The next-generation network

Published : May 27, 2000 00:00 IST


SANKHYA VAHINI will be a next-generation data network offering higher bandwidths that would make the connectivity faster. The network will be Internet Protocol (IP)-based, which will offer connectivity through international gateways to the entire world.

The Internet evolved out of voice telephony, or circuit-switching. Today circuit-switching works at very high speeds of 2.5 gigabits per second (Gbps). A single telephone call uses up to 64 kilobytes per second (Kbps).

Circuit-switching is done largely through Synchronous Digital Hierarchy (SDH), also known as Synchronous Optical Networking (SONET). SDH is a standard for high-speed transmission, which encodes bit streams into optical signals that are propagated over an optical fibre. Its flexibility is such that one can add, drop, and multiplex bit streams at various speeds.

However, since data transmission is inherently bursty, computer networks have evolved their own transmission protocols known as packet-switching. The data to be communicated are broken up into chunks known as packets, which are then routed over the data network as per the available routes and bandwidth on the network. There is no pre-determined path for a packet between two points. Packet-switching relies on routers to route the IP packets to their destination. This is a far more efficient way of utilis ing network capacity. For Sankhya Vahini, the IP packets will be carried over an SDH network, or directly over the optical network.

Optical fibres are a key component of modern communications network, largely because of the high speed of communications and virtually error-free transmission they offer. Sankhya Vahini will have an all-optical fibre network. The Department of Telecommun ication (DoT) already has a single-mode fibre, which is capable of high-speed long distance transmissions on the ground between cities. A pair of such fibres will be transferred to Sankhya Vahini. The network is being designed in a ring topography so tha t if there is any break in the fibre or equipment failure, data can be sent in the opposite direction.

While Sankhya Vahini will begin with an operating speed of 2.5 Gbps, it will be able to provide more capacity by using the Dense Wavelength Division Multiplexing (DWDM) technology. In DWDM, the same fibre carries multiple wavelengths of light, each repre senting a high-speed signal. These wavelengths can also be used for upgrading the network, or for new services such as video and voice transmission.

In addition, the network will also have fibre access to its users. This will be through city level networks, also known as Metropolitan Area Networks (MANs) or Metrorings. The city level networks will run at multi-gigabit speeds and will facilitate conne ctivity for users. Sankhya Vahini will utilise the space at existing telecom exchanges for building its city networks.

High-end routers will be used in the network. Routing is done in hardware and the speeds and control over the packets/data are much greater.

THE Sankhya Vahini is thus basically a network at three levels: the inter-city network using DWDM, the metrorings and the last mile connectivity (see diagram). In the first phase or in the first year of operation, originally scheduled to take off in 2000 , 10,000 route-km of fibre would be connected with a fibre bandwidth of 2.5 Gbps. The Sankhya Vahini network will have an architecture termed "Ring of Rings" having 10 nodes (New Delhi, Agra, Bhopal, Indore, Ahmedabad, Mumbai, Pune, Hyderabad, Bangalore and Chennai), metroring networks at each of the 10 nodes, 25 Points of Presence (POPs) (points external to the network from where one can hook on to the network) and advanced network management centres at each node. In terms of Internet access, the distr ibution over the Sankhya Vahini network will be in four tiers.

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