Upload
leminh
View
216
Download
2
Embed Size (px)
Citation preview
COSC 3213: Communication Networks
Course Instructor: Marvin Mandelbaum
Contact Information:
Instructor: Section E
Teaching Assistant:Office: CSE 3012
[email protected](416) 736-2100 X40630
URL:
http://www.cs.yorku.ca/course/3213Text: A. Leon-Garcia and I. Widjaja,
Communication Networks: Fundamentals Concepts and Key Architectures, McGraw Hill, 2nd
edition
Class Schedule:
T &TR 11:30 –
13:00 a.m., Room TEL 1005
Assessment:
15% Assignment / Quiz; 25% Mid-term Exam; 60% Final Exam
Office Hours: Instructor: CSE 3012, T &TR 13:00 –
14:00TA: TBA
2
3000 level General Prerequisites (as of 2008/09)
• cse2011.03 Data Structures• Grade point average of >= 4.5 in CS &
CSE1019• Math1300 and 1310 (Calculus)
[One of cse2001,cse2021,cse2031(Theory Computation, Comp Org., Software Tools)]
[One of Math1090,1025,(Logic for COSC, Applied Linear Algebra)]
3
Course Objectives
Introduce communication networks and understand how different components work including the underlying technology including hardware and software used.
Study basic concepts of digital communications including channel encoding, modulation, error detection and error correction schemes.
Understand different topologies used in local area networks (LAN)
Comprehend how an internet (wide area network or WAN) is formed
Introduce the concept of networking standards
Transmission Control Protocol / Internet Protocol (TCP/IP)
Open Systems Interconnection Reference model (OSI)
Demystify terminology !!!!!!
4
Course Outline
Circuit Switching, Message Switching, and Packet Switching.
OSI and TCP/IP Reference Model.
Theoretical limits (Nyquist Signaling rate and Shannon Channel Capacity theorems).
Time and Frequency Representations of Signals. Intro to Fourier Analysis.
Line Coding (Unipolar NRZ, Polar NRZ, Bipolar, Manchester, Differential Manchester)
Digital Communication (ASK, PSK, FSK).
Analogue Communication (AM, FM, PM).
Modems (V.90) and Transmission Media (Microwave, Twisted pair, Coaxial, Optical Fiber).
Error Detection (Parity Bit Checking, 2D Parity Codes, Checksum, Polynomial Codes, CRC).
Flow Control (ARQ, Sliding-window, Go-back-N, Selective Repeat).
Multiplexing: FDM and TDM; Group, Supergroup, and Mastergroup configurations in FDM; DS1, DS2, and DS3 configurations in TDM.
Telephone Network and Circuit Switches: Space Division Switches, Time-Division Switches.
LAN: MAC, Data Link Layer and Logical Link Control (LLC).
LAN: Medium Access Control I – ALOHA, Slotted ALOHA, CSMA, CSMA/CD
LAN Technologies: Ethernet (802.3), Token Ring (802.5), Wireless LANs (802.11)
TCP/IP: Network and transport layers (TCP, UDP and IP Protocols)
5
What is a Communication Network (1)?Communication network is a set of equipment, software, and facilities that allows transfer of information between geographically distant users.
Why Communication networks:
⎯
Resource Sharing: Data sharing between distant sites.
⎯
High Reliability: Provide alternative sources of data.
⎯
Parallel
Processing: Use multiple computers for a single application.
⎯
Scalability: Ability to increase system size based on demand.
Applications Examples:
⎯
Radio and TV
broadcasting: Single source transmits to multiple users; Real-time (low latency), Unidirectional (simplex).
⎯
Telephone
connection: One to one connection (connection-oriented), Real-time (low latency), Bidirectional (Duplex), Fixed location
⎯
Cellular Telephone: One to one connection through microwave (roaming), similar in service to telephone connection
6
What is a Communication Network (2)?
Examples (contd):
⎯
Electronic mail
(Email):
Not real-time, Not connection-oriented, Reliable.
⎯
World wide web
(WWW):
accessed through a uniform resource locator
(URL) identifying a home page developed using a hypertext language.
⎯
Video-on-demand:
Not real-time, Unreliable.
⎯
Streamed audiovisual services:
⎯
Audio and video conferencing: Real-time, Unreliable.
