Abstract:
Integration of the cellular network with an IP based network is disclosed. An integrated IP/cellular network can route packetized voice and data together in a more efficient manner. The present invention integrates IP based standards for a cellular IP solution with cellular centric vs. IP message gateway as the demarcation point. However, the present invention also provides support for cellular unique features for better performance. Multiple architectures are proposed to ease migration to a combined network as well as to show the various levels of support provided.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 60/138,221, filed Jun. 9, 1999, entitled “WIRELESS IP” by David J. Y. Lee et al., which application is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to cellular telephone systems, and, in particular, to wireless internet protocol (IP) use of cellular telephone systems. 
     2. Description of the Related Art 
     The Internet is quickly becoming an integral part of everyday life. As more people begin using the Internet, Internet traffic has grown at an exponential rate. Within a short time, Internet usage is expected to become as commonplace as voice telephone usage is today. 
     As such, the demand for data services is increasing. Several methods have been proposed to utilize the cellular telephone network for transfer of Internet Protocol (IP) data. However, the cellular network would require modification to properly perform IP data transfer. Most solutions include replacing the Mobile Switching Center (MSC) with a fast and powerful router, but there is no definite conclusion on how the IP should be implemented at the Base Station Controller (BSC) and/or the Base Transceiver Station (ITS). 
     Before any solution can be determined, each cellular network element must be reviewed for functionality. For example, the MSC functions include routing calls, inter-working to the Public Land Mobile Network (PLMN) and the Public Switching Telephone Network (PSTN), call processing, and roaming. The BSC functions include connections to the MSC (“the A interface”), mobility management, call processing and resource management. The BTS functions include signal modulation and demodulation, connection to the BSC (“the Abis interface”) and the RF channel (“the Air interface”). There are also other network elements like the Equipment Identity Register (EIR), Home Location Register/Visitor Location Register (HLR/VLR) and billing system to perform Authorization, Accounting and Authentication (AAA) related functions. 
     The current IP development supports most of these functions. For example, mobile IP/SIP solves the mobile roaming issues, the Diameter solves the AAA issues, H.323 solves the call control and services issues, and the Home Agent/Foreign Agent (HA/FA) solves the HLR and VLR issues. However, the current IP development in the cellular arena addresses each problem individually, without taking into account effects that solutions to the other problems will have on the current undertakings. As such, integrating these available IP-based features into a cellular network to provide high quality voice and data services are needed. 
     It can be seen, then, that there is a need in the art to integrate available IP-based features into a cellular network. It can also be seen that there is a need in the art for an integrated solution of IP features and cellular features that provide high-quality voice delivery. It can also be seen that there is a need in the art for an integrated IP and cellular network to provide high quality data services. 
     SUMMARY OF THE INVENTION 
     To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a system and a method for communicating over an internet protocol-based communications network. The system comprises a handoff server, a Base Transceiver Station (BITS), and a home agent (HA). The BTS communicates with a mobile telephone within a transmission area associated with the BTS, and the handoff server communicates with the BTS using a proprietary interface. The HA communicates with the handoff server for transmitting messages through an internet-protocol network, wherein messages between the HA and the mobile telephone use an internet protocol between the HA and the handoff server and the proprietary interface between the router and the BTS. The method comprises sending a message from a home agent (HA) to a router over an internet protocol based network forwarding the message from the router to a base transceiver station (BTS) using a proprietary format, and forwarding the message from the BTS to a mobile telephone that is within a geographical communications zone of the BTS. 
     An object of the present invention is to integrate available IP-based features into a cellular networks. Another object of the present invention is an integrated solution of IP features and cellular features that provide high-quality voice delivery. Another object of the present invention is an integrated IP and cellular network to provide high quality data services. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring now to the drawings in which like reference numbers represent corresponding parts throughout: 
         FIG. 1  illustrates a direct IP connection to the IWF as described in the related art; 
         FIG. 2  shows the current 3G architecture derived from TR45.6[2]; 
         FIG. 3  illustrates the existing standard based mapping between the cellular and IP networks; 
         FIG. 4  illustrates replacing the BSC with a router in accordance with the present invention; 
         FIG. 5  illustrates an inter-BSC handoff, in the configuration of  FIG. 4 ; 
         FIG. 6  illustrates that Asynchronous Transfer Mode (ATM) can be used as the communications layer 2 in the present invention; 
         FIG. 7  illustrates the architecture of the present invention using a hand-off server as a replacement for the BSC. 
