Fault tolerant wireless communication systems and methods

Systems and methods for fault tolerant communication are provided. A base site is coupled to a central office via a channel service unit. The channel service unit is coupled to the central office via primary and secondary communications links. A first and second permanent virtual circuit couple the channel service unit to a wireless carrier core network. When there is a fault on the primary communication link or the primary permanent virtual circuit user network interface of an aggregator, the secondary communication link is established and the secondary permanent virtual circuit is activated. Communications are then routed to the wireless carrier core network via the secondary communication link and the secondary permanent virtual circuit.

BACKGROUND OF THE INVENTION

The mobility afforded by wireless communication networks has resulted in increased usage of such networks. Private wireless networks and cellular networks are two common types of wireless communication networks. Private wireless networks, also known as wireless local loop (WLL) networks, are commonly operated by public safety agencies, taxi services and delivery services. Private wireless networks typically operate over a limited range of frequencies and within limited geographic areas. In contrast, cellular networks typically operate over a larger number of frequencies and provide coverage over larger geographic areas.

Although conventional cellular networks may provide sufficient reliability for the average user, there are a number of deficiencies which prevent widespread adoption by public safety agencies. For wireline communication public safety agencies can be provided with dedicated circuits and switches such that even when the Public Switched Telephone Network (PSTN) is overloaded with non-emergency traffic, communications between, and within, public safety agencies can still be completed. To provide reliability to wireless communications, public safety agencies typically employ private wireless networks which operate over frequencies reserved for public safety agencies.

Although these private radio networks reduce the likelihood that calls by public safety agencies are blocked from accessing the radio network, they are expensive to implement and maintain. For example, these networks typically require the use of specialized mobile stations which are more expensive than typical mobile stations, due to the relatively low demand for the specialized mobile stations compared to that of mass-produced mobile stations. As used herein, the term mobile station (MS) is intended to encompass any type of wireless communication device including wireless telephones, wireless Personal Digital Assistants (PDA), wireless pagers, portable computers with wireless modems and the like.

Compared to cellular networks, private wireless networks are more likely to have dead spots where a radio signal cannot be received by the public safety agency worker's mobile station. These dead spots can be extremely hazardous to the public safety agency workers, e.g., a police officer requesting backup, and to the citizenry in general, e.g., a public safety agency worker requesting an ambulance or fire trucks. Accordingly, public safety agencies desire the coverage area provided by conventional cellular networks and the reliability provided by private radio networks.

FIG. 1illustrates a conventional communication network. In the conventional communication network ofFIG. 1, a wireless carrier's cell sites110aand110b, are respectively coupled to base transceiver stations (BTSs)120aand120b. The wireless carrier relies upon connections through a public switched telephone network (PSTN) to provide a backhaul connection between the BTSs and the wireless carrier's core network150. Specifically, each of the BTSs120aand120bare respectively coupled to a central office130of the PSTN via communication links142and144. Typically, communication links142and144are T1 communication links. T1 communication links are digital communication links that have a large bandwidth, i.e., 1.544 Mbps. T1 communication links are leased from a PSTN operator by a wireless carrier, and result in significant monthly recurring costs.

A central office130aggregates a number of T1 links and forwards the information to a wireless carrier core network150via a high bandwidth communication link148, such as a channelized digital signal level 3 (DS-3) communication link. A channelized DS-3 communication link carries approximately 44.736 Mbit/sec of information. The wireless carrier core network150receives the channelized DS-3 communication link by an add-drop multiplexer160. The add-drop multiplexer160places the information on a network165, which provides the information to an add-drop multiplexer170within a mobile switching office (MSO)175. The network165can be any type of network, e.g., a synchronous optical network (SONET).

If the T1 communication link142or144between the BTSs120aand120band the central office130fails, then all communications for the particular cell site fail because the communications cannot be forwarded to the wireless carrier core network150. One technique for addressing the failure of the T1 connection is to provide a redundant T1 connection146. Accordingly, if the T1 connection142fails, the BTS120acan still communicate with the central office130using T1146. However, because the T1 connections are leased, and can be quite costly, when the primary communication link, e.g., T1142, is operating properly the expense of the secondary communication link, e.g., T1146, is largely wasted. T1 links between cell sites and central offices do not fail regularly, and accordingly, leasing a redundant T1 connection is a costly way to address a problem which rarely occurs.

Although failure of T1 links rarely occurs, to certain wireless users, such as public safety agencies, high availability is required for any communication network. Accordingly, it would be desirable to provide techniques for fault tolerant wireless communications with a minimum of expense.

