Scribes for Lecture-1

CS625:Advanced Computer Networks

Prepared by : G Rajesh (Y3111016)


It is an exchange of thoughts, messages, information, speech, signals, writing or behaviour. Requirements for a proper communication are medium+energy, protocol. Some of the design goals/criterion for communication are as follows:

  1. Availability of communication system

  2. Reliablility

  3. Scalability

  4. Security

    a. authenticity

    b. integrity

  5. Efficiency

    a. bandwidth

    b. speed

    c. energy

    d. cost

    e. spectral efficiency (in case of wireless networks)

2.Communication Networks

The various modes of communication are as follows:

  1. Before electronic age

    a. doves/pigeons

    b. postal system

  2. Telegraphy

  3. Telephone networks

  4. Internet

  5. Cellular/wireless networks

Internetworking is a concept of connecting different networks.

3.History of Internet

1961-62 : Packet-switching theory was introduced in the internet.

1969 : Host computers on ARPANET were connected to other nodes.

1972 : Email application was launched.

The host-to-host protocol called Network Control Protocol (NCP) was

completely implemented.

Mid 70's : The U.S. Department of Energy(DoE) established MFENet for its researchers

in Magnetic Fusion Energy.

80's : Formation of other major networks like NSFNET, USENET, etc.

1985-95 : Privatisation of NSFNET. The Backbone had then grown from six nodes with

56 kbps links to 21 nodes with multiple 45 Mbps links the Backbone had grown

from six nodes with 56 kbps links to 21 nodes with multiple 45 Mbps links.

4.Design Goals of Internet

4.1.Primary Goal

“To develop an effective technique for multiplexed utilization of interconnected networks.”

Each network may be of a different type. Hence, Gateways ( a layer of internet packet switches ) are used to interconnect the networks. These perform the necessary conversions ( if any ).

Other souces of variablility in the design are addressing, MTU ( maximum transfer unit ), delivery guarentees, delay/bandwidth, routing.

4.2.Other Goals

  1. Communication in the presence of failure.

It means that if two entities are communicating over the Internet, and some failure causes the Internet to be temporarily disrupted and reconfigured to reconstitute the service, then the entities communicating should be able to continue without having to reestablish or reset the high level state of their conversation.

  1. Multiple types of Service

It is required that the Internet architecture should support, at the transport service level, a variety of types of service. Usually the requirements differ in terms of speed, latency and reliablility. In general, there are two classes of applications : a) those which requires low bandwidth but low delay in delivery. Eg: remote login. b) those which are less concerned with delay but very concerned with thoughput. Eg: file transfer.

Such a goal caused TCP & IP to evolve as two layers. TCP provided the reliable sequenced data stream, while IP provided a basic building block called datagram.

  1. Accomodation of different networks.

  2. Distributed Management.

Individual networks (that constitute Internet) are managed and maintained by different organizations, each operating a subset of gateways. Hence, there is no centralized management of the Internet.

  1. Cost Effectiveness.

Internet architecture does not produce as cost effective a utilization of expensive communication resources as a more tailored architecture would. Internet packets are fairly long, and if short packets are sent the overhead is quite apparent. On the other hand, large packets for file transer have a very minute overhead.

  1. Dynamic host attachment & removal.

The host's connected to an individual network ( i.e. part of internet ) can be dynamically added or removed which makes Internet more scalable.

  1. Resource Acccounting.

It is a desirable goal when designing any kind of network. This gives the accounting details of the usage of resources by different host's connected in the network.

It is easy to achieve in the case of cellular networks, etc. where the underlying theory is circuit switching. Since, Internet architecture is built over packet switching, it has been difficult to achieve this goal.


It is a structuring technique which lets us to view the network as a succession of layers.


  1. Handles heterogenity

  2. Software reuse

  3. Modularity (i.e. Multiplicity of layers and independence among themselves)

  4. Extensibility

  5. New Technologies are allowed

6.Internet Service Semantics

  1. Best-effort : packet-switching datagram service.

  2. Packets may be a) dropped b) duplicated c)reordered.

  3. Packets cannot be created.