         FIG. 8  illustrates the SHO transfers of the architecture of  FIG. 7 ; 
         FIG. 9  illustrates an Intra-FA handoff through a FA update architecture as embodied in the present invention; 
         FIG. 10  illustrates an Intra-FA handoff through a HA update architecture as embodied in the present invention; 
         FIG. 11  illustrates an Inter-FA handoff architecture in accordance with the present invention; 
         FIG. 12  illustrates the current network architecture of the cellular telephone network; 
         FIG. 13  illustrates a stage  1  migration to an integrated IP-cellular network; 
         FIG. 14  illustrates the second stage of migration; and 
         FIG. 15  is a flow chart illustrating the steps used to practice the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the following description of the preferred embodiment, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration a specific embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. 
     Overview 
     The present invention concentrates on the architecture of such IP-based cellular networks. The present invention proposes several feasible implementations of IP functionality on BSC and BTS, or replaces the BSC or BTS completely. In addition, the present invention addresses some of the inter-workings with other IP networks and traditional telephone networks. Further, the present invention addresses some performance issues with the IP network in implementing real-time services. 
       FIG. 1  illustrates a direct IP connection to the IWF as described in the related art. 
     As shown in  FIG. 1 , IS 707 proposed system  100 , which uses a direct IP connection  102  to connect the BS/MSC  104  to the Interworking Function (IWF)  106 . This use of a direct IP connection from a mobile user  108  or user terminal  110  to the IWF  104  uses IP to transmit messages on the relay layer  112 . A direct IP connection  102  has minimal impact on the cellular system  100  because all the mobility management, call processing, and roaming functions remain within the cellular network. 
     However, only limited benefits can be achieved through this architecture. Mobility management, roaming, and Hand Offs (HO) are not addressed in the direct IP connection system  100 . 
     The present invention removes the MSC and provides IP functions within the BSC and BTS to produce more effective cost-savings on the infrastructure and rapid wireless data adoption. The present invention solves the problems of mobility management, roaming, and Hand Offs (“HO”) using an IP-based solution. 
     The present invention uses IP gateways for translating cellular call processing based messages, e.g., IS634, ISUP, and IS41, to IP based messages, e.g., H.323, SIP, Mobile IP, and Diameter. These translations need to reside in the demarcation point between the cellular and IP networks to support an IP ready handset. To support voice services using IP with a traditional handset that uses no IP address/stack, another level of translating mobile numbers to IP addresses is needed. This additional level of translation can be performed by an SS7 gateway responsible for the translation between the HLR and the IP network, or by migrating the HLR to Diameter. 
     Network Architecture 
       FIG. 2  shows the current Third Generation (3G) architecture  200  derived from TR45.6[2]. As can be seen from  FIG. 2 , the architecture  200  shows mobile phone  202  and mobile terminal  204  connecting with the cellular network  206 , the cellular network comprising the MSC, BTS, and BSC. The cellular network  206  has a radio-packet interface  208  to the Packet Data Serving Node (PSDN)  210 . The cellular network also has a connection to the VLR  212 . The Internet  214 , and, as such, IP, is used to couple the visited network  216  to the home network  218  and the target network  220 . As such, the 3G architecture  200  does not provide IP within the BSC and BTS. The architecture  200  lacks an interrelationship between IP/PLMN/PSTN so control messages and data pipes are transparent to the user. This translation includes a mapping of the mobile number to the TCP/IP address so that a regular handset  202  without an internal IP stack can also run on the IP network. Further, the architecture  200  lacks any features for the wireless part of the IP, e.g., radio network  206 , etc. to ensure cellular unique features can be supported. 
     Translation Between Cellular/PSTN/PLMN 
     Cellular traffic can “ride” on the IP network as long as the interface which terminates cellular based messaging maps the cellular based messages into compatible IP messages. Also, data on the cellular network can “ride” on the IP network, depending on the location of the IP gateway to the cellular network  FIG. 3  illustrates the existing standard based mapping between the cellular and IP networks. 
