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Understanding Network Architecture

Understanding Network Architecture. Access Methods CSMA/CD Carrier Sense Multiple Access/Collision Detect CSMA/CA Carrier Sense Multiple Access/Collision Avoid Token Passing Demand Priority Can’t buy this type of hardware any more. Access Methods.

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Understanding Network Architecture

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  1. Understanding Network Architecture • Access Methods • CSMA/CD • Carrier Sense Multiple Access/Collision Detect • CSMA/CA • Carrier Sense Multiple Access/Collision Avoid • Token Passing • Demand Priority • Can’t buy this type of hardware any more

  2. Access Methods • Carrier Sense Multiple Access with Collision Detection • Ethernet • Senses when the cable is connected (Carrier Sense) • Senses when no traffic is passing to transmit (multiple access) • Senses possible collisions (Collision Detect) • Computers contend for access on the wire • C03dem01, 02, 03, 04, 05, 06

  3. Packet Traffic Network Cable

  4. Collisions 5 Signal 1 0 5 Signal 2 0 10 Sum of 1 and 2 0 Ethernet threshold

  5. CSMA/CA • Carrier Sense Multiple Access Collision Avoidance • The computer announces that it wants to transmit. • Other computers wait until that computer transmits it’s data • Creates more traffic on the wire • c03dem07

  6. Token Ring • Special packets called tokens circulate in a ring from computer to computer. • If a free token is detected then a computer will take control and send it’s data • If a token is destined for a specific computer that computer takes the token • One one computer at a time can use the token so no collisions take place. • C03dem08, 09, 10, 11 ,12

  7. Demand Priority • 100VG-Any LAN (obsolete) • Hubs (repeaters) manage the packet passing by searching for requests • Similar to CSMA/CD except that the hubs be assign priorities. • More efficient since broadcasts are minimized across the network. • Was made obsolete by Ethernet • Vendors don’t sell 100VG NICs anymore • c03dem13,14

  8. Packet Contents • Contain data for passing between computers • Have timing, begin, and end markers • Have addressing (source/dest) information • Have error detection/correction • Have type identifiers so computers can filter out packets at a low level. • Contain requests for how to pass the packet

  9. Actual Ethernet Frame • 62 bits of preamble (alternating 1’s and 0’s) • 2 bits Start of Frame Delimiter (2 one’s) • Destination Ethernet Address • Source Ethernet Address • Length or Type • Data (if less than 46 bytes then pad to 46) • 4 bytes (32 bits) Frame Check Sequence

  10. Ethernet Packet Ethernet destination Address (first 32 bits) Ethernet Dest (last 16) Ethernet Src (16 bits ) Ethernet source Address (last 32 bits) Type Code or Length of packet (16 bits) Length from 512 to 4096 bytes IP header, TCP header, then your data Ethernet Checksum

  11. Network Traffic • All of the computers in you local area see all of the packets on the wire and have to decode them and see if a particular packet is addressed to this computer. • Each NIC has a unique address assigned to it. • When a packet is sent that unique address is build in to the packet. • Before connection is established the source computer sends out a broadcast (all 1’s in the data portion of the destination address. • The destination system (responds to a specific type of request) then replies with it’s address to finish the connection setup

  12. Network Installations • Cross connects • Blocks that connect wall jacks to hubs • May changes/removals easier • Patch panels • Allow changes from one network to another • Allow changes to wiring if a hubs fails

  13. Hub Advantages • Standard Telephone Wiring • Standard Punch Blocks and Cross Connects • Ability to disable a single port • Easier to monitor traffic patterns • Visible Indication of Link Status • If a wire is cut only one port is affected • Unless the backbone feed is cut!

  14. 5-4-3 Repeater Rule 10MB • 3 repeater rule Sys3 Sys 2 System 1 Repeater Repeater Repeater Repeater System 1 can talk to Sys 2 but not Sys3

  15. 5-4-3 Rule • 5 segments (between repeaters or work groups) • 4 repeaters • 3 segments can have computers attached. • Violation of this rule means one end of the network can’t talk to the other end.

  16. Repeater Repeater Network Diameter (100MB) • 205 Meter Limit 100M 100M 5M 10MB diameter is 500M

  17. Segmentation of the Network • Segmentation can control broadcast traffic on a network • Segmentation can enhance security on the network (limited traffic monitoring) • Segmentation can be implemented with bridges (2 port) and switches (multi ports) • If more segmentation is needed then a routed network may need to be installed.

  18. Repeater Repeater Repeater Repeater Switches and Bridges Bridge

  19. Bridge Insides LAN B LAN A Filter based on ethernet address Interface Interface

  20. Switch Insides A F B C G D Switching based on ethernet address E

  21. 100baseT to 10baseTHub/Bridge 10baseT 100baseT 100baseT to 10baseT Bridge Module 100baseT hub 10baseT hub

  22. 10MB Ethernet Rules • 3 repeater (populated) limit • 5 repeater per segment limit • 7 bridges per ethernet lan • Cable lengths • 1024 stations per ethernet lan

  23. 100 MB Ethernet Rules • 2 hubs no more than 5 meters apart • Total length of network segment is 205 meters. • Must use Cat 5 or better cable • Punch blocks must be Cat 5 certified

  24. How to get around limits? Hubs Switch ROUTER Firewall To the Internet (switching based on IP address) Other Lans

  25. Token Ring 4 or 16 MB/s Mic (Media Interface Connector at each computer)

  26. MAU or MSAU • Multistation Access Unit `` Ring in Ring out Computer Ports The MAU allows the ring to be installed in a star topology The MAU isolates a port if the attached computer fails

  27. Token ring operation • First computer on the network sends a token • The token travels around the ring • If a computer wants to transmit it takes control of the token • That computer sends it’s data and the frame goes around the ring to the destination computer. • The destination computer takes the token and marks the token as received. • The token continues until it arrives at the source computer who acknowledges the data. The sending computer then removes the token from the ring and sends a new token.

  28. More token passing • One 1 token can be on the ring at one time. • The token passing only goes in one direction. • Transfer rates are either 4 or 16 MBS • IBM POS (Point of Sale) systems still use token ring networks • Routers can handle mixed token ring to ethernet networks.

  29. Appletalk • LocalTalk • 230 Kbps, single twisted pair, obsolete • EtherTalk • uses ethernet • TokenTalk • AppleShare • File Sharing • Zones • Sort of like subnets or workgroups

  30. ARCnet • ARCnet hubs and nics are still available • Uses token bus access method • Can handle up to 255 network numbers per network. • Uses a single coax or twisted pair cable per computer • The cable is different than ethernet cable • The cable distances are longer than ethernet • 2.5 Mbps speed

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