It provides the list of services provided by the transport to the other neighboring layer in the communication model.

1. The Transport Layer
Chapter 4
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2. The Transport Service
• Services Provided to the Upper Layers
• Transport Service Primitives
• Berkeley Sockets
• An Example of Socket Programming:
– An Internet File Server
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3. Services Provided to the Upper
Layers
The network, transport, and application layers.
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4. Transport Service Primitives
The primitives for a simple transport service.
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5. Transport Service Primitives
The nesting of TPDUs, packets, and frames.
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6. Transport Service Primitives
A state diagram for a simple connection management scheme. Transitions
labeled in italics are caused by packet arrivals. The solid lines show the client's
state sequence. The dashed lines show the server's state sequence.
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7. Berkeley Sockets
The socket primitives for TCP.
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8. Elements of Transport
Protocols
• Addressing
• Connection Establishment
• Connection Release
• Flow Control and Buffering
• Multiplexing
• Crash Recovery
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9. Transport Protocol
(a) Environment of the data link layer.
(b) Environment of the transport layer.
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10. Addressing
TSAPs, NSAPs and transport connections.
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11. Connection Establishment
How a user process in host 1 establishes a connection
with a time-of-day server in host 2.
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12. Connection Establishment
(a) TPDUs may not enter the forbidden region.
(b) The resynchronization problem.
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13. Connection Establishment
Three protocol scenarios for establishing a connection using a
three-way handshake. CR denotes CONNECTION REQUEST.
(a) Normal operation,
(b) Old CONNECTION REQUEST appearing out of nowhere.
(c) Duplicate CONNECTION REQUEST and duplicate ACK.
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14. Connection Release
Abrupt disconnection with loss of data.
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15. Connection Release
The two-army problem.
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16. Connection Release
Four protocol scenarios for releasing a connection. (a) Normal case of a
three-way handshake. (b) final ACK lost.
6-14, a, b
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17. Connection Release
(c) Response lost. (d) Response lost and subsequent DRs lost.
6-14, c,d
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18. Multiplexing
(a) Upward multiplexing. (b) Downward multiplexing.
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19. Crash Recovery
Different combinations of client and server strategy.
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20. A Simple Transport Protocol
• The Example Service Primitives
• The Example Transport Entity
• The Example as a Finite State Machine
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21. The Example Transport Entity
The network layer packets used in our example.
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22. The Example Transport Entity
Each connection is in one of seven states:
1. Idle – Connection not established yet.
2. Waiting – CONNECT has been executed, CALL REQUEST sent.
3. Queued – A CALL REQUEST has arrived; no LISTEN yet.
4. Established – The connection has been established.
5. Sending – The user is waiting for permission to send a packet.
6. Receiving – A RECEIVE has been done.
7. DISCONNECTING – a DISCONNECT has been done locally.
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23. The Internet Transport Protocols:
UDP
• Introduction to UDP
• Remote Procedure Call
• The Real-Time Transport Protocol
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24. Introduction to UDP
The UDP header.
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25. Remote Procedure Call
Steps in making a remote procedure call. The stubs are shaded.
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26. The Real-Time Transport
Protocol
(a) The position of RTP in the protocol stack. (b) Packet nesting.
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27. The Real-Time Transport
Protocol
The RTP header.
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28. The Internet Transport Protocols: TCP
• Introduction to TCP
• The TCP Service Model
• The TCP Protocol
• The TCP Segment Header
• TCP Connection Establishment
• TCP Connection Release
• TCP Connection Management Modeling
• TCP Transmission Policy
• TCP Congestion Control
• TCP Timer Management
• Wireless TCP and UDP
• Transactional TCP
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29. The TCP Service Model
Some assigned ports.
Port Protocol Use
21 FTP File transfer
23 Telnet Remote login
25 SMTP E-mail
69 TFTP Trivial File Transfer Protocol
79 Finger Lookup info about a user
80 HTTP World Wide Web
110 POP-3 Remote e-mail access
119 NNTP USENET news
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30. The TCP Service Model
(a) Four 512-byte segments sent as separate IP datagrams.
(b) The 2048 bytes of data delivered to the application in a single
READ CALL.
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31. The TCP Segment Header
TCP Header.
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32. The TCP Segment Header
The pseudoheader included in the TCP checksum.
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33. TCP Connection Establishment
(a) TCP connection establishment in the normal case.
(b) Call collision.
6-31
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34. TCP Connection Management
Modeling
The states used in the TCP connection management finite state machine.
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35. TCP Transmission Policy
Window management in TCP.
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36. TCP Transmission Policy
Silly window syndrome.
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37. TCP Congestion Control
(a) A fast network feeding a low capacity receiver.
(b) A slow network feeding a high-capacity receiver.
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38. Transitional TCP
(a) RPC using normal TPC.
(b) RPC using T/TCP.
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39. Performance Issues
• Performance Problems in Computer Networks
• Network Performance Measurement
• System Design for Better Performance
• Fast TPDU Processing
• Protocols for Gigabit Networks
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40. References
[1] A. S. Tanenbaum, “Computer Network”, Pearson Education
[2] Forouzen, “Data Communication and Networking”, TMH
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