     Map  300  illustrates that cellular network  302  and the IP network  304  are mapped in a one-to-one correspondence, where call processing  306  maps into the H.323 SIP  308 , AAA  310  maps into diameter  312 , and MobilityManagement  314  maps into the Mobile IP SIP  316 . RF Resource Management  318  is left as a standalone feature for the cellular system  302 . However, the present map  300  does not take into account any integration between the cellular network  302  and the IP network  304 ; there is merely a translation of functions taking place. The present invention strips away the barriers between the cellular network  302  and IP network  304  and replaces those areas of each network  302  and  304  that are better served with features from the other network. 
     The present invention accesses the available networks and integrates the cellular and IP networks. In a traditional cellular system, the BSC is responsible for mobility management, call processing and radio resource management. The BSC also comprises a transcoder, vocoder, and a switching matrix. For a combined cellular/IP network, the BSC hardware functions can be replaced by a router and additional Digital Signal Processing (DSP) based software/hardware. 
     The MSC functionality includes call setup, connection and features, routing, authentication and accounting. These functions can be replaced by existing IP protocols and applications, e.g., H.323/SIP for call set up and connection, and Diameter for accounting, authentication, and authorization. The mobility functions can be replaced by mobile IP/SIP through tunneling between HA and FA, and HO can also be supported through tunneling. A Soft Hand Off (SHO) in a CDMA system can be supported by using the existing Asynchronous Transfer Mode (ATM) protocols. 
     IS 95 call processing, mobility management, and resource management related messages need to be translated and adapted to an IP based message schema. The SHO schema, which is crucial to the CDMA cellular network, is solved by the present invention by adopting an ATM protocol into the cellular network. ATM supports multimedia applications and high Quality of Service (QoS). ATM protocols are not optimized in capacity with small bandwidths. As more cellular frequencies are allocated for data services and for multimedia applications, e.g., convergence of voice and data, the statistical gain by combining all cellular frequencies make the implementation of ATM in a cellular network through the present invention worthwhile. 
     The ATM Virtual Tributary is a very inefficient way of emulating the circuit switching network. However, a VPI/VCI approach has proven to be more effective in a wider bandwidth environment. Also, network management overhead is imbedded in the ATM/SONET header in the existing proposal. The current TR45.5 proposal supports PPP on top of RLP. PPP allows direct connection from point to point and is the most efficient mean of connecting two points in the network. Although the IP community is enhancing MPLS for VPN and QoS, it is difficult to achieve the QoS provided by ATM since IP is connectionless originated. 
     Another issue addressed by the present invention is the mapping from the mobile number to an IP address. This can be done by the gateway responsible for phone numbers and IP addresses. 
     Wireless IP Architecture 
     The present invention provides multiple architectures for integrating IP and cellular telephone networks. For example, the first architecture replaces the BSC functionality with an application specific router, and eliminates unnecessary HOs to allow both data and voice to ride on the IP pipe. The MSC is eliminated and SS7 related messages will be placed in an IP format at the BSC and routed to IP network. The IP connection is established from the router to the mobile for data transfer, and the BSC has a link layer connection for voice and data applications. Intra-BSC SHO is maintained through the BSC mobility management functions, and inter-BSC HO is implemented through inter-BSC tunneling. 
     A second architecture enhances the BSC to have ATM connections to the handoff server (HS). The FA remains a function of BSC, and an ATM connection would be established from the BSC to the HS. Intra-BSC/Inter-BSC HO is maintained through ATM layer functionality, and an ATM connection from BSC to Hs supports SHO in a CDMA system. 
     A third architecture enhances both the BSC (HO router) and the BTS to have ATM and IP functionalities. The BSC is replaced with an HO server. The BTS supports ATM, and the QoS can be achieved by synchronizing BTSs involved in SHO by using a nail-up connection or by setting up pre-determined times for transmitting. The FA remains at the BTS, and IP connections between the mobile, BTS, and HO server are established. SHO are supported through direct PVC connections from the mobile to a SHO server which bypasses the BTS IP layer, and intra-BSC HO is maintained through a virtual IP connection. 
     A fourth architecture enhances the BTS to have IP functionality and BSC/FA functionality. This architecture makes IP BTS possible without depending on layer 2 capabilities since more QoS features will be developed for the IP layer. With CDMA synchronized and dedicated channel characteristics, it is highly possible to support this architecture. The architecture requires an efficient IP and lower layer interface to function properly. An IP connection from BTS to TE2 is established, and inter-BTS HO is maintained through BTS tunneling and updating the HA. 