⎯
Peer-to-peer applications such as Napster, Gnutella, Kazaa
file exchange
⎯
Searching for ExtraTerrestrial
Intelligence (SETI)
7
Block Representation: Communication Network
Source: generates dataTx: Converts data into tx signalsTransmission System: Carries signalsRx: Converts rx signal back into dataDestination: Accepts incoming data
8
Representation of a Communication Network
Equipment (hardware & software) and facilities that provide the basic communication service is represented by a white cloud.The equipment inside a communication network is virtually invisible to the user.Equipment includes repeaters, routers, bridges, servers, switches, multiplexers, hubs, modems, interconnecting wires, …Network architecture specifies the plan used to built and operate a communication network. TCP/IP and OSI are example of network architectures.Since the overall communication process is complex, network architecture partitions the overall communication process into separate functional areas called layers. TCP/IP consists of five layers, while OSI has seven layers.
CommunicationNetwork
Host Server
9
Services versus Applications
Service: the basic information transfer capability of a communication network.
Internet transfer of individual block of information.
Internet reliable transfer of a stream of bytes.
Real-time transfer of a voice signal.Applications use communication services to built a complete feature, hiding most of the technical details from the users.
E-mail and web built on reliable stream service.
Fax and modems built on basic telephone service.Newer applications use multiple (sometimes heterogeneous) networks.
SMS builds on Internet reliable stream service and cellular telephone text messaging
10
Evolution of Network Architectures (1)
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
Telegraphnetworks
Telephonenetworks
Internet, Optical& Wireless
networks
Info
rmat
ion
trans
fer r
ate
inbi
ts p
er se
cond
(bps
)
Next Generation
Internet
?
11
Evolution of Network Architectures (2)
Communication networks can basically be classified in the following categories:1.
Telegraph Networks
Used for digital transmission.
Uses message switching to transfer data from one node to the next one.2.
Telephone Networks
Used for transmission of both analog and digital information.
Uses circuit switching to transfer data.3.
Internet
Primarily used for computer applications.
Uses packet switching to transfer data.
Analogous to the postal mail service.
Provides “best-effort”
service with equal priority to every user.4.
Next-Generation Internet
Planned to provide “prioritized communication”
instead of “best effort”
service.
Will be based on multiservice packet switching network technology.
12
Telegraph Networks and Message Switching
(1)Pre-telegraph services used physical transport of the message using messenger pigeons, pony express, or ship service.In telegraphs, the message is typically converted into a digital signal and then transmitted across a network.In the eighteen century, optical telegraphs were initially used.
1.
Claude Chappe
invented the first optical telegraph in the 1790’s.2.
Semaphore mimicked a person with outstretched arms with flags in
each hand.
3.
Different angle combinations of arms and hands generated hundreds of possible signals.
4.
Code for enciphering messages kept secret.Later, electrical telegraphs using electrical signals were invented.
1.
William Sturgeon Electro-magnet (1825): used electrical current in a wire wrapped around a piece of iron to generate a magnetic force.
2.
Joseph Henry (1830): transmitted current over 1 mile of wire to ring a bell.3.
Samuel Morse (1835) used pulses of current to deflect electromagnet to generate dots & dashes.
Optical Telegraph
Electric Telegraph
13
Telegraph Networks and Message Switching
(2)In electric telegraphs, the message is typically converted into a digital signal and then transmitted across a network.Initially, Morse code was used to encode the alphanumeric message.Electrical signals were used to transmit the alphanumeric message.Later on 7-bit ASCII code was used to encode the messages.
•
— — — — —•
0•
· — — — —•
1•
· — ·•
R•
· ·•
I•
— — — — ·•
9•
— — · ·•
Z•
— — ·
—
•
Q•
· · · ·•
H•
— — — · ·•
8•
— · — —•
Y•
· — — ·•
P•
— — ·•
G•
— — · · ·•
7•
— · · —•
X•
— —
—
•
O•
· · — ·•
F•
— · · · ·•
6•
· — —•
W•
— ·•
N•
·•
E•
· · · · ·•
5•
· · · —•
V•
— —•
M•
— · ·•
D•
· · · · —•
4•
· · —•
U•
· — · ·•
L•
— · —
·
•
C•
· · · — —•
3•
—•
T•
— · —•
K•
— · · ·•
B•
· · — — —•
2•
· · ·•
S•
· — —
—
•
J•
· —•
A
•
Morse Code
•
Morse Code
•
Morse Code
•
Morse
Code
•
14Nodes/Switches
Message
Destination
Source
Message
Message
Message
Telegraph Networks and Message Switching
(3)Since point-to-point communications between every pair of subscriber is physically unrealizable, network nodes were created where several telegraph lines met.Each node operated on the principle of the store-and-forward operation.
