1

ELEN 602 Lecture 18

• Packet switches

• Traffic Management

2

RR

RR

S

SS

s

s s

s

ss

s

ss

s

R

s

R

Backbone

To internet or wide area network

Organization Servers

Gateway

Departmental Server

Campus Network

3

Interdomain level

Intradomain level

LAN level

Autonomous systemor domain

Border routers

Border routers

Internet service provider

Intradomain and Interdomain levels

4

RA

RB

RC

Route server

NAP

National service provider A

National service provider B

National service provider C

LAN

NAPNAP

(a)

(b)

5

Control

1

2

3

N

Line Card

Line Card

Line Card

Line CardIn

terc

onne

ctio

nFa

bric

Line Card

Line Card

Line Card

Line Card

1

2

3

N

…… ……

Components of Generic Switch/Router

6

Buffering

• Wherever contention is possible– input port (contend for fabric)– internal (contend for output port)– output port (contend for link)

• Head-of-Line Blocking

– input buffering

Switch

2

21

Port 1

Port 2

7

Crossbar Switches

8

CPU

1

2

3

N

NIC Card

NIC Card

NIC Card

NIC Card Mai

n M

emor

y

I/OBus

……

Workstation based Router

9

Workstation-Based

• Aggregate bandwidth – 1/2 of the I/O bus bandwidth – capacity shared among all hosts connected to switch– example: 800Mbps bus can support 8 T3 ports

CPU

Main memory

I/O bus

Interface 1

Interface 2

Interface 3

• Packets-per-second – must be able to switch

small packets– 100,000 packets-per-

second is achievable– e.g., 64-byte packets

implies 51.2Mbps

10

Self-Routing Fabrics

• Banyan Network– constructed from simple 2 x 2 switching elements– self-routing header attached to each packet– elements arranged to route based on this header– no collisions if input packets sorted into ascending order– complexity: n log2 n

001

011

110

111

001

011

110

111

11

High-Speed IP Router

• Switch (possibly ATM)

• Line Cards + Forwarding Engines– link interface– router lookup (input)– common IP path (input)– packet queue (output)

• Network Processor

– routing protocol(s)

– exceptional cases

12

High-Speed Router

Line card(forwarding buffering)

Line card(forwarding buffering)

Lin

e ca

rd(f

orw

ardi

ng

buff

erin

g)

Lin

e ca

rd(f

orw

ardi

ng

buff

erin

g)

RoutingCPU

Buffermemory

Routing softwarew/ router OS

Routing softwarew/ router OS

13

Packet

Packet

Virtual-circuit Packet Switching

14

t

t

t

t

31 2

31 2

321

Release

Connect request

CR

CR Connect confirm

CC

CC

Delays in virtual-circuit switching

15

SW 1

SW 2

SW n

Connect request

Connect request

Connect request

Connect confirm

Connect confirm

…

Signaling for virtual-circuit setup

16

Identifier Outputport

15 15

58

13

13

7

27

12

Nextidentifier

44

23

16

34

Entry for packetswith identifier 15

Example virtual-circuit routing table

17

Packet buffer

Transmission link

Arrivingpackets

Packet discardwhen full

Packet buffer

Transmissionlink

Arrivingpackets

Class 1 discardwhen full

Class 2discardwhen thresholdexceeded

(a)

(b)

FIFO Queuing:

FIFO Queuing with discard priority

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Transmission link

Packet discardwhen full

High-prioritypackets

Low-prioritypackets

Packet discardwhen full

When high-priorityqueue empty

HOL Priority queuing

19

Sorted packet buffer

Transmissionlink

Arrivingpackets

Packet discardwhen full

Taggingunit

Sorting packets according to priority tag

20

Transmission link

Packet flow 1

Packet flow 2

Packet flow n

C bits/second

Approximatedbit-levelround robinservice

Fair queuing

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Queue 1@ t=0

Queue 2@ t=0

1

t1 2

Fluid-flow system:both packets served at rate 1/2

Both packetscomplete serviceat t=2

0

1

t1 2

Packet-by-packet system:queue 1 served first at rate 1;then queue 2 served at rate 1.

Packet from queue 2being served

Packet fromqueue 1 beingserved

Packet fromqueue 2 waiting

0

Fluid-flow and packet-by-packet FQ

22

Rounds Generalize so R(t) is continuous, not discrete

R(t) grows at rate inverselyproportional to nactive(t)

Computing finishing times

23

Queue 1@ t=0

Queue 2@ t=0

2

1

t3

Fluid-flow system:both packets served at rate 1/2

Packet from queues served at rate 1

0

2

1

t1 2

Packet-by-packet fair queueing:queue 2 served at rate 1

Packet fromqueue 1 beingserved at rate 1

Packet fromqueue 2 waiting

0 3

Fluid-flow and packet-by-packet FQ

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Queue 1@ t=0

Queue 2@ t=0

1

t1 2

Fluid-flow system:packet from queue 1served at rate 1/4;

Packet from queue 1 served at rate 1

Packet from queue 2served at rate 3/4 0

1

t1 2

Packet-by-packet weighted fair queueing:queue 2 served first at rate 1;then queue 1 served at rate 1.

Packet from queue 1being servedPacket from

queue 2 beingserved

Packet fromqueue 1 waiting

0

Weighted Fair Queuing