computerNetwork

computer network

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• Pysical layer
  • Switching
  • Nyquist’s theorem
  • Shannon’s theorem
  • network media Types
• Data link layer
  • LLC: Logical Link Control
  • MAC: Media Access Control
• Network Layer

Pysical layer

Switching

• circuit switching
• message switching
• packet switching
  • datagram packet switching
  • circuit switching

Nyquist’s theorem

$R_{max} = 2H\,log_2V \quad bits/sec$

H is Bandwidth, V is the number of signal levels

Shannon’s theorem

$R_{max} = H\,log_2(1+S/N) \quad bits/sec$
S/N is signal to noise ratio

network media Types

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Data link layer

responsible for efficient and reliable communication across a physical layer

LLC: Logical Link Control

1. provided to network layer
2. link management
3. error control
   • send checksum together with data
4. flow control
   • stop and wait. poor link utilization

     Protocols in which the sender sends one frame then waits for an ackonwledgement before processing are called stop-and wait. 
     

   • sliding window

     purpose: to limit the maximum number of frames send by sender without waiting for acknowledgement.
     1. stop and wait
        send window size= 1, receive window size= 1
     2. go back n
        send window size> 1, receive window size= 1 
        the sender will retransmit the damage frame and all the frames that follow it
     3. selective repeat
        send window size> 1, receive window size> 1
        only the frames that are damaged are resent
     

5. frame synchronization
   • bit stuffing
6. addressing

MAC: Media Access Control

1. shared channel competition/access

   allocated the broadcast channel to the one of the competing stations.
   

2. Multiplexing

   - FDM
   - TDM
   - WDM
   - STDM???
   

3. CSMA/CD

   calculate
   

4. CSMA/CA Wireless
5. Ethernet
   

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Network Layer

the main function is routing packet from the sourcr machine to the destination machine.

store and forward Packet

Routing

1. Shortest Path routing

   By changing weight function, the algorithm will compute the shortest path.
   

2. Flooding

   ppt says little about this.
   

3. Distant Vector Routing

   Good news travels fast, bad news travels slow.
   

4. Link state Routing

   Each router need large memory to store the input states of the other routes
   

5. Hierarchical Routing

Flow control

Congestion control

The purpose of the congestion control is to prevent the network from congestion.

InterNetworking

The IP protocol

1. The IP dataframe
2. IP Address

   The address is extreme wasteful!
   1. CIDR
   2. NAT
   3. IPv4 -> IPv6
   

3. Subnets

Route Protocol

1. AS
2. IGP&EGP
3. RIP
4. BGP
   
   Diffrence between repeater, hub, bridge, switch and getway