T 2.44 Incompatible active and passive network components

Incompatible active network components can cause problems with communications protocols which have not yet been standardised completely, such as ATM or Tag switching. In such cases, the manufacturer needs to employ proprietary implementations to offset the missing, or partially available standards and allow for the use of the affected communications protocol.

Incompatibilities of this type can be caused if existing networks are extended with active network components from another vendor or networks are built using components from different vendors.

If active network components with different implementations of the same communications protocol are running parallel within the same network, this may impair the availability of the entire network, individual segments, or some services within the network. Two different cases can be distinguished depending on the type of incompatibility:

• Implementations of a communications protocol which are not able to operate with each other, can make communication between the related components impossible.

Example:ATM components might use different signalling protocols which are not able to operate together, e.g. in compliance with UNI (User Network Interface) Version 3.0 and UNI Version 3.1.

• Even if active network components are able to operate together in principle, certain services might be implemented in different ways. As a result, these services may be unavailable or at least not available in some segments of the network, although communication outside the scope of these services is still possible.

Example:Proprietary implementations of redundant LAN emulation servers for ATM networks are in existence. If an ATM network consists of two ATM switches, one of which possesses such a proprietary implementation while the other does not, communication based on LANE (LAN Emulation) is still possible, but the service implemented on a proprietary basis cannot be used.

A combination of incompatible, passive network components can also impair the availability of a network. Twisted-pair cables available in 100-ohm and 150-ohm designs cannot be used parallel without the use of the proper converter. An unsuitable combination of active and passive network components can also impair availability if, for example, a network access protocol is used for a medium which has not been foreseen for this purpose. For instance, ATM is not able to work with a 50-ohm coaxial cable.