The impact of CCITT message handling systems structure on performance

An overview of standards related to CCITT (International Consultative Committee for Telephone and Telegraph) message handling systems (MHS) is presented. The standards are concerned with communications between users of different electronic mail systems. At a gateway between systems, a user message is first transformed into a message protocol data unit (MPDU); the MPDU is transformed into session protocol data units (SPDUs); each SPDU is further transformed into transport protocol data units (TPDUs); and, finally, a TPDU is transformed into an X.25 data packet. One of the key factors affecting the performance of an MHS gateway is the number of X.25 data packets generated by a user message. The problem of MPDU size estimation is treated, and the calculation of the number of X.25 data packets based on a given MPDU size is described. An example is provided to illustrate the procedure. As an additional result, the optimal size for data synchronization between two consecutive minor synchronization points is established.<>