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ECE 333: Introduction to Communication Networks
`Fall 2002
`
`Lecture 1: Introduction
`
`(cid:127) Examples of communication networks/uses
`(cid:127) Course Goals
`(cid:127) History
`(cid:127) Classification of networks
`(cid:127) Related courses
`
`1
`
`Notes:
`This is an introductory course on communication networks.
`This course is still being developed in places; I hope you will forgive any ’’rough edges”
`that are still present in the course. Also I hope you will provide me with feedback
`during the quarter on what you like/dislike about the course and how it can be
`improved.
`Administrative details about the course are contained in the course information sheet
`handed out during lecture and available at
`http://www.ece.nwu.edu/-rberry/ECE333/infosheet01.pdf
`Please read over this sheet carefully before next lecture.
`The first couple of lectures will be very descriptive and at a high level; after these
`lectures, the course will become more technical and go into greater depth.
`
`2
`
`PETITIONERS - AMERICAN/SOUTHWEST, Exhibit 1026
`Page 1 of 13
`
`

`

`Questions:
`
`(cid:127) What is a communication network?
`
`(cid:127) Examples/Uses?
`
`A communication network is a system that allows users to
`exhange information.
`
`(cid:127) Users?
`(cid:127) Information?
`(analog vs. digital)
`
`3
`
`4
`
`PETITIONERS - AMERICAN/SOUTHWEST, Exhibit 1026
`Page 2 of 13
`
`

`

`Notes:
`A ’’user" can be a variety of things including a person, a computer program or a
`wireless sensor. Examples of ’’information” include data files, speech and video.
`We are primarily interested in networks where the information is represented
`digitally, i.e., as a sequence of binary digits (bits). Of course, some information
`signals, such as speech are inherently analog, however this information can still be
`represented as a digital sequence through sampling and quantization. Details of
`analog-to-digital conversion will not be dealt with in this class, but is covered in detail
`in other classes such as signals and systems (ECE 222), digital signal processing (ECE
`359), etc.
`Some common examples of communication networks include cable TV networks, the
`public telephone network and computer networks such as a local area network in an
`office or the Internet - which is actually a ’’network of networks.”
`Early communication networks were designed for a single purpose, e.g. telephone
`networks, cable TV networks, and computer networks. The trend in modern networks
`is towards networks that can satisfy a variety of different uses - these are sometimes
`called integrated service networks. A key reason for this trend is economic
`considerations - it is thought to be more cost effective to build and maintain a single
`multi-purpose network, than several single-purpose networks. Another fundamental
`reason behind this trend is the above fact that all information can be represented as
`bits, this allows a single network deigned to transfer bits between users to handle a
`variety of different information signals.
`
`Network components
`
`Networks consist of "Nodes" that communicate over "links"
`
`Nodes -
`
`Links - (point-to-point vs. broadcast)
`
`PETITIONERS - AMERICAN/SOUTHWEST, Exhibit 1026
`Page 3 of 13
`
`

`

`Notes:
`Nodes are computers, switches, routers, servers and other devices. Some nodes are
`classified as terminal nodes (often called hosts or end-users), which provide the
`interface between the "users” and the network - for example a users' desktop computer
`or a set-top box in a cable TV network. Other nodes, e.g. switches, routers, etc. are not
`identified with any user but handle information as it is sent between users. Still other
`nodes may provide various "helper” functions, such as directory services.
`The "links" are physical "channels" over which information is sent in the form of
`electromagnetic waves. One example of a link is an optical fiber where information is
`sent as a sequence of light pulses generated by a laser diode or LED. Another example
`is a radio link, where information is transmitted through the atmosphere as an
`electromagnetic wave radiated from an antenna.
`Links can be classified as either point-to-point or broadcast. Point-to-point links
`connect only two nodes, while broadcast links connect more than two nodes, i.e. when
`a signal is broadcast by one node on a broadcast link, all the other nodes on that link
`can receive it. Two issues become important - how to decide which node or nodes a
`signal is meant for and how to decide which node(s) can transmit at any time - this
`last problem is referred to as the medium access control problem.
`The arrangement of links and nodes is called the topology of the network.
`In many cases the non-terminal nodes and links are grouped together and called the
`"subnet" (this term has a different meaning in IP routing.).
`
`Communication over single point-to-point link
`
`Transmitter
`
`Channel
`
`Receiver
`
`(cid:127) Studied in ECE 307, ECE 378, ECE 380, etc.
`
`8
`
`PETITIONERS - AMERICAN/SOUTHWEST, Exhibit 1026
`Page 4 of 13
`
`

