Download TCP and UDP

TCP/IP Transport Layer Protocols
TCP/UDP
© 2004, Cisco Systems, Inc. All rights reserved.
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Objectives
•
Explain the role of Transport Layer protocols
– TCP (Transport Control Protocol)
– UDP (User Datagram Protocol)
•
Analyze the operation of TCP mechanisms that
support
– reliability
– reassembly and
– manage data loss.
•
Analyze the operation of UDP
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Packet handling on the Internet
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Transport Layer Role and Services
•Transport layer prepares application
data for transport over the network and
•Processes data for use by applications
•Assembles data received by network
layer
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Transport Protocols: TCP and UDP
• Two Transport Layer Protocols in TCP/IP
model
–UDP: user datagram protocol
–
Connection-less protocol.
–TCP: transmission control protocol
Connection-oriented protocol.
– Different applications use different
transport protocols based on the nature of
the application
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TCP Connection setup – Three way handshake
TCP offers reliable communication
Connection setup stage precedes
data transfer stage
Three way handshake procedure:
1. Sender sends in a request to
receiver to set up connection
Send SYN
SEQ = 100
2. Receiver accepts the
connection request, if feasible.
Acknowledges sender’s
request
3. Sender acknowledges receiver
confirmation
Established
SEQ 101, ACK 301
Once connection is setup, data
transfer can take place
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Data Transfer
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TCP Flow Control: How Fast to Send Data
• Flow Control is necessary so that
source does not transmit too fast for
a receivertoo fast for given receiver
• TCP Window size :Sender and
Receiver agree at Session
establishment stage about the size
of data sent at a time
Size of advertised window related to
receiver’s buffer space.
• Sender can send data up to
receiver’s advertised window.
• TCP window size can be
increased/decreased during data
transfer session
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Data
Not Ready
Buffer FULL
Ready
Process uses
Data
Data
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TCP Basic Window: How many bytes of
Data to send
Window size 1 Byte
Send 1
Receive 1
ACK 2
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TCP Basic Window –Window Size Negotiation
ACK 3
Window size 2
Send 3
bytes
ACK 5
Window size 2
Send 3
bytes
Send 2
bytes
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TCP Reliable Delivery
• Reliable delivery offered by
• Acknowledgements.
• Timeouts and
• Retransmissions.
• Ordered delivery.
•Sequence numbers.
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TCP reliable delivery– Sequencing Data
• Data generated by
application is broken
down into segments
• Segments are assigned
sequence numbers
• Different segments may
take different route to
destination
• Having taken different
routes , segments arrive
out of order
• TCP uses sequence
numbers to reconstruct
the data stream with
segments placed in the
correct order
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TCP Sequence and Acknowledgement
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TCP Reliable delivery: Handling lost packets
• Retransmission timer: When a data segment is
sent, a timer is started.
–If the segment is acknowledged before the
timer expires, the timer is stopped and reset.
–Otherwise, the segment is retransmitted
(and the timer is reset and started again).
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UDP: User Datagram Protocol
• “no frills,” “bare bones” Internet transport protocol
• “best effort” service, UDP segments may be:
–lost
–delivered out of order to application
• connectionless:
no handshaking between UDP sender, receiver
each UDP segment handled independently of
others
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UDP Protocol
•Different datagrams
may take different
route to destination
•Datagrams may
arrive out of order
•Out of order
datagrams are not
ordered
•Lost datagrams are
not sent
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Applications of UDP
• Often used for streaming
multimedia apps
loss tolerant
rate sensitive
• reliable transfer over UDP:
• Application is responsible
for error recovery of lost
data
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Summary: TCP and UDP
• TCP provides end-to-end communication. It
takes care of reliable, error-free transfer of data,
and in-sequence delivery
• UDP has less overhead compared to TCP, but does not
guarantee transfers
TCP is preferred to transfer files
UDP is preferred to transfer audio/video streams
In real-time streaming, we cannot afford the delay
consequent to packet retransmission
• Both protocols support multiplexing, i.e. they allow
several distinct streams of data between two hosts
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