Internet Engineering Task Force (IETF) S. Baillargeon
Request for Comments: 6802 C. Flinta
Category: Informational A. Johnsson
ISSN: 2070-1721 Ericsson
November 2012
Ericsson Two-Way Active Measurement Protocol (TWAMP) Value-Added Octets
Abstract
This memo describes an extension to the Two-Way Active Measurement
Protocol (TWAMP). Specifically, it extends the TWAMP-Test protocol,
which identifies and manages packet trains, in order to measure
capacity metrics like the available path capacity, tight section
capacity, and UDP delivery rate in the forward and reverse path
directions.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It has been approved for publication by the Internet
Engineering Steering Group (IESG). Not all documents approved by the
IESG are a candidate for any level of Internet Standard; see Section
2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6802.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Baillargeon, et al. Informational [Page 1]RFC 6802 Ericsson TWAMP Value-Added Octets November 2012
Table of Contents
1. Introduction ....................................................2
1.1. Requirements Language ......................................3
2. Purpose and Scope ...............................................3
3. Capacity Measurement Principles .................................4
4. TWAMP-Control Extensions ........................................5
4.1. Additional Considerations ..................................6
5. Extended TWAMP-Test .............................................6
5.1. Sender Behavior ............................................6
5.1.1. Packet Timings ......................................7
5.1.2. Session-Sender Packet Format ........................7
5.2. Reflector Behavior ........................................12
5.2.1. Session-Reflector Packet Format ....................13
5.3. Additional Considerations .................................13
6. Experiments ....................................................14
7. Security Considerations ........................................14
8. Acknowledgements ...............................................14
9. References .....................................................15
9.1. Normative References ......................................15
9.2. Informative References ....................................15
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 extension to the Two-Way Active
Measurement Protocol (TWAMP) [RFC5357]. It is called the Ericsson
TWAMP Value-Added Octets feature. This memo defines version 1.
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 delivery rate on both
forward and reverse paths using a single TWAMP test session. The
actual method to calculate the APC, TSC, or the UDP delivery rate
from packet-level performance data is not discussed in this memo.
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
[RFC5357] or immediately after the Server Octets in the Packet
Padding (to be reflected) [RFC6038] by the Session-Sender and are
reflected or returned by the Session-Reflector. The length of the
value-added octets in version 1 is 10 octets. The Valued-Added
Baillargeon, et al. Informational [Page 2]RFC 6802 Ericsson TWAMP Value-Added Octets November 2012
Octets feature does not change the basic roles and functions of the
TWAMP hosts, which are still responsible to include timestamp(s) and
sequence number(s) in the test packets.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. Purpose and Scope
The purpose of this memo is to describe the Ericsson TWAMP Valued-
Added Octets feature (version 1) for TWAMP [RFC5357].
The scope of the memo is limited to specifications of the following
enhancements:
o The definition of a structure for embedding a sequence of value-
added fields at the beginning of the Packet Padding [RFC5357] or
Packet Padding (to be reflected) [RFC6038] in the TWAMP-Test
packets
o The definition of new Session-Sender and Session-Reflector
behaviors
The motivation for this feature is to enable the measurement of
capacity metrics on both the forward and reverse paths using a single
TWAMP test session. Multiple TWAMP test sessions between a
controller and a responder with different Diffserv Code Points
(DSCPs) may also be used to evaluate the QoS impacts on the capacity
metrics.
This memo captures the prototype presented and demonstrated at IETF
80. It may be used as a reference for future work or may be used
during benchmark analysis to compare the accuracy or performance of
the available path capacity estimates under various condition or use
cases.
This memo does not extend the standard modes of operation through
assignment of a new value in the Modes field (see Section 3.1 of
[RFC4656] for the format of the Server Greeting message). This memo
does not define a vendor-specific or experimental mode since the
Modes field as currently defined does not explicitly reserve a value
or range of values for this purpose.
Baillargeon, et al. Informational [Page 3]RFC 6802 Ericsson TWAMP Value-Added Octets November 2012
This memo assumes the TWAMP controller is capable to send test
packets with value-added padding octets and the TWAMP responder is
configured to interpret the value-added padding octets embedded in
each TWAMP-Test packet. Bootstrapping such behavior at the TWAMP
responder is implementation specific. By default, the feature MUST
be disabled on the TWAMP host. The Value-Added Octets feature MUST
be deployed in an environment where both controller and responder are
managed by the same administrative entity and such entity has
established an agreement to operate the Value-Added Octets feature
between the pair of hosts or between specific UDP endpoints between
the pair of hosts. See Sections 4 and 5.3 for additional
considerations.
