Internet DRAFT - draft-ietf-ippm-twamp-value-added-octets
draft-ietf-ippm-twamp-value-added-octets
Network Working Group S. Baillargeon
INTERNET-DRAFT C. Flinta
Intended Status: Informational A. Johnsson
Expires: March 30, 2013 Ericsson
September 26, 2012
Ericsson TWAMP Value-Added Octets
draft-ietf-ippm-twamp-value-added-octets-09.txt
Abstract
This memo describes an extension to the TWAMP test protocol for
identifying and managing packet trains, which enables measuring
capacity metrics like the available path capacity, tight section
capacity and UDP delivery rate in the forward and reverse path
directions.
This memo contains the description of a working prototype. It does
not represent a consensus of the IETF community. The IETF community
is currently working on the problem statement and has not reached
consensus on the preferred method for measuring capacity metrics.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 30, 2013.
Copyright and License Notice
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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.
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Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Requirements Language . . . . . . . . . . . . . . . . . . . 4
2 Purpose and scope . . . . . . . . . . . . . . . . . . . . . . . 4
3 Capacity Measurement Principles . . . . . . . . . . . . . . . . 6
4 TWAMP Control Extensions . . . . . . . . . . . . . . . . . . . . 7
4.1 Additional Considerations . . . . . . . . . . . . . . . . . 7
5 Extended TWAMP Test . . . . . . . . . . . . . . . . . . . . . . 8
5.1 Sender Behavior . . . . . . . . . . . . . . . . . . . . . . 8
5.1.1 Packet Timings . . . . . . . . . . . . . . . . . . . . 8
5.1.2 Session-Sender Packet Format . . . . . . . . . . . . . 8
5.2 Reflector behavior . . . . . . . . . . . . . . . . . . . 13
5.2.1 Session-Reflector Packet Format . . . . . . . . . . 15
5.3 Additional Considerations . . . . . . . . . . . . . . . . 15
6 Experiments . . . . . . . . . . . . . . . . . . . . . . . . . 16
7 Security Considerations . . . . . . . . . . . . . . . . . . . 16
8 IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
9 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17
10 References . . . . . . . . . . . . . . . . . . . . . . . . . 17
10.1 Normative References . . . . . . . . . . . . . . . . . . 17
10.2 Informative References . . . . . . . . . . . . . . . . . 17
Author's Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
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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 extension to the Two-Way Active
Measurement Protocol [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 data 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
field [RFC5357] or immediately after the Server Octets in 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 in version 1 is 10 octets. The Valued-Added 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.
This memo contains the description of a working prototype. It does
not represent a consensus of the IETF community. The IETF community
is currently working on the problem statement and has not reached
consensus on the preferred method for measuring capacity metrics.
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].
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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 field
[RFC5357] 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 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 DSCPs may also be used to evaluate the
QoS impacts on the capacity metrics.
The motivation for this document is to capture the prototype
presented and demonstrated at the 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.
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 section 4 and section 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
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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 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 APC, TSC or UDP delivery rate 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.
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
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 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 APC, TSC and UDP delivery rate use
the packet intervals obtained from both end points in the estimation
process. The method to measuring the UDP delivery rate may also
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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 re-grouped 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.
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-cient) selects the mode or modes supported by the responder.
This feature is designed to retain backward compatibility with the
original TWAMP control and 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
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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 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.
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 field 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.
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The Valued-Added Octets feature must be immediately placed 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.
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The Session-Sender SHALL use the following TWAMP test packet format
when the Value-Added Octets version 1 is selected in conjunction with
the 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 |L|I| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Last Seqno In Train |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Desired Reverse Packet Interval |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Additional Packet Padding |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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The Session-Sender SHALL use the following TWAMP test packet format
when the Value-Added Octets Version 1 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 |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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The Session-Sender SHALL use the following TWAMP test packet format
when the Value-Added Octets Version 1 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)field.
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.
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The 2 bits after the Version field are used for flags: L and I.
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 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
Last Seqno in Train MUST be higher or equal to the 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 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 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.
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 is selected, the behavior of
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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 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). 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
duplicate test packet SHOULD be returned to the Session-
Sender as quickly as possible. The Session-Reflector MUST
NOT discard duplicate test packets.
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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 re-use (reflect) the value-added
padding octets (10 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.
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 with a new maximum train length
field in the Request-TW-Session message.
The Sender Discriminator (SD) field that is defined in the first
draft has been 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 IANA Considerations
This document has no actions for IANA.
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9 Acknowledgements
The authors thank Svante Ekelin for providing direction and comments
on this document.
10 References
10.1 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 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.
10.2 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,
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Microprocess Microsyst., 2007.
[Y1540] ITU-T Y.1540, Internet protocol data communication service
- IP packet transfer and availability performance
parameters, 2011.
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
Baillargeon, et al. Expires March 30, 2013 [Page 18]
