HFC (Hybrid Fibre/Co-ax) network has come out as a tool to materialise the conjunction of video service with telephone services. To have their global market say companies are targeting certain features viz
High quality, reliable telephone service throughout the system. Most advanced small business and residential features
Economically pursuing the effort so as to make the cable services redundant in the age of wireless communication.
The coagulation of two communication services comes as an attractive mode of revenue-generation for the cable operators throughout the world while ensuring the customer’s most stringent requirements.
Why Cable Telephony?
To understand the urge of Cable Telephony, the example of UK is most suitable. Cable operators have been tackling the residential market for quite some time, coming in on the back of Broadcast services. They are utilising ‘Centrex Exchange System’. This system provides some respite by eliminating the need of PBX.
Cable operators have ample bandwidth and fully digital switching system, which are essential in the battle of commoditiesed access provision. Altogether cable operators have strong regional support and customer care centres, which are important for the success of any communication network.
entrex Based Networking
Centrex is a series of systems, which involves a line from the operators’ switch to the PBX, which then splits to service a number of extensions. Centrex is a series of lines from the switch straight to the individual extensions. These lines are grouped and have their own feature set and billing options.
How Telephony over HFC Works
Cable Telephony over HFC works on the mode of digital telephony signals for transport to subscribers connected to HFC network. By using HFC as the local access transport, telephony, video and data can coexist. A single connection delivers all the services to the subscriber home. From an access network perspective, Co Axiom (a device for cable telephony produced by scientific-Atlanta and Siemens) operates as a Digital loop Carrier (DLC) using a Host Digital Terminal. As such, the system provides complete transparency to all services and is fully standards-compliant. Neither the subscriber nor the switch is aware that CoAxiom and HFC access is in use.
Cable operators have ample bandwidth and fully digital switching system which are essential in the battle of commoditised access provision. Altogether cable operators have strong re-gional support and customer care centres which are important for the success of any communication network,
Telephony over HFC is a simple but technical process engaging a few sub systems namely: -
HIU (Headend Interface Unit):-It is the access node interfacing to the PSTN (Public Switch Board Network). All interfaces are based on common open industry standards. It is located at the headend on hub. This product adapts base band digital telephony channels to upstream and downstream RF signals which are transmitted to/from the subscriber over the HFC network.
CIU/BIU/MDU (Customer Interface Units/Business Interface Units/Multiple Dwelling Units)
Subscriber access is facilitated by CIU, which mount to the side of home and MDU which are used for apartment complexes and curbside installations. The CIU and MDU are enclosed in a tamer proof housing, designed to withstand harsh environmental conditions. Each provides the conversion from RF to twisted-pair telephony and is capable of passing other signals via Co Axiom. An enhanced version of CIU, BIU is ideal for small business facilities. It may be configured with additional POTS/ and/or ISDN interfaces.
CAMS (CoAxiom Management System)
It is responsible for all day-to-day activities including remote configuration, fault and performance monitoring, software upgrades and other supervisory functions. A single CAMS platform can support Co-Axiom equipment at multiple remote distribution hubs.
For the growth and accountability over HFC Cable Telephony Services, following fundamental features are must.
Highest level of Reliability For the acceptability of the services they must be handy, economic and altogether reliable. That means it should be independent of environmental (terrestrial) or technical disturbances.
Carriers to be Frequency Agile
Placement and level control of both upstream and downstream carriers should be automatically controlled from headend.
Services must use narrow carriers
For this purpose Dynamic sub carrier Multiplexing of single carriers in the reverse direction is an ideal choice. Given the high level and random nature of noise in the reverse spectrum, single carriers will be less prone to disruption than wider TDMA channels. The loss of a single carrier should easily be averted unlike that for multiple channels. Which can lead to audible detection or multiple dropped calls.
Should Provide Hardware redundancy
The internal architecture of system headend equipment should be engineered to the highest availability with protection for failures of single or multiple units.
The equipment should be transparently brought on-line and should be able to monitor software quickly isolates the fault for servicing.
Compliance with international standards
The end product and service should be in compliance with global standards. With added flexibility to grow it can add to the vigour of the service.
Cable Telephony in Japan
In June 1997, Titus Communication Corporation became the first Japanese Cable Company to offer its broadband networks. Titus is a Joint venture of US West Media group, Time Warner, Toshiba and Itochu, franchised to pass two million homes.
The company’s fully interactive HFC network being built out in Kashiwa, Sagamihara, Kodaira and Gunme, is able to carry multiple services.
Titus is the first cable company of Japan to be granted a telephony license and is the first to offer phone services to customers. West Media Group joint ventures are also pursuing telephony services over HFC launches in Belgium and the Netherlands.
Modes of Carriage of Telephony
B-CDMA Inter Digital Communication Corporation launched its ‘ISDN (Integrated Services Digital Network) over the air’ capability in Asia with live demonstrations of Broadband-Code Division Multiple Access (B-CDMA) Wireless Local Loop (WLL) technology at ISDN rates.