GB2429373A - Maintaining location information at a node of a communications network - Google Patents

Abstract

In a UMTS telecommunications network, traffic to and from a home location register (HLR) is reduced by maintaining location information for a mobile terminal at a communications node. A network has several SGSNs (serving GPRS support nodes) handling mobile terminals, each SGSN being responsible for a number of RAs (routing areas). One SGSN 152 is designated as an 'anchor' node which stores location information on mobile terminals within a 'pool' of RAs for which that anchor SGSN is responsible. If a mobile moves from one SGSN 156 to another SGSN 158 in the same pool of RAs, then location information is sent only to the anchor SGSN 152 and not to the HLR of the network. If a mobile moves from pool to pool, then information is updated to the HLR. The anchor node stores location information for a mobile within its pool with no requirement to update the HLR, thus reducing traffic on the network. The pools of RAs would be configured to cover e.g. a town and the system would allow a user terminal to move around the town without updating the HLR as the user location is stored in the anchor SGSN of the pool.

Description

ANCHOR METHOD FOR A TELECOMMUNiCATIONS SYSTEM The present invention

relates to an anchor method for a telecommunication system.

In conventional UMTS systems the Home Location Register (HLR) is used as a location database for user terminals located within a network. In a packet switched domain, the serving GPRS support node (SGSN) and the gateway GPRS support node (GGSN) cooperate with the HLR to perform registration of the user terminals.

Each SGSN in a network controls one or more routing areas. A user terminal signals to the SGSN when it moves between routing areas. The SGSN informs the HLR, which updates its record as to the location of the user terminal.

A drawback with this method is that a significant amount of signalling is required, which increases costs within the network.

It would therefore be desirable to limit the signalling required within the current system.

According to the present invention there is provided telecommunication system comprising a user terminal and a plurality of communication nodes, wherein the communication nodes are associated with a pool of routing areas, wherein one communication node is selected as an anchor communication node and maintains location information whilst the user terminal is within the pool of routing areas.

Preferably, each communication node is uniquely associated with a plurality of routing areas within the pool of routing areas.

It is preferred that if a user terminal moves from a first routing area to a second routing area, each routing area being uniquely associated with the same communication node, location information is maintained by the communication node.

It is preferred that if a user terminal moves from a first routing area associated with a first communication node, to a second routing area associated with a second communication node, location information is updated to the anchor communication node.

Preferably, the system further comprises a home location register that is updated for a given user terminal only when said user terminal leaves a designated pool of routing areas.

It is particularly preferred that when a user terminal moves to a routing area in a different pool, the communication node associated with that routing area transmits updated location information to the home location register.

It is preferred that if the user terminal leaves the pooi of routing areas, and enters a second pool, a new anchor communication node is selected.

Preferably, the system further comprises a high level communication node that maintains a register of which individual user terminals it initiated most call/sessions.

Preferably the information maintained regarding the communication node and high level communication node with most call/session initiations for a specific user terminal is used to maintain the user terminal's location for a future incoming call/session.

Preferably, the home location register maintains a record of which communication node and which high level communication node originate high cal]lsession rates for each individual user terminal.

Preferably the high level node that is determined to originate most calls to a user terminal is nominated as a frequent session caller for that terminal.

When a call session is initiated, the high level communication node may determine whether it is the frequent session caller for that terminal. If it is not, it is preferred that the high level communication node requests location information from the home location register.

In the above arrangements it is particularly preferred that the communication nodes are SGSNs and the high level communication node is a GGSN.

According to a second aspect of the present invention there is provided a communication node associated with a plurality of routing areas, operable to maintain location information for a user terminal whilst said terminal remains within the plurality of routing areas.

According to a third aspect of the present invention there is provided a method of monitoring the location of a user terminal, comprising the steps of: determining when a user terminal is located within a plurality of routing areas; instructing a communication node to maintain location information whilst the user terminal is within said plurality of routing areas; and notifying a home location register only when said user terminal leaves said plurality of areas.

In a preferred step, means is provided to record which high level communication node initiates call/sessions to each user terminal.

Preferably, for a call/session to a particular user terminal, recorded information on the communication node and high level communication node is used to determine the location of the user terminal.

In order that the present invention be more readily understood specific embodiments thereof will now be described with reference to the accompanying drawings.

