1.1

Introduction

1.2

Textbook

1.3

Intro to data networks from an engineering perspective.

Broad coverage.

Network architectures.

Network protocols,

Layered design.

Protocol stack.

TCP/IP and the Internet,

Hands-on aspect.

Focus

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1-1 DATA COMMUNICATIONS

The term telecommunication means communication at a

distance. The word data refers to information presented

in whatever form is agreed upon by the parties creating

and using the data. Data communications are the

exchange of data between two devices via some form of

transmission medium such as a wire cable.

Components

Data Representation

Data Flow

Topics discussed in this section:

1.5

Criteria of Effectiveness of Data Communication

Delivery:

Data must arrive at the correct destination.

Data only arrive at the right destination.

Accuracy:

Data must be correct without any error.

Timeliness:

Data must be delivered in timely manner

Jitter:

Variation in the data arrival time at the detonation

Different applications have different requirements on these criteria

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Figure 1.1 Five components of data communication

• Message

• Sender

• Receiver

• Transmission medium

• Protocol

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Simplified Data Communications

Model

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Data Representation

• Text

• Numbers

• Images

• Audio

• Video

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Data Representation: Text

ASCII code: includes definitions for 128 characters

33 are non-printing control characters (now mostly

obsolete) that affect how text and space is processed

95 printable characters, including the space

Unicode: current prevalent coding system for text

32 bits to represent a symbol or char in any language in

the world

First 127 characters are ASCII code

Details can be found at Appendix A in the textbook

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Figure 1.2 Data flow (simplex, half-duplex, and full-duplex)

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Data Flow Examples

Simplex mode

Keyboard, mouse, traditional monitor

GPS device

Half duplex

Walkie-talkie

Advantage: entire bandwidth can be used for

transmission

Cons: not suitable for high interactive application

Full duplex

What’s a network?

“A computer network is defined as the interconnection of 2 or more independent computers.”

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1.13

1-2 NETWORKS

A network is a set of devices (often referred to as nodes)

connected by communication links. A node can be a

computer, printer, or any other device capable of sending

and/or receiving data generated by other nodes on the

network.

Distributed Processing

Network Criteria

Physical Structures

Network Models

Categories of Networks

Interconnection of Networks: Internetwork

Topics discussed in this section:

1.14

Communication Devices: Examples

Bluetooth alarm clock

switch

Wireless router

Common communication devicesNon-common communication devices

Bluetooth watches

Why network?

1.15

Some History

Before the Internet• Postal network.

– Delivers different types of objects (letters, packages, etc.) world-wide.

– Relatively high delay but relatively cheap.

– Sender and receiver identified by their postal address (name, number, street, city, etc.).

• Telephone network.

– Engineered to deliver real-time voice.

– Also world-wide.

– Low delay but more expensive.

– Users identified but telephone number.

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Evolution of Communications

Networks

About 50 years ago, a second communications network was created with the goal of providing a better transport mechanism for data.

In this class, we will study the technology underpinning data networks.

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1.18

1-3 THE INTERNET

Internet: Interconnection of Networks

Before Internet:

Many isolated Local Area Networks (LANs) existed

Those LANs had very different hardware and network

protocols

Protocol example: TCP/IP, IPX

A Brief History

The Internet Today (ISPs-Internet Service Providers)

Topics discussed in this section:

1.19

A Brief History

1961: Kleinrock - queueing theory shows effectiveness of packet-switching1964: Baran - packet-switching in military nets1967: ARPAnet conceived by Advanced Research Projects Agency1969: first ARPAnet node operational1972:

ARPAnet demonstrated publiclyNCP (Network Control Protocol) first host-host

protocol first e-mail programARPAnet has 15 nodes

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Network Criteria

• Performance:•Throughput: average rate of successful

message delivery

•Delay

•Other criteria

• Reliability: frequency of failure, recover time,

robustness

• Security

•becoming more important now

Network topology

A topology is a way of “laying out” the network. Topologies can be either physical or logical.

Physical topologies describe how the cables are run.

Logical topologies describe how the network messages travel

1.21

Network topology (cont.)

