Communication Network Protocols

Qiong Cheng

CSC 8320 (Fall 2007)

Outline

• Network Protocols

• OSI Protocol Suite

• TCP/IP Protocol Suite

• Protocol Examples in Internet Network and Ad Hoc Network

• References

Network protocols • Network protocols are sets of rules :

To regulate the exchange of messages To provide a reliable communication

• Human protocol vs network protocol:

Hi

HiGot thetime?2:00

TCP connection req.TCP connectionreply.Get http://www.rpi.edu/index.htm

<file>time

Network protocols are organized into a bunch of layers!

Protocol Suit & Protocol Implementation

• Layers for a standardized network architecture and the associated protocols are referred as protocol suite.

• Each protocol object has function specification and two different interfaces– service interface: defines operations on this protocol– peer-to-peer interface: defines messages exchanged with

peer

service interface

peer interface

Li+1 Li+1

LiLi

Abstraction and transparency are the keys of protocol design

OSI Protocol Suite

Physical Layer

• Specify the electrical and mechanical characteristics of physical communication link between a pair of nodes.

– Provide a reliable logical bit pipe – Bit synchronization– Coding method, the modulation technique, and wire and

connector specification.– Interface standards for data link layer.

R. Chow and T. Johnson. Distributed Operating Systems & Algorithms. 1997

Data Link Layer• Ensure reliable transfer of groups of bits (called

frames)

• Handle configuration setup, error controls, sequencing and flow control of frames– Full duplex vs. Half duplex– Errors– Sequencing– Flow control

Data Link Layer (cont.)“ link”

Network Layer

Send packets across the network through several link segments

– Routing

• Packet-by-packet / datagram-by-datagram

• Static routing decision / dynamic routing decision

• Centralized routing decision / decentralized one

• Multiple path routing

– Maintain the quality of service requested by the transport layer

– Error and flow control

Transport Layer

• Only interface between the communication sub network and the higher network-independent layers– Reliable end-to-end communication;– Transparency of network-dependent faults or problems;– Carry communication sessions;– Break message into packets;

• The OSI protocol suite implements two types of services at the transport layer: connection-oriented transport service and connectionless transport service.

Session Layer

• The session layer adds additional dialog and synchronization services to transport layer– Dialog : to facilitate the establishment of sessions– Synchronization : to allow processes to insert

checkpoints for efficient recovery from system crashes.

Presentation Layer

• Provide data encryption, compression, and code conversion for messages that use different coding schemes.

Application Layer

• The application layer is the OSI layer closest to the end user, which means that both the OSI application layer and the user interact directly with the software application.

• Some examples : Telnet, File Transfer Protocol (FTP), and Simple Mail Transfer Protocol (SMTP), DNS, Web/Http.

Client - Server Peer-to-peer

Reference Models for Layering

Application

Presentation

Session

Transport

Network

Datalink

Physical

Application

Transport

Internetwork

Host to Network

FTP

TCP

IP

Ethernet

Telnet HTTP

UDP

PacketRadio

Point-to-Point

TCP/IP ModelOSI Ref Model TCP/IP Protocols

“Bottom-up” approach & “Top-down” approach

Layering: logical and physical communication

applicationtransportnetwork

link

applicationtransportnetwork

link

applicationtransportnetwork

link

applicationtransportnetwork

link

networklink

data

dataMMMM

Ht

HtHn

HtHnHl

MMMM

Ht

HtHn

HtHnHl

The Web: the http protocolhttp: hypertext transfer

protocol• Web’s application layer

protocol• client/server model

– client: browser that requests, receives, “displays” Web objects

– server: Web server sends objects in response to requests

• http1.0: RFC 1945• http1.1: RFC 2068

PC runningExplorer

Server running

Apache Webserver

Mac runningNavigator

http request

http re

quest

http response

http re

sponse

http exampleSuppose user enters URL www.gsu.edu/College/index.html

1a. http client initiates TCP connection. Port 80.

