to the correct test session based on other
packet fields (e.g. fields in the IP header) is outside the scope of
this specification.
Capacity measurements introduce an additional consideration when the
test sessions operate in TWAMP Light. When the Session-Reflector does
not have knowledge of the session state, the measurement system will
only be capable to estimate or calculate the capacity metrics in the
forward path direction of transmission. Capacity measurements in the
reverse path direction requires the Session-Reflector to have
knowledge of the session state and be capable to identify the test
packets belonging to a specific test session. The method for creating
a session state from the initial test packets on the TWAMP Light
Session-Reflector is outside the scope of this specification.
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7 Security Considerations
The value-added padding octets permit new attacks on the responder
host communicating with core TWAMP [RFC5357]. The responder host MUST
provide a mechanism to protect or limit the use of its local memory
or buffer space.
The security considerations that apply to any active measurement of
live networks are relevant here as well. See [RFC4656] and [RFC5357].
8 IANA Considerations
This memo adds one mode to the IANA registry for the TWAMP Modes
field, and describes behavior when the new modes are used. This
field is a recognized extension mechanism for TWAMP.
8.1. Registry Specification
IANA has created a TWAMP-Modes registry (as requested in [RFC5618]).
TWAMP-Modes are specified in TWAMP Server Greeting messages and Setup
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 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).
8.2. Registry Contents
The TWAMP-Modes registry has been augmented as follows:
Value Description Semantics Definition
-------------------------------------------------------------------
128 Valued-Added Octets Ver 1 This memo, Section 2
new bit position (7)
9 References
9.1 Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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[RFC4656] Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
Zekauskas, "A One-way Active Measurement
Protocol(OWAMP)", RFC 4656, September 2006.
[RFC1242] Bradner, S., "Benchmarking Terminology for Network
Interconnection Devices", RFC 1242, July 1991.
[RFC5136] Chimento, P. and Ishac,J., "Defining Network Capacity",
RFC 5136, February 2008.
[RFC5357] Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
RFC 5357, October 2008.
[RFC6038] Morton, A., Ciavattone, L., TWAMP Reflect Octets and
Symmetrical Size Features, RFC6038 , October 2010.
[RFC2544] Bradner,S., McQuaid, J., "Benchmarking Terminology for
Network Interconnect Devices", RFC 2544, March 1999.
9.2 Informative References
[RRBNC] Ribeiro, V., Riedi, R., Baraniuk, R., Navratil, J.,
Cottrel, L., Pathchirp: Efficient available bandwidth
estimation for network paths, Passive and Active
Measurement Workshop, 2003.
[PDM] Dovrolis, C., Ramanathan, P., and Moore D., Packet
Dispersion Techniques and a Capacity Estimation
Methodology, IEEE/ACM Transactions on Networking,
December 2004.
[ENHJMMB] Ekelin, S., Nilsson, M., Hartikainen, E., Johnsson, A.,
Mangs, J., Melander, B., Bjorkman, M., Real-time
measurement of end-to-end available bandwidth using
kalman filtering, Proceedings to the IEEE IFIP Network
Operations and Management Symposium, 2006.
[SBW] Sommers, J., Barford, P., Willinger, W., Laboratory-based
calibration of available bandwidth estimation tools,
Microprocess Microsyst., 2007.
[Y1540] ITU-T Y.1540, Internet protocol data communication service
- IP packet transfer and availability performance
parameters, 2011.
[MRM] Morton, A., Ramachandran, G., Maguluri, G., Reporting
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Metrics Different Points of View, draft-ietf-ippm-
reporting-metrics-03, June 2010.
Author's Addresses
Steve Baillargeon
Ericsson
3500 Carling Avenue
Ottawa, Ontario K2H 8E9
Canada
EMail: steve.baillargeon@ericsson.com
Christofer Flinta
Ericsson
Farogatan 6
Stockholm, 164 80
Sweden
EMail: christofer.flinta@ericsson.com
Andreas Johnsson
Ericsson
Farogatan 6
Stockholm, 164 80
Sweden
EMail: andreas.a.johnsson@ericsson.com
Svante Ekelin
Ericsson
Farogatan 6
Stockholm, 164 80
Sweden
EMail: svante.ekelin@ericsson.com
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