draft-ietf-bmwg-lanswitch-01.txt   draft-ietf-bmwg-lanswitch-02.txt 
Network Working Group R. Mandeville Network Working Group R. Mandeville
INTERNET-DRAFT European Network Laboratories INTERNET-DRAFT European Network Laboratories
Expiration Date: May 1997 Nov 1996 Expiration Date: Jun 1997 Jan 1997
Benchmarking Terminology for LAN Switching Devices Benchmarking Terminology for LAN Switching Devices
< draft-ietf-bmwg-lanswitch-02.txt >
< draft-ietf-bmwg-lanswitch-01.txt >
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Abstract Abstract
The purpose of this draft is to define and discuss benchmarking terminology The purpose of this draft is to define and discuss benchmarking terminology
for local area switching devices. It is meant to extend the terminology for local area switching devices. It is meant to extend the terminology
already defined for network interconnect devices in RFCs 1242 and 1944 by already defined for network interconnect devices in RFCs 1242 and 1944 by
the Benchmarking Methodology Working Group (BMWG) of the Internet the Benchmarking Methodology Working Group (BMWG) of the Internet
Engineering Task Force (IETF). Engineering Task Force (IETF) and prepare the way for a discussion on
benchmarking methodology for local area switches.
LAN switches are one of the principal sources of new bandwidth in the local LAN switches are one of the principal sources of new bandwidth in the local
area and are handling a significantly increasing proportion of network area. The multiplicity of products brought to market makes it desirable to
traffic. The multiplicity of products brought to market makes it desirable define a set of terms to be used when evaluating the performance
to define a set of terms to be used when evaluating the performance
characteristics of local area switching devices. Well-defined terminology characteristics of local area switching devices. Well-defined terminology
will help in providing the user community with complete, reliable and will help in providing the user community with complete, reliable and
comparable data on LAN switches. comparable data on LAN switches.
1. Introduction 1. Introduction
The purpose of this draft is to discuss and define terminology for the The purpose of this draft is to discuss and define terminology for the
benchmarking of LAN switching devices. This draft covers local area devices benchmarking of local area network switches. Although it might be found
which switch frames at the Media Access Control (MAC) layer. It discusses useful to apply some of the terms defined here to a broader range of network
throughput, latency, address handling and filtering. interconnect devices, this draft primarily deals with devices which switch
frames at the Medium Access Control (MAC) layer. It defines terms in
relation to throughput, latency, address handling and filtering.
2. Term definitions 2. Term definitions
A previous document, "Benchmarking Terminology for Network Interconnect A previous document, "Benchmarking Terminology for Network Interconnect
Devices" (RFC 1242), defined many of the terms that are used in this Devices" (RFC 1242), defined many of the terms that are used in this
document. The terminology document should be consulted before attempting to document. The terminology document should be consulted before attempting to
make use of this document. A more recent document, "Benchmarking Methodology make use of this document. A more recent document, "Benchmarking Methodology
for Network Interconnect Devices" (RFC 1944), defined a number of test for Network Interconnect Devices" (RFC 1944), defined a number of test
procedures which are directly applicable to switches. Since it discusses a procedures which are directly applicable to switches. Since it discusses a
number of terms relevant to benchmarking switches it should also be consulted. number of terms relevant to benchmarking switches it should also be consulted.
skipping to change at line 92 skipping to change at line 93
List of issues or conditions that effect this term. List of issues or conditions that effect this term.
See Also: See Also:
List of other terms that are relevant to the discussion List of other terms that are relevant to the discussion
of this term. of this term.
2.2. Unidirectional traffic 2.2. Unidirectional traffic
Definition: Definition:
Unidirectional traffic is made up of a single or multiple streams of frames Single or multiple streams of frames forwarded in one direction only from
forwarded in one direction only from one or more ports of a switching device one or more ports of a switching device designated as input ports to one or
designated as input ports to one or more other ports of the device more other ports of the device designated as output ports.
designated as output ports.
Discussion: Discussion:
This definition conforms to the discussion in section 16 of RFC 1944 on This definition conforms to the discussion in section 16 of RFC 1944 on
multi-port testing which describes how unidirectional traffic can be offered multi-port testing which describes how unidirectional traffic can be offered
to ports of a device to measure maximum rate of throughput. to ports of a device to measure throughput.
