DOCSIS Cable Modem Technology Speaker Advisor 20120522 Outline

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 • Cable. Labs®: 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

INTRODUCTION • CATV : It started to distribute broadcast video signals to locations with poor or no reception in the late 1940 s, 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

INTRODUCTION

DOCSIS PROTOCOL STACK

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

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

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

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

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

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

DATA TRANSMISSION ON MULTIPLE UPSTREAM CHANNELS

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

REQUEST CLUSTER ALLOCATION SCHEME

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

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

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

REQUEST CLUSTER ALLOCATION SCHEME

NUMERICAL EXAMPLES

REFERENCES [1] Fellows, D. ; Jones, D. , “DOCSISTM cable 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

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