The Value-Added Octets Version 1 feature is intended to work in
conjunction with any TWAMP modes. When the Server and Control-Client
are configured or have agreed to use the Value-Added Octets Version 1
feature, then the Control-Client, the Server, the Session-Sender, and
the Session-Reflector must all conform to the requirements of that
feature, as identified below.
3. Capacity Measurement Principles
Most capacity estimation methods for APC [RRBNC] [PDM] [ENHJMMB]
[SBW] and for UDP delivery rate 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 bidirectional 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 APC, TSC, or UDP delivery rate in the forward direction.
Each train consists of a group of test packets that are separated
from each other by a packet interval, as shown in the figure below.
The packet interval is measured using either the first bit or the
last bit of two consecutive packets.
tt tt tt
|<---------->| |<---------->| |<---------->|
| | | | | |
+------------+ +------------+ +------------+
| Packet 1 | | Packet 2 | | Packet 3 |
+------------+ +------------+ +------------+
| | |
|<--------------------->|<--------------------->|
packet interval 1 packet interval 2
Baillargeon, et al. Informational [Page 4]RFC 6802 Ericsson TWAMP Value-Added Octets November 2012
The test packet size and 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
size and interval MAY vary within a train and/or between trains.
Determination of the packet size and interval 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 figure
above. 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 APC, TSC, and UDP delivery rate
use the packet intervals obtained from both endpoints in the
estimation process. The method of measuring the UDP delivery rate
may also require the rate of packet loss. The estimation process
itself, as well as any requirements on software or hardware, is
implementation specific.
The second measurement principle is referred to as "self-induced
congestion". According to this principle, in order to measure APC,
TSC, and UDP delivery rates, 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.
In order to fulfill the above measurement principles and to measure
the APC, TSC, and UDP delivery rates in the reverse direction, the
test packets at the Session-Reflector MUST be regrouped into trains
and then transmitted back to the Session-Sender with a provided
packet interval.
4. TWAMP-Control Extensions
TWAMP connection establishment follows the procedure defined in
Section 3.1 of [RFC4656] and Section 3.1 of [RFC5357]. The TWAMP-
Control protocol [RFC5357] uses the Modes field to identify and
select specific communication capabilities. According to the
standard specifications, the Value-Added Octets feature requires 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. Such bit position (and value) is not defined in
this memo. Bootstrapping the TWAMP Value-Added Octets Version 1
feature is implementation specific.
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RFC 6802 Ericsson TWAMP Value-Added Octets November 2012
Both the Reflect Octets mode and Symmetrical Size mode MAY 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.
4.1. Additional Considerations
In the TWAMP control architecture, the TWAMP reflector (server)
signals the modes it wishes to operate and the TWAMP controller
(control-client) selects the mode or modes supported by the
responder. This feature is designed to retain backward compatibility
with the original TWAMP-Control and TWAMP-Test protocols. As an
alternative, the user may opt for TWAMP Light architecture, which
does not require the TWAMP-Control protocol.
The methods to determine if the Value-Added Octets feature is
supported on a TWAMP reflector is implementation specific. When the
Value-Added Octets feature is not supported on a TWAMP reflector, the
TWAMP controller MUST NOT select the Value-Added Octets feature and
MUST NOT include any value-added octets in the test packets. If the
TWAMP controller inadvertently sends value-added octets in the test
packets to a TWAMP responder that does not support such feature, the
TWAMP responder shall treat the value-added octets as regular padding
octets and return the test packets as quickly as possible to the
Session-Sender as defined in [RFC5357].
5. Extended TWAMP-Test
The forward and reverse APC, TSC, and UDP delivery rate measurement
characteristics depend on the size and packet intervals of the test
packets. This memo allows variable packet sizes and packet intervals
between trains and even between packets in the same train. The
functionality is described below.
The TWAMP-Test protocol carrying the value-added padding octets is
identical to TWAMP [RFC5357] except for the definition of the first
10 octets in the Packet Padding that the Session-Sender expects to be
reflected. The new octets define fields for Value-Added Octets
Version, Flags, Last Sequence Number in Train, and Desired Reverse
Packet Interval. Each of these fields are described in detail below.
The Session-Sender and Session-Reflector behaviors are also modified.
5.1. Sender Behavior
This section describes the extensions to the behavior of the TWAMP
Session-Sender.
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5.1.1. Packet Timings
The Send Schedule is not utilized in TWAMP, and this is unchanged in
this memo.
5.1.2. 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
Symmetrical Size Features [RFC6038].
This feature allows the Session-Sender to set the first few octets in
the TWAMP-Test Packet Padding with information to communicate value-
added padding version number, flag bits, sequence number of the last
packet in a train, and desired reverse packet interval (or per-packet
waiting time) for the reverse path direction of transmission.
