Showing posts from April, 2007

Understanding Cable Broadband Technology

Below is an introduction to the terms, concepts and summary of the features of DOCSIS standard versions which i have compiled from several sources in an effort to learn about the cable broadband technology.

Cable Modem: is a device that is designed to bridge customer's home computing network to an external network, usually the Internet. This is accomplished by using the preexisting coaxial cable network, originally designed for the cable TV infrastructure, known as Community Antenna Television (CATV). Coaxial Cable (RG-6 type): Many video channels, each carried at a specific frequency, are superimposed by the cable provider onto a single carrier medium - a standard coaxial cable. This process modulates each channel so that it is exactly 6 MHz (8MHz in Europe) away from the previous channel, and the frequency range available for a CATV provider to use typically runs from 42 to 850 MHz. When a user is watching a channel, the TV is tuned to the frequency that represents the…

Understanding RRDTool

RRD Tool is a product that grew out of MRTG. It creates a very compact database structure for the storage of periodic data, such as is gathered by OpenNMS. RRD data is stored in files that are created when initialized to hold data for a certain amount of time. This means that with the first data collection these files are as large as they will ever get, but it also means that you will see an initially large decrease in disk space as collection is first started. Once the RRD file is full, the oldest data is discarded.

Each RRD is made up of Round-Robin Archives. An RRA consists of a certain number of steps. All of the data that is collected in those steps is then consolidated into a single value that is then stored in the RRD. For instance, if I poll a certain SNMP variable once a minute, I could have an RRA that would collect all samples over a step of five minutes, average the (five) values together, and store the average in the RRD.

Step: The first line, the rrd step siz…