The Anella Científica DQDB

With the aim of creating a high performance communications network to connect the most important research centers of Catalonia with CESCA, the Fundació Catalana per a la Recerca signed on April 1993 an agreement with Telefónica to install a network which was called "Anella Científica" (Scientific Ring). The network was entirely operative in December 1993 and was working until May 1998, when was replaced by the new Scientific Ring.

Phisically, the Anella Científica is based on a fiber-optic cable spread over the areas of Barcelonès and Vallès by Telefónica with a transmission capability of 34 Mbps.

The points of access of the Anella Científica are:

Half a hundred institutions connected through these access points. Institutions connected on May 1998 were:

It's important to consider that the Anella Científica was the first high speed network installed on he state and one of the firsts in Europe. At present, the Anella Científica is one of the networks which connects more users and transmits a bigger volume of traffic, as you can see on the statistics.

Technologies of the Anella Científica.

The Anella Científica was a MAN computer network of the DQDB type. This type of network was designed to interconnect Local Area Networks (LAN), as a technical solution that offers less costs and more reliability than leased lines.

A MAN can be defined as a high speed digital communications network able to integrate different kinds of traffic, including real time services, such as voice and video, and able to offer distributed switching between metropolitan geographical areas (100 Km or more). With high reliability in front of wire cuts or network faults.

DQDB architecture is based on subnetworks formed by two bidirectional buses with opposed transmission ways that permit the establishment of full-duplex communications among the connected nodes. That is, users are interconnected through optical cables that have ring structure, whereas input and output traffic is organized as a bus. In front of a wire cut or a problem in one of the nodes, the distribution of traffic is automatically reconfigured, assuring high connectivity and strength against faults.

The main characteristics of the DQDB architecture are:

- It uses conventional equipment for digital transmission (34 and 140 Mbps).

- It shares transmission media for synchronous and asynchronous services flexibly.

- It follows the CCITT E.164 numeration plan for ISDN.

- The structure of the transmission frame is compatible with the future B-ISDN.

- It provides security of access and privacity for user data, permitting the creation of closed groups of users and virtual private networks.

- It has the properties requested by public networks: availability, management, maintenance and giving of services.

- It has the operation, administration and maintenance functions, to control and integrate them in the public management system.

- It has a rating function that permits the adoption of any rate policy.

- Its architecture is reliable, and it has mechanisms of automatic reconfiguration in case of fault. In the same way, it has a high topological flexibility that permits to optimize the utilization of transmission resources.

The majority of protocols usually implemented in local networks (DECNET, IPX,...) can be used simultaneously in a MAN network. In the particular instance of the Anella, the TCP/IP protocol (typical of Internet networks) is used for the most part to communicate different points of access.