Abstract:
A method, network, and device for measuring and analyzing packet-switched traffic in a packet-switched radio telecommunication network. When cell-level location information for a mobile station ( 1 ) changes due to a handover, the location information is transmitted toward a packet core network ( 9 ) by adding the information to userplane packet headers such as a GPRS Tunneling Protocol (GTP) header ( 26 ). The measurement device measures the cell-level location information at a level ( 15   b ) in the network where the information from a plurality of mobile stations ( 1 ) is aggregated, together with PDP context information prior to analyzing information for the entire network.

Description:
BACKGROUND OF THE INVENTION 
   1. Technical Field of the Invention 
   The present invention relates generally to mobile telecommunication networks. More particularly, and not by way of limitation, the invention is directed to a location-signaling system and method for large-scale end-to-end quality-of-service monitoring of packet-switched telecommunication networks. 
   2. Description of Related Art 
   The detailed analysis of live General Packet Radio System (GPRS) and UMTS networks is of increasing importance as traffic on these networks increases and traffic measurements become available. Traffic measurements from these networks are extremely useful when analyzing such areas as network utilization information, network performance information indicating whether the users are getting what they paid for or what they expect, bottleneck information identifying bottlenecks in the network, system enhancement information for enhancing the network so that identified problems are eliminated, and dimensioning information for re-dimensioning of cells, links, and the like. 
   In the case of a circuit-switched service such as voice, for example, it has conventionally been sufficient to measure the call intensities, call durations, and the ratio of blocked calls to successful calls. In the case of packet-switched services such as Web browsing, File Transfer Protocol (FTP) services, e-mail, Multimedia Messaging Services (MMS), and the like, the above tasks are not at all trivial because the end-to-end or user-perceived performance depends on the interaction of many protocols at different interfaces and on various protocol layers. Furthermore, the use of shared resources leads to rather complicated queuing phenomena, which are difficult to model and analyze. 
   It is envisioned that measurement-based network analysis will soon become a primary tool for the network operator. In order to perform the measurements in a cost-effective manner, the measurement equipment should be inexpensive, and the number of measurement points should be limited to reduce equipment costs and to minimize having to synchronize measurements taken at different points in the network. 
   Measurement-based characterization of GPRS networks has been described in a document entitled, “Wireless Service Usage and Traffic Characteristics in GPRS networks”, by Roger Kalden, Tamás Varga, Bianca Wouters, and Bart Sanders (18th International Teletraffic Congress, Berlin, Germany, 31 Aug. through 5 Sep. 2003). In this document, packets on the so-called Gi interface are captured. The Gi interface connects the Gateway GPRS Support Node (GGSN) with external packet data networks and service providers such as Internet Service Providers (ISPs). Based on the Gi traffic traces, detailed traffic and end-to-end performance analysis results are delivered to operators. In order to identify user sessions (i.e., which user the packets belong to), communications between the GGSN and a Remote Authentication Dial-In User Service (RADIUS) server are also monitored. 
   When it is also desired to relate the end-to-end quality measurements and traffic load measurements to cells, this can be accomplished by capturing cell-level location information. Concerning the availability of this location information, two types of networks can be differentiated. In the first network type, the cell-level location information is only available in the radio access network (network of base stations and their controllers), while in the second network type, the cell-level location information is also available in the core network (network connecting access networks and other service networks). 
   For example, the mobility management architectures of GPRS and UMTS are different. In order to track the mobile stations, the cells in a GPRS/UMTS service area are partitioned into several groups. To deliver services to a mobile station, the cells in the group covering the mobile station page the mobile station to establish a radio link. To detect a location change of a mobile station, the cells broadcast their cell identities. The mobile station periodically listens to the broadcast cell identity, and compares it with a cell identity stored in the mobile station&#39;s buffer. If the comparison indicates that the location has changed, then the mobile station sends a location update message to the network. 
