Switching Architecture

7/29/2019 Switching Architecture

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Unit 18

Switching

Acknowledgments: These slides were originally developed by Prof. Jean Walrand for EE122.The past and current EE122 instructors including Profs. Kevin Fall, Abhay Parekh, Shyam Parekh,and Adam Wolisz have contributed to their evolution.


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TOC: Switching & Forwarding Why?

Switching Techniques

Switch Characteristics Switch Examples

Switch Architectures Summary

TOC Switching


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Direct vs. Switched Networks:

Direct Network Limitations:

Shared medium

Distance (coordination delay; propagation limitation)

Number of hosts (collisions; shared bandwidth; address tables)

Single link technology (cannot mix optical, wireless, )

Point-to-point links O(n2) links

Internetworking: Externality gain at low cost

Why?

Single

link

n links

SwitchesDirect Switched

TOC Switching Why?


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Circuit-Switching (e.g., Telephone net.) Packet-Switching Datagram (e.g., IP, Ethernet) Virtual Circuits (e.g., MPLS, ATM) Source Routing

Comparison

Techniques

TOC Switching Techniques


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Mechanism:

Circuit-Switching Link divided into fixed,independent circuits

Circuit SwitchConnection list

Time scale: connection

(e.g., TDM, WDM)

Packets not switched independently (establish circuit beforesending data)

Dedicated path and resources from source to destination Setup time; low delays and guaranteed resources thereafter

Features:

TOC Switching Techniques Circuit

(Typical Implementation: Time-Space-Time Switch)


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Mechanism:

Packet-Switching

Whole link shared byall packets

Packet Switch

Data separated into packets Switching decision (output port) for each individual packet Statistical multiplexing: Sum of peak rates may exceed

link bandwidth (as long as mean does not)

Features:

TOC Switching Techniques Packet


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PS - Datagram

General idea: no connection establishment, buteach packet contains enough info to specifydestination

Switches contain forwarding tables (but no per-connection state)

Forwarding tables contain info on which outgoingport to use for each destination

Two types of addressing: Layer 2 or Layer 3

TOC Switching Techniques Packet - Datagram


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Layer 2 (e.g., Ethernet)

Flat address space (no structure)

Forwarding table:

Exact match of destination L2 address

a

b

c

d

e

f

1 2

3

4

1 2

34

a 1b 4c 3

d 2e 2f 2

a 1b 1c 1

d 2e 3f 4

e|b|

ToFrom

TOC Switching Techniques Packet Datagram L2


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Layer 3 (e.g., IP)

L3-network (e.g., IP) Topological structure match prefix

Either fixed prefix length or longest match

E.g. 1

E.g. 2

E.g. 3


Fixed

11010001

11001101

Longest

11001001

10100111

11010000

11001000

10100000

01000000

1101

Other A

B

C

DA

C

B

11010101

110011

11100000

11001100


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Layer 3 (e.g., IP) E.g. 1

11011001 matches4 bits at A, 1 at B, 3 at C A = LPM4 bits at AA = EM


Fixed

11010001

11001101

Longest

11001001

10100111

11010000

11001000

10100000

01000000

1101

Other A

B

C

DA

C

B

11010101

110011

11100000

11011001

11001100


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Layer 3 (e.g., IP)E.g. 2

11001001 matches5 bits at A, 1 at B, 7 at C C = LPM


11001001Fixed

11010001

11001101

Longest

11001001

10100111

11010000

11001000

10100000

01000000

1101

OtherA

B

C

DA

C

B

11010101

110011

11100000

11001100


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Layer 3 (e.g., IP)

E.g. 301100101 matches

0 bit at A B0 bit at B, 0 at C, 2 at D D = LPM


Fixed

11010001

11001101

Longest

11001001

10100111

11010000

11001000

10100000

01000000

1101

Other A

B

C

DA

C

B

11010101

110011

11100000

01100101

11001100


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PS Virtual Circuit

Connection setup establishes a path through switches A virtual circuit ID (VCI) identifies path

Uses packet switching, with packets containing VCI

VCIs are often indices into per-switch connection tables;change at each hop

Statistical multiplexing is typically used

1

2 3

4 1

2 3

4

VC1

VC1

VC1

VC1

VC2

VC1

VC2

VC3

VC2In, VC Out, VC1, 1 4, 11, 2 4, 3

2, 1 4, 2

.