Unidirectional traffic SHOULD be offered to devices for: Unidirectional traffic is also appropriate for:
- the measurement of the minimum inter-frame gap - the measurement of the minimum inter-frame gap
- the creation of many-to-one or one-to-many port overload - the creation of many-to-one or one-to-many port overload
- the detection of head of line blocking - the detection of head of line blocking
- the measurement of throughput when congestion control mechanisms are active - the measurement of throughput when congestion control mechanisms are active
Unidirectional streams of traffic can be used to create different patterns Unidirectional traffic can be used to load the ports of a switching device
of traffic. For example unidirectional streams can be offered to two input in different ways. For example unidirectional traffic can be sent to two or
ports so as to overload a single output port (2-to-1) or they can be offered more input ports from an external source and switched by the device under
to a single input port and switched by the device under test to two or more test to a single output port (n-to-1) or such traffic can be sent to a
output ports (1-to-2). Such patterns can be combined to test for head of single input port and switched by the device under test to two or more
output ports (1-to-n). Such patterns can be combined to test for head of
line blocking or to measure throughput when congestion control mechanisms line blocking or to measure throughput when congestion control mechanisms
are active. are active.
When devices are equipped with ports running at different media rates the When devices are equipped with ports running at different media rates the
number of input streams required to load or overload an output port or ports number of input streams required to load or overload an output port or ports
will vary. will vary.
The measurement of the minimum inter-frame gap serves to detect violations
of the IEEE 802.3 standard.
Issues: Issues:
half duplex / full duplex half duplex / full duplex
Measurement units: Measurement units:
n/a n/a
See Also: See Also:
bidirectional traffic (2.3) bidirectional traffic (2.3)
multidirectional traffic (2.4) meshed traffic (2.4)
2.3. Bidirectional traffic 2.3. Bidirectional traffic
Definition: Definition:
Bidirectional traffic is made up of two or more streams of frames forwarded Two or more streams of frames forwarded in opposite directions between at
in opposite directions between at two or more ports of a switching device. least two or more ports of a switching device.
Discussion: Discussion:
This definition conforms to the discussions in sections 14 and 16 of RFC This definition conforms to the discussions in sections 14 and 16 of RFC
1944 on bidirectional traffic and multi-port testing. 1944 on bidirectional traffic and multi-port testing.
Bidirectional traffic MUST be offered when measuring the maximum rate of Bidirectional traffic MUST be offered when measuring throughput on full
throughput on full duplex ports of a switching device. duplex ports of a switching device.
Issues: Issues:
truncated binary exponential back-off algorithm truncated binary exponential back-off algorithm
Measurement units: Measurement units:
n/a n/a
See Also: See Also:
unidirectional traffic (2.2) unidirectional traffic (2.2)
multidirectional traffic (2.4) meshed traffic (2.4)
2.4. Multidirectional traffic 2.4. Meshed traffic
Definition: Definition:
Multidirectional traffic is made up of streams of frames that are switched Multiple streams of frames switched simultaneously between all of a
simultaneously between multiple ports of a switching device. When such designated number of ports of a switching device such that each of the ports
streams are fully meshed each of the ports under test will both send frames under test will both send frames to and receive frames from all of the other
to and receive frames from all of the other ports under test. ports under test.
Discussion: Discussion:
This definition extends the discussions in sections 14 and 16 of RFC 1944 on This definition follows from the discussions in sections 14 and 16 of RFC
bidirectional traffic and multi-port testing. 1944 on bidirectional traffic and multi-port testing and readily extends to
As with bidirectional multi-port tests, multidirectional traffic exercises configurations with multiple switching devices linked together over backbone
both the transmission and reception sides of the ports of a switching connections.