   In the GPRS/UMTS (R′99), procedures such as Attach, Paging, and Location Update are defined separately for circuit-switched and packet-switched services. In the circuit-switched domain, cells are partitioned into location areas. Visiting Location Registers (VLRs) track the location area of the mobile station. In the packet-switched domain, the cells are partitioned into routing areas. A routing area is typically a subset of a location area. The SGSN tracks the routing area of the mobile station. 
   In GPRS, the SGSN also tracks the cell of a mobile station when packets are delivered between the mobile station and the SGSN. In UMTS, the cells in a routing area are further partitioned into UMTS Terrestrial Radio Access Network (UTRAN) routing areas (URA). The UTRAN tracks the URA and the cell of the mobile station. 
   In the evolution from GPRS to UMTS, the UTRAN radio access network has been introduced, and radio-related mobility management is moved from the core network to the UTRAN as described in “3GPP TS 23.060 V3.14.0, General Packet Radio Service, Service Description, Stage 2, Release 1999, 2002-12”. This means that cell-level and URA-level location information is not communicated towards the core network. 
   Cell-level location information can be captured from the Radio Resource Control (RRC) protocol at the so-called Iub interfaces between the base stations and the Radio Network Controller (RNC), or by extracting the information from the RNC. Both solutions, however, have disadvantages. Firstly, in the UTRAN, the number of Iub links can be rather high. Since reliable statistical analysis of a network requires a large amount of network-wide data, the first solution would be rather complicated. The number of measurement points would be rather high, and the problem of collecting and merging measurement data from these points to the data processing location would have to be solved. The second solution suffers from the disadvantage that users are identified in RRC cell-update signaling by temporary IDs (i.e., cell radio network temporary identity (RNTI) and UTRAN RNTI). The time-varying nature of these IDs makes it difficult to associate the transactions measured at higher aggregation points with a mobility pattern tracked in an RRC trace. Furthermore the needed information in the RNCs is stored in a vendor-specific manner. Therefore, a measurement system that can be used in any type of UTRAN cannot be based on extracting information from the RNC. Yet another drawback is that, in order to ensure network security, safe operation of network nodes, and the like, operators typically do not allow for measuring teams (which may be external) to access important network nodes such as the RNC. Therefore, a solution with passive tapping at a standardized network interface is favored. 
   Thus there is a particular need for a cost-effective passive monitoring method that can be applied in the current mobility management architecture of UMTS networks. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a location-signaling system and method for large-scale end-to-end quality-of-service monitoring of packet switched telecommunications networks. The invention is especially useful for Universal Mobile Telecommunications System (UMTS) networks in which the detailed mobility information is only available in an access network where the level of aggregation is not sufficient for reliable passive measurement-based characterization. An important advantage of the invention is that only a few measurement points are needed. It is also advantageous that the existence of the cell-level location information in the UTRAN-to-core-network communication can be switched off in regular operation so that no extra load is generated in the network, and the operation of the network is left unchanged. 
   Accordingly, it is an object of the invention to enable cost-efficient collection of cell-level location information in the current mobility management architecture of mobile networks, especially UMTS networks. 
   The invention communicates cell-level location information towards the core network, and this information is later used by passive monitoring devices. 
   For a hard handover, the identity of the new cell is communicated towards the SGSN over the Iu interface. For a soft handover (i.e., for handover between dedicated channels), the identities of the cells in the new active set are communicated towards the SGSN over the Iu interface. Preferably, this information is added to user-plane packets only after a change in the cell information is observed by the RNC. In one embodiment, the cell-level location information is carried in the GPRS Tunneling Protocol (GTP) Extension Header described in “3GPP TS 29.060 V3.7.0, GPRS Tunneling Protocol across the Gn and Gp Interface, Release 1999, 2002-12”. Initially, the information may be a vendor-specific extension. If a node does not understand a certain extension in the header, the node answers with a list of extensions that are known by the node. Therefore the introduction of a new extension header does not cause interoperability problems. 