The Valued-Added Octets feature must be placed immediately after the
TWAMP header or immediately after any new field that could be added
to the TWAMP header or added to the beginning of the padding octets
in the future. Therefore, the placement of the first bit from the
valued-added octets depends on the mode(s) being selected.
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 and corresponding fields. Each flag bit indicates
if a specific field is used in the valued-added padding octets. The
version number and flag bits provide an effective method for
extracting information at Session-Reflector and Session-Sender. This
document defines version 1 with two flag bits: L and I.
The format of the test packet depends on the TWAMP modes. The Value-
Added Octets Version 1 feature is intended to work with any TWAMP
modes.
The Session-Sender SHALL use the following TWAMP-Test packet format
when the Value-Added Octets Version 1 feature is selected in
conjunction with the Unauthenticated mode:
Baillargeon, et al. Informational [Page 7]
RFC 6802 Ericsson TWAMP Value-Added Octets November 2012
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 |L|I| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Last Seqno In Train |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Desired Reverse Packet Interval |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Additional Packet Padding |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Baillargeon, et al. Informational [Page 8]RFC 6802 Ericsson TWAMP Value-Added Octets November 2012
The Session-Sender SHALL use the following TWAMP-Test packet format
when the Value-Added Octets Version 1 feature is selected 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 |L|I| Reserved | Last... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Seqno in Train | Desired... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reverse Packet Interval | Additional... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Packet Padding |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Baillargeon, et al. Informational [Page 9]RFC 6802 Ericsson TWAMP Value-Added Octets November 2012
The Session-Sender SHALL use the following TWAMP-Test packet format
when the Value-Added Octets Version 1 feature is selected 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 |L|I|...|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Last Seqno in... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Train | Desired Reverse Packet... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interval | Additional Packet Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
In the mode using Reflect Octets illustrated above, the value-added
padding octets are embedded in the Packet Padding (to be reflected).
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 and the corresponding fields. This memo
defines version 1 with two flag bits: L and I. When the Value-Added
Octets Version 1 feature is selected, the Session-Sender MUST set the
Ver field to 1.
The 2 bits after the Version field are used for flags: L and I.
Baillargeon, et al. Informational [Page 10]RFC 6802 Ericsson TWAMP Value-Added Octets November 2012
The Last Seqno in Train bit (L) is the first flag. When the Value-
Added Octets Version 1 feature is selected, the Session-Sender MAY
set the Last Seqno in Train bit L to 1.
The Desired Reverse Packet Interval bit (I) is the second flag. When
the Value-Added Octets Version 1 feature is selected, the Session-
Sender MAY set the Desired Reverse Packet Interval bit I to 1.
The Reserved field is reserved for future use. All 10 bits of the
Reserved field MUST be transmitted as zero by the Session-Sender.
If the Last Seqno in Train bit is set to 1, then the Last Seqno in
Train field 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 to which a test packet
belongs. The packets belonging to a train are determined by
observing the test packet Sequence Number in relation to the Last
Seqno in Train. The Last Seqno in Train MUST be higher or equal to
Sequence Number of the packet. It must also be higher than the Last
Seqno in Train for the previous train. If the L bit is set to 0, the
Session-Sender shall set all the bits in the Last Seqno in Train
field to zero.
If the Desired Reverse Packet Interval bit is set to 1, then the
Desired Reverse Packet Interval field MUST contain an unsigned 32 bit
integer generated by the Session-Sender. It MUST indicate the
desired packet 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 Session-Reflector
SHOULD return the test packet to the Session-Sender as quickly as
possible. The format of this field MUST be a fractional part of a
second as defined in the One-Way Active Measurement Protocol (OWAMP)
[RFC4656]. If the I bit is set to 0, the Session-Sender shall set
all the bits in the Desired Reverse Packet Interval field to zero.
The values of the above fields are usually provided by a measurement
method, tool, or algorithm. This measurement algorithm is outside
the scope of this specification.
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5.2. 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 feature 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 L and I flag bits.
o If L=1 and I=1, the Session-Reflector MUST read and extract the
information from the Last Seqno in Train field and the Desired
Reverse Packet Interval field in the value-added padding octets.
- The Last Seqno in Train 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). After the last packet of the train
has been received, 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 packet as quickly as possible. The last
packet within a train has Sender Sequence Number = Last Seqno
in Train.
- 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 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].
- 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.
- 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
Baillargeon, et al. Informational [Page 12]RFC 6802 Ericsson TWAMP Value-Added Octets November 2012
duplicate test packet SHOULD be returned to the Session-Sender
as quickly as possible. The Session-Reflector MUST NOT discard
duplicate test packets.
For any other combinations of the Version field and the L and I
flags, the Session-Reflector SHOULD return the test packet to the
Session-Sender as quickly as possible.
The Session-Reflector MUST implement the changes described above when
the Value-Added Octets Version 1 feature is selected.