Figure 1 shows a structure of parts of a UIMTS communication system; Figures 2 and 3 show an overview of parts of a UMTS communication system; Figures 4 and 5 illustrate and updated procedure according to the present invention; Figure 6 shows an example of a routing area pool arrangement; Figure 7 shows an example of reference signalling network architecture; Figure 8 shows a graph of estimated costs associated with the present invention; and Figure 9 is a flow chart describing a routing area update with reference to figs 4 and 5.

A communication system such as a telecommunications system comprises a plurality of user terminals, such as mobile phones, in radio communication with a base station, referred to hereafter as an access point, provided within a cell.

Figure 1 is a diagram schematically illustrating a structure of a conventional UMTS communication system. The UMTS communication system comprises a core network (CN) 100, a plurality of radio network subsystems (RNSs) 110 and 120, and a user terminal M. Bach of the RNSs and 120 comprise a radio network controller (RNC) and a plurality of access points (each handling a cell). More specifically, RNS 110 comprises RNC 111 and a plurality of access points 113 and 115, and the RNS 120 comprises an RNC 112 and a plurality of access points 114 and 116. The RNCs are classified as either a Serving RNC (SRNC), a Drift RNC (DRNC), or a Controlling RNC (CRNC), according to their functions. The SRNC and the DRNC are classified according to their functions for each user terminal.

An RNC that manages information on a user terminal and controls data exchange with a core network is an SRNC, and when data of a user terminal is transmitted to the SRNC, not directly but via a specific RNC, the specific RNC is called a DRNC of the user terminal.

The CRNC represents an RNC controlling each of the access points.

For example, in figure 2, if the RNC 111 manages information on the user terminal M, it serves as an SRNC of the user terminal M, and if data of the user terminal M is transmitted via the RNC 112, due to movement of the user terminal M, the RNC 112 becomes a DRNC of the user terminal M. The RNC 111 controlling the access point 113 becomes a CRNC of the access point 113.

The core network includes, for example, an Internet Protocol (IP) backbone network or other packet network, and/or a circuit switched (standard telephony) network. It will not be discussed further since it is of conventional type.

Each access point comprises a radio transmitter apparatus and a radio receiver apparatus, operating under the control of a control system comprising one or more programmable computers, so that it can send data to and receive data from the user terminals on the data downlink and data uplink respectively, and to and from the RNC. It can also control some aspects of the communications links within its cell, and to this end it can send signalling data to and receive signalling data from the user terminals on the signal downlink and signal uplink respectively.

Each user terminal comprises a radio transmitter apparatus and a radio receiver apparatus, operating under the control of a control circuit, together with a battery and/or other power supply, a user interface including input and output devices, and an output port for connection to other devices (such as a computer).

As these aspects of the equipment are conventional, well known to the reader, and unnecessary for an understanding of the present invention, further details are omitted herein.

Figure 2 shows a further overview of a UMTS communication system.

The system comprises a base station controller 150 controlling a plurality of access points 113, 114, 115, 116. A serving GPRS support node (SGSN) 152 controls the BSC 150 and the access points 113, 114, 115, 116. Together, these elements control network parameters, including a movability management function such as radio channel allocations, compression power levels, encryption and also charges to subscribers.

A SGSN is also operable to link with further SGSNs with the same network.

A Gateway GPRS support node (GGSN) 154 typically is connected to a number of SGSNs (although only one connection is shown in Figure 2) and also to the external network (such as the internet). The GGSN 154 supports the edge routing function of the network, and, to external packet data networks performs the operation of an IP router. The GGSN 154 also performs firewall and filtering functionality to protect the integrity of the GPRS core network 100.

Typically an SGSN 152 controls one or more routing areas (RA). In a network, a user terminal M transmits information to the SGSN 152 regarding its current routing area. Each RA is allocated a routing area identification (RAI). The RAI is composed of a location area code that uniquely identifies an area within the network, and a routing area code operable to identify a routing area within a location area.

Figure 3 shows an example of further architecture of a IJMTS communication system. This comprises a home location register (HLR) 200 that functions as the main network database. The information stored in the HLR 200 relates to all of the user terminals registered with that network. The GGSN 154, SGSN 152 and HLR 200 control the location registration of each user terminal in the network. Accordingly, if a call is made to a specific user terminal the network is able to locate the user terminal and set up the call session.