   In one exemplary embodiment, the transmission of cell-level location information can be switched off. In this way, the transmission of cell-level location information is active only during measurements. 
   In another exemplary embodiment, the cell-level location information is also forwarded on the Gn interface within the core network. In this case, the number of needed measurement points may be further decreased. The cell-level location information may also be encrypted before forwarding, and then decrypted in the monitoring device. 
   Thus, in one aspect, the invention is directed to a method of measuring packet-switched traffic in a packet-switched radio telecommunication network. The network includes a mobile station linked to a base station through a radio channel. The base station is linked to a radio access network, and the radio access network is linked to a support node in a packet core network. The method includes the steps of obtaining cell-level location information of the mobile station in a node in the radio access network; adding the obtained cell-level location information to user-plane packet headers; and transmitting the user-plane packets carrying the cell-level location information towards the packet core network. The cell-level location information is combined with packet data protocol (PDP) context information at a packet core network level. This is followed by measuring the cell-level location information (and other information, for example, the PDP context information) at the packet core network level. 
   In another aspect, the invention is directed to a method of measuring packet-switched traffic in a Universal Mobile Telecommunications System (UMTS) packet-switched radio telecommunication network having a plurality of mobile stations linked to a plurality of base stations through a plurality of radio channels. Each of the base stations is linked to a UMTS Terrestrial Radio Access Network (UTRAN), and a plurality of UTRANs are linked to a Serving General Packet Radio Service (GPRS) Support Node (SGSN) in a packet core network through an Iu interface link. The packet core network, in turn, is linked to a Gateway GPRS Support Node (GGSN) through a Gn interface link. The method includes the steps of passing cell-level location information for the mobile stations and PDP context information from the plurality of UTRANs to the SGSN via the Iu interface, or to the GGSN via the Iu interface links, the SGSN, the packet core network, and the Gn interface link. User-plane traffic for the entire network, including cell-level location information for the mobile stations and PDP context information combined from the plurality of UTRANs, is then measured on the Iu or the Gn interface link, respectively. 
   In yet another aspect, the invention is directed to a mobile telecommunication network for exchanging data packets. The telecommunication network includes an access network portion for connecting a plurality of mobile stations to the telecommunication network, a packet core network portion for connecting the access network portion to external networks, and at least one network monitoring device. The telecommunication network is characterized by the access network portion including nodes for transmitting data packets from the mobile stations towards the packet core network portion, wherein at least one of the nodes adds cell-level location information to the data packets that are transmitted towards the packet core network portion. In addition, the monitoring device is placed at a point in the telecommunication network where the monitoring device measures cell-level location information aggregated from a plurality of nodes. 
   In still yet another aspect, the invention is directed to a monitoring device for measuring and analyzing packet-switched traffic in a packet-switched radio telecommunication network. The monitoring device includes at least one measurement point for measuring cell-level location information of the mobile stations at a level in the network where the cell-level location information of a plurality of mobile stations is aggregated; and computing means for analyzing the measured aggregated cell-level location information. The monitoring device may also include means for obtaining PDP context information for the packet switched traffic and analyzing the PDP context information together with the measured cell-level location information for the entire network. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following, the essential features of the invention will be described in detail by showing the prior-art and two preferred embodiments, with reference to the figures of the attached drawings. 
       FIG. 1  is a block diagram showing a possible measurement arrangement according the location unaware prior-art solution. 
       FIG. 2  is a block diagram showing a possible measurement arrangement according the location aware prior-art solution. 
