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19I405 COMPUTER NETWORKS
Dr. R. Rekha
Associate Professor,
Department of IT,
PSG College of Technology,
Coimbatore – 641004
rra.it@psgtech.ac.in
Mobile: 9842163683
19I405 COMPUTER NETWORKS
PHYSICAL LAYER : Transmission media, Data communications, Switching techniques,
Network topologies, OSI and TCP/IP models, Protocols and Standards, Network components:
Hubs - Switches - Routers - Gateways. (9)
DATA LINK LAYER : Design issues, MAC addressing, MAC Protocols: Ethernet - Token
ring, Error detection and correction techniques: Checksum - Cyclic Redundancy Check -
Hamming code. (9)
INTERNET LAYER : IP addressing: Classful - Classless addressing, Sub-netting, Routing
algorithms: Distance vector - Link state routing, Protocols: IP-ARP-RARP, Software Defined
Network . (9)
TRANSPORT LAYER : Design Issues, Port and Socket addressing, Protocols:
UDP-TCP-SCTP, Flow, Error and Congestion control techniques, TCP connections, Quality
of service.
(9)
APPLICATION LAYER : Application layer services: DNS-WWW-Webmail, VoIP, Protocols:
HTTPS-SMTP-TFTP TELNET-SNMP. (9)
Total: L:45
Text book:
1. James F. Kurose , "Computer Networking: A Top-Down Approach
Featuring the Internet", 7th
Edition, Delhi, 2016.
2. William Stallings , "Data and Computer Communications", 10th
Edition,
Pearson Education, USA, 2017.
References:
1. Douglas E. Comer , "Computer Networks and Internets", 6th
Edition,
Pearson Education, USA, 2016.
2. Shashi Banzal , "Data and Computer Network Communication", 2nd
Edition, Firewall Media, Delhi, 2016.
3. Behrouz A. Forouzan , "Data Communication and Networking", 5th
Edition, Tata McGraw Hill, Delhi, 2017.
4. Larry Peterson, Bruce Davie , "Computer Networks: A Systems
Approach", 5th
Edition, Elsevier, USA, 2015.
Google Classroom
• https://classroom.google.com/c/NjU4MjY3
NTU0ODI4?cjc=oeuyusy
Unit 1
PHYSICAL LAYER
What is a Network?
A group or system of interconnected people or things.
What is a Computer Network?
• A set of computers which are
connected together.
• This can mean two computers
cabled together on the same desk,
or thousands of computers across
the world.
• The connections can be wired or
wireless.
Advantages of Computer Networks
• Enables users to share hardware like scanners
and printers.
– This reduces costs by reducing the number of
hardware items bought.
• Allows users access to data stored on others'
computers.
– This keeps everyone up-to-date on the latest
data
Advantages of Computer Networks
• Allow users run programs that are not installed on
their own computers but are installed elsewhere in
the network.
reduces the effort for networks administrators to
keep programs configured correctly and saves a
lot of storage space.
Data Communication
Definitions
• Data: information presented in any form
• Data Communication: exchange of data between
two devices via transmission medium (wire cable /
link).
• Data Communication System: Made up of a
combination of hardware (physical equipment) and
software (programs) to facilitate for effective
communication of data.
Definitions
• A network is a set of devices (often referred to
as nodes) connected by communication links.
• A node can be a host (such as a computer, a
laptop, a smart phone etc.) or a network device
(such as a switch, a router, etc.).
• A link is a communication pathway that
transfer data from one device to another.
5 Components of a Data Communication System
Protocol: is a set of rules that governs data communications. It
represents an agreement between the communicating devices.
Without a protocol two devices may be connected but not
communicating.
Characteristics of a Data Communication
System (Effectiveness)
❖ Delivery : System must deliver data to correct
destination.
❖ Accuracy: The system must deliver data accurately
❖ Timeliness: the system must deliver data in a timely
manner.
❖ Jitter: Variation in the packet arrival time. It is the
uneven delay in the delivery of audio or video packets.
Data Flow
• Path taken by data within a device, network, or
organization, as it moves from its source to its
destination
• Categorized by direction of flow:
❖ Simplex
❖ Half-duplex
❖ Full-duplex
Simplex
• Communication is unidirectional, one of the two
devices on a link can transmit; the other can only
receive (one-way street).
• Ex: keyboard (input), monitors (output)
Half-duplex
Each station can both transmit and receive , but not at
the same time. When one device is sending the other
can receive and vice versa. (one-lane road with two
direction).
Full-duplex
• Both stations can transmit and receive simultaneously.
(two way street with traffic flowing in both directions at
the same time). Ex: telephone network.
Signals going in either direction share the capacity of the link in
two ways:
Either the link must contain two physically separate transmission
paths one for sending and other for receiving.
Capacity of the channel is divided between signals traveling in both
direction
Network Criteria
• A network must be able to meet a certain number
of criteria.
Performance
• Can be measured in many ways!
– Transit time: the amount of time required for a
message to travel from one device to another.
– Response time: the elapsed time between an
enquiry and a response.
• Often evaluated by two networking metrics:
throughput and delay.
Throughput
• Network throughput is the amount of data moved
successfully from one place to another in a given time
period.
• Measured in bits per second (bps), megabits per
second (Mbps) or gigabits per second (Gbps).
• Throughput tells you how much data was transferred
from a source at any given time
• Bandwidth tells you how much
data could theoretically be transferred from a source at
any given time.
Delay
• Also known as latency.
• Corresponds to how long it takes a message to
travel from one end of a network to the other.
• Latency is measured strictly in terms of time.
• Effected by number of users and hence may
change from time to time (Traffic congestion).
Other Factors Affecting
Performance
Type of transmission media
Capabilities of connected Hardware
Efficiency of software.
Number of users
Network Criteria
• A network must be able to meet a
certain number of criteria.
✔ Performance
❖ Reliability
❖ Security
Reliability
• Accuracy of delivery.
• Measured by:
– Frequency of failures
– Time it takes to recover from a failure
– The network’s robustness in a catastrophe.
Network Criteria
• A network must be able to meet a
certain number of criteria.
✔ Performance
✔ Reliability
❖ Security
Security
• Examples:
– Protecting data from unauthorized access.
– Protecting data from damage.
– Implementing policies and procedures for
recovery from breaches and data losses.
Network Attributes
• There are a number of ways that computers
can be connected together to form
networks.
• Physical attributes of a network include:
❖ Type of connection
❖ Physical topology
Type of Connection
• For communication to occur, two devices must be
connected in someway to the same link at the
same time.
• Two possible connections:
– Point-to-point
– Multipoint
Physical Structures: Type of
connection
1. Point –to-point
•Dedicated link between two devices.
•Wire or cable to connect the two ends
• but other options ,such as microwave satellite are possible.
Type of connection
2. Multipoint
more than two specific devices share a single link
Network Configuration
• Physical attributes of a network
include:
✔ Type of connection
❖ Physical topology
Physical Topology
• Topology defines the structure of the
network of how all the components are
interconnected to each other.
• The term physical topology refers to the
way in which a network is laid out
physically.
• The way in which a network is laid out physically.
