GSM is the most representative and mature system in the second-generation digital cellular mobile communication system. It has large capacity, high spectrum utilization rate, good communication quality, many types of services, easy to keep secret, small and light user equipment, and open network. Road structure (ONI) and other advantages. The various interface regulations of the GSM system are clear, which not only facilitates the interconnection between the mobile devices of various communication companies, but also facilitates the intercommunication between the GSM system and ISDN, PSTN, PDN and other telecommunication networks. At present, the GSM system has become the main body of China's digital cellular mobile communication network.
1. Relevant interfaces and protocols of the switching subsystem (SSS)
The switching subsystem mainly completes the basic switching functions of the GSM system, call connection functions, user data management and mobility management. It consists of MSC (Mobile Service Switching Center) and VLR (Visiting Subscriber Location Register), and together with network entities such as BSS (Base Station Subsystem) and HLR (Home Location Register) form a complete GSM system. The GSM technical specifications define different interfaces to ensure the standardization of interfaces between functional entities.
The communication between the relevant interfaces of the switching subsystem is all supported by the No. 7 signaling system, and the communication between the GSM system and the PSTN prefers the No. 7 signaling system. GSM-specific and call-independent signaling uses MAP (Mobile Application Part), MAP protocol uses the services provided by No. 7 signaling system TCAP (Transaction Processing Application Part), and TCAP itself uses SCCP (Signaling Connection Control Part ) Provided services. The call-related signaling uses TUP (telephone user part) and ISUP (ISDN user part), which are used for communication between MSC and MSC with PSTN and ISDN, respectively.
Second, the switching subsystem test hardware configuration
In order to complete the testing of the switching subsystem, 2 MSC / VLR, 2 BSC (base station controller), 2 or more BTS (base station), 1 HLR, 1 short message service center (SC) and the switch to be tested are required PSTN switch connected to the subsystem. There should also be a signaling monitor that can monitor four signaling links simultaneously. If the test environment does not have 2 BSCs and more than 2 BTSs required for testing the relevant interfaces, the WG8610 analog simulation instrument can be used to simulate two BSC entities at the same time, and the mobile switching subsystem MSC / VLR under test through the two E1 interfaces Connected. The switching subsystem is also connected to external HLR and PSTN switches through two other E1 interfaces. The signaling monitor uses Agilent's Agilent37900D and ETP71 signaling monitors. The Agilent37900D signaling monitor can monitor not only the A interface and MAP signaling, but also SCCP and TCAP messages. Its maximum configuration can be up to 16 2M ports. It can monitor 40 signaling links at the same time, which can fully meet the test requirements. MTUP signaling between MSC and between MSC and PSTN uses ETP71 for monitoring. It should be noted that since there is no authentication center? AUC ?, all signaling flow tests related to authentication cannot be performed.
3. What the exchange subsystem needs to test
Before testing the switching subsystem, you should ensure that the transmission link between the relevant interfaces of the switching subsystem is working properly, the NO.7 signaling link has been activated, the testing of MTP, SCCP and TCAP has been completed, and various routes have been completed Set the data of the draw.
The switching subsystem test involves many contents, including: A interface test, service capability test, performance test, MAP validity test, MTUP validity test, OMC operation and maintenance function test. The following is a brief introduction, and the detailed message flow and test steps for each specific test item will not be repeated.
(1) A interface test
The A interface is the interface between the mobile service switching center of the digital cellular mobile communication network and the base station subsystem. In the test, the Agilent37900D signaling monitor was used to monitor the signaling process on the A interface. To ensure accurate analysis of the handover process, the Agilent37900D needs to be simultaneously Monitor two signaling links (one for each of the two BSCs), and coordinate the timer duration related to the A interface signaling.
(2) Business ability test
The main purpose of the service capability test is not to monitor the signaling process, but to strictly follow the test steps to verify whether the switching subsystem supports a service and whether the relevant data is correct. The service capability test includes telecommunication service test, bearer service test, supplementary service test, lock-up service test determined by the operator, and user contract limit test.
(3) Performance test
The performance test is mainly to detect the mobile network function of the switching subsystem. It includes basic call capability test, release control mode test, mobility management test, security management test, system billing function test, tracking test, and dual-band support capability Testing and VLR performance testing.
(4) MAP validity test
The effectiveness test of the MAP interface requires two sets of switching subsystems, or a set of switching subsystems and a tester with simulation function, which are alternately used as the A party and the B party. In the test, the Agilent37900D signaling monitor was used to monitor the signaling of each interface of the MAP. In order to analyze the cause when a problem occurred, the signaling process on the A interface should be monitored at the same time. MAP test items include version compatibility, update location, supplementary service processing, call processing, handover, user management, operation and maintenance, short message service, and inspection IMEI.
(5) MTUP validity test
According to the characteristics of the GSM system, MTUP made some specific provisions on the basis of TUP signaling. During the test, the following points should be noted when using the ETP71 signaling monitor to monitor the MTUP message flow:
· GSM only uses automatic connection, so there is no operator category in the calling user category;
· The GSM system does not establish an international bureau, so there are no messages and parameters related to international calls in the MTUP message;
· Due to the precious frequency resources, if the mobile called user is busy, the MSC will not send SLB messages;
GSM does not provide maintenance, so the MSC does not send CCL messages, and the G and E bits in the FSM and BSM messages are always 0;
The MSC does not send DPN messages, but only receives and forwards.
(6) OMC operation and maintenance function test
OMC is mainly responsible for the switching subsystem network operation and maintenance management, and should have a communication interface with the high-level telecommunications management network. Its functional tests include man-machine command test, data management test, alarm system test, system real-time control test, diagnosis and Restart test, service observation test, public equipment switching test and traffic statistics test.
The above test should meet the relevant technical specifications and test specifications of 900 / 1800MHz TDMA digital cellular mobile communication network.
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