Chapter 12

LAN Architecture and Infrastructure

Personal Computer LANsUses:

Departmental applications such as collaboration and project management tools and Internet access“Big data” applicationsIn-memory computing applicationsReal-time analytics supported by high-performance analytic appliance (HANA) boxesIn-house collaboration software applications that support project teams and other business teams

Expensive resources such as copiers, high-speed laser printers, and high-capacity network-attached storage (NAS) systems can be shared

Backend NetworksUsed to interconnect large systems such as mainframes, super-computers, and mass storage devices that typically need to transfer large volumes of data between one another

Sometimes called computer room networks

Physically small in size

Key requirements:• Bulk data transfer among a limited number of

devices in a small area• High reliability

Characteristics:High data rate

Data rates of 1000 Mbps or more are requiredHigh-speed interface

Mainframes and supercomputers may need to exchange high volumes of data over the network

Distributed accessNeeded to ensure that all devices get fair, efficient, and reliable access to the network

Limited distanceTypically employed in a computer room or a small number of contiguous rooms

Limited number of devicesContributes to network efficiency

Storage Area Network (SAN)Separate network of storage devices that are physically removed from, but still connected to, the networkDecouples storage tasks from specific servers and creates a shared storage facility across a high-speed networkMost use Fibre ChannelBusiness users access storage devices via server systems that are connected to both the LAN and the SANImproves client-to-storage access efficiency and direct storage-to-storage communications for backup and replication functions

Storage Area Network Configuration

High-Speed Office Networks

Evolution of office applications has required businesses to move to higher-speed LANsBandwidth hungry applications such as video, audio, data conferencing, computer-based training, and e-learning systems have significantly increased network data flowOther applications demanding bandwidth include fax machines, document scanners, interactive graphic, and collaboration software programs

Backbone LANs

Interconnect lower-cost, lower-capacity LANs within buildings or departments with a higher-capacity LAN (backbone LAN)The backbone network provides the infrastructure for the exchange of data and information among the LANs that it interconnectsTypically the backbone’s capacity is greater than that of the networks that connect to it

Factory LANsEssential to tie together automated equipment and robots to manage the production or manufacturing processMost dynamic and data-intensive part of a manufacturing organization is the factory floorSpecialized machines are likely to include programmable logic controllers (PLCs)The more a factory is automated, the greater the need for integrated communicationsRequire more flexible and reliable LANs than typical business office environments

A Factory LAN Should Be:

Of high capacityAble to handle a variety of data

traffic

Capable of having a large geographic

footprintHighly reliable

Able to specify and control

transmission delays

Tiered Local Area Networks

Tiered LAN StrategiesBottom-up strategy• Individual departments create

LANs independently• Decisions about the infrastructure

needed for each department LAN can be can be made quickly

• Potential exists for each department to develop its own cluster network

Top-down strategy• The company decides to map out

a total local networking strategy• Decision is centralized because it

impacts the entire operation or company

• Advantage is built-in compatibility to interconnect the users

Transmission MediumPhysical path between transmitter and receiver

Guided MediaWaves are guided along a solid medium, such as copper twisted pair, copper coaxial cable, or optical fiberThe medium itself is more important in determining the limitations of transmission

Unguided MediaTransmits electromagnetic signals but does not guide themReferred to as wireless transmissionExamples are the atmosphere and outer spaceThe bandwidth of the signal produced is more important than the medium in determining transmission characteristics

Transmission Medium and Signal Design Factors

• The wider the bandwidth of a signal, the higher the data rate that can be achieved

Bandwidth

• Impairments such as attenuation limit effective distance

Transmission impairments

• Interference from competing signals in overlapping frequency bands can distort or wipe out a signal

Interference

• A guided medium can be used to construct a point-to-point link or a shared link with multiple attachments

Number of receivers

Guided Transmission

Media

Types of Twisted Pair

Unshielded Twisted Pair (UTP)Ordinary telephone wire is an exampleLeast expensiveEasy to work with and installMost widely deployed communications medium in enterprise networks

Shielded Twisted Pair (STP)Twisted pair is shielded with a metallic braid or sheathing that reduces interferenceProvides better performance at lower data ratesMore expensive and difficult to work withPreferred over UTP in “noisy” work environments

Categories of UTP Cabling

Category 3 UTPCables and associated connecting hardware whose transmission characteristics are specified up to 16 MHz

Category 4 UTPCables and associated connecting hardware whose transmission characteristics are specified up to 20 MHz