Physical Topology
Mesh topology (for five devices)
• Every device has a dedicated point-to-point link to every other
devices on the network
• Fully connected mesh network has n(n-1)/2 duplex mode links
(physical connection) to link n devices.
• Every device on the network must have n-1 input/output (I/O)
ports
Advantages of a Mesh topology
• Privacy or security every message travels along a
dedicated line, only the intended recipient sees it.
Physical boundaries prevents other user from gaining
access to the message
• Eliminating the traffic problems The use of dedicated
links guarantees that each connection can carry its
own data load;
Advantages of a Mesh topology
• A mesh is robust. If one link becomes unusable, it
does not harm the entire system.
• Fault identification and fault isolation easy. This
enables the network manager to discover the precise
location of fault and aids in finding its cause and
solution.
Disadvantages of a Mesh topology
Large amount of cabling devices and I/O
ports required:
– Every device must be connected to every
other device, installation and
reconnection are difficult
– The sheer bulk of the wiring can be greater
than the available space can accommodate.
– The H/W required to connect each link
is(I/O ports and cable) expensive.
Disadvantages of a Mesh topology
So a mesh topology is usually implemented
in a limited fashion
(as a backbone connecting the main
computers of a hybrid network that can
include several other topologies)
Star topology
Each device has a dedicated point-to-point link only to a
central controller (hub)
Does not allow direct traffic between devices, if one device
want to send data to another , it send it to the hub, which
send it to other device
Advantages of a Star topology
1. Less expensive
– each device need only one link and I/O port to
connect it to any other devices.
2. Easy to install and reconfigure
3.Robustness:
– if one link fails, only that link affected and
other links remain active.
4.identification and fault isolation
Disadvantages of a Star topology
• The dependency of the whole topology on one
single point, the hub.
• If the hub goes down, the whole system is dead.
• Used in LAN
Tree topology : Is a variation of star
- Not every device plugs directly into the central hub. The
majority of devices connect to secondary hub that in turn is
connected to the central hub.
Tree topology : Advantage
Allows for more devices to be attached to a
single central hub
Bus topology
•Multipoint connection.
•Acts as a backbone to link all the devices in a network.
Bus topology
There is a limit on the number of taps a bus can
support and on the distance between those taps
• As a signal travels along the backbone, it becomes
weaker
Advantages of a Bus topology
Ease of installation, use less cabling than mesh or
star.
Example: Traditional Ethernet LAN
-
Disadvantages of a Bus topology
1.A fault in bus cable (break) stops all transmissions
• The damaged area reflects signals back the
direction of origin, creating noise in both
directions
2.Fault isolation & Reconnection
3.It can be difficult to add new devices (adding more
require modification or replacement of the backbone).
Ring Topology
• Each device has a dedicated point-to-point connection
only with the two devices on either side of it .
• A signal is passed along the ring in one direction from
device until it reaches its destination.
Ring Topology
Each device in the ring incorporate as repeater
Repeater :regenerates the signal
It receives a weakened signal, regenerates the bits
and pass them along.
Ring Topology
Advantages:
• Easy to install and reconfigure.
Each device is linked only to its immediate neighbors. To add or
delete a device requires hanging only 2 connections
• Fault isolation is simplified :
A signal is circulating at all times (token) if one device does not
receive a signal within specified period, it can issue an alarm. The
alarm alerts the network operator to the problem and its location
Disadvantages
• Unidirectional traffic.
A break in the ring (such as disabled station) can disable the entire
network. This can be solved by using dual ring
A hybrid topology: a star backbone with
three bus networks
Three packet-switching networks each contain n nodes. The
first network has a star topology with a central switch, the
second is a (bidirectional) ring, and the third is fully
interconnected, with a wire from every node to every other
node.
What are the best-, average-, and worst-case transmission
paths in hops?
Answer: star - 2, 2, 2 hops (best, average, worst)
ring - 1, N/4, N/2
full - 1, 1, 1
Network category is determined by its size,
the distance it cover and its physical
architecture.
Network Categories
Personal Area Networks
• Let devices communicate over the range of a person.
• A common example is a wireless network that connects a computer
with its peripherals.
– [Computer - attached monitor, keyboard, mouse, and printer.]
– Short-range wireless network called bluetooth to connect these
components without wires.
• Bluetooth networks use the master-slave paradigm
• The system unit (the PC) is normally the master,
– talking to the mouse, keyboard, etc., as slaves.
– The master tells the slaves what addresses to use,
– When they can broadcast,
– how long they can transmit,
– what frequencies they can use, and so on.
LAN ( Local Area Network)
• Privately owned and links the devices in a single office,
building or campus
• LANs designed to allow resources to be shared between PCs or
workstations.
– The resources may be H/W (e.g. printer) or S/W
(applications program) or data.
• In LANs one of the computers has a large capacity drive and
becomes a server to other clients.
• S/W stored on server and used as needed by the whole group.
• LAN use only one type of transmission medium.
• The most common LAN topologies are bus, ring and star.
Single-Building LAN
Used in business environments, links a
workgroup of task-related computer.
Multiple-building LAN
Local Area Network Example 1
• Two buildings with 4 departments
connected as a LAN that uses 3
servers.
Local Area Network Example 2
Local Area Networks
MAN (Metropolitan Area Network)
• Owned by private company or it may be a service
provided by public company
• Extended over an entire city.
• May be single network such as a cable television
network, or it may be connected to number of LANs
into a large network so that resources may be shared
LAN-TO- LAN.
MAN (Metropolitan Area Network)
• Example:
✔ Company can use MAN to connect
the LANs in all its offices throughout
the city.
MAN
WAN (Wide Area Network)
• Provides long distance transmission of data, voice , image
and video information over large areas ( country or whole
world)
• In contrast to LAN, WAN may utilize public or private
communication equipment or combination.
Wide Area Network
– A WAN would be most useful for large
companies with offices or factories in
widely separated areas, like Microsoft,
IBM, Ford, AT&T, etc.
Wide Area Network Example 1
Wide Area Network Example 2
Interconnection of Networks
Internetworking
To interconnect two or more
networks, one needs a gateway or
router.
Host-to-host connectivity is only
possible if there’s a uniform
addressing scheme and a routing
mechanism.
Messages can be sent to a single
destination (unicast), to multiple
destinations (multicast), or to all
possible destinations (broadcast).
Networks Models
• Computer networks are created by different
entities.
• Standards are needed so that these
heterogeneous networks can communicate.
• The two most known standards:
– OSI model: defines a seven layer network.
– Internet model: defines a five layer network.
Standards
• Provide guidelines to
– manufacturers,
– vendors,
– government agencies and
– other service provides
• Ensure the kind of interconnectivity
necessary in today's marketplace and
international communication.
Standards
• Two categories:
1.De facto: Have been adopted as
standards through widespread use.
2.De jure: officially recognized body.
