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Leon: Chapter 7: Packet-Switching Networks. We skip Chapter 6, because this material is covered in the LAN course. 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 - PowerPoint PPT Presentation
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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
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
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
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies 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
Peer-Peer Protocols Operating End-to-End Across Networks
Protocol Stack View. In C7 we are mostly concerned with the network layer
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
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
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies Figure 7.4
.
.
.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.
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
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
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
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
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
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
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
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
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
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
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
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
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
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
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
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
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
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
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
1
2
N
1
2
N
Figure 7.12
……
Routers perform demultiplexing and multiplexing functions
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
Networknodes
Message
SubscriberB
SubscriberA
Message
Message
Message
Figure 7.13
Message switching
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
t
t
t
t
Delay
Source
Destination
T
p
Minimum Delay = 3p + 3T
Switch 1
Switch 2
Figure 7.14
Delays in Message Switching
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
Packet 2
Packet 1
Packet 1
Packet 2
Packet 2
Figure 7.15
Datagram Packet Switching
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
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
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
Destinationaddress
Outputport
1345 12
2458
70785
6
12
1566
Figure 7.16
Routing table in connectionless packet switching
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
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.
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
t
t
t
t
31 2
31 2
321
Release
Connect request
CR
CR Connect confirm
CC
CC
Delays in virtual-circuit packet switching
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
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
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
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.
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
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