Internet Engineering Task Force Takumi Kimura
INTERNET-DRAFT NTT
Expires in: October 2003 Jerry Perser
Spirent
April 2003
Benchmarking Terminology for Protection Performance
<draft-kimura-protection-term-01.txt>
Status of this Memo
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Abstract
This document addresses common terminology and metrics for the
performance benchmarking of sub-IP layer protection technologies:
Automatic Protection Switching (APS) for SONET/SDH, Resilient Packet
Ring (RPR) for Ethernet, and Fast Reroute for Multi-Protocol Label
Switching (MPLS). The benchmarks describe the performance based on
the effects in the IP-layer, to avoid dependence on a specific sub-IP
layer protection technology.
Table of Contents
1. Introduction .............................................. 2
2. Existing definitions ...................................... 3
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3. Term definitions .......................................... 3
3.1 Path
3.1.1 Path ............................................... 3
3.1.2 Working Path ....................................... 4
3.1.3 Ordinary Path ...................................... 4
3.1.4 Recovery Path ...................................... 5
3.1.5 Recovery Span ...................................... 5
3.2 Protection
3.2.1 Path Failure ....................................... 6
3.2.2 Failure Detection .................................. 6
3.2.3 Switch-Over ........................................ 7
3.2.4 Protection Switching ............................... 7
3.2.5 Protection-Capable Node ............................ 8
3.2.6 Protection System .................................. 8
3.3 Reference Model for Protection Benchmarking
3.3.1 Pseudo-Failure Equipment ........................... 9
3.3.2 Trigger for Protection ............................. 9
3.3.3 Reference Model for Protection Benchmarking ........ 10
3.4 Metrics
3.4.1 Lost Packet ........................................ 11
3.4.2 Errored Packet ..................................... 12
3.4.3 Additive Latency ................................... 12
3.4.4 Induced Latency .................................... 12
3.4.5 Recovery Time ...................................... 13
4. Security Considerations ................................... 13
5. References ................................................ 14
6. Authors' Addresses ........................................ 14
1. Introduction
Reliability is needed in today's IP networks, because the Internet
has already become an important communication infrastructure, and
quality-sensitive applications are being used on it. To improve IP-
layer reliability, protection technologies have been implemented in
sub-IP layers. Automatic Protection Switching (APS) is for
SONET/SDH, Resilient Packet Ring (RPR) is for the Ethernet, and Fast
Reroute is for Multi-Protocol Label Switching (MPLS). Recovery time
in the IP-layer is different from that in sub-IP layers because of
the mechanism for recognition when interfaces go up and down and the
buffering effect of IP routers. Protection performance
specifications and methodologies for testing them are required to
allow an objective comparison of implementations.
Performance metrics are based on the effects in the IP layer, so that
they can be developed independent of protection technologies and that
we can compare different protection technologies.
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2. Existing definitions
This document draws on existing terminology defined in other BMWG
work. Examples include, but are not limited to:
Latency [RFC 1242, section 3.8]
Frame Loss Rate [RFC 1242, section 3.6]
Throughput [RFC 1242, section 3.17]
Device Under Test (DUT) [RFC 2285, section 3.1.1]
System Under Test (SUT) [RFC 2285, section 3.1.2]
Out-of-order Packet [Ref.[4], section 3.3.2]
Duplicate Packet [Ref.[4], section 3.3.3]
This document adopts the definition format in Section 2 of RFC 1242.
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.
3. Term definitions
3.1 Path
3.1.1 Path
Definition:
A sequence of nodes, <R1, ..., Rn>, with the following
properties:
- R1 is the ingress node and forwards IP packets, which input
into DUT/SUT, to R2 as sub-IP frames.
- Ri is a node which forwards data frames to R[i+1] for all i,
1<i<n, based on information in the sub-IP layer.
- Rn is the egress node and it outputs sub-IP frames from
DUT/SUT as IP packets.
Discussion:
The path is defined in the sub-IP layer in this document, unlike
an IP path in RFC 2026. For example, the SONET/SDH path, the
label switched path for MPLS, and optical path. One path may be
regarded as being equivalent to one IP link between two IP
nodes, i.e., R1 and Rn. The two IP nodes may have multiple
paths for protection. A packet will travel on only one path
between the nodes. Packets belonging to a microflow (RFC 2474)
will transverse one or more paths. The path is unidirectional.