Figure 1-3
Standards Organization
1.International Organization for
Standardization (ISO)
•Multinational body
•OSI
Standards Organization
2. International Telecommunication
Union Telecommunication standard
sector ( ITU-T)
– devoted to the research of standards for
telecommunication in general and for phone
and data system in particular
– Data transmission over telephone line
Modems standards :
– V- series( V32, V34,V90)
– X-series: data transmission over public
digital network (e- mail)
Standards Organization
3. American National Standards Institute
(ANSI)
– completely private, nonprofit corporation
Standards Organization
4. Institute of Electrical and
Electronics Engineers (IEEE)
–In the fields of electrical engineering,
electronics and all related branches of
engineering
–International standards for computing
and communications
PROTOCOL LAYERING
Advantages of protocol layering
• Modularity
• Allows to separate services from
implementation
• Intermediate systems need only some layers
Principles of protocol layering
• Each layer should be able to do two
opposite tasks – for bidirectional
communication
– Send/Receive, Encrypt/decrypt
• Two objects under each layer should be
identical
– Layer 3 – plain text at both sides
– Layer 2 – Cipher text at both sides
THE OSI MODEL
Established in 1947, the International Standards
Organization (ISO) is a multinational body dedicated to
worldwide agreement on international standards.
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.
The purpose of the OSI model is to show how to facilitate
communication between different systems.
OSI is not a protocol.
It is a model for understanding and designing a
network architecture
2.90
ISO is the organization.
OSI is the model.
Note
2.91
Figure 2.2 Seven layers of the OSI model
2.92
Figure 2.3 The interaction between layers in the OSI model
• The processes on each machine that
communicate at a given layer are called as
peer-to-peer processes.
• Each layer in the sending device adds its own
information to the message it receives
from the layer just above it and passes the
whole package to the layer just below it.
• Divided into 3 subgroups
• Layers 1, 2 and 3 – network support layers,
layers 5, 6 and 7 – user support layers
• Layer 4 – transport layer
2.94
Figure 2.4 An exchange using the OSI model
ENCAPSULATION
LAYER 1
PHYSICAL LAYER
2.97
Figure 2.5 Physical layer
• It coordinates the functions required to carry a bit
stream over a physical medium.
• It deals with the mechanical and electrical specifications
of the interface and transmission medium.
It concerns,
• Physical characteristics of interfaces and transmission
medium
• Representation of bits
• Data rate
• Synchronization of bits
• Line configuration: pt-pt, mp
• Physical topology
• Transmission mode: Simplex, half-duplex, full duplex
2.99
The physical layer is responsible for movements of
individual bits from one hop (node) to the next.
Note
Physical addresses
In Figure a node with physical address 10 sends a frame to a node with
physical address 87. The two nodes are connected by a link (bus topology
LAN). As the figure shows, the computer with physical address 10 is the
sender, and the computer with physical address 87 is the receiver.
2.101
Figure 2.6 Data link layer
2.102
Responsibilities are,
•Framing
•Physical addressing: adds the header to the frame
•Flow control
•Error Control: adds reliability to physical layer
•Access control: Determine which device has control over
the link at any given time.
2.103
The data link layer is responsible for moving
frames from one hop (node) to the next.
Note
2.104
Figure 2.7 Hop-to-hop delivery
2.105
IP addresses
Figure shows a part of an internet with 2 routers connecting 3 LANs. Each device has a pair of addresses
(logical and physical) for each connection. Each computer is connected to only one link and therefore
has only one pair of addresses. Each router, is connected to 3 networks (only 2are shown in the figure).
So each router has three pairs of addresses, one for each connection.
2.106
Figure 2.8 Network layer
2.107
Responsibilities
•Source to destination delivery of a packet
•Whereas the datalink layer oversees the delivery of the
packet between two systems on the same network
•But network layer ensures the packet from its origin to
its final destination.
2.108
Other Responsibilities are,
Logical addressing:
•Physical addressing implemented by the data link layer handles the
addressing problem locally.
•If packet passes the network boundary, we need Another addressing
Scheme.
Routing
2.109
The network layer is responsible for the
delivery of individual packets from
the source host to the destination host.
Note
2.110
Figure 2.9 Source-to-destination delivery
2.111
Figure 2.10 Transport layer
2.112
Responsibilities
• Process to Process delivery of the entire message
• Network layer does not recognize any relationship between
the packets
Other Responsibilities
• Service point addressing (Process to Process): SP address
• Segmentation and Reassembly: A message is divided into
transmittable segments with each segment containing a
sequence number.
• Connection control: Connectionless or connection oriented
• Flow control
• Error control: performed process to process
2.113
The transport layer is responsible for the delivery
of a message from one process to another.
Note
2.114
Most local-area networks use a 48-bit (6-byte) physical
address written as 12 hexadecimal digits; every byte (2
hexadecimal digits) is separated by a colon, as shown
below:
Example 2.2
07:01:02:01:2C:4B
A 6-byte (12 hexadecimal digits) physical address.
2.115
Port addresses
2 computers communicates via the Internet. The sender is running three processes at
this time with port addresses a, b, and c. The receiver is running two processes at this
time with port addresses j and k. Process a in the sender needs to communicate with
process j in the receiver. Note that although physical addresses change from hop to
hop, logical and port addresses remain the same from the source to destination.
2.116
The physical addresses will change from hop to hop,
but the logical addresses usually remain the same.
Note
2.117
Example 2.5
A port address is a 16-bit address represented by one
decimal number as shown.
753
A 16-bit port address represented
as one single number.
2.118
Figure 2.11 Reliable process-to-process delivery of a message
2.119
Figure 2.12 Session layer
2.120
Responsibilities
Dialog controller
It establishes, maintains, and
synchronizes the interaction among communicating systems.
Dialog control and synchronization (check points)
2.121
The session layer is responsible for dialog
control and synchronization.
Note
2.122
Figure 2.13 Presentation layer
2.123
• This presentation layer is concerned with the syntax and
semantics of the information exchanged
• Other responsibilities
• Translation
• Encryption
• Compression
2.124
The presentation layer is responsible for translation,
compression, and encryption.
Note
2.125
Figure 2.14 Application layer
2.126
Application layer enable the users, whether human or software
to access the network
Responsibilities
File transfer and access management
Mail services
Directory services: It provides distributed database sources and
access for global information about various objects and services.
2.127
The application layer is responsible for
providing services to the user.
Note
2.128
Figure 2.15 Summary of layers
TCP/IP PROTOCOL SUITE
The layers in the TCP/IP protocol suite do not exactly
match those in the OSI model.
The original TCP/IP protocol suite was defined as having
four layers: host-to-network, internet, transport, and
application.
However, when TCP/IP is compared to OSI, we can say
that the TCP/IP protocol suite is made of five layers:
physical, data link, network, transport, and application.
Physical and Data Link Layers
Network Layer
Transport Layer
Application Layer
Topics discussed in this section:
2.130
Figure 2.16 TCP/IP and OSI model
2.131
Physical and Datalink layers
TCP/IP does not define any specific protocol.
Network layer
•TCP/IP supports internetworking protocol (IP). It is an
unreliable and connectionless protocol.
•IP provides no error checking or tracking.
•IP transports data in packets called datagrams each of
which is transported separately.
•ARP: Address Resolution protocol is used to find the physical
address of the node when its internet address is known.
• Reverse Address Resolution Protocol allows a host to discover
its internet address when it knows only its physical address.
• Internet control message protocol is a mechanism used by hosts
and gateways to send notification of datagram problems back to
the sender.
• Internet Group Message protocol: It is used to facilitate the
simultaneous transmission of a message to a group of recipients.
