UCTI SPACC 04 Process to Process Delivery UDP and TCP

8/12/2019 UCTI SPACC 04 Process to Process Delivery UDP and TCP

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System Programming and Computer Control

Client-Server Model: Socket Interface

Slide 1Process to process delivery UDP and TCP

Process to Process Delivery:UDP and TCP

Prepared by: KL First Prepared on: 9-09-07 Last Modified on:

Quality checked by: xxx

Copyright 2007 Asia Pacific Institute of Information Technology

Level-2

System Programming and Computer ControlCE00352-2-SPCC
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System Programming and Computer Control Slide 2Process to process delivery UDP and TCP

Topic & Structure of the lesson

Process to Process Delivery

User Datagram Protocol (UDP)

Transmission Control Protocol (TCP)
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Key Terms you must be able to use

Client

Client-server paradigm

Connection establishment

Connection termination

Connectionless service

Connection-oriented service

Ephemeral port number

Finite state machine

Flow control

Keep-alive timer

Persistence timer

Port number

Process-to-process delivery

Receiver window Retransmission timer

Round-trip time (RTT)

Segment

Sender window Sequence number

Server

Silly windows syndrome

If you have mastered this topic, you should be able to use the following terms

correctly in your assignments and exams:-


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Key Terms you must be able to use

Sliding window

Socket address

State transition diagram

TCP timer

Three-way handshake

Time-waited timer

Transmission ControlProtocol (TCP)

User datagram User Datagram Protocol

(UDP)

Well-known port numbers

If you have mastered this topic, you should be able to use the following terms

correctly in your assignments and exams:-


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Position of transport layer


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8/77System Programming and Computer Control Slide 8Process to process delivery UDP and TCP

Transport layer duties



Packetizing

The transport layer creates packetsout of the

message received from the application layer.

Packetizing divides a long messageinto smallerones and encapsulated into the data field of the

transport-layer packet and headers are added.


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Addressing

The packet carrying the request must specify to

which server program the request must be

delivered.

The request packet must also specify the client

program that sent the packet.


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The transport layer is responsible for

process-to-process delivery.

Note:



Types of data deliveries



Process-to-Process Delivery

1. Client-Server Paradigm

2. Addressing

3. Multiplexing and Demultiplexing

4. Connectionless/Connection-Oriented5. Reliable/Unreliable



Client-server Paradigm

A process on the local host, called a client, needsservices from a process usually on the remote host,called a server.

Operating system today support both multiuser andmultiprogramming environments. A remote computercan run several server programs at the same time, justas local computers can run one or more clientprograms at the same time.

Local host

Local process

Remote host

Remote process



Addressing

A transport-layer address, called a port number,

to choose among multiple processes running on

the destination host.

The destination port number is needed for

delivery; the source port number is needed for

the reply.

Ephemeral portnumber are 16-bit integers

between 0 and 65,535.


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Addressing

The Internet has decided to use universal portnumbers for servers; these are called well-known port numbers.

The IP addressesand port numbersplaydifferent roles in selecting the final destinationof data.

The destination IP address defines the hostamong the different hosts in the world. After thehost been selected, the port numberdefines

one of the processes on this particular host.



IP addresses versus port numbers



Address IANA Ranges

The IANA (Internet Assigned Number Authority)has divided the port numbers into three ranges:

Well-known ports. The port ranging from 0 to 1023

are assigned and controlled by IANA.

Registered ports. The ports ranging 1024 to 49,151are not assigned or controlled by IANA. They canonly be registered with IANA to prevent duplication.

Dynamic ports. The ports ranging from 49,152 to65,535 are neither controlled nor registered. Theycan be used by any process.


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Socket address

The combination of an IPaddress and a port numberis called a socketaddress.

A transport-layer protocolneeds a pair of socket addresses: the clientsocket address and the server socket address.

The UDP and TCP header contains the port numbers.


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Multiplexing and demultiplexing

The addressing mechanism allows multiplexing and

demultiplexingby the transport layer.

Multiplexing: At the sender site, there may be several

processes that need to send packets. The protocolaccepts message from different processes. After

adding the header, the transport layer passes the

packet to the network layer.

Demultiplexing: At the receiver site, the transport layer

delivers each message to the appropriate process

based on the port number.


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Multiplexing and demultiplexing


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Connectionless vs Connection-Oriented

A transport-layer protocol can either be connectionless

or connection-oriented.

Connectionless Service

The packets are sent from one party to another with

no need for connection establishment or connection

release.

The packets are not numbered; they may be delayed,

or arrive out of sequence.