Each user terminal comprises a packet mobility management (PMM) function that controls core network level tracking. When the PMM is in an idle state, location of a given user terminal is known within an accuracy governed by the RAI, and paging is required to contact the user terminal M. When a packet switch signalling connection is established between the user terminal and the SGSN 152, the user terminal enters the PMMCONNECTED state and the SGSN 152 tracks the user terminal with the accuracy of the serving RNC (SRNC). A normal RA update takes place when a PS-attached user terminal (either in PMM-CONNECTED or in PMM-IDLE state) detects that it has entered a new RA. A PMM-JDLE user terminal also performs a periodic RA update when an external timer has expired.

Additionally, in a conventional system SGSNs belonging to the same local signalling area (LSA) are connected to each other through a local signalling transfer point (LSTP). All LSAs within the same region are connected to a regional signalling transfer point (RSTP).

From the foregoing it will be appreciated that the HLR 200 requires notification for every location registration and call/session delivery. This could result in increased call/session set up delay during busy periods in the network, and placing strain on the network and increase costs.

In the present arrangement, as shown by Figure 4, each SGSN 152, 156, 158 is associated with a plurality of routing areas.

The location of the user terminal is reported to an Anchor SGSN 152 located in the pooi area instead of the HLR as long as the user terminal roams within the pool area. For a given user terminal the serving SGSN during the last call arrival is preferably selected as the Anchor SGSN 152. When the user terminal M moves into a new pool area, the serving SGSN within the new pooi is selected as the new Anchor SGSN and a normal RA update is needed with the HLR 200.

Typically the pool of routing areas may be positioned in a city or town. Thus, whilst the user terminal roams around the pool area signalling to the HLR 200 is not required; the anchor SGSN 152 maintains user terminal location information.

Each user terminal calculates its own calllsession arrival probability (ie the probability that a call will be made to that user terminal) locally based on its history over a predetermined time period. This information may be used to determine an estimate of the call to mobility ratio for the user terminal. Furthermore, the HLR 200 keeps track of the SGSNs 152, 156, 158 and GGSNs 154 which originate relatively high call/session rates towards each user terminal M, and records them as Frequent Session Callers (FSCs).

All information is included in the user terminal's service profile. This information is of use when the network seeks to locate a user terminal to instigate an incoming call, and will be described in more depth later.

The procedure for a routing area update within the confined pool of routing areas will now be described, with reference to Figures 4 and 5.

A user terminal performs a routing area update when either an internal timer expires, or when the terminal detects that it has entered a new routing area. A user terminal can ascertain whether it has entered a new routing area by comparing the stored routing area identity for the routing area (RA) it is leaving with a routing area identity (RAI) for the new area received from the network 100.

If the user terminal moves from a first routing area to a second, both being under the control of the same SGSN 152, 156, 158 no further update is required because the SGSN already has all the required information on the user terminal.

If the user terminal M moves from a first routing area to a second routing area that are both controlled by different SGSNs, but with the same pool, the second SGSN sends a context required message to the first SGSN.

The first SGSN sends an acknowledgement to the second SGSN together with a copy of the subscriber's user profile corresponding to the user terminal. The first SGSN also sends a message to the anchor SGSN of the location and removes record of the user terminal. Thus, when a user terminal roams within the pool of routing areas its location is recorded by the anchor SGSN, and communication with the HLR 200 is not required. It is to be appreciated that the previous or new SGSN could be the anchor SGSN 152, and the above procedure amended accordingly. For example, if the first SGSN is the anchor SGSN, then there is not a need to remove record and send an update. The update can be performed internally.

If the user terminal M moves from a routing area in one pool to a routing area in a second pool, it becomes necessary for the GGSN 154 and the HLR 200 to be notified of the RA update. In this scenario the new SGSN sends a request to update PDP context to the GGSN 154 and a request to update the HLR 200 with regards to the user terminal M location. The HLR also updates the FSC regarding the new routing area location of the user terminal.

The GGSN 154 then updates the record, and sends an update PDP context response' to the new SGSN. The HLR 200 updates its database by noting the new anchor SGSN for the user terminal and fransmits an acknowledgement to the new anchor SGSN and instructions for the previous anchor SGSN to remove details of the user terminal location. The new anchor SGSN, rather than the HLR 200 will now be responsible for maintaining the location information for the user terminal whilst it remains within the pool associated with the anchor SGSN.

The above procedure is also set out in the flow diagram set out in figure 9 in conjunction with figures 4 and 5.

