csc581 communication networks ii chapter 7a: wide area network and switching techniques dr....

CSC581Communication Networks II

Chapter 7a: Wide Area Network and Switching Techniques

Dr. Cheer-Sun Yang

2

Topics

• Circuit switching (p. 23-24)

• Message switching (p. 25)

• Packet switching (p. 26-28)– Datagram– Virtual Circuit

• Example of Packet Switching Protocol:

X. 25 (Section 7.3)

3

Network Layer Functions

• Switching (layer 3 switching): packet switching

• Routing

• Fragmentation and assembly

• Congestion Control

• Internetworking

4

WAN vs. LAN

• Wide area network (WAN) is the “cloud” that we’ve been ignoring.

• A WAN covers much larger areas for which LAN protocols are inappropriate.

• Routing in WAN is more complex than that in LAN.

• Switching is a main topic in the design of WAN (circuit, message, packet switching).

5

WAN vs. LAN(cont’d)

• Error recovery at the network layer is needed.• Internetworking may require protocol conversion

performed by a protocol converter, including bridges and routers, or gateways.

• Packet fragmentation and assembly• Quality of Service (QoS) and Internet

Management are important.

Let’s start with another look of the big picture.

6

Simple Switched Network

Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks

7

Figure 7.1

t0t1

Network


8

Figure 7.2

Physicallayer

Data linklayer

Physicallayer

Data linklayer

End system

Networklayer

Networklayer

Physicallayer

Data linklayer

Networklayer

Physicallayer

Data linklayer

Networklayer

Transportlayer

Transportlayer

MessagesMessages

Segments

End system

Networkservice

Networkservice


9

3 2 11 2

21

3 2 11 2

21

21

Medium

A B

3 2 11 2

21

C

21

21

2 134 1 2 3 4

End system

End system

Network

1

2

Physical layer entity

Data link layer entity3 Network layer entity

3 Network layer entity

Transport layer entity4

Figure 7.3

10

Switching Networks

• Category of switching functions within a switch: space division switching, time division switching

• Category of switching techniques:– layer 1: circuit switching

– layer 2: cell switching (ATM), frame switching (frame ralay)

– layer 3: packet switching

11

Space Division Switching

• Developed for analog environment• Separate physical paths• Crossbar switch

– Number of crosspoints grows as square of number of stations

– Loss of crosspoint prevents connection

– Inefficient use of crosspoints• All stations connected, only a few crosspoints in use

