Modems

Topics: Cable modem, Modulation, Cable television Pages: 32 (5082 words) Published: September 18, 2013
Broadband System – P
Satellites are spaced every 2nd degrees above earth
"C" Band Toward satellite 6.0 GHz Toward earth 4.0 GHz

"L" Band Toward satellite 14.0 GHz Toward earth 12.0 GHz

TV TRANSMITTER

Headend

Cable area
1

DOCSIS, QPSK, QAM signal and Cable Modem System.

Understanding DOCSIS Operating System.

A Cable system operating with Cable Modems required,
•A bi-directional HFC or CATV system. •A Cable Modem Termination System at the Headend or Hub site. •A 100 BaseT or better connection to Internet or Servers. •A 6 MHz of 64 or 256 QAM data channel operating from: 88 to 870 MHz. •A 3.2 MHz of QPSK or 16 QAM operating between 16 to 40 MHz on the return section of the system for DOCSIS 1.0. •At least one Cable Modem installed at a customer on the system.

2

Understanding DOCSIS Operating System.

One standard that will be repeated very often in the following lecture; DOCSIS(™)

Data Over Cable Service Interface Specification.
DOCSIS specifications can be; DOCSIS 1.0, 1.1, 2.0 and 3.0
3

Understanding DOCSIS Operating System.

One other standard that will be repeated very often in the following lecture; CMTS.

Cable Modem Termination System
The above unit is what controls all the data to and from all Cablemodem on the HFC system. 4

Understanding DOCSIS Operating System.
The DOCSIS services, Data Over Cable Services Interfaces Specifications was developed by CableLabs and approved by the ITU. It also defines interface requirements for cable modems involved in high speed data distribution (both MPEG and IP data) aver cable system networks. Other devices that recognize and support the DOCSIS standard include HDTV's and Web enabled set-top boxes for regular televisions. There are two key components in the DOCSIS architecture: Cable modem (CM) which is located at the customer premise, and Cable Modem Transmission System (CMTS), which is located at the Headend of service provider s and used to aggregated traffic from multiple Cable Modems and then communicate with the backbone network. DOCSIS specifies modulation schemes and protocol for exchanging bidirectional signals between the two components over cable. Cable operators have the possibility of four (4) types of DOCSIS system.

•DOCSIS 1.0, DOCSIS 1.1, DOCSIS 2.0, DOCSIS 3.0
5

Understanding DOCSIS Operating System.

DOCSIS 1.0
High Speed Internet Access. Key features: Downstream transfert rates between 27 and 36 Mbps over a radio frequency path between 88 and 870 MHz in a 6.0 MHz spacing, and upstream traffic transfer rate between 320 Kbps and 10 Mbps over a RF path of 3.2 MHz between 5 and 42 MHz. But, because data over cable travels on a shared loop, individuals will see transfer rates drop has more users gain access.

6

Understanding DOCSIS Operating System.

DOCSIS 1.1
The types of services afforded by DOCSIS 1.1 differ from DOCSIS 1.0 technology, by; •QoS (Quality of Service). •Data fragmentation which permit voice services where latency matters more than sheer bandwidth. •Security upgrade •The ability to pre-equalize upstream traffic, thus doubling reverse path throughput (10 Mbps per 3.2 MHz spacing, versus 5 Mbps for DOCSIS 1.0) 7

Understanding DOCSIS Operating System.

DOCSIS 2.0
Added capacity for symmetric services by operating at 64 QAM and having new 6.4 MHz wide channel. It increased bandwidth for IP traffic by using enhanced modulation and improved error correction. The result for upstream transmission is 30.72 Mbps using 64 QAM, which is 3 times better than DOCSIS 1.1 and 6 times than DOCSIS 1.0. DOCSIS 2.0 is interoperable and compatible with DOCSIS 1.x The latest DOCSIS specification eDOCSIS has been published to the industry. eDOCSIS stands for embedded DOCSIS, which would provide a subordinate function at the core chip level to the host device. And, rather than leveraging a home networking protocol, an eDOCSIS device would feed directly into a cable network's DOCSIS channel....
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