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CS412 Introduction to Computer Networking & Telecommunication. Introduction. Topics. Introduction Metric Units Network Hardware Network Software Reference Models Example Networks Standards and Standards Organizations. Introduction. First two decades of computing

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Cs412 introduction to computer networking telecommunication

CS412 Introduction to Computer Networking & Telecommunication


Chi-Cheng Lin, Winona State University


  • Introduction

  • Metric Units

  • Network Hardware

  • Network Software

  • Reference Models

  • Example Networks

  • Standards and Standards Organizations


  • First two decades of computing

    • Highly centralized computer systems

  • Now

    • A large number of SEPARATE but INTERCONNECTED computers

      => Computer networks

What is computer network
What is Computer Network?

  • An INTERCONNECTED collection of AUTONOMOUS computers

    • Interconnected: Able to EXCHANGEINFORMATION via transmission media

      • Media: copper wire, fiber optics, microwaves, communication satellites

    • Autonomous: no master/slave relation

      • NOT autonomous:

        • One computer can control another one

        • e.g., a large computer with remote printers and terminals

What is telecommunication
What is Telecommunication?

  • What is data communication?

    • Exchange of data between two devices via some form of transmission media

    • Data are represented by bits – 0s and 1s

  • What is telecommunication?

    • Exchange of information over distance using electronic equipment

What is telecommunication1
What is Telecommunication?

  • Components of data communication

    • Sender, receiver, medium, message, and

    • Protocol: set of rules governing data communication

  • Key elements of a protocol

    • Syntax

      • Structure/format

    • Semantics

      • Meaning

    • Timing

      • When and how fast

Figure 1.1Five components of data communication

Why studying cs412
Why Studying CS412?

  • The instructor looks nice … (Don’t bet on it!)

  • It is part of our daily life now

  • The job market is good … (?)

  • You want to understand concepts and technologies of networking and telecom

    • Theory and practice

  • It is one of the most drastically changing field in CS and you like challenges

  • It makes you knowledgeable in this field

  • It is FUN!!

Distributed system vs computer network
Distributed System vs. Computer Network

  • Distributed system


      • A collection of independent computers appear as a single coherent system

    • Single model/paradigm to users

    • Middleware on top of OS

    • Example?

  • Computer network

    • No such coherence, model, middleware

    • Machines visible to users

      • Users log onto remote machines

Distributed system vs computer network1
Distributed System vs. Computer Network

  • A distributed system is a SOFTWARE system built on top of a network

  • Distinction between network and distributed system

    • Software (especially OS) rather than hardware

  • However, considerable overlap between the two subjects

Uses of computer networks
Uses of Computer Networks

  • Business applications

    • Resource sharing

    • Communication medium

    • E-commerce

  • Client-server model

    • Client requests, server performs & then replies

    • E.g., one or more file servers, many clients

Business applications of networks
Business Applications of Networks

  • A network with two clients and one server.

Uses of computer networks1
Uses of Computer Networks

  • Home applications

    • Access to remote information

      • On-line publishing, digital library, WWW

    • Person-to-person communication

      • Email, instant messaging, peer-to-peer communication, videoconferencing, Internet phone, E-learning

    • Interactive entertainment

      • Video on demand (VOD), games

    • E-commerce

      • Home shopping, electronic banking and investment, on-line auction

Home network applications 2
Home Network Applications (2)

  • In peer-to-peer system there are no fixed clients and servers.

Mobile users
Mobile Users

  • Notebook, PDA, cellular phone

  • M-commerce

  • Wireless networking and mobile computing

Metric units
Metric Units

  • The principal metric prefixes.

Network hardware
Network Hardware

  • By transmission technology

    • Broadcast links

      • smaller, geographically localized networks

    • Point-to-point links

      • larger networks

  • By scale

    • PAN

    • LAN

    • MAN

    • WAN

Broadcast network
Broadcast Network

  • A single communication channel shared by all machines on the network

  • Packets (short messages) sent by any machine are “received” by all the others

    • Address field of packet: whom it is intended

  • Message transmission

    • Unicast: one sends, one receives

    • Broadcasting: one sends, all receive

    • Multicasting: one sends, a group receives

Point to point networks
Point-to-Point Networks

  • Many connections between pairs of machines

  • Intermediate machines (called routers) might have to be visited by a packet from source to destination – more than one path is possible

  • Routing algorithms are important

    • Routing: process of finding a path from a source to the destination(s) in the network

Local area network lan
Local Area Network (LAN)

