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Topic 1: Introduction to communication networks
E&CE418
1 Communication network
• 1.1 Definitions– Telecommunications
• The conveyance of information by means of electrical signals
– What are the network components? • Links: guided media and unguided media
• Nodes: terminal or intermediate entities– Communication Network
• A set of nodes that are interconnected to permit the exchange of information
2
• What is a protocol?– A set of rules that nodes in a telecommunication connection use when they communicate
– Define the format and the order of messages exchanged between two or more entities, and actions taken on the transmission/receipt of a message
Communication network ‐> understand what, why, and how of networking protocols
3
All communication activities in a network are governed by protocols
1‐4
Examplea human protocol and a computer network protocol:
Hi
HiGot thetime?
2:00
connectionrequest
connectionresponseGet http://www.awl.com/kurose-ross
<file>
time
Any other human protocol?
1.2 Classifications of communication networks
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• Network scale or scope
Distance Location Network Abbre.
<2m Body area network BAN
<10m Room Personal area network PAN
10‐100m(1km) Building Local area network LAN
1‐10km city Metropolitan area network MAN
100‐100km country Wide area network WAN
• Characteristics of the channel (media)– Wireline network: guided media such as fiber optics, copper wires, twister‐pair cable, coaxial cable, etc.
– Wireless network: unguided media like radio link
6
Internet: a network of communication networks
7
Intelligent home network
• Entertainment/gaming
• Home control–Motion sensor/alarm
–Housework– Light system–Gardening, etc.
• Home office/webpad
• etc.
8
Intelligent transportation systems
9
• Traffic monitoring– Accident, incidents,
construction work, etc.
• Objectives:– Improved safety to drivers
– Improved traffic efficiency
– Reduced traffic congestion
– etc.
Telemedicine System
Internet
Health care providers
MBAN
Home network(WPAN/WLAN) Ambulance
MBAN in
10
Challenges and opportunities:
• A large number of users
• Emerging broadband multimedia services with various QoS requirements
• Heterogeneous networks interworking, etc.
To design and implement a communication network to meet the ever‐increasing user demands is critical and challenging
11
1.2 Classification (Cont’d)
• Type of switch– Circuit switching
– Packet switching
– Virtual circuit switching
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Circuit Switching
13
A
R1
R3R2
R4
B
Internet
‐A path from source to destination is established before a message is transmitted‐All links along the path between the source and destination are used during the entire transfer‐Data are transmitted along the dedicated path as rapidly as possible
Example: Traditional telephone
14
Circuit Switching
network resources (e.g., bandwidth) divided into “pieces”
• pieces allocated to calls
• resource piece idle if not used by owning call (no sharing)
dividing link bandwidth into “pieces”
frequency division
time division
15
Circuit Switching: FDM and TDM
FDM
frequency
time
TDM
frequency
time
4 users
Example:
Packet SwitchingA
R1
R3R2
R4
B
Example: Internet
A message is segmented into packets.Packets are then transmitted without prior reservation of link capacity.When a packet is received at a switch, it is inspected to determine the appropriate output link and transmitted when the output link is available. A packet switching network is also called store and forward network.
16
Introduction 1‐17
Packet Switching: Statistical Multiplexing
Sequence of A & B packets does not have fixed pattern, shared on demand statistical multiplexing.
10 Mb/sEthernet
1.5 Mb/s
statistical multiplexing
queue of packetswaiting for output
link
A
B
D E
C
Virtual Circuit Switching
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• Hybrid of packet and circuit switching networks– A message is broken into smaller fixed unit
– All packets that belong to the given message all follow the same path
– The resource of the path can be shared by other flows
• Example: ATM‐asynchronous Transfer Mode
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Network Taxonomy
Communicationnetworks
Circuit‐switchednetworks
FDM TDM
Packet‐switchednetworks
Networkswithout VCs
Networks with VC
Comparison
Circuit Switching Packet Switching
Dedicated path Yes * No
Bandwidth available Fixed Dynamic *
Potentially wasted Yes No *
Store and forward No Yes *
Call setup Required * Not needed
charging Per unit time * Per packet
Each packet follows the same route
Yes * No
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* Characteristics for virtual circuit‐switched networks
1.3 Benefits
• Resource sharing
• High reliability
• Access to remote information
• Person to person communication
• Interactive entertainment
• Others ...