CS4550: Computer Networks II OVERVIEW

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CS4550Computer Networks IIOVERVIEW

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overview - primitive concepts

• communication - movement of information from 1
  physical point to another.
• information - primitive (not defined) has some
  representation bits, letters, symbols. So
  communication is movement of information
  representation.
• examples page of book, sheet of music, spoken
  word, flash of light.

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overview - primitive concepts

• telecommunication - communication through
  distance, e.g., telephone or telegraph systems.
  Includes voice, radio, TV, and digital
  communications.
• data communication - moving digital data, ie,
  bits from one physical node to another.
• we are interested in both, not only data, because
  these are related and merging.

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Communication Model
Information Data Signals
application
application
Service layers
Service layers
Physical layer
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historical background

• telegraph networks, 1845-- 1st LD network, using
  electricity... digital signals
• telephone networks 1880-- analog signals, voice.
  
• radio networks, 1901-- broadcast analog signals.
  Voice.
• TV cable networks, 1970s -- wide-bandwidth analog
  signals.
• Internet, WWW, 1990s -- global computer digital
  signals

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Nodes, Bridges, Routers
To other LANS

• --gt two LAN internetwork, with both ethernet and
  TR LANs connected by a router

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basic switching techniques

• 4 major categories
• circuit switching - telephone system
• message switching - postal system
• packet switching - email, internet
• broadcasting - radio, TV networks

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Connection Types

• Connection Oriented Connectionless
• Connect request
• Connect Accept transmit
• Data
• Acknowledge receive
• Terminate Connection request
• Terminate connection Accept

Phases Dial Talk Hang-up
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circuit switching

• connection established before communication
• circuit or channel in network completely
  dedicated to a connection
• nice for voice but can be poor utilization of
  network resources - especially for data, internet
  traffic
• example telephone call

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message switching

• entire message sent and stored at each node
• more efficient than C.S., but difficult due to
  large variation in message sizes
• entire message received at each node before
  retransmitting

packet
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packet switching

• refinement of message switching
• fixed sized packets
• greatly improves utilization over message and
  switching (calculate transmission time)
• two forms of packet switching
• datagrams
• virtual circuit

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broadcasting

• one node transmits, all others receive
• examples radio broadcast, TV broadcast, local
  area networks, cable TV
• single channel, common frequency
• if more than one attempts to transmit,
  interference occurs

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Example 1Mbyte at 80Kbit/sec through 2 relay
nodes
Tc D/c Tm Data Volume/Transmission Rate
8MBits/80KB 100 sec
Td node delay msec Tt 3 Tm 2 Td
300 sec
Tp Td Tm / of Packets 100/333.3 sec Tt
Tpnodes Tm 33.32 100166.6sec