Measurement units:
n/a
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Issues:
"A bidirectional path", which transmits traffic in both
directions along the same nodes, consists of two unidirectional
paths. Therefore, the two unidirectional paths belonging to
"one bidirectional path" will be treated independently when
benchmarking for " a bidirectional path".
See Also:
3.1.2 Working Path
Definition:
A path that the DUT/SUT is using to forward packets.
Discussion:
An ordinary path (3.1.3) is a working path before protection,
while a recovery path (3.1.4) becomes a working path after
protection.
Measurement units:
n/a
Issues:
See Also:
Path (3.1.1)
Ordinary Path (3.1.3)
Recovery Path (3.1.4)
3.1.3 Ordinary Path
Definition:
A path which is a working path before protection.
Discussion:
Measurement units:
n/a
Issues:
See Also:
Path (3.1.1)
Working Path (3.1.2)
Path Failure (3.2.1)
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3.1.4 Recovery Path
Definition:
A path which is prepared against the eventuality of path
failure, and used to forward packets as a working path.
Discussion:
There are various types of recovery paths: a dedicated recovery
path (1+1), which has 100% redundancy for a specific ordinary
path, a shared recovery path (1:N), which is dedicated to the
protection for more than one specific ordinary path, and an
associated shared recovery path (M:N) for which a specific set
of recovery paths protects a specific set of more than one
ordinary path.
Measurement units:
n/a
Issues:
See Also:
Path (3.1.1)
Working Path (3.1.2)
Ordinary Path (3.1.3)
Path Failure (3.2.1)
3.1.5 Recovery Span
Definition:
A fraction of an ordinary path that includes a failure link or
node and is changed to other link(s) and node(s) for protection.
Discussion:
There are two types of recovery spans: a full recovery span,
which is a recovery span prepared between the ingress and egress
nodes of DUT/SUT, and a partial recovery span, which is a
recovery span prepared for only parts of an ordinary path
between ingress and egress nodes of DUT/SUT. For a full
recovery span, the whole of an ordinary path is changed to a
recovery span for protection, and the ordinary and recovery
paths do not overlap. For a partial recovery span, only a part
of an ordinary path is changed to a recovery span for
protection, and parts of the ordinary and recovery paths may
overlap.
Measurement units:
n/a
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Issues:
See Also:
Ordinary Path (3.1.3)
Recovery Path (3.1.4)
Path Failure (3.2.1)
3.2 Protection
3.2.1 Path Failure
Definition:
A condition that prevents packets from being forwarded on an
ordinary path as a working path, caused by fault(s) with link(s)
or node(s) in a sub-IP layer.
Discussion:
Measurement units:
n/a
Issues:
See Also:
Working Path (3.1.2)
Ordinary Path (3.1.3)
3.2.2 Failure Detection
Definition:
To detect working-path failure which is caused by fault(s) with
link(s) or node(s) in a sub-IP layer.
Discussion:
Measurement units:
n/a
Issues:
See Also:
Working Path (3.1.2)
Ordinary Path (3.1.3)
Path Failure (3.2.1)
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3.2.3 Switch-Over
Definition:
To change a working path, in cases of failure, from an ordinary
path to a recovery path.
Discussion:
Switch-over does not always replace an entire ordinary path with
other link(s) and node(s) for a partial recovery span.
Measurement units:
n/a
Issues:
See Also:
Working Path (3.1.2)
Ordinary Path (3.1.3)
Recovery Path (3.1.4)
Recovery Span (3.1.5)
Path Failure (3.2.1)
3.2.4 Protection Switching
Definition:
The detection of working-path failures and response to these by
switching the working path from the ordinary to the recovery
path.
Discussion:
A protection-switching scheme includes both the mechanisms for
failure detection and switch-over.
