Y. C. Chen

Department of Computer Science and Information Engineering

Spring 2005

Local Area Networks

Spring 2005 Local Area Networks 2

1.Overview2.Data Link Layer 3.Medium Access Control of LANs4.Physical Layer5.Metropolitan Area Networks6.Personal Area Networks7.Quality of Services 8.Security9.Applications

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OverviewTraditionally, communications networks can be viewed in 3 categories:

Wide Area Networks (WANs), which span a very large geographical area, such as from city to city or across countries and oceans. WANs are usually operated by transmission service providers.

Metropolitan Area Networks (MANs), which span a large area such as a city, or company sites in different locations within the same city. MANs are usually operated by organizations.

Local Area Networks (LANs), which span a limited area such as a company complex, a building, a campus, or even a small office. LANs are usually operated by a single organization.

In recent years, the so-called Personal Area Networks (PANs) become more and more popular. This is due to the advance in home broadband access so that multiple stations and peripherals form a small network in a single residential home. Topics regarding LANs, MANs and PANs will be discussed in the class.

Spring 2005 Local Area Networks 4

LAN characteristics are determined by

Local Area Networks (LANs)

Topologies MAC (Medium Access Control) Transmission media Size of coverage

Local Area Networks are privately-owned networks within a small area, usually a single building or campus of up to a few kilometers. Since it is restricted in size, that means their data transmission time can be known in advance, and the network management would be easier.

Spring 2005 Local Area Networks 5

Cost reductions through sharing of information and databases, resources and network services.

Increased information exchange between different departments in an organization, or between individuals.

The trend to automate communication and manufacturing process. Improve the community security. Increasing number and variety of intelligent data terminals, PCs and

workstations.

Motivations for Local Area NetworkingLocal area networks are usually privately owned with limited coverage, this means that the underlying network technologies and network services may be freely selected. This leads to network architectures markedly different from those of Wide Area Networks.

The growing demand for local area networks is due to technical, economic and organizational factors:

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A local area network is a small group of interconnected workstations and associated devices that share the resources within a small geographic area. Usually, a local area network may serve as few as several users or many more.

The nowadays main local area network technologies are: • Ethernet (Fast Ethernet, Gigabit Ethernet, 10G Ethernet)• Fiber Channel • Hipper LAN• Token ring • ATM LAN• FDDI (Fiber Distributed Data Interface)• Wireless LAN• ……..

There are also some other technologies such as 100VG, token bus,ARCnet, but those are almost obsolete.

Various Local Area Networks

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There are two methods of networking computers together, Peer-to-Peer, and Client-Server. The proper method to use depends on the requirements.

Peer-to-Peer Networking It offers a quick way to tie all your resources and people together. Users can access information from and share it directly with others in the network. Users can easily share files and directories in a peer-to-peer network. Client/Server Networking Clients are connected to a centralized server. The server provides centralized security, backup, and recover capability and controls access to sensitive files and expensive peripherals. A dedicated server improves data integrity, because the most current version of a document will be saved in one location. This type of network requires a network operating system.

LAN Approaches

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LAN Topologies

Bus (Including Tree) – All the stations are attached to a common medium, so there may be collision if two or more stations try to transmit at the same time. Traditional Ethernet uses bus topology.

Ring – All the stations are attached to the same medium which forms a ring structure, however, data from multiple stations may be transmitted upon receiving a token (FDDI, Token Ring, RPR). Ring networks suffer the complexity of token manipulation.

Star – A switched Ethernet basically uses a star topology. It becomes popular due to the fast growing bandwidth demand, and both bus and ring topologies are hard to be scaled up in bandwidth.

Mesh – it connects stations in an arbitrary manner. Mesh topology encounters some routing problems which are hard to be accommodated.

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Bus Topology

BusExtender

Example: Traditional Ethernet

LAN Topologies

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Hub/Tree (also the bus) Topology

Example: 100VG-AnyLAN

LAN Topologies

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Examples: FDDI, Token ring

Each station attaches to the network via a repeater Data are transmitted in packets which contains source address

and destination address The station will copy the data destined to itself, and the source is

responsible for removing the data from the ring Media can be twisted pair, coaxial cable, or optical fiber

Repeater

Station

Ring Topology

LAN Topologies

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Digital Switch Digital PBX (Private Branch eXchange) Switched Ethernet Star Coupler - Passive - Optical fiber, baseband coaxial - Active - Twisted pair

