Abstract:
A packet-based telecommunication system ( 100 ) is disclosed, comprising a first media gateway ( 124 ) having a first CODEC structure ( 130 ), a second media gateway ( 126 ) having a dual function CODEC structure ( 132 ), wherein the dual function CODEC structure is adapted to provide tandem free operation between itself and the first CODEC structure, and wherein the dual function CODEC comprises a first element ( 134 ) adapted to negotiate tandem free operation, and a second element ( 136 ) communicatively coupled to the first element and adapted to selectively convert data coding responsive to the first element.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to packet switched communications networks and, in particular, to a system providing efficient transport of coded data over a packet-based core network. 
     BACKGROUND OF THE INVENTION 
     The usage of, and demand for, mobile telecommunications continue to increase at a staggering rate. Wireless telecommunications service providers are constantly seeking new ways to improve and expand the services they provide while lowering their investment and operational costs. This ever-increasing demand has driven the development of new and improved topologies and protocols for wireless communications systems. It is now possible to route voice communications, in packetized form, over Internet Protocol (IP) systems conventionally associated with computer data communications. Such capabilities hold the promise increasing efficiency and decreasing costs associated with wireless communications. 
     Interest grows in IP-based communications as an alternative to conventional circuit switched systems. Circuit switched systems require dedicated channels, reserving an ISUP (ISDN user part) link for any given communication. Therefore, any given call effectively monopolizes a line (e.g. trunk or E1/T1 line) between call origin and destination; requiring a separate line for each call processed. Even in conventional “wireless” communications systems, a call is generally only wireless between the mobile unit and its closest base station, which thereafter typically routes the call on circuit switched infrastructure. For example, in a typical GSM (Global System for Mobile communications) network, once a signal is received at the base station, it is thereafter routed via circuit switched infrastructure to the mobile switching center (MSC) and the rest of the GSM system. 
     It should thus easily be appreciated that as demand continues to increase, infrastructure associated with circuit switched systems must increase correspondingly. This results in increased system overhead, reduced call volume bandwidth, and increased user costs to cover the additional overhead. 
     In comparison, IP communications packetize voice data for transmission over existing IP networks; enabling users to communicate (e.g. via phone calls or computer-based conferencing applications) as long as they want for only the cost of the access to the IP network. IP infrastructure is ubiquitous; and use of IP infrastructure is not dedicated (i.e. multiple users utilize, one packet at a time, the same resources), lowering system overhead and use costs. 
     Although IP network communication is, in some respects, advantageous over circuit switched communication, other considerations limit the commercial usefulness of conventional IP network implementations. Consider, for example, a wireless communications scenario where communication originates in a radio access network (e.g., universal mobile telephony system (UMTS)), is transferred across an IP based core network (backbone), and is delivered to an external, circuit-switched network (e.g., public switched telephone network (PSTN)). Generally, radio access networks typically utilize low bit rate speech encoding (e.g., 13 Kb/s), while traditional circuit switched networks utilize high bit rate speech encoding (e.g., 64 Kb/s). Conversion and formatting from one encoding to the other is required to successfully deliver speech data from one network to the other. The conversion and formatting functions are usually executed by a CODEC (Coder-DECoder). 
     Conventional communications systems generally perform the conversion from lower bit rate encoding to higher bit rate encoding as the data enters the network backbone. As data from the radio access network enters a media gateway (MGW) that serves as its interface with the IP backbone, the conversion is executed by a CODEC in the media gateway. The data is then transferred across the IP network at the higher bit rate encoding, delivered to another MGW for transfer to the external public network. Thus, the higher bit rate encoded speech must be packetized for transmission over the IP backbone. This is less efficient than packetizing and transmitting the lower bit rate encoded speech, and decreases effective system bandwidth. In many conventional systems, even where the call will terminate in a similar radio access network, speech data is superfluously converted twice: from low to high bit rate upon entering the IP backbone, transmitted over the IP backbone at high bit rate, and from high to low bit rate upon transfer out of the IP backbone. This is obviously inefficient, and degrades overall system performance. 
