1. The Load Balancing Schemes Observations
IEEE WG
Orlando, Florida USA
March 11~16, 2007

2. This slide observes three existing load balancing schemes from the different aspects, giving out the pros and cons of these different load balancing solutions.

3. RPR based technology aspect
For TTL load balancing scheme, it’s based on the RPR technology itself, using TTL to scope the frame transmission, avoid the frame duplication and data loop, using the interconnected RPR stations’ bidirectional flooding to realize the load balancing.
For the Hash load balancing scheme and VLAN (or other specific RPR fields) load balancing, the extra information (i.e. hash value, vlan id or other value) is introduced into the RPR interconnected stations to decide the forwarding behavior, thus realizing the load balancing and avoiding the frame duplication and data loop.

4. Service transmission deterministic aspect
For TTL and Hash load balancing scheme, it’s possible that the same service flow would go through the different interconnected RPR stations, possibly inducing the service Qos inconsistency.
For the VLAN (or other specific RPR fields) load balancing, the same service flow always go through the same interconnected RPR station, ensuring the service Qos consistency.

5. The shortest path aspects
For TTL load balancing scheme, to get the shortest path, the network must be carefully provisioned, the matched nodes are opposing on the ring. Or else for example when the matched node are co-located in one box or place, it’s not the shortest path. In the casual interconnected ring only the path on the destination ring can be shortest, the total path is usually not the shortest one.
For the Hash load balancing scheme and VLAN (or other specific RPR fields) load balancing, it’s always possible that the path traffic go through are not the shortest one.

6. Accidentally frame duplication
For TTL load balancing scheme, if one node on the ring is changed to passthrough mode when the flooding traffic is in flight, the frame is duplicated.
For the Hash load balancing scheme and VLAN (or other specific RPR fields) load balancing, in the above situation, it’s possible to avoid the frame duplication through the unidirectional flooding, the frame can be stripped off the ring by the source address. (If bidirectional flooding is used, the problem still exists.)

7. The tributary interface support
For TTL load balancing scheme, when the interconnected stations support the tributary interface, in order to fully communicate with all the nodes across the rings and prevent the frame duplication, there should be some specific mechanism to be used.
For the Hash load balancing scheme and VLAN (or other specific RPR fields) load balancing, interconnected stations tributary interface is supported as it is for the any other rings stations tributary interface.

8. Unexpected persistent flooding
For TTL and VLAN (or other specific RPR fields) load balancing scheme, the traffic paths are determined by the bridge learning and are symmetrical, there is no persistent flooding.
For the Hash load balancing scheme, it’s possible the path that bridge learns violates the path picked by the hash value, to result in the unexpected persistent flooding.

9. Interaction with xSTP
For TTL load balancing scheme and Hash load balancing, both interconnected stations are actively forwarding traffic, there should be some tweaks to spoof xSTP that there are no loop path.
For VLAN (or other specific RPR fields) load balancing, the network topologies is conformance with xSTP.

10. Load balancing extent
For TTL load balancing scheme, to which extent the load is balanced is dependent on the interconnected ring topologies and the remote bridge numbers behind the RPR bridge.
For the Hash load balancing, it depends on the specific hash algorithm to balance the traffic.
For VLAN (or other specific RPR fields) load balancing, traffic can be distributed to the interconnected RPR bridges by different services through the reasonable configuration, load can be balanced between the interconnected RPR bridges, it’s independent of the RPR ring topologies and the remote bridge numbers behind the RPR bridge.

11. Thank you