Arba Minch University
Arba Minch Institute of Technology
Faculty of Electrical and Computer Engineering
Data communication and computer networks
ECEg- 4211
Arba Minch University
Arba Minch Institute of Technology
Faculty of Electrical and Computer Engineering
Chapter One
Introduction
Data Communications, Data Networks, and the Internet
Introduction
Effective and efficient data communication and networking facilities are
vital to any enterprise.
Three different forces have consistently driven the architecture and
evolution of data communications and networking facilities
• traffic growth at a high & steady rate
• development of new services
• advances in technology
3
A Communications Model
Figure The communication between a workstation and a server over a public telephone network. 4
A Communications Model
Source
– generates data to be transmitted
Transmitter
– Converts data into transmittable signals
Transmission System
– Carries data
Receiver
– Converts received signal into data
Destination
– Takes incoming data
5
Communications Tasks
Transmission system utilization Addressing
Interfacing Routing
Signal generation Recovery
Synchronization Message formatting
Error detection and correction Security
Flow control Network management
6
Networking
Point-to-point communication not usually practical
– Devices are too far apart
– Large set of devices would need impractical number of
connections
The solution is a communications network
7
Two broad categories of communications networks:
– Local Area Network (LAN)
– Wide Area Network (WAN)
8
Wide Area Networks (WANs)
span a large geographical area (states, countries,
continents).
consists of a number of interconnected switching
nodes
WANs have been implemented using one of two
technologies:
Circuit switching
Packet switching
More recently, Frame relay and Asynchronous Transfer
Mode (ATM ) networks have assumed major roles
9
Circuit Switching
uses a dedicated communications path established for the
duration of the conversation
comprising a connected sequence of links
with a dedicated logical channel
eg. telephone network
10
Packet Switching
data is sent in a sequence of small chunks, called packets
packets passed from node to node between the source and
destination
used for terminal-to-computer and computer-to-computer
communications
11
Frame Relay
packet switching systems have large overheads to
compensate for errors
modern systems are more reliable
errors can be caught in end system
Frame Relay provides higher speeds
with most error control overhead removed
12
Asynchronous Transfer Mode
ATM - evolution of frame relay
fixed packet (called cell) length
with little overhead for error control
anything from 10Mbps to Gbps
constant data rate using packet switching technique with
multiple virtual circuits
13
Local Area Networks
designed for small physical areas (smaller scope)
building or small campus
usually owned by same organization as attached devices
LANs come in a number of different configurations
switched LANs, eg Ethernet
wireless LANs
14
LAN Topologies
15
Metropolitan Area Networks
MAN
middle ground between LAN and WAN
private or public network
high speed
large area – city or metro
16
The Internet
Internet evolved from ARPANET
developed by the Advanced Research Projects Agency
(ARPA) of the U.S. Department of Defense
first operational packet-switching network
applied to tactical radio communication (packet radio)
& satellite communication (SATNET).
had a need for interoperability
led to standardized TCP/IP protocols
17
Internet Elements
18
Example Configuration
19
The Need for a Protocol Architecture
Protocol architecture is a layered structure of hardware and
software that supports the exchange of data ben systems and
supports distributed applications
When computers, terminals and/or other data processing
devices exchange data:
– The Procedures involved to exchange data between devices can
be complex
– High degree of cooperation required between communicating
systems
See the example in the next slide.
20
Example: File transfer b/n two computers
Requires a data path to exist (either a direct link or via a comm.
network)
Tasks:
– The source system must either activate the data communication path or inform the
communication network of the identity of the desired destination system
– Source determines that destination is ready
– The file transfer app at the source must ascertain that the destination file management app
is ready to accept and store files for user
– File format conversion
Instead of implementing the logic as a single module, the task is broken up
into subtasks, each of which is implemented separately.
21
Layered Protocol Architecture
Modules arranged in a vertical stack
Each layer in the stack:
– Provides functions needed to perform communications for layers above
– using functions provided by layers below
– The peer layers communicate by means of formatted blocks of data that
obey a set of rules or conventions known as a protocol.
Ideally, layers should be defined, so that changes in one layer do not
require changes in other layers.
modularization eases maintenance, updating of system
22
Key Features of a Protocol
A protocol is a set of rules or conventions that allow peer layers to
communicate.
