draft-ietf-bmwg-call-00.txt   draft-ietf-bmwg-call-01.txt 
Network Working Group R. Craig Network Working Group R. Craig
INTERNET-DRAFT Cisco Systems INTERNET-DRAFT Cisco Systems
Expiration Date: May 1997 Nov 1996 Expires in six months March 1997
Terminology for Cell/Call Benchmarking Terminology for Cell/Call Benchmarking
<draft-ietf-bmwg-call-00.txt> <draft-ietf-bmwg-call-01.txt>
Status of this Memo Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas, documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts. working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
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Issues: Issues:
See also: See also:
3.1.6 Impact of Signalling on Forwarding 3.1.6 Impact of Signalling on Forwarding
Definition: cells per second versus calls per second Definition: cells per second versus calls per second
Discussion: some devices use the same engine for cell forwarding Discussion: some devices use the same engine for cell forwarding
and call maintenance. In this case, interaction between the two and call maintenance. In this case, interaction between the two
will be inevitable. More interesting, however, would be the case functions will be inevitable. More interesting, however, would be
where the two processing functions are clearly separate, yet still the case where the two processing functions are clearly separate,
interact. yet still interact.
Measurement units: cells per second versus calls per second Measurement units: cells per second versus calls per second
Issues: Issues:
See also: See also:
3.2 Cell/Packet Interaction 3.2 Cell/Packet Interaction
This group applies to cell-based switches, connection-oriented or This group applies to cell-based switches, connection-oriented or
not. not.
3.2.1 Packet disassembly/reassembly time (peak) 3.2.1 Packet disassembly/reassembly time (peak)
Definition: the length of time to disassemble a layer 3 packet Definition: the length of time to disassemble a layer 3 packet
into layer 2 cells, or reassemble cells into a packet. into layer 2 cells, or reassemble cells into a packet.
Discussion: with no packet or cell loss or corruption. Discussion: with no packet or cell loss or corruption. To arrive
at a baseline, one could measure the switching rate for cells
derived from ~1440 byte frames which are flowing across the switch
as cells, then forward those same frames into the switch from an
interface which would require them to be disassembled. For
example, the baseline measurement is taken while switching cells
OC3-OC3. Then switch FDDI or POS-OC3 and take the delta in
performance as the SAR overhead.
Measurement units: the appropriate fraction of a second Measurement units: the appropriate fraction of a second
Issues: Issues:
See also: See also:
3.2.2 Packet disassembly/reassembly rate (sustained) 3.2.2 Packet disassembly/reassembly rate (sustained)
Definition: the maximum sustained rate at which packets can be Definition: the maximum sustained rate at which packets can be
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Issues: production of a stream of traffic containing internal Issues: production of a stream of traffic containing internal
checksums sufficiently strong to detect cell re-ordering (the IP checksums sufficiently strong to detect cell re-ordering (the IP
checksum is not). The ISIS LSP checksum is. checksum is not). The ISIS LSP checksum is.
See also: See also:
3.3 Switch Fabric 3.3 Switch Fabric
This group applies to all switches. This group applies to all switches.
3.3.1 Switch type
Definition: the type of switch architecture.
Discussion: Is this of any importance? We are concerned with
interesting "metrics" and how they affect the performance of a
device. I'm not sure switch architecture falls into this category
except as an perhaps interesting bit of trivia.
Measurement units: n/a
Issues:
See also:
3.3.2 Topology Table Size 3.3.2 Topology Table Size
Definition: number of network elements supported. Definition: number of network elements supported.
Discussion: switches may support a limited topology due to static Discussion: switches may support a limited topology due to static
table sizes or processing limitations. This is true whether it's table sizes or processing limitations. This is true whether it's
a "LAN" switch running spanning tree or a "WAN" switch running a "LAN" switch running spanning tree or a "WAN" switch running
OSPF. The effect of a limited topology table on a switch in a OSPF. The effect of a limited topology table on a switch in a
real-world environment can be disastrous. real-world environment can be disastrous.
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switched networks (among the switches themselves) as well as the switched networks (among the switches themselves) as well as the
spanning tree recalculation among multiple LAN switches. spanning tree recalculation among multiple LAN switches.
Measurement units: frames per second 1) with maximum diversity of Measurement units: frames per second 1) with maximum diversity of
addresses, 2) with routing instability introduced. addresses, 2) with routing instability introduced.
Issues: Issues:
See also: See also:
3.3.4 "Bandwidth"
Definition: internal bandwidth of the switch fabric.
Discussion: open to some interpretation ;-). Should probably be
stated as some combination of the slowest and fastest elements in
the switching path.
Measurement units: bits per second
Issues:
See also:
3.3.5 Throughput (from RFC1242) (Cell forwarding rate) 3.3.5 Throughput (from RFC1242) (Cell forwarding rate)
Definition: The maximum rate at which none of the offered frames Definition: The maximum rate at which none of the offered frames
are dropped by the device. are dropped by the device.
Discussion: This metric probably overlaps work being done in the Discussion: This metric probably overlaps work being done in the
ATM Forum. ATM Forum.
Measurement units: cells per second Measurement units: cells per second
Issues: Issues:
See also: See also:
3.3.6 Non-Blocking factor 3.3.6 Blocking Probability
Definition: simultaneous communication amongst multiple ports. Definition: likelihood of successful simultaneous communication
amongst multiple ports.
Discussion: a switch is termed "non-blocking" if multiple ports Discussion: a switch is termed "non-blocking" if multiple ports
are able to communicate across the switch fabric at the same time. are able to communicate across the switch fabric at the same time.