     Some previous systems have attempted to overcome these limitations by eliminating the conversion to the higher bit rate altogether. This is typically achieved by negotiation of the CODEC in the terminating MGW (i.e. the one receiving the call) with the CODEC in the originating MGW, whereby each CODEC essentially performs no conversion. Speech data is thus introduced to, transmitted over, and delivered from the IP backbone at the lower bit rate encoding. Although this approach is, in certain ways, advantageous over prior solutions, it is still impractical as it Liz fails in many common call flow scenarios, such as call forwarding to a PSTN. This results in reduced system reliability or, alternatively, system inefficiency due to redundant call processing and constructs. 
     SUMMARY OF THE INVENTION 
     From the foregoing, it can be appreciated that a need exists for a providing efficient, reliable, and cost-effective IP network communication in a variety of wireless telecommunication applications. It is desirable that such a system provide robust and versatile structure and methods by which low bit rate encoded data may be transported over a packet based network, even if the destination for the data is a high bit rate external network; overcoming the limitations of conventional systems. 
     The present invention provides a system for low bit rate encoded data transport over a packet based network, regardless of whether the destination for the data is a low or high bit rate network. The present invention provides a dual CODEC functionality by which conversion to high bit rate encoding is executed after transport across a packet based network, and only when required by the terminating network. 
     More specifically, the present invention provides a packet-based telecommunication system comprising a first media gateway having a first CODEC structure and a second media gateway having a dual function CODEC structure, wherein the dual function CODEC structure is adapted to provide tandem free operation between itself and the first CODEC structure. 
     The present invention further provides a dual function CODEC, utilized in packet based telecommunications, comprising a first element adapted to negotiate tandem free operation, and a second element communicatively coupled to the first element and adapted to selectively convert data coding responsive to the first element. 
     The present invention also provides a method of providing efficient communication between a low bit rate network and a high bit rate network over a packet based network by providing within the packet based network a first CODEC associated with the low bit rate network, providing within the packet based network a second CODEC associated with the high bit rate network, transferring low bit rate data from the first CODEC to the second CODEC, and using the second CODEC to convert the low bit rate data received from the first CODEC to high bit rate data. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figure in which: 
     FIG. 1 is an illustrative diagram of one embodiment of a communications network configured according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While the making and the use of the present invention is discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts which can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention, do not delimit the scope of the invention. 
     The present invention defines a system providing efficient transport of coded data over a packet-based core network, and efficient, reliable, and cost-effective IP network communication in a variety of wireless telecommunication applications. The present invention provides robust and versatile structure and methods by which low bit rate encoded data may be transported over a packet based network, regardless of whether the destination for the data is a low or high bit rate network. The present invention provides a dual CODEC functionality by which conversion to high bit rate encoding is executed after transport across a packet based network, and only when required by the terminating network. 
     It should be understood that the principles and applications disclosed herein can be applied to a wide range of wireless telecommunications systems where communication across a packet based network between two or more differing bit rate networks is required. The teachings of this disclosure may be applied in adapting a variety of system topologies and protocols. For purposes of illustration and explanation, the present invention is hereafter described in reference to a UMTS access and core network, and UMTS and PSTN terminating networks. 
     Summarizing briefly, the present invention provides for low bit rate Adaptive Multi Rate (AMR) coded speech to be transferred over a UMTS IP backbone, even if the call will terminate on an external (e.g., PSTN) network. When a UMTS mobile call will terminate on an external network, a tandem free operation (TFO) capable dual CODEC is activated in a MGW interfacing with the external network. The first portion of this dual CODEC attempts negotiating TFO with the CODEC in the MGW interfacing with the access network. If TFO negotiation is successful, low bit rate coded speech can be transported over the backbone network. In that case, the second portion of the dual CODEC translates the low bit rate coded speech into high bit rate coded speech (e.g., 64 Kb/s PCM), before terminating on the external network. 
     If, however, TFO negotiation between the dual CODEC and the CODEC in the MGW interfacing with the access network is not successful, TFO is negotiated between the 2 potions of the dual CODEC. In this case, 64 Kb/s PCM is transported over the backbone, but no coding is done in the MGW interfacing with the external network. 