  • Private-owned Networks

  • Within a single building/campus

  • Size: up to a few kilometers

  • Characteristics

    • Size

      • Restricted by size

         worst-case transmission time bounded and known in advance

         network management simplified


  • Characteristics

    • Transmission technology

      • Machines attached to a single cable

      • Speed/capacity (High): 10 - 100 Mbps, Gbps

        • Mbps/Gbps: Megabit/Gigabit per second

        • 1 megabit=1,000,000 (not 220=1,048,576) bits

      • Delay (low): microseconds, nanoseconds

      • Errors: very few


  • Characteristics

    • Topology – the way in which a network is laid out

      • Examples: Bus, Ring



Figure 1.7Categories of topology

Figure 1.8Fully connected mesh topology (for five devices)

Figure 1.9Star topology

Figure 1.10Bus topology

Figure 1.11Ring topology

Lan topology
LAN - Topology

  • Bus (linear cable)

    • Only one machine can transmit at a time

    • Arbitration mechanism needed to resolve conflicts when two or more computers want to transmit simultaneously

      • Centralized or Distributed

    • Example: IEEE 802.3 (Ethernet):

      • Bus-based broadcast network with decentralized control operating at 10 Mbps to 10Gbps.

      • If two or more packets collide, each computer just waits a random time and tries again later.

Lan topology1
LAN - Topology

  • Ring

    • Bits propagate around the ring

    • Arbitration mechanism is needed, too

    • Example: IEEE 802.5 (IBM Token Ring)

      • Ring-based LAN operating at 4 and 16 Mbps

      • Arbitration is based on “token”

        • Only token holder can transmit

Lan channel allocation
LAN - Channel Allocation

  • Needed as all computers share one communication pathway

  • Static channel allocation

    • Divide up time into discrete intervals

    • Run a round robin algorithm

    • Allow each machine to broadcast only when its time slot comes up

    • Problem: Wasting channel capacity

Lan channel allocation1
LAN - Channel Allocation

  • Dynamic channel allocation

    • Centralized

      • A central entity determines who goes next

    • Decentralize

      • No central entity

      • Each machine decides for itself to transmit or not

      • Algorithms needed to resolve potential chaos

Metropolitan area network man
Metropolitan Area Network (MAN)

  • Covers city

  • Examples

    • Cable TV network

    • IEEE 802.16 high-speed wireless Internet access

Metropolitan area networks
Metropolitan Area Networks

  • A metropolitan area network based on cable TV.

Wide area network wan
Wide Area Network (WAN)

  • Country or continent

  • Components

    • Host (end system)

      • Machine running user (application) programs

    • Communication subnet (subnet)

      • Connecting hosts

      • Carrying messages from host to host

Wan subnet components
WAN - Subnet Components

  • Transmission lines

    • Move bits between machines

  • Switching elements

    • Specialized computers that connect two or more transmission lines

    • Determine out going line for incoming data

    • ROUTER

Wan hosts and subnet
WAN - Hosts and Subnet









: Host

: Router

Wan architecture
WAN - Architecture

  • Contains numerous cables or telephone lines

  • Each cable connects a pair of routers

  • Two routers must communicate indirectly if they are not connected by a cable

  • There might be more than one route between two hosts and it might change from time to time

    • E.g., Route from H1 to H2

Wan architecture1
WAN - Architecture

  • An intermediate router in a WAN

    • Receives a packet in its entirety

    • Queues the packet until required output line is free

    • Forwards the packet

  • Subnet using the principle above is called

    • Store-and-forward or packet-switched subnet

Wide area networks
Wide Area Networks

  • A stream of packets from sender to receiver.

Topology lans vs wans
Topology – LANs vs WANs

  • Local networks

    • Bus, Ring, Star

    • Tree

  • WANs typically irregular

Wan broadcast systems
WAN - Broadcast Systems

  • Satellite system

    • Each router has an antenna

    • Sometimes routers are connected to a substantial point-to-point subnet, with some of them having a satellite antenna

    • Inherently broadcast

Wireless network
Wireless Network

  • System interconnection

    • Example: Bluetooth

  • Wireless LANs

    • Easy to install

    • IEEE Standard 802.11

  • Wireless WANs

    • IEEE Standard 802.16

Wireless networks
Wireless Networks

Bluetooth configuration Wireless LAN

Wireless network1
Wireless Network

  • Combinations of wired and wireless networking (e.g., flying LAN)

Home network categories
Home Network Categories

  • Computers

    • Desktop PC, PDA, shared peripherals

  • Entertainment

    • TV, DVD, VCR, camera, stereo, MP3

  • Telecomm

    • Telephone, cell phone, intercom, fax

  • Appliances

    • Microwave, fridge, clock, furnace, aircon

  • Telemetry

    • Utility meter, burglar alarm, babycam


  • What is internetwork?