2. http client sends http request message into TCP connection socket

1b. http server waits at port 80. “accepts” connection, notifying client

3. http server receives request message, forms response message, sends message into socket

time

http example (cont.)

5. http client receives response message, displays html.

Parsing html file, finds 10 referenced jpeg objects

6. Steps 1-5 repeated for each of 10 jpeg objects

4. http server closes TCP connection.

time

http request message: general format

GET www.gsu.edu/College/index.htmlHTTP/1.0 User-agent: Mozilla/4.0 Accept: text/html, image/gif, image/jpeg Accept-language : fr

(extra carriage return, line feed)

request line(GET, POST,

HEAD commands)header

linesCarriage return,

line feed indicates end of message

http message format: response

HTTP/1.0 200 OK Date: Thu, 06 Aug 1998 12:00:15 GMT Server: Apache/1.3.0 (Unix) Last-Modified: Mon, 22 Jun 1998 …... Content-Length: 6821 Content-Type: text/html data data data data data ...

status line(protocol

status codestatus phrase)

header lines

data, e.g., requestedhtml file

Web Caches (proxy server)

Client sends all http requests to web cache– if object at web cache,

web cache returns object

– else requests object from origin server, then returns http response to client

Goal: satisfy client request without involving origin server

client

Proxyserver

client

http request

http re

quest

http response

http re

sponse

http re

quest

http re

sponse

http requesthttp response

origin server

origin server

ftp: the file transfer protocol

• Two parallel TCP connections opened:• Control: exchange commands, responses between

client and server.• Data: file data to/from server• ftp server maintains “state”: current directory, earlier

authentication

• ftp: RFC 959• ftp server: port 21

FTPserver

FTPuser

interface

FTPclient

local filesystem

remote filesystem

user at host

TCP control connection

port 21

TCP data connectionport 20

TCP socketsSocket: a door between application process and end-to-

end-transport protocol (UCP or TCP)TCP service: reliable transfer of bytes from one process

to another

process

TCP withbuffers,

variables

socket

controlled byapplicationdeveloper

controlled byoperating

system

host orserver

process

TCP withbuffers,

variables

socket

controlled byapplicationdeveloper

controlled byoperatingsystem

host orserver

internet

Client/server socket interaction: TCP

wait for incomingconnection requestconnectionSocket =welcomeSocket.accept()

create socket,port=x, forincoming request:

welcomeSocket = ServerSocket()

create socket,connect to hostid, port=x

clientSocket = Socket()

closeconnectionSocket

read reply fromclientSocket

closeclientSocket

Server (running on hostid) Client

send request usingclientSocketread request from

connectionSocket

write reply toconnectionSocket

TCP connection setup

Ad Hoc Networks Dynamic Topology

Node mobility in Ad Hoc networks has had a great effect in the designing of routing protocols

Node mobility creates a dynamic topology, i.e., changes in the connectivity between the nodes as a direct function of the distance between each other

R. Rajaraman. Topology control and routing in ad hoc networks: a survey. ACM SIGACT News [Volume 33 ,  Issue 2  (June 2002) ]

Mobility (proactive vs. reactive)

S

D

S

D

Must wait for the updates to be transmitted, processed and

new routing tables be built

Timer Based

Proactive

A new route request is sent and a new route is

found

On Demand

Reactive

Destination Sequenced Distance Vector (DSDV)

• Routing tables define the number of hops for every network destination

• Nodes communicate their routing table to their neighbors periodically and when there is a significant new information available

• Routing information is normally transmitting using a broadcasting or multicasting mode

C. Perkins and P.Bhagwat. Highly Dynamic Destination Sequenced Distance Vector Routing (DSDV) for Mobile Computers. ACM Sigcomm 94

