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DOCSIS™ Cable Modem Technology

DOCSIS™ Cable Modem Technology. Speaker: 陳羿仲 Advisor: 吳和庭 2012/05/22. Outline. INTRODUCTION DOCSIS PROTOCOL STACK DATA TRANSMISSION ON MULTIPLE UPSTREAM CHANNELS REQUEST CLUSTER ALLOCATION SCHEME NUMERICAL EXAMPLES REFERENCES. INTRODUCTION.

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DOCSIS™ Cable Modem Technology

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  1. DOCSIS™ Cable Modem Technology Speaker: 陳羿仲 Advisor: 吳和庭 2012/05/22

  2. Outline • INTRODUCTION • DOCSIS PROTOCOL STACK • DATA TRANSMISSION ON MULTIPLE UPSTREAM CHANNELS • REQUEST CLUSTER ALLOCATION SCHEME • NUMERICAL EXAMPLES • REFERENCES

  3. INTRODUCTION • CableLabs®:a number of cable operators create Cable the Television Laboratories • DOCSIS™(Data Over Cable Service Interface Specification): a standard for data transmissions on CATV/HFC networks

  4. INTRODUCTION • CATV:It started to distribute broadcast video signals to locations with poor or no reception in the late 1940s,it was called community antenna TV (CATV) • HFC: A system with fiber for the long-haul runs and coaxial cable to the houses is called an HFC(Hybrid fiber-coaxial ) system

  5. INTRODUCTION

  6. INTRODUCTION

  7. INTRODUCTION

  8. DOCSIS PROTOCOL STACK

  9. DOCSIS PROTOCOL STACK • Physical layer: • includes the modulation schemes used on the coax network • For DOCSIS, these are 64-quadrature amplitude modulation (QAM) and 256-QAM on the forward • quadrature phase shift keying (QPSK) and 16QAM on the reverse

  10. DOCSIS PROTOCOL STACK • MPEG-2 Transmission Convergence layer: • DOCSIS CM data is encapsulated in 188-byte MPEG-2 frames • This allows the data to be multiplexed with other MPEG streams on the same carrier on the forward path

  11. DOCSIS PROTOCOL STACK • Media access control (MAC) layer: • Controls CM access to the return path • there maybe many CMs trying to transmit simultaneously on the return path • MAC protocol provides an orderly method for the CMTS to tell a CM when it gets to transmit and for how long

  12. DOCSIS PROTOCOL STACK • Data link encryption layer: • there has to be a method to protect user data from malicious users

  13. DATA TRANSMISSION ON MULTIPLE UPSTREAM CHANNELS • In DOCSIS, an upstream channel is shared by many stations • An upstream channel is a TDMA type shared channel

  14. DATA TRANSMISSION ON MULTIPLE UPSTREAM CHANNELS • Channel will divide into fixed length time slots called minislots • A series of minislots to be used for reservation requests, called a request cluster • Before transmission, the station must send a request in a request cluster

  15. DATA TRANSMISSION ON MULTIPLE UPSTREAM CHANNELS

  16. REQUEST CLUSTER ALLOCATION SCHEME • Binary Exponential Back-off scheme • The request cluster size is set to a power of 2 ,Say 2^x • X is a positive integer called the back-off window • Each station generates one of the values from 0 to (2^x-1) • If two or more stations generate a same number, a collision occurs

  17. REQUEST CLUSTER ALLOCATION SCHEME

  18. REQUEST CLUSTER ALLOCATION SCHEME Too large: • if only one collision occurs when the request cluster is large, say 512, then it allocates 1024 minislots for the next round • Useless request cluster would increase • Stations which want transmission data will wait the large request cluster goes past

  19. REQUEST CLUSTER ALLOCATION SCHEME Too small: • When collisions have been resovled, the request cluster is set to the minimum value • When under a heavy-load condition, collisions occur many times, there will make many stations fail reservation and try again

  20. REQUEST CLUSTER ALLOCATION SCHEME Proposed Scheme • R:the number of request minislots safely received in the request cluster • C:the number of collided minislots in the request cluster

  21. REQUEST CLUSTER ALLOCATION SCHEME

  22. NUMERICAL EXAMPLES

  23. NUMERICAL EXAMPLES

  24. REFERENCES [1] Fellows, D.; Jones, D. , “DOCSISTMcable modem technology”, IEEE Communications Magazine, Page(s): 202 - 209, Mar 2001 [2] Saito, T.; Satake, S.; Inai, H., ”Performance evaluation of a request cluster allocation scheme for multi-channel DOCSIS ”, TENCON 2010 – 2010 IEEE Region 10 Conference,Page(s): 1472 - 1477 ,21-24 Nov. 2010

  25. Q&A Thank you for Listening

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