    • A collection of interconnected networks

  • "Internet" and "internet"

    • internet: internetwork

    • Internet: the worldwide internetwork using TCP/IP protocol suite

  • Problem: Communication between networks with different SW/HW

    • Solution: Gateways

      • Machines connect different, incompatible networks

      • Connection and translation

Figure 1.16Internet today

Network software
Network Software

  • Old computer networks:

    • HW main concern

    • SW afterthought

    • Not working now!

  • Network SW is now highly structured

    • Protocol Hierarchies

    • Implemented in hardware or firmware

Protocol hierarchies
Protocol Hierarchies

  • What is protocol?

    • Agreement between communication parties on HOW communication is processed

  • Layered architecture

    • Reduce design complexity- Lower layer offers service to higher layer

    • Hiding implementation details

    • Layer n on one machine talks to layer n on another

    • Rules and conventions used in layer n’s talk: Layer n protocol

Protocol hierarchies1
Protocol Hierarchies

  • Peers

    • Entities comprising corresponding layers on different machines

    • Virtual communication using protocol

    • Peer process abstraction make network design becomes that of individual layers

  • Physical communication

    • Sender: Data and control passed to layer below

    • Data transmitted via physical media

    • Receiver: Data and control passed to layer above

Layers protocols and interfaces
Layers, Protocols, and Interfaces

Virtual Communication

Physical Communication

Protocol hierarchies2
Protocol Hierarchies

  • Interface between two adjacent layers

    • Defines primitive operations and services a lower layer offers to the upper one

    • Minimizes amount of information passed between two layers

    • Simplifies replacement of implementation

      • E.g., telephone lines  satellite channels

Protocol hierarchies3
Protocol Hierarchies

  • Network architecture

    • Set of layers and protocols

    • Implementation and interface specification not included

  • Protocol stack

    • A list of protocols used by a certain system, one protocol per layer

Multilayer communication example
Multilayer Communication - Example

  • Philosopher-translator-secretary architecture

    • It is ok if

      • Dutch is

        replaced by


      • fax is

        replaced by


Information flow example
Information Flow - Example

  • Virtual communication for layer 5

    • Header: control information

Layer 1


00011100011100001110 …

00011100011100001110 …

Key design issues for the layers
Key Design Issues for the Layers

  • Sender/receiver identification mechanism

  • Transmission direction modes

    • Simplex

      • Data only travel in one direction

    • Half-duplex

      • Data can travel in either direction, but not simultaneously

    • Full-duplex

      • Data can travel in both directions simultaneously

  • Number of logical channels and properties

Key design issues for the layers1
Key Design Issues for the Layers

  • Error control

    • Error-detecting

    • Error-correcting

  • Sequencing

  • Flow control 

    • Needed for fast sender, slow receiver

    • Approaches

      • Feedback mechanism

      • Transmission rate agreement

Key design issues for the layers2
Key Design Issues for the Layers

  • Message disassembling, transmitting, reassembling

  • Multiplexing

    • The process of combining signals from multiple sources fortransmission across a single data link

    • Multiple connections can share the link

  • Routing

    • Selecting the best path for sending a packet from one point toanother

Connection oriented and connectionless services
Connection-Oriented and Connectionless Services

  • Two basic types of services

    • Connection-oriented

    • Connectionless

  • Consider reliability …

    • Reliable Connection-oriented

      Unreliable Connectionless

  • Note that: Connection  Reliability

Connection oriented service
Connection-Oriented Service

  • A connection is established first, then used, and then released when done.

  • Works like a pipe:

    • Sender pushes data in at one end

    • Receiver takes them out, often in the same order, at the other end

  • Analogy

    • Telephone system

Connectionless service
Connectionless Service

  • No need to set up a connection first

  • Each message carrying full destination addressis routed independently of others

    • No guarantees on the order

  • Analogy

    • Postal system

Service primitives
Service Primitives

  • Service is formally specified by a set of primitives (e.g., OS’s system calls) available to users or entities

  • Five service primitives for implementing a simple connection-oriented service.

Service primitives1
Service Primitives

  • Packets sent in a simple client-server interaction on a connection-oriented network.

Relationship of services to protocols
Relationship of Services to Protocols

  • Service

    • Set of primitives a layer provides to the layer above it

    • Define WHAT operations

      not HOW implemented

  • Protocol

    • Set of rules governing format and meaning of message exchanged by peer entities within a layer

    • Used by entities to implement service definition

Services to protocols relationship
Services to Protocols Relationship

  • The relationship between a service and a protocol.