– Non-blocking


12

User 1

SwitchLink

User n

User n-1

(a) Network

(b) Switch Control

123

N

123

N

Connectionof inputs to outputs

Figure 4.21


13

N

1 2

1

N

2

N-1

Figure 4.22

14

Crossbar Matrix

15

Multistage Switch

• Reduced number of crosspoints

• More than one path through network– Increased reliability

• More complex control

• May be blocking


16

nxk

nxk

nxk

nxk

N/n x N/n

N/n x N/n

N/n x N/n

kxn1

2

N/n

Ninputs

1

2

3 3

N/n

Noutputs

1

2

k

2(N/n)nk + k (N/n)2 crosspoints

kxn

kxn

kxn

Figure 4.23


17

nxk

nxk

nxk

N/n x N/n

N/n x N/n

N/n x N/n

kxn1

N/n

Desiredinput

1

jm

N/n

Desiredoutput

1

2n-1

kxn

kxn

n-1

N/n x N/nn+1

N/n x N/n2n-2

free path freepath

n-1busy

n-1busy

Figure 4.24


18

12

24

12

24

FromTDM

DeMUX

ToTDMMUX

24 23 12

2 241 23

Read slots inpermuted order

Figure 4.25


19

nxk

nxk

nxk

nxk

N/n x N/n kxn1

2

N/n

Ninputs

1

3

1

12

n

input TDM frame with n slots

output TDM frame with k slots

Figure 4.26


20

nxk N/n x N/n

N/n x N/n

N/n x N/n

kxn1 1

2

N/n

1

2

k

kxn

kxn

nxk2

nxkN/n

first slot

kth slot

first slot

kth slot

Figure 4.27


21

nxk

nxk

nxk

nxk

N/n x N/nTime-Shared

SpaceSwitch

kxn1

2

N/n

Ninputs

1

2

3 3

N/n

Noutputs

TDMn slots

n slots

n slots

n slots

kxn

kxn

kxn

TDMk slots

TDMk slots

TSI Stage TSI StageSpace Stage

Figure 4.28


22

2x3

2x3

3x21

2

1

23x2D1

B1 A1B2 A2

C1D2 C2

B1 A1

C1D1

A1

B1

C1

D1

A1 C1

B1 D1

Figure 4.29


23

Figure 4.30


24

Signal

Source

Signal

Release

Signal

Destination

GoAhead Message

Figure 4.31


25

(a) Routing in a typical metropolitan area

(b) Routing between two LATAs

1

2 3

4

5

LATA 1 LATA 2

net 1

net 2

A B

C D

Figure 4.32


26

local telephone office

Dis

trib

utio

n F

ram

e

Serving Area I/f

Serving Area I/f

Pedestal

feeder cable

Switch

distribution cable

Figure 4.33


27

Original signal

Hybrid transformer

Received signal

Echoed signal

Receive pair

Transmit pair

Figure 4.34


28

Localanalog

Localdigital

Digitaltrunks

LocalSwitch

Tie lines

Foreign exchange

Channel-switched traffic (digital leased lines)

Circuit-switched traffic

Digitalcross-connect

System

Figure 4.35


29

Physical SONET

Topology usingADMs and DCCs

Logical Topology

Switches see thistopology

DCC

Figure 4.36

ADM

ADM

ADM

ADM

ADM

ADM


30

Basic Rate Interface (BRI): 2B+D

Primary Rate Interface (PRI): 23B+D

BRI

PRI

BRI

PRI

CircuitSwitched Network

ChannelSwitched NetworkPrivate

SignalingNetwork

PacketSwitched Networks

Figure 4.37


31

SPC

Control Signaling Message

Figure 4.39


32

Switch

Processor

Office B

Switch

Office A

ProcessorSignaling

ModemModem

Trunks

Figure 4.39


33

STP

STP

STP

STP

SSP SSP

Transport Network

Signaling Network

SSP = Service switching point (signal to message)STP = Signal transfer point (message transfer)SCP = Service control point (processing)

SCP

Figure 4.40


34

SSP

SSP

Transport Network

ExternalDatabase

SignalingNetwork Intelligent

Peripheral

Figure 4.40


35

Application Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer

Presentation Layer

Session Layer

SCCP

MTP Level 3

MTP Level 2

MTP Level 1

ISUPTCAPTUP

Figure 4.42

36

Time Division Switching

• Partition low speed bit stream into pieces that share higher speed stream

• e.g. TDM bus switching– based on synchronous time division multiplexing

– Each station connects through controlled gates to high speed bus

– Time slot allows small amount of data onto bus

– Another line’s gate is enabled for output at the same time

37

Control Signaling Functions

• Audible communication with subscriber• Transmission of dialed number• Call can not be completed indication• Call ended indication• Signal to ring phone• Billing info• Equipment and trunk status info• Diagnostic info• Control of specialist equipment

38

Control Signal Sequence• Both phones on hook• Subscriber lifts receiver (off hook)• End office switch signaled• Switch responds with dial tone• Caller dials number• If target not busy, send ringer signal to target subscriber• Feedback to caller

– Ringing tone, engaged tone, unobtainable

• Target accepts call by lifting receiver• Switch terminates ringing signal and ringing tone• Switch establishes connection• Connection release when Source subscriber hangs up

39

Switch to Switch Signaling

• Subscribers connected to different switches

• Originating switch seizes interswitch trunk

• Send off hook signal on trunk, requesting digit register at target switch (for address)

• Terminating switch sends off hook followed by on hook (wink) to show register ready

• Originating switch sends address

40

Control Signals

41

Location of Signaling

• Subscriber to network– Depends on subscriber device and switch

• Within network– Management of subscriber calls and network– ore complex

42

In Channel Signaling

• Use same channel for signaling and call– Requires no additional transmission facilities

• Inband– Uses same frequencies as voice signal– Can go anywhere a voice signal can– Impossible to set up a call on a faulty speech path

• Out of band– Voice signals do not use full 4kHz bandwidth– Narrow signal band within 4kHz used for control– Can be sent whether or not voice signals are present– Need extra electronics– Slower signal rate (narrow bandwidth)

43

Drawbacks of In Channel Signaling

• Limited transfer rate

• Delay between entering address (dialing) and connection

• Overcome by use of common channel signaling

44

Common Channel Signaling

• Control signals carried over paths independent of voice channel

• One control signal channel can carry signals for a number of subscriber channels