SUMMARY OF THE INVENTION

Systems and methods for fault tolerant wireless communication systems are provided. In accordance with the present invention, a base transceiver station is coupled to an aggregator via primary and secondary communication links. Specifically, the base transceiver station is coupled to a channel service unit. The channel service unit is coupled to the aggregator via the primary and secondary communications links. The aggregator is coupled to a switch of a wireless communication core network via a primary and secondary permanent virtual circuit (PVC). When a fault occurs on either the primary communication link or the primary PVC user network interface of the aggregator, the secondary communication link is established and the secondary PVC is activated.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2aillustrates an exemplary communication system in accordance with one embodiment of the present invention, in which elements with the same reference numerals asFIG. 1have the same function as that described above in connection withFIG. 1. InFIG. 2acell site110ais a fault tolerant cell site, while cell site110bis not a fault tolerant cell site. In accordance with one aspect of the present invention, fault tolerance is achieved, in part, using channel service unit (CSU)225. The CSU225can be any type of CSU that supports a primary T1 communication link and an ISDN primary rate interface (PRI) through a dial-up modem for a secondary communication link, e.g., those manufactured by Paradyne Corporation of Largo, Fla.

CSU225couples BTS120ato the central office230via a primary142and secondary245-247communication links. The primary communication link142can be, for example, a T1 communication link. The secondary communication link can be an ISDN PRI communication link. The primary and secondary communication links are coupled to user network interfaces (UNIs) on different ports of the equipment in the central office. When the primary communication link142fails, the CSU225dials into modem250, thereby establishing communications links245and246. Modem250is coupled to equipment in the central office230via communication link247which is typically an extremely reliable local connection within the central office. AlthoughFIG. 2aillustrates only a single cell site being coupled to modem250, the modem250can support a number of cell sites, effectively providing one-for-n redundancy.

Because the ISDN PRI communication link is much cheaper to maintain then a T1 link, a fault tolerant communication system is provided with a minimal additional cost for the redundant communication link. Specifically, ISDN communication links typically require a small recurring charge for access and additional charges based upon actual usage.

The central office230includes multi-service aggregators (MSA)235aand235b, e.g., ATM switches or IP routers. MSA235ais coupled to CSU225via a T1 communication link142and modem250. Specifically, CSU225is coupled to the PSTN via communication link245. The PSTN is coupled to modem250via communication link246, and the modem250is coupled to the MSA235avia communication link247. Communication links142and247are coupled to UNIs236aand237aon different ports on the MSA235a. The different ports and UNIs can be on the same or different cards of the MSA235a. Coupling the communication links142and247to different cards on the MSA235a(if applicable), provides additional fault tolerance such that if the port or UNI on the MSA235a, which is coupled to the primary communication link142, fails due to a port, UNI or card failure, the secondary communication link247is not affected because it is coupled to a different card. MSA235bis coupled to BTS120bvia a single T1 communication link144.

A primary permanent virtual circuit (PVC) is established between MSA235aand a multi-service switch (MSS)270for the communications received over the primary communication link142, and a secondary PVC is established for communications received over the secondary communication link245-247. Specifically, the primary PVC is established between UNI236a, where the primary communication link142is coupled to MSA235a, and UNI271of MSS270. Similarly, the secondary PVC is established between UNI237a, where communication link247is coupled to MSA235a, and UNI271of MSS270, which is the same UNI as is used to terminate the primary PVC. The network protocol used to implement the PVCs between the MSA235aand the MSS270can be frame relay, asynchronous transfer mode (ATM), internet protocol/multi-protocol label switching (IP/MPLS), or the like.

When the primary communication link or the primary PVC UNI236afails, the MSA235aactivates the corresponding secondary PVC. The secondary PVC uses the same external bandwidth and path which were previously reserved for the failed primary PVC. As used herein, the external bandwidth and path refers to the bandwidth and path between an MSA and UNI271on the MSS.

Because the primary PVC has already reserved bandwidth on a route to MSS270, the secondary PVC requires no reserved allocation of bandwidth on communication link248a. Bandwidth on the connections between MSA235aand MSS270is thus conserved by activating the secondary PVC only when the primary communication link or primary PVC UNI of an aggregator fails. Additionally, if both the primary and secondary PVCs were always active, the secondary PVC could have a sub-optimal path setup to the MSS270because of the bandwidth reserved by the primary PVC.