2.135
Transport Layer
•IP is host-host protocol.
•UDP and TCP are – Process to Process.
•UDP is connectionless protocol and unreliable
•TCP provides full transport layer services to applications.
•TCP is reliable stream protocol.
•TCP divides a stream of data into smaller units called segments.
•Stream Control Transmission Protocol
•SCTP provides support for newer applications such as
voice over the internet protocol (VOIP)
Application Layer
•Equivalent to the combined session, presentation and application
Layers in the OSI model
2.136
2-5 ADDRESSING
Four levels of addresses are used in an internet employing
the TCP/IP protocols: physical, logical, port, and specific.
Physical Addresses
Logical Addresses
Port Addresses
Specific Addresses
Topics discussed in this section:
2.137
Figure 2.17 Addresses in TCP/IP
2.138
Figure 2.18 Relationship of layers and addresses in TCP/IP
2.139
Bit Rate
- Used to describe digital signals
- Bit rate is the number of bits sent in 1 second
- Expressed in bits per second (bps)
Bandwidth in bits per second
- It can also refer to the number of bits per second that a
channel / link / network can transmit
- For ex, the bandwidth of a fast ethernet is 100 mbps
means that this network can send 100 mbps
2.140
Problem 1: Assume a text page is an average of 24 lines
with 80 characters in each line. We need to download
text documents at the rate of 100 pages per second. What
is the required bit rate of the channel?
Problems
2.141
Problem 1:
Assume a text page is an average of 24 lines with 80
characters in each line. We need to download text
documents at the rate of 100 pages per second. What is
the required bit rate of the channel?
Solution:
If we assume that one character requires 8 bits, the bit
rate is
100 X 24 X 80 X 8 = 1,536, 000 bps
Problems
Problem 2: Bit rate of a channel is 2 kbps. What is the
duration of each bit (bit interval)?
Problems
2.143
Problem 2: Bit rate of a channel is 2 kbps. What is the
duration of each bit (bit interval)?
Solution: bit interval is the inverse of bit rate.
So, bit interval = 1 / (bit rate)
= 1 / 2000
= 0.0005 secs / 500µs
Problems
2.144
Transmission time:
The time taken to push out (transmit) a packet from the host to the
transmission medium is called Transmission delay.
Transmission Time = (packet size in terms of number of
bits) / channel bandwidth in bits per second
Problem 3: What is the transmission time of a packet
sent by a station if the size of the packet is 2 million bytes
and the bandwidth of the channel is 300 kbps?
Problems
2.145
Problem 3: What is the transmission time of a packet
sent by a station if the size of the packet is 2 million bytes
and the bandwidth of the channel is 300 kbps?
Solution:
Transmission time = (packet size) / bandwidth
= (20,00,000 X 8 bits) / 3,00,000 bps
= 1,60,00,000 / 3,00,000
= 53.33 s
Problems
2.146
Problem 4: If the bandwidth of the channel is 5 kbps,
how long does it takes to send a frame of 1,00,000 bits
out of this device (transmission time)?
Problems
2.147
Propagation time
It is the amount of time needed for a packet to reach the
destination.
Propagation time = distance / velocity
Problems
2.148
Latency (Delay)
-It defines how long it takes for an entire message to
completely arrive at the destination from the time the
first bit is send out from the source.
-Types are,
Latency or total delay = Propagation + Transmission +
Queuing + Processing
Problems
2.149
Problem 5: What is the total delay (latency) for a frame
of size 5 million bits that is being sent on a link with 10
routers each having a queuing time of 2µs and a
processing time of 1µs. The length of the link is 2000
km. The speed of signal inside the link is 2 X 10^8 m / s.
The link has a bandwidth of 5 Mbps. Which component
of the total delay is dominant? Which one is negligible?
Problems
2.150
Problem 5 – Solution
Transmission time (Tt) = 50,00,000 / 5 mbps = 1 s
Propagation time (Tp) = 2000 km / (2X 10^8) = 0.01 s
Queuing Time (Tq) = 10 X 2 µs = 20 µs = 0.00002 s
Processing Time (Tpr) = 10 X 1 µs = 10 µs = 0.00001 s
Latency = 1 + 0.01 + 0.00002 + 0.00001 = 1.01003 s
Problems
• Three Phases
– Setup Phase
– Data transfer phase
– Tear down phase
Total delay = 3T+3P+W1+W2
In virtual circuit resource are reserve for
the time interval of data transmission
between two nodes.
Working of Virtual Circuit:
•In the first step a medium is set up between the two end nodes.
•Resources are reserved for the transmission of packets.
•Then a signal is sent to sender to tell the medium is set up and transmission can
be started.
•It ensures the transmission of all packets.
•A global header is used in the first packet of the connection.
•Whenever data is to be transmitted a new connection is set up
Addressing-Global,Local
• Total delay = 3T + 3P + Setup delay + Teardown delay
Network Components
HUB
SWITCH
WORKING OF A SWITCH
HUB versus SWITCH
Router
Inter LAN Communication
The Internet
Internet
• A collaboration of more than 100 of 1000
interconnected network.
• 1960 - The Advanced Research Projects
Agency (ARPA)
– Department of defense (US)
– Interested in finding a way to connect computers
• so that the researchers they funded could share their
findings, to reduce costs and eliminating duplication of
effort.
• In 1967
– ARPA presented its ideas for ARPANET, small
network of connected computers (mainframe).
Brief History
• In 1969,
– ARPANET was reality.
– Four nodes at the UNV. Of California,(at los angles
and Santa Barba), Univ. of Utah, SRI (Stanford
Research Institute) were connected
– Connected via IMPs(Interface Message Processor)
computers to form a network.
– Software called Network Control Protocol (NCP)
provided communication between the hosts.
Brief History
• In 1972,
– Protocol to achieve end -to-end delivery of packets on
dissimilar networks – diverse packet size, transmission rate
– Introduced Gateway
– Transmission Control Protocol (TCP) – NCP new version.
– Authorities made decision to split TCP into two protocols:
• IP: Internetworking protocol to handle datagram routing and
• TCP: responsible for higher-level-functions such as error detection,
segmentation and reassembly.
Internet today
• Made up of many wide and local area
networks joined by connecting devices and
switching stations.
• Most end users use the services of internet
service providers (ISPs).
– ISP - company that provides Internet
connections and services to individuals and
organizations.
Internet service providers
(ISPs)
• Hierarchical organization of the Internet
includes:
– International Internet Service Providers
• provide internet services to the whole countries.
• undersea cables or over the land cables.
• Customer - corporate sector and national ISPs.
• Expereo, StarX
– National Internet Service Providers
• Provides Internet access in cities/towns nationwide
• Airtel, TATA, Jio
– Local Internet Service Providers
• SkyLink, InfoNet
Internet service providers
(ISPs)
Protocols and Standards
Protocols and Standards
• Protocols
• Standards
• Standards Organization
Protocols
• Set of rules that governs data communications.
• Protocol defines :
– What is communicated?
– How it is communicated?
– When it is communicated?
Protocols
• Key elements of a protocol: Syntax, semantics and
timing
• Syntax: Structure or format of the data, meaning the
order in which they are presented.
