computer communications

Computer Communications

Hi! I am Prof.Doug Lyon

I Welcome you to this class

Computer Communications I: System Analysis

Course Number : CpE 471 Meets : Monday 5-

7:30Room : Dana 123Prof : Doug LyonOffice Hours : 1:30–2:30

MWF

and by appointment

Computer Communications I: System Analysis

Text: Data and Computer

communications by

William Stallings,

MacMillan Co. Fourth

Edition

Grading

Home work is optional Attendance is optional Final is optional Grade is average quiz score

Grading

A 15 min. cumulative open-book/ open-notes calculators permitted quiz every week (but not today!) Next quiz 9/13/93 since no class 9/6/93

Grading

Lowest two quizzes dropped (or are optional, i.e. sick days)

You MUST pick one of the following:

Final = 4 quiz grades

PROJECT

Project = 4 quiz gradesYou will be responsible for

obtaining software for your project. STELLA should be at the book store. STELLA is optional. Call them at 603-643-9636 for a copy

PROJECT

Project examples: Symbolic Computation, teaching aids, functional simulation etc. See me for projects.

Paper = 4 quiz grades. Survey of approved journal

articles

Topics include ,but are not limited to,(by chapter)

TOPICS:Week 1-

History ,architectural overview and design issues in computer communications.CH1

Outline

Outline

Week2-Theoretical basis for data communications,bandwidth-limits , data transmission,signal parameters, media,attenuation delay. Fourier analysis.Fiber optics. CH 2.1,2.2

Outline

Week3-Data encoding,Modulation Techniques .Information Theory. FM,AM,PM,sampling Theorem, coding,Modems,RS232 interfacing,serial standards,CH-2.3

Week4,5-Digital TransmissionPCM encodingsystems,X.21,AX.21. CH2.4

Outline

Week6-Transmission and switching FDM,TDM,STDM.Multiplexing ISDN.

CH 2.5,2.6Week 7-Coding and interface

standards,error detection and interfacing.

Outline

Week 8,9-Data link control,control of retransmission,HDLC protocol

PROJECT

The project and paper are due on

11/29/93 (day after Thanksgiving weekend). A late project has 10

points out of 100 removed from

the project grade per day late, resulting in a 0 after 12/9/93

Outline

Week 10-Introduction to Queueing Theory,M/M/ 1, networks of M/M/1, queues,simulating queueing systems,applications of queueing.CH: Appendix A

Outline

Week 11-Circuit switching,virtual curcuits, packet switching and datagram packet switching.ATM,data kit.

Outline

Week 12-Circuit switching,PBX,Networkcontrol, routing algorithms for point-top-point networks.

Week 13-Packet switching,virtual circuits and datagrams.Routing Algorithms. Hardware networks.

Outline

Week 14-Radio and satellite networks:Explores design and performance issues for antenna-based communication nets.Wireless packet radio systems

Outline

Week 15-LANs,examine CSMA/CD, various topologies,alternative mediums and access control techniques.

A COMMUNICATION MODEL

Source Channel

noise

Destination

xmitted signal rcvd signal

DATA COMMUNICATION NETWORK

comm.net

comm net node

net station i.ecomputer terminal or telephone

DATA COMMUNICATION NETWORKS

Communication networks

switched unswitched

Switched

Circuit Switched Packet Switched


Unswitched(broadcast nets)


packet radio satellite local

Packet switched nets are store and forward nets.

ckt switched nets have dedicated communication paths (i.e. telephone)

For example:


net station

node

A Broadcast Comm. Net can be WAN, the media is unshared


Dish

LAN EXAMPLES:


Ethernet with a bus topology:


Ring topology net:

Note: No switching nodes ,media is shared in LAN

For packet radio,every station can hear every other,the media is shared so this is a LAN technology


Agent input device transmitter channel

channel receiver output device

This course addresses the communication systems parts between the input and output devices.

Computer Communications Architecture

The Three Layer ModelApplication run on computer which use

networks

network layer - xchange of data between computer

and network transport layer - error detection and correction application layer - file xfer etc.


