docsis cable modem technology speaker: advisor: 2012/05/22
TRANSCRIPT
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
Thank you for Listening