Relationship of services to protocols1
Relationship of Services to Protocols

  • Analogy: Object-oriented languages

    • Service :: Object

      • Users do not know the implementation of a service

    • Protocol :: Implementation

      • The protocol of the service is invisible to users

      • Do you have to understand http (hypertext transport protocol) before you can surf the Internet?

Reference models
Reference Models

  • Two reference models will be discussed

    • OSI reference model

    • TCP/IP model

Osi reference model
OSI Reference Model

  • ISO/OSI (Open Systems Interconnection) Reference Model

  • NOT a network architecture itself

    • Exact services and protocols are not specified

    • Just "what should be done" in each layer

    • However, standards are produced for all layers

Osi reference model1
OSI Reference Model

  • Seven layers

    • Layer 7: application layer

    • Layer 6: presentation layer

    • Layer 5: session layer

    • Layer 4: transport layer

    • Layer 3: network layer

    • Layer 2: data link layer

    • Layer 1: physical layer (lowest)

  • Diagram of OSI reference model

    • Note: this is one of the most important figures in the whole book!!

Physical medium





Host B

Host A


Physical layer
Physical Layer

  • Transmitting raw bits (0s and 1s)

  • Design issues

    • Representation of bits

      • How is 0/1 represented?

    • Data rate: number of bits sent per second

      • How long does a bit last?

    • Transmission mode

    • Mechanical, electrical, procedural interfaces

    • Underlying physical transmission medium

Data link layer
Data Link Layer

  • Takes a raw transmission facility and transforms it into a line (link) that appears free of undetected transmission errors to networklayer

  • Basic function

    • Breaks up input data to data frames

    • Transmits data frames

    • Processes acknowledgement frames sent back from receiver

Data link layer1
Data Link Layer

  • Responsibilities (cont’d)

    • Physical addressing

    • Framing

      • creating and recognizing frame boundaries

    • Error control (adjacent nodes)

      • Errors: damaged, lost, duplicate

    • Flow control (adjacent nodes)

      • Traffic regulation between fast sender and slow receiver

    • Medium access control

      • Shared channel access control in broadcast networks

Network layer
Network Layer

  • Subnet operation control

  • Responsibilities

    • Logical addressing

    • Routing

      • Static tables

      • Determined at the start of conversation

      • Dynamic

    • Congestion control

    • Quality of service

    • Accounting

    • Heterogeneous network interconnection

Transport layer
Transport Layer

  • End-to-end layer

    • Talk to destination machine directly (virtually)

    • Layers 4 through 7 are end-to-end

    • Layers 1 through 3 are node-to-node

  • Basic function

    • Split data from session layer into smaller units

    • Pass units to network layer

    • Ensure units arrive correctly at the other end

Transport layer1
Transport Layer

  • Determine services provided to session layer (and ultimately to users)

    • Error-free point-to-point channel that delivers messages in theorder in which they were sent

    • Transport of isolated messages w/o guarantee about order

    • Broadcasting

  • Normally, a distinct network connection is created for each transportconnection required by session layer

Transport layer2
Transport Layer

  • Responsibilities include

    • Service-point addressing

      • Which message belong to which connection (application):

        • Information in header  

        • Needed as multiprogramming in a host

    • (End-to-end) Flow control Compare to the

    • (End-to-end) Error control Data Link layer

Session layer
Session layer

  • Session establishment between users on different machines

  • Responsibilities

    • Dialogue control

      • Deciding who sends, and when

    • Token management

      • Control of same operation not to be performed at the same time

    • Synchronization

      • Inserting checkpoints (checkpointing)

Figure 3-11 from Forouzan’s 2/e

Session Layer

The McGraw-Hill Companies, Inc., 1998


Presentation layer
Presentation Layer

  • Syntax/semantics of information

  • Responsibilities

    • Encoding

      • Convert from data representation used in one host to the standard abstract data structure and back

    • Encryption

    • Compression

Application layer
Application Layer

  • Provides interface and support for services to users (human, software, robots)

  • Application services

    • Network virtual terminal (telnet)

    • File transfer

    • Email

    • Network management

    • Hypertext transfer

Figure 3-14 from Forouzan’s 2/e

Summary of Layer Functions

The McGraw-Hill Companies, Inc., 1998


Tcp ip reference model
TCP/IP Reference Model

  • Goals

    • Internetworking

    • Fault tolerance

    • Flexible architecture

  • Four layers of TCP/IP Reference Model

    • Host-to-network layer

    • Internet layer

    • Transport layer

    • Application layer

Internet layer
Internet Layer

  • Packet-switching, connectionless

  • Packets injected to network

    • Independent travel

    • Out-of-order arrival

  • Analogy

    • Mail system

  • IP (Internet Protocol)