TOC Switching Techniques Packet VC


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Source Routing

12

3

4

12

3

4

1

23

4

1

23

4

1

23

4

1

23

4

4

source

3 4

4 3 4

4 3 4

Each packet specifies the sequence of routers(or of output ports) from source to destination

TOC Switching Techniques Source Routing


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Comparison

lowlowhighRobustness*

yesflexiblenoneResource

reservations

lowflexiblehighBandwidthutilization

nonelowhighForwarding cost

Circuitswitching

Virtual circuitswitching

Datagram

*The idea is that in case of failure, circuit and VC are lost;datagram routing can adapt after routing update .

TOC Switching Techniques Comparison


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Characteristics of Switch/Router

Ports

Fast Ethernet, OC-3, ATM, Protocols

ST, Link Agg., VLAN, OSPF, RIP, BGP, VPN,

Load Balancing, WRED, WFQ

Performance

Throughput, Reliability, Power,

TOC Switching Characteristics


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Examples

Juniper M160

Cisco GSR Cisco 7600

Cisco catalyst 6500 Extreme Summit

Foundry ServerIron

TOC Switching Examples


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Cisco GSR - 12416

WAN Router Large throughput; SONET links

Up to 16 line cards at 10 Gbps each

Crossbar Fabric

Line Cards:1-port OC-192c

4-port OC48cMany others(ATM, Ethernet, )

Cisco GSR 12416

6ft

19

2ft

TOC Switching Examples GSR


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Juniper M160

WAN Router Large throughput; SONET links

Crossbar Fabric

Line Cards:

1-port OC-192c4-port OC48c

Many others(ATM, Ethernet, )

Juniper M160

3ft

2.5ft

19

Capacity:

80Gb/s

Power: 2.6kW

TOC Switching Examples M160


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Cisco 7600

MAN-WAN Router

Up to 128 Gbps with Crossbar

Fabric 10Mbps 10Gbps LAN

Interfaces

OC-3 to OC-48 SONET

Interfaces MPLS, WFQ, LLQ, WRED,

Traffic Shaping

TOC Switching Examples 7600


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Cisco cat 6500 From LAN to Access

48 to 576 10/100 Ethernet Interfaces

10 GE, OC-3, OC-12, OC-48, ATM

QoS, ACL Load Balancing; VPN

Up to 128Gbps

(with crossbar)

L4-7 Switching VLAN

IP Telephony (E1, T1, inline-power Ethernet)

SNMP, RMON

TOC Switching Examples Cat6k


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Extreme - Summit

48 10/100 ports 2 GE (SX, LX, or LX-70)

17.5Gbps non-blocking 10.1 Mpps Wire speed L2 Wire speed L3 static or RIP OSPF, DVRMP, PIM,

TOC Switching Examples Summit


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Foundry - ServerIron

Server Load Balancing Transparent Cache Switching

Firewall Load Balancing Global Server Load Balancing Extended Layer 4-7 functionality including URL-, Cookie-,

and SSL Session ID-based switching Secure Network Address Translation (NAT) and

Port address translation (PAT)

TOC Switching Examples ServerIron


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Architectures

Generic Architecture First Generation Second Generation Third Generation

Input Functions Output Functions Interconnection Designs

OUT IN VOB

Combined IN/OUTTOC Switching Architectures


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Generic

Input and output interfacesare connected through an

interconnect

A interconnect can beimplemented by

Shared memory low capacity routers (e.g.,

PC-based routers)

