Topologies

• The structure of the network– Physical topology

• Actual layout of the media

– Logical topology• How the hosts access the media

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

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

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!

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

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

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

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

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

Repeaters

• Regenerate and retime signals at the bit level

• Allows data to travel further• Single-port “in”• Single-port “out”• Layer 1

– bits

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

Hubs

• Regenerate & retime network signals– done at bit level for many hosts

• “Multi-port Repeater”• Create a central connection point• Increases reliability• Layer 1

Active Hubs

• Use energy from a power supply to regenerate signals

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

Intelligent Hubs

• Console ports

• Can be programmed to manage network traffic

Dumb Hubs

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

Hubs in other topologies

• Token Ring– MAU– Media Access Unit

• FDDI– MAU is called a concentrator

• All Layer 1

Bridges

• Layer 2 device• Connects two LAN segments• Filters traffic based on MAC

address– local traffic is kept local

– other traffic is directed out

Switches

• Layer 2 device• “Multi-port bridge”• Decisions based on MAC

addresses• Switch data out of the port

where the receiving host is connected

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

Routers

• Layer 3• Can make decisions based on

groups/ classes of addresses• Can connect different layer 2

technologies– Ethernet, FDDI, Token-Ring

Routers

• Backbone of the Internet• Examines incoming packets,

switches to correct outgoing port• Most important regulating devices

on large networks

Clouds

• Suggests another network (perhaps Internet)

• Does not supply details• Really a collection of devices• Layer 1-7

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

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