Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
2000-02-07
2004-02-17
Vu, Huy D. (Department: 2665)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S467000, C370S352000, C455S439000, C455S517000, C709S227000, C709S228000
Reexamination Certificate
active
06693886
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to conducting communications over packet-switched networks such as Internet Protocol (IP) networks. More particularly, the present invention relates to conducting mobile communications over IP networks.
Voice or telephony services can now be provided over packet-switched networks, such as the Internet. These packet-switched networks are commonly referred to as IP networks, IP telephony networks or Voice over IP (VoIP) networks because the Internet Protocol according to various IP based standards is the primary protocol used. One such IP based standard, for example, is the International Telecommunication Union (ITU) H.323 Standard.
The H.323 Standard provides a foundation for audio, video, and data communications across IP networks. By complying with the H.323 Standard, multimedia products and applications from multiple vendors can interoperate, allowing users to communication without concern for compatibility. The H.323 Standard is part of a larger series of communications standards that enable audio video conferencing across a range of networks.
The H.323 Standard defines four major components for network based communications, namely, terminals, Gateways (GW) Gatekeepers (GK) and Multipoint Control Units (MCU).
Terminals are the client endpoints on the network that provide realtime two-way communications. All terminals which comply with the H.323 standard must also support the ITU H.245 Standard, which is used to negotiate channel usage and capabilities. Further, terminals which comply with the H.323 standard are required to implement the ITU Q.931 and the H.225 standards for call signaling and call setup, including for example, Registration/Admission/Status (RAS) processing. Optional capabilities in terminals which comply with the H.323 standard are MCU capabilities.
A gateway is an optional element when implementing the H.323 standard. Each gateway provides many services the most common being a translation function between the H.323 standard conferencing endpoints and other terminal types. Each gatekeeper acts as a central point for all calls or communications within a zone serviced by the gatekeeper and provides call communication control services to registered endpoints. The gatekeeper could be considered a virtual switch. The MCU supports conferences between three or more endpoints.
Each of the above described endpoints, GW, GK, and MCU can be implemented by use of apparatus such as a personal computer (PC), workstation, server, etc.
The above described H.323 standard as defined is intended to operate in fixed packet-switched networks where the endpoints, for example, terminals such as workstations, PC's, etc., that conform to the H.323 standard, do not move to a new zone serviced by another gatekeeper. Further, packet-switched networks defined according to the above described H.323 standard are not intended to accommodate the communications (i.e., message signaling) between a Mobile Station (MS) and a Mobile Services Switching Center (MSC). Such message signaling is defined according to e.g., the GSM or the Code Division Multiple Access (CDMA) standards.
In a typical mobile system (e.g., GSM), the signaling between each MS and the MSC is based on circuit switched connectivity, (e.g., in GSM system Signaling Connection Control Part (SCCP)/Link Access Protocol on the D-Channel (LAPD)/Link Access Protocol on the Dm-Channel Message (LAPDm) connectivity that is achieved by using dedicated timeslots in A- and Abis-interfaces). Since a timeslot based circuit switched connectivity model is used, there usually is not any addressing information present in signaling messages. The timeslot itself, is sufficient for addressing the circuit switched connection to the MS. Also, whenever there are more than one simultaneous logical signaling connection between the MSC and one MS, all of these logical connection transactions use the same circuit switched connection for signaling needs. The different logical connections are distinguished by Protocol Discriminator and Transaction Identifier (TI) parameters. For call control purposes the two first parameters are always the same, but the TI distinguishes between two (or more) logical call control sessions. Such as, for example, where one call is active and another is on hold. It should be noted that each TI must be unique for the MS.
IP telephony networks, on the other hand, do not rely on timeslot-based circuit switched connectivity. In H.323 based telephony networks the signaling is done using H.225.0 standard call control messages that provide logical call identifier and are transmitted over Internet Protocol (IP) connections. An IP telephony network may prefer a centralized signaling model, in which signaling messages, between endpoints A and B are routed through the logical switch (e.g., GK or Call Processing Server (CPS)). For Example, each connection between endpoints A and B according to the Q.931 standard includes A-GK and GK-B legs. Each connection is distinguished by a Call Identifier (ID). The same Call ID is used for both legs of the end-to-end connection.
Since in a mobility aware IP telephony network it is possible that one transaction is external (controlled the by MSC) and another internal (controlled by the GK), there is a strong possibility that TIs used for these transactions may clash. This can occur due to the fact that the MSC is not aware of the internal call transactions. An external call is one that is signaled through the network gateway (NW-GW) and possibly controlled by an external switch such as the MSC. An internal call on the other hand is one that is signaled entirely within the IP telephony network or a sub-network thereof (except with respect to the radio interface) and is controlled by the logical switch of the sub-network such as the GK.
Two alternatives have been proposed to solve the above noted problems.
The first alternative provides only one IP telephony call control connection per active MS and then tunnels simultaneous mobile (cellular) call control messages inside that same IP telephony call control connection. Thus, mapping is performed only between mobile identity which corresponds to circuit switched connectivity, and the IP telephony call control connection. Such is performed without taking the TI into consideration, except for performing TI reallocation when TI clashes occurs.
The second alternative provides for the opening of one “raw” IP connection per active MS and then tunneling all IP telephony call control messages through the one “raw” IP connection.
The above described first alternative has one clear benefit, in that handover is easier since only one IP telephony call control connection needs to be re-routed. However, a disadvantage of the first alternative is that support of supplementary services is virtually impossible. Since the same Call ID namely, the same IP telephony call control connection, is used for all calls per MS, then it would be very hard to make call transfers for any individual call. Also, the first alternative may easily lead to situations where the Call ID isn't end-to-end anymore. Namely, the Network Gatway (NW-GW)-GK leg and GK-Radio Access Gateway (RA-GW) leg of the same call may have different Call ID's. This increases the complexity of the GK.
The second alternative has some advantages, the handover is easier since only one IP telephony call control connection needs to be re-routed. The second alternative also allows for supplementary services support. However, neither alternative is H.323 standard compliant and therefore they do not suit well to an IP telephony network.
To solve the above mentioned TI clashes between internal and external calls, the above described alternatives propose that the GK change the TI value of the external call in such a way that the MSC notices no change. Namely, towards the MSC the GK uses the TI value allocated by the MSC and towards the MS the GK uses some other TI value such as 2.
The above solution however has one major disadvantage. Since the MSC and t
Haikonen Janne
Pruuden Peeter
Antonelli Terry Stout & Kraus LLP
Molinari Michael
Nokia IP Inc.
Vu Huy D.
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