– Example:
Protocols
• Semantics: Refers to the meaning of each
section of bits.
• Example: does an address identify the route
to be taken or the final destination of the
message.
Protocols
• Timing:
– When data should be sent?
– How fast they can be sent?
•Example: If a sender produces data at 100Mpbs
but the receiver can process data at only 1Mpbs,
transmission will overload the receiver and data
will be largely lost.

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Unit_1.pdf computer networks and computer topology

  • 1. 19I405 COMPUTER NETWORKS Dr. R. Rekha Associate Professor, Department of IT, PSG College of Technology, Coimbatore – 641004 rra.it@psgtech.ac.in Mobile: 9842163683
  • 2. 19I405 COMPUTER NETWORKS PHYSICAL LAYER : Transmission media, Data communications, Switching techniques, Network topologies, OSI and TCP/IP models, Protocols and Standards, Network components: Hubs - Switches - Routers - Gateways. (9) DATA LINK LAYER : Design issues, MAC addressing, MAC Protocols: Ethernet - Token ring, Error detection and correction techniques: Checksum - Cyclic Redundancy Check - Hamming code. (9) INTERNET LAYER : IP addressing: Classful - Classless addressing, Sub-netting, Routing algorithms: Distance vector - Link state routing, Protocols: IP-ARP-RARP, Software Defined Network . (9) TRANSPORT LAYER : Design Issues, Port and Socket addressing, Protocols: UDP-TCP-SCTP, Flow, Error and Congestion control techniques, TCP connections, Quality of service. (9) APPLICATION LAYER : Application layer services: DNS-WWW-Webmail, VoIP, Protocols: HTTPS-SMTP-TFTP TELNET-SNMP. (9) Total: L:45
  • 3. Text book: 1. James F. Kurose , "Computer Networking: A Top-Down Approach Featuring the Internet", 7th Edition, Delhi, 2016. 2. William Stallings , "Data and Computer Communications", 10th Edition, Pearson Education, USA, 2017. References: 1. Douglas E. Comer , "Computer Networks and Internets", 6th Edition, Pearson Education, USA, 2016. 2. Shashi Banzal , "Data and Computer Network Communication", 2nd Edition, Firewall Media, Delhi, 2016. 3. Behrouz A. Forouzan , "Data Communication and Networking", 5th Edition, Tata McGraw Hill, Delhi, 2017. 4. Larry Peterson, Bruce Davie , "Computer Networks: A Systems Approach", 5th Edition, Elsevier, USA, 2015.
  • 6. What is a Network? A group or system of interconnected people or things.
  • 7. What is a Computer Network? • A set of computers which are connected together. • This can mean two computers cabled together on the same desk, or thousands of computers across the world. • The connections can be wired or wireless.
  • 8. Advantages of Computer Networks • Enables users to share hardware like scanners and printers. – This reduces costs by reducing the number of hardware items bought. • Allows users access to data stored on others' computers. – This keeps everyone up-to-date on the latest data
  • 9. Advantages of Computer Networks • Allow users run programs that are not installed on their own computers but are installed elsewhere in the network. reduces the effort for networks administrators to keep programs configured correctly and saves a lot of storage space.
  • 11. Definitions • Data: information presented in any form • Data Communication: exchange of data between two devices via transmission medium (wire cable / link). • Data Communication System: Made up of a combination of hardware (physical equipment) and software (programs) to facilitate for effective communication of data.
  • 12. Definitions • A network is a set of devices (often referred to as nodes) connected by communication links. • A node can be a host (such as a computer, a laptop, a smart phone etc.) or a network device (such as a switch, a router, etc.). • A link is a communication pathway that transfer data from one device to another.
  • 13. 5 Components of a Data Communication System Protocol: is a set of rules that governs data communications. It represents an agreement between the communicating devices. Without a protocol two devices may be connected but not communicating.
  • 14. Characteristics of a Data Communication System (Effectiveness) ❖ Delivery : System must deliver data to correct destination. ❖ Accuracy: The system must deliver data accurately ❖ Timeliness: the system must deliver data in a timely manner. ❖ Jitter: Variation in the packet arrival time. It is the uneven delay in the delivery of audio or video packets.
  • 15. Data Flow • Path taken by data within a device, network, or organization, as it moves from its source to its destination • Categorized by direction of flow: ❖ Simplex ❖ Half-duplex ❖ Full-duplex
  • 16. Simplex • Communication is unidirectional, one of the two devices on a link can transmit; the other can only receive (one-way street). • Ex: keyboard (input), monitors (output)
  • 17. Half-duplex Each station can both transmit and receive , but not at the same time. When one device is sending the other can receive and vice versa. (one-lane road with two direction).
  • 18. Full-duplex • Both stations can transmit and receive simultaneously. (two way street with traffic flowing in both directions at the same time). Ex: telephone network. Signals going in either direction share the capacity of the link in two ways: Either the link must contain two physically separate transmission paths one for sending and other for receiving. Capacity of the channel is divided between signals traveling in both direction
  • 19. Network Criteria • A network must be able to meet a certain number of criteria.
  • 20. Performance • Can be measured in many ways! – Transit time: the amount of time required for a message to travel from one device to another. – Response time: the elapsed time between an enquiry and a response. • Often evaluated by two networking metrics: throughput and delay.
  • 21. Throughput • Network throughput is the amount of data moved successfully from one place to another in a given time period. • Measured in bits per second (bps), megabits per second (Mbps) or gigabits per second (Gbps). • Throughput tells you how much data was transferred from a source at any given time • Bandwidth tells you how much data could theoretically be transferred from a source at any given time.
  • 22. Delay • Also known as latency. • Corresponds to how long it takes a message to travel from one end of a network to the other. • Latency is measured strictly in terms of time. • Effected by number of users and hence may change from time to time (Traffic congestion).
  • 23. Other Factors Affecting Performance Type of transmission media Capabilities of connected Hardware Efficiency of software. Number of users
  • 24. Network Criteria • A network must be able to meet a certain number of criteria. ✔ Performance ❖ Reliability ❖ Security
  • 25. Reliability • Accuracy of delivery. • Measured by: – Frequency of failures – Time it takes to recover from a failure – The network’s robustness in a catastrophe.
  • 26. Network Criteria • A network must be able to meet a certain number of criteria. ✔ Performance ✔ Reliability ❖ Security
  • 27. Security • Examples: – Protecting data from unauthorized access. – Protecting data from damage. – Implementing policies and procedures for recovery from breaches and data losses.
  • 28. Network Attributes • There are a number of ways that computers can be connected together to form networks. • Physical attributes of a network include: ❖ Type of connection ❖ Physical topology
  • 29. Type of Connection • For communication to occur, two devices must be connected in someway to the same link at the same time. • Two possible connections: – Point-to-point – Multipoint
  • 30. Physical Structures: Type of connection 1. Point –to-point •Dedicated link between two devices. •Wire or cable to connect the two ends • but other options ,such as microwave satellite are possible.
  • 31. Type of connection 2. Multipoint more than two specific devices share a single link
  • 32. Network Configuration • Physical attributes of a network include: ✔ Type of connection ❖ Physical topology
  • 33. Physical Topology • Topology defines the structure of the network of how all the components are interconnected to each other. • The term physical topology refers to the way in which a network is laid out physically.