Example: ATM LAN

Star Topology

LAN Topologies

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IBM 相容型

IBM 相容型

IBM 相容型

IBM 相容型

IBM 相容型

LAN Topologies

Mesh Topology

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Wireless LAN Topologies

PAU

PAU

Infrastructure

Portable-to-fixedNetwork

Fixed-wire replacement

Server

Ad hoc

50-100 m

10-20 m

LAN Topologies

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LAN Interconnection

Traditional LAN interconnection devices Repeater – it operates at OSI layer 1 and transmits data bits over

a physical medium. Bridge – it operates at OSI layer 2 and is commonly used to

connect similar LAN segments. Switch – it operates at OSI layer 2 or layer 3 and is used to

interconnect multiple similar or dissimilar LANs. Router – it operates at OSI layer 3. A router is used to

interconnect individual networks whose sizes vary from very small to very large. Routers may be categorized into backbone router (or core router), border router and access router depending on their role in the network.

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Example: Switched EthernetSwitched Ethernet provides high performance, high bandwidth, and flexibility required for today's LAN. Switches allow different nodes of a network to communicate directly with each other in a smooth and efficient manner, and provide a separate connection for each node in a organization's internal network. Basically, a LAN switch creates a series of instant networks that contain only the two devices communicating with each other at that particular moment. Layer 2 switching provides the dedicated bandwidth and network segmentation critical for directly connecting users to the network, while Layer 3 provides for switching and routing, maximizing speed, bandwidth, and flexibility in the network core or aggregation points. There are three main techniques for Ethernet switching:

Store and Forward: Switch receives the full frame to it's memory and then decides what to do with it.

Cut Through: Switch makes the decision on re-transmission when it has received the destination MAC address.

Fragment Free (Modified Cut Through): Switch makes the decision on re-transmission after it has received the first 64 bytes of the frame.

Switched LAN

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LAN Access Methods

Broadcasting – In a broadcast LAN, transmitted information will be received by all stations simultaneously. The medium access schemes are random access such as CSMA/CD which may cause contention, and controlled access such as token-passing, in which no contention will occur.

Switching – In a switched architecture, a switch forward data packets to their destinations that may be a single user station or another LAN segment.

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LAN Selections - Wired

Wired LANMedium

access

control

Fixe

d sl

ots

Control token

CSMA/CD

Transm

ission

media

RF modem

Headend

Broadband

CATVThick-wireThin-wire

BasebandCarrier band Co

axia

lca

bleTwisted pair

Fiber optic

Topologies

Star

Ring

Bus

Hub/tree

Ap

pl i

cat i

on

do

ma

ins

Universities/hospitals

Office automation

Factory automation

Standards

bodies

Closed systemsISO

IEEE

NBS

EIAECMA

EIA: Electrical Industries Association (USA)ECMA: European Computer Manufacturers AssociationNBS: National Bureau of Standards

EIA: Electrical Industries Association (USA)ECMA: European Computer Manufacturers AssociationNBS: National Bureau of Standards

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LAN Selections - Wireless

Wireless LAN

Medium

access

control

FDMA CS

MA

/CA

CDMA

Tran

smis

sion

med

ia

Infrared

Radio

Topologies

Ad hoc

Infrastructure

Applications

Sta

nd

ard

s

IEEE ETSI (Hipper LAN)

CDMA: Code Division Multiple Access ETSI: European Telecom. Standards InstituteCSMA/CD: CSMA with Collision Detection FDMA: Frequency Division Multiple AccessCSMA/CA: CSMA with Collision Avoidance TDMA: Time Division Multiple Access

CDMA: Code Division Multiple Access ETSI: European Telecom. Standards InstituteCSMA/CD: CSMA with Collision Detection FDMA: Frequency Division Multiple AccessCSMA/CA: CSMA with Collision Avoidance TDMA: Time Division Multiple Access

