Chapter 2

Network Design Essentials

Good Network Design

• Analyzing network requirements
• Selecting network topology
• Selecting equipment to match topology

Designing a Network Layout

• Topology
  • physical layout of resources
  • how resources communicate
  • allow for expansion
  • meet security requirements

Standard Topologies

• Three basic connection topologies:
  • Bus - Single cable segment
  • Star - Central connection point
  • Ring - Forming a loop

Bus Topology

• Bus Communication
  • How the signal is sent
  • Signal bounce
  • Cable termination to prevent bounce

Bus Environment

• One computer sends at a time
• Passive topology
  • only listen for data
• Adding computers slows network
• Cable failure downs entire network

Signal Bounce

• Occurs when cable ends are not terminated
• Other computers cannot send data

Cable Termination

• A terminator is attached to each end
• Prevents signals from bouncing

Cable Failure

• Cable break
  • Cable is physically cut
  • One end becomes disconnected
• Halts all network activity
• Computers can still function standalone

Bus Network Expansion

• Ethernet 10Base2 (thinnet)
• Expanded by BNC barrel connector
• Distance causes signal to weaken
  • attenuation
• A repeater boost signal strength
  • amplifies errors

Star Topology

• Star Environment
  • Central connection point
    • hub or concentrator
  • each device has separate wire
    • home run
  • More cable required
  • Cable failure is device isolated
    • except for hub

Ring Topology

• Ring Environment
  • Device connects to next in line
  • Circle of cable
  • Device receives signal
    • acts on signal or
    • passes signal along
  • Signals travel in only one direction

Token Passing

• Active topology
  • each device receives/sends
  • Packet of data is passed around ring
  • receipt of token is acknowledged
• Single ring/dual ring
• Fair sharing of network resources

Hubs

Hub Environment

• Also known as concentrator
• Star network
• Central point of connection
• Active hubs
• Passive hubs

Active Hubs

• Majority of installed hubs today
• Receive, regenerate, pass on signals
• Have many ports (8 or more)
• Multiport repeaters
• Electrical power required

Passive Hubs

• Central connection point
• Wiring panel
• Punch down block
• Passes along signals
• No electrical power required

Hybrid Hubs & Switches

• Connect different cable types
• Maximize network efficiency
• Utilize different topologies
• Enjoy the benefits of each topology

Major Topology Variations

Three variations or combinations:

• Mesh
• Star bus
• Star ring

Mesh Topology

• Every device interconnected
• Most expensive
• Most Fault tolerant
• Cable fault tolerant
• Device fault tolerant

Star Bus Topology

Star Bus Environment

• Star hubs
• Interconnected on a bus backbone
• Device failure minimized
• Hub failure affects only that star

Star Ring Topology

• Network wired as star
• Network traffic handled as ring
• Failure limited to single device
• Individual machine backups
• Outer hubs can be connected to inner ring

Selecting a Topology

Check the advantages and disadvantages of each topology

Constructing a Network Layout

• Before construction think it through
• Evaluate network requirements
• How will the network be used?
• LAN is a four-letter word (spelled "PLAN")

Important Questions

• How many computers to attach?
• How many servers to attach?
• What applications to run?
• Peer to Peer or Server based?
• Fault tolerance/budget available?

Sketch the Network

• Mark device locations on blueprint
• Allow users equal access in sketch
• Topology questions get answered
• Budget concerns are identified
• Prepare for system mapping

Map the network

• Layout should be consistent with current network
• Layout should be maintained as network changes
• Third-party tools available to assist in design