The modified packet session delivery procedure is modified in the present arrangement. Specifically, when receiving a PDP (packet data protocol) PDU (protocol data unit) signal from the network, the GGSN 154 ascertains whether it is frequent session caller GGSN for the user terminal M. If it is, the GGSN 154 transmits a PDU notification request to the anchor SGSN regarding the user terminal. The anchor SGSN 152 checks to see if it is the serving SGSN for the user terminal. If so, the SGSN sends a request PDP context activation signal to the user terminal, instructing the user terminal to prepare for the call. If the anchor SGSN is not the serving SGSN, the anchor SGSN will forward the request to the serving SGSN.

If the GGSN 154 is not the frequent session caller for the user terminal, the GGSN 154 requests location information for the user terminal M from the home location register 200 by sending an 1MSI message.

To further aid the understanding of the invention, simulated results of the above are set out below.

Assume that the call interarrival time T to be exponentially distributed with rate X, and the RA residence time tm follows a Gamma distribution with mean 1/km, and having probability density function fm(t) and has a Laplace transform given by f (S)(yXm/(5 m1(S+yXm))'. The call-to- Mobility Ratio (CMR) is defined as the ratio of the call arrival rate to the mobility rate: CMR=Xc/Xm. For demonstration purposes, consider that the square routing area layout of Figure 6. Nine routing areas are arranged in a square to form a pool area.

If the user terminal is the central routing area of the region, then it may move in one of the four directions or stay in the same routing with the equal probability Po = 0.2. Assuming the possibility of moving out of the pool area is, for a boundary RA, such as RA1, RA3, RA7 and RA9, the possibility of moving to one of the three RAs (including itself) is P1 = (1-)I4. Let Pu be the one step transition probability from RA1 to RA, the transition matrix of the random walk is: l'l P1 0 P1 0 0 0 0 0 26 P2 P2 P2 0 P2 0 0 0 0 6 o P1 Pi 0 0 p 0 0 0 26 P2 0 0 P2 P2 0 P2 0 0 6 0 Po 0 Po P0 P0 0 P0 0 0 o 0 P2 0 P2 P2 0 0 P2 6 o 0 0 P1 0 0 Pi Pi 0 26 o 0 0 0 P2 0 P2 P2 P2 ö o 0 0 0 0 P1 0 P1 P1 26 0 0 0 0 0 0 0 0 0 1 Using the Chapman-Kolmogorov equation, the rn-step transition matrix Ifm=(m) I p, If m>1 = p x the following cost parameters are defined based on the reference architecture in Fig. 7; C1 is defined as the cost for a query or an update with the HLR via a remote A-link, the RSTP, the D-link, the LSTP and the local A-link; C2 is defined as the cost for a query or an update with the GSN via a local A-links, the LSTP, the D-links and the RSTP; C3 is the cost for a query or an update with the GSN via the local A-links and the LSTP, c is defined as the probability that a session originated from the non-FSCs.

In order to show the cost reduction produced by the proposed scheme relative to the 3GPP UIMTS scheme, the relative total costs per unit time have been plotted - shown in figure 8 - which is the sum of the average location update cost per unit time and the average session delivery cost per unit time, over various CMR from 0.01 to 100 where a = 0.2, 6 = 0.2. Four sets of values for the cost parameters are used in this simulation (Ci, C2, C3): set 1 -- (15, 8, 1), set 2 -- (15, 4, 1), set 3 -- (6, 4, 1) and set 4 -- (4, 3, 1) , where 3 FSCs are considered. It can be seen from the Figure 8 that, compared to the standard UMTS strategy, the present arrangement always provides a cost reduction. For low CMR the reduction in total cost is very significant when the cost for updating/querying with the HLR C1 is relatively high (parameter sets land 2).

The effect of the user terminal's mobility and service pattern on the cost of the proposed strategy is also investigated by classifying the subscribers based on 6 and a where two sets of cost parameters are considered (6, a, Cl, C2, C3): set 1 -- (0.1, 0.1, 6, 4, 1), set 2 -- (0. 3, 0.1, 6, 4, 1), set 3 -- (0.1, 0.5, 6,4, 1), set 4-- (0.3, 0.5, 6,4, 1), set 5 --(0.1,0.1, 15,4, 1), set 6 -- (0.3, 0.1, 15, 4, 1), set 7 -- (0.1, 0.5, 15, 4, 1) and set 8 -- (0.3, 0.5, 15, 4, 1) . The results, as illustrated in Fig. 7, show that: 1) For low a (most of the sessions originated from the RSCs) the proposed strategy with replication technique can achieve tremendous reduction in the total cost when the cost for updating the HLR is relatively high (set 5 and set 6); 2) Lower cost can also be achieved when the cost for updating with the HLR is relative low with low a (set 1 and set 2); 3) The worst performance of the proposed scheme can be expected with high a, because updating the frequent session caller GGSNs and SGSNs upon each routing area change is costly (set 3, 4, 7 and 8). This can be avoided by limit the number of FSC to within 3, and, in the case of high CMR, no FSC is applied.