CSMA/CDT

DM

A

Pulse-position modulation

Direct modulation

Multi-subcarrier

modulation

Single-carriermodulation

Transmission schemes

Carriermodulation

Spread spectrum

On-offkeying

Direct Sequence

Frequency hopping

AirportsWarehouses

Retail stores

Old buildings

Hospitals

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IEEE LAN Standards

802.1 Higher Layer LAN Protocols

802.3MAC

CSMA/CD

802.4MAC

TokenBus

802.5MAC

TokenRing

802.6MAC

DQDB

802 Execu

tive Co

mm

ittee

802.10 LA

N S

ecurity

DataLink

Phy-sical

802.9MAC

Isoc.LAN

802.11MAC

WLAN

802.12MAC

100VG

802.15MAC

PAN

802.16MAC

Broad-band

WirelessAccess

802.17MAC

RPR

802.2 Logical Link Control

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IEEE LAN Standards

802.1 Higher LAN Protocols 802.2 Logical link control (LLC) (No Activity) 802.3 CSMA/CD (Ethernet) 802.4 Token Bus (No Activity) 802.5 Token Ring (No Activity) 802.6 Metropolitan area network (No Activity) 802.7 Broadband technical advisory (No Activity) 802.8 Fiber optic technical advisory (Obsolete) 802.9 Integrated services LAN (No Activity) 802.10 Interoperable LAN Security (No Activity) 802.11 Wireless LAN 802.12 100 VG-AnyLAN (No Activity) 802.14 Cable-TV based broadband (Obsolete) 802.15 Wireless Personal Area Network 802.16 Broadband Wireless Access (WiMAX) 802.17 Resilient Packet Ring (RPR)

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LAN LAYERS

OSI LAYERS

Logical link control(LLC)

Medium access control(MAC)

Physical (PHY)

Higher layers

Application

Presentation

Session

Transport

Network

Data link

Physical

Layers of LAN and OSI Model

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Outline Structure of a LAN Station

Logical Link Control

CSMA/CD Token Reserved

Physical signaling

P’

P’

AUI

Broadband Baseband Fiber

Physical Medium Attachment

LLC

MAC

PLS

DTE

MAUPMA

MDI

AUI: Attachment Unit Interface

LLC: Logical Link Control

MAC: Medium Access Control

MAU: Medium Access Unit

PLS: Physical Signaling

PMA: Physical Medium Attachment

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Layered Architecture Regardless the mode of operation of the underlying MAC sublayer - CSMA/CD, token ring, wireless - a standard set of user services is defined for use by the LLC sublayer to transfer LLC PDUs to a correspondent layer. These user service primitives are:

• MA_UNITDATA.request

• MA_UNITDATA.indication

• MA_UNITDATA.confirm

LLC layer

MA_UNITDATA.request

MA_UNITDATA.confirm

MA_UNITDATA.request

MA_UNITDATA.confirm

MAC layer Peer LLC layer

MA_UNITDATA.indication

MA_UNITDATA.indication

For a CSMA/CD LAN, the confirm primitive indicates that the request has been successfully (or not) transmitted, while for a token LAN it means that the request has been successfully (or not) delivered.

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Layered Architecture Each service primitive has its associated parameters.

Those parameters in the MA_UNIDATA.request primitive are - the required destination address (individual, group or broadcast address)- a service data unit (LLC PDU), - and the required class (i.e. priority) of service associated with the PDU.The MA_UNIDATA.confirm primitive includes a parameter that specifies the success or failure of the associated MA_UNIDATA.request primitive. The confirm primitive is not generated as a result of a response from the remote LLC sublayer, but rather by local MAC entity. If the parameter indicates success, this simply shows that the MAC protocol entity was successful in transmitting the service data unit into the network medium. If unsuccessful, the parameter indicates why the transmission attempts failed. For example, ‘excessive collision’ is a typical failure parameter if it is a CSMA/CD network.

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Layered Architecture

Network

L_DATA.req(NPDI)

L_DATA.ind(NPDI)

MAC layer Network

L_DATA.ind(NPDU)

L_DATA.req (NPDU)

MA_UNITDATA.req(UI)

MAC layer

MA_UNITDATA.ind(UI)

MA_UNITDATA.req(UI)

LLC LLC

MA_UNITDATA.req(UI)

Physicalmedium

Source DTE Destination DTE

LLC/MAC sublayer interactionsLLC protocol is based on the high-level link control (HDLC) protocol, thus it supports two types of user service: connectionless and connection-oriented. Almost all LAN installations use connectionless protocol, therefore the only primitive used is L_DATA.request, and all data is transferred using the unnumbered information (UI) frame. Parameters used for this primitive are source/destination address and user data ( network-layer protocol data unit;NPDU ).

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Layered Architecture Interlayer primitives and parameters

Network protocol entityNPDU

L_DATA.requestDSAP+DASSAP+SAService classLength indicator

User data(NPDU)

LLC protocolentity

DSAP SSAP (NPDU)LLC PDU

MA_UNIDATA.req DA SAService classLength indicator

User data(LLC PDU)

MAC protocolentity

Preamble SFD DA SA LLC PDU FCS

LLC

MAC

Link

Network

LLCserviceprimitive

MACserviceprimitive

physical layer