Bus (can be both logical and physical)

Star (physical only)

Ring (can be both logical and physical)

Mesh (can be both logical and physical)

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1.23

Categories of topology

Bus

A bus is the simplest physical topology. It consists of a single cable that runs to every workstation

This topology uses the least amount of cabling, but also covers the shortest amount of distance.

Each computer shares the same data and address path. With a logical bus topology, messages pass through the trunk, and each workstation checks to see if the message is addressed to itself. If the address of the message matches the workstation’s address, the network adapter copies the message to the card’s on-board memory.

1.24

have to completely reroute the cable and

possibly run two additional lengths of it.

if any one of the cables breaks, the entire

network is disrupted. Therefore, it is very

expensive to maintain.

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Bus topology

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1.27

A bus topology connecting three stations

Example: first generation Ethernet that using cable for wiring

Con: any tap device failure will cause the whole system fail

Star Topology

A physical star topology branches each network device off a central device called a hub, making it very easy to add a new workstation.

Also, if any workstation goes down it does not affect the entire network. (But, as you might expect, if the central device goes down, the entire network goes down.)

Some types of Ethernet and ARCNet use a physical star topology. Figure 8.7 gives an example of the organization of the star network.

1.28

Star Topology(cont.)

Star topologies are easy to install. A cable is run from each workstation to the hub. The hub is placed in a central location in the office.

Star topologies are more expensive to install than bus networks, because there are several more cables that need to be installed, plus the cost of the hubs that are needed.

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Star Topology

1.30

1.31

A star topology connecting four stations

Example: Ethernet switch/hub, Wifi access point

Pro: robust against a node’s failure or a link failure

Con: single point of failure at the hub

Ring

Each computer connects to two other computers, joining them in a circle creating a unidirectional path where messages move workstation to workstation.

Each entity participating in the ring reads a message, then regenerates it and hands it to its neighbor on a different network cable.

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The ring makes it difficult to add new computers.

Unlike a star topology network, the ring topology network will go down if one entity is removed from the ring.

Physical ring topology systems don’t exist much anymore, mainly because the hardware involved was fairly expensive and the fault tolerance was very low.

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Ring Topology

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1.35

Figure 1.8 A ring topology connecting six stations

Example: IBM token ring LAN (less popular now).

Mesh

The mesh topology is the simplest logical topology in terms of data flow, but it is the most complex in terms of physical design.

In this physical topology, each device is connected to every other device

This topology is rarely found in LANs, mainly because of the complexity of the cabling.

If there are x computers, there will be (x × (x–1)) ÷ 2 cables in the network. For example, if you have five computers in a mesh network, it will use 5 × (5 – 1) ÷ 2, which equals 10 cables. This complexity is compounded when you add another workstation.

For example, your five-computer, 10-cable network will jump to 15 cables just by adding one more computer. Imagine how the person doing the cabling would feel if you told them you had to cable 50 computers in a mesh network—they’d have to come up with 50 ×(50 – 1) ÷ 2 = 1225 cables!

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Because of its design, the physical mesh topology is very expensive to install and maintain.

Cables must be run from each device to every other device. The advantage you gain from it is its high fault tolerance.

With a logical mesh topology, however, there will always be a way of getting the data from source to destination.

It may not be able to take the direct route, but it can take an alternate, indirect route. It is for this reason that the mesh topology is still found in WANs to connect multiple sites across WAN links. It uses devices called routers to search multiple routes through the mesh and determine the best path.

However, the mesh topology does become inefficient with five or more entities.

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Mesh Topology

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1.39

A fully connected mesh topology (five devices)

1

2

3

45 n(n-1) half-duplex links

n(n-1)/2 duplex links

Pro: robustness

Con: many cabling/installation and need many I/O ports on nodes

Advantages and Disadvantages of Network

Topologies

1.40

Topology Advantages Disadvantages

Bus Cheap. Easy to install. Difficult to reconfigure.

Break in bus disables

entire network.

Star Cheap. Easy to install.

Easy to reconfigure.

Fault tolerant.

More expensive than bus.

Ring Efficient. Easy to install. Reconfiguration difficult.

