Computer Networks

Computer Networks
RIDA ZAMAN
2K15-CSE-69
1
CREATED
BY
RIDA
ZAMAN

TOPICS COVERED IN THIS PRESENTATION
ARE:
1. DATA COMMUNICATION
2. COMMUNICATION MODEL
3. DATA COMMUNICATION MODEL
4. OSI REFERENCE MODEL
5. TCP/IP PROTOCOL
6. ADDRESSING
7. LAN AND WAN
8. NETWORK TOPOLOGIES
9. TRANSMISSION MEDIUM
10. COMMUNICATION
11. SWITICHING TECHNOLOGIES
12. ROUTING
13. SUBNETTING
2
CREATED BY RIDA ZAMAN
TOTAL
NUMBER OF
SLIDES ARE:
115

1.DATA COMMUNICATION
3
CREATED
BY
RIDA
ZAMAN

DATA COMMUNICATION
 Data communication is
the transfer of data or
information between two
devices via some form of
transmission medium.
4
Device A Device B
DATA

2.COMMUNICATION MODEL
5
CREATED
BY
RIDA
ZAMAN

COMMUNICATION MODEL
The basic purpose of communication model is the exchange of data between two parties.
The components in the communication model are :
1. Source
2. Transmitter
3. Transmission system
4. Destination
5. Receiver
6

COMMUNICATION MODEL
7
source
Transmission
system Receiver Destination
Transmitter
The device
generates data to be
transmitted
Encodes the data in such a way to
produce signals that can be
transmitted across some sort of
transmission sys in to signal
Transmission line to
connect source and
destination
It accepts the signal
and convert in to the
form that is accepted
by destination
It accepts the signal and
convert in to the form
that is accepted by
destination

3.DATA COMMUNICATION MODEL
8
CREATED
BY
RIDA
ZAMAN

DATA COMMUNICATION MODEL
9
source
Transmission
system Receiver Destination
Transmitter
Digital Bit
Stream
Analog
Signal
Analog
Signal
Digital Bit
Stream
Text

4.OSI REFERENCE MODEL
10
CREATED
BY
RIDA
ZAMAN

THE OSI REFERENCE MODEL
 Established in 1947, the International Standards Organization
(ISO) is a multinational body dedicated to worldwide agreement
on international standards. Almost three-fourths of countries in
the world are represented in the ISO. An ISO standard that
covers all aspects of network communications is the Open
Systems Interconnection (OSI) model. It was first introduced in
the late 1970s.
11

TOPIC DISCUSSED IN THIS SECTION
Layered Architecture
Layer-to-layer Communication
Encapsulation
Layers in the OSI Model
Summary of OSI Layers
12

 ISO is the organization;
 OSI is the model.
Note
13

THE OSI MODEL
14

OSI LAYERS
15

AN EXCHANGE USING THE OSI MODEL
16

17
 The physical layer is responsible for
moving individual bits from one
 (node) to the next.
Note

SUMMARY OF OSI REFERENCE MODEL
18

5.TCP/IP PROTOCOL
19
CREATED
BY
RIDA
ZAMAN

TCP/IP PROTOTCOL SUITE
 The TCP/IP protocol suite was developed prior to the OSI model.
Therefore, the layers in the TCP/IP protocol suite do not match
exactly with those in the OSI model. The original TCP/IP protocol
suite was defined as four software layers built upon the hardware.
Today, however, TCP/IP is thought of as a five-layer model with the
layers named similarly to the ones in the OSI model. Figure 2.7
shows both configurations.
20

TOPIC DISCUSSED IN THE SECTION
Comparison between OSI and TCP/IP
Layers in the TCP/IP Suite
21

LAYERS IN THE TCP/IP PROTOCOL SUITE
22

TCP/IP AND OSI MODEL
23

A PRIVATE INTERNET
24

COMMUNICATION AT THE PHYSICAL
LAYER
25
A
Physical
layer
Physical
layer
R1 R3 R4 B
Source Destination
Legend
011 ... 101
0
1
1
.
.
.
1
0
1
011 ... 101
Link 3 Link 5 Link 6
Link 1