  • 34. • The way in which a network is laid out physically. Physical Topology
  • 35. Mesh topology (for five devices) • Every device has a dedicated point-to-point link to every other devices on the network • Fully connected mesh network has n(n-1)/2 duplex mode links (physical connection) to link n devices. • Every device on the network must have n-1 input/output (I/O) ports
  • 36. Advantages of a Mesh topology • Privacy or security every message travels along a dedicated line, only the intended recipient sees it. Physical boundaries prevents other user from gaining access to the message • Eliminating the traffic problems The use of dedicated links guarantees that each connection can carry its own data load;
  • 37. Advantages of a Mesh topology • A mesh is robust. If one link becomes unusable, it does not harm the entire system. • Fault identification and fault isolation easy. This enables the network manager to discover the precise location of fault and aids in finding its cause and solution.
  • 38. Disadvantages of a Mesh topology Large amount of cabling devices and I/O ports required: – Every device must be connected to every other device, installation and reconnection are difficult – The sheer bulk of the wiring can be greater than the available space can accommodate. – The H/W required to connect each link is(I/O ports and cable) expensive.
  • 39. Disadvantages of a Mesh topology So a mesh topology is usually implemented in a limited fashion (as a backbone connecting the main computers of a hybrid network that can include several other topologies)
  • 40. Star topology Each device has a dedicated point-to-point link only to a central controller (hub) Does not allow direct traffic between devices, if one device want to send data to another , it send it to the hub, which send it to other device
  • 41. Advantages of a Star topology 1. Less expensive – each device need only one link and I/O port to connect it to any other devices. 2. Easy to install and reconfigure 3.Robustness: – if one link fails, only that link affected and other links remain active. 4.identification and fault isolation
  • 42. Disadvantages of a Star topology • The dependency of the whole topology on one single point, the hub. • If the hub goes down, the whole system is dead. • Used in LAN
  • 43. Tree topology : Is a variation of star - Not every device plugs directly into the central hub. The majority of devices connect to secondary hub that in turn is connected to the central hub.
  • 44. Tree topology : Advantage Allows for more devices to be attached to a single central hub
  • 45. Bus topology •Multipoint connection. •Acts as a backbone to link all the devices in a network.
  • 46. Bus topology There is a limit on the number of taps a bus can support and on the distance between those taps • As a signal travels along the backbone, it becomes weaker
  • 47. Advantages of a Bus topology Ease of installation, use less cabling than mesh or star. Example: Traditional Ethernet LAN -
  • 48. Disadvantages of a Bus topology 1.A fault in bus cable (break) stops all transmissions • The damaged area reflects signals back the direction of origin, creating noise in both directions 2.Fault isolation & Reconnection 3.It can be difficult to add new devices (adding more require modification or replacement of the backbone).
  • 49. Ring Topology • Each device has a dedicated point-to-point connection only with the two devices on either side of it . • A signal is passed along the ring in one direction from device until it reaches its destination.
  • 50. Ring Topology Each device in the ring incorporate as repeater Repeater :regenerates the signal It receives a weakened signal, regenerates the bits and pass them along.
  • 51. Ring Topology Advantages: • Easy to install and reconfigure. Each device is linked only to its immediate neighbors. To add or delete a device requires hanging only 2 connections • Fault isolation is simplified : A signal is circulating at all times (token) if one device does not receive a signal within specified period, it can issue an alarm. The alarm alerts the network operator to the problem and its location Disadvantages • Unidirectional traffic. A break in the ring (such as disabled station) can disable the entire network. This can be solved by using dual ring
  • 52. A hybrid topology: a star backbone with three bus networks
  • 53.
  • 54. Three packet-switching networks each contain n nodes. The first network has a star topology with a central switch, the second is a (bidirectional) ring, and the third is fully interconnected, with a wire from every node to every other node. What are the best-, average-, and worst-case transmission paths in hops? Answer: star - 2, 2, 2 hops (best, average, worst) ring - 1, N/4, N/2 full - 1, 1, 1
  • 55. Network category is determined by its size, the distance it cover and its physical architecture. Network Categories
  • 56.
  • 57. Personal Area Networks • Let devices communicate over the range of a person. • A common example is a wireless network that connects a computer with its peripherals. – [Computer - attached monitor, keyboard, mouse, and printer.] – Short-range wireless network called bluetooth to connect these components without wires. • Bluetooth networks use the master-slave paradigm • The system unit (the PC) is normally the master, – talking to the mouse, keyboard, etc., as slaves. – The master tells the slaves what addresses to use, – When they can broadcast, – how long they can transmit, – what frequencies they can use, and so on.
  • 58. LAN ( Local Area Network) • Privately owned and links the devices in a single office, building or campus • LANs designed to allow resources to be shared between PCs or workstations. – The resources may be H/W (e.g. printer) or S/W (applications program) or data. • In LANs one of the computers has a large capacity drive and becomes a server to other clients. • S/W stored on server and used as needed by the whole group. • LAN use only one type of transmission medium. • The most common LAN topologies are bus, ring and star.
  • 59. Single-Building LAN Used in business environments, links a workgroup of task-related computer.
  • 61. Local Area Network Example 1 • Two buildings with 4 departments connected as a LAN that uses 3 servers.
  • 62. Local Area Network Example 2
  • 64. MAN (Metropolitan Area Network) • Owned by private company or it may be a service provided by public company • Extended over an entire city. • May be single network such as a cable television network, or it may be connected to number of LANs into a large network so that resources may be shared LAN-TO- LAN.
  • 65. MAN (Metropolitan Area Network) • Example: ✔ Company can use MAN to connect the LANs in all its offices throughout the city.
  • 66. MAN
  • 67. WAN (Wide Area Network) • Provides long distance transmission of data, voice , image and video information over large areas ( country or whole world) • In contrast to LAN, WAN may utilize public or private communication equipment or combination.
  • 68. Wide Area Network – A WAN would be most useful for large companies with offices or factories in widely separated areas, like Microsoft, IBM, Ford, AT&T, etc.
  • 69. Wide Area Network Example 1
  • 70. Wide Area Network Example 2
  • 72. Internetworking To interconnect two or more networks, one needs a gateway or router. Host-to-host connectivity is only possible if there’s a uniform addressing scheme and a routing mechanism. Messages can be sent to a single destination (unicast), to multiple destinations (multicast), or to all possible destinations (broadcast).
  • 73.
  • 74. Networks Models • Computer networks are created by different entities. • Standards are needed so that these heterogeneous networks can communicate. • The two most known standards: – OSI model: defines a seven layer network. – Internet model: defines a five layer network.
  • 75. Standards • Provide guidelines to – manufacturers, – vendors, – government agencies and – other service provides • Ensure the kind of interconnectivity necessary in today's marketplace and international communication.
  • 76. Standards • Two categories: 1.De facto: Have been adopted as standards through widespread use. 2.De jure: officially recognized body.
