The present invention relates to protocol analysis, and more particularly to determining a transmission parameter in a transmission system at an interface between nodes of the transmission system.
According to the Global System for Mobile (GSM) communications digital cellular radio standard, which is used in many developed countries around the world, a subscriber occupies a radio frequency of the cellular network which is only assigned to the subscriber. The frequency is occupied by the subscriber for as long as the subscriber maintains connection to the network, regardless of whether there are speech pauses and regardless of the services purchased by the subscriber which are offered by the associated providers. Since radio frequencies are a scarce resource which cannot be copied any number of times, this state is considered worthy of improvement. After this system of the second generation (2G) of mobile communication, there followed as a 2.5G system the General Packet Radio Service (GPRS) standard. As a representative of the third generation (3G) the Universal Mobile Telecommunications Standard (UMTS) network then followed. Via this network a multiple number of subscribers may be served compared with the GSM network, the channels available being distributed more efficiently when there is less speech activity so less capacity is used. Moreover, the capacity may be varied as a function of the purchased services. With the UMTS network diverse information is transmitted on the channels, i.e., information addressed between nodes of the transmission system, information addressed to a plurality of subscribers, and information addressed to only one particular subscriber. The information breaks down into useful information and management information. For monitoring instruments or protocol testers or the like to which only a particular interface in a cellular network of this kind is accessible, there now is the problem that they have to find out from a connection already established how individual channels are occupied in order to enable decoding and hence further processing of the data transmitted.
Further information on the terms used below in connection with the UMTS network may be obtained from documentation available via the domain www.3GPP.org. Document 3GPP TS 25.301 provides an overview of channel usage in a UMTS network. Documents 3GPP TS 25.427 and 3GPP TS 25.435 deal with frame protocol (FP), document 3GPP TS 25.321 deals with Medium Access Control (MAC) protocol, document 3GPP TS 25.322 with Radio Link Control (RLC) protocol, document 3GPP TS 25.331 with Radio Resource Control (RRC) protocol and document 3GPP TS 25.433 with Node B Application Part (NBAP) protocol. Further information on Access Link Control Application Part (ALCAP) protocol may be obtained from ITU Recommendation ITU 0.2630.2. With regard to Service Specific Connection Oriented Protocol (SSCOP), reference is made to ITU Recommendation ITU Q.2110.2.
For a better understanding of the problem addressed by the present invention, FIG. 1 shows a part of a UMTS network with a Mobile Switching Center (MSC) 10, three Radio Network Controllers (RNCS) 14A, 14B, 14C, three Nodes B 16A, 16B, 16C, and three user equipments (UEs) 18A, 18B, 18C. Between the MSC 10 and each RNC 14 there is arranged one lu interface each, between the RNC 14B and each Node B 16A, 16B, 16C there is arranged one lub interface each, between the RNCs 14A, 14B, 14C there is arranged one lur interface each and between user equipments 18A to 18C and Node B 16B there is arranged one Uu interface each.
The functions of Node B 16 may be summarized as follows. Node B 16 forms a logical node, such as the Base Transceiver System (BTS) in a GSM network; it is responsible for the transmitting and receiving in one or a plurality of radio cells to/from user equipment; it terminates the lub interface, i.e., the NBAP and the ALCAP; it is used for radio frequency (RF) power control; and it controls a predeterminable number of radio cells. Node B 16 thus is a base station to which a plurality of transmitter and receiver antennas are connected, with each such antenna combination defining a radio cell.
The RNC 14 controls the use and the integrity of the radio resources. The RNC 14 terminates RANAP (Radio Access Network Application Protocol), NBAP, ALCAP (Access Link Control Application Part), RNSAP (Radio Network Subsystem Application Part) and RRC/RLC/MAC protocols, and it forms the central element of a UMTS network. The RNC 14 thus is a radio switching station to which a plurality of radio base stations are connected.
