We propose a methodology for the early estimation of communication implementation choices eftarting from an abstract transaction level system model (TLM). The reference version of TLM considered is the OSCI library. The methodology is based on the ion of metrics that abstract useful information from the initial system model. The metrics are precisely defined upon a general, formal model of transaction level system descriptions. A set of design problems of relevant interest, such as shared communication resources assignment, pipelining partitioning, bandwidth and latency constraints estimation, is considered to show some potential applications of the metrics proposed.