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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%
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ELEN 602 Lecture 1 2
Some Communication Networks
• Flying Pigeons
• Marathon Runners
• Reflecting Mirrors
• Telephone
• Telegraph
• Cable TV
• Internet
• Satellite-based cable/telephone
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ELEN 602 Lecture 1 3
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
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ELEN 602 Lecture 1 4
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.
1.
2.
3.
4.
5.
6.
Web Access Steps
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ELEN 602 Lecture 1 5
Realplayer example
Copyright © 1995-2000, RealNetworks, Inc. All rights reserved. RealPlayer is a trademark of RealNetworks, Inc.
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ELEN 602 Lecture 1 6
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.
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ELEN 602 Lecture 1 7
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
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ELEN 602 Lecture 1 8
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.)
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ELEN 602 Lecture 1 9
t0t1
Network
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ELEN 602 Lecture 1 10
Network
(a) A switch provides the network to a cluster of users
(b) A multiplexer connects two access networks
Access network
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ELEN 602 Lecture 1 11
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
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ELEN 602 Lecture 1 12
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
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ELEN 602 Lecture 1 13
(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
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ELEN 602 Lecture 1 14
Tandem
CO
Toll
CO COCO
CO
Tandem
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ELEN 602 Lecture 1 15
(a) Time-Shared Computers & Cables for Input Devices
(b) Dial In
C...T T
C...
T
T
T
ModemPool
PSTN Modem T
T = terminal
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ELEN 602 Lecture 1 16
C
T T TT
Response from terminal
Poll to terminal
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ELEN 602 Lecture 1 17
T
T
Host...
T
Address Info
Mux
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ELEN 602 Lecture 1 18
T
T
.
.
.T
...
...
...
New York City
San Francisco
Chicago Atlanta
Host
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ELEN 602 Lecture 1 19
UCLA RAND TINKER
USC
NBS
UCSB
HARV
SCD
BBN
STAN
AMES
AMES McCLELLAN UTAH BOULDER GWC CASE
CARN
MITRE
ETAC
MIT
ILL
LINC
RADC
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ELEN 602 Lecture 1 20
(a) (b)
transceivers
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ELEN 602 Lecture 1 21
G
G
G
G
G
net 1
net 2
net 3
net 4
net 5
G = gateway
G
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ELEN 602 Lecture 1 22
Technology
Regulation Market
Standards
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ELEN 602 Lecture 1 23
time
Capability
Initial class ofinvention
Second type ofinvention
Third type ofinvention
time
Capability
(a) (b)