Local Area Networks

1
Chapter 12

• Local Area Networks

2
LAN Characteristics

• Small geographical area
• High speed
• Commonly 10 Mbps to 100 Mbps
• Privately owned

3
LAN Advantages

• Hardware sharing
• Printers, hard disks
• Software sharing
• Server-based software
• Fast response compared to mainframe networks
• Local network control and management
• Information sharing

4
LANs and the OSI Model

• LAN standards developed by IEEE 802 committee
• Formed in February 1980
• 802 model adds detail to OSI
• Layer 2 split into MAC and LLC
• Logical Link Control performs
• Frame assembly/disassembly
• Flow control
• Error Control
• Media Access Control performs
• Access functions for shared media - Token ring
  and CSMA/CD

5
LANs and the OSI Model
6
LAN Topologies

• Ethernet
• Most popular
• Logical configuration bus
• Physical configuration bus (old) or star
  (modern)
• Token ring
• Logical configuration ring
• Physical configuration ring (old) or star
  (modern)
• Reasons for physical star configuration
• LAN wiring distances
• Equipment security hub is in one room
• Easier repair and troubleshooting

7
Logical Ring, Physical Star
8
LAN Media

• Cable
• UTP - most popular, inexpensive
• Coax - harder to work with, faster than UTP
• Fiber - expensive interfaces
• Hub
• Place where LAN cables come together
• Possible functions
• Repeater, switch, error detection, diagnostics
• Other names (depends on function)
• MAU - Multistation Access Unit (token ring)
• Concentrator
• Multiplexer

9
LAN Standards

• IEEE responsible for LAN standards

10
LAN Standards
11
LAN Standards

• IEEE 802.3 - Ethernet
• Developed by Xerox, DEC, Intel
• MAC protocol - CSMA/CD
• Bus architecture
• 10BASE5 10 Mbps, uses coax, 500m max segment
  length
• 10BASE2 10 Mbps, uses coax, 185m max segment
  length
• 10BASE-T 10 Mbps, uses UTP, 100m max segment
  length
• 100BASE-TX 100 Mbps, uses 2 pair of a CAT 5 UTP
  cable, 100m max segment length

12
Ethernet Logical Connection (unswitched)
13
Ethernet Physical Connection (unswitched or
switched)
14
Ethernet Varieties
15
LAN Standards

• IEEE 802.5 - Token Ring
• Developed by IBM
• MAC - Token ring
• 4 Mbps on UTP
• 16 Mbps on STP or CAT 5 UTP

16
LAN Standards

• FDDI - Fiber Distributed Data Interface
• Developed by ANSI standards organization
• Two counter-rotating rings
• Primary ring carries data traffic
• In case of failure, ring reconfigures to use both
  rings in closed loop
• Token based
• Priority access - some stations get more time
• 200 km max length, 2 km max between stations
• FDDI-II
• Adds circuit-switched networks
• Can have constant data-rate connection between
  station
• Good for voice and video

17
LAN Expansion

• Issues
• Distance between LAN segments or different LANs
• Protocol conversions
• Speed differences
• Interconnection devices
• Bridges
• Switches
• Routers
• Brouters
• Gateways

18
LAN Interconnection Devices
19
Bridge

• Operates at OSI layers 1 and 2
• Connects LAN segments operating with same
  protocol
• i.e Ethernet LANs
• Decides which traffic should cross the bridge
• Higher speed than routers

20
Switch

• Connects two or more segments on a frame-by-frame
  basis
• Faster than bridges
• Cut-through switch
• Switch looks at destination address only and
  routes it to the desired segment
• Collision can occur
• Store-and-forward switch
• Stores whole frame
• Holds until destination segment is free

21
Switch
22
Router

• Operates at OSI layers 1, 2, and 3
• Connects networks that use internetwork addresses
• Builds routing tables giving possible paths
• Can route based on traffic loads

23
Brouter

• Combination of bridge and router
• Bridges some messages and routes others

24
Gateways

• Operates at OSI layers 1 through 4 and higher
• Connect networks that can have different
  protocols
• Can perform protocol translation
• i.e. Token ring to Ethernet
• Can be slow

