Load Balancing in Microwave Networks

Abstract: Microwave links are very commonly used in carrier networks especially towards the access side. They not only ease deployment of a network but are also very cost effective. However, they bring along a multitude of challenges which are characteristic of the wireless technology. Microwave links are fickle. Being exposed to varying weather conditions, they experience bandwidth fluctuations. This is true especially in the case of links operating at higher frequencies. The unpredictable nature of microwave links makes it quite challenging to plan capacity in a network beforehand. Radio links employ adaptive modulation. They operate on a range on modulation schemes each of which offers different throughput and bit error rates. When operating at a low bit rate modulation scheme, a situation may arise where the microwave link is not able to support the entire traffic incident from the backbone network. As a result, the microwave link will suffer from congestion and packets arriving at the microwave link will eventually be dropped. The switching nodes that precede the microwave link along a communication path are unaware of the microwave link conditions and, therefore, continue to transmit traffic at a high rate. Large carrier networks cannot afford to have performance inconsistencies like data loss and increased latency. Service degradation, even for a very short duration, can have dire consequences in terms of customer dissatisfaction and revenue loss. The goal of this thesis is to use MPLS-TP Linear Protection to load balance traffic across alternative paths in a network where links use adaptive modulation. Rerouted traffic must take other paths so that the congested microwave link is completely avoided. The idea is augmented by the use of a radio condition signaling mechanism between the packet switching node and the microwave node that precede a microwave link. The microwave node sends radio condition control messages to the preceding packet switching node to rate limit traffic and avoid congestion at the microwave link. The result of this thesis work is a system prototype that achieves the stated goal. Evaluation of the prototype is carried out through graphical results, generated by a traffic generator, that advocate the correctness, performance and robustness of the system.