WOLLEGA UNIVERSITY
College of Engineering and Technology
Data Communication and
Computer Networking
Chapter One
Introduction
Outline
Introduction


Concept of communication
Communication Model
Protocols and Architecture



Protocols
OSI layer
TCP/IP
Data Communication and
Computer Networking
 What is data communication?

Data communications deals with the
transmission of signals in a reliable and efficient
manner.

Exchange of digital information between two
digital devices is data communication
Data Communication and
Computer Networking
 What is networking?
Networking deals with the technology and
architecture of the communications networks
used to interconnect communicating devices.
This field is generally divided into the topics
of local area networks (LANs) and wide area
networks (WANs).
Communication Model
Components of data
communication
 A data communications system has five components
1.Message. The message is the information (data) to be
communicated.
2. Sender. The sender is the device that sends the data
message.
3. Receiver. The receiver is the device that receives the
message.
Cont..
4. Transmission medium. The transmission medium is
the physical path by which a message travels
from sender to receiver.
5. Protocol. A protocol is a set of rules that govern data
communications
Types of data communication
(Data Flow)
1. Simplex
 Unidirectional, as on a one-way street
 Only one of the two devices on a link can transmit;
the other can only receive
Example:
Keyboards and traditional monitors
Cont.….
2. Half-Duplex
Each station can both transmit and receive, but not at the same time.
When one device is sending, the other can only receive, and vice versa
Example:
Walkie-talkies and CB (citizens band) radios
Cont.…
3. Full-Duplex
- Both stations can transmit and receive simultaneously.
- sharing can occur in two ways:
a. the link must contain two physically separated paths, one
for sending and the other for receiving;
b. the capacity of the channel is divided between signals traveling in both
directions.
Example:
Telephone line
Transmission Media
Overview
 Guided - wire
 Unguided - wireless
Characteristics and quality determined by
medium and signal
For guided, the medium is more important
For unguided, the bandwidth produced by
the antenna is more important
Key concerns are data rate and distance
Design Factors
 Bandwidth

Higher bandwidth gives higher data rate
 Transmission impairments

Attenuation
 Interference
 Number of receivers

In guided media more receivers (multi-point)
introduce more attenuation
Guided Transmission Media
 Twisted Pair
 Coaxial cable
 Optical fiber
Twisted Pair
Cont.…..
Twisted Pair - Applications
 Most common medium
 Telephone network

Between house and local exchange (subscriber
loop)
 Within buildings

To private branch exchange (PBX)
 For local area networks (LAN)

10Mbps or 100Mbps
Twisted Pair - Pros and Cons
Pros
 Cheap
 Easy to work with
Cons
 Low data rate
 Short range
Coaxial Cable
Coaxial Cable Applications
 Most versatile medium
 Television distribution

Cable TV
 Long distance telephone transmission


Can carry 10,000 voice calls simultaneously
Being replaced by fiber optic
 Short distance computer systems links
 Local area networks
Optical Fiber
Optical Fiber - Benefits
 Greater capacity

