Topologies

1
Topologies

• The structure of the network
• Physical topology
• Actual layout of the media
• Logical topology
• How the hosts access the media

2
Physical Topologies

• Bus
• Uses a single backbone cable
• All hosts connect directly to backbone
• Ring
• Connects each host to the next, and the last to
  the first
• Physical ring of cable

3
Physical Topologies

• Star
• Connects all cables to a central point of
  concentration
• Usually a hub or switch at center
• Extended Star
• Links stars by linking hubs or switches

4
Physical Topologies

• Hierarchical
• Similar to extended star
• Links star LANs to a computer that controls
  network traffic
• Mesh
• Each host is connected to all other hosts
• No breaks, ever!

5
Logical Topologies

• Broadcast
• Each host sends its data to all other hosts
• First come, first served to use the network
• Ethernet
• Token Passing
• Controls access by passing token
• Host can send when it has the token

6
LAN Devices

• Devices that connect to a LAN are called hosts
• Hosts are not part of any layer
• Operate at all layers
• Symbols not standardized
• Bear a resemblance to device

7
Network Interface Cards

• Network adapter
• printed circuit board or PCMCIA board
• Adapts the host device to the network medium
• Each has a unique MAC address
• Media Access Control
• No standard symbol
• Implied on each host

8
Transceivers

• Converts one type of signal or connector to
  another
• AUI to RJ-45 on router
• Attachment Unit Interface
• Layer 1
• only looks at bits
• Found on routers

9
Media

• Carries a flow of information
• Bits and bytes
• Layer 1
• Media selection is based on
• Cable length
• Cost
• Ease of installation
• Total number of computers on the media

10
Repeaters

• Regenerate and retime signals at the bit level
• Allows data to travel further
• Single-port in
• Single-port out
• Layer 1
• bits

11
5-4-3 Rule for Repeaters

• Five Repeater Rule
• You can connect 5 segments with 4 repeaters, but
  only 3 cable segments can have hosts on them

12
Hubs

• Regenerate retime network signals
• done at bit level for many hosts
• Multi-port Repeater
• Create a central connection point
• Increases reliability
• Layer 1

13
Active Hubs

• Use energy from a power supply to regenerate
  signals

14
Passive Hubs

• Simply split signal to multiple users
• Like a Y cable
• Do not regenerate bits
• Do not extend cable length
• Only allow two or more hosts to connect to same
  cable segment

15
Intelligent Hubs

• Console ports
• Can be programmed to manage network traffic

16
Dumb Hubs

• Take an incoming network signal and repeat it to
  every port

17
Hubs in other topologies

• Token Ring
• MAU
• Media Access Unit
• FDDI
• MAU is called a concentrator
• All Layer 1

18
Bridges

• Layer 2 device
• Connects two LAN segments
• Filters traffic based on MAC address
• local traffic is kept local
• other traffic is directed out

19
Switches

• Layer 2 device
• Multi-port bridge
• Decisions based on MAC addresses
• Switch data out of the port where the receiving
  host is connected

20
Switches

• Looks outwardly like a hub
• Makes data transmission more efficient
• Combines connectivity of hub with the traffic
  regulation of a bridge on each port

21
Routers

• Layer 3
• Can make decisions based on groups/ classes of
  addresses
• Can connect different layer 2 technologies
• Ethernet, FDDI, Token-Ring

22
Routers

• Backbone of the Internet
• Examines incoming packets, switches to correct
  outgoing port
• Most important regulating devices on large
  networks

23
Clouds

• Suggests another network (perhaps Internet)
• Does not supply details
• Really a collection of devices
• Layer 1-7

24
Segments

• Common path for data transmission
• Each time a device is used to extend cable length
  or manage data flow, a new segment is created

25
Segments

• Function of a segment is to act as an efficient
  local LAN that is part of a larger network
• Segment, as applied to LANs, is completely
  different from the Layer 4 PDU known as a segment