    • Packet routing

    • Congestion control

Transport layer3
Transport Layer

  • Two end-to-end protocols

    • UDP (User Datagram Protocol)

    • TCP (Transmission Control Protocol)

  • UDP (User Datagram Protocol)

    • Unreliable, connectionless

    • Widely used for

      • client-server type request-reply queries

      • speech, video

Transport layer4
Transport Layer

  • TCP

    • Reliable connection-oriented

    • Incoming byte stream (form application layer) is fragmented into discrete messages and passed onto internet layer

    • Message is reassembled at destination

    • Flow control

    • Analogy




Applications and host to network layers
Applications and Host-to-Network Layers

  • Application layer

    • No session and presentation layers


  • Host-to-network layer

    • Host has to connect to to the network using some protocol so it can send IP packets

Osi and tcp ip models
OSI and TCP/IP Models

  • Correspondence

















Data Link



Osi and tcp ip models1
OSI and TCP/IP Models

  • Similarities

    • Stack of independent protocols

    • Layer functionality

    • Transport layer 

    • Application layer

Differences between osi and tcp ip models
Differences between OSI and TCP/IP Models

  • OSI

    • Distinction between services, interfaces, and protocols(perhaps the biggest contribution)

    • Better Protocol-Hidden

    • Model first, then protocols

      • Pro: No bias, more general

      • Con: Designers did not have

        • much experience with the subject

        • a good idea of which functionality to put in which layer

    • No thought given to internetworking

    • 7 layers

    • Communication

      • Connection-Oriented and connectionless in network layer

      • Only connection-oriented in transport layer

Differences between osi and tcp ip models1
Differences between OSI and TCP/IP Models

  • TCP/IP:

    • No clear distinction between services, interfaces, and protocols

    • Worse protocol-hidden

    • Protocol first, then model

      • Pro: Protocols fit model perfectly

      • Con: Model does not fit any other protocol stacks(not general)

    • 4 layers

    • Communication

      • Connectionless in network layer

      • Both in transport layer (good for request-response protocols)

Summary of reference models
Summary of Reference Models

  • OSI

    • OSI model exceptionally useful for discussing computer networks

    • OSI protocols not popular

  • TCP/IP

    • TCP/IP model practically nonexistent

    • TCP/IP protocols widely used

  • Modified framework is used in the text

Summary of reference models1
Summary of Reference Models

  • Modified framework is used in the text

Figure 2.3Peer-to-peer processes

Figure 2.4An exchange using the Internet model

Figure 2.5Physical layer


The physical layer is responsible for transmitting individual bits from one node to the next.

Figure 2.6Data link layer


The data link layer is responsible for transmitting frames from one node to the next.

Figure 2.7Node-to-node delivery

Example 1

In Figure 2.8 a node with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by a link. At the data link level this frame contains physical addresses in the header. These are the only addresses needed. The rest of the header contains other information needed at this level. The trailer usually contains extra bits needed for error detection

Figure 2.8Example 1

Figure 2.9Network layer


The network layer is responsible for the delivery of packets from the original source to the final destination.

Figure 2.10Source-to-destination delivery

Example 2

In Figure 2.11 we want to send data from a node with network address A and physical address 10, located on one LAN, to a node with a network address P and physical address 95, located on another LAN. Because the two devices are located on different networks, we cannot use physical addresses only; the physical addresses only have local jurisdiction. What we need here are universal addresses that can pass through the LAN boundaries. The network (logical) addresses have this characteristic.

Figure 2.11Example 2

Figure 2.12Transport layer


The transport layer is responsible for delivery of a message from one process to another.

Figure 2.12Reliable process-to-process delivery of a message

Example 3

Figure 2.14 shows an example of transport layer communication. Data coming from the upper layers have port addresses j and k (j is the address of the sending process, and k is the address of the receiving process). Since the data size is larger than the network layer can handle, the data are split into two packets, each packet retaining the port addresses (j and k). Then in the network layer, network addresses (A and P) are added to each packet.

Figure 2.14Example 3

Figure 2.15Application layer


The application layer is responsible for providing services to the user.

Figure 2.16Summary of duties

Example networks
Example Networks

  • The Internet

  • Connection-Oriented Networks

    • X.25, Frame Relay, and ATM

  • Ethernet

  • Wireless LANs: 802:11

Standards and Standards Organizations

  • Why standards?

  • Categories

    • de facto

    • de jure

  • Organizations

    • ITU-T (formerly CCITT)

    • ISO

    • ANSI

    • IEEE

    • IETF

    • ATM Forum