The Transport Layer

Chapter 4

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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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Services Provided to the Upper Layers

The network, transport, and application layers.

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Transport Service Primitives

The primitives for a simple transport service.

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Transport Service Primitives

The nesting of TPDUs, packets, and frames.

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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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Berkeley Sockets

The socket primitives for TCP.

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Elements of Transport Protocols

• Addressing• Connection Establishment• Connection Release• Flow Control and Buffering• Multiplexing• Crash Recovery

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Transport Protocol

(a) Environment of the data link layer.(b) Environment of the transport layer.

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Addressing

TSAPs, NSAPs and transport connections.

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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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Connection Establishment

(a) TPDUs may not enter the forbidden region.(b) The resynchronization problem.

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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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Connection Release

Abrupt disconnection with loss of data.

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Connection Release

The two-army problem.

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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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Connection Release

(c) Response lost. (d) Response lost and subsequent DRs lost.

6-14, c,d

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Multiplexing

(a) Upward multiplexing. (b) Downward multiplexing.

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Crash Recovery

Different combinations of client and server strategy.

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A Simple Transport Protocol

• The Example Service Primitives• The Example Transport Entity• The Example as a Finite State Machine

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The Example Transport Entity

The network layer packets used in our example.

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The Example Transport EntityEach 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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The Internet Transport Protocols: UDP

• Introduction to UDP• Remote Procedure Call• The Real-Time Transport Protocol

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Introduction to UDP

The UDP header.

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Remote Procedure Call

Steps in making a remote procedure call. The stubs are shaded.

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The Real-Time Transport Protocol

(a) The position of RTP in the protocol stack. (b) Packet nesting.

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The Real-Time Transport Protocol

The RTP header.

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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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The TCP Service Model

Some assigned ports.

Port Protocol Use21 FTP File transfer23 Telnet Remote login25 SMTP E-mail69 TFTP Trivial File Transfer Protocol79 Finger Lookup info about a user80 HTTP World Wide Web

110 POP-3 Remote e-mail access119 NNTP USENET news

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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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The TCP Segment Header

TCP Header.

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The TCP Segment Header

The pseudoheader included in the TCP checksum.

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TCP Connection Establishment

(a) TCP connection establishment in the normal case.(b) Call collision.

6-31

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TCP Connection Management Modeling

The states used in the TCP connection management finite state machine.

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TCP Transmission Policy

Window management in TCP.

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TCP Transmission Policy

Silly window syndrome.

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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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Transitional TCP

(a) RPC using normal TPC.(b) RPC using T/TCP.

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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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References

[1] A. S. Tanenbaum, “Computer Network”, Pearson Education

[2] Forouzen, “Data Communication and Networking”, TMH

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