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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
-
7:30

Room :

Dana 123

Prof :

Doug Lyon

Office 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 grades

•
You 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 2.5,2.6

•
Week 7
-
Coding and interface
standards,error detection and
interfacing.


Outline

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

PROJECT

•

T
he 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


DATA COMMUNICATION
NETWORK


comm.net


comm net node

net station i.e

computer terminal or telephone

DATA COMMUNICATION
NETWORKS


Communication networks

switched

unswitched



Switched

Circuit Switched

Packet Switched

DATA COMMUNICATION
NETWORKS

Unswitched(broadcast nets)

DATA COMMUNICATION
NETWORKS

packet radio


satellite


local

Packet switched nets are store and forward nets.

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

For example:


DATA COMMUNICATION
NETWORKS

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

DATA COMMUNICATION
NETWORKS

Dish

LAN EXAMPLES:

DATA COMMUNICATION
NETWORKS


Ethernet with a bus topology:


DATA COMMUNICATION
NETWORKS


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

DATA COMMUNICATION
NETWORKS

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 Model

Application 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.




Computer Communications
Architecture

File xfer modules

•
xmits passwords

•
file commands

•
file records


Computer Communications
Architecture

•
communications service module

–
error correction

–
encryption

–
keeps track of data to ensure delivery


•
Network Access Module

-
net specific stuff


Computer Communications
Architecture


Computer Communications
Architecture

•
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 Communications
Architecture


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)



=

number of links

Transmission Terminology



Multipoint guided transmission allows shared medium

Transmission Terminology

ANSI Defs:

–
simplex
-

one direction only

–
half
-
duplex
-

two
-
way but not at the
same time.

–
full
-
duplex
-

simultaneous two way
transmission


Transmission Terminology

•
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


Analog and Digital Data
Transmission

•
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?


Analog and Digital Data
Transmission

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


for all a

Analog and Digital Data
Transmission

A signal, s(t) is discrete iff

for some
a

For example, the function s(t) has multiple values

or does not exist and there fore the limit does not

exist.

Analog and Digital Data
Transmission

•
Let the function f be defined on the set
S. f is continuous at a point P0 of S iff

whenever

Analog and Digital Data
Transmission

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


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 <
-
> bits

•
In 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




Signal Strenth

•
Example

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

Signal Strenth


dBw=decibel watt

Signal Strenth


About Those Exponents...


The Laws of Exponents give us the laws of logarithms