     Wireless IP Architectures 
     Replace BSC with Router 
       FIG. 4  illustrates replacing the BSC with a router in accordance with the present invention. In architecture  400 , the MSC is removed from architecture  400  and the BSC  402  is replaced with a router (BSC router)  404 , that has enhanced IP routing and Foreign Agent (FA)  406  functions. The router  404  interfaces with the BTS  408 ,  410 , and  412 , which interface with the mobile telephone  414  throughout each BTS  408 - 412  coverage area. The Internet (IP network)  416 , and other network features  418 , interface directly with the router  404 , instead of interfacing with the MSC as shown in  FIG. 1 . The Home Agent (HA)  420  now interfaces through the IP network  416 . 
     The interface between the BTS  408 - 412  and the BSC  402  is replaced with a similar or the same interface between the BTS  408 - 412  and the router  404 . Intra-BSC  404  handoffs are handled as before since all mobility management functions still remain in the BSC router  404 . From the BSC router  404  to the IP network  416 , IP-based communications are used. In addition, the FA  406  is added to the BSC router  404  to handle the tunneling between the HA  420  and the FA  406 . Inter-BSC router  404  hand-offs are done by the first FA  406  anchoring during the handoff, and the HA  420  updating when completing the handoff. 
     As shown in  FIG. 4 , a packet destined for the mobile telephone  414  (IP address 2.2.2.1) will be routed from the HA  420  (IP address 2.2.2.*) through the FA  406  (IP address 1.1.1.*). When an intra-BSC router  404  handoff occurs, e.g., between BTS  408  and BTS  410 , the FA  406  does not change, and therefore there is no impact on the IP network  416 .  FIG. 4  also illustrates division line  422 , where all communications on the left of line  422  are proprietary in nature, e.g., CDMA, TDMA, etc, whereas communications on the right of line  422  use IP. Coverage areas  424 - 428  are shown as corresponding with BTS  408 - 412 , respectively. 
     Inter-BSC Handoff 
       FIG. 5  illustrates an inter-BSC handoff in the configuration of  FIG. 4 . 
     Configuration  400  as shown in  FIG. 5  illustrates two BSC routers BSC 1  router  404 A and BSC 2  router  404 B, and two Foreign Agents FA 1   406 A and FA 2   406 B associated with the BSC routers  404 A and  404 B respectively. An incoming data packet is routed from the HA  420  (IP address 2.2.2.*) through the IP network  416  to BSC 1  router  404 A, and to the FA 1   406 A (IP address 1.1.1.*). This is then passed to the BSC 2  router  404 B and FA 2   406 B (IP address 3.3.3.*) and finally delivered to the mobile telephone  414 . 
     When a HO is completed, the HA  420  is updated with the new FA address, e.g., FA 2   406 B, and future data packets will be sent directly to BSC 2  router  404 B. 
     In this architecture  400 , the voice service, assuming the mobile handset  414  does not have an IP stack, is supported by converting CDMA voice packets to a “voice over IP” coding scheme with DSP (QCELP/G.729), and is transmitted through the IP route set up by H.323, or any other IP application protocols for setting up the IP path from HA  420  to mobile telephone  414 . Mobile to mobile calls can be supported with no vocoding between two mobiles. Control messages (call processing related, IS634 in this case) are translated into H.323 messages. If the user terminal or mobile telephone  414  supports an IP stack, H.323 will be set up all the way to the user terminal or mobile telephone  414 . 
     ATM Connection Between BSC and HS 
       FIG. 6  illustrates that Asynchronous Transfer Mode (ATM) can be used as the communications layer 2 in the present invention. 
     Between BSC router  404  and BTS  408 - 412 , ATM can be used as the proprietary interface along paths  600  and  602 . Further, ATM can be used between BTS  408 - 412  and mobile  414  along connection  604  if desired. The use of ATM between BSC router  404  and BTS  408 - 412 , and the use of ATM between BTS  408 - 412  and mobile telephone  414  supports a more flexible QoS, as well as supporting additional multimedia services. Soft Hand Offs (SHO) in architecture  400  can also be supported through many available ATM features. For example, a nail-up connection can be established from the BSC router  404  to the mobile telephone  414  through circuit emulation. The connection  604  can also be supported by predefining the timing for the frame to be transmitted from the BTS  408 - 413  to the mobile telephone  414 . The timing connection is possible since CDMA is a synchronized system and each mobile telephone  414  has a dedicated channel. Frames for the SHO region can be scheduled to be transmitted at a predefined time. This might introduce a certain delay, however, the transmission is possible with higher bandwidths and higher processing power. With this architecture  400 , the soft handoff can be easily resolved. 
