Network Protocol Architecture

8/7/2019 Network Protocol Architecture

1/19

Network Protocol Architecture


2/19

Layered Protocols for Networking

Applicationlayer

Presentationlayer

Session

layer

Transportlayer

Networklayer

Data linklayer

Applicationlayer

Transportlayer

Physicallayer

Networklayer

Link layer

ISO/OSI Reference Model TCP/IP Model

Physical layer


3/19

Why Layers?

Divide and conquer: easier to design

Mix and match: e.g., IP over wireless link Changes isolated


4/19

What each layer does

Physical: bits (0/1), voltages, wires, pins

Data Link: framing, error detection Network: addressing, routing

Transport: end-to-end delivery, congestion

and flow control

Application: specific to application need


5/19

The IP Hourglass

IP

TCP, UDP

HTTP, FTP, NNTP, SMTP,telnet, ...

coax, twisted pair, fiber,wireless, ...

Ethernet,

FDDI, SONET

Physical Layer

Data Link Layer

Network Layer

Transport Layer

Application Layer

Spanning layer


6/19

Some Protocols in TCP/IP Suite


7/19

TCP/IP Model

Appl

Trans

port

Net

work

Link

Net

work

Link

Net

work

Link

Appl

Trans

port

Net

work

Link

Host A Host BRouter 1 Router 2

end-to-end

point-to-point

point-to-point

end-to-end


8/19

Message Flow

Appl

Trans

port

Net

work

Link

Net

work

Link

Net

work

Link

Appl

Trans

port

Net

work

Link



9/19

Encapsulation

Appl

Trans

port

Net

work

Link

Net

work

Link

Net

work

Link

Appl

Trans

port

Net

work

Link


Data

Data

Data

Data


10/19

Example

HTTP

TCP

IP

Link

IP

Link

IP

Link

HTTP

TCP

IP

Link


Data

Data

Data

HTTP header

TCP header

IP header

Data

TCP payload

IP payload

Frame payload

Frame header

Frame trailer


11/19

Protocol Techniques

For bit corruption

Parity

Checksum

CRC

For out-of-order delivery

Sequence numbers

Duplication

Sequence numbers


12/19

Protocol Techniques

(continued)

For lost packets

Positive acknowledge and retransmission

For replay (excessive delay)

Unique message ID

For data overrun

Flow control


13/19

Flow Control

Needed because

Sending computer system faster than receiving computer

Sending application faster than receiving application

Related to buffering

Two forms

Stop-and-go

Sliding window


14/19

Stop-And-Go Flow Control

Sending side

Transmits one packet

Waits for signal from receiver

Receiving side

Receives and consumes packet

Transmits signal to sender

Inefficient


15/19

Sliding Window Flow Control

Receiving side

Establishes multiple buffers and informs sender

Sending side

Transmits packets for all available buffers

Only waits if no signal arrives before transmission

completes

Receiving side

Sends signals as packets arrive


16/19

Illustration Of Sliding

Window On Sending Side

123456789101112

123456789101112

123456789101112

window

window

window

(a)

(b)

(c)

already acknowledgedstill unsent

Window tells how many packets can be sent

Window moves as acknowledgements arrive


17/19

Performance

Stop-and-go

Slow

Useful only in special cases

Sliding window

Fast

Needed in high-speed network


18/19

Comparison Of Flow Control

computer 1 computer 2 computer 1 computer 2

send

packet

sendpacket

sendpacket

sendpacket

sendack

sendack

sendack

sendack

done

sendfourpackets

sendfouracks

done

(a) (b)


19/19

Why Sliding Window?

Simultaneously

Increase throughput

Control flow

Speedup

Tw = min (B, Tg W)

where

* B is underlying hardware bandwidth,

* Tw is sliding window throughput

* Tg is stop-and-go throughput

* W is the window size

Documents

Network Protocol Architecture