26
 The unit of communication at the
physical layer is a bit.
Note

COMMUNICATION AT THE DATA LINK
LAYER
27
A
Physical Physical
Data link
Data link
R1 R3 R4 B
Source Destination Data
D Header
H
Legend
Link 1 Link 3 Link 5 Link 6
Frame
D2 H2
F
r
a
m
e
D
2
H
2
Frame
D2 H2
Frame
D2 H2

28
 The unit of communication at the data
link layer is a frame.
Note

COMMUNICATION AT THE NETWORK
LAYER
29
A
Physical Physical
Data link
Data link
R1 R3 R4 B
Network
Network
D Header
H
Legend

30
network layer is a datagram.
Note

COMMUNICATION AT TRASPORT LAYER
31
A
Physical Physical
Data link
Data link
R1 R3 R4
B
Network
Network
Transport Transport
D Header
H
Legend

32
transport layer is a segment, user
datagram, or a packet, depending on
the specific protocol used in this layer.
Note

COMMUNICATION AT APPLICATION LAYER
33
A
Physical Physical
Data link
Data link
R1 R3 R4
B
Network
Network
Transport Transport
Application
Application Source Destination Data
D Header
H
Legend
Message
D5 D5
D5

34
application layer is a message.
Note

6.ADDRESSING
35
CREATED
BY
RIDA
ZAMAN

ADDRESSING
36
 Four levels of addresses are used in an internet
employing the TCP/IP protocols: physical address,
logical address, port address, and application-
specific address. Each address is related to a one
layer in the TCP/IP architecture, as shown in
Figure 2.15.

TOPIC DISCUSSED IN THE SECTION
37
 Physical Addresses
 Logical Addresses
 Port Addresses
 Application-Specific Addresses

ADDRESSES IN THE TCP/IP PROTOCOL SUIT
38

PHYSICAL ADDRESS
39
Data
87 10
1 packet
accepted
Data
87 10
4

EXAMPLE IN PREVIOUS FIG:
40
 In Previous fig a node with physical address 10 sends a frame to a node with physical
address 87. The two nodes are connected by a link (a LAN). At the data link layer, this frame
contains physical (link) addresses in the header. These are the only addresses needed. The
rest of the header contains other information needed at this level. As the figure shows, the
computer with physical address 10 is the sender, and the computer with physical address 87
is the receiver. The data link layer at the sender receives data from an upper layer. It
encapsulates the data in a frame. The frame is propagated through the LAN. Each station
with a physical address other than 87 drops the frame because the destination address in
the frame does not match its own physical address. The intended destination computer,
however, finds a match between the destination address in the frame and its own physical
address.

41
Data
A P
20 10 Data
A P
20 10
Physical
addresses
changed
Data
A P
33 99
Data
A P
33 99
Physical
addresses
changed
Data
A P
95 66 Data
A P
95 66
LOGICAL ADDRESS

EXAMPLE OF PREVIOUS FIG
42
 Previous Figure shows a part of an internet with two routers connecting three LANs.
Each device (computer or router) has a pair of addresses (logical and physical) for
each connection. In this case, each computer is connected to only one link and
therefore has only one pair of addresses. Each router, however, is connected to three
networks. So each router has three pairs of addresses, one for each connection.
Although it may be obvious that each router must have a separate physical address
for each connection, it may not be obvious why it needs a logical address for each
connection. We discuss these issues in Chapters 11 and 12 when we discuss routing.
The computer with logical address A and physical address 10 needs to send a packet
to the computer with logical address P and physical address 95. We use letters to
show the logical addresses and numbers for physical addresses, but note that both
are actually numbers, as we will see in later chapters.