1.
Message arriving on each line was decoded to extract the destination address. (addressing)
2.
Next-hop in route determined by the destination address of the message (routing).3.
Each message was stored until the next-hop is available for transmission (store).4.
On availability of the next-hop, entire message is transmitted to the next node (forwarding). Message Switching
15
1
2
34
N
. . .
Pairwise
interconnections
No. of connections = N(N −
1)/2Access network
No. of connections = N
Switch
1
2
34
N
. . .
Telephone Networks and Circuit Switching (1)
Alexander Graham Bell (1875) discovered that voice signals can be transmitted over electrical wires.
Microphones used to voice pressure variations (sound) into an analogous electrical signal.Electrical circuits communicated the signals between the communications parties.Loudspeakers converted the electrical signals back into audible sound.
Telephone patent was first granted in 1876 with the Bell Telephone Company founded in 1877.To provide interconnectivity between multiple users, two types of connections are possible.
16
Telephone Networks and Circuit Switching (2)
Pick up phone
Listen for Dial tone.
Dial number of the destination.
Exchange voice signals
1.
2.
3.
4.
5.
Telephonenetwork
Telephonenetwork
Telephonenetwork
Telephonenetwork
Telephonenetwork
Hang up to terminate the connection.6.
Connection set up
Information transfer
Connection release
17
Computer Networks and Packet Switching (1)The initial computer networks (SAGE, SABRE, etc.) were terminal-oriented networks (main frames) with a single central computer shared by multiple users.Each user had access to a dummy terminal (keyboard with monitor) connected with a dedicated line to the central computer.A user would type instructions using the dummy terminal.The instructions would be passed on to the central computer, where they were executed, and the results, returned to the dummy terminal, were displayed on the terminal. To allow fair access to the central computer, time-sharing techniques were employed.
Central computer
Terminal
Terminal
. . .
TerminalModem ModemTelephoneNetwork
18
Computer Networks and Packet Switching (2)Modification # 1:
Use a multidrop
line to connect terminals with the central computerDedicated communication lines were expensive so two simplex lines were used to interconnect the dummy terminals with the central computer.Time sharing (medium access control) was provided by polling frames that polled each terminal in a sequential order.Address in the header of the polling frame was used to identify the terminal.If a terminal wanted to communicate to the central computer, it would do so when polled.The central computer would execute the instruction and pass the result back to the terminal.
Host computer
TerminalTerminal . . . Terminal
Terminals at different locations in a cityMust avoid collisions on inbound line
Polling frames & output frames
input frames
19
Computer Networks and Packet Switching (3)Modification # 2:
Use multiplexing to (a) transmit multiple messages simultaneously and (b) to detect communication errors.Multiplexers provided a second approach for sharing the communication line.Message from each terminals was encapsulated into a frame with destination address and an error detection code (for example the CRC code).The central computer would sort out the messages from each terminal, perform possible detection of errors, carry out the necessary processing, and return the results inside a frame.The multiplexer would separate the results and direct each result to the appropriate terminal.
. . .
CRC Information Header
Header Information CRC
Central computer
Terminal
Terminal
Terminal
Multiplexer
Frame
20
Computer Networks and Packet Switching (3)
The second generation of networks were
Computer-to-computer networks.As cost of computers dropped, dumb terminals were replaced by self-computing terminals.Interconnecting such computers was required to support: (1) file transfers; (2) remote telnet to allow execution of a program on another computer; and (3) parallel processing to execute a single program over multiple computers.Circuit or message switching resulted in long communication delays. Packet switching was introduced in which long messages are broken into multiple packets.Each packet has the destination address and is transmitted independently on the network.
21
Computer Networks and Packet Switching (4)
ARPANET was the first research wide area network (WAN) commecting several universities.ARPANET operated on the principle of packet switching.Host generates message.Each message is converted into several smaller packets.Each packet contains source and destination addresses and is transferred independently. At the destination computer, the packets are combined into a single message.
UCLA RAND TINKER
USC
NBS
UCSB
HARV
SCD
BBN
STAN
AMES
AMES McCLELLAN UTAH BOULDER GWC CASE
CARN
MITRE
ETAC
MIT
ILLLINC
RADC
22
History of Networks
1.
SAGE (Semi-Automatic Ground Environment System):
⎯
First computer network developed in 1950 for air-defense purposes
2.