• Common control channel for these subscriber lines• Associated Mode

– Common channel closely tracks interswitch trunks

• Disassociated Mode– Additional nodes (signal transfer points)– Effectively two separate networks

45

Common v. In Channel Signaling

46

Signaling Modes

47

Signaling System Number 7

• SS7• Common channel signaling scheme• ISDN• Optimized for 64k digital channel network• Call control, remote control, management and

maintenance• Reliable means of transfer of info in sequence• Will operate over analog and below 64k• Point to point terrestrial and satellite links

48

SS7 Signaling Network Elements

• Signaling point (SP)– Any point in the network capable of handling SS7

control message

• Signal transfer point (STP)– A signaling point capable of routing control messages

• Control plane– Responsible for establishing and managing connections

• Information plane– Once a connection is set up, info is transferred in the

information plane

49

Transfer Points

50

Signaling Network Structures

• STP capacities– Number of signaling links that can be handled– Message transfer time– Throughput capacity

• Network performance– Number of SPs– Signaling delays

• Availability and reliability– Ability of network to provide services in the face of

STP failures

51

Circuit Switching Routing

• Many connections will need paths through more than one switch

• Need to find a route– Efficiency– Resilience

• Public telephone switches are a tree structure– Static routing uses the same approach all the time

• Dynamic routing allows for changes in routing depending on traffic– Uses a peer structure for nodes

52

Alternate Routing

• Possible routes between end offices predefined

• Originating switch selects appropriate route

• Routes listed in preference order

• Different sets of routes may be used at different times

53

Alternate Routing Diagram

54

Problems RE Circuit Switching

• Circuit switching designed for voice– Resources dedicated to a particular call– Much of the time a data connection is idle– Data rate is fixed

• Both ends must operate at the same rate

55

Message Switching

• A message is broken into smaller data units, called messages.

• Each message is sent to the destination via different paths.

• At each node, the message is stored temporarily prior to retransmission. This concept is called store-and-forward.

56

Message Switching (cont’d)

• In circuit switching, a single route is dedicated to the exchange of all messages. In message switching, different message data units can be transmitted via different routes.

57

Message Switching (cont’d)

• In circuit switching, a connection between the two parties is required, whereas in message switching, a message can be sent and stored for later retrieval.

• However, since the size of each message data unit is quite large, error recovery is costly. The message data unit is broken into a smaller chunkm called packet.

• Packet switching is more realistic.


58

Networknodes

Message

SubscriberB

SubscriberA

Message

Message

Message

Figure 7.13


59

t

t

t

t

Delay

Source

Destination

T

p

Minimum Delay = 3p + 3T

Switch 1

Switch 2

Figure 7.14

61

Packet Switching

• The size of a packet is design dependent.• Each packet contains the destination

address or some other designator indicating where it should go.

• When the packets all arrive, they are reassembled.

• Network Layer protocol is responsible for routing, fragmentation/reassembly.

62

Basic Operation

• Data transmitted in small packets– Typically 1000 octets– Longer messages split into series of packets– Each packet contains a portion of user data plus some

control info

• Control info– Routing (addressing) info

• Packets are received, stored briefly (buffered) and past on to the next node– Store and forward


63

Figure 7.4

.

.

.MUX

Network access

Node


64

LAN

Bridge

LAN 1

LAN 2

(a) (b)

Figure 7.5


65

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

Figure 7.6


66

Interdomain level

Intradomain level

LAN level

Autonomous systemor domain

Border routers

Border routers

Figure 7.7

Internet service provider


67

RA

RB

RC

Route server

NAP

National service provider A

National service provider B

National service provider C

LAN

NAPNAP

(a)

(b)

Figure 7.8

68

Advantages

• Line efficiency– Single node to node link can be shared by many packets

over time– Packets queued and transmitted as fast as possible

• Data rate conversion– Each station connects to the local node at its own speed– Nodes buffer data if required to equalize rates

