CHAPTER 2

Students completing this chapter should be able to:

•Explain the importance of bandwidth in networking. •Use an analogy from their experience to explain bandwidth. •Explain the difference between bandwidth and throughput. •Calculate data transfer rates. •Explain why layered models are used to describe data communication. •Explain the development of the Open System Interconnection model (OSI). •List the advantages of a layered approach. •Identify each of the seven layers of the OSI model. •Identify the four layers of the TCP/IP model. •Describe the similarities and differences between the two models. •Briefly outline the history of networking. •Identify devices used in networking. •Understand the role of protocols in networking. •Define LAN, WAN, MAN, and SAN. •Explain VPNs and their advantages. •Describe the differences between intranets and extranets.

    

Networking Fundamentals

Evolution of Networking

Local Area Networks (LAN)

Businesses needed a solution that would successfully address the following three problems: How to avoid duplication

of equipment and resources

How to communicate efficiently

How to set up and manage a network

Wide-area networks (WANs)

A way for information to move efficiently and quickly

WANs could connect user networks over large geographic areas

Examples of data Networks

Networking Devices

Equipment that connects directly to a network segment is referred to as a device. These devices are broken up into two classifications.

Network Devicesend-user devices

End user devices

End-user devices that provide users with a connection to the network are also referred to as hosts

These devices allow users to share, create, and obtain information.

Host devices are physically connected to the network media using a network interface card (NIC)

Network interface card(NIC)

A NIC is a printed circuit board that fits into the expansion slot of a bus on a computer motherboard, or it can be a peripheral device.

Network interface card(NIC)

Laptop or notebook computer NICs are usually the size of a PCMCIA card.

Each individual NIC carries a unique code, called a Media Access Control (MAC) address

End User Devices

Network devices

Network devices provide transport for the data that needs to be transferred between end-user devices. Network devices provide extension of cable connections, concentration of connections, conversion of data formats, and management of data transfers.

Network Devices

Repeater

A repeater is a network device used to regenerate a signal. Repeaters regenerate analog or digital signals distorted by transmission loss due to attenuation.

Bridges

convert network transmission data formats as well as perform basic data transmission management.

provide connections between LANs. perform a check on the data to determine

whether it should cross the bridge or not. This makes each part of the network more efficient

Bridges

Switches

Workgroup switches add more intelligence to data transfer management.

They can determine whether data should remain on a LAN or not

They can transfer the data only to the connection that needs that data.

Switches

Routers

Routers have all the capabilities listed above. regenerate signals concentrate multiple connections convert data transmission formats, and manage data transfers They can also connect to a WAN, which allows them to connect

LANs that are separated by great distances

Network topology

Network topology defines the structure of the network. One part of the topology definition is the physical topology, which is the actual layout of the wire or media. The other part is the logical topology, which defines how the media is accessed by the hosts for sending data

Logical topology

The logical topology of a network is how the hosts communicate across the medium

- broadcast

Ethernet

- token passing

Token Ring

Fiber Distributed Data Interface (FDDI)

Different topologies

A protocol

A protocol is a formal description of a set of rules and conventions that govern a particular aspect of how devices on a network communicate.

Protocols determine the format, timing, sequencing, and error control in data communication

Protocols

Protocols control all aspects of datacommunication, which include the following: (IEEE, ANSI , TIA , EIA , ITU )

How the physical network is built How computers connect to the network How the data is formatted for transmission How that data is sent How to deal with errors

Local-area networks (LANs)

LANs consist of the following components:

Computers Network interface

cards Peripheral devices Networking media Network devices

Some common LAN

technologies are:

Ethernet Token Ring FDDI

LANs technologies

Wide-area networks (WANs)

WANs interconnect LANs, which then provide access to computers or file servers in other locations.

Some common WANtechnologies are: Modems Integrated Services

Digital Network (ISDN) Digital Subscriber Line

(DSL) Frame Relay US (T) and Europe (E)

Carrier Series – T1, E1, T3, E3

Synchronous Optical Network (SONET)

WANs and WAN Devices

Metropolitan-area networks (MANs)

A MAN is a network that spans a metropolitan area such as a city or suburban area. A MAN usually consists of two or more LANs in a common geographic area .

Storage-area networks (SANs)

A SAN is a dedicated, high-performance network used to move data between servers and storage resources SANs offer the following features: Performance – SANs enable concurrent access of disk

or tape arrays by two or more servers at high speeds. Availability – SANs have disaster tolerance built in,

because data can be mirrored using a SAN up to 10 kilometers (km) or 6.2 miles away.

Scalability – Like a LAN/WAN, it can use a variety of technologies. This allows easy relocation of backup data, operations, file migration, and data replication between systems.

Storage-area networks (SANs)

Virtual private network (VPN)

A VPN is a private network that is constructed within a public network infrastructure such as the global Internet. Using VPN, a telecommuter can access the network of the company headquarters through the Internet by building a secure tunnel between the telecommuter’s PC and a VPN router in the headquarters

Types of VPNs

Access VPNs – Access VPNs provide remote access to a mobile worker and small office/home office (SOHO) to the headquarters of the Intranet or Extranet over a shared infrastructure.

Intranet VPNs – Intranet VPNs link regional and remote offices to the headquarters of the internal network over a shared infrastructure using dedicated connections

Extranet VPNs – Extranet VPNs link business partners to the headquarters of the network over a shared infrastructure using dedicated connections

A VPN is a service that offers secure, reliable connectivity over a shared public network infrastructure such as the Internet.

