cmpe 150 – winter 2009 lecture 3 january 13, 2009 p.e. mantey
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CMPE 150 -- Introduction to Computer Networks
Instructor: Patrick Mantey [email protected] http://www.soe.ucsc.edu/~mantey/
Office: Engr. 2 Room 595J Office hours: Tuesday 3-5 PM TA: Anselm Kia [email protected] Web site: http://www.soe.ucsc.edu/classes/cmpe150/Winter09/
Text: Tannenbaum: Computer Networks (4th edition – available in bookstore, etc. )
Today’s Agenda
Standards Layered Network Architecture -
review Networks and History Physical Layer
Signals and Systems Fourier Analysis Communication Theory
Standards Required to allow for interoperability between
equipment Advantages
Ensures a large market for equipment and software Allows products from different vendors to
communicate Disadvantages
Freeze technology May be multiple standards for the same thing
Network Standardization
Who’s Who in the Telecommunications World
Who’s Who in the International Standards World
Who’s Who in the Internet Standards World
ITU
Main sectors• Radiocommunications• Telecommunications Standardization• Development
Classes of Members• National governments• Sector members• Associate members• Regulatory agencies
IEEE 802 Standards
The 802 working groups. The important ones are marked with *. The ones marked with are hibernating. The one marked with † gave up.
A Critique of the OSI Model and Protocols
Why OSI did not take over the world
Bad timing Bad technology Bad implementations Bad politics
A Critique of the TCP/IP Reference Model
Problems: Service, interface, and protocol not
distinguished Not a general model Host-to-network “layer” not really a layer No mention of physical and data link layers Minor protocols deeply entrenched, hard to
replace
Internet Layering
Level 5 -- Application Layer (rlogin, ftp, SMTP, POP3, IMAP, HTTP..)
Level 4 -- Transport Layer(a.k.a Host-to-Host)(TCP, UDP, ARP, ICMP, etc.)
Level 3 -- Network Layer (a.k.a. Internet) (IP)Level 2 -- (Data) Link Layer / MAC sub-layer
(a.k.a. Network Interface or Network Access Layer)
Level 1 -- Physical Layer
Example Networks
The Internet Connection-Oriented Networks:
X.25, Frame Relay, and ATM
Ethernet Wireless LANs: 802:11
Characteristics Internet Layer
Connectionless Internet Protocol (IP) Task is to deliver packets to destination
Transport Layer Transmission Control Protocol (TCP)
Connection-oriented Reliable
User Datagram Protocol (UDP) Connectionless Unreliable
TELCO Networks
Connection-Oriented Networks X.25 Frame Relay ATM
Fixed Route (set up at start of call) Quality of Service Billing – for connection time
T1
• Time-division multiplexed stream of 24 telephone channels
• The basic technology upon which all T-carrier facilities are based
• Uses a full-duplex digital signal over two wire pairs.
• Bandwidth of 1.544 Mbps through telephone-switching network
• Uses AMI or B8ZS coding.
SONET
• Synchronous Optical NETwork• Synchronous Digital Hierarchy (SDH) Europe• Internet for CARRIERS• Worldwide standard• Multiplex multiple digital channels• Management support for
– Operations– Administration– Maintenance
X.25 and Frame Relay• X.25 -- First Public Data Network – 1970s
– Call and connect “Data Terminal Equipment”
– Simple packet structure
– Implemented “virtual circuit” connections
– Flow control, hop-by-hop error control
– Multiplexing – up to 4095 circuits at a time
• Frame Relay – 1980s (up to 2Mbps)
– Limited error control, flow control
– VC based packet switching --“wide area LAN”
Asynchronous Transfer Mode• Vintage mid -1980s • Goal to unify voice networks and data networks• Packet Switching with virtual circuits (“channels”)• Fixed-length packets (“cells”) - @ 53 bytes
– 5 byte header, 48 byte “payload”– Virtual channel header (VCI)– No retransmission link-by-link
Error correction codes only• Envisioned to reach the end user• Used widely today for backbones
The ARPANET
(a) Structure of the telephone system.(b) Baran’s proposed distributed switching
system.
The ARPANET (3)
Growth of the ARPANET (a) December 1969. (b) July 1970.(c) March 1971. (d) April 1972. (e) September 1972.
SIGNALS and SYSTEMS
What is a signal?
What is a system?
Signal: time varying function produced by physical device (voltage, current, etc.)
SIGNALS and SYSTEMS
What is a signal?
What is a system?
Signal: time varying function produced by physical device (voltage, current, etc.)
System: device or process (algorithm) having signals as input and output
Input x(t) output y(t)
SIGNALS and SYSTEMS
Periodic signals --
f(t+T) = f(t) Period = T (seconds)
Frequency = 1/ Period
(“cycles” / sec. = Hertz (Hz)
001/f T
SIGNALS and SYSTEMS
Periodic signals --
f(t+T) = f(t) Period = T (seconds)
Frequency = 1/ Period
(“cycles” / sec. = Hertz (Hz)
Radian frequency:
(radians/sec.)2 f
Fourier Series
2
0 0
0
2
0 0
0
1( )cos(2 ) ( )
1( )sin(2 ) ( )
n
n
a x t nf t d t
b x t nf t d t
00
0 0
0 00 0
1
2
1 2( ) 2 2
fT
t f t
d t f dt dt dtT T
is the “fundamental frequency”
0 01
1( ) cos(2 ) sin(2 )
2
N
n i nn
x t a a nf t b nf t
Fourier Series
Integration limits: when 0 2t , then
0 0 0
2 2 1
2 /t
T T
so we get:
0 01
1( ) cos(2 ) sin(2 )
2
N
n i nn
x t a a nf t b nf t
0
0
00 0
00 0
2( )cos(2 )
2( )sin(2 )
T
n
T
n
a x t nf t dtT
b x t nf t dtT
Fourier Series
Euler:
0 01
1( ) cos(2 ) sin(2 )
2
N
n i nn
x t a a nf t b nf t
2 cos(2 ) sin(2 )ij f ti ie f t j f t
02( ) jn f tn
n
x t c e
02( ) jn f t
in
x t c e
Fourier Series
02( ) jn f tn
n
x t c e
0
0
0
2
02
1( )
T
jn tn
T
c x t e dtT
We can show2 2
n n nc a b 1tan ( / )n nb a ;
recall that2 2 1cos( ) sin( ) cos( tan ( ))
ba b a b
a