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Network and Transport Layer ​

IP ​

  • IP is a protocol which governs the data format of packets sent over the Internet.
  • The main functions provided by IP are addressing and network routing.

IPv4 ​

  • address: 32bits
  • header size: 20bytes+opt
  • checksum
  • Version
  • Type of service
  • Total length
  • Time to live
  • Source address, destination address
  • protocol

IPv6 ​

  • 40-byte header
  • 16-byte address
  • Version
  • Traffic class
  • Flow label
  • Payload length
  • Hop limit
  • Next header

Transition ​

  • Dual stack
  • Tunneling strategy
  • Header translation strategy

Routing ​

  • Delivery

  • Forwarding

  • Shortest Path Routing

    • Dijkstra

  • Flooding Algorithm

  • Distance Vector Routing

    • Count-to-Infinity Problem

  • Link State Routing

    • Learning about the neighbors
    • Measuring Line Cost
    • Building Link State Packets
    • Distributing the Link State Packets
    • Computing the new routes

  • Broadcast and Multicast Routing

    • emulated using multiple point-to-point unicast connections
    • Each router contains either a list of destinations or a bit map indicating the desired destinations. When a packet arrives at a router, the router checks all the destinations to determine the set of route lines that will be needed.

  • Hierarchical Routing

    • divided into regions
    • Each router knows the internal structure within its own region, but only knows the inter-connection points of other regions.

TCP(Transport Control Protocol) ​

  • When a sender transmits a segment, it also starts a timer.
  • When the segment arrives at the destination, the receiving TCP entity sends back a segment (with data if any) bearing an acknowledgement number equal to the next sequence number it expects to receive.
  • If the sender’s timer goes off before the acknowledgement is received, the sender transmits the segment again.
  • Source port and destination port
  • Sequence number and acknowledgement number
  • TCP header length
  • Six 1-bit flags
  • Window size
  • Checksum
  • Options

congestion control ​

Data Traffic ​

The main focus of congestion control and quality of service is data traffic.

  • Open-loop(预防)
  • Closed-loop(缓解)
    • Backpressure(一个一个向前)
    • Choke packet(直接最前)

Metrics Used to Monitor a Subnet for Congestion ​

Percentage of all packets discarded for lack of buffer space; • Average of queue lengths; • Number of packets that time out and are retransmitted; • Average packet delay; • Standard deviation of packet delay, etc

Load Shedding ​

discard packets: Random manner/ Application-based or algorithm-based

  • RED Algorithm

Jitter Control ​

抖动控制

QOS ​

Techniques for achieving good quality of service:

  • Buffering;
  • Traffic shaping;
  • Resource reservation;
  • Admission control.