43
 The physical addresses will change
from hop to hop, but the logical
addresses remain the same.
Note

44
A Sender Receiver P
Internet
a Data
j
A P
H2
a Data
j
A P
a Data
j
Data
a Data
j
A P
H2
a Data
j
A P
a Data
j
Data
PORT NUMBER

EXAMPLE OF PREVIOUS SLIDE
45
 Previous Figure shows two computers communicating via the
Internet. The sending computer is running three processes at this
time with port addresses a, b, and c. The receiving computer is
running two processes at this time with port addresses j and k.
Process a in the sending computer needs to communicate with
process j in the receiving computer. Note that although both
computers are using the same application, FTP, for example, the
port addresses are different because one is a client program and
the other is a server program, as we will see in Chapter 17.

46
 The physical addresses change from
hop to hop, but the logical and port
addresses usually remain the same.
Note

7.LAN AND WAN
47
CREATED
BY
RIDA
ZAMAN

LOCAL AREA NETWORK
48
Switch
PC PC PC
Printer
PC
?

WIDE AREA NETWORK
49
leased lines from a larger provider
form part of the WAN
Some type of “shared” media

8.NETWORK TOPOLOGIES
50
CREATED
BY
RIDA
ZAMAN

NETWORK TOPOLOGIES
51
The physical topology of a network refers to the
configuration of cables, computers, and other peripherals.
There are several basic network topologies:
1. STAR
2. BUSS
3. RING
4. TREE

BUSS TOPOLOGY
52
Bus Topology
Each node is connected one after the other
(like christmas lights)
Nodes communicate with each other along the
same path called the backbone

RING TOPOLOGY
53
 The ring network is like a bus network, but the “end” of
the network is connected to the first node
 Nodes in the network use tokens to communicate with
each other
Backbone

STAR TOPOLOGY
54
 Each node is connected to a device in the center of
the network called a hub
 The hub simply passes the signal arriving from any
node to the other nodes in the network
 The hub does not route the data
Hub

BRANCH TREE TOPOLOGY
55
 Tree topology allows for the expansion
of an existing network

MESH TOPOLOGY
56
 The mesh topology connects all
devices (nodes) to each other for
redundancy and fault tolerance.
 It is used in WANs to interconnect
LANs and for mission critical networks
like those used by banks and financial
institutions.
 Implementing the mesh topology is
expensive and difficult.

NETWORKING DEVICES
57
HUB, Switches, Routers, Wireless Access Points, Modems etc.

9.TRANSMISSION MEDIUM
58
CREATED
BY
RIDA
ZAMAN

TRANSMISSION MEDIA
 Two main categories:
 Guided ― wires, cables
 Unguided ― wireless transmission, e.g. radio, microwave,
infrared, sound, sonar
 We will concentrate on guided media here:
 Twisted-Pair cables:
 Unshielded Twisted-Pair (UTP) cables
 Shielded Twisted-Pair (STP) cables
 Coaxial cables
 Fiber-optic cables
59

TWISTED-PAIR CABLES
 If the pair of wires are not twisted, electromagnetic noises from, e.g.,
motors, will affect the closer wire more than the further one, thereby
causing errors
60

UNSHIELDED TWISTED-PAIR (UTP)
 Typically wrapped inside a plastic cover (for mechanical protection)
 A sample UTP cable with 5 unshielded twisted pairs of wires
61
Metal
Insulator

SHIELDED TWISTED-PAIR (STP)
 STP cables are similar to UTP cables, except there is a metal foil or
braided-metal-mesh cover that encases each pair of insulated wires
62

CATEGORIES OF UTP CABLES
EIA classifies UTP cables according to the quality:
 Category 1 ― the lowest quality, only good for voice, mainly found in very old buildings,
not recommended now
 Category 2 ― good for voice and low data rates (up to 4Mbps for low-speed token ring
networks)
 Category 3 ― at least 3 twists per foot, for up to 10 Mbps (common in phone networks in
residential buildings)
 Category 4 ― up to 16 Mbps (mainly for token rings)
 Category 5 (or 5e) ― up to 100 Mbps (common for networks targeted for high-speed data
communications)
 Category 6 ― more twists than Cat 5, up to 1 Gbps
63

COAXIAL CABLES
 In general, coaxial cables, or coax, carry signals of higher freq (100KHz–
500MHz) than UTP cables
 Outer metallic wrapping serves both as a shield against noise and as the
second conductor that completes the circuit
64

