Synthesis Scheme of Iub Interface CDR in TD-SCDMA Tester

introduction

As the commercial network testing of TD-SCDMA, the third-generation mobile communication standard with China's independent intellectual property rights, is coming to an end, large-scale 3G networks are about to be established across the country. As an important supporting technology for networking, the development of testers is very important.

One of the main uses of 3G signaling test systems is to quickly diagnose network faults and reduce network interruption time. When a 3G system fails, test equipment is needed to access key signaling link monitoring points and perform protocol testing and analysis. Generally speaking, universal mobile telecommunica- tion system (UMTS) network faults can be divided into two categories: UMTS terrestrial radio access network (UTRAN) side faults and core network (CN) side faults. Since the network structure and protocol of 3GPP R4 (Release 4) UTRAN have changed significantly compared with the GSM system, problems are more likely to occur; while the R4 core network and the GSM system are basically the same, the probability of problems is relatively small. Since the Iub and Iu interfaces are the most important test interfaces in UTRAN, it is generally necessary to collect data and perform correlation analysis on these two interfaces at the same time [1-3].

To effectively diagnose 3G networks

To detect network failures, network engineers need to have a comprehensive and in-depth understanding of UMTS interfaces and related protocols, so that they can quickly find the existing problems and analyze the key fields. All these tasks are inseparable from the cooperation of a 3G signaling test device with comprehensive decoding, call tracking and statistics functions.

CDR (call data record) stands for call data record in PSTN. Now it is extended to mean a complete process. CDR synthesis is the basis of the above functions. Messages in the network are classified according to the signaling process and these messages are linked together in an indexed manner, which makes it easier to complete advanced functions such as call tracking and call loss statistics [4-5].

In this paper, we will take the CDR synthesis of each protocol between Iub interfaces in TD-SCDMA UTRAN and multi-protocol association as an example to describe the CDR synthesis method. This method is also applicable to WCDMA systems.

1. Signaling messages in the Iub interface

Figure 1 is a diagram showing the relationship between protocols in the Iub interface. The Iub interface protocol stack contains three protocol planes, namely the radio network control plane, the transport network control plane and the user plane, which correspond to the signaling processes of the three protocols, namely NBAP (Node B application part), ALCAP (access link control application protocol) and Iub FP (frame protocol) messages [6]. The protocols carried by FP include radio resource control (RRC) and packet data convergence protocol (PDCP). These three protocols are closely related. When the radio network controller (RNC) initiates the transport channel management or radio connection management related processes, it is implemented through the relevant processes of the NBAP protocol, such as Common Transport Channel Setup, Radio Link Setup, Radio Link Addition, etc. However, at the same time, the user plane link needs to be allocated or deleted. On the Iub interface, user data (FP) is transmitted through AAL2 in the ATM structure. At this time, a control mechanism needs to be established. ALCAP defines the way to establish and release the transport bearer with the user plane, so the ALCAP protocol is needed to complete these operations. Generally speaking, if the user plane is not involved, there are only NBAP process messages in the Iub interface. When the user plane is involved, the situation is much more complicated [7].

Fig.1
Relation graph of Iub interface

RNC will be involved in user plane operations in the following two situations: one is when operating the common transmission channel of the cell; the other is when providing a dedicated channel for the UE. In the process of operating the transmission channel, the user plane only has FP synchronization messages, and there will be no RRC messages. When RNC is involved in operating the UE, it is necessary to first establish a wireless connection (RRC connection) between the RNC and the UE. The establishment process is as follows: the UE first requests the RNC to establish an RRC connection. After receiving the request, the RNC chooses whether to establish a dedicated channel for the UE according to the specific situation. If a dedicated channel (dedicated channel, DCH) is to be established, the RNC will request to establish a wireless link or reconfigure the wireless link through the NBAP protocol. After the Node B successfully responds, the RNC will allocate the AAL2 link required for the DCH through the ALCAP protocol. After successful allocation, the RNC sends an RRC establishment success message through the forward access channel (forward access channel, FACH). If a dedicated channel does not need to be established for the UE, then there will be no NBAP and ALCAP process mentioned above. The RNC will directly send an RRC establishment success message through the FACH, which will indicate that the UE can only [page]

All messages are transmitted to the RNC via the common transport channel. Figure 2 shows the types of messages that may appear in the Iub interface.

Fig.2 Messages in Iub interface

So far, the Iub interface processes can be summarized into four categories:

①Pure NBAP process;

②NBAP process + ALCAP process + FP (public transmission channel, synchronization message);

③NBAP process + ALCAP process + FP (DCH, including synchronization message and RRC message);

④RRC process (public channel transmission, shared channel transmission).

② and ③ can be classified into the same category. It is not difficult to see that the CDR synthesis of the Iub interface can be synthesized by NBAP, ALCAP, FP, and RRC messages first, and then multiple protocols are associated. Although RRC is above FP, the message of an RRC process may appear in multiple FPs, so the two are distinguished here.

2. Basic principles and implementation algorithms of Iub interface CDR synthesis

The following is a detailed introduction to the message synthesis of process type ③ (NBAP process + ALCAP process + FP) in the above section, because this is the most complex type.

The CDR synthesis method includes three other types of CDR synthesis methods. Specifically, taking mobile oriented call (MOC) as an example (see Figure 3), the basic principles of RRC connection establishment, how to implement NBAP, ALCAP, FP, RRC message synthesis, multi-protocol association, etc. are described.