       FIG. 3  is a block diagram depicting the preferred embodiment of a telecommunications network to be analyzed. 
       FIG. 4  is a block diagram depicting another embodiment of a telecommunications network to be analyzed. 
       FIG. 5  is a flow chart showing the steps of the method of analyzing the network. 
       FIG. 6  is an exemplary bitmap illustrating the outline of a GTP header. 
       FIG. 7  is an exemplary bitmap showing the outline of an Extension Header Format. 
       FIG. 8  is an exemplary Cell-Level Location Information Extension Header. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In  FIG. 1 , an exemplary telecommunication network is shown according to the location unaware prior art solution, where mobile stations  1  communicate with base stations  2  through radio channels. The base stations are grouped to Radio Network Controllers  5 , which are connected to a 3G SGSN  7  through Iu interfaces  6 . The 3G SGSN is linked to a packet core network  9  and to a GGSN  10  through Gn interfaces  8 . The GGSN is linked to a corporate network  12  and to an ISP network  13  through Gi interfaces  11 . Additionally, two Wireless Application Protocol (WAP) Gateways  14  are connected to the ISP network. Measurement point  15  is attached to a link between the GGSN  10  and the ISP network  13 , thereby accessing session information from the network. 
   The session management information in both GPRS and UMTS is communicated between the mobile stations and the core network (i.e., the network containing the SGSNs and GGSNs), and the relevant information (i.e., the PDP context) is available at the Gi interface, which aggregates the traffic of a large number of users. This prior art solution can be used to deliver network wide performance statistics. These statistics do not depend on the location of the data transfer. 
   In  FIG. 2 , an exemplary telecommunication network is shown according to the location aware prior art. The network illustrated in  FIG. 2  is similar to the network of  FIG. 1  as far as the relations of the 3G SGSN  7 , the packet core network  9 , the GGSN  10 , the corporate network  12 , the ISP network  13 , the WAP gateways  14 , the mobile stations  1 , and the base stations  2  are concerned. Measurement points  15   a  of a monitoring system  4  are attached to each link between the base stations  2  and the RNCs  5 , thereby accessing cell-level location information from the UTRAN. 
   In this case, the cell-level location information is not sent on the Iu and Gn interfaces, and therefore the number of required measurement points  15   a  may be very high. In order to synchronize the traces collected at different measurement points  15   a , the measurements are executed in parallel. This means that a simple solution, such as connecting a laptop equipped with the necessary tapping hardware and software to a measurement point, is not feasible. 
     FIG. 3  is a block diagram depicting the preferred embodiment of a telecommunications network to be analyzed. Network elements are the same as shown in  FIG. 2 . In this embodiment, the cell-level location information (cellinfo) is obtained in the radio network controller (RNC) (not shown) in the UTRAN. The RNC is responsible for tracking the mobility of users, but normally keeps this information for its own use. In the present invention, the cell-level location information is added by the RNC to user data packets, and is then forwarded toward the packet core network. The packets are forwarded over the Gn interface  8 , so one measurement point  15   b  at the Gn interface is sufficient. 
     FIG. 4  shows an exemplary telecommunication network according to one embodiment of the present invention. Network elements are the same as shown in  FIG. 3  In  FIG. 4 , two UTRANs  3  are linked to the 3G SGSN  7  through Iu interfaces  6 . Measurement points  17  are attached to the Iu interfaces thereby accessing cell-level location information (cellinfo) from the UTRANs at a higher aggregation level than the measurement points  15  in  FIG. 2 . Monitors  16  are connected to the measurement points  17 . 
   As shown, the cell-level location information is signaled on the Iu interface link  6  between the UTRAN and the 3G SGSN, so measurement points  17  are needed on the Iu interface link  6  to collect the cell-level location information. 
   In GSM/GPRS networks, a mobile station communicates with only a single cell at a time. In CDMA-based networks, however, a mobile station may communicate with several cells at a time. These cells may be associated with one or more base stations. In the former case we speak about “softer” handover, while the latter is called “soft” handover. 
   When collecting cell-level traffic statistics in Wideband CDMA networks, packets transmitted during soft or softer handover can be taken into account by signaling the active set (AS) (i.e., the set of connected cells) after a change in the active set has occurred. Therefore, in the present invention, the following information may be communicated towards the core network: 
   
