4. 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
5. 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).
7. 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.
8. 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
9. 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
10. 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
11. 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
12. 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
13. 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
17. 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
18. Twisted Pair - Pros and Cons
Pros
Cheap
Easy to work with
Cons
Low data rate
Short range
20. 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
25. 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.
27. 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
28. 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
30. 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
31. Advantages of Bus Topology
Works well for small networks
Relatively inexpensive to implement
Easy to add to it
32. 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
33. 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
34. 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
35. 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
36. 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
37. 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
38. 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
40. 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
43. 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.
44. 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.
45. 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.
46. 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.
47. 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.
48. 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
50. 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.
51. 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.
52. 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.
53. 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.
54. 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
55. 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.
61. 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
62. Presentation Layer Function
Protocol conversion
Data translation
Encryption
Character set conversion
Expansion of graphics command
63. 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)
65. Session Layer Function
Performs name recognition and related
security
Synchronization between sender and receiver
Assignment of time for transmission
Start time
End time etc.
66. 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
67. Transport Layer
Purpose
Repackage proper and efficient delivery of
packages
Error free
In sequence
Without duplication
68. 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
70. Network Layer
Provides network-wide
addressing and a mechanism
to move packets between
networks (routing)
Responsibilities:
– Network addressing
– Routing
Example:
– IP from TCP/IP
71. Network Layer
Purpose
Addressing and routing the packets
Example application at the router
If the packet size is large, splits into small
packets
72. 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
73. Network layer
The network layer is responsible for
the delivery of individual packets from
the source host to the destination host.
74. 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
75. Data Link Layer
Places data and
retrieves it from the
physical layer and
provides error
detection capabilities
76. 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
77. 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
78. Data link layer
The data link layer is responsible for
moving frames from one hop (node) to
the next.
79. 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
80. 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.
81. 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)
82. 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.
83. 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
84. Physical layer
The physical layer is responsible
for the movement of individual bits
from one hop (node) to the next.
85. 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
86. 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.
87. Protocols at each layer
7.) Application
6.) Presentation
5.) Session
4.) Transport
3.) Network
2.) Data Link
1.) Physical
89. 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 )
90. 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
91. 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
92. Protocols at the Datalink layer
Ethernet
Uses CSMA/CD (Carrier sense Multiple access
with collision detection)
Token Ring
93. 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
94. Straight Through
The straight-through cable is used to connect
Host to switch or hub
Router to switch or hub
95. Straight Through
Straight Through
All order of the wirings is the same as the other
side.
1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8
1→8
96. Crossover Cable
The crossover cable can be used to connect
Switch to switch
Hub to hub
Host to host
98. Crossover Cable
Crossover
We need to change the order of the transmission and
receiving wirings.
1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1→8
99. 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.
103. 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
104. How to Wire
Step 1 – Strip cable end
Avoid cutting into conductor insulation
105. How to Wire
Step 2 – Untwist wire ends
Sort wires by insulation colors
106. How to Wire
Step 3 – Arrange wires
Verify the order of the wires is correct
107. How to Wire
Step 4 – Trim wires to size
Trim all the wires to the same length
Leave about ½” of wires exposed
108. How to Wire
Step 5 – Attach connector
Maintain wire order, left-to-right, with RJ45 tab
facing downward
109. How to Wire
Step 6 – Check
Do all wires extend to end?
Is sheath well inside connector?
110. How to Wire
Step 7 – Crimp
Crimp the RJ45 plug with the crimping tool