The main objectives of the project are to:

- Investigate the potential of two means of increasing network efficiency: use of a multi-link protocol such as the string mode; and use of high speed switching.
- Design, implement test and evaluate in a realistic environment, a string mode algorithm and a high speed switch.
- Design, implement, and test a 34 Mbit/s PDH/ATM Mapper.
- Elaborate economically sound introduction strategies.
The main objectives of the research were to:
investigate the potential of 2 means of increasing network efficiency; the use of a multilink protocol such as the string mode and the use of high speed switching;
design, implement, test and evualate in a realistic environment, a string mode algorithm and a high speed switch;
design, implement and test a 34 megabits per second PDH asynchronous transfer work (ATM) mapper;
elaborate economically sound introduction strategies.

The research addressed the following issues:
system studies on traffic handling algorithms, aimed at increased network efficiency;
experimentation with string mode and high speed ATM switching technologies;
technoeconomic evaluations of solutions to meet the early market opportunities with ATM based equipment.

The research has resulted in:
the issuing of preliminary specifications for network and traffic models;
the issuing of a system specification for a 34 megabits per second PDH/ATM mapper, as well as a design specification for a high speed switch;
the issuing of a preliminary specification for string mode implementation;
the definition of preliminary configurations for string mode and high speed switch demonstrators;
the definition of a generic model for the access network which will be used for technoeconomic evaluations in cooperation with other projects.

In the network evolution phase towards an asynchronous transmission (ATM) based integrated broadband communications network (IBCN) a strong demand must be expected for services that allow interconnection of physically separate high speed ATM islands. String Mode is a multilink protocol that will meet this need while offering an improvement of network resource utilization in conjunction with statistical multiplexing.

The String Mode protocol that distributes a high bit rate ATM connection on parallel physical resources is currently being implemented in a realistic network environment by the use of a 'virtual network' concept that allows a large ATM network to be simulated with limited hardware resources.

String Mode is compatible with existing ATM network installations and the results from the implementation work so far indicate that a cost effective implementation is realistic. String Mode can be considered as a pragmatic solution to the problem of interworking between high speed ATM networks through a lower speed intermediate public network, in a transition phase towards a global ATM network.
Technical Approach

Traffic engineering activities are based on source and node models which have been developed within the project. The performance of string mode algorithms has been evaluated by simulation techniques.

To ensure their full integration in the B-ISDN, satellite links have been investigated as a component of the network architecture and an optimised ATM layer protocol devised.

A complete demonstrator of the String Mode protocol has been developed allowing simulation of a multi-node ATM network by means of a module which allows multiple passes through a single ATM switch with variable transmission delays on each pass.

The project work on high speed ATM switching is based a switch structure which decouples switching speed from the technology employed. It avoids queue access bottle-necks and intensively exploits parallelism and pipe-lining techniques. Implementation is based on a combination of two full custom ASICs, one developed within the STRATOSPHERIC project the other under an ESPRIT project. The physical design is of a 4x4 matrix. The matrix is cascadable, allowing multi-stage configurations.

The 34 Mbit/s Mapper has been validated in UNOM (R2023) ATM testbed.

Techno-economic studies are performed in close co-operation with other projects, particularly TITAN. Three case studies have been performed to investigate respectively PSTN evolution, CATV evolution and application of String Mode.

Key Issues

- System studies on traffic handling algorithms, aiming at increased network efficiency.
- Experiments with string mode and high speed ATM switching technologies.
- Techno-economic evaluations of solutions to meet the early market opportunities with ATM based equipment.

Expected Impact

The project has demonstrated technical viability of two techniques (High Speed ATM switching and String Mode) which increase network efficiency and hence reduce the cost of the ATM implementation. Cost effective introduction strategies developed by the project will help foster early market opportunities for broadband services.