The Macramé Network Testbed

The requirement to study different topologies for a large number of nodes, imposes a system design and implementation which is highly modular and flexible while maintaining a low cost per node. This has been achieved by building the testbed from three basic modules, which are packaged in VME mechanics :

Traffic Modules

A traffic node can simultaneously send and receive data at the full link speed of 100 MBaud. A series of packet descriptors is used to define the traffic pattern. The packet destination address, the packet length and the time to wait before dispatching the next packet is programmable. Each traffic node has memory for up to 8k such packet descriptors. To reduce the number of external connections, sixteen traffic nodes are connected directly to an on-board STC104 packet switch to form a traffic module. The remaining 16 ports of the switch are brought out to the front panel for inter module connections.

Switch Units

In order to build indirect networks, i.e. topologies where not all the switches have terminal nodes attached directly to them, a switch unit is required. It consists of one STC104 packet switch with all 32 ports brought out to the front panel through differential buffers.

Timing Modules

To measure latency, the timing modules transmit and analyse time stamped packets which cross the network between chosen points.

Further details on the design of the testbed have been presented in [4].