device. Since ports are not divided into two groups every port forwards As with bidirectional multi-port traffic, meshed traffic exercises both the
frames to and receives frames from every other port. The total number of transmission and reception sides of the ports of a switching device. Since
individual unidirectional streams offered in a multidirectional test for n ports are not divided into two groups every port forwards frames to and
switched ports equals n x (n - 1). This compares with n x (n / 2) such receives frames from every other port. The total number of individual
streams in a bidirectional multi-port test. It should be noted however that streams when traffic is meshed over n switched ports equals n x (n - 1).
bidirectional multiport tests create a greater load than multidirectional This compares with n x (n / 2) such streams in a bidirectional multi-port
tests on backbone connections linking together two switching devices because test. It should be noted that bidirectional multiport traffic can load
none of the transmitted frames are forwarded locally. Backbone tests SHOULD backbone connections linking together two switching devices more than meshed
use bidirectional multi-port traffic. traffic.
Multidirectional traffic on half duplex ports is inherently bursty since Meshed traffic on half duplex ports is inherently bursty since ports must
ports must interrupt transmission intermittently to receive frames. When interrupt transmission whenever they receive frames. Bursty meshed traffic
offering such bursty traffic to a device under test a number of variables which is characteristic of real network traffic simultaneously exercises
have to be considered. They include frame size, the number of frames within many of the component parts of a switching device such as input and output
bursts as well as the interval between bursts. The terms burst, burst size buffers, buffer allocation mechanisms, aggregate switching capacity,
and inter-burst gap are defined in sections 2.5, 2.6 and 2.7 below. processing speed and behavior of the medium access controller.
Bursty multidirectional traffic is characteristic of real network traffic. When offering bursty meshed traffic to a device under test a number of
It simultaneously exercises many of the component parts of a switching variables have to be considered. These include frame size, the number of
device such as input and output buffers, buffer allocation mechanisms, frames within bursts as well as the interval between bursts. The terms
aggregate switching capacity, processing speed and behavior of the media burst, burst size and inter-burst gap are defined in sections 2.5, 2.6 and
access controller. 2.7 below.
Measurement units: Measurement units:
n/a n/a
Issues: Issues:
half duplex / full duplex half duplex / full duplex
See Also: See Also:
unidirectional traffic (2.2) unidirectional traffic (2.2)
bidirectional traffic (2.3) bidirectional traffic (2.3)
burst (2.5)
burst size (2.6)
inter-burst gap (2.7)
2.5 Burst 2.5 Burst
Definition: Definition:
A group of frames transmitted with the minimum inter-frame gap allowed by A sequence of frames transmitted with the minimum inter-frame gap allowed by
the media. This definition allows for single frame bursts and infinite bursts. the medium.
Discussion: Discussion:
This definition follows from the discussion in section 21 of RFC 1944. It is This definition follows from discussions in section 3.16 of RFC 1242 and
useful to consider isolated frames as single frame bursts. section 21 of RFC 1944 which describes cases where it is useful to consider
isolated frames as single frame bursts.
Measurement units: Measurement units:
n/a n/a
Issues: Issues:
See Also: See Also:
burst size (2.6) burst size (2.6)
2.6 Burst size 2.6 Burst size
Definition: Definition:
The number of frames in a burst. The number of frames in a burst.
Discussion: Discussion:
Burst size can range from one to infinity. In unidirectional streams there Burst size can range from one to infinity. In unidirectional streams there
is no theoretical limit to the burst length. Bursts in bidirectional and is no theoretical limit to burst length. When traffic is bidirectional or
multidirectional streams of traffic on half duplex media are finite since meshed bursts on half duplex media are finite since ports interrupt
ports interrupt transmission intermittently to receive frames. transmission intermittently to receive frames.
On real networks burst size can increase with window size. This makes it On real networks burst size will normally increase with window size. This
desirable to test devices with small as well as large burst sizes. makes it desirable to test devices with small as well as large burst sizes.
Measurement units: Measurement units:
number of N-octet frames number of N-octet frames
Issues: Issues:
See Also: burst (2.5) See Also:
burst (2.5)
2.7 Inter-burst gap (IBG) 2.7 Inter-burst gap (IBG)
Definition: Definition:
The interval between two bursts. The interval between two bursts.
Discussion: Discussion:
This definition conforms to the discussion in section 20 of RFC 1944 on This definition conforms to the discussion in section 20 of RFC 1944 on
bursty traffic. bursty traffic.