Category 5 UTPCables and associated connecting hardware whose transmission characteristics are specified up to 100 MHz

Table 12.1Comparison of Shielded and

Unshielded Twisted Pair

Table 12.2Twisted Pair Categories and Classes

UTP = Unshielded twisted pairS/UTP = Screened unshielded twisted pairS/STP = Screened shielded twisted pair

Coaxial Cable (Coax)Consists of a hollow outer cylindrical conductor that surrounds a single inner wire conductorInner conductor is held in place by either regularly spaced insulating rings or a solid dielectric materialOuter conductor is covered with a jacket or shieldMuch less susceptible to interference and crosstalk than twisted pairMore expensive than STP but provides greater capacity

Optical Fiber

Thin (2 to 125 µm), flexible medium capable of conducting an optical rayHas a cylindrical shape and consists of three concentric sections

The two innermost are two types of glass with different indexes of refractionCenter one is called the coreThe next layer is the claddingThese are covered by a protective, light-absorbing jacket

Optical fibers are grouped together into optical cables

The following characteristics distinguish optical fiber from twisted pair or coaxial cable:

Greater capacity

• The potential bandwidth, and hence data rate, of optical fiber is immense

Smaller size and lighter weight

• Optical fibers are considerably thinner

• Reduction in weight reduces structural support requirements

Lower attenuation

• Attenuation is significantly lower for optical fiber and is constant over a wide frequency range

Electromagnetic isolation

• Optical fiber systems are not affected by external electromagnetic fields

• Fibers do not radiate energy, causing little interference with other equipment and providing a high degree of security from eavesdropping

• Fiber is inherently difficult to tap

Fiber Optic TypesMultimode step-index fiber

The reflective walls of the fiber move the light pulses to the receiver

Multimode graded-index fiberActs to refract the light toward the center of the fiber by variations in the density

Single mode fiberThe light is guided down the center of an extremely narrow core

Two different types of light source are used in fiber optic systems:

Light-emitting diode (LED)Less costly, operates over a greater temperature range, has a longer operational life

Injection laser diode (ILD)Operates on the laser principle, is more efficient, can sustain higher data rates

Structured CablingNeed a cabling plan that deals with the selection of cable and the layout of the cable in a building

Plan should be easy to implement and accommodate future growth

Structured cabling system is a generic wiring scheme with the following characteristics:

Refers to the telecommunications infrastructure wiring within a building or campusIncludes cabling to support all types of information transfer, including voice, LANs, video and image transmission, and other forms of data transmissionIndependent of vendor and end-user equipmentDesigned to encompass distribution to all work or living areas within the building

Elements of a

Structured Cabling Layout

Cable Distances

LAN Protocol Architecture

LAN architecture primarily focuses on the protocols used by LAN devices to share transmission mediaIs best described in terms of a layering of protocols that organize the basic functions of a LAN

Physical media access control (MAC)Logical link control (LLC)

IEEE 802 Protocol Layers

Compared to OSI Model

LAN Protocols in Context

Logical Link Control (LLC)

Specifies the mechanisms for addressing stations across the medium and for controlling

the exchange of data between two users

Can be thought of as residing between the network layer and the media access control

sublayer of the data link layer

Enables LANs with different MAC protocols to interface with a common network layer

protocol, such as IP

Three services are provided as alternatives for attached devices using LLC:

Unacknowledged connectionless

service

• Datagram-style service

• Very simple and does not involve any of the flow control and error control mechanisms

Connection-mode service

• Similar to that offered by typical data link control protocols such as HDLC

• A logical connection is set up between two users exchanging data

• Flow control and error control are provided

Acknowledged connectionless

service

• Cross between the previous two services

• Provides that datagrams are to be acknowledged, but no prior logical connection is set up

Media Access Control (MAC)Function is to provide a means of controlling access to the transmission medium in order to provide an orderly and efficient use of that capacityThe relationship between LLC and the MAC protocols can be seen by considering the transmission formats involved:

User data are passed down to the LLC layer, which prepares a link-level frame, known as an LLC protocol data unit (PDU)This PDU is then passed down to the MAC layer, where it is enclosed in a MAC frame

LLC PDU in a MAC Frame Format

Summary Personal computer LANs

Backend networks and storage area networks

High-speed office networks

Backbone LANs

Factory LANs

LAN configuration

Tiered LANs

Chapter 12: LAN Architecture and Infrastructure

Guided transmission media Twisted pair Coaxial cable Optical fiber Structured cabling

LAN protocol architecture IEEE 802 reference

model Logical link control Media access

control