DSDV Operation - Example

Destination

Next Hop

Metric Sequence No

Install Time

A B 2 S406_A T001_D

B B 1 S128_B T001_D

C B 2 S564_C T001_D

D D 0 S710_D T001_D

E F 2 S392_E T002_D

F F 1 S076_F T001_D

G F 2 S128_G T002_D

H F 3 S050_H T002_D

A H

G

F

E

D

C

BD’s Routing Table

D’s Advertised Routing Table

Destination

Metric Sequence No

A 2 S406_A

B 1 S128_B

C 2 S564_C

E 2 S392_E

F 1 S076_F

G 2 S128_G

H 3 S050_H

DSDV Operation – Example (A moves)

A

H

G

F

E

D

C

B

A

• When A moves and it is detected by G and H • G and H advertise their updated routing information• All neighbor nodes update routing table • These neighbor nodes advertise to their neighbors• Termination when destination is reached

Dynamic Source Routing (DSR)

• If the sender doesn’t have a route to a destination it then attempts to find out by using a routing discovery process

• While waiting for the routing discovery to complete the sender continues sending and receiving packets with other hosts

• Each host uses a route maintenance procedure to monitor the correct operation of a route

D. Johnson, Y. Hu and D. Maltz. The Dynamic Source Routing Protocol (DSR) for Mobile Ad Hoc Networks for IPv4 [Feb. 2007]

DSR – Route Discovery

A B

G

D

E

H

node discards packets having been seen

s

D

C

F

Source broadcasts a route packet with the address of the source and destination

A neighbor that receives the request looks up its route cache to look for a route to destination. If not found it appends its address into the packet and re-broadcasts it

A-BH

AH

A

H

A H

A-DH

A-C

H

DSR – Route Discovery

A B

G

D

E

H

s

C

F

A-B

-GH

A-B-E H

D

A-B-E

-FH

node discards packets having been seen

DSR – Route maintenance

A B

G

D

E

H

s

C

F

Reply packet follows the reverse path of the route request packet recorded in broadcast packet

A-B-G-H

DA-B-G-H

A-B

-G-H

Route Discovery: at source AA need to send to G

Lookup Cache for route A to G

Route found

?

Start Route Discovery Protocol

Route Discovery finished

Packet in

buffer? Send packet to next-hop

done

Buffer packet

no

Write route in packet header

yes

yes

no

Continue normal

processingwait

Route Discovery: At an intermediate node

Accept route request packet

<src-id> in recently

seen requests

list?

Discard route

request

yes

no

Host address

already in partial route?

Discard route

request

yes

Store <src-id> in list

Broadcast packet

Send route reply packet

done

my-Addr

=target?

noAppendmy-Addr to partial route

no

yes

DSR header format - Route Request Option

DSR header format - Route Reply Option

DSR header format - Source Route Option

DSR header format - Acknowledgement Option

DSR header format - Acknowledgement Request

Option

DSR header format - Error Option

Reference1. [RFC 4728] D. Johnson, Y. Hu and D. Maltz. The Dynamic

Source Routing Protocol (DSR) for Mobile Ad Hoc Networks for IPv4 [Feb. 2007]

2. R. Rajaraman. Topology control and routing in ad hoc networks: a survey. ACM SIGACT News [Volume 33 ,  Issue 2  (June 2002) ]

3. C. Perkins and P.Bhagwat. Highly Dynamic Destination Sequenced Distance Vector Routing (DSDV) for Mobile Computers. ACM Sigcomm 94

4. D. B. Johnson and D. A. Maltz, “Dynamic Source Routing in Ad-Hoc Wireless Networks,” In Mobile Computing, edited by T. Imielinski and H. Korth, Chapter 5, pages 153-181, Kluwer Academic Publishers, 1996.

5. Andrew S. Tanenbaum. Computer Networks 6. C. Pomalaza-Ráez. Ad Hoc Networks Routing7. R. Chow and T. Johnson. Distributed Operating Systems &

Algorithms. 1997