• Packets are accepted even when network is busy– Delivery may slow down

• Priorities can be used

69

Switching Technique

• Station breaks long message into packets

• Packets sent one at a time to the network

• Packets handled in two ways– Datagram– Virtual circuit


70

Network

Packet switch

Transmission link

Figure 7.9

71

Structure of Switch/Router

• Line card• Interconnection Fabric• Control• Input ports• Output ports


72

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

Figure 7.10

…… ……


73

CPU

1

2

3

N

NIC Card

NIC Card

NIC Card

NIC Card Mai

n M

emor

y

I/OBus

Figure 7.11

……


74

1

2

N

1

2

N

Figure 7.12

……

75

Datagram

• Each packet treated independently

• Packets can take any practical route

• Packets may arrive out of order

• Packets may go missing

• Up to receiver to re-order packets and recover from missing packets


76

Packet 2

Packet 1

Packet 1

Packet 2

Packet 2

Figure 7.15


77

t

t

t

t

31 2

31 2

321

3p + 2(T/3) first bit received

3p + 3(T/3) first bit released

3p + 5 (T/3) last bit released

Lp + (L-1)P first bit received

Lp + LP first bit released

Lp + LP + (k-1)P last bit releasedwhere T = k P

3 hops L hops

p

p + P

p + P

Source

Destination

Switch 1

Switch 2

Figure 7.16


78

Destinationaddress

Outputport

1345 12

2458

70785

6

12

1566

Figure 7.16

79

Virtual Circuit

• Preplanned route established before any packets sent

• Call request and call accept packets establish connection (handshake)

• Each packet contains a virtual circuit identifier instead of destination address

• No routing decisions required for each packet• Clear request to drop circuit• Not a dedicated path

80

Virtual Circuits vs Datagram

• Virtual circuits– Network can provide sequencing and error control– Packets are forwarded more quickly

• No routing decisions to make

– Less reliable• Loss of a node looses all circuits through that node

• Datagram– No call setup phase

• Better if few packets

– More flexible• Routing can be used to avoid congested parts of the network


81

Packet

Packet

Figure 7.17


82

t

t

t

t

31 2

31 2

321

Release

Connect request

CR

CR Connect confirm

CC

CC


83

SW 1

SW 2

SW n

Connect request

Connect request

Connect request

Connect confirm

Connect confirm

Figure 7.20

…


84

Identifier Outputport

15 15

58

13

13

7

27

12

Nextidentifier

44

23

16

34

Entry for packetswith identifier 15

Figure 7.21


85

31 2

31 2

321

Minimum Delay = 3p+T t

t

t

tSource

Destination

Switch 1

Switch 2

Figure 7.22

86

ATM Networks and Layer 2 Packet Switching-Cell Switching• Asynchronous Transfer Mode (ATM)


87

MUX

`

Wasted bandwidth

ATM

TDM

4 3 2 1 4 3 2 1 4 3 2 1

4 3 1 3 2 2 1

Voice

Data packets

Images

Figure 7.37


88

2

3

N

1Switch

N

1…

5

6

video 25

video

voice

data

32

32 61

25

32

3261

75

67

39

67

N

1

32

video 75

voice 67

data 39

video 67

Figure 7.38

…

…


89

c ATMSw1

ATMSw4

ATMSw2

ATMSw3

ATMDCC

ab

de

VP3 VP5

VP2

VP1

a

bc

deSw = switch

Figure 7.39


90

Physical Link

Virtual Paths

Virtual Channels

Figure 7.40


91

1 2 NN-1

Figure 7.41

…


92

Packet buffer

Transmission link

Arrivingpackets

Packet discardwhen full

Packet buffer

Transmissionlink

Arrivingpackets

Class 1 discardwhen full

Class 2discardwhen thresholdexceeded

(a)

(b)

Figure 7.42


93

Transmission link


High-prioritypackets

Low-prioritypackets


When high-priorityqueue empty

Figure 7.43


94

Sorted packet buffer

Transmissionlink

Arrivingpackets


Taggingunit

Figure 7.44


95

Transmission link

Packet flow 1

Packet flow 2

Packet flow n

C bits/second

Approximatedbit-levelround robinservice

Figure 7.45


96

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

Figure 7.46


97

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

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

Figure 7.47


98

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


0 3

Figure 7.48


99

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


0

Figure 7.49

100

Reading Assignment

• 7.1 Network Services • 4.4 Layer 1 switching: Circuit Switching• 7.2 Packet Networks• 7.3 Layer 3 Switching: Message Switching,

Virtual Circuit Packet Switching, Datagram Packet Switching

• 7.6 Layer 2 Switching: ATM Cell Switching

csc581 communication networks ii chapter 7a: wide area network and switching techniques dr....

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