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Ch 5- Network Layer

  • Introduction:
  • Design Issues
  • Inter connecting devices, IP protocols & subnets
  • Routing Algorithms
    • Routing Classification
    • Goal of Routing Algorithm
    • Shortest path routing, Flooding, Optimality principles
    • Distance vector routing, Link state routing
    • Broadcast, multicast, anycast routing
  • Congestion Control
  • Quality of service
  • Internetworking, Addressing
  • n/w layer protocols, IPv4 and IPv6

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Ch 5- Network Layer (Congestion)

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Computer Networks - A Tanenbaum – 3rd edition Cover Page (Image reference)

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Congestion Control

  • Congestion:
  • Too many packets present in the network (traffic) that causes packet delay and loss that degrades performance. This situation is called congestion
  • Handling congestion is the responsibility of the Network and Transport layers working together (here n/w layer)
    • Approach: The presence of congestion means that the load is greater than the resources can handle. 🡪 Two solutions come to mind: ( increase the resources or decrease the load. )
      • Traffic-aware routing
      • Admission control
      • Traffic throttling
      • Load shedding

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With too much traffic, performance drops sharply.

CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall , 2011

Congestion Control

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Traffic-Aware Routing

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Admission Control

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Traffic throttling

CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall , 2011

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Load Shedding (1)

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Load Shedding (2)

CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall , 2011

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Quality of service

QOS: Mechanism to control amount and the rate of traffic sent to the n/w

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  • Application requirements

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  • Traffic Shaping
    • Leaky Bucket
    • Token Bucket

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Application Requirements

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  • Network performance (Delay & throughput)
    • Traffic Profile (CBR, VBR, Bursty traffic)
  • Quality of service (Traffic shaping)
    • Mechanism to control amount and the rate of traffic sent to the n/w
    • Leakey Bucket: Steps Bursty traffic in to fixed rate traffic by avg. the data rate
    • Leakey Algo: fetched packet from queue at constant rate

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    • Tocken Bucket Algo: Allows Bursty traffic at a regulated maximum rate

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Traffic Profiles

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Network Performance

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Traffic Shaping

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(a) Shaping packets. (b) A leaky bucket. (c) A token bucket.

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QOS-Traffic Shaping

    • It is mechanism to control the amount and the rate of the traffic sent to the network
    • Leakey Bucket: algo shapes Bursty traffic in to fixed traffic by averaging the data rate

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QOS-Traffic Shaping

    • Leakey Bucket: Bursty traffic in to fixed traffic by averaging the data rate .
    • For e.g.

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QOS-Traffic Shaping

Token Bucket: it allows Bursty traffic at regulated maximum rate

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What is the different between �Token bucket and Leakey bucket algo.

Computer Networks

Token Bucket

Leakey Bucket

  • Token dependent
  • Token independent
  • If bucket is full, token is discarded

but not the packet

  • If bucket is full, then packets are

discarded

  • Packet can only transmit when there

are enough tokens

  • Packets are transmitted continuously
  • Allows large bursts to be send at

faster rate

  • Sends the packet at a constant rate
  • Saves tokens to send large bursts
  • No concept of token

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End of Part-3 (Ch-5 Network layer)

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Thanks.

By Hitesh Barot

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