outline

Basic Components

• Nodes
• Links

Communication Links

• Over Telephone
• Over dicated wires

Figure 12.1a

Figure12.1b

• 
• Two forms of information representation

Conversion

• Digital -------> Analog
• Analog ------> Digital
• This is where modems come into play

Figure 12.2

• 
• Modulation of a carrier to encode binary information

Transmission Media (Links)

• Twisted-pair copper wire (ex: tel)
  • cheap, low rate, low range, noise
• Coaxial Cable (ex: TV Cable)
  • more exp., higher rate, higher range, noise tolerance
• Fiver-optic
  • expensive, very fast, no noise, long distance

Figure 12.3

• 
• Transmission time of an image at different transmission speeds

Ubiguitous Computing

• "Computers everywhere"!

Local Area Networks (LAN)

• Connects several nodes within a small geographical area. => lab, office
• Polular ones: Ethernet, Token Ring

Ethernet

• 1970 by Xerox Pane
• 10Mbs
• Fast Ethernet 100Mbs

Figure 12.4a

Figure 12.4b

• 
• An Ethernet LAN implemented using cables

Communication Protocol

• How does machines communicate? CSMA/CD
• each machine has an Ethernet Address
• each message contains the address of the receiver
• everybody recieves every message
• discards, if not theirs

Figure 12.6a

Figure 12.6b

Figure 12.6c

• 
• Sending messages across an ethernet

Wide Area Networks (WAN)

• 
• General structure of a Wide area network

Protocol

• Uses Store - and - forward, packet switching protocol
• Packets: representation of messages. (unit)
• 

Protocol 2

• Routing: Process selecting specific packets
• Shortest path: Complexity?
• Topological change
• Network failures

Figure 12.8

• 
• Store-and-Forward Packet Switching

Network configuration

• Internet is a collection of LANS & WANS connected by routers.
• 
• Typical LAN/WAN Network Configuration

Network configuration 2

• 1. Node A on LAN1 broadcasts a message containing the destaination address "Node B, LAN2"
  2. Every node on LAN1 recieves this message, but only router R1 accepts it, becuae R1 has the ecplicit responsibility to accept and handle all messages destined for nodes outside LAN1.

Network configuration 3

• 3. Router R1 reconfigures the message so that it is consistent whit the protocols and formats of messages sent through the WAN. R1 then passes the message into the WAN via node C.

Network configuration 4

• 4. The message is routed from node C to node D using the store-and-forward packet-switching protocols just described. When the message arrives at node D, it is passed onto router R2.

Network configuration 5

• 5. R2 again reformats the message, this time to be consistent with the protocols and formats of LAN2, which need not be the same protocols used by LAN1. Then it broadcasts the message on LAN2, where is it recieved by all nodes.

Network configuration 6

• 6. Node B, the node whose address is contained in the destination address field, accepts the message. All other nodes on LAN2 disregard it. The message has correctly arrived at its destination.

Internet & WWW

• Gateways: Provides connectivity between different WANs.
• How different networks communicate?

"Networks of Networks"

TCP

• Transport Content Protocol
• Technology borrowed from telephone co.
• country code, city code, phone # etc.
• 01 317 274 9727

Cerf and Kahn

• Developed two conventions in the networking work:
• Addressing - hierarchical addressing scheme that uniquely identifies a computer user located anywhere in the world.
• Protocols (TCP/IP) - describes the rules and procedures that networks would use for sddressing, message formats, routing, and error control

Figure 12.12

• 
• State of Networking in the late 1980s

The World Wide Web

• Hypertext: Collection of coduments connected by pointers]
• 
• Operations of the web

Figure 12.15a

Figure 12.15b

Figure 14.6

Figure 20.1