Data rates of hundreds of Gbps
 Smaller size & weight
 Lower attenuation
 Electromagnetic isolation
 Greater repeater spacing
Optical Fiber - Applications
 Long-haul trunks
 Metropolitan trunks
 Rural exchange trunks
 Subscriber loops
 LANs
Transmission Characteristics
of Guided Media
Types of Networks Based On
geographical coverage
 Local-area network (LAN) A network that
connects a relatively small number of
machines in a relatively close geographical
area.
Cont.….
 Metropolitan-area network (MAN) The
communication infrastructures that have been
developed in and around large cities
Cont.…..
 Wide-area network (WAN) A network
that connects two or more local-area
networks over a potentially large geographic
distance
 Often one particular node on a LAN is set up
to serve as a gateway to handle all
communication going between that LAN and
other networks
Types of Networks Based on
physical arrangement
 Bus topology : In this configuration every
computer (node) shares the networks total
bus capacities.
 In this configuration adding more computers
will reduce the access speed on the network.
 Each computer communicates to other
computers on the network independently this
is referred to as PEER-TO-PEER
networking
 All nodes are connected to a single communication
line that carries messages in both directions
Bus topology
How a Bus Peer to Peer
Network Works
 All computers on a network have a distinct
address just like your house does
 a message would be send from one computer
with the address of another computer attached
to the message
 The message is broadcasted to all the
computers on the network until the addressed
PC accepts the message
Advantages of Bus Topology
 Works well for small networks
 Relatively inexpensive to implement
 Easy to add to it
Disadvantages of Bus
Topology
 One of the main problems with this type of
network is that it is not very fault tolerant, a
break or defect in the bus would affect the
whole network
 Management costs can be high
 Potential for congestion with network traffic
Ring Topology
 In Ring topology each node is connected to
the two nearest nodes so the entire network
forms a circle
 Data only travels in one direction on a Ring
network
How Ring Topology works
 A node has information to send to another computer
on the network so it sends the information out on
the network to the PC it is connected to, if the
information is for this PC (the recipients NIC
address is attached to the message, which is like
putting an address on an envelope) then the PC
accepts the data
 Otherwise it passes the information on to the next
PC by repeating the data back out on the line
 This method of repeating the data helps keep the
integrity of the data readable by other computers
Cont.…..
 As it is better to have computers take turns
using the connecting Data cable, Ring
topologies incorporated a system called
Token passing
 In this topology, to transmit on the wire your
computer must have control of the token or
wait for the token to be free
 Larger Token Ring networks use multiple
tokens
Advantages of Ring Topology
 Easier to manage; easier to locate a defective
node or cable problem
 Well-suited for transmitting signals over long
distances on a LAN
 Handles high-volume network traffic
 Enables reliable communication
Disadvantages of Ring
Topology
 Expensive
 Requires more cable and network equipment
at the start
 Not used as widely as bus topology


Fewer equipment options
Fewer options for expansion to high-speed
communication
Star topology
 In a Star topology every node is connected
through a central device such as a Hub,
Switch or Router
 Compared to a Ring or Bus topology a Star
topology requires that more thought be put
into its setup
Star topology
Advantages of Star Topology
 Good option for modern networks
 Low startup costs
 Easy to manage
 Offers opportunities for expansion
 Most popular topology in use; wide variety
of equipment available
Disadvantages of Star
Topology
 Hub is a single point of failure
 Requires more cable than the bus
Tree topology
 Generalization of bus topology with no
closed loops
Advantages of Tree Topology
 It is an extension of Star and bus Topologies,
so in networks where these topologies can't
be implemented individually for reasons
related to scalability, tree topology is the best
alternative.
 Expansion of Network is possible and easy.
Cont.….
 Here, we divide the whole network into
segments (star networks), which can be
easily managed and maintained.
 Error detection and correction is easy.
 Each segment is provided with dedicated
point-to-point wiring to the central hub.
 If one segment is damaged, other segments
are not affected.
Disadvantages of Tree
Topology
 Because of its basic structure, tree topology,
relies heavily on the main bus cable, if it
breaks whole network is crippled.
 As more and more nodes and segments are
added, the maintenance becomes difficult.
 Scalability of the network depends on the
type of cable used.
Protocols and Architecture
 What is layering in Networked
computing?
 Breaks down communication into smaller,
simpler parts.
 The process of breaking up the functions or
tasks of networking into layers reduces
complexity.
Cont.…

Each layer provides a service to the layer
above it in the protocol specification.

Each layer communicates with the same
layer’s software or hardware on other
computers.
Why a layered model?
 Easier to teach communication process.
 Speeds development, changes in one layer
does not affect how the other levels works.
 Standardization across manufactures.
 Allows different hardware and software to
work together.
 Reduces complexity
The OSI Reference Model
The OSI Model
 OSI “ Open Systems Interconnection".
 OSI model was first introduced in 1984 by
the International Organization for
Standardization (ISO).
 Outlines WHAT needs to be done to send
data from one computer to another.
Cont.….
 Protocols stacks handle how data is prepared
for transmittal (to be transmitted)
 In the OSI model, The specification needed
are contained in 7 different layers that
interact with each other.
What is “THE MODEL?”
 Commonly referred to as the OSI reference model.
 The OSI model
 is a theoretical blueprint that helps us understand how data
gets from one user’s computer to another.
 The OSI isn’t a physical model. Rather, it’s a set of guidelines
that application developers can use to create and implement
applications that run on a network.
Cont.….
 It is also a model that helps develop standards so that all of
our hardware and software talks nicely to each other.
 It aids standardization of networking technologies by
providing an organized structure for hardware and software
developers to follow, to insure there products are compatible
with current and future technologies.
7 Layer OSI Model
 Why use a reference model?


