Large centralized computer systems have traditionally been the mainstay of large corporations. Centralized databases developed as a result of large-scale computing systems. Under this configuration, all processing, storage, and retrieval of data is done at a central site. The growth of distributed databases has paralleled the growth of relational database technology. Managing the distributed database is a distributed distributed database management system (DBMS), which monitors such functions as query optimization, concurrence control, and transaction handling. Determining a single set of communications requirements for all distributed DBMSs is difficult, because architectures and features depend on whether they are aimed at high-volume, online transaction environments or decision-support and revenue-generating applications. Each of these environments requires different network characteristics, depending on the number of distributed queries or updates made and the level of fragmentation and replication. Propagation delay is perhaps the most significant obstacle to distributed DBMSs.