Data Communication Network Topology, Lecture notes of Data Communication Systems and Computer Networks

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Computer Communication &

Networks

Lecture 2

Introduction to Data Communication

Source Reference – Engr. Waleed Ejaz (University of Engineering and Technology – Taxila)

Data Communications  The term telecommunication means communication at a distance. The word data refers to information presented in whatever form is agreed upon by the parties creating and using the data. Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable.

Five Components of Data Communication

1. Message
2. Sender
3. Receiver
4. Medium
5. Protocol

Direction of data flow

Simplex

Half Duplex

Full Duplex

Terminology  The throughput or bandwidth of a channel is the number of bits it can transfer per second  The latency or delay of a channel is the time that elapses between sending information and the earliest possible reception of it

Network topologies  Topology defines the way hosts are connected to the network

Bandwidth and Latency

1. telecommunications: range of radio frequencies: a range of radio frequencies used in radio or telecommunications transmission and reception 2. computing: communications capacity: the capacity of a communications channel, for example, a connection to the Internet, often measured in bits per second 3. a data transmission rate ; the maximum amount of information (bits/second) that can be transmitted along a channel

Latency

A synonym for delay, is an expression of how much time it takes for transmission from one designated point to another

Bandwidth

Categories of Topology

A hybrid topology: a star backbone with three bus networks

Hierarchical organization of the Internet

What’s a protocol?

human protocols:

 “what’s the time?”

 “I have a question”

 introductions

… specific msgs sent

… specific actions taken when msgs received, or other events

network protocols:

 machines rather than humans

 all communication activity in Internet governed by protocols

Protocol  protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt

a human protocol and a computer network protocol:

Hi Hi Got the time? 2: TCP connection req. TCP connection reply. Get http://gaia.cs.umass.edu/index.htm time

Layered Tasks An example from the everyday life

Hierarchy?

Services

Why layered communication?  To reduce complexity of communication task by splitting it into several layered small tasks  Functionality of the layers can be changed as long as the service provided to the layer above stays unchanged  makes easier maintenance & updating  Each layer has its own task  Each layer has its own protocol