HYBRID ROUTING TECHNIQUE FOR SWITCHING COMMUNICATION NETWORK

• US 3,705,523 A
• Filed: 09/21/1970
• Issued: 12/12/1972
• Est. Priority Date: 09/21/1970
• Status: Expired due to Term

• Current Assignee: Frank B. Alouisa
• Original Assignee: Frank B. Alouisa
• Inventors: Alouisa, Frank B.
• Primary Examiner(s): Brown, Thomas W.
• Application Number:
  US05/073,919
• Time in Patent Office: 813 Days
• Field of Search: 179/18EA
• US Class Current: 379/221.01
• CPC Class Codes: H04Q 2213/13141 Hunting for free outlet, circuit or channel
• CPC Class Codes: H04Q 2213/13388 Saturation signaling systems
• CPC Class Codes: H04Q 3/545 using a stored programme

Abstract

A hybrid routing technique for an analog or digital switching communication network containing several switching centers for contacting a called subscriber at a destination switching center whose location in the network need not be known to the calling subscriber and for providing a deterministic route back from the destination switching center to the originating switching center. The entire system is substantially simultaneously flooded once in parallel radial fashion with a flood signal of simple format containing information representing the calling switching center, the called subscriber and the time or origination of the call; local subscriber directories at each of the switching centers of the network are examined substantially simultaneously to determine which of the switching centers is the destination switching center. The selection of a route between the called and the calling subscribers is done independently of the locating of the called subscriber and allows effective selection of routes, based on an abundance of information available at the switching centers concerning the current status of the network and regardless of transmission delays along the routes.

Claims

1. A routing procedure for a switching network having a plurality of switching centers each having a local subscriber memory and a search memory, adjoining ones of said switching centers being interconnected by communication links each consisting of at least one signalling channel and several message channels wherein a calling subscriber at an originating switching center is connected to a called subscriber at a destination switching center whose location in the network need not be known to said calling subscriber comprising the steps of;

producing at said originating switching center in response to initiation of the calling subscriber'"'"''"'"'s call containing the directory address of the called subscriber a flood signal of minimal format containing the aforesaid address of the called subscriber, the address of the originating switching center and the time of initiation of the calling subscriber'"'"''"'"'s call;

propagating said flood signal over said signalling channel from said originating switching center simultaneously to all switching centers in the network adjoining said originating switching center;

propagating substantially simultaneously over said signalling channel only the flood signal initially received at said other switching centers to all network switching centers adjoining each said other switching center except the switching center from which said flood signal has just been received; and

examining a search memory at each of the switching centers other than the originating switching center receiving said flood signal for a previous receipt thereof.

2. A routing procedure for a switching network according to claim 1 further including the step of entering the flood signal propagated from each said other switching center into the search memory thereof.

3. A routing procedure for a switching network according to claim 1 further including the step of sending an acknowledge signal from each said other switching center to the switching center responsible for the received flood signal.

4. A routing procedure for a switching network according to claim 2 further including the steps of providing a timing signal at each switching center upon propagating said flood signal therefrom, said timing signal being of duration exceeding the combined time required for transmission of said flood signal and said acknowledge signal over the network link having the longest delay;

and discontinuing processing of said call at said switching center if an acknowledge signal is not received at that switching center prior to termination of said timing signal.

5. A routing procedure for a switching network according to claim 3 further including the steps of entering the flood signal propagated from each said other switching center into the search memory thereof;

and erasing the flood signal entered into the search memory at each said other switching center in response to the receipt of acknowledge signals from all switching centers adjoining the corresponding switching center.

6. A routing procedure for a switching network according to claim 2 further including the steps of examining substantially simultaneously the local subscriber memory at each of said other switching centers after entry of said flood signal into the corresponding search memory thereof to determine whether said switching center is the destination switching center.

7. A routing procedure for a switching network according to claim 6 further including the step of establishing a route between the destination switching center and said originating switching center along message channels of a preselected combination of links.

8. A routing procedure for a switching network according to claim 1 further including the step of discontinuing processing of a flood signal received at a given one of said other switching centers when the examination of said search memory reveals a previous receipt of said flood signal.

9. A routing procedure for a switching network according to claim 2 further including the step of queueing at each said other switching center the flood signals for different subscriber calls arriving at that other switching center.

10. A routing procedure for a switching network according to claim 8 further including the step of queueing at each of said other switching centers the flood signals for different subscriber calls arriving at that other switching center.

11. A routing procedure for a switching network according to claim 9 further including the step of erasing the queue entry of the flood signal for the calling subscriber'"'"''"'"'s call at a given one of said other switching centers when examination of the search memory reveals previous receipt of the same flood signal.

12. A routing procedure for a switching network according to claim 10 further including the step of erasing the queue entry of the flood signal for the calling subscriber'"'"''"'"'s call at a given one of said other switching centers when examination of the search memory reveals previous receipt of the same flood signal.

13. A routing procedure for a switching network according to claim 6 further including the steps of sending a route attempt signal for said destination switching center over a signalling channel to an adjoining switching center which is along the route preselected for interconnecting said destination switching center and said originating switching center upon receipt of said flood signal at said destination switching center;

and forwarding said route attempts signal along signalling channels to other switching centers along said preselected route in the absence of a route blocked condition.

14. A routing procedure for a switching network accOrding to claim 13 including the steps of initiating a time-out signal at said originating switching center at the time of flood signal propagation therefrom and of duration determined by the time normally required for complete flooding of the entire switching network;

and discontinuing call processing at said originating switching center if a route attempt signal is not received at said originating switching center before termination of said time-out signal.

