home
	Content: • General • Internet over Cable • Voice over Cable (VoCable) • Links for more information General For millions of people, television brings news, entertainment and educational programs into their homes. Many people get their TV signal from cable television (CATV) because cable TV provides a clearer picture and more channels. This however has not been always the case - some 50 years ago, when experimenting with cable TV started, cables were connected to a better situated antenna and did not made neither the picture any better nor multiplied the channel numbers. The real improvement started sometime around 1970s when microwave transmitting/receiving from specially dedicated towers to the customer premises were introduced (called CATV systems). Each television channel required a 6 MHz of bandwidth and early systems operated with a bandwidth of 200 MHz, allowing 33 channels. As technology progressed, the bandwidth increased to 300, 400, 500 and now 550 MHz, with the number of channels increasing to 91. In 1989, General Instruments demonstrated that it was possible to convert an analog cable signal to digital and transmit it in a standard 6-MHz television channel. Using MPEG compression, CATV systems installed today can transmit up to 10 channels of video in the 6-MHz bandwidth of a single analog channel. When combined with a 550-MHz overall bandwidth, this allows the possibility of nearly 1,000 channels of video on a system. Internet over Cable Until recently cable TV was used only for ... well, TV. Internet popularity changed this as well and today many people who have cable TV can get a high-speed connection to the Internet from their cable provider -- like other people get it via ADSL. How does this work? Just some of the available bandwidth is not used for TV but for Internet - simple like that. When a cable company offers Internet access over the cable, the data sent from the Internet to an individual computer utilise a 6-MHz channel. On the cable, the data looks just like a TV channel. Upstream data -- information sent from an individual back to the Internet -- usually requires even less of the cable's bandwidth, since most people download far more information than they upload. Putting both upstream and downstream data on the cable television system requires two types of equipment: a cable modem on the customer end and a Cable-Modem Termination System (CMTS) at the cable provider's end. Between these two types of equipment, all the computer networking, security and management of Internet access over cable television is put into place. It is important to notice that the downstream information flows to all connected users, just like in an Ethernet network - it's up to the individual network connection to decide whether a particular block of data is intended for it or not. Furthermore this means that a cable internet connection is a shared connection, i.e. as many the local users are - typically 500 to 2,000 homes on a modern hybrid fiber-coaxial (HFC) network, as small the available bandwidth to each individual user becomes when working in parallel. On the upstream side, information is sent from the user to the CMTS - other users don't see that data at all. The narrower upstream bandwidth is divided into slices of time, measured in milliseconds, in which users can transmit one "burst" at a time to the Internet. The division by time works well for the very short commands, queries and addresses that form the bulk of most users' traffic back to the Internet. A CMTS may enable as many as 1,000 users to connect to the Internet through a single 6-MHz channel. Since a single channel is capable of up to around 36 megabits per second (Mbps) of total throughput depending on the modulation scheme used, this means that users may see far better performance than is available with standard dial-up modems (of course if not many heavy bandwidth eater users are in your neighbourhood - an individual cable modem subscriber may experience access speeds from 500 Kbps to 1.5 Mbps or more depending on the network architecture and traffic load - 2 000 simultaneously downloading users will get just about 18 Kbps - much less than a dial-up modem - life however proves that such in parallel downloading is very unlikely to happen). In addition to speed, cable modems offer another key benefit: constant connectivity. Because cable modems use connectionless technology, much like in an office LAN, a subscriber's PC is always online with the network. That means there's no need to dial-in to begin a session, so users do not have to worry about receiving busy signals. Additionally, going online does not tie up their telephone line. Voice over cable (VoCable) As this is a data network which utilises the Internet Protocol (IP), and, as the path between the modem and the termination is a sort of "dedicated" one (small delays and packet loss compare to the normal Internet), in addition to internet access, CATV systems become very attractive for provision of VoIP. Cable-based IP telephony holds the promise of simplified and consolidated communication services provided by a single carrier at a lower total cost than consumers currently pay to separate Internet, television, and telephony service providers. Unlike for example PSTN, which was developed from the outset as a point-to-point communication technology, cable networks were designed originally to broadcast one signal to many recipients. To enable cable-based IP telephony, modifications must be made to the way bandwidth is allocated and packets are delivered without using the bulk of the cable spectrum because most of the bandwidth will continue to be used for TV broadcasts. Callers must be able to send and receive only their own voice packets, and these packets must be given priority over data packets to ensure that callers experience smooth, uninterrupted conversations. The first step in this process was addressed by the Data over Cable Service Interface Specification (DOCSIS). DOCSIS established universal ground rules for the transmission of packets across cable networks, ensuring that packets won't be routed incorrectly. DOCSIS was later enhanced (in version 1.1) with quality of service (QoS) and security features that are necessary for voice communication. DOCSIS 1.1 also enables the prioritisation of packet traffic. This allows cable operators to give certain packets (i.e. voice) the right of way and allows other traffic to be sent with a "best-effort" priority as determined by bandwidth availability. In Europe a similar standard called "EuroDOCSIS" is known. Basically it is DOCSIS with the addition of an 8 MHz bandwidth downstream channel (within a 100 to 860 MHz spectrum), different forward-error correction and upstream bandwidth of 5 to 65 MHz. Cable networks operators have already started offering telephony services and the first Cable modems providing telephony services are already on the market. They usually provide standard telephony sockets in order to ensure that standard telephones, which do not necessarily support VoIP, can be used. This means that if you are switching from a standard PSTN to telephony over cable services you would just plug your existing telephone into your new cable modem and be served - and this well can be one of the swissvoice PSTN corded or cordless telephones. Links for more information The European Telecommunications Standards Institute (ETSI) is developing a comprehensive set of standards on Cable Modems more information on which you could find here http://portal.etsi.org/at/kta/IP_Cable/ipcablecom.asp. More information on Cable can be found at: • CableLabs - the originator of the DOCSIS http://www.cablemodem.com/ • The European Cable Communications Association http://www.ecca.be/ • EuroPacketCable http://epcweb.ifn.ing.tu-bs.de/ • Cable Modem Info http://www.cablemodeminfo.com/cmbasicsx.html-ssi To find out more about the swissvoice IP products portfolio click here.