     BIS Riding the IP on ATM with a HO Server (No BSC) 
       FIG. 7  illustrates the architecture of the present invention using a hand-off server  702  as a replacement for the BSC and/or BSC router described with respect to  FIGS. 4-6 . In architecture  700 , the ATM is used as the layer 2 protocol. The mobile telephone  414 , the BTS,  408 - 412 , and the HO server  702  are running IP on top of ATM. While in normal, non-SHO operation, the mobile telephone  414  is connected to the BTS  408  through a Permanent Virtual Circuit (PVC 1 )  704 , and the BIS  408  is connected to the HO server  702  through IP ATM (PVC 2 )  706 . While in the SHO area, the mobile telephone  414  is connected to the HO server  702  directly through ATM (PVC 3 )  708 . Therefore, there is only one IP hop between the soft HO server  702  and the user terminal or mobile telephone  414 . Synchronization can be achieved for the SHO application. In this architecture  700 , the IP is running on top of the ATM layer. The BSC is eliminated from the architecture  700  of the network. In the SHO region, the traffic path is running on PVC 3   708 . This architecture is more efficient in the use of system resources, since statistical multiplexing can be applied. 
     Utilization of a virtual IP on top of ATM, the data path gets switched from PVC 1   704  and PVC 2   706  to PVC 3   708 , which creates only one IP hop between the soft HO server  702  and the user terminal or mobile telephone  414 , which makes transmit synchronization achievable. There are direct ATM as well as IP connections from the BTS  408 - 412  to the mobile telephone  414 . The present invention&#39;s approach of pushing the ATM to the BTS layer supports SHO issues more effectively. Some of the BSC functionality is then pushed to the BIS  408 - 412 , e.g., power control. 
       FIG. 8  illustrates the SHO transfers of the architecture of  FIG. 7 . When mobile telephone  414  is within zone  424  associated with BTS  408 , PVC 1   706 A, which connects BTS  408  to HO server  702 , is used to connect the mobile telephone  414  to the HO server  702 . When mobile telephone  414  is within zone  426  associated with BTS  410 , PVC 1   706 B, which connects BTS  410  to HO server  702  is used to connect mobile telephone  414  to the HO server  702 . However, in SHO regions, PVC 3   708  is used to connect mobile telephone  414  to the HO server  702  directly without using either BTS  408  or  410 , or PVC 1   706 A or PVC 1   706 B. 
     BTS with IP (Independent of Layer 2 Protocol) 
     When the IP stack is pushed into the BTS, the issue of SHO arises because there is no way to guarantee layer 3 packet synchronization. However, with enhancements to the IP layer on QoS, the IP can support most features that are currently supported by ATM. With wider bandwidth, higher processing power, and effective interfacing between IP and layer 2, the IP can support more time critical or QoS sensitive applications. Since CDMA systems are synchronized and each mobile has a dedicated channel, it is possible for BTS/MS to transmit and receive data at predetermined system times. This is similar to what is implemented in the CDMA system to support voice only services while transmitting and receiving voice at predefined times. However, the IP/layer 2 interface needs to be developed so messaging between these two layers can be effective and guaranteed for limited time delays only. 
     Intra FA Handoff (FA Update) 
       FIG. 9  illustrates an Intra-FA handoff through a FA update architecture as embodied in the present invention. Architecture  900  of the present invention shows the BTS 1   412  establishing an IP connection with the mobile telephone at position  902 . As mobile telephone  414  moves to position  904 , BTS 1   412 , or mobile telephone  414 , realizes that mobile telephone  414  must be handed off to another BTS, in this case BTS 2   410 . The mobile telephone  414  then sends a HO message to both BTSs  410  and  412 , as shown by messages  906  and  908 . The mobile telephone  414  is served by the BTS 1   412  via path  912  from BTS 1  to mobile telephone  414  and path  914  from the FA  406  to BTS 1   412  until the mobile telephone  414  reaches position  910 , when it can be anchored to BTS 2   410  via BTS 1   412  and path  916 , and the BTS 1   412  sends a location update to the FA  406  via path  914  for the mobile telephone  414 . The mobile IP packet is then delivered to the mobile telephone  414  via path  918 , which is from FA  406  through BTS 1   412  to BTS 2   410  to mobile telephone  414  until the FA  406  is updated, whence the mobile telephone  414  will receive packets directly from the FA  406  to the BTS 2   410  via path  920  after the FA  406  is updated and the handoff is completed. 
