Abstract
Resilient Packet Ring (RPR) is an emerging standard for a packet based
ring network. The MAC protocol defined by RPR is primarily intended
for use in a metro (MAN) or wide area (WAN) environment, supporting
link capacities of multiple gigabits per second.
Being an IEEE 802 standard, RPR is required to support transparent
bridging. Transparent bridging was originally designed for shared
medium networks, like Ethernet. RPR is not such a shared medium
network, hence some new problems are encountered.
Two different solutions for bridging in RPR are discussed in this
work. The first, named basic bridging, is the one defined in the
existing draft standard. This bridging strategy relies heavily on
broadcasting on the rings, thus giving a poor utilisation of the
network resources. The second strategy, enhanced bridging, reduces and
eventually eliminates this broadcasting. The price to pay is a need
for more memory in the stations on the ring to keep mapping tables.
A simulation model of RPR networks has been developed and used in this
work to evaluate the performance of the two bridging
strategies. Through three simulated network scenarios, different
aspects of the enhanced bridging algorithm are highlighted and
compared to the basic strategy.
This work shows that enhanced bridging at least halves the load on the
network produced by a bridged traffic flow compared to basic bridging.
This is done by eliminating the need for broadcasting. Enhanced
bridging depends on mapping tables in the RPR stations. Simulations
are performed that show the effect of limiting the size of these
tables. The last scenario shows how local traffic on a ring is
affected by the choice of bridging algorithm. The simulations show
that by reducing the traffic load in the network, the enhanced
bridging algorithm gives improved latency and jitter characteristics
for local traffic.