l7a_tcp_udp_ex

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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001

TCP/IP - Example

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TCP/IP Protocol Suite

Application

Transport

Internet

Data Link

Physical

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TCP/IP And OSI Model

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L5 data

L5 data H4

L4 data H3

L3 data H2T2

01010101010110101

L5 data

L5 data H4

L4 data H3

L3 data H2T2

01010101010110101

5

4

3

2

1

5

4

3

2

1

Transmission medium

An Exchange Using the TCP Model

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TCP/IP Model - An Example

• The application being used is SMTP (electronic mail)• The message content is “hi” (ASCII - 68+69)• How this message flows through all the layers till it finally

reaches the destination.

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Application Layer

ApplicationEg. SMTP - Email

Application

Presentation

Session

6869

Message(2 bytes)

Local part@Domain name

Address of themailbox on thelocal site

The domain nameof the destination

Message formatting, data compression, data encryption,and synchronization of data exchange

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Transport Layer

TCP UDP

TransportH

TCP Header(20 bytes)

User datagram(22 bytes)

6869

2 bytes

End-to-end delivery of message, addressing service points,reliable delivery, multiplexing

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TCP Header

- 520 - 520

- 6869

5H

5

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Network Layer

IP

NetworkH

IP header(20 bytes)

Datagram(42 bytes)

Source-to-destination delivery, addressing, address resolution

User datagram(22 bytes)

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IP Header

4H 5H 0026H

0.0.0

80H 11H

9594H

128.194.55.152

128.194.55.254

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Data Link & Physical Layer

Data link

Physical

Protocols defined by theunderlying layer

10010101010001

H

Frame(68 bytes)

Bits

Header(14 bytes)

Datagram

Delivering data units, flow control, error detection, access control, conversion of data bits into electric signals and transmission

T

Trailer(4 bytes)

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802.3 MAC Frame

• Destination address : 00:c0:02:16:67:36• Source address : 00:80:5f:57:a9:a8• Type : 0800H (IP)

Type

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UDP: Example

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USER DATAGRAM PROTOCOL

• Connectionless• Unreliable• Simple• Packet Oriented• Simple Application Interface

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UDP Frame

Source Port(16 Bits)

Destination Port(16 Bits)

Length(16 Bits)

Checksum(16 Bits)

DATA

Length of Datagram

Optional : 16 bit one’s complement sum of the pseudo IP header, the UDP Header and the Data.

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PROTOCOLS USING UDP

• SNMP • DNS• BOOTP• TFTP• SUNRPC• SNMPTRAP• NFS• RIP• GDP• BIFF• WHO• SYSLOG

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UDP FRAME CAPTURED

ADDR HEX ASCII0000: 00 60 2f dd 1d 20 08 00 20 8f 9b 39 08 00 45 00 | .`/.. .. ..9..E.0010: 00 48 7c 20 40 00 ff 11 b0 8e 82 bf a3 74 82 bf | .H| @........t..0020: a6 02 a5 f2 00 35 00 34 f9 ba 4f 04 01 00 00 01 | .....5.4..O.....0030: 00 00 00 00 00 00 01 32 03 31 36 36 03 31 39 31 | .......2.166.1910040: 03 31 33 30 07 69 6e 2d 61 64 64 72 04 61 72 70 | .130.in-addr.arp0050: 61 00 00 0c 00 01 | a..…

UDP: ----- UDP Header -----UDP:UDP: Source port = 42482

UDP: Destination port = 53 (Domain)UDP: Length = 52

UDP: Checksum = F9BA (correct)UDP: [44 byte(s) of data]

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UDP DATAGRAMS in JAVA

• Applications that communicate via datagrams send and receive completely independent packets of information. These clients andservers do not have and do not need a dedicated point-to-point channel. The delivery of datagrams to their destinations is not guaranteed. Nor is the order of their arrival.

Definition: A datagram is an independent, self-contained message sent over the network whose arrival, arrival time, and content are not guaranteed.

• The java.net package contains two classes to help you write Java programs that use datagrams to send and receive packets over the network: DatagramSocket, DatagramPacket, and MulticastSocket

• An application can send and receive DatagramPackets through aDatagramSocket. In addition, DatagramPackets can be broadcast to

multiple recipients all listening to a MulticastSocket.

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To Send Datagrams

int port;InetAddress address;DatagramSocket socket = null;DatagramPacket packet;byte[] sendBuf = new byte[256];

DatagramSocket socket = new DatagramSocket();

byte[] buf = new byte[256];InetAddress address =

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To Receive Datagrams

int port;InetAddress address;DatagramSocket socket = null;DatagramPacket packet;byte[] sendBuf = new byte[256];

DatagramSocket socket = newDatagramSocket(port);

byte[] buf = new byte[256];

packet = new DatagramPacket(buf, buf.length);

socket.receive(packet);

l7a_tcp_udp_ex

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