  • 78. Standards Organization 1.International Organization for Standardization (ISO) •Multinational body •OSI
  • 79. Standards Organization 2. International Telecommunication Union Telecommunication standard sector ( ITU-T) – devoted to the research of standards for telecommunication in general and for phone and data system in particular – Data transmission over telephone line Modems standards : – V- series( V32, V34,V90) – X-series: data transmission over public digital network (e- mail)
  • 80. Standards Organization 3. American National Standards Institute (ANSI) – completely private, nonprofit corporation
  • 81. Standards Organization 4. Institute of Electrical and Electronics Engineers (IEEE) –In the fields of electrical engineering, electronics and all related branches of engineering –International standards for computing and communications
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  • 86. Advantages of protocol layering • Modularity • Allows to separate services from implementation • Intermediate systems need only some layers
  • 87. Principles of protocol layering • Each layer should be able to do two opposite tasks – for bidirectional communication – Send/Receive, Encrypt/decrypt • Two objects under each layer should be identical – Layer 3 – plain text at both sides – Layer 2 – Cipher text at both sides
  • 88. THE OSI MODEL Established in 1947, the International Standards Organization (ISO) is a multinational body dedicated to worldwide agreement on international standards. 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.
  • 89. The purpose of the OSI model is to show how to facilitate communication between different systems. OSI is not a protocol. It is a model for understanding and designing a network architecture
  • 90. 2.90 ISO is the organization. OSI is the model. Note
  • 91. 2.91 Figure 2.2 Seven layers of the OSI model
  • 92. 2.92 Figure 2.3 The interaction between layers in the OSI model
  • 93. • The processes on each machine that communicate at a given layer are called as peer-to-peer processes. • Each layer in the sending device adds its own information to the message it receives from the layer just above it and passes the whole package to the layer just below it. • Divided into 3 subgroups • Layers 1, 2 and 3 – network support layers, layers 5, 6 and 7 – user support layers • Layer 4 – transport layer
  • 94. 2.94 Figure 2.4 An exchange using the OSI model
  • 98. • It coordinates the functions required to carry a bit stream over a physical medium. • It deals with the mechanical and electrical specifications of the interface and transmission medium. It concerns, • Physical characteristics of interfaces and transmission medium • Representation of bits • Data rate • Synchronization of bits • Line configuration: pt-pt, mp • Physical topology • Transmission mode: Simplex, half-duplex, full duplex
  • 99. 2.99 The physical layer is responsible for movements of individual bits from one hop (node) to the next. Note
  • 100. Physical addresses In Figure a node with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by a link (bus topology LAN). As the figure shows, the computer with physical address 10 is the sender, and the computer with physical address 87 is the receiver.
  • 101. 2.101 Figure 2.6 Data link layer
  • 102. 2.102 Responsibilities are, •Framing •Physical addressing: adds the header to the frame •Flow control •Error Control: adds reliability to physical layer •Access control: Determine which device has control over the link at any given time.
  • 103. 2.103 The data link layer is responsible for moving frames from one hop (node) to the next. Note
  • 105. 2.105 IP addresses Figure shows a part of an internet with 2 routers connecting 3 LANs. Each device has a pair of addresses (logical and physical) for each connection. Each computer is connected to only one link and therefore has only one pair of addresses. Each router, is connected to 3 networks (only 2are shown in the figure). So each router has three pairs of addresses, one for each connection.
  • 107. 2.107 Responsibilities •Source to destination delivery of a packet •Whereas the datalink layer oversees the delivery of the packet between two systems on the same network •But network layer ensures the packet from its origin to its final destination.
  • 108. 2.108 Other Responsibilities are, Logical addressing: •Physical addressing implemented by the data link layer handles the addressing problem locally. •If packet passes the network boundary, we need Another addressing Scheme. Routing
  • 109. 2.109 The network layer is responsible for the delivery of individual packets from the source host to the destination host. Note
  • 112. 2.112 Responsibilities • Process to Process delivery of the entire message • Network layer does not recognize any relationship between the packets Other Responsibilities • Service point addressing (Process to Process): SP address • Segmentation and Reassembly: A message is divided into transmittable segments with each segment containing a sequence number. • Connection control: Connectionless or connection oriented • Flow control • Error control: performed process to process
  • 113. 2.113 The transport layer is responsible for the delivery of a message from one process to another. Note
  • 114. 2.114 Most local-area networks use a 48-bit (6-byte) physical address written as 12 hexadecimal digits; every byte (2 hexadecimal digits) is separated by a colon, as shown below: Example 2.2 07:01:02:01:2C:4B A 6-byte (12 hexadecimal digits) physical address.
  • 115. 2.115 Port addresses 2 computers communicates via the Internet. The sender is running three processes at this time with port addresses a, b, and c. The receiver is running two processes at this time with port addresses j and k. Process a in the sender needs to communicate with process j in the receiver. Note that although physical addresses change from hop to hop, logical and port addresses remain the same from the source to destination.
  • 116. 2.116 The physical addresses will change from hop to hop, but the logical addresses usually remain the same. Note
  • 117. 2.117 Example 2.5 A port address is a 16-bit address represented by one decimal number as shown. 753 A 16-bit port address represented as one single number.
  • 118. 2.118 Figure 2.11 Reliable process-to-process delivery of a message
  • 120. 2.120 Responsibilities Dialog controller It establishes, maintains, and synchronizes the interaction among communicating systems. Dialog control and synchronization (check points)
  • 121. 2.121 The session layer is responsible for dialog control and synchronization. Note
  • 123. 2.123 • This presentation layer is concerned with the syntax and semantics of the information exchanged • Other responsibilities • Translation • Encryption • Compression
  • 124. 2.124 The presentation layer is responsible for translation, compression, and encryption. Note
  • 126. 2.126 Application layer enable the users, whether human or software to access the network Responsibilities File transfer and access management Mail services Directory services: It provides distributed database sources and access for global information about various objects and services.
  • 127. 2.127 The application layer is responsible for providing services to the user. Note
  • 129. TCP/IP PROTOCOL SUITE The layers in the TCP/IP protocol suite do not exactly match those in the OSI model. The original TCP/IP protocol suite was defined as having four layers: host-to-network, internet, transport, and application. However, when TCP/IP is compared to OSI, we can say that the TCP/IP protocol suite is made of five layers: physical, data link, network, transport, and application. Physical and Data Link Layers Network Layer Transport Layer Application Layer Topics discussed in this section:
  • 130. 2.130 Figure 2.16 TCP/IP and OSI model
  • 131. 2.131 Physical and Datalink layers TCP/IP does not define any specific protocol. Network layer •TCP/IP supports internetworking protocol (IP). It is an unreliable and connectionless protocol. •IP provides no error checking or tracking. •IP transports data in packets called datagrams each of which is transported separately. •ARP: Address Resolution protocol is used to find the physical address of the node when its internet address is known.
  • 132.
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  • 134. • Reverse Address Resolution Protocol allows a host to discover its internet address when it knows only its physical address. • Internet control message protocol is a mechanism used by hosts and gateways to send notification of datagram problems back to the sender. • Internet Group Message protocol: It is used to facilitate the simultaneous transmission of a message to a group of recipients.
