Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2000-08-07
2004-04-13
Maung, Nay (Department: 2684)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C370S331000
Reexamination Certificate
active
06721565
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to telecommunications systems, and more particularly to systems and methods for supporting handover of wireless calls between wireless telecommunications systems or components thereof which support differing call models, including circuit and packet call models.
BACKGROUND OF THE INVENTION
An important feature in many wireless telecommunications systems is mobility, whereby a user involved in a call may move from a first location supported by a first set of wireless infrastructure equipment, to a second location supported by a second set of wireless infrastructure equipment, without significantly disrupting the call. Many early wireless telecommunications systems were developed to provide mobile telephone service. Early mobile telephone systems typically employed a single radio base station positioned to cover a large geographic area, albeit with limited capacity. A mobile user could travel widely within the covered area and expect to maintain a call provided that the user did not move to a location where the radio-frequency path to the base station became unusable. When cellular mobile telephone systems, comprising a large number of radio base stations each serving much smaller adjacent areas or “cells”, were developed, it was essential to allow users involved in calls to move from cell to cell throughout the system's coverage area without disrupting the call.
The function and implementing processes of causing a stable call currently being served by a first radio base station (or another similar element of a wireless system providing an over-the-air interface) to be served by a second radio base station are referred to as a “handoff” or “handover”. Handovers were initially provided among cells of a single system and of like technology. However, standard protocols have been developed to allow handovers among cells of different systems, and to allow handovers among cells and/or systems of differing technology. For example, standard protocols allow calls to be maintained as users cross boundaries from one wireless system to another system, perhaps operated by a different entity and using a different type or brand of infrastructure equipment. For example, protocols of this type include the standardized intersystem operations protocol known as ANSI-TIA/EIA 41-D: Cellular Radiotelecommunications Intersystem Operations, a publication of the American National Standards Institute, and the GSM 09.02 Mobile Application Part (MAP) protocol, a publication of the European Telecommunications Standards Institute (ETSI). Moreover, standard protocols have also been developed to permit handovers among systems/cells of differing (but cooperative) air interface technologies using the same call model. For example, some subscriber handsets and system infrastructure equipment may execute a handover of a call from a cell employing digital transmission technology, such as CDMA or TDMA, to a cell employing analog transmission technology, such as AMPS. The capability of performing handovers between GSM and UMTS systems has also been described. Although the need for mobility historically may have motivated the use of handovers, handovers can provide important functionality even in applications which do not require mobility by allowing load balancing and improving reliability.
Existing wireless telecommunications systems which provide handovers have employed a circuit call model. The term “call” is used herein to refer to a session of information transfer between a set of terminals via a telecommunications system or network, and is intended to include, but not be limited to traditional circuit voice calls, packet voice calls, circuit data calls, connectionless calls, or packet data calls, and multimedia variants thereof. The term “circuit” as applied to a call refers to a mode of information transfer which occurs between defined endpoints over reserved network resources, and in which units of data are not individually addressed. Once a path or route is established for a circuit call, no further routing or addressing is required. It is recognized that some components carrying a circuit call may be implemented using packet- or cell-based technologies. The term “packet” as applied to a call refers to a mode of information transfer in which a stream of information is divided into packets or units, and in which each packet or unit is individually addressed. A packet call does not necessarily reserve network resources. The term “call model” refers to the procedures, states, and state transitions required to set up, maintain, modify, and end a call. A circuit call model is a call model used to establish and control circuit calls. Examples of known circuit call models include: ITU-T Signaling System No. 7, ANSI-41, ANSI-136, ANSI-95, and GSM 04.08. A packet call model is a call model used to establish and control packet calls. Examples of known packet call models include IETF RFC-2543 (Session Initiation Protocol (SIP)) and ITU Specification H.323.
New telecommunications systems, including wireless systems, have been proposed or are being developed which employ a packet call model. Packet call models imply that during a call, certain resources and facilities may be allocated on an as-needed basis to carry the call's bearer traffic, and that the particular resources and facilities used may vary with each packet. Packet systems may support an end-to-end packet call—that is, a call where each terminal is adapted for packet communications, and the call is carried over a packet network. However, a large fraction of the world's telecommunications infrastructure employs circuit technology, and therefore, many packet systems are being designed to interwork calls with existing circuit networks, at least at certain well-defined interfaces. Thus, a call could originate at a packet terminal, but be terminated at a circuit terminal, or vice versa. Systems for interworking calls in conventional land-side packet and circuit networks are known in the art, and such a system is sold by Lucent Technologies, Murray Hill, N.J., under the designation PACKETSTAR Voice Gateway.
New packet wireless systems are likely to be constructed in phases, and it is likely that such systems will initially be deployed to overlay existing circuit wireless systems, in which system operators have made extremely large investments. Accordingly, it will be desirable to provide handovers between packet and circuit system for suitably equipped subscriber handsets and other terminals. Such handovers, advantageously, would allow subscribers to be served by the new packet system in locations where it is available, and to be served by the existing circuit system in locations where the packet system is not available or temporarily lacks capacity. In addition to providing for mobility, handovers between these systems would also allow load balancing and improve reliability.
However, existing circuit systems have employed network topology and handover processes which are uniquely suited to the circuit call model. In particular, commercially deployed circuit systems employ an anchor Mobile Switching Center, or “anchor MSC”, to control a call throughout its duration. The anchor MSC is generally the first MSC to have substantive control over a call. During a call, even though the user may move into the service area of another system, which generally would be controlled by a different MSC, certain other features are controlled by the anchor MSC, and the call's bearer traffic is routed through the anchor MSC. The current serving MSC controls handoffs.
The topology of packet wireless systems, according to proposed standards, differs significantly from that of existing circuit wireless systems. In particular, in proposed packet wireless systems, the system elements providing control functions may be different from the system elements providing switching, transmission, and vocoding functions. The packet wireless systems do not employ an anchor MSC component. Furthermore, packet wireless networks employ both
Ejzak Richard Paul
Gafrick John Matthew
Lassers Harold Aaron
Martin Ronald Bruce
Lucent Technologies - Inc.
Maung Nay
Trinh Tan
LandOfFree
Handover of wireless calls between systems supporting... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Handover of wireless calls between systems supporting..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Handover of wireless calls between systems supporting... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3226836