Path Switching and Routing
The following is brief description of the components constituting this module.
Time Slot Manager
The Time Slot Manager manages the time slot resources associated with the XEN. The time switching logic of the time-space-time switching for Xenon is contained in it. The time-space-time switching for a call is done when the Space Slot Manager allocates path resource for the call. The Time Slot Manager also connects the E1 slot for the V5.2 subscriber or ISUP circuit to the path resource allocated for the call. It may be noted that the system creates the time slot resources when it comes up.
Space Slot Manager
The Space Slot Manager resides on CAS and manages the space slot resources in Xenon. The space switching logic of the time-space-time switching for Xenon is contained in it. The path switching or the time-space-time switching for a call is done when the Space Slot Manager allocates path resource for the call. It may be noted that the system creates the space slot resources when it comes up. The Space Slot Manager performs the following functions.
- It allocates the path resource for a call on request.
- It performs the path switching for the call.
- It gets the call routing done by the Routing Manager.
- It de-allocates the path resource for a call on request.
- It deletes the path switching when the call is over.
Path Switching logic allocates and connects a free path resource between the originating XEN and the terminating XEN. The path consists of a space slot and time slots in the originating and terminating XENs. The path switching allocation algorithm searches for a common space slot that is free in both the originating and terminating XENs. This is required because the space switch cannot switch in time, so the same time slot should be allocated at both the ends to form the t-s-t path.
More details about space switching can be found in the CAS section.
The Routing Manager resides on CAS. It contains the Directory to Equipment Number translation data for all the V5.2 subscribers in Xenon. It also contains the Routing data for ISUP trunks in Xenon. It may be noted that this data is created on receipt of OMC commands. The Routing Manager performs the call routing based on called party digits dialed by the calling subscriber.
Equipment Number defines a uniform way to address V5.2 subscribers and SS7 digital trunks. Xenon currently supports the following two formats:
The V5.2 Equipment Number uniquely identifies a V5.2 subscriber by specifying the XEN ID, Interface Number and Subscriber Port Number in that interface.
|V5.2 Equipment Number Definition|
|XEN ID||V5.2 Interface Number||Subscriber Port Number|
The ISUP Equipment Number uniquely identifies a digital trunk circuit that can be used to connect the call to another subscriber. The XEN ID, Digital Trunk Number and the Circuit Number in that digital trunk uniquely identify the ISUP trunk to be used in the call.
|ISUP Equipment Number Definition|
|XEN ID||Digital Trunk Number||Circuit Number|
The following steps are involved in routing a call that terminates on this exchange:
- Routing Manager checks if the called number resides on the same switch. This is done by checking if the leading digits of the dialed number match the exchange code assigned to the exchange.
- If the leading digits and the exchange code match, Directory Number to V5.2 Equipment Number translation table is used to identify the Equipment Number of the called subscriber.
- The XEN Id in the equipment number is used to route the call to the appropriate XEN card.
If the called subscriber does not reside in this exchange, the call will be forwarded to the next exchange that can handle the call. This is done by selecting a free trunk circuit towards the next exchange. The steps involved in this process are:
- The leading digits for the call do not match the exchange code, so that call must be destined for some other exchange.
- The leading digits are used to access the Routing data and obtain a route towards the called subscriber. The route consists of a pool of free trunk resources towards the next exchange.
- The Routing Manager selects the first free ISUP equipment number from the route.
- The XEN id in the equipment number is used to route the call to the appropriate XEN processor.
The Routing Manager does not distinguish between V5.2 subscriber originating calls and incoming ISUP calls.