CS 447 Networks and Data Communication Packet Encapsulation Concept and Application Department of Computer Science Southern Illinois University Edwardsville

CS 447 Networks and Data Communication

Packet EncapsulationConcept and Application

Department of Computer ScienceSouthern Illinois University Edwardsville

Fall, 2015

Dr. Hiroshi FujinokiE-mail: [email protected]

Packet_Encapsulation/001

Concept of packets

User Data User DataComputer Network

Internet

Request

ResponseRequest (1)

Response with tag (2)

Request (3)Response (4)

Internet

Request

Response

Without Packets

Computer NetworkUser Data User Data

Internet

Request

ResponseRequest (1)



Internet

Request

Response

With Packets Packet

Packet Header (e.g. packet sequence #)(e.g. destination address)



Concept of packet encapsulation: Layered Protocol Architecture

User Data

OSI 7-Layer Model TCP/IP Model

7 layers

Network Cable

User Data

4 layers

Network Cable

Host ComputerHost Computer



User Data (User Data Packet)

Header = Information specific to each protocol layer

Header

TCP Packet

IP Packet

Packet Encapsulation Visualized (1):

TCP Layer

IP Layer

Network Layer FrameDatalink Layer

Physical Layer FramePhysical Layer

Protocol Data Unit (PDU)

A packet = Header + PDU



User Data (User Data Packet)Header

TCP Packet

IP Packet


TCP Layer

IP Layer

Network Layer FrameDatalink Layer

Physical Layer FramePhysical Layer

Protocol Data Unit (PDU)

Packet Encapsulation



Packet Encapsulation Visualized (3):A packet in TCP layer

PDU in IP layer

A packet (header + PDU) in an upper protocol layer=

PDU in the next protocol layer

IP Layer IP Packet

TCP Layer TCP Packet

User Data




A packet in TCP layer

IP Layer

PDU in IP layer

IP Packet

At IP protocol layer, information in TCP headerwill be handled as if it were a part of user data

Any change in TCP will notaffect internal design of IP

PacketEncapsulation

TCP Layer TCP Packet



User Data User Data

What is possible if we have packet encapsulation?

Corresponding protocol layer can communicate

Internet

Request

ResponseRequest (1)



Internet

Request

Response

NW

Communicate using the

information in the packet header 4

3

2

1

4

3

2

1



Definition of Packet Encapsulation:

• A protocol layer can handle packets from the lower layer without knowing anything about the layer

This property guarantees the independence of each protocol layer in a protocol stack

• The entire packet in a lower protocol layer becomes the PDU for the next upper protocol layer

• Without packet encapsulation, most of the advantages in the layered structure will not be utilized

• Without packet encapsulation, each protocol layer has to know the rules in any lower layers


Ext_Int/001

Protocol layers

Sender ReceiverExternal Operation

The top fourlayers in OSI7-layer model

Transport Layer

Application Layer

Presentation Layer

Session Layer

Underlying Network

Internal Operation

The bottom threelayers in OSI7-layer model

Network Layer

DataLink Layer

Physical Layer

Transport Layer

Application Layer

Presentation Layer

Session Layer

Network Layer

DataLink Layer

Physical Layer

External and Internal Operations


InternalOperation

External Operation

Virtual Circuit

Virtual Circuit

Datagram

Datagram

A

B C

D


Ext_Int/002

Example: External Virtual Circuit and Internal Datagram

External Operation(Virtual Circuit)

Internal Operation(Datagram)



3

2

1

3

2

1

3

2

1

3

2

1

Protocol layers Datagram Network

12

3

Sender Receiver

TCP

IP

TCP

IP

Packets will bere-ordered


Ext_Int/003

Example: External Datagram and Internal Datagram

External Operation(Datagram)




3

2

1

3

2

1

3

2

1

3

2

1

Protocol layers Datagram Network

12

3

Sender Receiver

UDP

IP

UDP

IP

Packets will not bere-ordered


Ext_Int/004

Example: External Virtual Circuit and Internal Virtual Circuit


Internal Operation(Virtual Circuit)



3

2

1

Protocol layers Virtual Circuit Network

123

Sender Receiver

2

1

3

ISDN Telephone Network

3

2

1

2

1

3


Ext_Int/005

Example: External Datagram and Internal Virtual Circuit





Protocol layers Virtual Circuit Network

123

Sender Receiver

Ext_Int/006


InternalOperation

External Operation

Virtual Circuit

Virtual Circuit

Datagram

Datagram TCP/IP (Internet) UDP/IP (Internet)

ISDN Telephone(Digital Telephone Network)

Analog Public Telephone


Ext_Int/007

Documents

CS 447 Networks and Data Communication Packet Encapsulation Concept and Application Department of Computer Science Southern Illinois University Edwardsville