1.1 Basic Concepts
1.1.1 Traffic measurement
The CCITT Blue Paper calls it traffic measurement and the national standard calls it traffic statistics and
measurement or traffic statistics. The definition in the CCITT Blue Paper is:
It measures the traffic and load in the switching office or around the telephone network to provide the data about the telecom network running.
The traffic measurement provides a data basis to check whether the telephone network reaches the desired capacity and to design, run, and manage the telephone network, making the best use of the resources. Here “the best” includes two aspects: reasonable allocation of the resources and economy.
In this text, unless otherwise stated, statistics and measurement are used to indicate the same meaning. Measurement includes three basic elements: measurement entity, measurement object, and measurement time.
1.1.2 Measurement entities
It refers to the quantity that needs to be collected for a specific measurement. For example, to measure the traffic and congestion of the trunk, you need to obtain the number of outgoing call seizure attempts and the outgoing call seizures of the trunk.
The alias of the measurement entity is counter or measurement index. The traffic measurement terminal displays it as “measurement index” and this text describes it as “measurement entity”.
1.1.3 Measurement object
It refers to the physical or logical entity to be measured, such as a circuit group, circuit subgroup, office direction, or destination.
It should be noted that the traffic measurement is designed with references to the ITU Traffic Engineering Specifications. The following is the correspondence between Huawei concepts and ITU concepts.
1.1.4 MSC trunk group -- circuit subgroup
[MSC trunk group] refers to a set of trunks in the switch with the same attributes. There are several methods for selecting lines for the trunk circuits in the same MSC trunk group.
[Circuit subgroup] refers to a group of circuits with the same features (such as the signaling mode and transmission path). A circuit group can be composed of multiple circuit subgroups.
1.1.5 MSC subroute -- circuit group
[MSC subroute] is the element that makes up the MSC route. It is composed of MSC trunk groups that are numbered according to the modules.
[Circuit group] is a group of circuits regarded as a unit in service design.
1.1.6 MSC route -- route
[MSC route] is composed of MSC subroutes. MSC route includes all the possible paths for a call to reach the destination. When a route (subroute) to a destination is busy, some other routes can be selected based on some rules.
[Route] refers to one or several circuit groups for connection between the switching offices (the switching offices are not necessarily connected directly by the circuit groups).
1.1.7 MSC office direction -- circuit group
[MSC office direction] is the direction of the route to the equipment connected physically and directly by the trunks to the switch.
[Circuit group] is a group of circuits regarded as a unit in service design.
From the above comparison we can tell that if the MSC data configuration method is the recommended one, as is the current case, we can obtain the correspondence between MSC concepts and concepts.
1.1.8 Measurement time
It refers to time factors when the traffic measurement is conducted.
The time factors in the traffic measurement include measurement level, record day level, and record period level. There is the corresponding user input interface in the traffic terminal, providing flexible combinations.
1.1.9 Measurement type
Measurement type is the effective combination of the measurement entity and the measurement object. The switch needs to trigger several events during the service processing. An event may aim at a certain object or a certain object group. This requires the measurement entity and object to have a clear definition of the multi-element relationship.
1.1.10 Measurement unit
Measurement unit: a specific measurement, which is fully described by measurement entity, measurement object, measurement time information, output routing information and scheduling information. The description information tells what, when and how to measure, and when and where the result can be output.
1.1.11 Subset of the measurement unit
Subset of the measurement unit: a set composed of several measurement units that have the same attributes. Each subset of the measurement unit describes a party of the switching equipment. For example, the global traffic measurement subset and the bearer traffic object measurement subset. Or we can call it a measurement task, i.e. a measurement task for us to select in the traffic measurement system. The following sections will give a detailed description of these measurement tasks.
1.1.12 TrBaffic statistics report
Traffic statistics report describes the result of a traffic measurement. It includes the measurement object and measurement entity, the measurement period, and the start date and end date of the measurement period. The purpose of it is to provide a basis for global and whole-network performance measurement, planning, and operational management.
1.1.13 Output routing information
Output routing information specifies where the measurement results will be sent for recording (such as terminal or the NMS). The arrangement of the output routing information reflects the architecture of a traffic measurement system to some extent.
1.1.14 Output scheduling information
Output scheduling information specifies when the measurement results will be output as required by the user (i.e. a concept of the measurement period).
1.2 Traffic Flow Model
1.2.1 Traffic flow model
The traffic measurement model of the MSC switch is as follows:
Figure 1-1 Traffic measurement model of the MSC switch
Where:
A: Originating traffic
B: Incoming traffic
C: System originating traffic
F: Local traffic
G: Outgoing originating traffic
H: originating system terminating traffic
J: incoming system terminating traffic
K: Incoming terminating traffic
L: Transit traffic
O: system originating terminating traffic
P: system originating outgoing traffic
Q: terminating traffic
R: Outgoing traffic
S: System terminating traffic
Traffic in the flow directions of C, H, J, O, P and S are usually small and can be calculated through traffic addition and subtraction of other flow directions. Therefore the traffic measurement of GSM MSC focuses on 8 flow directions (A, B, F, G, K, L, Q and R), as is called statistics of 8 major flow directions.