     Intra FA HO (HA Update) 
       FIG. 10  illustrates an Intra-FA handoff through a HA update architecture as embodied in the present invention. 
     Architecture  900  of the present invention shows the BTS 1   412  establishing an IP connection with the mobile telephone at position  902 . As mobile telephone  414  moves to position  904 , BTS 1   412 , or mobile telephone  414 , realizes that mobile telephone  414  must be handed off to another BTS, in this case BTS 2   410 . The mobile telephone  414  then sends a HO message to both BTSs  410  and  412 , as shown by messages  906  and  908 . The mobile telephone  414  is served by the BTS 1   412  via path  912  from BTS 1  to mobile telephone  414  and path  914  from the FA  406  to BTS 1   412  until the mobile telephone  414  reaches position  910 , when it can be anchored to BTS 2   410  via BTS 1   412  and path  916 , and the BTS 1   412  sends a location update to the FA  406  via path  914  for the mobile telephone  414 . The FA  406  then sends an update to the HA  420 . The mobile IP packet is then delivered to the mobile telephone  414  via path  918 , which is from FA  406  through BTS 1   412  to BTS 2   410  to mobile telephone  414  until the FA  406  is updated, whence the mobile telephone  414  will receive packets directly from the FA  406  to the BTS 2   410  via path  920  after the FA  406  and HA  420  are updated and the handoff is completed. 
     Inter FA HO 
       FIG. 11  illustrates an Inter-FA handoff architecture in accordance with the present invention. Architecture  1100  illustrates two FAs,  406  A and  406 B. Similar to  FIGS. 9 and 10 , BTS 2   412  establishes an IP connection  1102  with the mobile telephone  414  at position  1104 . The mobile telephone  414 , as it moves from position  1104  to  1106 , requires a hand off and sends a message to both BTS  412  and BTS  410  via paths  1108  and  1110 . While communicating through BTS  412  exclusively, messages from the HA  420  are transmitted and received at the mobile telephone  414  via FA  406 A and IP network  416 , and path  1112  to BTS  412 . However, since BTS  410  is coupled to FA  406 B, an inter-FA handoff (HO) must occur. 
     The mobile telephone at position  1114  is served by BTS  410  by anchoring to the IP network  416  and HA  420  through BTS  410 . Until the updates to the FA  406 B and HA  420  are completed, BTS  410  uses communications path  1114  to communicate to FA  406 B, which uses communications path  1116  to communicate to FA  406 A, which uses communications paths  1118  and  1120  to communicate to the IP network  416  and ultimately the HA  420 . Once the handoff between FA  406 A and FA  406 B is complete and the FA  406 A and  406 B and HA  420  are updated with the mobile telephone  414  position, communication from the mobile telephone  414  occurs through path  1122  and  1120  to the IP network  416 . 
     Migration Strategy and Potential Benefits 
       FIG. 12  illustrates the current network architecture of the cellular telephone network. 
     Cellular network  1200  comprises MSC  1202  coupled to BSC  402  via IS 634 protocol connections. MSC  1202  is also coupled to PSTN  1204  via SS7/ISUP protocols, and to PLMN  1206  via IS41 protocols. Each BSC  402  is coupled to BTS  408 - 412 , which communicate to mobile telephones  414  via IS95 protocols. 
       FIG. 13  illustrates a stage  1  migration to an integrated IP-cellular network. The present invention also proposes a migration strategy for existing cellular operators to painlessly transfer from the current architecture  1200  to a network architecture  1300  which incorporates the IP into the cellular network. 
