ro- geneous subsystems the operator has adopted and has to maintain; this heterogeneity stems, e.g., from the mergers and acquisitions, upgrades to new versions and types of equipment, etc. The incumbent operators have highly complex systems composed of a large number of diverse subsystems with complex (also proprietary) interfaces between them. New operators who may have started with a greenfield implementa- tion, on the other hand, are likely to operate with a more manageable infrastructure with a smaller number of harmonized subsystems where standard interfaces are used more often. Interface implementation efforts differ dramatically among the two. As a result, new entrants (software vendors), who have a rather limited number of personnel available, have a limited capability to cover integration work only in upcoming markets where the integration work is simplified by the use of web-based integration technologies (based on IETF standards) as well as by the use of business process management tools. The total efforts for interface implementation encompass: Initial implementation of interfaces, i.e., initial implementation of protocol stacks Development of new variations of interfaces Configuration of the interfaces for individual customers, mainly consisting of adapting data formats to the needs of an individual customer; and Maintenance of interfaces In order to assess the total interface development and maintenance efforts, we need to first determine (on a year-by-year basis): For each type of protocols, the number of versions/variations For each variation, the efforts (initial, variant development, configuration, main- tenance) needed The efforts needed for implementing an interface greatly depend on the type of protocols being used. Many types of protocols may need to be implemented, among them proprietary, OSI based (FTAM, CMISE/CMIP), CORBA, web-based (HTTP, SOAP, LDAP, RADIUS), and other standards-based protocols (FTP, GTP, MAP, etc.). Protocols may also have several versions, hence resulting in a number 