FIBER-OPTIC CABLES
 Light travels at 3108 ms-1 in free space and is the fastest possible speed in the Universe
 Light slows down in denser media, e.g. glass
 Refraction occurs at interface, with light bending away from the normal when it enters a less
dense medium
 Beyond the critical angle  total internal reflection
65

 An optical fiber consists of a core (denser material) and a cladding (less dense material)
 Simplest one is a multimode step-index optical fiber
 Multimode = multiple paths, whereas step-index = refractive index follows a step-function profile
(i.e. an abrupt change of refractive index between the core and the cladding)
 Light bounces back and forth along the core
 Common light sources: LEDs and lasers
66
CORE CLADDING

10.COMMUNICATION
67
CREATED
BY
RIDA
ZAMAN

DATA COMMUNICATION CHANNELS
 The following is a discussion on the THREE main types of
transmission circuits (channels), simplex, half duplex and full
duplex.
1. Simplex
2. Half Duplex
3. Full Duplex
68

SIMPLEX
Data in a simplex channel is always one way. Simplex channels are not often used because it is not
possible to send back error or control signals to the transmit end. An example of a simplex channel
in a computer system is the interface between the keyboard and the computer, in that key codes
need only be sent one way from the keyboard to the computer system
69

HALF DUPLEX
A half duplex channel can send and receive, but not at the same time. Its like a one-lane
bridge where two way traffic must give way in order to cross. Only one end transmits at a
time, the other end receives.
70

FULL DUPLEX
Data can travel in both directions simultaneously. There is no need to switch from transmit
to receive mode like in half duplex. Its like a two lane bridge on a two-lane highway.
71

11. SWITICHING TECHNOLOGIES
72
CREATED
BY
RIDA
ZAMAN

SIMPLE SWITCHING NETWORK
73

SWITCHING NODES
 Nodes may connect to other nodes, or to some stations.
 Network is usually partially connected
 However, some redundant connections are desirable for reliability
Two different switching technologies
 Circuit switching
 Packet switching
74

CIRCUIT SWITCHING
 Circuit switching:
 There is a dedicated communication path between two stations (end-to-end)
 The path is a connected sequence of links between network nodes. On each physical link, a
logical channel is dedicated to the connection.
 Communication via circuit switching has three phases:
 Circuit establishment (link by link)
 Routing & resource allocation (FDM or TDM)
 Data transfer
 Circuit disconnect
 Dellocate the dedicated resources
 The switches must know how to find the route to the destination and how to
allocate bandwidth (channel) to establish a connection.
75

PUBLIC CIRCUIT SWITCHED NETWORK
 Subscribers: the devices that attach to the
network.
 Subscriber loop: the link between the subscriber
and the network.
 Exchanges: the switching centers in the network.
 End office: the switching center that directly
supports subscribers.
 Trunks: the branches between exchanges. They
carry multiple voice-frequency circuits using
either FDM or synchronous TDM.
76

PROBLEM OF CIRCUIT SWITCHING
 designed for voice service
 Resources dedicated to a particular call
 For data transmission, much of the time the connection is idle (say, web
browsing)
 Data rate is fixed
 Both ends must operate at the same rate during the entire period of connection
 Packet switching is designed to address these problems.
77

PACKET SWITCHING
 Data are transmitted in short packets
 Typically at the order of 1000 bytes
 Longer messages are split into series of packets
 Each packet contains a portion of user data plus some control info
 Control info contains at least
 Routing (addressing) info, so as to be routed to the intended destination
 Recall the content of an IP header!
 store and forward
 On each switching node, packets are received, stored briefly (buffered) and passed on to the next
node.
78

USE OF PACKETS
79

ADVANTAGES OF PACKET SWITCHING
 Line efficiency
 Single node-to-node link can be dynamically shared by many packets over time
 Packets are queued up and transmitted as fast as possible
 Data rate conversion
 Each station connects to the local node at its own speed
 In circuit-switching, a connection could be blocked if there lacks free resources. On a
packet-switching network, even with heavy traffic, packets are still accepted, by delivery
delay increases.
 Priorities can be used
 On each node, packets with higher priority can be forwarded first. They will experience less delay
than lower-priority packets.
80