The key features of a protocol are:
– Syntax: concerns the format of the data blocks
– Semantics: Includes control information (coordination, error handling)
– Timing: speed matching, sequencing
23
TCP/IP Protocol Architecture
developed by US Defense Advanced Research Project Agency
(DARPA)
for ARPANET packet-switched network
used by the global Internet
generally referred to as the TCP/IP protocol suite
protocol suite comprises a large collection of standardized
protocols
24
TCP/IP Layers
Application
Transport
Internet
Network access /data link layer
Physical
The TCP/IP Layers and
Example Protocols
25
Physical Layer
concerned with the physical interface between a data transmission
device (e.g., workstation, computer) and a transmission medium or
network
concerned with specifying:
– characteristics of the transmission medium
– signal levels
– data rates
– other related matters
26
Network Access / data link Layer
concerned with the exchange of data b/n an end system and the
network to which it is attached.
concerned with issues like :
– destination address provision
– invoking specific services like priority
– access to & routing data across a network for two end systems
attached to the same network
27
Internet Layer
routing functions across multiple networks
for systems attached to different networks
The Internet Protocol (IP) is used at this layer to provide the
routing function across multiple networks
implemented in end systems and routers
Router is a processor that connects two networks and whose primary
function is to relay data from one network to the other on its route from
the source to the destination end system.
28
Transport Layer (TCP)
common layer shared by all applications
provides reliable delivery of data
in same order as sent
commonly uses Transmission Control Protocol (TCP)
29
Application Layer
provide support for user applications
need a separate module for each type of application
30
Operation of TCP and IP
31
Addressing Requirements
two levels of addressing required
each host on a subnet needs a unique global network
address
its IP address
each application on a (multi-tasking) host needs a unique
address within the host
known as a port
32
Operation of TCP/IP
The addition of control information to data is referred to as encapsulation
The combination of data from the next higher layer and control information is
known as a protocol data unit (PDU)
33
Transmission Control Protocol (TCP)
usual transport layer is (TCP)
provides a reliable connection for the transfer of data
between applications
a TCP segment is the basic protocol unit
TCP tracks segments between entities for duration of each
connection
34
User Datagram Protocol (UDP)
an alternative to TCP
no guaranteed delivery
no preservation of sequence
no protection against duplication
minimum overhead
adds port addressing to IP
35
TCP/IP Applications
have a number of standard TCP/IP applications such as
Simple Mail Transfer Protocol (SMTP)
File Transfer Protocol (FTP)
Telnet
36
Some TCP/IP Protocols
37
OSI Reference Model
Open Systems Interconnection
Reference model
• provides a general framework for standardization
• defines a set of layers and services provided by each
layer
• one or more protocols can be developed for each
layer
developed by the International Organization for
Standardization (ISO)
38
A layered model
Seven layers – seven has been presented as the
optimal number of layer
Theoretical system too late (published in 1984)!
by that time TCP/IP started to become the de facto
standard
39
Layer 1: Physical Layer
• The physical layer is responsible for transmitting raw
data bits over a physical medium.
• It deals with the electrical, mechanical, and functional
aspects of the network interface.
40
Layer 2: Data Link Layer
• The data link layer provides error detection and correction
as well as framing and flow control mechanisms.
• It ensures reliable point-to-point and point-to-multipoint
communication over a network.
• Basic function
Breaks up input data to data frames
Transmits data frames sequentially
Processes acknowledgement frames sent back from
receiver for reliable transmission
41
Layer 3: Network Layer
• The network layer handles routing and forwarding of data
packets between different networks.
• It determines the best path for data transmission and
addresses issues related to logical addressing and network
topology
42
Layer 4: Transport Layer
• The transport layer ensures end-to-end communication
between devices by segmenting and reassembling data
streams.
• It also provides error recovery, flow control, and
multiplexing capabilities.
43
Layer 5: Session layer
• The session layer establishes, maintains, and terminates
connections between applications.
• It manages the session between two communicating devices and
handles synchronization and dialogue control.
• Dialog control
• Allows two systems to enter into dialog
• It allows the communication between two processes to take place in
either half-duplex or full-duplex.
• Synchronization
• It allows a process to add checkpoints into a stream of data
• So that if a failure of some sort occurs between checkpoints, the
layer can retransmit all data since the last checkpoint. 44
Layer 6: Presentation layer
• Concerned with the syntax and semantics of the information exchanged
between two systems
• Functions
Translation
At the sender it changes the information from its sender –
dependent format into common format.
At receiving, changes the common format into its receiver-
dependent format eg, ASCII to Unicode, Unicode to ASCII
Encryption
To ensure privacy and security
Compression
Data compression reduces the number of bits contained in the
information.
It is important in the transmission of multimedia such as audio or
video 45
Layer 7: Application Layer
• Provides interface and support for services to users
(human, software, robots)
• Examples
• File transfer
• Email
46
OSI Layers
47
OSI v TCP/IP
48