     For a more detailed description, reference is now made to FIG.  1 . FIG. 1 depicts a wireless communications system  100  illustrating various aspects of the present invention. System  100  may generally comprise a first access network  102  (e.g., a radio access network), an IP-based core network  104 , and a second access network, of similar or different configuration and topology as network  102 . Two such varieties of second access networks are illustrated, a radio access network  106  and an external public network (e.g., PSTN)  108 . 
     Network  102  may comprise a radio network controller (RNC)  110  communicatively coupled to one or more base telephony stations (BTS)  112 . Each BTS  112  may have one or more mobile subscriber units (i.e. a cell phone)  114  communicatively associated therewith. For purposes of illustration and explanation, network  102  and unit  114  will hereafter be assumed as call origination. 
     Network  106  may comprise a radio network controller (RNC)  116  communicatively coupled to one or more BTS  118 . Each BTS  118  may have one or more mobile subscriber units  120  communicatively associated therewith. Network  108  may comprise a variety of circuit switched and land based infrastructure (not shown), providing communications capabilities to user unit  122 . 
     Network  104  may comprise an originating MGW  124 , associated and communicatively coupled with network  102 . Network  104  may also comprise a terminating MGW  126 , associated and communicatively coupled with either (or both) terminating networks  106  and  108 . MSCs  124  and  126  are communicatively coupled together via link  128 , which may comprise a variety of other structures and protocols not shown within network  104 . MGW  124  comprises a CODEC structure  130 . MGW  126  comprises a dual function CODEC structure  132 . Structure  132  comprises first element  134  and second element  136 . Elements  134  and  136  may comprise separate CODEC structures that inter-operate to functionally render structure  132 , or elements  134  and  136  may comprise distinct functional portions of a single CODEC structure  132 . 
     As communication is initiated by unit  114  through network  102 , low bit rate encoded data (e.g., 13 Kb/s) is transferred over  138  to CODEC  130 . Assuming that the call destination is unit  120  in network  106 , which is of a compatible data encoding to network  102 , the data does not require conversion to high bit rate encoding. Element  134  negotiates with CODEC  130 , via link  128 , for both to abstain from any code conversion. Thus, the tandem of CODEC  130  and CODEC element  134  are free from coding operation, hence tandem free operation (TFO). The data transfers  140 , in 13 Kb/s format, over the IP backbone to element  134 , where it is then transmitted  142  to network  106  for delivery to the terminating unit  120 . Bandwidth for the transfer  140  is thus increased by nearly 500%. 
     Assuming now that the call destination is unit  122  in network  108 , the call data will require conversion to 64 Kb/s before entering network  108 . The present invention, however, attempts to transport the data across the IP backbone via TFO (at the low bit rate encoding); realizing improved bandwidth advantages and performing the code conversion just before delivery to external network  108 . Element  134  attempts negotiating TFO with CODEC  130 . If TFO negotiation is successful, the data transfer  144  between CODECs  130  and  132  is low bit rate coded speech. After that transfer, element  136  translates the low bit rate coded speech into high bit rate coded speech before transfer  146  to terminating network  108 . 
     If TFO negotiation between element  134  and CODEC  130  is not successful, CODEC  130  performs conversion to high bit rate encoded data and transfer  144  is at the high bit rate. TFO is negotiated between elements  134  and  136 , such that no further coding is done to the data in MGW  126  before transfer  146  to terminating network  108 . 
     The present invention thus provides independent CODEC elements; one performing TFO negotiation and establishing low bit rate transfers over the packet based backbone, and that may be switched in to provide conversion to high bit rate encoding when required. Thus, the limitations of conventional systems (e.g., in call forwarding scenarios) are overcome. 
     The embodiments and examples set forth herein are presented to best explain the present invention and its practical application and to thereby enable those skilled in the art to make and utilize the invention. However, those skilled in the art will recognize that the foregoing description and examples have been presented for the purpose of illustration and example only. For example, although the present invention has been described herein within the context of UMTS wireless and PSTN telecommunications networks, the present invention may be implemented in any of a number of different telecommunications systems. The description as set forth 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 without departing from the spirit and scope of the following claims.