`

`Some Common Network Topologies
`
`STAR
`
`RING
`
`TREE
`
`FULLY CONNECTED
`
`IRREGU LAR MESH
`
`Additional Terminology
`
`Host
`
`Router
`
`Router
`
`Subnet
`
`Host
`
`Host
`
`9
`
`10
`
`PETITIONERS - AMERICAN/SOUTHWEST, Exhibit 1026
`Page 5 of 13
`
`

`

`Benefits of Communication Networks:
`
`(cid:127) Improved communication/convenience.
`
`(cid:127) Cost benefits - resource sharing.
`
`(cid:127) Reliability.
`
`Course Goals
`
`Understand some basic problems that all networks must address.
`
`Understand how these problems are dealt with in current networks,
`what are the trade-offs between various approaches.
`
`Learn some basic methods for performance analysis for networks.
`
`Emphasis is on conceptual understanding of basic principles - not
`on learning detailed specifications of particular standards.
`
`11
`
`12
`
`PETITIONERS - AMERICAN/SOUTHWEST, Exhibit 1026
`Page 6 of 13
`
`

`

`Some History
`
`I. Telephone Network:
`
`(cid:127) Telephone invented in 1876.
`
`(cid:127) Manual switching (1880’s).
`
`(cid:127) Electromechanical switches (1890’s).
`
`(cid:127) Computerized switches (1970’s).
`Common channel signaling & digital transmission.
`
`History
`
`II. Computer Networks
`
`1940’s
`
`Computers invented
`
`50’s - 60’s
`
`Central CPU with many remote job entry points
`
`70’s
`
`Central CPU with shared communication links,
`Separate front-end processors.
`
`Early 80’s
`
`General network with "subnet" at center, LAN’s
`
`Late 80’s
`
`General internetworks
`
`Late 90’s
`
`Internet, multiple backbones, multimedia
`
`13
`
`14
`
`PETITIONERS - AMERICAN/SOUTHWEST, Exhibit 1026
`Page 7 of 13
`
`

`

`Recent Growth of Internet
`
`Internet Domain Survey Host Count
`
`—o— Old
`—■—Adjusted
`■ New
`
`120,000,000
`
`100,000,000
`
`80,000,000
`
`60,000,000
`
`40,000,000
`
`20,000,000
`
`Jan-011--
`
`Jan-33--
`
`Jan-3B--
`
`Jan-9?--
`
`Jan-3E--
`
`-- 1
`
`Jan-3 5 -i
`
`Jan-34- i
`- 1
`Jan-33- i
`
`Jan-32 n i
`4 I
`Jan-31 HF
`
`Source: Internet Software Consortiun [www.isc.org]
`
`Source: Internet Software Consortium (http://www.isc.org/)
`
`Aug. 1981
`Jul. 2001
`
`213 Hosts
`117,288,000 Hosts
`
`15
`
`Some reasons for growth of communication networks:
`
`1. Improvements in VLSI technology
`faster, cheaper small computers
`
`2. Fiber optic communication
`high speed, low error rate links
`
`3. Critical mass of users
`Economies of scale, increased user value
`
`4. Applications
`e.g. web browsers
`
`16
`
`PETITIONERS - AMERICAN/SOUTHWEST, Exhibit 1026
`Page 8 of 13
`
`

`

`Classifying Networks
`
`I. By size or distance between communication devices.
`
`PAN
`LAN
`MAN
`WAN
`
`Personal Area Network
`Local Area Network
`Metropolitan Area Network
`Wide Area Network
`
`Different economics.
`
`Different technologies appropriate.
`
`Classifying Networks
`
`II. By Service Characteristics:
`
`(cid:127) Information formats
`(cid:127) Latency (Delay)
`(cid:127) Reliability
`(cid:127) Throughput
`(cid:127) Number of users
`(cid:127) Number of recipients
`- Multi-cast, broadcast, etc.
`
`17
`
`18
`
`PETITIONERS - AMERICAN/SOUTHWEST, Exhibit 1026
`Page 9 of 13
`
`