Measurement units:
n/a
Issues:
See Also:
Working Path (3.1.2)
Ordinary Path (3.1.3)
Recovery Path (3.1.4)
Recovery Span (3.1.5)
Path Failure (3.2.1)
Failure Detection (3.2.2)
Switch-Over (3.2.3)
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3.2.5 Protection-Capable Node
Definition:
A node that includes functional elements to handle protection
switching.
Discussion:
Both end nodes of a recovery span for an ordinary path must be
protection-capable nodes.
Measurement units:
n/a
Issues:
See Also:
Ordinary Path (3.1.3)
Recovery Path (3.1.4)
Recovery Span (3.1.5)
Protection Switching (3.2.4)
3.2.6 Protection System
Definition:
A system which consists of two or more protection-capable nodes
connected to each other by link(s) and node(s) constructing
ordinary paths and recovery paths.
Discussion:
When a working-path failure occurs, the system detects the
failure and switches the working path from the failed ordinary
path to the recovery path. Some technologies for this are in
sub-IP layers, i.e., MPLS-based recovery, SONET/SDH-based
recovery and optical path recovery.
Measurement units:
n/a
Issues:
See Also:
Working Path (3.1.2)
Ordinary Path (3.1.3)
Recovery Path (3.1.4)
Recovery Span (3.1.5)
Path Failure (3.2.1)
Failure Detection (3.2.2)
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Switch-Over (3.2.3)
Protection Switching (3.2.4)
Protection-Capable Node (3.2.5)
3.3 Reference Model for Protection Benchmarking
3.3.1 Pseudo-Failure Equipment
Definition:
Equipment which creates a pseudo path failure after receiving a
signal from a tester.
Discussion:
An pseudo-failure equipment is used in benchmarking protection
systems, since it provides more reliable and reproducible
testing than actual path failure.
Measurement units:
n/a
Issues:
See Also:
Path Failure (3.2.1)
Trigger for Protection (3.3.2)
3.3.2 Trigger for Protection
Definition:
A signal which is sent from a tester to make a piece of pseudo-
failure equipment create a pseudo failure in an ordinary path.
Discussion:
Measurement units:
n/a
Issues:
See Also:
Working Path (3.1.2)
Ordinary Path (3.1.3)
Path Failure (3.2.1)
Pseudo-Failure Equipment (3.3.1)
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3.3.3 Reference Model for Protection Benchmarking
Definition:
A fundamental model that is used in benchmarking protection
systems. A System Under Test (SUT) consists of two protection-
capable nodes connected by both an ordinary path and a recovery
path. An pseudo-failure equipment is placed at a point along
the ordinary path. A tester is set outside the two nodes and it
generates IP traffic. The tester also sends the triggers for
protection that cause the piece of pseudo-failure equipment to
simulate path failures.
+-----------+
+--------------------| Tester |<-------------------+
| +-----------+ |
| | Trigger |
| | for Protection |
| Ordinary v |
| +--------+ Path +---------+ +--------+ |
| | |-------| Failure |------>| | |
+--->| Node 1 | +---------+ | Node 2 |----+
| |- - - - - - - - - - - - >| |
+--------+ Recovery Path +--------+
| |
+-------------------------------------------+
System Under Test (SUT)
Figure 1
Discussion:
Figure 1 shows a reference model for protection benchmarking. A
SUT consists of two protection-capable nodes connected by both
an ordinary path and a recovery path. The ordinary path has
pseudo-failure equipment. A tester, which is placed outside the
two nodes, continuously sends IP packets that include sequence
numbers and time stamps to one of the nodes and receives packets
from the other node. After the tester has sent a trigger for
protection to the pseudo-failure equipment, the system detects
the failure and switches from the failed ordinary path to the
recovery path. The tester records the sequence numbers and time
stamps in the IP packets as well as the packet-reception times,
during the time it takes protection switching to detect and
finish responding to a failure.
Measurement units:
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n/a
Issues:
See Also:
Working Path (3.1.2)
Ordinary Path (3.1.3)
Recovery Path (3.1.4)
Path Failure (3.2.1)
Failure Detection (3.2.2)
Switch-Over (3.2.3)
Protection Switching (3.2.4)
Protection-Capable Node (3.2.5)
Pseudo-Failure Equipment (3.3.1)
Trigger for Protection (3.3.2)
3.4 Metrics
Performance metrics for protection benchmarking will include
Lost Packet (related to Frame Loss Rate in RFC 1242), Errored
Packet, Induced Latency, Out-of-order Packet (Ref.[4]),
Duplicate Packet (Ref.[4]), and Recovery Time.
