Cable TV infrastructure is another infrastructure with a huge installed base and with great potentials for delivery of broadband connections. The penetration of cable TV networks varies from country to country. In Denmark, for example, cable TV penetration is about 70%.
A cable TV system is a distributive system, where the resources are organized as a number of 8 MHz channels for broadcast TV distribution. Cable TV systems have a huge capacity; however, the total capacity depends on how modern the system is and, consequently, on how much frequency bandwidth of the coax is utilized.
When cable TV infrastructure is used for broadband provision, a number of 8 MHz channels are allocated to broadband provision. In an 8 MHz channel, it is possible to transmit between 27 and 56 Mbps depending on the deployed modulation technology and some other parameters, such as level of error correction. To enlarge the IP/broadband capacity in the cable TV system, several solutions can be used:
· Using new standards with more efficient modulations technology
· Modernize the cable TV system and utilize more frequencies (channels) in the system
· Reallocate more channels from TV to broadband
· Digitize the cable TV distribution system. Consequently, one TV service will occupy fewer frequencies and in this way it is possible to free some resources for IP services
Or more radically:
· Remove dedicated TV transmission and use the whole capacity for IP and also deliver TV over IP. This solution is however strongly dependent on the development of IPTV technology
Cable TV infrastructure is optimally positioned in the future broadband market due to its capabilities in offering triple/multi-play services. This is because the network is optimized for TV distribution and capable of delivering broadband. Many other broadband infrastructures face a huge challenge in delivering broadcast TV.
One of the weaknesses of Cable TV network in relation to broadband is that it is a shared medium, i.e. a number of users share the capacity in a network segment. Another problem which is connected to the current structure is that it is not a simple task to open the cable networks to a third party operator and establish competition. This is both due to the ‘shared medium’ aspect and because the cable TV networks are not standardized.
An important element in the utilization of Cable TV structure for broadband is the introduction of VoIP with QoS support. Particularly in DOCSIS 1.1, there are specific procedures for establishing prioritization to minimize delay and jitter which are highly necessary for VoIP. The problem is, however, that because of the aforementioned problem of opening the network to third party operators, the general ‘best effort’ VoIP operators cannot take advantage of these QoS improving measures.