Serves as an outline of rules for how protocols can be
used to allow communication between computers.
Each layer has its own function and provides support to
other layers.
 Other reference models are in use.


Most well known is the TCP/IP reference model.
We will compare OSI and TCP/IP models
Cont.….
 As computing requirements increased, the
network modeling had to evolve to meet ever
increasing demands of larger networks and
multiple venders.
 Problems and technology advances also
added to the demands for changes in network
modeling.
What Each Layer Does
Application Layer
Gives end-user applications
access to network resources
Where is it on my computer?
Workstation or Server
Service in MS Windows
Application Layer
 Purpose

User application to network service interface
 Examples



File request from server
E-mail services
etc.
Application Layer Function
 General network access
 Flow control
 Error recovery
Presentation Layer
Presentation Layer
 Purpose

Formats data for exchange between points of
communication

Ex: Between nodes in a network
 Example:

Redirector software

Formats for transmission to the server
Presentation Layer Function
 Protocol conversion
 Data translation
 Encryption
 Character set conversion
 Expansion of graphics command
Session Layer
Allows applications to maintain
an ongoing session
Where is it on my computer?
Workstation and Server
Service (MS)
Windows Client for
NetWare (NetWare)
Session Layer
 Purpose

Oversee a communication session

Establish

Maintain

Terminate
Session Layer Function
 Performs name recognition and related
security
 Synchronization between sender and receiver
 Assignment of time for transmission


Start time
End time etc.
Transport Layer
 Provides reliable data
delivery
 It’s the TCP in TCP/IP
 Receives info from upper
layers and segments it
into packets
 Can provide error
detection and correction
Transport Layer
 Purpose

Repackage proper and efficient delivery of
packages
 Error
free
 In sequence
 Without duplication
Transport Layer Function
 For sending data

Repackage the message to fit into packets


Split long messages
Assemble small messages
 On receiving data


Perform the reverse
Send an acknowledgment to the sender
 Solve packet problems

During transmission and reception
Transport layer
The transport layer is responsible
for the delivery of a message from
one process to another.
Network Layer
 Provides network-wide
addressing and a mechanism
to move packets between
networks (routing)
 Responsibilities:
– Network addressing
– Routing
 Example:
– IP from TCP/IP
Network Layer
 Purpose

Addressing and routing the packets
 Example application at the router

If the packet size is large, splits into small
packets
Network Layer Function
 Address messages
 Address translation from logical to physical

Ex: nganesa ----------> 102.13.345.25
 Routing of data


Based on priority
Best path at the time of transmission
 Congestion control
Network layer
The network layer is responsible for
the delivery of individual packets from
the source host to the destination host.
Network Addresses
 Network-wide addresses
 Used to transfer data across subnets
 Used by routers for packet forwarding
 Example:

IP Address
 Where is it on my computer?

TCP/IP Software
Data Link Layer
Places data and
retrieves it from the
physical layer and
provides error
detection capabilities
Data Link Layer
 Purpose

Manages the flow of data over the physical
media
 Responsible for error-free transmission over
the physical media
 Assures error-free data submission to the
Network Layer
Data Link Layer Function
 Point of origin

Packages data for transmission over physical line
 Receiving end

Packages data for submission to the network layer
 Deals with network transmission protocols

IEEE 802. protocols
Data link layer
The data link layer is responsible for
moving frames from one hop (node) to
the next.
Sub-layers of the Data Link
Layer
 MAC (Media Access Control)


Gives data to the NIC
Controls access to the media through:
 CSMA/CD
Carrier Sense Multiple
Access/Collision Detection
 Token passing
Sub-layers of the Data Link
Layer
 LLC (Logical Link Layer)


Manages the data link interface (or Service
Access Points (SAPs))
Can detect some transmission errors using a
Cyclic Redundancy Check (CRC). If the packet
is bad the LLC will request the sender to resend
that particular packet.
Physical Layer
• Determines the specs
for all physical
components
 Cabling
 Interconnect methods
(topology / devices)
 Data encoding (bits to
waves)
 Electrical properties
• Examples:
 Ethernet (IEEE 802.3)
 Token Ring (IEEE 802.5)
 Wireless (IEEE 802.11b)
Physical Layer
 Purpose