`

`Classifying Networks
`
`III. By Basic Design Approaches:
`
`(cid:127) Broadcast vs. point-to-point
`(cid:127) Circuit switched vs. packet switched
`(cid:127) Connection-oriented vs. connectionless
`
`19
`
`Notes:
`LANs cover a small geographic area such as a single room or a campus. Common LAN
`technologies include Ethernet and Token Ring networks. LANs often use broadcast
`links and have regular topologies such as a star, ring or bus.
`MANs are city sized networks, or perhaps a large campus, they use similar
`technologies to LANs, but offer higher speeds. Examples of MAN technologies are
`FDDI and DQDB.
`WANs cover a larger area, such as an entire country. They typically have an irregular
`topology and consist of switches or routers interconnected by point-to-point links.
`The basic service a network offers is the ability to transmit information, however
`specific characteristics of this service can differ from network to network.
`In a circuit-switched network, information is sent over a circuit or dedicated channel
`between the sender and receiver that is reserved for the duration of the session. In a
`packet-switched network information is sent as packets over a common channel, no
`resources are reserved & each packet must contain some information to identify it.
`In a connection-oriented network, a connection must first be established between
`users before information can be sent. The network must keep "state" information so
`that it knows which connections are established. In a connectionless network, no
`connection set-up is required and no state is required in within the network. All circuit
`switched networks are connection oriented, packet switched networks may be either
`connection oriented or connectionless.
`
`PETITIONERS - AMERICAN/SOUTHWEST, Exhibit 1026
`Page 10 of 13
`
`

`

`Sessions, messages, packets,...
`
`Users set up sessions (also called connections, conversations, etc.) to
`interchange information.
`
`Sessions viewed as sequence of messages or possibly a single message.
`101011
`11100
`10
`001
`
`Within the network, messages may be grouped or divided into packets of
`data (more about this next time).
`
`21
`
`Examples of sessions
`
`Interactive: Short messages, small delay, high reliability.
`
`File transfer: Long messages, moderate delay, very high reliability.
`
`Digitized voice: Short messages, strict delay, moderate reliability, regular
`data rate.
`
`Image transfer: Long messages, small delay, moderate reliability.
`
`Real-time Video: Long messages, strict delay, variable date rate (if
`compressed), moderate reliability.
`
`PETITIONERS - AMERICAN/SOUTHWEST, Exhibit 1026
`Page 11 of 13
`
`

`

`Comments on modeling
`
`In modeling networks, there are a variety of sources of uncertainty.
`
`(cid:127) Arrival times of packets, sessions, ...
`(cid:127) Lengths of packets, sessions, ...
`(cid:127) Destination of packets.
`(cid:127) Whether errors occur in packets.
`(cid:127) When a link or node fails.
`
`The main tool used for modeling this uncertainty is probability theory.
`
`23
`
`Modeling uncertainty
`
`Simple Example: Consider a sequence of packets that are sent across a link
`in a network. When packets cross a link various errors can occur causing the
`packet to not be received correctly.
`
`Suppose that each packet independently arrives correctly with probability p
`and is arrives in error with probability 1-p.
`
`What is the probability that n packets are in error out of 100?
`
`What is the average number of packets that will arrive correctly
`out of 100?
`
`What is the fraction of packets that will arrive correctly over a
`very long period of time?
`
`24
`
`PETITIONERS - AMERICAN/SOUTHWEST, Exhibit 1026
`Page 12 of 13
`
`

`

`Related (undergraduate) courses:
`
`EE curiculum
`Systems -
`Communication systems & networking
`ECE 307 Communication systems
`ECE 378 Digital Communications
`ECE 380 Wireless Communications
`
`Also courses in photonics (ECE 383 fiber optic communication), digital
`signal processing, etc.
`
`CE curriculum
`High performance computing -
`Parallel and distributed computing
`ECE 358
`Intro, to Parallel Computing
`ECE 362 Computer Architecture Projects
`
`CS-
`
`CS 340
`
`Intro to Networking
`
`25
`
`PETITIONERS - AMERICAN/SOUTHWEST, Exhibit 1026
`Page 13 of 13
`
`

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