802.1D – Expedited Traffic

Sept 23, 2004 CS573: Network Protocols and Standards

1

802.1D – Expedited Traffic

Network Protocols and Standards

Autumn 2004-2005

Sept 23, 2004 CS573: Network Protocols and Standards 2

Expedited Traffic Preview Traffic types

Network Control Voice Video Controlled Load Excellent Effort or CEO Effort Best Effort Background


Traffic Types Problem: Different applications with

varying data communication requirements Solutions:

Design a network according to given requirements

Differentiate between traffic classes For different applications, IEEE enumerated

traffic types in a typical LAN environment


Traffic Types: Network Control Network Control

Characterized by “must get there” requirement

Maintain and support the network infrastructure

Placed above “voice” Meaningless to require that the [voice]

traffic be delivered with a maximum delay when the correct [network] infrastructure is absent …


Traffic Types: Voice Interactivity is the desired feature End-to-end delay of 100ms to

150ms What about the delay on a single

LAN? 10ms is specified

Data Rates are several kb/s to few tens kb/s


Traffic Types: Video Interactivity may not be the

required feature Specifications for Interactive video

such as Video Conferencing aren’t too different from the voice specifications

For non-interactive video High data rates (1Mb/s to 8Mb/s)

Achieving 10ms delay is difficult LAN delay of 100ms is specified


Traffic Types: Controlled Load Important business applications subject

to some form of “admission control” Critical but no delay requirements Some biz applications might be more

appealing if the response is better As if a user is using the network alone!!!

Load on the network is fairly controlled More control on the “other” traffic Idea came from IntServ


Traffic Types: Excellent Effort Excellent Effort or CEO best-effort Applicable to data traffic

Requirements are traditionally not very stringent

File transfer will happen… when? Some important people in a

company might need faster data transfers without having to wait for long


Traffic Types: Best Effort LAN traffic as we know today The default traffic class


Traffic Types: Background Bulk transfers Other activities permitted on the

network but should not impact the use of network by other applications

Example: backups


How Many Types? Every switch is not able to handle all

types of traffic How many traffic types should be used?

Initial answer: 2 High and Low People came up with other applications and

scenarios Finally 8 levels were specified

Only 7 traffic classes have been uniquely identified so far


Traffic Type to User Priority Mapping

User Priority

Acronym Traffic Type

1 BK Background

2 -- Spare

0 (default) BE Best Effort

3 EE Excellent Effort

4 CL Controlled Load

5 VI Video

6 VO Voice

7 NC Network ControlAll manufacturers should agree to this mapping…


User Priority Regeneration On an incoming port of a bridge, you

would like to maintain the priority Not all MAC layer frame formats include

priority field in their headers IEEE 802.5 token ring defines 8 priority levels Ethernet, IEEE 802.3 do not include a priority

field For maximum flexibility, user priority for

frames received on a given port may be regenerated according to information that is preset by management procedures


Traffic Type to User Priority Mapping

User Priority

Default Regenerated

Priority

Range

0 0 0-7

1 1 0-7

2 2 0-7

3 3 0-7

4 4 0-7

5 5 0-7

6 6 0-7

7 7 0-7User priority value for the outgoing frame should be either thevalue received in the frame itself (by default!) or mappedto some value in the range 0—7 (preset for that port!).


Example

H1 sends voice to D1H2 sends controlled load to D2H3 sends best effort to D2

What should Bridge B1 do?


Example


Example

- Bridge B1 sets priority of incoming frames on port 2(traffic type to user priority mapping)

- Bridge B1 places all the frames in the outgoing queues (user priority to traffic class mapping)


User Priority to Traffic Class Mapping

For a given bridge, there may be more than one traffic class specified, thus one transmission queue for each traffic class

Frames are assigned to the transmission queues on the basis of their user priority, using the traffic class table that is part of the state information associated with that port


RecommendedTraffic Type to Traffic Class

Mapping#Queu

esDefining Traffic Type

1 BE

2 BE VO

3 BE CL VO

4 BK BE CL VO

5 BK BE CL VI VO

6 BK BE EE CL VI VO

7 BK BE EE CL VI VO NC

8 BK -- BE EE CL VI VO NC


RecommendedUser Priority to Traffic Class

MappingNumber of Available Traffic Classes (Queues)

1 2 3 4 5 6 7 8

User

PRIORITY

0 0 0 1 1 1 1 1 2

1 0 0 0 0 0 0 0 0

2 0 0 0 0 0 0 0 1

3 0 0 1 1 1 2 2 3

4 0 1 1 2 2 3 3 4

5 0 1 1 2 3 4 4 5

6 0 1 2 3 4 5 5 6

7 0 1 2 3 4 5 6 7


ExampleUser Priority to Traffic Class

Mapping

The number next to the queues represents the priorityclass for that queue; higher values represent higherpriority. The next step is to determine the frameselection and the outgoing priority of the frame

Consider the previous example:


Selection of Frames for Transmission According to IEEE 802.1D (portion of new

802.1D that was previously 802.1p), selection of frames for transmission is based on highest priority first Frames are selected from a given transmission

queue if all the queues corresponding to numerically higher values of traffic supported by that port are empty at the time of selection

Other algorithms as selected by the management may also be supported


Outbound Access PrioritiesUser

PriorityOutbound Access Priority for different MAC methods

8802-3 8802-4 8802-5(usual)

8802-5(alter)

8802-6 802.9a 8802-12

FDDI

0 0 0 0 4 0 0 0 2

1 0 1 1 4 1 0 0 0

2 0 2 2 4 2 0 0 1

3 0 3 3 4 3 0 0 3

4 0 4 4 4 4 0 4 4

5 0 5 5 5 5 0 4 5

6 0 6 6 5 6 0 4 6

7 0 7 6 6 7 0 4 6


ExampleFrame Selection and outbound Priority

Mapping


Conclusions Expedited Traffic Capabilities

Not intended to provide guaranteed quality of service

Allows the transmission of time critical data to be expedited when it is in competition with other non time critical data


Selective Multicast: Preview Part of IEEE 802.1D standard Reasons of Selective Multicast

Broadcasting of multicast traffic overloads slower links

Even for high speed links, transmitting something that no one will use is not a good idea

Solution Allow users to explicitly indicate their interest in

receiving traffic on given multicast addresses


Use of FDBs Bridges maintain filtering databases for

unicast addrresses Static Entries

Explicitly configured by management Dynamic Entries

Automatically entered into the FDB by the normal operation of the bridge

Each entry (static or dynamic) consist of: A MAC address specification A port map specifying the filtering state for

that MAC address


Basic Filtering Services A bridge must support these

services Allow the specification of:

For individual MAC addresses Static entries Dynamic entries

For a specific group MAC address Static entries No static entry Broadcast


Extended Filtering Services Add the following capabilities

For individual addresses Static entries may contain a value which indicates

that the dynamic filtering information should be used For a specific group MAC address

Static entries may contain a value which indicates that the dynamic filtering information should be used

Group registration entries that are created and maintained through the use of GMRP protocol

Entries corresponding to all group addresses which may not have a specific group MAC address entry OR unregistered group addresses

802.1D – Expedited Traffic

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