older OSS would communicate with the newer through some interface. This unification of network management systems, includ- ing OSS, has been an important contribution of OSS vendors and their system integration partners over the last decade. There are still many service providers who would enjoy great cost savings if they carried out such a unification project. Such a project should be carried out in partnership with an OSS vendor with the appropriate software. Such an OSS vendor should also have experience in building interfaces between inherited (or "legacy") management systems, and their own OSS product. Upon sale of an OSS software product to a telecom carrier, an OSS vendor will commonly find a range of network hardware in use by the carrier which the carrier OSS for Telecom Networks mediation device transport transport transport legacy subnetwork PDH equipment Figure 2.10 SDH network with legacy PDH subnetwork. wants to continue to use. Such hardware may even use a proprietary protocol which is outside industry standards. The OSS vendor will then set to work building an interface to that hardware. If the carrier still has the documentation for that legacy hardware, then the task of building the interface is made easier. If the carrier does not have the documentation, then the specifications for its protocol need somehow to be worked out, and there are methods for doing this although it can be time con- suming and expensive. OSS vendor Clarity International has done just this for many carriers the world over. The carrier must weigh the value of keeping the legacy hard- ware, often more than 20 years old, with the cost of building custom interfaces SO that it can be brought within the purview of a new OSS system. 2.5 Configuration Management OSS functionality for configuration management includes: 1. installation and configuration 2. path and capacity implementation 3. network protection. In the case of installation and configuration, an OSS chiefly includes support func- tions for installing network equipmen