The above 8 major flow directions are called global traffic flow directions. The global traffic measurement offers the traffic distribution and their connection types of the 8 flow directions. The following Figure illustrates the flow directions of the simplified traffic measurement model.
Figure 1-2 Flow directions of the global traffic measurement
From Figure 1-2, we can see that: A >= F + G, B >= K + L, Q <= F + K, and R <= G + L. The above inequality means that there are call losses due to various causes during the switching processing.
As for global traffic measurement, the measurement entities involved in each traffic measurement are distributed at different stages of service processing.
The forthcoming sections will use the abbreviations of the 8 major flow directions. They are:
Originating traffic -----------ORG;
Intra-office traffic -------INT:
Originating outgoing traffic -------- ORGOEX;
Incoming traffic --------- EX;
Incoming terminating traffic ------- IEXTE;
Transit traffic ------- TRA;
Incoming traffic --------TE;
Outgoing traffic -------- OEX.
1.2.2 Note
The concept of “fixed subscriber” in traffic measurement.
You need to determine the definition of “fixed subscriber” with the mobile network operator. The subscribers with incoming and outgoing calls are all fixed subscribers, i.e., the subscribers going through TUP and ISUP are regarded as fixed subscribers. So all the incoming calls, outgoing calls, and transit calls are regarded as of the fixed subscribers, regardless whether the peer office is PSTN or GSM. The mobile to mobile calls are possible only in the case of intra-office calls.
1.3 Introduction to the MSC Traffic Measurement System
The traffic measurement of MSC and the related networks can provide basic data for the following tasks:
Design, plan, and management of the switches and the switching network
Performance monitoring of the switches and the network
Network management
Operation and maintenance of the switches and the network
Fees and market survey
Forecasting
1.3.1 Structure of the MSC Traffic Measurement System
The software structure of the MSC traffic measurement system is as follows:
1.3.2 Functions and Features of the MSC Traffic Measurement System
Features of the MSC traffic measurement system:
1) Support the data dictionary function: the measurement types, measurement entities, and measurement objects are described in the data dictionary to guarantee the portability, maintainability and expandability.
2) There are 3 time segments in a day for measurement by data or by week. For example, you can specify the measurement task to be performed at 9:00~11:00, 13:00~16:00 and 20:00~21:00 each Saturday and each Sunday.
3) Support record period from 1 minute to 24 hours.
4) Support the simple report function. You can choose any measurement entity of your concern or of the same measurement function type. If the measurement object is the same, you can even choose measurement entities of different measurement types and register them into the same task.
5) Support user-defined measurement entity: based on the measurement entities provided by the switching equipment, the subscriber can define measurement entities by arithmetic expressions. The operand can be a constant, measurement period, or the measurement entities provided by the switch.
6) Support the function of registering several measurement objects in a task.
7) By using the re-registration mechanism, the measurement tasks will not be lost during the switchover or re-loading operations. All re-registration processes are transparent to the user.
8).Provide the self-healing mechanism. For example, if the switch time fluctuates greatly, the system can make recovery after self-test to avoid the hanging of the tasks.
9) Support task activation/deactivation.
10) Support the modification of task measurement period.
11) Support real-time query of measurement entities to make testing and maintenance easier.
12) Enhanced timeliness: counters and real-time traffic scanning are used for the number of calls and traffic so that they can be measured in the real time. Scanning precisions of 1m, 10s, and 1s are provided to ensure the accuracy of the measurement.
1.4 Implementation Principle of the MSC Traffic Measurement System
1.4.1 An example of the correspondence between the measurement index and the service-layer report
The following is a simple call flow:
1) Call attempts
2) Number of mobile calling subscriber authentication failures
3) Number of mobile calling encryption mode setup failures
4) Number of mobile calling subscriber outgoing calls barred times
5) Number of overflows due to mobile calling BSS trunk busy
6) Number of mobile calling subscriber traffic channel assignment failures
7) Number of wrong dials
8).Number of subscriber premature releases.
9) Number of call losses due to switching network congestion.
10) Number of call losses due to common resource request failure
11) Connected times
12) Answer times
1.5 Functions of the MSC Traffic Measurement Console
1.5.1 Task functions of the MSC traffic measurement console
I. Task management function
The task management function includes creation and deletion of a measurement task, modification of the measurement period, activation and deactivation of a measurement task, and query of the measurement task information and status.
The measurement entities in a switch are organized and managed according to the measurement types. But in practice the user may hope to put the measurement entities that reflect the same switching service function together and measure and output them in a task (especially in the case of creating a traffic measurement report). For example, there are 8 measurement types that reflect the global traffic and each type includes “call attempts”, “connected times”, and “answer times”. If no effective output method is available, the user needs to register 8 measurement tasks. The MSC traffic measurement system allows the user to select the measurement entities of different measurement types on the condition that the measurement object is the same.
In practice, the user may often hope to measure several objects when creating a measurement task. So at the creation of a new measurement task, the MSC traffic measurement system provides a method for inputting several measurement objects. The traffic measurement process will decompose the task into several sub-tasks according to the objects input by the user. The display of output can be sorted by time or by objects.
