Convergence, yet another buzzword, is a favourite not onlywith the communications and IT industries, but also with the Prime Minister andhis cabinet colleagues. But, what is convergence in the first place?

Simply speaking, convergence signifies the merging ofconventional communications such as speech, fax, and data with interactive andbroadcast video (TV) over the same communications backbone.

Public and Private Communications

Communications takes two forms—private or within anorganization, and public which is between individuals, between organizations,between organizations and individuals. The former has very focussed needs—mostlyspeech, fax, data, and voice-data conferencing to carry out the day-to-dayoperations of the organization. This does not normally call forvideoconferencing. The bandwidth requirements are low, and for mostapplications, fractional T1 lines (64 Kbps or multiples thereof) and analoglines meet the communication needs. Cost-effective solutions and connectivityoptions for this sector are already available.

Public communications, which enables us to communicate withanybody connected to the public network, is where the need for convergence isfelt most. And since video communications—broadcast or interactive—needshigh bandwidth, it calls for broadband connectivity.

It is best to keep public and private communicationssegregated. The latter needs high degree of security and closeness. The formercalls for openness. Most networking woes of computer professionals start withtheir attempts to combine public and private communications in the same network,introducing complexities of bandwidth management and maintenance of security.These complexities disappear as soon as private and public and private networksare separated. The security is easily achieved in private networks by denyingphysical access to outsiders. Bandwidth requirements of the fixed nature ofcommunications in the private networks are predictable, and hence, can bepredetermined and easily managed.

Convergent public communications networks call for highbandwidth. There are two ways in which this can be achieved. One is over cableTV networks, which facilitate Internet access through set-top boxes (cablemodems) and the use of Net-to-phone for telephony. However, the quality oftelephony is not toll quality. Further, this does not facilitate direct faxmessages.

The second option is to extend broadband connectivity to thehomes and work places. The original approach was to use optical fibreconnections to individual telephones. However, the current cost of opto-electroniccoupling equipment makes this a non-viable option.

The availability of the DSL technology, in its various forms—high-speed(H), symmetric (S), asymmetric (A)—makes extending of broadband services tothe normal telephone subscriber, a cost-effective reality.

Any telephone subscriber desiring a broadband connectionneeds to have a xDSL (where x denotes the type of connection H, S, or A) modemat his premises, and a similar one at the telephone exchange. A minimum of twooutlets is available at each modem on either end of the telephone line. At thesubscriber-end one of these outlets is connected to the telephone instrument,and the other to the computer or any other video device like the television. Atthe exchange-end, one of the outlets is connected to the MDF of the telephoneexchange, and the other is connected to the Digital Subscriber Line AccessMultiplexer (DSLAM) also located at the exchange premises. The DSLAM multiplexesthe digital streams from each of the xDSL modems and passes the aggregate to thecarrier which transports it to the City Broadband Gateway which is linked to thesource of video signals, radio signals, Internet gateways, etc.

Converged Transport Network

The transport section of the telecom network is alreadyconverged, in the sense that this network is already carrying inter-city TVtraffic, and inter-city traffic for Internet access to the Internet gatewaysover high-bandwidth fibre optic and/or digital microwave networks using SDHtechnology. Currently, this is the exclusive preserve of the DoT. However, underthe NTP ’99, other organizations in the public and private sector are likelyto be allowed to enter this arena. In anticipation of this opening up of theTransport Network to competition, the Railways has already made budgetaryprovisions for laying fibre optic cables over 62,000 km of tracks to provide aready backbone to prospective operators to supplement its revenues. The PowerGrid Corp has similar plans for laying fibre optic cables along the extensivepower transmission network of the country.

The task that lies ahead is to facilitate convergence throughthe access portion of the total telecom network into the level of the telephonesubscriber.

All computers connected to this network have their individualIP address, and messages meant for these addresses will reach their destination.All broadcast receivers connected to the network will receive all broadcastmessages—video, radio, speech, information, etc. Since existing telecomservice providers already have extensive cable networks which is an essentialingredient for DSL modems to function, they are best equipped to extendbroadband services to the telephone subscriber. MTNL has already embarked on aplan for extending broadband services to its telephone subscribers and no doubtthat DoT/DTS will also follow suit, as also the various private basic serviceoperators.

PK Mitra
Managing Director, MIDAS Automations & Telecommunications Pvt Ltd