Shared bus

Medium capacity routers

Point-to-point (switched)

bus

High capacity routers

input interface output interface

Inter-

connect

TOC Switching Architectures Generic


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Route

TableCPU

BufferMemory

LineInterface

MAC

LineInterface

MAC

LineInterface

MAC

Typically < 0.5Gbps aggregate capacityLimited by rate of shared memory

Shared Backplane

LineInterface

CPU

Mem

ory

Slide by Nick McKeown

First Generation

TOC Switching Architectures First


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RouteTable

CPU

LineCard

BufferMemory

LineCard

MAC

BufferMemory

LineCard

MAC

BufferMemory

FwdingCache

FwdingCache

FwdingCache

MAC

BufferMemory

Typically

< 5Gb/s aggregate capacityLimited by shared bus

Slide by Nick McKeown

Second Generation

TOC Switching Architectures Second

Thi d G i


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LineCard

MAC

LocalBuffer

Memory

CPUCard

LineCard

MAC

LocalBuffer

Memory

Switched Backplane

LineInterface

CPU

Memory Fwding

Table

Routing

Table

FwdingTable

Typically< 50Gbps aggregate capacity Slide by Nick McKeown

Third Generation

TOC Switching Architectures Third

I t F ti


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Input Functions

Packet forwarding: decide to which output

interface to forward each packet based on theinformation in packet header

examine packet header

lookup in forwarding tableupdate packet header

TOC Switching Architectures Input Functions

O


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Output Functions Buffer management: decide when and

which packet to drop

Scheduler: decide when and which

packet to transmit

1

2

Scheduler

Buffer

TOC Switching Architectures Output Functions

Output Functions (2)


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Output Functions (2) Packet classification: map each packet to a

predefined flow/connection (for datagramforwarding)

use to implement more sophisticated services (e.g.,

QoS)

Flow: a subset of packets between any twoendpoints in the network

1

2

Scheduler

flow 1

flow 2

flow n

Classifier

Buffermanagement

TOC Switching Architectures Output Functions

O t t Q d


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Output Queued Only output interfaces

store packets

Advantage

Easy to designalgorithms: only onecongestion point

DisadvantageRequires an output

speedup Ro/C = N, where

N is the number ofinterfaces not feasiblefor large N


Backplane

CRO

TOC Switching Architectures Output Queued

I t Q


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Input Queues

Only input interfacesstore packets

Advantages Easy to build Simple algorithms

Disadvantages

HOL Blocking In practice:

Speedup of 2 suffices


Backplane

CRO

TOC Switching Architectures Input Queued

N t H d f li Bl ki


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Note: Head-of-line Blocking

The cell at the head of an input queue cannot betransferred, thus blocking the following cells

Output 1

Output 2

Output 3

Input 1

Input 2

Input 3

Cannot betransferredbecause of

outputcontention

Being transferred

Cannot be transferredbecause of HOL blocking

TOC Switching Architectures Input Queued: HOL

Virtual Output Buffers


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Virtual Output Buffers

OUT buffers at each input port

Complexity: Matching Problem

Full throughput algorithm Good Heuristic

Note: Figure from Prof. Varaiyas notes for EE228b

Crossbar

TOC Switching Architectures VOB

VOB: Full Throughput


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VOB: Full Throughput

Maximum Weighted Matching:

A = 14

B = 11

C = 15

D = 10

B + C > A + D => Serve (B, C)

TOC Switching Architectures VOB: Full Throughput

VOB: Good Heuristic i SLIP


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VOB: Good Heuristic i-SLIP Inputs request permission to send from outputs

Outputs grant permissions to inputs (round-robin)

Inputs accept permissions (round-robin)

Request Grant2

1

3

3

1

2

Last GrantLast Accept

Accept Iter

TOC Switching Architectures VOB: iSLIP

Combined IN/OUT


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Combined IN/OUT

Both input and output interfaces store packets Advantages

Easy to built

Utilization 1 can beachieved with limited

input/output speedup(


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Switching needed for big networks Internetworking externality Circuit

Packet VC: QoS possible Packet Datagram

L2: Limited by flat address space

L3: Exact Match: Easy lookup less efficient Longest Prefix Match

Switch functions: control and data Different Architectures:

cost vs. performance

Summary

TOC Switching Summary

Switching Architecture

Documents

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