     As shown in  FIG. 13 , architecture  1300  uses the IP pipe  1302  with an H.323 protocol to communicate between MSS  1202  and BSC  402 . The IP pipe  1302  can be used in parallel with the IS634 connections  1304 , or as a substitute for the IS634 connections  1304 . Further, the IP pipe  1302  can be used to couple the BSC  402  to the as shown by paths  1306  and  1308  BTS  412 . This connection between BSC  402  and BTS  408 - 412  can be in parallel with connection  1310  between BSC  402  and BTS  408 - 412 , or as a replacement for connection  1310 . As such, the IP pipe  1302  can be installed in sections between MSC  1202  and BSCs  402 , and from BSCs  402  to BTS  408 - 412 , to minimize the impact to the current cellular system  1200 . As needed, the IS634 paths  1304  and/or the paths  1310  can be removed from the cellular system  1200  to migrate the system to an IP-based cellular transmissions system  1300 . 
     Initially, the current infrastructure is transformed to an IP backbone using the IP pipe  1302  for voice and data transfer. This requires a co-existence of both the IP and SS7 based networks. The PLMN network element platform can be shifted to a PC/router/DSP based platform, and the current backbone can be transformed to a private managed IP network for more efficient data transfer. This allows current carriers to maintain current call processing signaling on existing PLMN infrastructures, transmit voice and data by using the IP pipe, reduce further infrastructure investments, and set up a migration foundation for the next generation backbone. 
       FIG. 14  illustrates the second stage of migration. The second stage of migration is shown in architecture  1400 , which pushes the IP as close to the mobile user as possible. This is performed by integrating existing SS7 related features into an IP based system using the IP pipe  1302 , merging existing PLMN network elements into the IP network and using a single IP network to cover PLMN and other network traffic. This approach takes advantages of available and expanding IP networks and features. The main benefits of pushing IP stack down the network chain as far as possible are a unified network management interface, increased availability of applications, and an efficient use of bandwidth. 
     The IP pipe  1302 , or the “backbone” of the system, is used to unify the MSC  1202 , BSC  402 , and BTS  408 - 412 , while maintaining the MSC  1202  role as gatekeeper for the PLMN  1206  and providing a gateway for the PSTN  1204  PCM trunks  1402  at PSTN gateway  1404 . This unifies all of the voice and data traffic on the IP Pipe  1302 , and allows the system to operate at higher efficiencies. 
     A third stage of migration uses a VPN for wireless data transfer. After inter-working functions are fully integrated as described with respect to  FIGS. 14 and 15 , e.g., SS7, H.323, ISUP, IS41, etc., cellular traffic can eventually run on a VPN to a VPN with guaranteed QoS and time of arrival. 
     Process Chart 
       FIG. 15  is a flow chart illustrating the steps used to practice the present invention. 
     Block  1500  illustrates the step of sending a message from a home agent (HA) to a router over an internet protocol based network. 
     Block  1502  illustrates the step of forwarding the message from the router to a base transceiver station (BTS) using a proprietary format. 
     Block  1504  illustrates the step of forwarding the message from the BTS to a mobile telephone that is within a geographical communications zone of the BTS. 
     CONCLUSION 
     The present invention presents four proposals on migrating the current cellular network to an IP-based network. The traditional issues associated with cellular network, e.g., mobility, call processing, HO, AAA, voice, and data services are addressed by integrating several standard proposals in the IP/cellular industries. With QoS enhancements at the IP layer, and a wider available bandwidth, the present invention provides a total IP solution that supports soft hand offs. With the advancement in IP networks, the present invention also envisions a solution for cellular operators that subscribe a VPN among all the BTS for guaranteed services. 
     This concludes the description of the preferred embodiment of the invention. The following paragraphs describe some alternative methods of accomplishing the same objects. The present invention, although described with specific protocols, can use other protocols to accomplish the same goals. 
     In summary, the present invention discloses a system and a method for communicating over an internet protocol-based communications networks. The system comprises a handoff server, a Base Transceiver Station (BTS), and a home agent (HA). The BTS communicates with a mobile telephone within a transmission area associated with the BTS, and the handoff server communicates with the BTS using a proprietary interface. The HA communicates with the handoff server for transmitting messages through an internet-protocol network wherein messages between the HA and the mobile telephone use an internet protocol between the HA and the handoff server and the proprietary interface between the router and the BTS. The method comprises sending a message from a home agent (HA) to a router over an internet protocol based network, forwarding the message from the router to a base transceiver station (BTS) using a proprietary format, and forwarding the message from the BTS to a mobile telephone that is within a geographical communications zone of the BTS. 
     The foregoing description of the preferred embodiment of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.