They are the most cost-effective method of establishing a point-to-point connection between remote users and an enterprise customer's network

Benefits of VPNs

Intranets and extranets

Intranets are designed to permit access by users who have access privileges to the internal LAN of the organization.

Extranets refer to applications and services that are Intranet based, and use extended, secure access to external users or enterprises.

Importance of bandwidth

Bandwidth is defined as the amount of information that can flow through a network connection in a given period of time.

Pipe Analogy for Bandwidth

Highway Analogy for Bandwidth

Measurement

In digital systems, the basic unit of bandwidth is bits per second (bps). Bandwidth is the measure of how much information, or bits, can flow from one place to another in a given amount of time, or seconds.

Limitations

Bandwidth varies depending upon the type of media as well as the LAN and WAN technologies used. The physics of the media account for some of the difference.

The actual bandwidth of a network is determined by a combination of the physical media and the technologies chosen for signaling and detecting network signals.

Distance and bandwidth

File Transfer Time Calculations

Throughput

Throughput refers to actual measured bandwidth, at a specific time of day, using specific Internet routes, and while a specific set of data is transmitted on the network

Digital versus analog

Electromagnetic waves are called analog because they have the same shapes as the light and sound waves produced by the transmitters

Analog bandwidth is measured by how much of the electromagnetic spectrum is occupied by each signal. The basic unit of analog bandwidth is hertz (Hz), or cycles per second.

In digital signaling all information is sent as bits, regardless of the kind of information it is. Voice, video, and data all become streams of bits when they are prepared for transmission over digital media.

Unlimited amounts of information can be sent over the smallest or lowest bandwidth digital channel.

Networking Models

The concept of layers is used to describe communication from one computer to another

As the data passes between layers, each layer adds additional information that enables effective communication with the corresponding layer on the other computer

The OSI and TCP/IP models have layers that explain how data is communicated from one computer to another.

Network Comparisons

Layer Communication

Layer 4 on the source computer communicates with Layer 4 on the destination computer. The rules and conventions used for this layer are known as Layer 4 protocols.

OSI model

OSI layers

The OSI reference model explains how packets travel through thevarious layers to another device on a network

Dividing the network into seven layers provides the followingadvantages: It breaks network communication into smaller, more manageable

parts. It standardizes network components to allow multiple vendor

development and support. It allows different types of network hardware and software to

communicate with each other. It prevents changes in one layer from affecting other layers. It divides network communication into smaller parts to make

learning it easier to understand.

The OSI Model - Layer 1

The OSI Model - Layer 2

The OSI Model - Layer 3

The OSI Model - Layer 4

The OSI Model - Layer 5

The OSI Model - Layer 6

The OSI Model - Layer 7

Peer-to-peer communications

Each layer of the OSI model at the source communicate with its peer layer at the destination

The protocols of each layer exchange information, called protocol data units (PDUs).

Each layer depends on the service function of the OSI layer below it.

The lower layer uses encapsulation to put the PDU from the upper layer into its data field; then it adds whatever headers and trailers the layer needs to perform its function.

Peer-to-peer communications

TCP/IP model

Application layer handles issues of representation, encoding, and dialog control.

The transport layer deals with the quality of service issues of reliability, flow control, and error correction

Internet layer divides TCP segments into packets and send them from any network

Network layer is concerned with all of the components, both physical and logical, that are required to make a physical link

Common TCP/IP Protocols

The relationship between IP and TCP is an important one. IP can be thought to point the way for the packets, while TCP provides a reliable transport

Comparing TCP/IP with OSI

TCP

IP

Ethernet

Detailed encapsulation process

If one computer (host A) wants to send data to another computer (host B), the data must first be packaged through a process called encapsulation.

Encapsulation wraps data with the necessary protocol information before network transit.

Data Encapsulation

Data Encapsulation example

An understanding of the following key points should have been achieved:

Understanding bandwidth is essential when studying networking Bandwidth is finite, costs money, and the demand for it increases

daily Bandwidth is measured in bits per second, bps, kpbs, Mbps, or

Gbps Limitations on bandwidth include type of media used, LAN and WAN

technologies, and network equipment Throughput refers to actual measured bandwidth, which is affected

by factors that include number of users on network, networking devices, type of data, user’s computer and the server

The formula T=S/BW (transfer time = size of file / bandwidth) can be used to calculate data transfer time

Comparison of analog and digital bandwidth

An understanding of the following key points should have been achieved:

Network communication is described by layered models The OSI and TCP/IP are the two most important models of network

communication The International Organization for Standardization developed the OSI model

to address the problems of network incompatibility The seven layers of the OSI are application, presentation, session,

transport, network, data link, and physical The four layers of the TCP/IP are application, transport, internet, and

network access The TCP/IP application layer is equivalent to the OSI application,

presentation, and session layers Fundamental networking devices are hubs, bridges, switches, and routers The physical topology layouts include the bus, ring, star, extended star,

hierarchical, and mesh A WAN consists of two or more LANs spanning a common geographic area

An understanding of the following key points should have been achieved:

A SAN provides enhanced system performance, is scalable, and has disaster tolerance built in

A VPN is a private network that is constructed within a public network infrastructure

Three main types of VPNs are access, Intranet, and Extranet VPNs

Intranets are designed to be available to users who have access privileges to the internal network of an organization

Extranets are designed to deliver applications and services that are Intranet based, using extended, secured access to external users or enterprises