Bidirectional and multidirectional streams of traffic are inherently bursty Bidirectional and meshed streams of traffic are inherently bursty since
since ports share their time between receiving and transmitting frames. The ports share their time between receiving and transmitting frames. External
rate of transmission of an external source of traffic is a function of the sources offering bursty traffic for a given frame size and burst size must
number of frames per burst, frame length and the inter-burst gap. External adjust the inter-burst gap to achieve a specified rate of transmission.
sources offering bursty multidirectional traffic for a given frame size and
burst size MUST adjust the inter-burst gap to achieve a specified rate of
transmission.
When a burst contains a single frame inter-burst gap and inter-frame gap are
equal.
When a burst is infinite the interburst gap equals the minimum inter-frame gap.
Measurement units: Measurement units:
nanoseconds nanoseconds
microseconds microseconds
milliseconds milliseconds
seconds seconds
Issues: Issues:
See Also: burst size (2.6), load (2.8) See Also:
burst size (2.6)
2.8 Load, nominal and real 2.8 Port load
Definition: Definition:
The amount of traffic per second that a port transmits and receives. The number of frames per second that a switched port transmits and receives.
Discussion: Discussion:
Load can be expressed in a number of ways: bits per second, frames per Port load can be expressed in a number of ways: bits per second, frames per
second with the frame size specified or as a percentage of the maximum frame second with the frame size specified or as a percentage of the maximum frame
rate allowed by the media for a given frame size. A unidirectional stream of rate allowed by the medium for a given frame size. In the case of
7440 64-byte Ethernet frames per second is equivalent to a 50% load given bidirectional or meshed traffic port load is the sum of the frames
that the maximum rate of transmission on an Ethernet is 14880 64-byte frames transmitted and received on a port per second. The load on an Ethernet port
per second. which is transmitting and receiving a total of 7440 64-byte frames per
In the case of bidirectional or multidirectional traffic port load is the second equals 50% given that the maximum rate of transmission on an Ethernet
sum of the frames transmitted and received on a port per second. is 14880 64-byte frames per second.
There is room for varying the balance between incoming and outgoing traffic There is room for varying the balance between incoming and outgoing traffic
when loading ports with bidirectional and multidirectional traffic. In the when loading ports with bidirectional and meshed traffic. When offering
case of bidirectional traffic a 100% load can be created by offering a n% meshed traffic to a device the equal distribution of load over all ports
load on one port and a (100 - n)% load on the opposite port. will help avoid unwanted or inadvertent port overloading in throughput tests.
Multidirectional traffic will be equally distributed over all ports under
test when all ports are offered 50% of the target load. Measurement units:
It has to kept in mind that an external source may not deliver frames to a bits per second
device under test at the desired rate due to collisions on CSMA/CD links or frames per second with the frame size specified
the action of congestion control mechanisms. Because of this it is often as a percentage of the maximum frame rate allowed by the medium for a given
necessary to distinguish between the desired or target load (nominal load) frame size.
and the actual load (real load) offered to the device under test.
External sources of Ethernet traffic MUST implement the truncated binary Issues:
exponential back-off algorithm when executing bidirectional and
multidirectional performance tests to ensure that the external source of See Also:
traffic is accessing the medium legally. bidirectional traffic (2.3)
meshed traffic (2.4)
overload (2.9)
2.9 Overload
Definition:
Loading a port or ports in excess of the maximum rate of transmission
allowed by the medium.
Discussion:
Overloading can serve to exercise input and output buffers, buffer
allocation algorithms and congestion control mechanisms.
Port overloading with unidirectional traffic requires a minimum of two input
and one output ports when the medium rate of all ports is the same. The
number of input ports will vary according to the media rates of the output
port or ports under test.
Port overloading with bidirectional and meshed traffic requires the sum of
the traffic transmitted and received on each port to exceed the maximum rate
of transmission allowed by the medium. To distribute port overload equally,
the external source of traffic must transmit at the same rate situated
between more than 50% and a 100% of the maximum medium rate to each of the
ports under test.
Measurement units:
N-octet frames per second
Issues:
See Also:
bidirectional traffic (2.3)
meshed traffic (2.4)
port load (2.8)
2.10 Intended rate
Definition:
The number of frames per second that an external source attempts to send to
a port of a device under test.
Discussion:
An external source may not transmit frames to a device under test at the
intended rate due to collisions on CSMA/CD links or the action of congestion
control mechanisms. This makes it useful to distinguish between intended
rate and the rate at which the source can be observed to send frames to a
device under test.
An external source should have sufficient internal resources to transmit
frames at the intended rate and in the case of Ethernet must implement the
truncated binary exponential back-off algorithm when executing bidirectional
and meshed performance tests to ensure that it is accessing the medium legally.
Frames which are not successfully transmitted by the external source of Frames which are not successfully transmitted by the external source of
traffic to the device under test MUST NOT be not counted as transmitted traffic to the device under test MUST NOT be counted as transmitted frames
frames in performance benchmarks. in performance benchmarks.
Measurement units: Measurement units:
bits per second bits per second
N-octets per second N-octets per second
(N-octets per second / media_maximum-octets per second) x 100 (N-octets per second / media_maximum-octets per second) x 100
Issues: Issues:
token ring token ring
2.9 Overload See also:
offered rate (2.11)
2.11 Offered rate
Definition: Definition:
Loading a port or ports in excess of the maximum rate of transmission The number of frames per second that an external source can be observed to
allowed by the media. send to a port of a device under test.
Discussion: Discussion:
Overloading can serve to exercise input and/or output buffers, buffer Offered rate may differ from intended rate due to collisions on half duplex
allocation algorithms and congestion control mechanisms. Unidirectional media or congestion control mechanisms.
overloads require a minimum of two input and one output ports when all ports The frame count on a port of a device under test may exceed the rate at
run at the same nominal speed. which an external device offers frames due to the presence of spanning tree
Bidirectional and multidirectional overloading occurs when the sum of the BPDUs (Bridge Protocol Data Units) on 802.1D-compliant switches or SNMP
traffic transmitted and received on each port exceeds the maximum media frames. If such frames cannot be inhibited, they MUST be left out of frame
rate. The external source of traffic MUST transmit at the same rate situated counts in performance benchmarks.
between more than 50% and a 100% of the maximum media rate to each of the
ports under test in order to equally distribute an overload over all ports Measurement units:
under test. bits per second
N-octets per second
(N-octets per second / media_maximum-octets per second) x 100
Issues:
token ring
See also:
intended rate (2.10)
2.12 Maximum load
Definition:
The load which results on a port when traffic is transmitted or addressed to
it at the maximum rate allowed by the medium.
Discussion:
Maximum port load may be less than the maximum rate allowed by the medium
when the offered rate of the external sources sending traffic to the device
or system under test is less than the intended rate.
Measurement units:
bits per second
frames per second with the frame size specified
as a percentage of the maximum frame rate allowed by the medium for a given
frame size.
Issues:
See Also:
bidirectional traffic (2.3)
meshed traffic (2.4)
port load (2.8)
intended rate (2.10)
offered rate (2.11)
forwarding rate (2.13)
forwarding rate at maximum load (2.14)
2.13 Forwarding rate
Definition:
The number of frames per second that a device is observed to deliver to the
correct output port in response to a known intended rate.
Discussion:
Forwarding rate does not take frame loss into account and must only be
sampled on the output side of the ports under test. It can be measured on
devices offered unidirectional, bidirectional or meshed traffic.
The forwarding rates of switching devices which exhibit no frame loss may be
reduced through the action of congestion control mechanisms.
Measurement units: Measurement units:
N-octet frames per second N-octet frames per second
Issues: nominal/real load Issues:
See Also: See Also:
port load (2.8)
intended rate (2.10)
offered rate (2.11)
forwarding rate at maximum load (2.14)
2.10 Speed 2.14 Forwarding rate at maximum load
Definition: Definition:
The number of frames that a device is capable of delivering to the correct The number of frames per second that a device is observed to successfully
destination port in a given time interval. The maximum speed of a switching deliver to the correct output port at maximum load.
device is the highest number of frames it can deliver during a one second
interval to the correct destination port.
Discussion: Discussion:
Switching devices which exhibit no frame loss may be found to deliver frames Forwarding rate at maximum load may be less than the maximum rate at which a
to their proper destination ports at differing rates. This may be due to the device might be observed to successfully forward traffic.
action of congestion control mechanisms at high loads or the relative
aggressiveness of the truncated binary back-off algorithm. Speed MUST only
be sampled on the output side of the ports under test. This is because an
input port may receive frames at higher rates when the device under test
drops frames.
Measurement units: Measurement units:
N-octet frames per second N-octet frames per second
Issues: Issues:
See Also: See Also:
maximum load (2.12)
forwarding rate (2.13)
2.11 Flooded frame 2.15 Flooding
Definition: Definition:
A unicast frame which is received on ports which do not correspond to the Frames received on ports which do not correspond to the destination MAC
frame's destination MAC address information. address information.
Discussion: Discussion:
When recording throughput statistics it is important to check that frames When recording throughput statistics it is important to check that frames
have been forwarded to their proper destinations. Flooded frames MUST NOT be have been forwarded to their proper destinations. Flooded frames MUST NOT be
counted as received frames. counted as received frames. Both known and unknown unicast frames can be
flooded.
Measurement units: Measurement units:
N-octet valid frames per second N-octet valid frames per second
Issues: Issues:
Spanning tree BPDUs. Spanning tree BPDUs.
See Also: See Also:
2.11 Backpressure 2.16 Backpressure
Definition: Definition:
A jamming technique used by some switching devices to avoid frame loss when Techniques whereby switching devices avoid frame loss by impeding external
one or more of its ports are saturated. sources of traffic from transmitting frames to congested ports.
Discussion: Discussion:
Some switches are designed to send jamming signals back to traffic sources Some switches send jam signals, for example preamble bits, back to traffic
when ports begin to saturate. Such devices may incur no frame loss when sources when their transmit and/or receive buffers start to overfill.
ports are offered target loads in excess of 100% by external traffic Switches implementing full duplex Ethernet links may use IEEE 802.3x Flow
sources. Jamming however affects traffic destined to congested as well as Control for the same purpose. Such devices may incur no frame loss when
uncongested ports so it is important to measure the maximum speed at which a external sources attempt to offer traffic to congested or overloaded ports.
device can forward frames to both congested and uncongested ports when Jamming and flow control normally slow all traffic transmitted to congested
backpressure mechanisms are active. input ports including traffic intended for uncongested output ports.
Measurement units: Measurement units:
N--octet frames per second between the jamming port and an uncongested frame loss on congested port or ports
N--octet frames per second between the port applying backpressure and an
uncongested
destination port destination port
Issues: Issues:
not explicitly described in standards jamming not explicitly described in standards
See Also: See Also:
forward pressure (2.12) forward pressure (2.17)
2.12 Forward pressure 2.17 Forward pressure
Definition: Definition:
A technique which modifies the truncated binary exponential backoff An illegal technique whereby a device retransmits buffered frames without
algorithm to avoid frame loss when congestion on one or more of the ports waiting for the interval calculated by the normal operation of the back-off
under test occurs. algorithm.
Discussion: Discussion:
Some switches avoid buffer overload by retransmitting buffered frames Some switches illegally inhibit or abort the truncated binary exponential
without waiting for the interval calculated by the normal operation of the backoff algorithm and force access to the medium to avoid frame loss.
backoff algorithm. It is useful to measure how aggressive a switch's backoff The backoff algorithm should be fair whether the device under test is in a
algorithm is in both congested and uncongested states. Forward pressure congested or an uncongested state.
reduces the number of collisions when congestion on a port builds up.
Measurement units: Measurement units:
intervals in microseconds between transmission retries during 16 successive intervals in microseconds between transmission retries during 16 successive
collisions. collisions.
Issues: Issues:
not explicitly described in standards truncated binary exponential backoff algorithm
See also: See also:
backpressure (2.11) backpressure (2.16)
2.13 Head of line blocking 2.18 Head of line blocking
Definition: Definition:
A pathological state whereby a switch drops frames forwarded to an Frame loss observed on an uncongested output port whenever frames are
uncongested port whenever frames are forwarded from the same source port to received from an input port which is also attempting to forward frames to a
a congested port. congested output port.
