T 2.44 Incompatible active and passive network components

Incompatible active network components may cause problems to occur in the environment of non-standardised or incompletely standardised communication procedures, e.g. ATM or tag switching. In order to be able to use the communication procedure concerned, the manufacturers are forced to use proprietary implementations due to the missing or only partially present standards.

These kinds of incompatibility problems may occur if existing networks are complemented by active network components of other manufacturers or if networks are installed with network components of different manufacturers.

If active network components with different implementations of the same communication procedure are operated jointly in the same network, the availability of the entire network, of individual sub-areas, or of certain services may be lost. Depending on the type of incompatibility, two cases can be differentiated:

• No communication is possible using the related components in the event of non-interoperable implementations of a communication procedure.

Examples:

• ATM components may use different signalling protocols, e.g. according to UNI (User Network Interface) version 3.0 and UNI version 3.1, that are not interoperable.
• Specific services may be implemented differently even on active network components which are theoretically interoperable. As a consequence, the services concerned are not available at all or not available in the entire network, although communication using these components is possible.
• There are proprietary implementations of redundant LAN emulation servers for ATM networks. For example, if an ATM network consists of two ATM switches, one of which disposes of such a proprietary implementation while the other does not, communication via LANE (LAN emulation) is possible, but the service implemented proprietarily cannot be used.

However, the combination of incompatible passive network components may also endanger the availability of a network. For example, twisted pair cables may be designed with 100 and 150 Ohms, at which these designs must not be used together without a corresponding compiler. An inappropriate combination of active and passive network components may also have negative effects on availability, for example if a network access protocol is operated on a medium not defined for this. For example, ATM cannot be operated using a 50 Ohm coaxial cable.