computer communications. hi! i am prof.doug lyon i welcome you to this class
TRANSCRIPT
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
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
net station
node
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 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.
Computer Communications Architecture
File xfer modulesxmits passwordsfile commandsfile 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
Applications Applications
Transport layer 1 2 3
Transport layer 1 2 3
network access
network accessCom net
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
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
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
lim s(t) s(a)
t a
s(t) is continuous (i.e. analog) iff
for all a
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.
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
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
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