Fig.3 Message
flow.of MOC

As shown in Figure 3, the message flow above the dotted line is the RRC establishment process, which will also be the main part of CDR synthesis. First, the UE sends the rrcConnectionRequest message through the RACH random access channel to request the establishment of an RRC connection. The message contains the IMSI/TMSI and the establishment reason parameters. After receiving the request, the RNC initiates the radio link establishment request intiatingMessage Id-radioLinkSetup (if the radio link has been established, it will initiate the radio link resource reconfiguration request). After the NodeB confirms the request through successfulOutcome ID-radioLinkSetup, the RNC will allocate a DCH dedicated channel for the UE, that is, call the ALCAP protocol to allocate an AAL2 link to carry the DCH. After the DCH is synchronized, all RRC messages of the UE will be transmitted on the DCH. After successful allocation, the RNC initiates rrcConnectionSetup to establish an RRC connection, and the NodeB confirms it through rrcConnectionSetupComplete. At this point, the RRC is successfully established, and the NAS (Non-Access Stratum) message will be sent to the RNC through RRC message encapsulation, and then sent to the MSC through the Iu interface. [page]

The association method of each protocol of the Iub interface is described as follows (see the indication of each connection arrow in Figure 3, and the synthesis of NAS messages is not considered for the time being):

●NBAP message association: NBAP messages of the same process are associated using the Transaction ID parameter in the message, and messages between different NB·AP processes involving the same UE are associated using the Id-CRNC-CommunicationContextID parameter.

●ALCAP message correlation: ACLAP messages of a process can be correlated through OSAID and DSAID parameters.

●RRC message association: RRC messages of the same process can be associated through RRC Transaction ID, and RRC messages of the same UE can be associated through I·MSI/TMSI. RRC messages in the public transport channel can be distinguished based on the UEID in the MAC to determine whether they belong to the same UE.

The multi-protocol association of the Iub interface is as follows (see the indication of each connection arrow in Figure 3):

NBAP messages and RRC messages are associated with each other through Time Slots and User Codes in TDD mode and through Scrambling codes in FDD mode.

●NBAP message and ALCAP message association: Association is performed by making the BindingID parameter value in the NBAP message equal to the SUGR parameter value in the ERQ message of ALCAP.

●ALCAP message and RRC (in DCH) message association: The VPI/VCI/CID of the DCH channel in the RRC message is associated with the PathID (VPI/VCI is equal to PathID after conversion) and ChannelID (CID=ChannelID) in the ERQ message of ALCAP.

According to the above, each protocol is first synthesized, and then the protocols are synthesized. The synthesis between the protocols is performed at a certain time period, and the final result is the required Iub interface CDR information.

3. Analysis of Iub interface CDR synthesis algorithm

The CDR synthesis algorithm mainly searches and matches based on some key parameters to determine whether they belong to the same message flow. Therefore, in this process, some temporary storage methods are needed to save unmatched messages, which is more complicated in memory allocation and involves dynamic memory allocation. In addition, the synthesis algorithm involves a lot of searching and matching, so it is necessary to establish many indexes that are convenient for searching. It is very important to establish a good indexing method, but it is also time-consuming to establish these indexes. Therefore, specific indexing methods should be used according to specific circumstances. In the design process, we have also used other indexing methods besides balanced binary trees, such as binary trees and hash tables.

The synthesis between protocols is a periodic operation, and the length of the time period will also affect the efficiency of the synthesis. If the interval is too short, the process completed each time is very small, and it also takes time; if the time is too long, it lacks real-time performance. We use a multi-threaded approach to complete multi-protocol association with a single thread, and the effect is very good. Figure 4 shows the execution result of this method applied to the TD-SCDMA network tester.

Fig.4
Result display

4. Conclusion

Through in-depth analysis and research of the message flow of the Iub interface, combined with the Iu interface, using C++ language for coding testing, the effect of CDR synthesis can be well achieved, and the protocol association between multiple protocols and even multiple interfaces can be realized. This program module has been applied to the TD-SCDMA network tester of the Key Laboratory of Communication Network and Test Technology of Chongqing University of Posts and Telecommunications, and the effect is

good.

References:

[1] 3GPP TS 25.401 V5.9.0.UTRAN overall descrIPtion [EB/OL].(2003-09-20)[2006-05-30].http://WWW.3gpp.org/ftp/Specs/2004- 09/Rel-5/25_series/25401-590.zip.

[2] 3GPP TS 25.430 V4.4.0.UTRAN Iub Interface: General Aspects and Principles [EB/OL].(2002-09-18)[2006-05-30].http://WWW.3gpp.org/ftp /specs/2004-09/Rel-4/25_series/25430-490.zip.

[3] Li Xiaowen, Li Guiyong, Chen Xianliang, et al. TD-SCDMA third generation mobile communication system, signaling and implementation [M]. Beijing: Posts and Telecommunications Press, 2003.

[4] Zhang Yi, Xian Jiqing. TD-SCDMA signaling test software design scheme [J]. Journal of Chongqing University of Posts and Telecommunications (Natural Science Edition). 2003, 15(1): 32-34.

[5] Liu Wei, Zhang Zhizhong. Development of IP data acquisition card for TD-SCDMA network tester [J]. Journal of Chongqing University of Posts and Telecommunications (Natural Science Edition). 2005, 17(6): 853-856.

[6] 3GPP TR 25.931 V4.4.0.UTRAN functions, examples on signaling procedures[EB/OL].(2002-06-18)[2006-05-30].http://WWW.arib.or.jp/ IMT-2000/V310Sep02/S3g/R99/25/25931-370.pdf.

[7] ITU-T Q2630.1.AAL type 2 signaling protocol-Capability Set 1[EB/OL].(1999-12-20)[2006-05-30].http://WWW.itu.int/ rec/T-REC-Q.2630.1/en.