Discussion: Discussion:
It is important to verify that a switch does not propagate frame loss to It is important to verify that a switch does not slow transmission or drop
ports which are not congested whenever overloading on one of its ports occurs. frames on ports which are not congested whenever overloading on one of its
other ports occurs.
Measurement units: Measurement units:
frame loss recorded on an uncongested port when receiving frames from a port frame loss recorded on an uncongested port when receiving frames from a port
which is also forwarding frames to a congested destination port. which is also forwarding frames to a congested port.
Issues: Issues:
Input buffers input buffers
See Also: See Also:
unidirectional traffic (2.2)
2.14 Address handling 2.19 Address handling
Definition: Definition:
The number of MAC addresses per port, per module or per device which a The number of MAC addresses per n ports, per module or per device which a
switch can cache and successfully forward frames to without flooding or switch can cache and successfully forward frames to without flooding or
dropping frames. dropping frames.
Discussion: Discussion:
Users building networks will want to know how many nodes they can connect to Users building networks will want to know how many nodes they can connect to
a switch. This makes it necessary to verify the number of MAC addresses that a switch. This makes it necessary to verify the number of MAC addresses that
can be assigned per port, per module and per chassis before a switch begins can be assigned per n ports, per module and per chassis before a switch
flooding frames. begins flooding frames.
Measurement units: Measurement units:
number of MAC addresses number of MAC addresses
Issues: Issues:
See Also: See Also:
Address learning rate (2.20)
2.15 Address learning rate 2.20 Address learning rate
Definition: Definition:
The maximum rate at which a switch can learn MAC addresses before starting The maximum rate at which a switch can learn new MAC addresses before
to flood or drop frames. starting to flood or drop frames.
Discussion: Discussion:
Users may want to know how long it takes a switch to build up its address Users may want to know how long it takes a switch to build its address
tables. This information is useful to have when considering how long it tables. This information is useful to have when considering how long it
takes a network to come up when many users log on in the morning or after a takes a network to come up when many users log on in the morning or after a
network crash. network crash.
Measurement units: Measurement units:
frames per second with each successive frame sent to the switch containing a frames per second with each successive frame sent to the switch containing a
different source address. different source address.
Issues: Issues:
See Also: address handling (2.14) See Also: address handling (2.19)
2.16 Filtering illegal frames 2.21 Illegal frames
Definition: Definition:
Switches do not necessarily filter all types of illegal frames. Some Frames which are over-sized, under-sized, misaligned or with an errored
switches, for example, do not store frames before forwarding them to their Frame Check Sequence.
destination ports. These so-called cut-through switches forward frames after
reading the destination and source address fields. They do not normally Discussion:
filter over-sized frames (jabbers) or verify the validity of the Frame Check Switches, unlike IEEE 802.1d compliant brdiges, do not necessarily filter
Sequence field. Other examples of illegal frame types are under-sized frames all types of illegal frames. Some switches, for example, which do not store
(runts), misaligned frames and frames followed by dribble bits. frames before forwarding them to their destination ports may not filter
over-sized frames (jabbers) or verify the validity of the Frame Check
Sequence field. Other illegal frames are under-sized frames (runts) and
misaligned frames.
Measurement units: Measurement units:
N-octet frames filtered or not filtered N-octet frames filtered or not filtered
Issues: Issues:
See Also: See Also:
2.17 Broadcast rate 2.22 Maximum broadcast forwarding rate
Definition: Definition:
The number of broadcast frames forwarded by the device under test per The number of broadcast frames per second that a switch can deliver to all
second. The maximum broadcast rate corresponds to highest number of ports at maximum load.
broadcast frames a switch can forward either locally or over a backbone
connection.
Discussion: Discussion:
There is no standard forwarding mechanism used by switches to forward There is no standard forwarding mechanism used by switches to forward
broadcast frames. It is useful to determine the broadcast forwarding rate broadcast frames. It is useful to determine the broadcast forwarding rate
both locally and over backbone connections. for frames switched between ports on the same card, ports on different cards
in the same chassis and ports on different chassis linked together over
backbone connections.