     
       
             
             
             
             
             
           
             
             
             
             
             
           
         
             
                 
                 
             
             
                 
               Cell id 
               Cell id 
               Flag 
               Meaning 
             
             
                 
                 
             
           
           
             
                 
             
           
        
         
             
               Soft 
               Cell ID 
               — 
               ADD 
               Cell with “Cell ID” 
             
             
               handover 
                 
                 
                 
               added to AS 
             
             
                 
               Cell ID 
               — 
               DROP 
               Cell with “Cell ID” 
             
             
                 
                 
                 
                 
               dropped from AS 
             
             
                 
               Cell ID 1   
               Cell ID 2   
               REPLACE 
               Cell with “Cell ID 1 ” 
             
             
                 
                 
                 
                 
               replaced by cell 
             
             
                 
                 
                 
                 
               with “Cell ID 2 ” in 
             
             
                 
                 
                 
                 
               the AS 
             
             
               Hard 
               Cell ID 
               — 
               REPLACE 
               Hard handover to 
             
             
               handover 
                 
                 
                 
               cell with “Cell ID” 
             
             
                 
             
           
        
       
     
   
   If the network operator makes the measurement in its own network, it is easy to create a post-processing tool, which encrypts all the sensitive location information before analysis, as it is done today with, for example, the International Mobile Subscriber Identity (IMSI). In order to prevent the unauthorized seizure of this information via eavesdropping over the interface, the particular interface may be IPSec tunneled, or the information may be encrypted in the GTP header. 
     FIG. 5  is a flow chart showing the steps of the method of analyzing the network. At step  21 , cell-level location information of the mobile stations is observed. At step  22 , the cell-level location information is added to the user-plane packet headers. At step  23 , the cell-level location information is transmitted towards the packet core network. At step  24 , the cell-level location information, user traffic, and the PDP context information are measured at a higher aggregation level. Finally, at step  25 , user-plane traffic from the entire network is analyzed, including cell-level location information and PDP context information. 
     FIGS. 6-8  outline one possible embodiment of the invention for carrying the cell-level location information in a UMTS network using standardized features of the GTP protocol. 
     FIG. 6  is an exemplary bitmap illustrating the outline of a GTP header. As described in 3GPP TS 29060, the GTP header is a variable length header used for both the GTP-C and the GTP-U protocols. There are three flags that are used to signal the presence of additional optional fields. Important for this invention is the so called ‘E’ flag  26 , which is used to signal the presence of an Extension Header field. The Extension Header field is used to enable future extensions of the GTP header as defined herein, without the need to use another version number. If, and only if, one or more ‘E’ flags are set, the Extension Header will be present. The ‘E’ flag indicates the presence of a meaningful value of the Next Extension Header field. When the ‘E’ flag is set to ‘0’, the Next Extension Header field is either not present, or if present, is not to be interpreted. When the ‘E’ flag is set to ‘1’, the Next Extension Header field is present, and shall be interpreted, as described below. The Next Extension Header Type field  27  defines the type of Extension Header that follows this field in the GTP-PDU. Outline of the GTP header indicating the exact location of the ‘E’ flag  26  and the Next Extension Header Type field  27  is shown in the figure. 
     FIG. 7  is an exemplary bitmap showing the outline of an Extension Header Format. The Extension Header Length field 28 specifies the length of the particular extension header in  4  octets units. The Next Extension Header Type field  29  specifies the type of any extension header that may follow a particular extension header. If no such header follows, then the value of the Next Extension Header Type field  29  shall be ‘0’. To indicate the presence of cell-level location information, the value of the Next Extension Header Field may be set to ‘00000011’. The length of the Extension header is defined in a variable length of 4 octets, i.e. m+1=n*4 octets, where n is a positive integer. 
     FIG. 8  is an exemplary Cell-Level Location Information Extension Header. Fields for Cell Identifier of the REPLACED cell  30  are present if the Cell Change Type Flag  31  indicates ‘REPLACE’. The identified cell is the cell being replaced in the active set. The detailed coding of the Cell Identifier is as follows: 
                                                                                 8   7   6   5   4   3   2   1                                    octets   Octets 1 to 6 contain the value part           1-6   (starting with octet 2) of the           Routing Area Identification IE           defined in 3GPP TS 04.08, not           including 3GPP TS 04.08 IEI       octets   Octets 7 and 8 contain the value part       7-8   (starting with octet 2) of the Cell           Identity IE defined in 3GPP TS 04.08           not including 3GPP TS 04.08 IEI                    
The value of the Cell Change Type flag  31  is coded as follows:
 
   
     
       
             
             
           
         
             
                 
             
             
               Value 
               Meaning 
             
             
                 
             
           
           
             
               00000001 
               ADD 
             
             
               00000010 
               DROP 
             
             
               00000011 
               REPLACE 
             
             
                 
             
           
        
       
     
   
   Although two preferred embodiments of the present invention have been illustrated in the accompanying drawings and described in the foregoing Detailed Description, it is understood that the invention is not limited to the embodiment disclosed, but is capable of numerous rearrangements, modifications, and substitutions without departing from the scope of the invention. For example, although embodiments are described above with reference to UMTS communications network, the present invention is applicable to any type of mobile telecommunications network. The specification contemplates any all modifications that fall within the scope of the invention defined by the following claims.