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NET7.PPT

  1. 1. Session T2: Campus LAN Interconnection An Introduction to Concepts and Technologies
  2. 2. ethernet: one ethernet is one "collision domain"  cabling rules ("4-repeater", etc.) allow growth of a single ethernet  limited distance:~2500m or less, depending on cable type  limited number of stations: 1024 (architecturally); 100 (practical, olden days); 20-30? (practical, today)  when you grow beyond these limits, build another ethernet and connect the two together the issue: expanding a local network 
  3. 3. the issue: expanding a local network... A C D B A C D B A C D B A C D B  Appends data  Intermediate stations repeat data  Receiver copies data and continues to repeat  Sender generates new token one token ring is one "token path"  limited distance: ~2000m or so, depending on cabling  limited number of stations: 250 or fewer, depending on traffic
  4. 4. why connect or split LANs? why connect LANs?  to allow sharing of files, devices, etc. why split LANs?  to provide physical security/isolation  to implement policies (user groups, etc)  to give greater average bandwidth per user ("segmentation" or "microsegmentation") so, what are our options for interconnecting the LAN segments we create?
  5. 5. the issue, restated: which LAN frames should be forwarded from one segment to another? a LAN frame on an ethernet:  SNA, IP, IPX, AppleTalk Address  Token-Ring, Ethernet Address  Also known as MAC address (Media Access Control) ?
  6. 6. LAN interconnection technologies Presentation Session Transport Network Data Link Physical Application OSI reference model hubs/multiplexors bridges/switches routers application gateways tunneling/encapsulation
  7. 7. bridge bridge operation:  at layer 1, connects two physical LAN segments  at layer 2, connected LANs look like a single logical LAN e.g., bridge forwards LAN broadcasts  forwards frames based on layer 2 info (e.g., MAC address) thus, independent of higher layer protocols  easy to implement -- little or no configuration B B B B B B B B B B B B
  8. 8. transparent bridge bridges agree on a single path through the network  path is called a "spanning tree" all LAN traffic follows that single path  frames forwarded based on MAC address parallel bridges may exist, but are inactive ("blocking") B B B B B B B B
  9. 9. source routing bridge commonly used in token ring networks (not ethernet)  each ring is given a ring number (unique in the whole bridged LAN)  each bridge is given a bridge number (unique between same pair of rings) end stations discover routes via a broadcast process  bridges place path of broadcast in the frame (routing info field)  that same path (rings and bridges) is then used for other frames frames forwarded based on routing info field in frame for connection-oriented protocols, broadcast occurs only when connection is established parallel active paths are allowed
  10. 10. B B B B B B B B A B B? B? B? B? B? B B B B B B B B A B B via Rt 1! B via Rt 2! source routing bridge... B?
  11. 11. switch basically a fast, multiport, layer-two device  i.e., similar in function/capability to a bridge  fast, since functions often performed in hardware  low latency -- good for fast response time  easy implementation, low cost each port connects to a separate LAN segment  shared or dedicated  dedicated ports may operate in full-duplex mode
  12. 12. router router isolates logical subnetworks for more efficient network utilization  layer 2 traffic not typically forwarded unless addressed to router  each subnetwork is given an identification--e.g., IP subnet; IPX network number end station sends traffic to router; router forwards toward ultimate destination router must understand the layer 3 protocol(s) it is to handle--complexity, configuration routing protocols allow router to understand network topology
  13. 13. R R R Net A Net C Net D Net E Net B router... R
  14. 14. choosing technologies--considerations protocols (IP, IPX, NetBIOS, SNA, Appletalk, ...)  how do they work?  do they have a layer 3 structure (are they "routable?")  how often do they broadcast? how much traffic? end user response time--delay/latency in the interconnection device administration  configuration of router vs bridge/switch  network operations--e.g., moves/changes  network management, troubleshooting, etc. cost
  15. 15. example - distributed backbone with bridges B B B hubs bridges hubs Physical Logical
  16. 16. example - distributed backbone with bridges pro:  easy to implement--little configuration  inexpensive  administration is easy con:  potential bridge congestion, depending on which bridge used  bridge management harder since bridges distributed
  17. 17. example - collapsed backbone with bridges Ring 001 Ring 002 Backbone Ring Bridge Bridge hubs bridges Physical backbone hub Logical
  18. 18. example -- collapsed backbone with bridges pro:  same as distributed bridge design, plus centralized bridges/backbone hub are easier to manage servers can be centralized while still physically connected to floor LAN segments con:  same as distributed bridge design  riser cable considerations fiber? copper? distance? port cost on device?
  19. 19. example - collapsed backbone router subnet A subnet B hubs Physical backbone router Logical
  20. 20. example -- collapsed backbone router pro:  conceptually simple  popular solution  more powerful device than bridge--faster, more intelligence  router limits broadcast traffic between subnets con:  more expensive device than bridge  operation, management much more complex than bridge  user moves more complicated to handle--subnets  broadcast traffic not usually a problem in campus-- different from a WAN link
  21. 21. example - collapsed backbone switch hubs Physical switch Logical switch
  22. 22. example -- collapsed backbone switch advantages:  same pros as bridged network -- low cost, easy implementation and administration  avoids subnet issues with user moves  higher performance and lower latency than bridge or router  servers can be attached to dedicated switch ports for higher performance  being deployed today as front end to router Trend today is to use switching within a campus, and routing for lower speed WAN links
  23. 23. what about campus backbone technologies? generic picture: LANs (ethernet, token ring) connected with some kind of high speed backbone 2 or 3 popular backbone technologies the issues of interconnection devices are still the same as before  latency; intelligence; administration; cost; etc....... B B B B Fast Enet FDDI ATM
  24. 24. "big pipe" technologies ...i.e., a faster flavor of what you have today  e.g., fddi, fast ethernet strengths  simplicity; scalability; faster speed to attached devices considerations  sensitive to wiring installation quality  upgrades may be required to hub and all stations  adapter/CPU performance  some problems cannot be solved with more bandwidth --- latency! (bigger pipe doesn't change the interconnection device--still use switches or routers)
  25. 25. cell switching (ATM) ATM: a layer 2 technology based on cell switching  low latency for high throughput  multiple traffic types in cells--mixed voice, data, multimedia scalable from low to high speeds  25Mbps to ... 155Mbps? 622Mbps? 2.4Gbps?  individual links can be different speeds Quality of Service (QoS) allows (will allow) applications to specify the network service characteristics they need LAN Emulation allows applications to use ATM without change
  26. 26. ATM strengths  mixed traffic (voice/video/data/multimedia)  high speed; scalable speed  very low latency  Quality of Service support  point to point technology allows broadcast control (see IBM's MSS Server) considerations  cost  complexity/learning curve
  27. 27. campus LAN interconnection summary interconnection devices: bridge, switch, router  switches preferred today within campus fast; low latency; easy implementation/administration  routers good for controlling use of low speed WAN links campus backbone technologies  big pipes: fast ethernet, fddi easy to deploy; faster speed to attached devices; may or may not solve response time/performance issues  ATM supports voice, video, data; gives true traffic control for new applications; issues are cost, education

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