Networking Notes 6 - Network Performance Measures

Network Performance Measures

• Throughput
  • How much data travels across the network
• Average packet delay
  • How long does it take for a packet to arrive at its destination
  • How responsive is the system to user commands
  • Can the network support real-delivery such as audio and video

Routing Algorithm

“Good” path:

• The minimum cost path
• Other definitions are possible

Hop count

The number of routers a packet must go through

Least-cost routing

Associate a cost with each link

• Bandwidth
• Delay
• Reliability

To make routing decision:

• Topology of the network

• Traffic load

• Link cost

• Information should always keep up-to-date

• More information

Fixed Routing

• Central Directory is usually stored at a network control center

• Matrix table

• No different between Datagram and VC

• Advantages

  • Simplicity
  • Work Well in a reliable network with a stable load
    (IPLC?)

• Disadvantages

  • Lack of flexibility
  • Do not react to network congestion or failures

Flooding Algorithm

Packet sent to every neighbor node

• No network information required

• Evenually a number of copies will arrive at destination

• Guarantees the packet reaches the destination in the shortest time

• Duplicate packets are generated.

• Node can remember packets already forwarded

• Advantage

  • Very rebust
  • Used for sending emergency messages

• Disadvantage

  • High traffic load

Random Algorithm

The outgoing link is chosen at random
Round-robin?

• Advantages
  • Robust and simple
  • no network information
  • Less traffic load compare to flooding
• Disadvantages
  • Longer path
  • Performance not guaranteed

Adaptive Routing

Used by almost all packet switching network
** routing decision changes as network conditions change**

• Failure Link

• Network congestion

• Require network information

• Network information must be exchanged among the nodes

• Decisions are more complex

• Advantages

  • Impoved performance
  • Congestion control

• Disadvantages

  • Substantial processing burden on nodes
  • Increased network traffic traffic due to the exchange of network information
  • Reacting too quickly can cause oscillation

Distance Vector Routing

Each node communicates only with directly-attached neighborsA routing table is created by building up a common set of routers in close proximity to each other, hence the term “distributed”.
Each router on the network must maintain a two-dimensional Vector Table, which records the best known distance from its own router to each router.
A router periodically builds a routing table by exchanging vector tables with neighboring routers (not broadcast to all routers).
When a router receives a vector table from its neighbors and then corrects its own vector table, the contents of the vector table are continually corrected and retransmitted, and the entire network state is gradually passed to each router.
As the routing tables on the routers become more complete, it becomes possible to find the best path. The vector table is sent only to the neighboring routers, which consumes less bandwidth and does not cause broadcast oscillation.

Link State Routing

Information sharing - each router shares its knowledge of its neighbourhood with all routers in the network.
After all LASs from all nodes are gathered, the entire map of the network can be constructed.

Least-Cost Algorithms

• Dijkstra’s Algorithm
• Bellman - Ford Algorithm

We Will come back for the Algorithm later