To achieve one-for-n redundancy, each of the n cell sites which are to be protected by a secondary PVC use the same UNI237athat terminates link247on MSA235a. Each of the n primary PVCs is established between n different UNIs on MSA235a, e.g., UNI236afor exactly one of the n primary PVCs, and an associated UNI of MSS270, to establish connectivity and reserve bandwidth required for communication. There does not have to be a unique UNI on MSS270for each of the n unique UNIs of the primary PVCs on MSA235a. For each such primary PVC, a corresponding secondary PVC is created between the UNI237aand the same UNI of MSS270that terminates the corresponding primary PVC. Accordingly, one-for-n redundancy is achieved by connecting the primary PVCs to different UNIs of the aggregator, and all of the secondary PVCs to the same UNI on an aggregator port that is different from the aggregator ports that are used by any of the primary PVCs.

The MSAs235aand235bare coupled to each other via communication link249. MSAs235aand235bare coupled to MSS270via communication links248aand248b, respectively. The communication link249between MSA235aand235bprovides additional redundancy to the system. Specifically, if communication link248abetween MSA235aand MSS270fails, MSA235acan route the communications to MSA235bvia communication link249. The communications received by MSA235aare routed by MSA235bto MSS270via communication link248b. The network protocols used to implement the PVCs between the MSA235aand the MSS270can be frame relay, ATM, IP/MPLS, or the like, provided that the MSA235bis the same type of equipment as MSA235a.

FIG. 2aillustrates MSAs235aand235bas being located in the same central office230. In such a case, communication link249between the MSAs can be a patch cable. However, MSAs235aand235bcan be located in different central offices. Accordingly, the MSAs can be coupled to each other using a DS-3, OC-3 or any other type of connection of sufficient bandwidth.

FIG. 2billustrates an exemplary communication system in accordance with another embodiment of the present invention, in which elements with the same reference numerals asFIG. 2ahave the same function as that described above in connection withFIG. 2a. In this embodiment, CSU225activates a wireless link on failure of T1 communication link142. This wireless link comprises link252, which connects the CSU225to a local cell site antenna, link253, which connects an antenna to MSA235a, and a radio link254between the two antennas. The radio link254can be a microwave, 802.16 or other similar type of communication link. AlthoughFIG. 2billustrates only a single cell site being coupled to the antenna which is attached to MSA235a, this antenna can support a number of cell sites effectively providing one-for-n redundancy.

FIG. 3aillustrates an exemplary method for setting-up a fault tolerant communication system in accordance with exemplary embodiments of the present invention. For each cell site which is to be fault tolerant, the BTS is coupled to the CSU via a communication link (step305). The CSU is coupled to a wireless carrier core network via a primary communication link and a primary PVC (step310). The CSU is also coupled to the wireless carrier core network via secondary communication link and secondary PVC (step315).

FIG. 3billustrates an exemplary method for operating a fault tolerant communication system in accordance with the present invention. The CSU exchanges information over the primary communication link and primary PVC (step325). If there are no faults along the primary communication link or the primary PVC UNI of the aggregator (“No” path out of decision step330), then the CSU continues to exchange information over the primary communication link and primary PVC (step325). If, however, there is a fault on the primary communication link or the primary PVC UNI of the aggregator (“Yes” path out of decision step330), then the secondary communication link is established and secondary PVC associated with the primary PVC is activated (step335). As discussed above, the secondary PVC uses the external bandwidth and path previously reserved for the primary PVC. Once the secondary communication link is established and secondary PVC is activated, the CSU exchanges information over the secondary communication link and secondary PVC (step340).

If the fault on the primary communication link or the primary PVC UNI of the aggregator has not been cleared (“No” path out of decision step345), then the CSU continues to exchange information over the secondary communication link and secondary PVC (step340). If, however, the fault on the primary communication link or the primary PVC UNI of the aggregator has been cleared (“Yes” path out of decision step345), then the CSU exchanges information over the primary communication link and primary PVC (step325).

The method described above inFIG. 3bin connection with the CSU is equally applicable to the MSAs. Specifically, when there is a communication link between the MSAs, the MSAs can determine whether a fault exists on the communication link to the MSS. When a fault occurs between the MSA and the MSS, the MSA will then forward the communications to another MSA, which will forward the communications to the MSS. Once the fault between an MSA and the MSS has been cleared, the MSA will then return to routing communications to the MSS over its primary communication link.

Although exemplary embodiments of the present invention have been described with a primary communication link being a T1 communication link and a secondary communication link being an ISDN or wireless communication link, the present invention can also employ other types of primary and secondary communication links, as long as they have sufficient bandwidth to support communications to and from the cell site. For example, the primary communication link can be an E1 communication link with a secondary communication link being an ISDN communication link, or the primary and secondary communication links can both be wireless communication links.