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