PACKET SWITCHING TECHNIQUE
Two approaches
1. Datagram approach
2. Virtual circuit approach
81

DATAGRAM
 Each packet is treated independently, with no reference
to packets that have gone before.
 Each node chooses the next node on a packet’s path.
 Packets can take any possible route.
 Packets may arrive at the receiver out of order.
 Packets may go missing.
 It is up to the receiver to re-order packets and recover
from missing packets.
 Example: Internet
82

VIRTUAL CIRCUIT
 In virtual circuit, a preplanned route is established before any
packets are sent, then all packets follow the same route.
 Each packet contains a virtual circuit identifier instead of
destination address, and each node on the pre stablished route
knows where to forward such packets.
 The node need not make a routing decision for each packet.
 Example: X.25, Frame Relay, ATM
83

VIRTUAL CIRCUIT
 A route between stations is set
up prior to data transfer.
 All the data packets then follow
the same route.
 But there is no dedicated
resources reserved for the
virtual circuit! Packets need to
be stored-and-forwarded.
84

12. ROUTING
85
CREATED
BY
RIDA
ZAMAN

ROUTING
 Way to travel
 Find the best route on the basis of following parameter
1. Distance
2. Time
3. Frequency
4. Traffic Evaluation
It is responsibility of routing data algorithm to travel data efficiently and
without any lost
86

TYPES OF ROUTING
1. Random Routing
2. Adaptive Routing
3. Static Routing
4. Alternate Routing
5. Dynamic Routing
87

RANDOM ROUTING
88
E
D
C
B
A
F
1
2 3
4
7 8
6
It doesn’t measures any
parameter to select a route it
select any rout randomly
Example:
Like here in this graph the best
rout for reaching D from A is
A>B>D, but it randomly select
the route so it selected A>C>D
Which is costly
RANDOM ROUTE
BEST ROUTE

ADAPTIVE ROUTING
89
E
D
C
B
A
F
1
2 3
4
7 8
6
It consider following parameter
to choose one route from
multiple routes
Example:
Like here in this graph the best
rout for reaching D from A is
A>B>D, so it will select it coz it
select the best among all.
BEST ROUTE

STATIC ROUTING
90
E
D
C
B
A
F
1
2 3
4
7 8
6
Its route is fixed but best available
route is available that is not adopted
Example
The best available route to reach D
from A is A>B>D but we wont select it
coz in static routing the route is fixed
which is in this graph from A>C>E>F>D
to reach D from A.
FIXED ROUTE
BEST ROUTE

DYNAMIC ROUTING
91
in this the path calculation is
again and again
200.100.10.1/30 200.100.10.5/30
2621XM
JAKARTA
200.100.10.0/30
200.100.10.2/30 200.100.10.6/30
2621XM
MEDAN
2621XM
SURABAYA
200.168.10.0/24 200.168.20.0/24
2960-24TT
SW-MEDAN
2960-24TT
SW-SURABAYA
LAPTOP-PT
LAPTOP-1
LAPTOP-PT
LAPTOP-0
200.168.10.2/24 200.168.20.2/24

ALTERNATE ROUTING
92
1. Possible routes are pre
defined
2. Routing decision is based on
current traffic status and
historical traffic patterns
X Y
I J
K
ROUTE A
INTREMIDIATE SWITICHING NODES
END OFFICE

ROUTING STRATEGIES
93
1. FIXED-R
2. FLOODING-R
3. RANDOM-R
4. ADOPTIVE-R

FIXED-R
94
Sends data to a specific path
1
2
3
4
5
6
Example : data is sending towards
Pc 4 from Pc 1
FILE
FORWARDED
FILE RECIVED

FIXED-R
95
Sends data to a specific path
1
2
3
4
5
6
Example : data is sending towards
Pc 4 from Pc 1
FILE
FORWARDED
FILE RECIVED