25
Bridge vs. Gateway
26
LAN Backbones and Switches

• Backbones sometimes used to connect LAN segments
• May have same or different protocol
• Usually higher speed than segment
• Throughput may be limited
• LAN switches have intelligence and multiple paths
  through them
• High throughput
• Can interface to WAN
• Disadvantage - switch failure prevents segment
  interconnects

27
One Type of Backbone LAN
28
LAN Servers

• Types
• File, print, communications
• Servers usually dedicated and run special software

29
Servers

• File server
• Fast machine with large hard disks
• Shared programs and files
• Reduces resource management of LAN workstations
• Print server
• Interfaces workstations to one or more printers
• Communications server
• Provide capability to communicate with other
  networks or LANs
• Works along with routers, bridges, gateways

30
Network Attachment

• Workstations connect to LAN through network
  interface card (NIC)
• Dumb terminals
• Connect to a terminal control unit
• Terminal control unit connects to network through
  NIC

31
LAN Software

• For workstation
• Applications communicate with LAN through
  application program interface (API)
• The IBM/DOS API is Network Basic Input-Output
  System (NetBIOS)
• Operates at OSI layers 2 and 5 (data link and
  session)
• Operating system contains network software like
  TCP/IP
• For server
• Network operating system (NOS)
• Two approaches

32
LAN Software

• For server
• Network operating system (NOS)
• Two NOS approaches
• Add networking and client/server apps on top of
  existing operating system(IBM and Microsoft)
• Create separate operating system for networking
  (Novell)
• LAN design includes choosing software

33
LAN Performance

• LAN Protocols
• CSMA/CD
• Good throughput until traffic threshold reached
• Above threshold more collisions occur
• Token ring
• Not as sensitive to traffic level since token
  passing is timed
• Doubling LAN speed does not mean twice the
  throughput due to network overhead
• Error rates affect performance
• Errors require retransmission of bad frames
• Lots of retransmissions slows the network

34
LAN Performance

• LAN software (protocol stack)
• Some LAN software performs better than others
• Server speed
• Faster disks and processors mean faster file
  downloads
• Speed and efficiency of server hardware and
  software is a big factor on improving LAN
  performance

35
LAN Selection Criteria

• Important to consider the requirements when
  choosing LAN capability
• Use a checklist
• Analyze costs
• Installation, software upgrades, workstation
  upgrades, cabling, maintenance
• Consider alternatives
• Make sure there is a LAN administrator to
  maintain network
• Guideline
• 1000 per node installation, assuming
  full-featured, high-capacity LAN and existing
  workstations

36
LAN Selection Guide Management Viewpoint

• Objectives of LAN Why are you proposing this
  solution and what problems will it solve?
• Number of users and their geographic spread
• Applications to be used
• Performance required
• Cost constraints
• Security requirements
• Availability of wiring that can be used, or must
  new wiring be installed?

37
LAN Selection Guide Management Viewpoint

• Availability and sophistication of technically
  trained people to install and maintain the LAN
• Vendor support and training provided
• Expected expansion of the LAN in the future
• Workstations to be used Already have them or
  need to buy them?
• Other LANs in the organization
• Required interfaces to other networks

38
LAN Cost Configurations

• Workstations upgrade existing ones or buy new
  ones
• Servers large personal computers, usually
  dedicated to performing server functions
• Printers upgrade or buy new ones
• Cabling installation
• Bridges, routers, brouters, gateways
• Software NOS, applications, LAN management
• Training of users and the LAN administrator
• Consultants
• LAN administrator new or existing person
• Maintenance maybe an external contract
• Space need secure place for servers and
  networking equipment

39
LAN Management

• Effort to manage LAN can be significant
• Some considerations
• Organization
• Access
• Security
• Documentation
• Backup
• Performance monitoring
• Management software available
• Usually performed by NOS

40
LAN Security

• Includes LAN, its data, and its users
• LAN administrator is responsible
• Keep key components in locked room
• Other policies
• Password policies
• Data encryption on network and disk files
• Regular backups
• Virus scans
• Policies regarding downloading files and storing
  on LAN disks

41
Case Study Dow Cornings LANs

• LAN use grew rapidly
• Different technologies and purposes
• Learned that each LAN needed an administrator
• Started program to install global, LAN-based
  network
• Required existing LANs to be upgraded
• User training required
• Standardized desktop PCs
• Chose Ethernet
• Began 1995, ended 1997