MAC Connectors

MAC originally supports different types of connectors (that is external nodes providing connectivity) and classifies them according to the taxonomy depicted figure below. MAC supports infrastructure-based connectors with IEEE 802.11 and GPRS/UMTS interfaces. They are considered always reliable, i.e., MAC assumes that these connectors always try to forward the traffic of associated clients (and are expected to succeed, apart from dependability issues due to traffic congestion) and do not endanger user privacy (no traffic auditing). Security issues are not the primary focus of the MAC research project and out of the scope of the paper. In addition, MAC supports peer-based connectors with IEEE 802.11 and Bluetooth interfaces (namely peer connectors). MAC dynamically determines the degree of reliability of these connectors depending on connector runtime behavior (based on user preferences, interaction history, and client location).

In addition to reliability, MAC considers other crucial aspects that deeply differentiate the runtime behavior of infrastructure and peer connectors. First of all and most important, MAC distinguishes fixed and mobile connectors. Understanding whether a peer connector is either fixed or mobile is crucial (and a challenging issue) because it directly impacts on the stability of offered connectivity: mobile peer connectors may become unavailable with higher probability because it is easier that they exit the client radio range.

Types of connectors supported in MAC.

The classification of connectors into reliable/unreliable and fixed/mobile sub-classes is a rather static decision, expected not to change during a service session. MAC determines the classes of eligible connectors for a given client only at the beginning of its service session. In addition to that static context, exclusively for mobile peer connectors, MAC also keeps an innovative and highly dynamic context indicator: the mutual degree of mobility between a mobile client and eligible mobile peer connectors. In particular, MAC classifies mobile connectors as either transient or joint, depending on the fact that, respectively, the connectors move with either different or the same speed (in both module and direction) of the considered client. The transient/joint sub-class obviously depends on mobility behaviors at runtime and its correct dynamic determination/update is a key point for MAC effectiveness in terms of channel durability and limited overhead.