Measurement units: Measurement units:
N-octet frames per second N-octet frames per second
Issues: Issues:
See Also: See Also:
broadcast latency broadcast latency (2.23)
2.18 Broadcast latency 2.23 Broadcast latency
Definition: Definition:
The time it takes a broadcast frame to go through a switching device and be The time required by a switch to forward a broadcast frame to each port
forwarded to each destination port. located within a broadcast domain.
Discussion: Discussion:
Since there is no standard way for switches to process broadcast frames, Since there is no standard way for switches to process broadcast frames,
broadcast latency may not be the same on all receiving ports of a switching broadcast latency may not be the same on all receiving ports of a switching
device. Broadcast latency SHOULD be determined on all receiving ports both device. The latency measurements SHOULD be bit oriented as described in 3.8
locally and, if applicable, over backbone connections. of RFC 1242. It is useful to determine broadcast latency for frames
forwarded between ports on the same card, ports on different cards in the
same chassis and ports on different chassis linked together over backbone
connections.
Measurement units: Measurement units:
The latency measurements SHOULD be bit oriented as described in 3.8 of RFC nanoseconds
1242 and reported for all connected receive ports. microseconds
milliseconds
seconds
Issues: Issues:
See Also: See Also:
broadcast rate broadcast forwarding rate (2.20)
3. Acknowledgments 3. Index of definitions
In order of appearance Ajay Shah of Wandel & Goltermann, Jean-Christophe 2.1 Reminder of RFC 1242 definition format
Bestaux of European Network Laboratories, Stan Kopek of Digital Equipment 2.2 Unidirectional traffic
Corporation, Henry Hamon of Netcom Systems and Kevin Dubray of Bay Networks 2.3 Bidirectional traffic
were all instrumental in getting this draft done. 2.4 Meshed traffic
2.5 Burst
2.6 Burst size
2.7 Inter-burst gap (IBG)
2.8 Port load
2.9 Overload
2.10 Intended rate
2.11 Offered rate
2.12 Maximum load
2.13 Forwarding rate
2.14 Forwarding rate at maximum load
2.15 Flooding
2.16 Backpressure
2.17 Forward pressure
2.18 Head of line blocking
2.19 Address handling
2.20 Address learning rate
2.21 Illegal frames
2.22 Maximum broadcast forwarding rate
2.23 Broadcast latency
4. Acknowledgments
In order of appearance Jean-Christophe Bestaux of European Network
Laboratories, Ajay Shah of Wandel & Goltermann, Henry Hamon of Netcom
Systems, Stan Kopek of Digital Equipment Corporation, Kevin Dubray of Bay
Networks, and Doug Ruby of Prominet were all instrumental in getting this
draft done.
A special thanks goes to the IETF BenchMark WorkGroup for the many A special thanks goes to the IETF BenchMark WorkGroup for the many
suggestions it collectively made to help shape this draft. suggestions it collectively made to help shape this draft.
The editor The editor
Bob Mandeville Bob Mandeville
4. Editor's Address 5. Editor's Address
Robert Mandeville Robert Mandeville
ENL (European Network Laboratories) ENL (European Network Laboratories)
email: bob.mandeville@eunet.fr
35, rue Beaubourg 35, rue Beaubourg
75003 Paris 75003 Paris
France France
phone: +33 6 07 47 67 10
fax: + 33 1 42 78 36 71
!!!PLEASE TAKE NOTE!!!
ENL HAS MOVED TO A NEW SITE:
Robert Mandeville, ENL
European Network Laboratories
6 Parc Ariane, le Mercure
Blvd des Chenes
78284 Guyancourt
France
NEW LAB PHONE, FAX, VOICE MAIL: +33 1 39 44 12 05
mobile phone: +33 6 07 47 67 10 mobile phone: +33 6 07 47 67 10
phone: +33 1 39 44 12 05
fax: + 33 1 39 44 12 06
email: bob.mandeville@eunet.fr
 End of changes. 

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