Deals with the transmission of 0s and 1s over the
physical media

Translation of bits into signals
 Example



Pulse duration determination
Transmission synchronization
etc.
Physical Layer Function
 Encode bits into signals

Carry data from the data link higher layers
 Define the interface to the card




Electrical
Mechanical
Functional
Example: Pin count on the connector
Physical layer
The physical layer is responsible
for the movement of individual bits
from one hop (node) to the next.
Physical Layer
 What are the Physical Layer components on my computer?
 NIC



Network Interface Card
Has a unique 12 character Hexadecimal number permanently burned
into it at the manufacturer.
The number is the MAC Address/Physical address of a computer
 Cabling



Twister Pair
Fiber Optic
Coax Cable
How Does It All Work
Together

Each layer contains a Protocol Data
Unit (PDU)
 PDU’s are used for peer-to-peer
contact between corresponding
layers.
 Data is handled by the top three
layers, then Segmented by the
Transport layer.
 The Network layer places it into
packets and the Data Link frames
the packets for transmission.
 Physical layer converts it to bits and
sends it out over the media.
 The receiving computer reverses
the process using the information
contained in the PDU.
Protocols at each layer
 7.) Application
 6.) Presentation
 5.) Session
 4.) Transport
 3.) Network
 2.) Data Link
 1.) Physical
Protocols at each layer
Protocols at the application
layer
 HTTP:

browser and web server communication
 FTP :

file transfer protocol
 POP3: Retrieve email

POP3 is designed to delete mail on the server as soon as the user has
downloaded it
 SMTP (simple message transfer protocol )
Protocols at the transport layer
 Transmission
control protocol (TCP),
 Connection oriented
 Connection established before sending data
 Reliable
 user
datagram protocol (UDP)
 Connectionless
 Sending data without establishing connection
 Fast but unreliable
Protocol at the network layer
 IP


Path selection ,
routing and addressing
 ICMP (Internet Control Message Protocol )

sends error messages relying on IP
a requested service is not available
 a host or router could not be reached

Protocols at the Datalink layer
 Ethernet

Uses CSMA/CD (Carrier sense Multiple access
with collision detection)
 Token Ring
Ethernet Cabling
 Ethernet cabling is an important discussion,
especially if you are planning on taking the
Cisco exams.
 Three types of Ethernet cabing are available:



Straight-through cable
Crossover cable
Rolled Cable
Straight Through
 The straight-through cable is used to connect
 Host to switch or hub
 Router to switch or hub
Straight Through
 Straight Through

All order of the wirings is the same as the other
side.
1→8
1 2345 678
1 2345 678
Crossover Cable
 The crossover cable can be used to connect
 Switch to switch
 Hub to hub
Host to host
Crossover Cable
Crossover Cable
 Crossover

We need to change the order of the transmission and
receiving wirings.
1 2345 678
1 2345 678
1→8
Rolled Cable
 Although rolled cable isn’t used to
connect any Ethernet connections
together, you can use a rolled Ethernet
cable to connect a host to a router
console serial communication (com)
port.
Rolled Cable
How to Wire
Making connections – Tools
 Cat5e cable
 RJ45 connectors
 Cable stripper
 Scissors
 Crimping tool
How to Wire
 RJ45 connector
How to Wire
Making connections – Steps
1. Strip cable end
2. Untwist wire ends
3. Arrange wires
4. Trim wires to size
5. Attach connector
6. Check
7. Crimp
8. Test
How to Wire
Step 1 – Strip cable end
 Avoid cutting into conductor insulation
How to Wire
Step 2 – Untwist wire ends
 Sort wires by insulation colors
How to Wire
 Step 3 – Arrange wires
Verify the order of the wires is correct
How to Wire
 Step 4 – Trim wires to size
Trim all the wires to the same length
Leave about ½” of wires exposed
How to Wire
 Step 5 – Attach connector

Maintain wire order, left-to-right, with RJ45 tab
facing downward
How to Wire
 Step 6 – Check


Do all wires extend to end?
Is sheath well inside connector?
How to Wire
 Step 7 – Crimp
Crimp the RJ45 plug with the crimping tool
How to Wire
 Step 8 – Test
Does the cable work?
What type of cable is used?
What type of cable is used for
each connection?
Thanks
End