FLOODING-R
96
Sends data to all possible paths
1
2
3
4
5
6
Example : data is send towards all
Pc’s From Pc 1
FILE
FORWARDED
FILE RECIVED
FILE RECIVED
FILE RECIVED
FILE RECIVED
FILE RECIVEd

RANDOM-R
97
• Node selects one outgoing path for
retransmission of incoming packets
• Selection can be random or round robin
• Can select outgoing path based on probability
calculation
• No network info needed
• Route is typically not least cost nor minimum
hop
NODE

ADOPTIVE-R
98

13. SUBNETTING
99
CREATED
BY
RIDA
ZAMAN

IP ADDRESS
 IP address is a numerical label assigned to each device connected to
a computer network that uses the internet protocol for
communications
 IP address consist of 32-bits (4-bytes). The first octet (byte) of an IP
address is enough for us to determine the class to which it belong
and depending on the class to which the IP address belongs we can
determine which portion of the IP address is the Network ID and
which is the host ID
100

NETWORK ADDRESS
 The network address is the first address in a range of IP addresses
and used to communicate with all network devices on a particular
network. The network address contains zero’s in the host portion of
IP address
 The network ID in IP address tells us of which network the device is
part of
101

HOST ADDRESS
 Host address is a physical address of a
device in a network
 Host ID in an IP address identifies that
unique device with in a network
102

IP ADDRESS CLASSES
 IP addresses are split up in to some categories including
 Class A,B,C,D (multicast) and E (reserved)
103

CLASS A
 In class A addresses the first
octet is the network portion and
remaining octets for host
104

CLASS B
 In class B the first two octets are
the network portion and the
remaining two are host portion
105

CLASS C
 In class C the first 3 octets are the
network portion and remaining
ones are for host
106

CLASS D
 Class D addresses are used for
multicasting applications the class
D is not used for normal
networking operations in class D
the first three
107

CLASS E (RESERVED)
 Class E is reserved for multicasting
,in multicasting data is not
destined for a particular host,
that’s why there is no need to
extract host address from the IP
address and class D doesn’t have
any subnet mask this IP address is
reserved for experimental purpose
108

BROADCAST ADDRESS
 A broadcast address is used to
indicate that information being
sent out should be delivered to
every client in the local are
network
 These addresses are always the
highest number possible in a
particular network address or
subnet
109

SUBNET MASK
Subnet mask is also referred to as
address mask it is a 32-bit value that
is used to distinguish the network ID
from the host ID in an IP address
 All bits corresponding to the Net
ID set to 1
 All bits corresponding to the Host
ID set to 0
110

SUB NETTING
 Sub netting allows to create multiple logical networks that exist within
a single class A,B,C network
 If you don’t subnet you can only use one network from your class A,B,C
network which is simply on realistic
 If a major network class A,B,C breaks into smaller sub networks we can
create a network of interconnected sub networks
 Each data link on this network would then have a unique
network/sub network ID
111

HOW TO SUBNET A NETWORK
To subnet a network extent the mask(subnet mask) using some of the bits
from the host ID portion of the address to create a sub network ID
Q: USE 4TH BIT SUBNETTING AND FIND THE ADDRESS OF 4TH
SUBNETWORK AND 5TH HOST?
112
EXAMPLE: IP=192.100.20.11
S.M=255.255.255.240 –> HOST BIT

STEP-1: FIRST COVERT THE HOST BIT OF S.M INTO BINARY
240= 1111 0000
BINARY EQUIVALENT OF HOST BIT 240 IS 11110000 IT MEANS
ALL 1’S FOR SUBNETWORK AND ALL 0’S FOR HOST
1111 0000
113
FOR SUBNETWORK FOR HOST

NOW FIND THE ADDRESS OF 4TH SUBNETWORK & 5TH HOST
1111 0000
0100 0101
114
Binary equivalent of 4 Binary equivalent of 5
THE RESULTANT BYTE IS :
01000101 which is equals to 69
Means the address of 5th host on 4th sub network is:192.100.20.69

115
THE
END

Computer Networks

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