Local Area Networks Y. C. Chen Department of Computer

1
Local Area Networks

• Y. C. Chen
• Department of Computer Science and Information
  Engineering
• Spring 2005

2

• Overview
• Data Link Layer
• Medium Access Control of LANs
• Physical Layer
• Metropolitan Area Networks
• Personal Area Networks
• Quality of Services
• Security
• Applications

3
Overview

• Traditionally, 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.

4
Local Area Networks (LANs)
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.
LAN characteristics are determined by

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

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Motivations for Local Area Networking
Local 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

• 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.

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Various Local Area Networks

• 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.

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LAN Approaches

• 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.
  

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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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LAN Topologies
Bus Topology
Example Traditional Ethernet
Bus Extender
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LAN Topologies
Hub/Tree (also the bus) Topology
Example 100VG-AnyLAN
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LAN Topologies
Ring Topology

• 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

Examples FDDI, Token ring

Repeater


Station





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LAN Topologies
Star Topology

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

Example ATM LAN









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LAN Topologies
Mesh Topology

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LAN Topologies
Wireless LAN Topologies
Infrastructure
Ad hoc
Fixed-wire replacement
PAU
PAU
10-20 m
Server
Portable-to-fixed Network
50-100 m
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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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Switched LAN

• Example Switched Ethernet
• Switched 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.

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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
Office automation
Universities/hospitals
Factory automation
Star
Closed systems
ISO
Application domains
Ring
IEEE
Topologies
Standards bodies
Bus
Wired LAN
Hub/tree
NBS
Transmission media
EIA
ECMA
Medium access control
Fiber optic
CSMA/CD
Coaxial cable
Twisted pair
Fixed slots
Carrier band
Control token
Broadband
Baseband
Headend
RF modem
CATV
Thin-wire
Thick-wire
EIA Electrical Industries Association
(USA) ECMA European Computer Manufacturers
Association NBS National Bureau of Standards
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LAN Selections - Wireless
Airports
On-off keying
Warehouses
Old buildings
Pulse-position modulation
Retail stores
Hospitals
Ad hoc
Direct modulation
Multi-subcarrier modulation
Applications
Topologies
Transmission schemes
Carrier modulation
Wireless LAN
Infrastructure
Single-carrier modulation
Spread spectrum
Medium access control
Transmission media
Standards
Direct Sequence
CDMA
Radio
Frequency hopping
FDMA
CSMA/CD
CSMA/CA
TDMA
IEEE
ETSI (Hipper LAN)
Infrared
CDMA Code Division Multiple Access
ETSI European Telecom. Standards
Institute CSMA/CD CSMA with Collision Detection
FDMA Frequency Division Multiple
Access CSMA/CA CSMA with Collision Avoidance
TDMA Time Division Multiple Access
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IEEE LAN Standards
802.1 Higher Layer LAN Protocols
802.2 Logical Link Control
802.3 MAC CSMA/ CD
802.4 MAC Token Bus
802.5 MAC Token Ring
802.6 MAC DQDB
802.9 MAC Isoc. LAN
802.11 MAC WLAN
802.12 MAC 100VG
802.15 MAC PAN
802.16 MAC Broad- band Wireless Access
802.17 MAC RPR
Data Link
802.10 LAN Security
802 Executive Committee
Phy- sical
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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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Layers of LAN and OSI Model
OSI LAYERS
LAN LAYERS
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Outline Structure of a LAN Station
LLC MAC PLS
Logical Link Control
DTE
CSMA/CD Token Reserved
Physical signaling
AUI Attachment Unit Interface LLC Logical Link
Control MAC Medium Access Control MAU Medium
Access Unit PLS Physical Signaling PMA Physical
Medium Attachment
P
AUI
P
Broadband Baseband Fiber
MAU
Physical Medium Attachment
PMA
MDI
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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

Peer LLC layer
LLC layer
MAC layer
MA_UNITDATA.request MA_UNITDATA.confirm
MA_UNITDATA.indication
MA_UNITDATA.request MA_UNITDATA.confirm
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
LLC/MAC sublayer interactions LLC 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 unitNPDU ).
Source DTE
Destination DTE
Network
Network
LLC
LLC
MAC layer
MAC layer
L_DATA.req (NPDI)
MA_UNITDATA.req (UI)
MA_UNITDATA.ind (UI) MA_UNITDATA.req (UI)
L_DATA.ind (NPDU) L_DATA.req (NPDU)
Physicalmedium
MA_UNITDATA.req (UI)
L_DATA.ind (NPDI)
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Layered Architecture
Interlayer primitives and parameters
Network
Network protocol entity
NPDU
LLC service primitive
LLC protocol entity
LLC
LLC PDU
DSAP SSAP (NPDU)
MA_UNIDATA.req
MAC service primitive
Link
User data(LLC PDU)
MAC protocol entity
MAC
Preamble SFD DA SA LLC PDU FCS
physical layer