5.2.1 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 reuse (reflect) the value-added padding
octets (10 octets) provided in the Sender's Packet Padding.
o The Session-Reflector MAY reuse the rest of the padding octets in
the Sender's Packet Padding.
The truncation process [RFC5357] is recommended when the Symmetrical
mode is not used. The Session-Reflector MUST truncate exactly 27
octets of padding in Unauthenticated mode and exactly 56 octets in
Authenticated and Encrypted modes.
5.3. Additional Considerations
The Session-Reflector supporting the Value-Added Octets feature
should revert back to the standard Session-Reflector behavior if it
cannot interpret the value-added padding octets in a given test
packet. Section 5.2 also describes such behavior. For instance, the
test packet is returned as quickly as possible to the Session-Sender
when the Last Seqno in the Train is not what is expected.
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
may be restricted to estimating or calculating the capacity metrics
in the forward path direction of transmission only. Capacity
measurements in the reverse path direction is best handled with a
Session-Reflector supporting knowledge of the session state and being
capable of identifying the test packets belonging to a specific test
session. A method for creating a session state from the initial test
packet may be implemented on the TWAMP Light Session-Reflector. This
is outside the scope of this specification.
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6. Experiments
This memo describes the protocol used in the current working
prototype implementation of the Value-Added Octets feature in the
Ericsson lab. The prototype has been tested in real network
environments. The conclusion from these tests is that the Value-
Added Octets feature is able to enable estimation of capacity metrics
such as available path capacity in both the forward and reverse
directions of the network path.
During the experiments with the protocol described in this memo, we
have identified a need for the controller and responder to use the
same maximum train length. The reflector must be able to buffer the
whole train received from the controller. In order to reduce the
risk for buffer overrun, the maximum train length should be
negotiated. This can be resolved through configuration, introduction
of a new field in the value-added octets, or a new maximum train
length field in the Request-TW-Session message.
The Sender Discriminator (SD) field, which was proposed in an early
draft of this document, was removed because of complications with
different Session-Reflector implementations. A Session-Reflector may
not be able to easily identify the SD field or associate it with a
specific Session-Sender, which may skew the test results.
The flags defined in the value-added octets now indicate the usage of
fields and not the presence of fields. This modification was needed
to simplify the responder implementation in the working prototype.
7. Security Considerations
The value-added padding octets permit DoS attacks on the responder
host communicating with core TWAMP [RFC5357]. For instance, a DoS
condition could arise when the Last Seqno in Train is too large to
handle, potentially causing undesirable processing delay or discard
of the TWAMP-Test packets. The responder host MUST provide a
mechanism to protect or limit the use of its local memory, buffer
space, or maximum transmission time for a train.
The security considerations that apply to any active measurement of
live networks are relevant here as well. See [RFC4656] and
[RFC5357].
8. Acknowledgements
The authors thank Svante Ekelin for providing direction and comments
on this document.
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RFC 6802 Ericsson TWAMP Value-Added Octets November 2012
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.
[RFC4656] Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
Zekauskas, "A One-way Active Measurement Protocol
(OWAMP)", RFC 4656, September 2006.
[RFC5136] Chimento, P. and J. Ishac, "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. and L. Ciavattone, "Two-Way Active Measurement
Protocol (TWAMP) Reflect Octets and Symmetrical Size
Features", RFC 6038, October 2010.
9.2. Informative References
[ENHJMMB] Ekelin, S., Nilsson, M., Hartikainen, E., Johnsson, A.,
Mangs, J., Melander, B., and M. Bjorkman, "Real-Time
Measurement of End-to-End Available Bandwidth Using
Kalman Filtering", Proceedings to the IEEE/IFIP Network
Operations and Management Symposium, 2006.
[PDM] Dovrolis, C., Ramanathan, P., and D. Moore, "Packet-
Dispersion Techniques and a Capacity-Estimation
Methodology", IEEE/ACM Transactions on Networking,
December 2004.
[RRBNC] Ribeiro, V., Riedi, R., Baraniuk, R., Navratil, J., and
L. Cottrel, "pathChirp: Efficient Available Bandwidth
Estimation for Network Paths", Passive and Active
Monitoring Workshop, 2003.
[SBW] Sommers, J., Barford, P., and W. Willinger, "Laboratory-
based Calibration of Available Bandwidth Estimation
Tools", Microprocessors and Microsystems, 2007.
[Y1540] International Telecommunications Union, "Internet
protocol data communication service - IP packet transfer
and availability performance parameters", ITU-T
Recommendation Y.1540, 2011.
Baillargeon, et al. Informational [Page 15]RFC 6802 Ericsson TWAMP Value-Added Octets November 2012
Authors' 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
Baillargeon, et al. Informational [Page 16]