15. A routing procedure for a switching network according to claim 14 further including the step of sending from said originating switching center a distinctive signal to said called subscriber in response to discontinuance of said call processing.

16. A routing procedure for a switching network according to claim 13 further including the step of allocating a message channel in said link between a given said other switching center and the switching center adjoining thereto along said preselected route as said route attempt signal is sent out of the given switching center.

17. A routing procedure for a switching network according to claim 16 further including the step of propagating a route available signal from said originating switching center upon receipt thereby of said route attempt signal.

18. A routing procedure for a switching network according to claim 17 further including the steps of generating a timing signal of predetermined duration at said destination switching center at the time of sending out the route attempt signal therefrom;

and discontinuing processing of the call at the destination switching center if an acknowledge signal is not received by said destination switching center from the originating switching center within said predetermined time.

19. A routing procedure for a switching network according to claim 16 further including the step of propagating a busy signal from the destination switching center to said calling subscriber at said originating switching center if the called subscriber is busy with another call.

20. A routing procedure for a switching network according to claim 16 further including the step of completing the message connection already allocated at each switching center along the preselected route during the route attempt procedure to establish a useable message connection between the called and calling subscribers.

21. A procedure for locating a called party in a switching network having a plurality of interconnected switching centers, adjoining ones of which are joined by links each consisting of at least one signalling channel and several message channels, said network having an originating switching center to which a calling subscriber is connected and a destination switching center at a location in the network which need not be known to the calling subscriber comprising;

propagating substantially simultaneously throughout said network only along one of said signalling channels of the links interconnecting all switching centers of said network a flood signal containing information indicative of the called party, the originating switching center and the time of initiation of the calling subscriber'"'"''"'"'s call.

22. A routing procedure for a switching network according to claim 21 further including the steps of, examining a local subscriber memory at each switching center to determine if said switching center is the destination switching center;

sending a route attempt signal from said destination switching center over a signalling channel to an adjoining switching center which is along a route preselected for interconnecting said destination switching center and said originating switching center upon receipt of said flood signal at said destination switching center; and

forwarding said route attempt signal along signalling channels to intermediate switching centers along said preselected route in the absence of a route blocked condition.

23. A routing procedure for a switching network according to claim 22 further including the step of, allocating a message channel in said link between a given switching center and the adjacent switching center along said preselected route as said route attempt signal is sent from said switching center.

24. A routing procedure for a switching network according to claim 23 further including the steps of, propagating a route available signal from said originating switching center upon receipt of said route attempt signal;

and completing the message connection already selected at each switching center along the preselected route during the route attempt procedure to establish a complete message connection between the calling and called subscribers.

25. A routing procedure for a switching network having a plurality of switching centers wherein a calling subscriber at an originating switching center is connected to a called subscriber at a destination switching center whose location in the network is unknown to said calling subscriber comprising;

entering into a search memory of limited capacity at said originating switching center the directory address of the called subscriber;

examining a local subscriber memory at said originating switching center to determine if said directory address is contained therein;

examining the search memory at said originating switching center, if the local subscriber memory does not contain said directory address, for the existence therein of the same directory address owing to a prior call from another calling subscriber at said originating switching center to the same called subscriber;

making up a complete flood signal of minimal format at said originating switching center if no evidence of a prior call to the same called subscriber is found during the search memory examination, said flood signal containing information indicative of the originating switching center and the time of initiation of the calling subscriber'"'"''"'"'s call, as well as said directory address of the called subscriber;

propagating said flood signal out of band from said originating switching center simultaneously to all adjacent switching centers in the network;

examining the search memory of each of the switching centers other than the originating switching center receptive of said flood signal fro a previous receipt thereof;

propagating out of band only the flood signal initially received at all of said other switching centers simultaneously to all adjoining network switching centers except the one from which said flood signal has just been received;

entering the flood signal propagated from each said other switching center into the corresponding search memory thereof;

examining the local subscriber memory of each switching center after entry of said flood signal into said corresponding search memory to determine if said switching center is the destination switching center; and

establishing a preselected message route between the destination switching center and said originating switching center.

26. A routing procedure according to claim 22 further including the steps of determining from current information in said network whether a preselected route is available between said destination switching center and said originating switching center before sending said route attempt signal;

generating a route blocked signal at an intermediate switching center in response to receipt of said route attempt signal from the adjoining switching center indicating availability of said route when a condition subsequently occurs that all links along said route become blocked;

propagating said route blocked signal along the preselected route over which the route attempt signal was sent;

selecting another route of next lower preference in response to propagation of said route blocked signal; and

repeating the aforesaid route attempt process and alternate route selection process until a route has been found along which no links are blocked.

27. A routing procedure for a switching network having a plurAlity of switching centers, adjoining ones of which are interconnected by communication links, wherein a calling subscriber at an originating switching center is connected to a called subscriber at a destination switching center whose location need not be known to said calling subscriber, including the steps of, entering into a search memory at said originating switching center a directory address of the called subscriber;

searching a local subscriber memory at the originating switching center to determine whether said called subscriber is at said originating switching center;

examining said search memory if the search of said local subscriber memory is negative to determine whether another calling subscriber at said originating switching center has already called the same called subscriber;

generating a flood signal at said originating switching center which includes said directory address of the called subscriber, information designating the originating switching center and information designating the time of initiation of the calling subscriber'"'"''"'"'s call; and

propagating said generated flood signal along links interconnecting said originating switching center and adjoining switching centers.

28. A routing procedure for a switching network according to claim 27 further including the step of sending a busy signal to said calling subscriber when the examination of said memory indicates initiation of a prior call to the same called subscriber by another calling subscriber at the originating switching center.