Review of key networking techniques:

1

• Review of key networking techniques
• Reliable communication over unreliable channels
• Error detection and correction
• Medium access control
• routing
• Congestion control

2

• Reliable communication over unreliable channels
• Positive acknowledgement with retransmission
  (PAR)
• Sender progresses only after receiving positive
  ACK
• Sender retransmits if timeout
• Receiver only accepts the correct packet (a
  sequence number is required to do this).
• Sliding window protocol
• PAR pipelined communication.
• Senders allows multiple outstanding packets
• Receivers buffer out of order packets

3

• Error detection/correction
• CRC checksum
• Sender/receiver agrees on the generator
• Sender makes sure that all messages sent can be
  divisible by the generator
• Add n 0-bits to the message
• Perform binary division
• Add the remainder to the message
• Receiver verifies a message is valid by dividing
  the message by the generator
• CRC checksum used in Ethernet frame
• Internet checksum
• 1s complement of the sums of 16 bit numbers
• Used in UDP, TCP, etc.

4

• Error detection/correction
• Error correction.
• Is typically more expensive than detecting errors
  and retransmission
• Used only when retransmission is expensive or
  when retransmission is inefficient
• Ad hoc mobile networks
• Satellite link
• Real time applications (Video streaming)

5

• Medium access control
• Use when multiple stations can access a shared
  channel
• There are three types of medium access control
  protocols.
• Protocols that allow collisions try out your
  luck and fix the problem if collision occurs.
• Collision free protocols make sure that no
  collision can possibly happen
• Limited collision protocols have the combined
  advantages of the previous two types of protocols.

6

• Protocols that allow collisions
• ALOHA, slotted ALOHA, CSMA, CSMA/CD
• Collision free protocols
• Bitmap method, binary countdown, token based.
• Limited collision protocols
• Adaptive tree walk

7

• Routing
• Flooding
• Shortest path routing (Dijkstra algorithm)
• Centralized algorithm
• Distributed routing algorithms have two
  components
• Maintaining the topology information
• Compute the routes
• Distance vector algorithm
• Each router distributes its routing table to its
  neighbors
• Each router updates its routing table based on
  the tables received from its neighbors.

8

• Routing
• Link state algorithm
• Each router obtain the link information for links
  directly connected to the router
• Each router flood the network with the link state
  information (all routers in the system receive
  link state packets).
• Shortest path algorithm is used to compute routes
  based on the link state database.

9

• Congestion control
• Congestion is a global event.
• Congestion happens when the network cannot handle
  the number of data injected into the network.
• Congestion control techniques
• Open loop or close loop
• Can be done either in the network layer or
  transport layer
• Traffic shaping
• Leaky bucket algorithm and token bucket algorithm
• Admission control
• Chock packet
• Hop-by hop chock packet
• Load sheding

10

• Congestion control mechanism in the Internet
• Done in TCP
• Slow start, AIMD
• Early random drop.