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FrameworkInside&OutApplication

FrameworkInside&OutApplication. ATM Quick Review 1. Understand why ATM is a good candidate 2. Are you on the right way?(Don’t just think about ATM) Tag Switching On ATM 1. How does it work over ATM? 2. Are Tags over ATM panacea? Conclusions.

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FrameworkInside&OutApplication

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  1. FrameworkInside&OutApplication • ATM Quick Review 1.Understand why ATM is a good candidate 2. Are you on the right way?(Don’t just think about ATM) • Tag Switching On ATM 1. How does it work over ATM? 2. Are Tags over ATM panacea? • Conclusions

  2. ATM Review • Packet Networks(IP pushing routers) 1. User data+overhead bits (routing,flow,error) 2. Packets: protocol dependant(200—65,545bytes) 3. Results: larger overhead, smaller user data • Cell Networks(ATM Stressing switches) 1. User data(in form of cells)+a small header 2. Cells: use ATM switches (53bytes) 3. Results: Fast and efficient switching

  3. ATM Review Cont… • ATM is great: 1. ATM network=ATM switches+ATM endpoints 2. Well-defined job of ATM switches 3. Three-layer architecture 4. Virtual connections: a. connection oriented b. two types of connections: VC and VP c. switching refers to: VCI and VPI  Q:IS ATM A GOOD CANDIDATE?(where to cut in?)

  4. ATM Review Cont… • Cutting-in Points for Tag switching: 1. Fast forwarding—table lookup, similar to ATM 2. Improved performance—upgrading ATM at low cost 3. Easy network evolution—implemented in stages over ATM

  5. ATM Review Cont… • “Tags” control over all, once implemented? NO!! 1.Traditional ATM is not impacted (“ship in the night”) 2. No Problem with other network if properly configured and upgraded. (“mixed network”)

  6. Tag Switching over ATM • How Tag switching works in ATM? 1. Implementing two components 2. Using VPI & VCI and input port# as index 3. Swap them off with outgoing VPI & VCI and output port# 4. You done! ATM switches are now ATM-LSRs

  7. Tag Switching Over ATM Cont… • Are “tags” in ATM are panaceas?(several points worth seriously considering……) 1.Time-to-Live (TTL) 2. “Hot-tag” problems 3. Hardware limitation

  8. Tag Switching over ATM Cont… • TTL—loop-related problem 1. In IP: TTL decremented by 1/hop 2. ATM: tag values are encoded in data link layer(AAL header) and forwarded by layer-2 ATM switches(no TTL field) 3. Once loop forms, ATM efficiency lost!

  9. Tag Switching over ATM Cont… • “hot-tag”—resource problem 1.Tags are resources, everybody wants them! 2.What if lack of outgoing tags? What if incoming tags “illegal”? What if tag assignments conflicting each other? 3.Possible solutions: ATM strip off the labels and use IP ATM could get confused and just discard

  10. Tag Switching over ATM • Hardware limitation—Encoding problem ATM switchessay:don’t expect me do too much! 1.ATM switches are different from a “generic MPLS encapsulation” hardware 2.ATM switches have no capability for encoding translation(ATM network encoded the same way) 3.ATM switches VPI & VCI encoding cannot perform label merging( application limitation)

  11. Conclusions • Pushing and Stressing will continue… 1. Net has changed, fired by WWW 2. Random, any-to-any traffic and multimedia 3. Who will win? • Tag switching comes in and expanding… 1. Faster forwarding 2. Improved scalability 3. Improved performance for low cost 4. Ease of network evolution

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