ELEN 602 Lecture 11 ELEN 602 Computer Communications & Networks Instructor: Narasimha Reddy Contact:...

ELEN 602 Lecture 1 1

ELEN 602 Computer Communications & Networks

Instructor: Narasimha Reddy

Contact: [email protected], 845-7598, 320 F Wisenbaker

Textbook: Communication Networks by Leon-Garcia & Widjaja

Class notes available: http://ee.tamu.edu/~reddy/ee602_02.html

Teaching Assistant/Grader: To Be Announced

TA Office Hours: To Be Announced

Grading: Homeworks: 30%, Tests: 60%, Project: 10%


Some Communication Networks

• Flying Pigeons

• Marathon Runners

• Reflecting Mirrors

• Telephone

• Telegraph

• Cable TV

• Internet

• Satellite-based cable/telephone


The caller picks up the phone triggering the flow of current in wires that connect to the telephone office.

The current is detected and a dial tone is transmitted by the telephone office to indicate that it is ready to receive the destination number.

The caller sends this number by pushing the keys on the telephone set. Each key generates a pair of tones that specify a number. (In the older phone sets the user dials a number which in turn generates a corresponding number of pulses.)

The equipment in the telephone office then uses the telephone network to attempt a connection. If the destination telephone busy, then a busy tone is returned to the caller. If the destination telephone is idle, then ringing signals are sent to both the originating and destination telephones.

The ringing signals are discontinued when the destination phone is picked up and communication can then proceed.

Either of the users terminate the call by putting down a receiver.

Telephone Office

1.

Telephone Office

2.

Telephone Office

3.

4.

Telephone Office

5.

6.

Telephone Office

Telephone Office

Telephone Functioning


The user clicks on a link to indicate which document is to be retrieved.

The browser must determine the address that contains the document. It does this by sending a query to its local name server.

Once the address is known the browser establishes a connection to the specified machine, usually a TCP connection. In order for the connection to be successful, the specified machine must be ready to accept TCP connections.

The browser runs a client version of HTTP, which issues a request specifying both the name of the document and the possible document formats it can handle.

The machine that contains the requested document runs a server version of HTTP. It reacts to the HTTP request by sending an HTTP response which contains the desired document in the appropriate format.

The TCP connection is then closed and the user may view the document.

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2.

3.

4.

5.

6.

Web Access Steps


Realplayer example

Copyright © 1995-2000, RealNetworks, Inc. All rights reserved. RealPlayer is a trademark of RealNetworks, Inc.


Steps in Communication - US Mail

• Compose the letter -- based on the user/office/personal

• Package it for transport -- put it in an envelope, address (to and from) it, leave it in a well-known port (mailbox)

• Postman picks up the mail, local post office sorts it for further transport

• Number of letters may be bundled and transported to remote city

• Remote post office sorts them by local addresses, postman delivers it to the To-mailbox

• Remote person picks up the mail, receives the message.


Work in generic communication

• Addressing -how to address the comm. for transport

– telephone numbers, US Mail addresses, IP addresses

• Name-to-address translation -- phone directory, address book, DNS name resolution

• Routing -- which way to send a piece of comm. to reach B from point A

– East-coast US mail may go to Houston -New York

• Transport -- how to actually move the data/mail/bits/

– Trucks/planes with US mail, telephone wires, LAN

– Multiplexing of different pieces of communication


What you will learn in this class?

• Addressing (IPv4 and IPv6)

• Routing (routing protocols)

• Name resoultion (DNS)

• Transport

– Physical media (Ethernet, SONET, FDDI, ATM etc.)

– Multiplexing (switches/routers)

– Queuing theory -(delay/loss analysis)

– Protocols (TCP/IP)

• Some Applications - (http/email etc.)


t0t1

Network


Network

(a) A switch provides the network to a cluster of users

(b) A multiplexer connects two access networks

Access network


Metropolitan network A consists of access subnetworks a, b, c, d.

National network consists of regional subnetworks .

Metropolitan network A is part of regional subnetwork .

A

A

Metropolitan

1*

a

c

b

d

(a)

(b)

2

34


Tra

nsm

issi

on c

apac

ity

(bit

s/se

con

d)

1.0E+00

1.0E+02

1.0E+04

1.0E+06

1.0E+08

1.0E+10

1.0E+12

1.0E+14

1850 1875 1900 1925 1950 1975 2000

Printing telegraph

Baudot multiplex

T-1 carrier

T-4 carrier

SONET OC-48

DWDM


(a) A switch in the form of an operator with a patch cord panel (not shown)

(b) Cords interconnect user sockets providing end-to-end connection


Tandem

CO

Toll

CO COCO

CO

Tandem


(a) Time-Shared Computers & Cables for Input Devices

(b) Dial In

C...T T

C...

T

T

T

ModemPool

PSTN Modem T

T = terminal


C

T T TT

Response from terminal

Poll to terminal


T

T

Host...

T

Address Info

Mux


T

T

.

.

.T

...

...

...

New York City

San Francisco

Chicago Atlanta

Host


UCLA RAND TINKER

USC

NBS

UCSB

HARV

SCD

BBN

STAN

AMES

AMES McCLELLAN UTAH BOULDER GWC CASE

CARN

MITRE

ETAC

MIT

ILL

LINC

RADC


(a) (b)

transceivers


G

G

G

G

G

net 1

net 2

net 3

net 4

net 5

G = gateway

G


Technology

Regulation Market

Standards


time

Capability

Initial class ofinvention

Second type ofinvention

Third type ofinvention

time

Capability

(a) (b)

ELEN 602 Lecture 11 ELEN 602 Computer Communications & Networks Instructor: Narasimha Reddy Contact:...

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