SABRE: an airline reservation system introduced in 1964
3.
ARPANET:
⎯
Developed in mid 1960s at height of cold war to survive a nuclear war.
⎯
Based on packet switching technology such that part of the network is working under any circumstances.
4.
NSFNET:
⎯
Developed in mid 1970s to connect research institutions and universities in U.S.
5.
ARPANET and NSFNET connected in 1983.
6.
Internet was the gluing technology for (5). Growth continued exponentially with the size of networks doubling almost every year.
7.
Other networks connected to Internet include Aurora (MIT, IBM, UPenn, Bell core); Blanca (resulting from XUNET project in AT&T), CASA (a network for supercomputers based in CA), Nectar (CMU to UPitt), Vistanet
(Univ. in North Caroliona), and many others
23
Comparison of Switching Techniques (1)
1. Circuit switching (designed by telephone companies)
⎯
End-to-end path is established between the transmitter and receiver .
⎯
Complete block of data is transmitted and circuit terminated.
⎯
Tx
and Rx are inaccessible
for the duration of the connection .
2. Message switching (designed for telegraphic networks):
⎯
No physical path is established between Tx
and Rx.
⎯
Connection is established between the Tx
and first switching office (router).
⎯
Entire block of data is transmitted to the switching office.
⎯
Block is forwarded one hop at a time.
⎯
No limit on block size, switching stations inaccessible for duration of transfer.
3. Packet switching (used in Internet):
⎯
A tight limit is placed on maximum block size.
⎯
Data is broken in different sub-blocks and each sub-block is transmitted one hop at a time, one after the other.
24
Timing Diagram
TX time
Propagation time
Start TX
Complete TX
Station A: Source
Transmitter
Station B: Destination
Receiver
25
Comparison of Switching Techniques (2)
Timing of events for: (a) circuit switched; (b) message switched; and (c)
packet switched networks
26
Comparison of Switching Techniques (3)
Circuit Switching Message Switching Packet Switching
Connection-oriented service. Connectionless service. Connectionless service.
Efficiency Highly inefficient due to long setup time.
Improvement over circuit switching because the entire connection is not established.
Best under normal working conditions.
Routing Complete path is established once at initialization of connection.
Intelligent adaptive routing algorithms are required at each switching station.
Intelligent adaptive routing algorithms are required at each router for each packet.
Synchroniza tion
No problem No problem Each packet may use a different path and hence arrive out of order
Congestion No problem Can be an issue. A big issue since numerous packets from different sources are roaming in the network.
Data Loss No problem until a connection is dropped in the middle of transfer
A router will be accepting data from various sources and may overflow.
Highest probability of overflow and data loss.
27
Functions required in Communication Networks
⎯ Basic user services:
including smtp, ftp, telnet, http, video conferencing, …
⎯ Switching: transfer information between communication lines.
⎯ Transmission:
ability to transmit (store and forward) information across a medium
⎯ Addressing:
identify communication lines and stations
⎯ Multiplexing:
means for coupling information from different sources together
⎯ Routing:
identify the shortest path between the source and destination
⎯ Congestion control:
identify congestion of data and /or ways to prevent it
⎯ Flow control: prevent overwhelming of a slower computer
⎯ Quality of service (QoS): allocate different class of service to different users
⎯ Compatibility:
connect heterogeneous networks
⎯ Error detection:
identify errors and / or correct them
⎯ Security:
prevent eavesdropping
⎯ Management:
monitor and recover from faults, manage bills etc.
28
Types of Networks (1)
Networks are typically classified in three types: LAN, MAN, and WAN
1. Local area networks (LAN)⎯
Small networks confined to a few kilometer (<= 1 km).
⎯
Speeds confined to 100 Mbps. Newer LANs run at up to 10 Gbps.
⎯
Uses the principal of broadcasting (one transmits, others listen)
⎯
Various Topologies including Token bus
and Token ring
are possible
Terminator
Token Bus Token Ring
29
Types of Networks (2)
2. Metropolitan area networks (MAN)⎯
Covers up to a city (<= 10 km), Example: Cable TV network, IEEE 802.16
⎯
Cable network were initially designed for TV and later extended to Internet
⎯
Internet is fed into a head for subsequent re-distribution
30
Types of Networks (3)
3. Wide area networks (MAN)
⎯
Spans a continent (<= 10000 km), Example: Internet
⎯
Interconnects various LAN using switches (routers) and transmission lines
⎯
Uses packet switching in conjunction with the store and forward technology