3.4.1 Lost Packet
Definition:
A packet that is lost during the time it takes protection
switching to detect and finish responding to a failure.
Discussion:
The input traffic rate SHOULD be less than or equal to the
Throughput (RFC 1242) which is the smallest of two Throughputs
for paths before and after protection switching. This metric is
related to the Frame Loss Rate defined in RFC 1242 but we are
interested in the number of lost packets during testing.
Measurement units:
Packet count
Issues:
See Also:
Protection Switching (3.2.4)
Throughput (RFC 1242)
Frame Loss Rate (RFC 1242)
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3.4.2 Errored Packet
Definition:
A received packet that fails at least one error detection
scheme.
Discussion:
The error detection scheme can be sub-IP (FCS), IP (IP
checksum), or other layers (TCP checksum).
Measurement units:
Packet count
Issues:
See Also:
3.4.3 Additive Latency
Definition:
Difference in recovery-path latency against ordinary-path
latency.
Discussion:
If a recovery path takes more hops than an ordinary path, the
latency (additive latency) is increased by protection switching.
Measurement units:
Seconds
Issues:
See Also:
Ordinary Path (3.1.3)
Recovery Path (3.1.4)
Latency (RFC 1242)
3.4.4 Induced Latency
Definition:
Difference in measured maximum latency during testing against
the maximum value of ordinary and recovery path latencies.
Discussion:
This latency may be induced by buffering in nodes during
protection switching.
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Measurement units:
Seconds
Issues:
See Also:
Ordinary Path (3.1.3)
Recovery Path (3.1.4)
Latency (RFC 1242)
3.4.5 Recovery Time
Definition:
Time duration when protection switching in response to path
failure has finished and stability is restored enabling packets
to be forwarded normally, i.e., abnormal and abnormally received
packets (lost, errored, out-of-order, and duplicated) are no
longer present, induced latency is decreased, and latency
becomes stable.
Discussion:
Recovery time may be the sum of failure detection time, switch-
over time and the time taken for the system to be stabilized.
Measurement units:
Seconds
Issues:
See Also:
Ordinary Path (3.1.3)
Recovery Path (3.1.4)
Failure Detection (3.2.2)
Switch-Over (3.2.3)
Protection Switching (3.2.4)
Latency (RFC 1242)
Lost Packet (3.4.1)
Errored Packet (3.4.2)
Out-of-order Packet (Ref.[4])
Duplicate Packet (Ref.[4])
Induced Latency (3.4.4)
4. Security Considerations
This document only addresses terminology for the performance
benchmarking of protection systems, and the information contained in
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this document has no effect on the security of the Internet.
5. References
[1] Bradner, S., "The Internet Standards Process -- Revision 3",
RFC 2026, October 1996.
[2] Bradner, S., Editor, "Benchmarking Terminology for
Network Interconnection Devices", RFC 1242, July 1991.
[3] Mandeville, R., "Benchmarking Terminology for LAN
Switching Devices", RFC 2285, February 1998.
[4] Perser, J., et al., "Terminology for Benchmarking Network-layer
Traffic Control Mechanisms",
Internet Draft, Work in Progress,
draft-ietf-bmwg-dsmterm-05.txt, February 2003.
[5] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[6] Paxson, V., et al., "Framework for IP Performance Metrics",
RFC 2026, May 1998.
6. Authors' Addresses
Takumi Kimura
NTT Service Integration Laboratories
3-9-11 Midori-cho
Musashino-shi, Tokyo 180-8585
Japan
Phone: +81 422 59 3026
EMail: takumi.kimura@lab.ntt.co.jp
Jerry Perser
Spirent Communications
26750 Agoura Road
Calabasas, CA 91302
USA
Phone: + 1 818 676 2300
EMail: jerry.perser@spirentcom.com
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