File xfer modulesxmits passwordsfile commandsfile records


communications service module–error correction–encryption–keeps track of data to ensure delivery

Network Access Module-net specific stuff


Applications Applications

Transport layer 1 2 3

Transport layer 1 2 3

network access

network accessCom net


The transport layer will break data into chunks adds control information and this is called a PDU or protocol data unit

Network access layer is told which computer but not which SAP

(SAP)service acess points 1 2 and 3 are used to uniquely identify the application communicating


Computer 1 Computer 2

FTP1 FTP2

Communication Service module

Communication Service module

Network Access Module

Network Access Module

Comm msgs

Protocol Data Units

TPDU1 = transport protocol data unit := transport hdr, chunk1

TPDU2 = transport hdr, chunk2

NPDU = network protocol data unit network hdr, TPDU

Protocol Data Units

Application data = chunk1 + chunk2 + ...

Destination SAP (service access points)

TPDU has destination SAP so that appropriate application obtains data

Protocol Data Units

Sequence # TPDU’s may be sent in any

order,and by different routes and

may arrive at different times.TPDU may have error detection or correction codes built-in

NPDU destination address (i.e. IP address) facilities requires (i.e. priority)

Transmission Terminology

point-to-point :- guided transmission is unshared

I.e. O(N**2) connectivity (completely connected)

L12

(N 2 N ) = number of links


Multipoint guided transmission allows shared medium


ANSI Defs:–simplex - one direction only–half-duplex - two-way but not at the same time.

– full-duplex - simultaneous two way transmission


CCITT– CCITT vs ANSI– simplex = half-duplex– duplex = full-duplex

CCITT = international telegraph and telephone consultive committee

Analog and Digital Data Transmission

data - entities which convey meaning

signals - encoding of data

signaling - act of sending a signal

transmission - communication of data by propagation and processing

of signals


digital data

- takes on discrete values, i.e. text integers.

analog data

- takes on continuously varying patterns of

intensity, i.e.. sound

But what is digital? What is Analog? How do we defines these things?


lim s(t) s(a)

t a

s(t) is continuous (i.e. analog) iff

for all a


A signal, s(t) is discrete iff

lim s(t) s(a)

t afor some a

For example, the function s(t) has multiple values or does not exist and there fore the limit does not exist.


Let the function f be defined on the set S. f is continuous at a point P0 of S iffLim f (Pn ) f (P0 )

n whenever Pn P0 ,Pn S


If f is defined on an interval [a, b] and is continuous at then given an

0 there exists a s. t .

f (x ) f (x0 ) for all x1 x2 x1 ,x2 S

DATA and SIGNALS

Modem (modulator/demodulator) modulation involves two waveforms:

The modulating signal (the message) and the carrier wave which is altered by the modulating signal

The complementary process is called demodulation

Bits <-> modem <-> analog signal <-> modem <-> bits

DATA and SIGNALS

Codec := coder-decoder

analog <-> codec <-> bitsIn General a digital waveform has

infinite bandwidth.Band limited channels low-pass filter

square waves, this rounds their corners.

Rule of thumb: if a signal is W bps, you may need 2W Hz bandwidth.

Signal Strenth

attenuation := a loss of signal strength–signal strength falls off logarithmically so the decibel is used to measure the loss

–Decibel gains and losses are computed via simple addition and subtraction.

Signal Strenth

Let number of decibels

P1 ,P2 power values

Log = Log10

Ndb 10 log10P1

P2

Ndb

Signal Strenth Example

P1 10 mw, P2 5 mw

loss=10log(5/10)=-3 dB

if P =V2

RP power drops accross resistor R

V = voltage drop accross resistor R

Signal Strenth

N dB 10 logP1

P2

10logV1

2 / RV1

2 / R20 log

V1

V2dBw=decibel watt

power (dbw) = 10 log Power (w)

1 (w)

Signal Strenth

0 dBw = 10log 1w1w

voltage (dBmv) (decibel - milivolt) = 20log10voltage (mv)

1 mv

About Those Exponents...

aman amn

am

anam n

am n amn

The Laws of Exponents give us the laws of logarithms

computer communications

Documents

data communications

communication paths

data transmission

data kit

data link control

optional final

satellite networks

optional grade