Thus, it will be apparent that the present arrangement allows for a history record to be compiled for each user terminal, by the collection of information by both the user terminal and the home location register 200. The HLR is a database that saves user terminal profiles based on the information collected by the user terminal.

Information collected by the user terminal includes which SGSN and GGSN originate calls towards the user terminal. This information is used by the home location register to determine which GGSN 154 is the frequent session caller for the user terminal. This information is also operable to be used to determine the sigma parameter, - defined as the probability that a call/session originated from a GGSN/SGSN that is not the frequent session caller for the user terminal.

Thus, the present arrangement reduces the signalling costs compared to standard core network level location management strategy. What is disclosed is a user-oriented local anchor scheme that is based on each user terminal's service record and mobility pattern, and consequently reduces the signalling cost compared to conventional core network level location management strategy. Particularly preferred is that the pool of routing areas is applied to areas of heavy signalling traffic, such as city centres.

The user terminal reports its location changes to an anchor communication node instead of a home location register, and, consequently, no PDP context update with the GGSN is required, provided that the user terminal remains with the pool of routing areas. In parallel with this, the HLR maintains and updates a frequent session caller SGSN and GGSN for each user terminal based on each user's profile and location.

It is to be appreciated that the above embodiments are described for information only and should not be used to limit the invention as set out in the appended claims.

Claims (17)

Claims.

1. A telecommunication system comprising a user terminal and a plurality of communication nodes, wherein the communication nodes are associated with a pooi of routing areas, wherein one communication node is selected as an anchor communication node and maintains location information whilst the user terminal is within the pool of routing areas.

2. A telecommunication system according to claim 1, wherein each communication node is uniquely associated with a plurality of routing areas within the pooi of routing areas.

3. A telecommunication system according to claim 2 wherein, if a user terminal moves from a first routing area to a second routing area, each routing area being uniquely associated with the same communication node, location information is maintained by the communication node.

4. A telecommunication system according to claim 2 wherein if a user terminal moves from a first routing area associated with a first communication node, to a second routing area associated with a second communication node, location information is updated by the anchor communication node.

5. A telecommunication system according to any preceding claim, wherein the anchor communication node is selected as the serving communication node during the last call arrival.

6. A telecommunication system according to any preceding claim, wherein the home location register is updated for a given user terminal only when said user terminal leaves a designated pooi of routing areas.

7. A telecommunication system according to any preceding claim, wherein, when a user terminal moves to a routing area in a different pooi, the communication node associated with that routing area transmits updated location information to the home location register

8. A telecommunication system according to any preceding claim, wherein if the user terminal leaves the pool of routing areas, and enters a second pool, a new anchor communication node is selected.

9. A telecommunication system according to any preceding claim, wherein the system further comprises a high level communication node that maintains a register of which individual user terminals it initiated most calls/sesions.

10. A telecommunication system according to claim 9, wherein the information maintained regarding the high level communication node with most call/session initiations for a specific user terminal is used to maintain the user terminal's location for a future incoming call/session.

11. A telecommunication system according to any preceding claim, wherein the communication node is an SGSN.

12. A telecommunication system according to any preceding claim, wherein the high level communication node is a GGSN.

13. A communication node operable to perform the system of any preceding claim.

14. A communication node associated with a plurality of routing areas, operable to maintain location information for a user terminal whilst said terminal remains within the plurality of routing areas.

15. A method of monitoring the location of a user terminal, comprising the steps of: determining when a user terminal is located within a plurality of routing areas; instructing a commimication node to maintain location information whilst the user terminal is within said plurality of routing areas; and notifying a home location register only when said user terminal leaves said plurality of areas.

16. A method according to claim 15 wherein means is provided to record which communication node and high level communication node initiates call/sessions to each user terminal.

17. A method according to claim 16, wherein recorded information on the communication node and high level communication node is used to determine the location of the user terminal.