Very expensive.

Mesh Simplest. Most fault tolerant. Reconfiguration extremely difficult.

Extremely expensive.

Very complex.

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A hybrid topology: a star backbone with three bus networks

Hybrid Topology

Fundamental Network Classifications

Local Area Networks (LANs): A local area network (LAN) is a computer network covering a small geographic area, like a

home, office, or group of buildings

Wide Area Networks (WANs): Wide Area Network (WAN) is a computer network that covers a broad area (i.e., any network

whose communications links cross metropolitan, regional, or national boundaries). Or, less formally, a network that uses routers and public communications links

The largest and most well-known example of a WAN is the Internet.

WANs are used to connect LANs and other types of networks together, so that users and computers in one location can communicate with users and computers in other locations

Metropolitan Area Network (MAN):o A metropolitan area network (MAN) is a network that interconnects users with computer resources

in a geographic area or region larger than that covered by even a large local area network (LAN) but smaller than the area covered by a wide area network (WAN). The term is applied to the interconnection of networks in a city into a single larger network (which may then also offer efficient connection to a wide area network). It is also used to mean the interconnection of several local area networks by bridging them with backbone lines. The latter usage is also sometimes referred to as a campus network.

1.43

Fundamental Network Classifications (cont)

1.44

Client

Client Client

Client Client

Client

The Local Network (LAN)

Fundamental Network Classifications (cont)

1.45

Wide Area Network (WAN)

Fundamental Network Classifications (cont)

1.46

Metropolitan Area Network (MAN)

Intranet and Internet Specifications

Intranet: An intranet is a private network that is contained within an enterprise. It may consist of many interlinked local area networks and also use leased lines in the wide area network.

An intranet uses TCP/IP, HTTP, and other Internet protocols and in general looks like a private version of the Internet. With tunneling, companies can send private messages through the public network, using the public network with special encryption/decryption and other security safeguards to connect one part of their intranet to

another.

Internet: is a worldwide system of computer networks - a network of networks in which users at any one computer can, if they have permission, get information from any other computer (and sometimes talk directly to users at other computers).

1.47

Client and Server computer role in

networking Server computer is a core component of the network,

providing a link to the resources necessary to perform any task.

A server computer provides a link to the resources necessary to perform any task.

The link it provides could be to a resource existing on the server itself or a resource on a client computer.

Client computers normally request and receive information over the network client. Client computers also depends primarily on the central server for processing activities

1.48

Peer-to peer network

A peer-to-peer network is a network where the computers act as both workstations and servers.

great for small, simple, and inexpensive networks.

In a strict peer-to-peer networking setup, every computer is an equal, a peer in the network.

Each machine can have resources that are shared with any other machine.

There is no assigned role for any particular device, and each of the devices usually runs similar software. Any device can and will send requests to any other.

1.49

Peer-to peer network (cont..)

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1.51

Types of connections: point-to-point and multipoint

Whether the link capacity is shared or not

Client/Server Networking

In this design, a small number of computers are designated as centralized servers and given the task of providing services to a larger number of user machines called clients

1.52

Client/Server Networking (cont..)

1.53

1.54

Categories of Networks

Categories of Networks

Local Area Networks

(LAN)

IEEE 802.3

IEEE 802.4

IEEE 802.5

Metropolitan Area Networks

(MAN)

High-speed DSL

Cable TV network

Wide Area Networks

(WAN)

Frame Relay

ATM

1.55

An isolated LAN connecting 12 computers to a hub in a closet

1.56

WANs: a switched WAN and a point-to-point WAN

1.57

A heterogeneous network made of four WANs and two LANs

1.58

Hierarchical organization of the Internet now

1.59

1-4 PROTOCOLS AND STANDARDS

In this section, we define two widely used terms: protocols

and standards. First, we define protocol, which is

synonymous with rule. Then we discuss standards, which

are agreed-upon rules.

Protocols – similar to human language

(syntax, semantics, timing)

Standards – public recognized protocols for open market

Standards Organizations

Internet Standards – Internet draft (work in progress)

Request for Comment (RFC) (published, final standard)

Topics discussed in this section: