ERCIM News No.19 - October 1995 - VTT

The Frame Synchronized Ring - A High Bit Rate Bus

by Pertti Raatikainen

The Frame Synchronized Ring (FSR) is a new bus concept which is based on the ring topology, and whichsupports very high bit rates. It is developed as a basic component for thedemanding future broadband applications. The FSR offers gigabit rate transmission capacity, and itapplies especially well to multiprocessor implementations.

The modern high-speed communication networks bring along broadband applications with an ever increasing demand for processing power from network components and terminals. Traditionally, increasing packetization density and the speed of the integrated circuits (IC) have been relied upon when designing processing units for the future applications.

The modern broadband networks set, however, significantly higher speed requirements for data manipulation. The increase of the IC capacity no longer meets the needs of the applications, and, in the most demanding broadband applications, the necessary processing power can be guaranteed only by distributing the processing of the tasks. The traditional microprocessor buses cannot offer fast enough transmission channels between powerful processing units, for which reason there is a need for more efficient bus solutions.

The FSR bus

VTT Information Technology has developed a bus concept which offers gigabit data rates between processing units. The bus is based on the ring topology and consists of nodes connected together with parallel unidirectional databus segments. Data is transmitted in fixed length slots which are released by the receiving node.

The solution, compared to many other efficient bus structures, is simple. Its efficiency is based especially on the bus control signals and the efficient bus access mechanism. The bus control and manipulation of the control information is distributed between the nodes and is implemented in the hardware, which guarantees real-time control actions even at high clock rates. The control schemes of the nodes and the bus are patented.

The modernity of the FSR is portrayed well by the fact that several bus concepts, based on the ring topology, have been brought to attention recently. A comparison of the VTT's bus concept to other high speed rings has shown competitive performance and, in some respects, the FSR is more efficient than its competitors. Compared to the traditional backplane buses, i.e. multidrop buses, the FSR exhibits superior performance.

A performance analysis and simulations of the FSR have been carried out in co-operation with Lappeenranta University of Technology and Helsinki University of Technology.


The FSR, as an efficient and low cost solution, applies very well to various high speed applications. One promising application area can be found in the field of digital signal processing. This could include for example real-time video and digital image processing. Another interesting area is broadband communication, where protocol and equipment applications such as routers, concentrators and multiplexers are good targets for the FSR. Since the FSR is an open concept and not limited to specific applications, it can be utilized in a great variety of applications.

An example of practical implementations is the FSR functioning as a video switch for 100 Mbps video connections. In parallel with the video signals, the control and maintenance information is transmitted with only a few megabit data rate.In another implementation, the FSR is used as a multiplexer/demultiplexer to merge and separate 2 to 155 Mbps channels.

Please contact:
Pertti Raatikainen - VTT
Tel: +358 0 456 6508