Business Data Communications

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Four 1

Business Data Communications

Chapter Four

Components of a Local Area Network


Primary Learning Objectives

Identify key components that compose a local area network (LAN)

Understand the meaning of “topology” Describe selected LAN physical components Describe selected LAN logical components Identify common LAN devices Explain Standard versus Fast Ethernet Define metered versus site licensing Understand LAN design considerations


Local Area Network (LAN) Components Are physical and logical Physical or hardware elements include:

NICs, servers, clients, printers, cables, hubs, switches, routers

Logical or software elements include: Network operating systems, client operating

systems, device drivers, monitoring and troubleshooting tools

Logical elements also incorporate documented procedures


Local Area Network (LAN) Components Both physical and logical elements need to be

installed, configured, and maintained Once implemented, elements must be

monitored Monitoring may reveal that troubleshooting is

required: To troubleshoot is to evaluate the causes of a

problem so as to take corrective measures Troubleshooting tools can be hardware, software,

a combination of these, or documented procedures


Local Area Network (LAN) Components - Hardware


Local Area Network (LAN) Components - Software


Topology

A topology: Is an additional LAN characteristic Is both logical and physical Refers to the way that pieces of a network are

physically connected Determines how network-connected devices access

the physical network Three common topologies are:

Star Ring Bus


Topology – Star

A traditional star topology has a central controlling device

Other networked devices connect to the central device using point-to-point circuits

The central device is usually a mainframe or mini-computer

Devices connecting to the mainframe/mini-computer are referred to as terminals

A star can centralize network resources and management, but can also be a single point of failure


Topology – Standard Star


Topology – Ring

Developed by IBM IBM also developed the Token Ring Protocol, later

formalized as the 802.5 by the IEEE Uses a single cable such that a closed loop is

created, hence the term “ring” Circling the ring, in one direction, is a token:

Used by networked devices that need to communicate

Either free or busy Performs well in networks with heavy traffic Not widely implemented due to cost and

complexity


Topology – Ring


Topology – Bus

Uses a central cable, but does not form a closed loop Conceptually more like a pipeline along which network

communications travel Uses a broadcast mechanism

Data packets placed on the bus go to all devices on the bus

The bus topology most commonly uses the IEEE 802.3 Ethernet protocol

802.3, a contention-based protocol using CSMA/CD In a network with high traffic volume a standard bus

using 802.3 can lack efficiency


Topology – Bus


LAN Physical Components

The Physical components of a LAN’s hardware include:

Network Interface Cards (NICs) Media Servers Clients Hubs Switches Routers


LAN Physical Components --Network Interface Card When selecting a NIC, certain features must be

evaluated: Bus width Cache Direct memory access Bus mastering Throughput Auto-sensing capability

NICs have a physical address, expressed hexadecimally for Ethernet cards: 08:00:5A:28:E4:F8

The 1st six digits identify the manufacturer; the last six, the card serial number


LAN Physical Components --Network Interface Card Internal NICs are plugged

into an expansion slot on the computer’s motherboard

The PCI slots on this Intel motherboard could be used for an internal NIC

PCI Slots in White


LAN Physical Components --Media

“Media” is plural, “medium” is singular and refers to a specific type of physical circuit

In LANs, the most common medium is unshielded twisted wire Pair, or UTP

UTP is categorized from CAT 1, lowest quality, to CAT 7, highest quality

The higher category number the greater the throughput capacity

CAT 5, a popular UTP choice, supports speeds from 10 Mbps to 100 Mbps

LAN wiring most often runs from the networked device to a wiring closet


LAN Physical Components –Servers

Servers generally control and manage networked resources in a LAN

Depending on use, key server elements include: Primary memory or RAM Cache NIC capacity Processor; speed as well as number must be considered Hard Drive; capacity as well as speed must be

considered Operating system Degree of fault tolerance: mirroring versus duplexing

Server farms play an important role in today’s society


LAN Physical Components –Clients

Clients connect users to the network A client could be a desktop computer, a powerful

workstation, a cell phone, a personal digital assistant, or any number of other networkable devices

Like servers, clients require a NIC Clients require an operating system appropriate to

the way they are to be used: Modern client operating systems incorporate “network

aware” capability, and can be configured in a peer-to-peer network

Most LANs configure clients in a client/server model


LAN Physical Components –Clients


LAN Devices

Two devices particularly associated with LANs are switches and routers

Switches: Create Point-to-point circuits between themselves

and their connected devices Have largely replaced hubs in modern Ethernet LANs Are less expensive than routers, and have displaced

but not eliminated routers, causing routers to be pushed to the edge of the network

Are capable, based on the switch, of multilayer support for the data link and/or network layers


LAN Devices

A Cisco 3550 Series Switch Note that the ports offer

different speed capacities: 10 Mbps 100 Mbps 1000 Mbps


LAN Devices

Routers: Function at the network layer of the OSI and TCP/IP

models Are capable of connecting different logical networks Are required for different logical networks to

communicate with each other Are more expensive than switches Use routing tables that are updated either manually,

or automatically through software Do not broadcast packets


LAN Devices

A Cisco 12410 series router


Standard versus Fast Ethernet

The underlying Ethernet 802.3 architecture has not changed

What has changed: The types of devices used within an Ethernet LAN

(switches instead of hubs) The diameter an Ethernet LAN can be configured for

(250 meters versus 2,500 meters) Switches can be used in a hierarchy:

Faster, more expensive switches at the top Slower, less expensive switches at the bottom

For Fast Ethernet, 100BaseX has been the market winner



Standard Ethernet LANs have a limit of 2,500 meters, due to the physics of how packets are transmitted on UTP



If the segment length is too long, errors result.



An Ethernet switching hierarchy

This type of hierarchy allows network planners to leverage capacity based on need, resulting in cost savings


Metered Licensing versus Site Licensing

In a business, two common forms of licensing are metered licensing and site licensing

Licensing is a critical issue in the network, legally and ethically

Licensing policies should be part of any business’s documented network procedures

Licensing documentation is often used in audits, both internal and external to the business



With a metered license: The business buys a limited number of licenses for a

given application Software maintains a count of the number of licenses As users login to use the application, the metered

license counter is incremented When the maximum value is reached, new users will be

denied access to the application, until an already logged-in user terminates his or her session

If the metered value is too small, user frustration results If the metered value is too large, cost inefficiency results



With a site license: The business is buying a licensing right to use

an application for the entire organization, covering the entire site

For an application used by a majority of staff, clients, or general users, a site license can offer cost savings

An application that is rarely used, or used only by a few, is a questionable candidate for site licensing


LAN Design Considerations

There is no one solution that is right for all businesses

Designing a LAN solution requires answering numerous questions:

What is the budget? What applications must be supported? What staff is available or required? What are the security issues? What scale is the network for? What are the facility requirements? What areas of the network are most vulnerable? What documentation is available or required?


In Summary

LAN Components are either physical, logical, or both A LAN has a topology Common elements within a LAN include media,

servers, clients, NICs, switches, and routers Most LANs use a form of Ethernet Newer forms of Ethernet have not changed

Ethernet's underlying architecture LAN licensing is an important legal and ethical issue LAN design must be driven by a business’s specific

requirements

Business Data Communications

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