# Tandem services

Tandem services allow a Q.SIG application to support a transit node. A transit node is a node that exists between two other nodes and routes messages from one node to the other, as shown in the following illustration:

Transit node

NMS ISDN supports the bridge calls tandem service. This service filters messages routed through the transit node between two served users so the application at the transit node receives only basic call control messages. Facilities and notification information is automatically forwarded.