Sarvajanik College Of Engineering
And Technology
Subject Name :- Computer Networks
Subject Code :- 2140709
Branch :- Computer Engineering Eve. (COE)
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Group Members And Topic
 170420107559 – Uttam Thummar
 170420107560 – Dhriti Uttamchandani
 170420107561 – Keyur Vadodariya
 170420107562 – Aditya Vaghela
Topic:- Transport Layer - Introduction & Services,
Multiplexing & Demultiplexing
 Guided By :- Prof. Jaydeep Barad
Prof. Pariza Kamboj
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Introduction
 Transport layer protocol provides logical communication between
application processes running on different hosts.
 Transport layer protocol are implemented in the end system but not
in network routers.
 On sending side , the transport layer converts the application layer
messages it receives from sending application process into transport
layer packets, known as transport layer segments.
 On the receiving side ,the transport layer reassembles segments ,
into messages ,passes to application layer.

Transport layer in OSI networking system
 Another purpose of Transport layer protocol is to ensure data
integrity by evaluating checksum. It is the value added to the data on
the source, defining data. If the checksum at the recipients end does
not match the initial checksum, the data would be retransmitted.

Functions of Transport layer
 This layer breaks messages into packets.
 It perform error recovery if the lower layer are not adequately error
free.
 Function of flow control if not done adequately at network layer.
 Function of multiplexing and demultiplexing sessions together.
 This layer can be responsible for setting up and releasing connection
across the network.

TRANSPORT LAYER SERVICES
Transport Layer is the second layer of TCP/IP model.
It is an end-to-end layer used to deliver messages to a host.
 It is termed as end-to-end layer because it provides a point-to-point
connection rather than hop-to- hop, between the source host and destination host
to deliver the services reliably
 The unit of data encapsulation in Transport Layer is a segment.
The standard protocols used by Transport Layer to enhance it’s functionalities are
 TCP(Transmission Control Protocol),
 UDP( User Datagram Protocol),
 DCCP( Datagram Congestion Control Protocol) etc.

1) Process to process delivery –
While Data Link Layer requires the MAC
address (48 bits address contained inside the
Network Interface Card of every host
machine) of source- destination hosts to
correctly deliver a frame in a similar way
Transport Layer requires a Port number to
correctly deliver the segments of data to the
correct process amongst the multiple processes
running on a particular host
TRANSPORT LAYER SERVICES

2. End-to-end Connection between
hosts –
 Transport layer is also responsible for
creating the end-to-end Connection
between hosts for which it mainly uses
TCP and UDP.
 TCP is a secure, connection- orientated
protocol which uses a handshake TCP
ensures reliable delivery of messages
and is used in various applications.
 It is a often used in multicasting
protocols.
TRANSPORT LAYER SERVICES

3. Congestion Control –
 Congestion is a situation in which too many sources over a network
attempt to send data and the router buffers start overflowing due to
which loss of packets occur.
 It uses open loop congestion control to prevent the congestion
and closed loop congestion control to remove the congestion in a
network once it occurred.
TRANSPORT LAYER SERVICES

4. Data integrity and Error correction –
 Transport layer checks for errors in the messages coming from
application layer by using error detection codes, computing
checksums, it checks whether the received data is not corrupted and
uses the ACK and NACK services to inform the sender if the data is
arrived or not and checks for the integrity of data.
TRANSPORT LAYER SERVICES

5. Flow control –
 Transport layer provides a flow control mechanism between the
adjacent layers of the TCP/IP model. TCP also prevents the data loss
due to a fast sender and slow receiver by imposing some flow
control techniques. It uses the method of sliding window protocol
which is accomplished by receiver by sending a window back to the
sender informing the size of data it can receive.
TRANSPORT LAYER SERVICES

Multiplexing :-
 Gathering data from multiple application processes of sender,
enveloping that data with header and sending them as a whole to the
intended receiver is called as multiplexing.
Demultiplexing :-
 Delivering received segments at receiver side to the correct app
layer processes is called as demultiplexing.
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TRANSPORT LAYER SERVICES

Multiplexing
 The Transport Layer at source collects
data from various application process.
 These Segments contains :-
 Source Port No.
 Destination Port No.
 Header Files and Data.
 These Segment’s are passed to the
Network Layer which adds the source
& destination IP address to get the
Datagram
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Demultiplexing
 Dest. Host receives IP Datagrams
 each datagram has source IP address,
destination IP address.
 each datagram carries 1 transport-
layer segment.
 each segment has source, destination
port number.
 Dest. Host uses IP addresses & port
numbers to direct segment to
appropriate socket.
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How Multiplexing & Demultiplexing is Done15

Types Of Multiplexing & Demultiplexing
1. Connection Less Multiplexing & Demultiplexing
 Protocol - UDP
 Unreliable because UDP
2. Connection Oriented Multiplexing & Demultiplexing
 Protocol – TCP
 Reliable because TCP
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Connection Less Mux - Demux
 Create sockets with port
numbers
 DatagramSocket
mySocket1 = new
DatagramSocket(99111);
 DatagramSocket
mySocket2 = new
DatagramSocket(99222);
UDP socket identified by two-
tuple
 dest IP address
 dest port number
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 When host receives UDP
segment:
 checks destination port
number in segment
 directs UDP segment to
socket with that port
number
 IP datagrams with same
destination port but different
source IP addresses and/or
source port numbers directed
to same socket

Connection Less Mux - Demux18

Connection-Oriented Multiplexing and
Demultiplexing
 TCP socket identified by 4-tuple:
 Source IP Address
 Source Port Number
 Destination IP Address
 Destination Port Number
 Mux: Server uses all four values along with other data to form
a segment for a socket.
 Demux: Receiver uses all four values to direct segment to
appropriate socket.

Connection-Oriented Multiplexing and
Demultiplexing
 Two arriving TCP segments with different source IP
addresses or source port numbers will be directed to
different sockets.
 Server host may support many simultaneous TCP
sockets.
 Each socket identified by its own 4-tuple.
 Web servers have different sockets for each connecting
client.
 Non-persistent HTTP will have different socket
for each request.

Refrences
 Computer Networking-A Top-Down approach, 5thedition, Kurose
and Ross, Pearson.
 www.geekesforgeeks.org
 Data Communications and Networking (4th edition), Behrouz
Forouzan, McGraw Hill
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Thank You23