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CS 453 Computer Networks

CS 453 Computer Networks

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CS 453 Computer Networks

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  1. CS 453Computer Networks Lecture 17 Medium Access Control Sublayer Bluetooth, Switching and VLAN

  2. Bluetooth Developed out of an interest by a cell phone manufacturer for a way for cell phone to connect to other devices sans cables SIG created from Erricson, IBM, Intel, Nokia, and Toshiba… … to develop standards Bluetooth SIG standards in 1999 IEEE jumped in later …became 802.15

  3. Bluetooth Ever wonder where the name came from? Harold Gormson (Harold I of Denmark), a Viking king

  4. Bluetooth 802.11 intended to serve buildings Range ~ hundred meters Bluetooth intended to serve a room Much more of a personal area network Short run cable replacement (at least originally) Range: 10 meter (that was the idea anyway)

  5. Bluetooth Bluetooth architecture Small radio cell – piconet Piconet about 10 meters Multiple piconets can be bridged Cell has one master node… … and up to seven slave nodes Can have up to 255 parked nodes Master does all parking (valet?)

  6. Bluetooth Bluetooth architecture Master does all control Slave only does what Master says This allow very cheap slave electronics (plan was for under $5 per chip All communications must be master/slave, slave/master… Never slave/slave Bandwidth allocation via TDM

  7. Bluetooth Bluetooth architecture 3 classes of radios used in Bluetooth Class 3 radios – have a range of up to 1 meter or 3 feet Class 2 radios – most commonly found in mobile devices – have a range of 10 meters or 30 feet Class 1 radios – used primarily in industrial use cases – have a range of 100 meters or 300 feet From:

  8. Bluetooth Bluetooth architecture Uses 2.4 Ghz ISM band Uses FHSS 1600 Hops/second Dwell time 625 microseconds 79 channels 1 Mhz each FSK modulation Uses same band/same channels as 802.11, garage door remotes, cordless phones, etc.

  9. Bluetooth Bluetooth application profiles From: Tanenbaum, 2003, pg. 312

  10. Bluetooth Bluetooth links ACL – Asynchronous Connection Less Packet switching irregular data Slave can only have one ACL link with master Synchronous Connection Oriented Real-time data Like voice, etc. Slave can have up to 3 SCO links to master

  11. Bluetooth Bluetooth SCO payload always 240 bits ACL payload 80, 160, 240 Master uses even slots Slave uses odd slots

  12. Bluetooth Bluetooth frames Ack = piggybacking Ack on frame Seq = number frames (one bit?) Header repeated 3 times Addr = address of one of eight active devices Type = ACL, SCO, Polling, null Flow = slave wants pause

  13. Bluetooth More Information:

  14. Logical Link Control - LLC Let’s backup a bit Recall that we have discussed the Medium Access Control Sublayer… And that it is a sublayer of the Data Link Layer… …the bottom half, in fact The top half is another sublayer known as the Logical Link Control sublayer or LLC

  15. Logical Link Control - LLC • The MAC sublayer can take several forms depending the the physical medium used at the physical layer, protocols, etc. • Remember the different bandwidth allocation schemes/protocols for IEEE 802.11? • These are the MAC sublayer • LLC takes care of error correction, flow control,…

  16. Logical Link Control - LLC • LLC also provides a consistent interface to the Network Layer • For Ethernet and other IEEE 802 protocols… • LLC receives packet from Network layer… • And prepends an LLC header to the packet… • This goes in the payload field of the frame • LLC header contains a • source process address, • destination process address • Control field (sequence and acknowledgement numbers)

  17. Logical Link Control - LLC • LLC is standardized as IEEE 802.2

  18. Data Link Layer Switching We have briefly discussed hubs and switches… And mentioned repeaters, and routers… …there are more… So what is the difference?

  19. Data Link Layer Switching • Bridges – interconnect LANs • Operate at the DLL level • Repeaters on pass on traffic (electrically) • Extend network medium range • Never looks at frames • Bridges examine frame – decide to forward frame from one LAN to another • Can translate from one LAN type to another

  20. Data Link Layer Switching • Reasons for Bridges • Network Autonomy – departments, organizational units • Geography – different buildings – employ different medium • Distance exceeds medium max – stretch network past cable length limits • Load Balancing – keeping local traffic local • Isolation of bad traffic - keep bad traffic burst from saturating network – limit to seqment • Security - prevent frames from being propagated (and snooped) across the entire network

  21. Data Link Layer Switching From: Tanenbaum (2003), pg. 321 Frame formats for 802.3, 802.11, 802.16

  22. Data Link Layer Switching 802.11 to 802.3 Bridge From: Tanenbaum (2003), pg. 321

  23. Data Link Layer Switching A B C D Bridge • Bridge • Bridge sees all frames on both LANs • A to B frames seen by bridge, but not forwarded • A to C frames seen by bridge and forwarded From: Tanenbaum (2003), pg. 321

  24. Data Link Layer Switching • So, what’s the difference between Bridges and Switches? • Not much • Bridges connect LANs • Switches connect stations • Both operate at the DLL level • Bridges may only have a few ports – • For connecting LAN segments • Switches usually have many ports • For connecting stations From: Tanenbaum (2003), pg. 321

  25. Hubs, Switches, Routers, etc.

  26. VLANs • Virtual Local Area Network • Remember that having a network broken down into multiple LANs and connected with bridges had some advantages • Political “territory” • Security • Load control • Fault isolation • ..and others

  27. VLANs • That is based on the physical topology of the network • Wouldn’t it be nice if you could accomplish the same thing logically rather than physically • That is a VLAN A B C D Bridge

  28. VLANs • For example, supple that station A and D are in the research department… • …and B and C in accounting • You would want A and D to be in the research VLAN while B and C should be in the accounting VLAN A B C D Bridge

  29. VLANs • Oh, and we need this to be transparent… • Meaning that we should be able to move a station from one physical LAN to another and it still be in its appropriate VLAN • A few ways to accomplish this • Have switches and bridges keep track of machine in a VLAN by MAC address • Have switches and bridges keep track of machines in a VLAN by port (this gets sticky) • Have stations announce their VLAN – changing the 802 spec?

  30. VLANs • IEEE did just that … changed the 802 frame format ---IEEE 802.1Q From: Tanenbaum, 2003, pg 335