  • 135. 2.135 Transport Layer •IP is host-host protocol. •UDP and TCP are – Process to Process. •UDP is connectionless protocol and unreliable •TCP provides full transport layer services to applications. •TCP is reliable stream protocol. •TCP divides a stream of data into smaller units called segments. •Stream Control Transmission Protocol •SCTP provides support for newer applications such as voice over the internet protocol (VOIP) Application Layer •Equivalent to the combined session, presentation and application Layers in the OSI model
  • 136. 2.136 2-5 ADDRESSING Four levels of addresses are used in an internet employing the TCP/IP protocols: physical, logical, port, and specific. Physical Addresses Logical Addresses Port Addresses Specific Addresses Topics discussed in this section:
  • 138. 2.138 Figure 2.18 Relationship of layers and addresses in TCP/IP
  • 139. 2.139 Bit Rate - Used to describe digital signals - Bit rate is the number of bits sent in 1 second - Expressed in bits per second (bps) Bandwidth in bits per second - It can also refer to the number of bits per second that a channel / link / network can transmit - For ex, the bandwidth of a fast ethernet is 100 mbps means that this network can send 100 mbps
  • 140. 2.140 Problem 1: Assume a text page is an average of 24 lines with 80 characters in each line. We need to download text documents at the rate of 100 pages per second. What is the required bit rate of the channel? Problems
  • 141. 2.141 Problem 1: Assume a text page is an average of 24 lines with 80 characters in each line. We need to download text documents at the rate of 100 pages per second. What is the required bit rate of the channel? Solution: If we assume that one character requires 8 bits, the bit rate is 100 X 24 X 80 X 8 = 1,536, 000 bps Problems
  • 142. Problem 2: Bit rate of a channel is 2 kbps. What is the duration of each bit (bit interval)? Problems
  • 143. 2.143 Problem 2: Bit rate of a channel is 2 kbps. What is the duration of each bit (bit interval)? Solution: bit interval is the inverse of bit rate. So, bit interval = 1 / (bit rate) = 1 / 2000 = 0.0005 secs / 500µs Problems
  • 144. 2.144 Transmission time: The time taken to push out (transmit) a packet from the host to the transmission medium is called Transmission delay. Transmission Time = (packet size in terms of number of bits) / channel bandwidth in bits per second Problem 3: What is the transmission time of a packet sent by a station if the size of the packet is 2 million bytes and the bandwidth of the channel is 300 kbps? Problems
  • 145. 2.145 Problem 3: What is the transmission time of a packet sent by a station if the size of the packet is 2 million bytes and the bandwidth of the channel is 300 kbps? Solution: Transmission time = (packet size) / bandwidth = (20,00,000 X 8 bits) / 3,00,000 bps = 1,60,00,000 / 3,00,000 = 53.33 s Problems
  • 146. 2.146 Problem 4: If the bandwidth of the channel is 5 kbps, how long does it takes to send a frame of 1,00,000 bits out of this device (transmission time)? Problems
  • 147. 2.147 Propagation time It is the amount of time needed for a packet to reach the destination. Propagation time = distance / velocity Problems
  • 148. 2.148 Latency (Delay) -It defines how long it takes for an entire message to completely arrive at the destination from the time the first bit is send out from the source. -Types are, Latency or total delay = Propagation + Transmission + Queuing + Processing Problems
  • 149. 2.149 Problem 5: What is the total delay (latency) for a frame of size 5 million bits that is being sent on a link with 10 routers each having a queuing time of 2µs and a processing time of 1µs. The length of the link is 2000 km. The speed of signal inside the link is 2 X 10^8 m / s. The link has a bandwidth of 5 Mbps. Which component of the total delay is dominant? Which one is negligible? Problems
  • 150. 2.150 Problem 5 – Solution Transmission time (Tt) = 50,00,000 / 5 mbps = 1 s Propagation time (Tp) = 2000 km / (2X 10^8) = 0.01 s Queuing Time (Tq) = 10 X 2 µs = 20 µs = 0.00002 s Processing Time (Tpr) = 10 X 1 µs = 10 µs = 0.00001 s Latency = 1 + 0.01 + 0.00002 + 0.00001 = 1.01003 s Problems
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  • 157. • Three Phases – Setup Phase – Data transfer phase – Tear down phase
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  • 165. Total delay = 3T+3P+W1+W2
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  • 168. In virtual circuit resource are reserve for the time interval of data transmission between two nodes.
  • 169. Working of Virtual Circuit: •In the first step a medium is set up between the two end nodes. •Resources are reserved for the transmission of packets. •Then a signal is sent to sender to tell the medium is set up and transmission can be started. •It ensures the transmission of all packets. •A global header is used in the first packet of the connection. •Whenever data is to be transmitted a new connection is set up
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  • 177. • Total delay = 3T + 3P + Setup delay + Teardown delay
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  • 188. HUB
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  • 192. SWITCH
  • 193. WORKING OF A SWITCH
  • 195. Router
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  • 214. Internet • A collaboration of more than 100 of 1000 interconnected network. • 1960 - The Advanced Research Projects Agency (ARPA) – Department of defense (US) – Interested in finding a way to connect computers • so that the researchers they funded could share their findings, to reduce costs and eliminating duplication of effort. • In 1967 – ARPA presented its ideas for ARPANET, small network of connected computers (mainframe).
  • 215. Brief History • In 1969, – ARPANET was reality. – Four nodes at the UNV. Of California,(at los angles and Santa Barba), Univ. of Utah, SRI (Stanford Research Institute) were connected – Connected via IMPs(Interface Message Processor) computers to form a network. – Software called Network Control Protocol (NCP) provided communication between the hosts.
  • 216. Brief History • In 1972, – Protocol to achieve end -to-end delivery of packets on dissimilar networks – diverse packet size, transmission rate – Introduced Gateway – Transmission Control Protocol (TCP) – NCP new version. – Authorities made decision to split TCP into two protocols: • IP: Internetworking protocol to handle datagram routing and • TCP: responsible for higher-level-functions such as error detection, segmentation and reassembly.
  • 217. Internet today • Made up of many wide and local area networks joined by connecting devices and switching stations. • Most end users use the services of internet service providers (ISPs). – ISP - company that provides Internet connections and services to individuals and organizations.
  • 218. Internet service providers (ISPs) • Hierarchical organization of the Internet includes: – International Internet Service Providers • provide internet services to the whole countries. • undersea cables or over the land cables. • Customer - corporate sector and national ISPs. • Expereo, StarX
  • 219. – National Internet Service Providers • Provides Internet access in cities/towns nationwide • Airtel, TATA, Jio – Local Internet Service Providers • SkyLink, InfoNet
  • 222. Protocols and Standards • Protocols • Standards • Standards Organization
  • 223. Protocols • Set of rules that governs data communications. • Protocol defines : – What is communicated? – How it is communicated? – When it is communicated?
  • 224. Protocols • Key elements of a protocol: Syntax, semantics and timing • Syntax: Structure or format of the data, meaning the order in which they are presented. – Example:
  • 225. Protocols • Semantics: Refers to the meaning of each section of bits. • Example: does an address identify the route to be taken or the final destination of the message.
  • 226. Protocols • Timing: – When data should be sent? – How fast they can be sent? •Example: If a sender produces data at 100Mpbs but the receiver can process data at only 1Mpbs, transmission will overload the receiver and data will be largely lost.