The functions of the protocol used at the lub interface may be described as follows: management of the lub transport resources; logical operation and maintenance of Node B 16, particularly lub link management; radio cell configuration management; radio network performance measurements; resource event management; management of the CTCH (Common Transport Channel); radio resource management; and radio network configuration alignment. It further includes the implementation of a specific operation and maintenance transport, and the function of system information management. In addition, the following functions are realized at the lub interface: traffic management for common channels, i.e., for channels which apply to all subscribers connected to the relevant Node B 16, particularly access control means; power management; and data transfer. Moreover, it takes over the functions of traffic management for dedicated channels, i.e., channels allocated to a particular subscriber, notably radio link management, radio link supervision, channel allocation/deallocation, power management, measurement report, and dedicated transport channel management as well as data transfer.
FIG. 2 shows the protocols and layers involved at the lub interface. The bottom-most protocol layer is the physical layer 20 on which there are based frame protocols 22 and other SSCOP 24 protocols of a data link layer. Layer 24 is followed by the ALCAP 26 and the NBAP 28 which serve the base station management. The NBAP link serves in particular the configuration of the radio cells and it opens the channels for the radio cells. The ALCAP link defines the usage of the channels opened by the NBAP. While ALCAP 26 is specific to an ATM (Asynchronous Transfer Mode) transport layer, there is no ALCAP for an Internet Protocol (IP) transport layer. In the following, however, an ATM transport layer is assumed so that it is possible to describe the differentiation between NBAP and ALCAP. The present invention may also be applied to an IP transport layer, the differentiation between NBAP and ALCAP then not being applicable.
ALCAP 26 and NBAP 28 serve the communication between the RNC 14 and Node B 16—information addressed between nodes. The individual frame protocols 22 are the channel types FACH (Forward Access Channel), RACH (Random Access Channel) and PCH (Paging Channel) which are passed on to all subscribers of a Node B 16—information addressed to all subscribers, and DCH (Dedicated Channel) which is transmitted specifically to a particular subscriber—information addressed to only one subscriber. In order to be able to represent a plurality of logical command levels on a frame protocol, logical channels MAC 30 and RLC 32 are based on the aforementioned frame protocols. RRC 34 is based on the MAC/RLC protocols 30, 32.
FIG. 3 shows a detailed schematic representation of the links used between an RNC 14 and a Node B 16. First an ALCAP link and an NBAP link, which serve the communication between RNC 14 and Node B 16, then an FP PCH link for radio cell No. 1, i.e., all the subscribers assigned to radio cell 1, an FP RACH link for radio cell No. 1, an FP FACH link for radio cell No. 1, and finally an FP DCH link for the user equipment No. 1. Further FP links for radio cell No. n have been added as examples. As is seen from FIG. 3, the links ALCAP and NBAP end in the respective nodes, while the links PCH, RACH and FACH are passed on the Node B side to the plurality of subscribers and link DCH passes on the Node B side to a specific subscriber. In a GSM network the information transmitted in the six aforementioned channels is transmitted in a single channel, and thus the problem of differentiating between the individual channels, as in the present case of the UMTS network, does not occur at all.
To be able to execute, for example, a protocol monitoring task on an lub interface, it is necessary to know the occupancy of the individual channels. For further evaluations, the configuration for the links NBAP, ALCAP 28, 26 and of the common and dedicated control channels is required for each Node B 16 connected to the RNC 14 and each radio cell. Unfortunately, the control channels are dynamically opened with varying parameters or protocols. An exchange of the configuration parameters of the frame protocols 22 and of the MAC 30 and the RLC 32 for these channels is transmitted via the links NBAP 28 and ALCAP 26 only during the initialization phase of each Node B 16. In an active UMTS network it is, however, not possible to re-initialize the Nodes B 16 in order to determine the channel configuration for monitoring purposes each time a monitoring instrument or a test instrument is switched on.
A proprietary method was tried where the physical layer was evaluated in terms of the length of the used data packets. This method was based on the fact that the length of the data packets may be configured by the user. The type of data was defined through user-specified lengths. The corresponding lengths were determined and stored in a database in a user-related way, i.e., particularly sorted by providers and operators of the respective networks. Now, if the lub interface of a particular operator is to be monitored, the corresponding data entry is queried and the corresponding parameters loaded. However, this method does not provide a satisfactory solution for monitoring tasks in which the corresponding parameters employed by the user are not known or are changed in the meantime.
What is desired is to further develop the proprietary method in such a way that the performance of protocol monitoring tasks is made easier.