Transport layer services

Transport Layer Services
Dr.T.Abirami , Associate Professor , Department of IT , Kongu
Engineering College

INTRODUCTION
• The packets at the transport layer in the Internet are called user datagrams,
segments, or packets
• In the Transport layer, data travels in the form of segments.
• To provide the communication services directly to the application processes
running on different hosts.
• transferring data from one point to another in the Internet.
• Transport Layer is responsible for delivering messages between hosts.
• The transport layer is responsible for creating an end to end connection
between source IP and the destination IP.
• For establishing this end to end connection, the Transport layer is using two
major protocols TCP and UDP.
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Major duties of the Transport layer are:
• Creating an end-to-end connection between hosts in different
networks,
• Error recovery,
• Flow control,
• Ensuring complete data transfer in TCP
• Congestion avoidance
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List of the major protocols works in the
Transport later are:
• TCP( Transmission Control Protocol)
• UDP( User Datagram Protocol)
• DCCP (Datagram Congestion Control Protocol)
• SCTP (Stream Control Transmission Protocol)
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Transport-Layer Services
• Process-to-Process Communication : A process is running program
that uses the services of the transport layer
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Addressing: Port Numbers
• A process on the local host, called a client, needs services from a process
usually on the remote host, called a server
• To define the processes, we need second identifiers, called port numbers.
• the port numbers are integers between 0 and 65,535 (16 bits).
• The server process must also define itself with a port number.
• TCP/IP has decided to use universal port numbers for servers; these are called
well-known port numbers.
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ICANN Ranges
• the port numbers into three ranges:
1. well-known,
2. registered, and
3. dynamic (or private)
• Well-known ports. The ports ranging from 0 to 1023 are assigned and controlled by
ICANN. These are the well-known ports.
❑ Registered ports. The ports ranging from 1024 to 49,151 are not assigned or
controlled by ICANN. They can only be registered with ICANN to prevent duplication.
❑ Dynamic ports. The ports ranging from 49,152 to 65,535 are neither controlled nor
registered. They can be used as temporary or private port numbers.
ICANN is the Internet Corporation for Assigned
Names and Numbers.
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Socket Addresses
• A transport-layer protocol in the TCP suite needs both the IP address
and the port number, at each end, to make a connection.
• The combination of an IP address and a port number is called a
socket address.
• The client socket address defines the client process uniquely just as
the server socket address defines the server process uniquely
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Encapsulation and Decapsulation
• The Transport layer encapsulates the data by adding the appropriate
header to each piece. These data pieces are now called as data
segments.
• The header contains the sequencing information so that the data
segments can be reassembled at the receiver’s end.
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Encapsulation & De-encapsulation
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Multiplexing and Demultiplexing
• Multiplexing is a technique used to combine and send the multiple
data streams over a single medium.
• The process of combining the data streams is known as multiplexing
Why Multiplexing?
• The transmission medium is used to send the signal from sender to
receiver. The medium can only have one signal at a time.
• If there are multiple signals to share one medium, then the medium
must be divided
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Flow Control
• It is technique that observes proper flow of data from sender to receiver.
• Flow control is technique that gives permission to two of stations that are
working and processing at different speeds to just communicate with one
another.
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Flow Control
• If the receiver is overloaded with too much data, then the receiver
discards the packets and asking for the retransmission of packets.
• This increases network congestion and reducing the system
performance.
• Transport layer use two buffers:
• one at the sending transport layer and the other at the receiving
transport layer.
• A buffer is a set of memory locations that can hold packets at the
sender and receiver.
• When the buffer of the sending transport layer is full, it informs the
application layer to stop passing chunks of messages
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Error Control
The transport layer checks for errors in the messages coming from the 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 has
arrived or not and checks for the integrity of data.
TCP is a reliable transport layer protocol. Error control includes mechanisms for detecting
corrupted segments, lost segments, out-of-order segments, and duplicated segments.
1. Detecting and discarding corrupted packets.
2. Keeping track of lost and discarded packets and resending them.
3. Recognizing duplicate packets and discarding them.
4. Buffering out-of-order packets until the missing packets arrive
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Sequence Numbers
• the transport-layer packet to hold the sequence number
• Packets are numbered sequentially.
• If the header of the packet allows m bits for the sequence
number, the sequence numbers range from 0 to 2m − 1
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Acknowledgment
• use both positive and negative signals as error control
• The receiver side can send an acknowledgment (ACK) for each of a
collection of packets that have arrived safe
• When a packet is sent, the sender starts a timer. If an ACK does not
arrive before the timer expires, the sender resends the packet.
• Duplicate packets can be silently discarded by the receiver.
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Congestion Control
• Congestion in a network may occur if the load on the network—the
number of packets sent to the network—is greater than the capacity
of the network—the number of packets a network can handle.
• Congestion in a network or internetwork occurs because routers and
switches have queues—buffers that hold the packets before and after
processing
• control the congestion and keep the load below the capacity
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Connectionless and Connection-Oriented
Protocols
Connection-Oriented Services
• Users of connection-oriented services follow a sequence of operations:
• Establish connection
• Send information
• Release connection
• To provide connection-oriented services, it is necessary to establish a
connection first, and then start the communication, send the
information, and then release the connection.
• This type of service is more reliable, because if there is an error on the
receiver’s end, the sender can resend the information.
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Connectionless Protocols
• a router treats each packet individually.
• The packets are routed through different paths through the network
according to the decisions made by routers.
• The network or communication channel does not guarantee data
delivery from the host machine to the destination machine in
connectionless service.
• The data to be transmitted is broken into packets. These
independent packets are called datagrams.
• The system routes each packet independently, just like postal
packages, so there’s no way to be sure you’ll get all of the information
in correct order.
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• the source process (application program) needs to divide its
message into chunks of data of the size acceptable by the transport
layer and deliver them to the transport layer one by one.
• The transport layer treats each chunk as a single unit without any
relation between the chunks. When a chunk arrives from the
application layer, the transport layer encapsulates it in a packet and
sends it.
• To show the independency of packets, assume that a client process
has three chunks of messages to send to a server process. The
chunks are handed over to the connectionless transport protocol in
order
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• The delivery of messages at the server is not in order (0, 2, 1).
• If these three chunks of data belong to the same message, the server process may have received a strange message
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Connection-oriented protocols Connectionless protocols
authentication is needed no authentication necessary
checks whether message is received, sends
again if error occurs
no guarantees of delivery
more reliable less reliable
stream based message based
long and steady bursts of communication
congestion is not possible congestion is possible
packets follow the same route packets do not follow same route
high range bandwidth required low range bandwidth adequate
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Transport layer services

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Transport layer services