If a popular destination port can accept connections from more We are interested in the probability of blocking occurring in the
than one source port, the number of those connections is the non- 1:1, N:1, and N:M scenarios.
blocking factor. We are interested in the number of ports which
can simultaneously transmit to a single port (N), the number of
ports which can simultaneously receive from N other ports (M), and
the total number of ports on the switch (P).
Measurement units: N:1, N:M:P (switch-wide measurement)
Issues:
See also:
3.4 Buffering
This group applies to all switches.
3.4.1 Buffering strategy
Definition: central pool of buffers versus distributed pools.
Pools of one size versus multiple MTU sizes.
Discussion: There are tradeoffs in each approach: bus bandwidth
and arbitration cycles for centrality, over-configuration of
memory for distributed pools and one-size-fits-all, greater number
of drops due to buffer exhaustion with MTU-tailored buffers.
The effectiveness of the given strategy is revealed by the One may calculate the "ideal" throughput in the absence of
performance of the device in overload conditions. For example, blocking, then take the delta with the experimental case and treat
one might cause the majority of input buffers to migrate to one that as an empirical measurement of blocking probability, if
port which is experiencing a sustained burst of traffic, and then enough samples are taken.
cause another port to burst, creating input drops due to lack of
buffers while the device re-allocates its buffer pool.
Measurement units: underruns (can't feed transmitting interface Measurement units: percentage likelihood of blocking.
quickly enough, indicative of bus bw or access problem),
input/output drops (buffer exhaustion), overruns (another
indicator of either buffer or CPU exhaustion)
Issues: Issues:
See also: See also:
3.4.2 Buffering per output
Definition: the number of buffers per output port and their size.
Discussion: It must also be noted whether the buffers are local
to the line card, whether they are dynamically allocated from a
central pool, whether they are MTU-tailored, and so on.
Measurement units: octets
Issues:
See also: 3.4.1
3.4.3 Buffering per input
Definition: the number of buffers per input port and their size.
Discussion: see 3.4.2
Measurement units: octets
Issues:
See also: 3.4.1
3.5 Congestion Control 3.5 Congestion Control
This group applies to all switches. This group applies to all switches.
3.5.1 Congestion avoidance 3.5.1 Congestion avoidance
Definition: effectiveness of measures taken by the switch to Definition: effectiveness of measures taken by the switch to
avoid congestion. avoid congestion.
Discussion: connections that are bursting above their committed Discussion: connections that are bursting above their committed
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The basic idea is that ill-behaved connections should not starve The basic idea is that ill-behaved connections should not starve
others for resources. others for resources.
Measurement units: latency, cell drops Measurement units: latency, cell drops
Issues: Issues:
See also: See also:
3.5.3 Queueing strategies
Definition: the method used for queueing frames.
Discussion: FIFO, WFQ, SFQ, tail drop, RED. Queue per interface,
per rate or per connection?
Measurement units:
Issues:
See also:
3.6 Inter-switch protocols 3.6 Inter-switch protocols
This group applies to all switches. This group applies to all switches.
3.6.1 Impact of Routing on Forwarding 3.6.1 Impact of Routing on Forwarding
Definition: interaction between routing protocol and data Definition: interaction between routing protocol and data
forwarding operations. forwarding operations.
Discussion: No amount of routing fluctuation should have an Discussion: No amount of routing fluctuation should have an
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Measurement units: Measurement units:
Issues: Issues:
See also: See also:
3.7 Quality of Service 3.7 Quality of Service
This group applies to all switches. This group applies to all switches.
3.7.1 Traffic Management 3.7.1 Traffic Management Policing
Definition: impact of misbehaving class on others, for example Definition: impact of misbehaving class on others, for example
data forwarding on voice or video frames and vice versa. data forwarding on voice or video frames and vice versa.
Discussion: we wish to quantify the potential interaction amongst Discussion: we wish to quantify the potential interaction amongst
the various classes of service. Constant bit rate (CBR), variable the various classes of service. Constant bit rate (CBR), variable
bit rate (VBR) (real and non-real time?), and available bit rate bit rate (VBR) (real and non-real time?), and available bit rate
(ABR) streams are established, within their respective service (ABR) streams are established, within their respective service
levels, but sufficient to subscribe the trunk to 90%. The bit levels, but sufficient to subscribe the trunk to 90%. The bit
rate of each is increased until it has exceeded its allocation by rate of each is increased until it has exceeded its allocation by
a degree which should cause loss or delay in the other streams. a degree which should cause loss or delay in the other streams.
Measurement units: cells (lost) per second, latency Measurement units: cells (lost) per second, latency
Issues: some switches perform compression and silence Issues: some switches perform compression and silence
suppression. Should these features be disabled? suppression. Should these features be disabled?
See also: See also:
3.7.2 Mapping of IP ToS/Precedence onto QoS
Definition: some method is required to map IP type of service
and/or precedence values onto the switch's notion of quality of
service.
Discussion:
Measurement units:
Issues:
See also:
3.8 Multicast 3.8 Multicast
3.8.1 Cell replication 3.8.1 Cell replication
Definition: the device's ability to forward a cell to multiple Definition: the device's ability to forward a cell to multiple
ports simultaneously (multicast). ports simultaneously (multicast).
Discussion: Discussion:
Measurement units: replication factor 1:N and cells per second Measurement units: replication factor 1:N and cells per second
measured at ingress versus cells per second measured at the measured at ingress versus cells per second measured at the
egresses egresses.
Issues: Issues:
See also: See also:
3.8.2 Impact of multicast on unicast 3.8.2 Impact of multicast on unicast
Definition: switch's ability to insulate unicast traffic from the Definition: switch's ability to insulate unicast traffic from the
effects of multicast. effects of multicast.
 End of changes. 

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