There is no acknowledgment either. Example UDP.


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Connection Oriented Service

A connection is first established between the sender and thereceiver. Data are transferred. At the end, the connection isreleased. Example: TCPis a connection-oriented protocol.

Connection Establishment

1. Host A sends a packet to announce its wish for connection and includesits initialization information about traffic from A to B.

2. Host B send a packet to acknowledge (confirm) the request of A.

3. Host B sends a packet that includes its initialization information about

traffic from B to A.4. Host A sends a packet to acknowledge (confirm) the request of B.

This connection establishment implies four steps. However,since steps 2 and 3 can occur at the same time, they can be

combined into one step.


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Connection Termination

Connection in one direction is terminated, the other party cancontinue sending data in the other direction. Therefore, fouractions needed to close the connections in both directions:

1. Host A sends a packet announcing its wish for connection termination.

2. Host B sends a segment acknowledging (confirming) the request of A.After this, the connection is closed in one direction, but not in the other.Host B can continue sending data to A.

3. When host B has finished sending its own data, it sends a segment toindicate that it wants to close the connection.

4. Host A acknowledges (confirms) the request of B.

The four-step connection termination cannot be reduced tothree steps because the two parties may not wish to terminateat the same time. In other words, connection termination is

asymmetric.


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Error control


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User Datagram Protocol (UDP)

1. Port Numbers

2. User Datagram

3. Applications

UDP does not add anything to the services of IP except for providing process-to-process communication instead of host-to-host communication. Also, it performsvery limited error checking.

UDP is very simple protocol with a minimum of overhead.

UDP is a convenient protocol for multimedia and multicasting applications.


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UDP is a connectionless, unreliable

protocol that has no flow and error

control. I t uses port numbers tomultiplex data from the application

layer.

Note:


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Well-known ports used by UDP

Port Protocol Description

7 Echo Echoes a received datagram back to the sender

9 Discard Discards any datagram that is received

11 Users Active users

13 Daytime Returns the date and the time

17 Quote Returns a quote of the day19 Chargen Returns a string of characters

53 Nameserver Domain Name Service

67 Bootps Server port to download bootstrap information

68 Bootpc Client port to download bootstrap information

69 TFTP Trivial File Transfer Protocol

111 RPC Remote Procedure Call

123 NTP Network Time Protocol

161 SNMP Simple Network Management Protocol

162 SNMP Simple Network Management Protocol (trap)
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User Datagram Format

Source port number. This is the port number used by theprocess running on the source host.

Destination port number. This is the port number used by theprocess running on the destination host.

Length. This is a 16-bit field that defines the total length of theuser datagram, header plus data.

Checksum. This field is used to detect errors over the entireuser datagram (header plus data). This ensures that those

fields have not been changed from the source to thedestination. The calculation of the checksum and its inclusion ina user datagram are option. If the checksum is not calculated,the field is filled with 0s.


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User datagram format

UDP Packets, called user datagrams, have a fixed-size header of 8 bytes.


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The calculation of checksum and its

inclusion in the user datagram areoptional.

Note:


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UDP is a convenient transport-layer

protocol for applications that provide

f low and error control. I t is also usedby multimedia applications.

Note:


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Transmission Control Protocol (TCP)

Port Numbers

ServicesSequence Numbers

Segments

Connection

Transition Diagram

Flow and Error Control

Silly Window Syndrome

TCP is called a stream connection-orientedand reliable transport protocol.


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Port Numbers

Like UDP, TCP uses port numbers as tranport-

layer addresses.

If an application can use both UDP and TCP,the same port number is assigned to this

application.


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Stream delivery

TCP, is steam-oriented protocol. In UDP, a process(an application program) sends a chunk of bytes toUDP for delivery. UDP adds its own header to thischunk of data, which is now called a user datagram,

and delivers it to IP for transmission. The process maydeliver several chunks of data to the UDP, but UDPtreats each chunk independently without seeing anyconnection between them.

TCP, on the other hand, allows the sending process todeliver data as a stream of bytes and the receivingprocess to obtain data as a stream of bytes. TCPcreates an environment in which the two processesseem to be connected by an imaginary. tube that

carries their data across the Internet.


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Stream delivery


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Sending and receiving buffers

The sending and the receiving processes may

not produce and consume data at the same

speed. TCP needs buffers for storage.

There are two buffers, the sending buffer and

the receiving buffer, for each direction.

One way to implement a buffer is to use acircular array of 1-byte locations.


