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

• 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

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

INTRODUCTION

INTRODUCTION

INTRODUCTION

DOCSIS PROTOCOL STACK

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

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

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

DOCSIS PROTOCOL STACK

• Data link encryption layer:

there 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

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

Q&A

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