computer communications
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
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Computer Communications
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Hi! I am Prof.Doug Lyon
I Welcome you to this class
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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
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Computer Communications I: System Analysis
Text: Data and Computer
communications by
William Stallings,
MacMillan Co. Fourth
Edition
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Grading
Home work is optional Attendance is optional Final is optional Grade is average quiz score
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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
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Grading
Lowest two quizzes dropped (or are optional, i.e. sick days)
You MUST pick one of the following:
Final = 4 quiz grades
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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
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PROJECT
Project examples: Symbolic Computation, teaching aids, functional simulation etc. See me for projects.
Paper = 4 quiz grades. Survey of approved journal
articles
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Topics include ,but are not limited to,(by chapter)
TOPICS:Week 1-
History ,architectural overview and design issues in computer communications.CH1
Outline
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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
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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
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Outline
Week6-Transmission and switching FDM,TDM,STDM.Multiplexing ISDN.
CH 2.5,2.6Week 7-Coding and interface
standards,error detection and interfacing.
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Outline
Week 8,9-Data link control,control of retransmission,HDLC protocol
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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
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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
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Outline
Week 11-Circuit switching,virtual curcuits, packet switching and datagram packet switching.ATM,data kit.
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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.
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Outline
Week 14-Radio and satellite networks:Explores design and performance issues for antenna-based communication nets.Wireless packet radio systems
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Outline
Week 15-LANs,examine CSMA/CD, various topologies,alternative mediums and access control techniques.
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A COMMUNICATION MODEL
Source Channel
noise
Destination
xmitted signal rcvd signal
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DATA COMMUNICATION NETWORK
comm.net
comm net node
net station i.ecomputer terminal or telephone
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DATA COMMUNICATION NETWORKS
Communication networks
switched unswitched
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Switched
Circuit Switched Packet Switched
DATA COMMUNICATION NETWORKS
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Unswitched(broadcast nets)
DATA COMMUNICATION NETWORKS
packet radio satellite local
Packet switched nets are store and forward nets.
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ckt switched nets have dedicated communication paths (i.e. telephone)
For example:
DATA COMMUNICATION NETWORKS
net station
node
A Broadcast Comm. Net can be WAN, the media is unshared
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DATA COMMUNICATION NETWORKS
Dish
LAN EXAMPLES:
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DATA COMMUNICATION NETWORKS
Ethernet with a bus topology:
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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
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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.
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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.
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Computer Communications Architecture
File xfer modulesxmits passwordsfile commandsfile records
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Computer Communications Architecture
communications service module–error correction–encryption–keeps track of data to ensure delivery
Network Access Module-net specific stuff
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Computer Communications Architecture
Applications Applications
Transport layer 1 2 3
Transport layer 1 2 3
network access
network accessCom net
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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
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Computer Communications Architecture
Computer 1 Computer 2
FTP1 FTP2
Communication Service module
Communication Service module
Network Access Module
Network Access Module
Comm msgs
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Protocol Data Units
TPDU1 = transport protocol data unit := transport hdr, chunk1
TPDU2 = transport hdr, chunk2
NPDU = network protocol data unit network hdr, TPDU
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Protocol Data Units
Application data = chunk1 + chunk2 + ...
Destination SAP (service access points)
TPDU has destination SAP so that appropriate application obtains data
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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)
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Transmission Terminology
point-to-point :- guided transmission is unshared
I.e. O(N**2) connectivity (completely connected)
L12
(N 2 N ) = number of links
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Transmission Terminology
Multipoint guided transmission allows shared medium
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Transmission Terminology
ANSI Defs:–simplex - one direction only–half-duplex - two-way but not at the same time.
– full-duplex - simultaneous two way transmission
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Transmission Terminology
CCITT– CCITT vs ANSI– simplex = half-duplex– duplex = full-duplex
CCITT = international telegraph and telephone consultive committee
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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
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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?
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Analog and Digital Data Transmission
lim s(t) s(a)
t a
s(t) is continuous (i.e. analog) iff
for all a
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Analog and Digital Data Transmission
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.
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Analog and Digital Data Transmission
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
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Analog and Digital Data Transmission
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
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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
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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.
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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.
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Signal Strenth
Let number of decibels
P1 ,P2 power values
Log = Log10
Ndb 10 log10P1
P2
Ndb
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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
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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)
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Signal Strenth
0 dBw = 10log 1w1w
voltage (dBmv) (decibel - milivolt) = 20log10voltage (mv)
1 mv
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About Those Exponents...
aman amn
am
anam n
am n amn
The Laws of Exponents give us the laws of logarithms