chap6 network layer protocol

7/30/2019 chap6 network layer protocol

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The Transport Layer

Chapter 6


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The Transport Service

Services Provided to the Upper Layers

Transport Service Primitives

Berkeley Sockets


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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 (2)

The nesting of TPDUs, packets, and frames.


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Transport Service Primitives (3)

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


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Transport Protocol

(a) Environment of the data link layer.

(b) Environment of the transport layer.


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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(1)

Packet lifetime can be restricted to a known maximum

using one of the following techniques

1. Restricted subnet design

2. Putting a hop counter in each packet

3. Time stamping each packet


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Connection Establishment (2)

Three protocol scenarios for establishing a connection using athree-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 (2)

The two-army problem.


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

6-14, c,d


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Flow Control and Buffering

(a) Chained fixed-size buffers. (b) Chained variable-sized buffers.

(c) One large circular buffer per connection.


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The Internet Transport Protocols: UDP

Introduction to UDP

Remote Procedure Call


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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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TCP Protocol

- TCP has TCP entity- Break data into pieces not exceeding than 64KB & send as IP

datagram

- 16 bit port number

- Below 1024 are well known ports

- inetd (internet daemon)


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The TCP Service Model

Some assigned ports.

Port Protocol Use21 FTP File transfer23 Telnet Remote login

25 SMTP E-mail69 TFTP Trivial File Transfer Protocol

79 Finger Lookup info about a user80 HTTP World Wide Web

110 POP-3 Remote e-mail access

119 NNTP USENET news


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The TCP Segment Header

TCP Header.


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The TCP Segment Header (2)

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 Release

- Connections are full duplex

- Send FIN to release connection


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TCP Transmission Policy

Window management in TCP.


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TCP Transmission Policy

- Ex. Telnet connection to interactive editor that react on every key

stroke

- creates 21 byte TCP segment & 41 byte IP datagram

- Wastage of bandwidth

- delay Ack

- Nagle's Algorithm

Send first byte & buffer all until outstanding byte is

acknowledged

Send all buffered characterStart buffering again until they are all acknowledged


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TCP Transmission Policy (2)

Silly window syndrome.


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Clark solution

- Prevent the receiver from sending window update for 1 byte- forced to wait until it has decent amount of space available

- Receiver should not update window size until it can handle

maximum size

- Sender should not send tiny segments & wait till large data comes


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TCP Congestion Control

- Do not inject the packets until old one delivered

- Congestion can be prevented by

Specifying suitable window size

receiver can specify window based on it's buffer size

problem may occur due to internal congestion within network


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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

chap6 network layer protocol

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