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Sending and receiving buffers

At the sending site, the buffer has three types of locations. The white section containsempty locations that can be filled by the sending process.

The blue area hold bytes that have been sent but not yet acknowledged.

The bytes in blue locations area acknowledged, the location is recycled and availablefor use by the sending process.

After both processes have no data left to send and the buffers are empty, the two

TCPs destroy their buffers.


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TCP segments

TCP groups a number of bytes together into a packetcalled a segment.

TCP adds a header to each segment and delivers the

segment to the IP layer for transmission.

The segments are encapsulated in an IP datagram

and transmitted.

The segments are not necessarily the same size. Inreality segments carry hundreds, if not thousands, of

bytes.


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Byte Numbers

TCP numbers all data bytes that are transmitted

in a connection. Numbering is independent in

each direction.

When TCP receives bytes of data from the

process and stores them in the sending buffer,

it numbers them.

The numbering does not necessary start from

0; it starts with a randomly generated number

between 0 and 2321.


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The bytes of data being transferred in

each connection are numbered by

TCP. The numbering starts with a

randomly generated number.

Note:


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Example 1

Imagine a TCP connection is transferring a file of 6000 bytes. The

first byte is numbered 10010. What are the sequence numbers for

each segment if data are sent in five segments with the first foursegments carrying 1000 bytes and the last segment carrying 2000

bytes?

Solution

The following shows the sequence number for each segment:Segment 1==> sequence number: 10,010 (range: 10,010 to 11,009)Segment 2 ==> sequence number: 11,010 (range: 11,010 to 12,009)Segment 3==> sequence number: 12,010 (range: 12,010 to 13,009)Segment 4 ==> sequence number: 13,010 (range: 13,010 to 14,009)

Segment 5 ==> sequence number: 14,010 (range: 14,010 to 16,009)


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The value of the sequence number

f ield in a segment defines the number

of the first data byte contained in thatsegment.

Note:


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TCP segment format

The unit of data transfer between two devicesusing TCP is a segment.

The segment consist of a 20- to 60-byte

header, followed by data from the application

program.

The header is 20 bytes if there are no optionsand up to 60 bytes if it contains options.

C f


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TCP segment format

Next slide discuss the above header fields


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Header

Acknowledgment number: This 32-bit field defines the bytenumber that the sender of the segment is expecting to receivefrom the other party. If the byte numbered x has beensuccessful received, x+1 is the acknowledgment number.

Header length: This 4-bit field indicates the number of 4-bytewords in the TCP header. The length of the header can bebetween 20 and 60 bytes. Therefore, the value of this field canbe between 5 (5x4 = 20) and 15 (15x4 =60).

Reserved: This field defines 6 different control bits or flagswhich can be set at a time. These bits enable flow control,connection establishment and termination, and the mode ofdata transfer in TCP.

C t l fi ld


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Control field

Description of flags in the control field


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Description of flags in the control field

Flag Description

URG The value of the urgent pointer field is valid.

ACK The value of the acknowledgment field is valid.

PSH Push the data.

RST The connection must be reset.

SYN Synchronize sequence numbers during connection.

FIN Terminate the connection.


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Three-step connection establishment

F t ti t i ti


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Four-step connection termination

St t f TCP


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States for TCP

State Description

CLOSED There is no connection.

LISTEN The server is waiting for calls from the client.

SYN-SENT A connection request is sent; waiting for acknowledgment.

SYN-RCVD A connection request is received.

ESTABLISHED Connection is established.

FIN-WAIT-1The application has requested the closing of the

connection.

FIN-WAIT-2 The other side has accepted the closing of the connection.

TIME-WAIT Waiting for retransmitted segments to die.

CLOSE-WAIT The server is waiting for the application to close.

St t t iti di


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State transition diagram


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Sender buffer


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Sender buffer

Receiver window


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Receiver window

Sender buffer and sender window


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Sender buffer and sender window

Slidi th d i d


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Sliding the sender window

E di th d i d


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Expanding the sender window

Sh i ki th d i d


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Shrinking the sender window


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I n TCP, the sender window size is

totally controlled by the receiver

window value (the number of empty

locations in the receiver buffer).

However, the actual window size can

be smaller if there is congestion in the

network.

Note:


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Some points about TCPs sliding windows:

Note:

The source does not have to send a fullwindows worth of data.

The size of the window can be increased ordecreased by the destination.

The destination can send an acknowledgment

at any time.

L t t


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Lost segment

L k l d


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Lost acknowledgment

TCP timers


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TCP timers

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UCTI SPACC 04 Process to Process Delivery UDP and TCP