Electrical computers and digital data processing systems: input/ – Input/output data processing – Transfer direction selection
Reexamination Certificate
1998-06-08
2001-02-27
Lee, Thomas C. (Department: 2782)
Electrical computers and digital data processing systems: input/
Input/output data processing
Transfer direction selection
C710S105000, C710S120000, C370S352000, C370S395430, C370S400000, C370S466000
Reexamination Certificate
active
06195714
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to synchronous transfer mode (STM) call completions and, in particular, to the completion of calls which originate and terminate in an STM network but at least a portion of the call connection is completed using an asynchronous transfer mode (ATM) network.
BACKGROUND OF THE INVENTION
The public switched telephone network (PSTN) is a synchronous transfer mode (STM) network in which time division multiplex (TDM) switches are interconnected by transport links commonly referred to as “trunks”. Each trunk supports a plurality of “channels” which are time slots used by individual calls. Although the STM network is reliable and robust, the demand for voice and other voice-band data services is taxing the capacity of current network facilities.
Consequently an interest has developed in using alternate facilities to complete voice grade connections. Many local exchange carriers (LECs) are experiencing tandem network congestion and are seeking economical ways to grow their tandem networks. Inter-exchange carriers (IECs) would like to consolidate their voice and data traffic on a single multi-service network. The currently most attractive alternate facility is a network which operates in an asynchronous transfer mode (ATM) protocol. ATM has a now matured to an extent that it provides a viable alternative to STM facilities.
ATM uses a fixed data packet size of 53 octets called a “cell”. A cell includes a header of 5 octets and a payload of 48 octets for transferring user information. There are known methods for converting STM voice and voice-band call data to ATM cells and vice versa.
Call setup and control in the PSTN is commonly effected using an out-of-band signaling network known as a common channel signaling network. Most of the North American PSTN is equipped to operate with a common channel signaling protocol called Signaling System
7
(SS
7
). ATM networks, however, use a different signaling protocol in which signaling messages are transported through the network in cells like those used for carrying payload data. The signaling systems of the PSTN and ATM networks are therefore incompatible and STM calls cannot be transferred directly to or from an ATM network.
Methods and apparatus for transferring voice and voice-data services over ATM networks are known, however. One ATM network architecture designed for that purpose is described in U.S. Pat. No. 5,568,475 entitled ATM NETWORK ARCHITECTURE EMPLOYING A COMMON CHANNEL SIGNALING NETWORK, which issued Oct. 22, 1996 to Doshi et al. In the ATM network architecture described by Doshi et al, each switch in the ATM network is equipped with a signal processor that is capable of sending and receiving common channel signaling messages. The signal processor translates STM trunk identification information into ATM Permanent Virtual Circuit (PVC) information to permit STM calls to be transported through the ATM network using virtual trunks. While this ATM architecture provides an option for a migration of PSTN voice services to an ATM protocol, it appears to suffer from certain drawbacks. First, the architecture requires that all ATM switches be enabled with SS
7
signaling capability and that the SS
7
network overlay the entire ATM network. Second, the use of PVCs in the ATM network has the potential to tie up ATM resources unnecessarily, preventing those resources from being used for other purposes, even during off-peak calling hours.
There therefore exists a need for a method and apparatus for transferring STM calls in a multi-service ATM network which requires only a small investment in infrastructure and ensures efficient use of ATM network resources.
Simply transferring STM calls through an ATM network to relieve congestion in the PSTN is not in itself enough, however. In North America, the current call setup rate is 4,000,000 calls per busy hour and PSTN usage is expected to double over the next five years. Despite the current call volume, call setup within an STM node requires only 20 msec, and service is delivered with 99.999% availability.
There therefore exists a need for a method and apparatus for transferring STM calls in a multi-service ATM network which ensures that calls transferred through the ATM network are rapidly set up so that current PSTN service levels are sustained.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a method of transferring STM calls through an ATM network by provisioning ATM edge nodes with apparatus which is adapted to send, receive and interpret common channel signaling messages related to STM calls and to dynamically map STM trunks to switched virtual circuits in a multi-service ATM network.
It is a further object of the invention to provide a method for transferring STM calls through a multi-service ATM network in which native ATM signaling is used in the ATM network.
It is yet a further object of the invention to provide a method of transferring STM calls through an ATM network in which cached switched virtual circuits (SVCs) are used for STM calls.
It is a further object of the invention to provide a method of transferring STM calls through an ATM network in which cached cross-connections are also used for STM calls.
It is another object of the invention to provide an apparatus for transferring STM calls through an ATM network, the apparatus including a voice interface control unit associated with each edge node in the ATM network.
It is a further object of the invention to provide an apparatus for transferring STM calls through an ATM network which includes a signaling interface to receive and send common channel signaling messages associated with STM calls.
It is yet a further object of the invention to provide an apparatus for transferring STM calls through an ATM network in which the voice interface control unit dynamically maps a trunk channel carrying the cell to an SVC in the ATM network.
It is yet a further object of the invention to provide an apparatus for transferring STM calls through an ATM network in which the voice interface control unit exchanges messages with a peer associated with a destination edge node in the ATM network to enable the peer voice control unit to set up egress of the call from the ATM network to a trunk in the STM network.
In accordance with a first aspect of the invention, there is provided apparatus for enabling the transport of synchronous transfer mode (STM) calls through an asynchronous transfer mode (ATM) network, the apparatus being associated with each edge node in the ATM network designated to serve as a gateway for the STM calls, comprising in combination:
a signaling interface adapted to receive and send common channel signaling messages associated with STM calls transferred to the ATM network;
a voice interface control unit adapted to route calls through the ATM network when an STM call seeks admission at the associated edge node, and to set up egress of a call from the ATM network when the associated node is an ATM destination node for the call; and
a TDM peripheral device for terminating STM trunks and converting STM calls to ATM cells and vice versa.
In accordance with a further aspect of the invention, there is provided a method of transferring synchronous transfer mode (STM) calls through a multi-service asynchronous transfer mode (ATM) network comprising:
provisioning ATM edge nodes for the ingress and egress of the STM calls, each edge node having an associated TDM peripheral adapted to convert STM calls to ATM cells and vice versa, a signaling interface adapted to send and receive common channel signaling messages related to STM calls transferred to an associated edge node for admission to the ATM network, and a voice interface control unit which is adapted to route STM calls through the ATM network and setup the egress of STM calls routed through the network by another voice interface control unit; and
using native ATM signaling to set up switched virtual circuits between edge nodes for the STM calls.
In accordance with yet a further aspect of the invention, th
Li Li
Morris Todd Douglas
Du Thuan
Lee Thomas C.
Nortel Networks Limited
Wood Max R.
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