Leon: Chapter 7: Packet-Switching Networks

Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies

Leon: Chapter 7:Packet-Switching Networks

We skip Chapter 6, because this material is covered in the LAN course


C7: Outline

7.1 Network Services and Internal Network Operation 7.2 Packet Network Topology 7.3 Datagrams and Virtual Circuits

• 7.4 Routing in Packet Networks

• 7.5 Shortest Path Algorithms

• 7.6 ATM Networks (Skip)

• 7.7 Traffic Management and QOS

• 7.8 Congestion Control

Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies Figure 7.1

t0t1

Network

Top level view: a network transfers info among users

The figure simply shows transmission of a single block or a stream of info


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

Peer-Peer Protocols Operating End-to-End Across Networks

Protocol Stack View. In C7 we are mostly concerned with the network layer


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

Layer 3 Entities work together to provide services to Layer 4 Entities

Spatial view


.

.

.MUX

Network access

Node

Packet Network Topologies:

How do users access a packet-switching network?

One way is shown. Today the MUX might be a shared DSL or Cable Modem. More likely it would be a router that permits a LAN connection between the PCs.


LAN

Bridge

LAN 1

LAN 2

(a) (b)

Figure 7.5

Mostly users at one geographic site are connected with one or more Local Area Networks

(a) Broadcasts frames to all PCs. (b) A bridge usually just connects LANs to make a larger broadcast segment, but a LAN switch isolates traffic to a particular LAN, unless it needs to be sent to another LAN


A large site usually sets up many LANs

• LANs are connected usually connect by switches or routers to isolate traffic to a particular segment if possible

• Such a network of LANs is called a campus network

• The next slide shows a campus network with a backbone internal to the organization

• It also has a gateway to connect to other networks, usually the Internet

• A site with remote locations might lease lines or share frame relay interconnections. A multiplexer or router helps share the line by queueing packets to be sent


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

The s = LAN switch. The S is usually a router


More about the typical campus network

• The campus backbone is usually a high speed LAN FDDI at 100Mbps is common, or Gigabit Ethernet

• The traffic within an extended LAN segment is delivered using 48-bit physical addresses; however applications use 36-bit IP addresses. The Address Resolution Protocol ARP automatically builds tables to relate the two.

• To connect the campus network to the larger Internet, we go one more step up the hierarchy. The campus network is then called an autonomous system


Interdomain level

Intradomain level

LAN level

Autonomous systemor domain

Border routers

Border routers

Figure 7.7

Internet service provider

The autonomous system connects to the rest of the internet via border routers at ISP Points of Presence


Role of the National Service Providers

• About 20 in US

• See Russ Haynal page on resources navigators.com/isp.html

• Some of the largest are bankrupt

• Connections at NAP and MAEs


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

NSPs are connected at Network Access Points

Details


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

…… ……

Components of a Generic Switch/Router


CPU

1

2

3

N

NIC Card

NIC Card

NIC Card

NIC Card Mai

n M

emor

y

I/OBus

Figure 7.11

……

Building a router from a PC


1

2

N

1

2

N

Figure 7.12

……

Routers perform demultiplexing and multiplexing functions


Networknodes

Message

SubscriberB

SubscriberA

Message

Message

Message

Figure 7.13

Message switching


t

t

t

t

Delay

Source

Destination

T

p

Minimum Delay = 3p + 3T

Switch 1

Switch 2

Figure 7.14

Delays in Message Switching


Packet 2

Packet 1

Packet 1

Packet 2

Packet 2

Figure 7.15

Datagram Packet Switching


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

Delays in Packet Switching; note that pipelining can speed transfer vs. message switching


Destinationaddress

Outputport

1345 12

2458

70785

6

12

1566

Figure 7.16

Routing table in connectionless packet switching


Packet

Packet

Figure 7.17

Virtual Circuit Packet Switching

A virtual connection is set up for the duration of the call, which simplifies routing. Other streams can use the same physical links, so we still have advantage of sharing resources.


t

t

t

t

31 2

31 2

321

Release

Connect request

CR

CR Connect confirm

CC

CC

Delays in virtual-circuit packet switching


SW 1

SW 2

SW n

Connect request

Connect request

Connect request

Connect confirm

Connect confirm

Figure 7.20

…

Signaling message exchanges in virtual circuit set up


Identifier Outputport

15 15

58

13

13

7

27

12

Nextidentifier

44

23

16

34

Entry for packetswith identifier 15

Figure 7.21

Example of a virtual circuit routing table for an input port. ID is virtual circuit number. Abbreviated headers can be used.


31 2

31 2

321

Minimum Delay = 3p+T t

t

t

tSource

Destination

Switch 1

Switch 2

Figure 7.22

Standard virtual circuits have same delay to send k packets and the datagram variety, plus the set up phase

"Cut through" packet switching speeds by starting output transmission as soon as header is decoded

Leon: Chapter 7: Packet-Switching Networks

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