The measurement task deletion function is to delete the measurement task permanently.
The task modification function can be used to modify the record period of a created task.
Task activation/deactivation function: if the user hopes that the result is temporarily not output for an existing task, he/she can use the task deactivation function instead of being deleting it, and activate the task when it is required to output the result.
The task information query function can be used to query the information of the task in the switch. The information is the static data information of the task, including the status of the task, the type of measurement function, the time attribute of the task, measurement entity, and measurement object.
The task status query function is used to query the current status of the task in various modules of the switch, which reflects the stage at which the task is running. If a task runs wrong, the user can query its status and make remedies accordingly. The transition of the task status is as follows:
II. Task time management function
Time information of the task refers to all information necessary for specifying the start, duration and periodicity of a specific measurement. The MSC traffic measurement system fully complies with ITU E502 in terms of the traffic measurement time with enhanced functions. A variety of scheduling modes is available for the measurement time. There are several layers and types of time information according to the start, duration and periodicity, as shown in the following Figure.
Note:
From the moment the switch starts running, the measurement is made all the time, corresponding to the permanent task in the MSC traffic measurement system.
The measurement is made from the specified date for an unspecified period (without pre-defining the end date), corresponding to the semi-permanent task in the MSC traffic measurement system.
The measurement is made from the specified date for a specified period (the end date is pre-defined), corresponding to the limited period task in the MSC traffic measurement system. The measurement is made either continuously or discontinuously in the measurement period. The discontinuous measurement can be either periodic or non-periodic.
III. Task output function
The MSC traffic measurement system offers the task print function for printing the measurement results of a task in the form of a measurement report to a file, i.e. output in the Excel worksheet or in the text format for the maintenance personnel to edit and typeset.
1.5.2 Description of the special functions
I. User-defined measurement entities
The measurement entities that a switch provides are pre-defined. But the user’s demands may vary with different users. For example, the user may hope that only the names of the desired measurement entities are displayed during the result output; several measurement entities can be combined together to display the output after arithmetic operations; some of the measurement entities, such as the call successfully rate, can be calculated by the user-defined formula, instead of by the formula provided by the equipment supplier. To best meet the user’s demands, the MSC traffic measurement system provides the function of user-defined measurement entities., i.e. the user can define their own measurement entities by applying arithmetic expressions based on the original measurement entities and register them to the task. This function is very useful during the report output.
II. Real-time query of the measurement entities
All the measurement entities of the MSC traffic measurement system are stored in the global counting area for the user to query in real time. This function is largely used in testing and maintenance.
III.The mode of data dictionary description
The MSC traffic measurement system is implemented on the basis of the data dictionary description. So one feature of the MSC traffic measurement system is its good scalability. The user can perform add or delete operations easily by modifying the data dictionary to meet the multi-node type demands without altering the program.
1.6 Introduction to the Measurement Types of the MSC Traffic Measurement System
Some new measurement types are added in the MSC traffic measurement system according to the feature of MSC.
1.6.1 Global traffic measurement subset
Global traffic measurement provides the traffic description on a global basis. By analysing the measurement reports of the global traffic, various information can be obtained (including status of calls in all directions, Call QoS, network quality) to serve as the reference for traffic alleviation and error correction. Its measurement types include: Originating traffic, internal traffic, originating outgoing traffic, incoming traffic, incoming terminating traffic, transit traffic, terminating traffic, outgoing traffic, and other call proceeding types.
1.6.2 Call processing measurement subset
This measurement subset is largely used to measure the processing at different stages in the call service process to meet the mobile exchange’s requirement for NSS traffic measurement. The data that this measurement subset offers can be a basis for evaluating the QoS and service grade of the switching equipment. Its measurement types include: Call drop rate, call answered rate, MTC successful rate, and call delivery successful rate.
1.6.3 Bearer object traffic measurement subset
It offers the measurement of the traffic bearer objects, including physical and logical bearer objects, such as trunk, office direction, and destination code. The performance indices of these objects, in particular the object groups (e.g. trunk group and office direction), have largest influence on the performance of the call service. They are the basic data for the exchange and the network maintenance and planning management. Therefore the MSC/VLR traffic measurement system provides for these object groups the automatic measurement (i.e. semi-permanent counting) of trunk groups in each office direction and can report the measurement result at any time. The contents include the measurement of trunks in each office direction and each destination code. Its measurement types include measurement on interworking circuit groups and measurement on call destinations.
1.6.4 MSC basic table measurement subset
The MSC basic table measurement subset complies with GSM 12.04 and provides the measurement of miscellaneous items of MSC. Its measurement type includes the MSC basic table measurement.
1.6.5 Basic service performance measurement subset
The basic service performance measurement subset is used to observe how the MSC processes the GSM basic service and its traffic, hence to know the processing capability of the NSS equipment and provide reference data for the network management, network planning, and QoS evaluation. Its measurement types include: Location management service measurement, authentication procedure measurement, TMSI reallocation procedure measurement, cipher mode setting procedure measurement, handover measurement, single-cell handover measurement, inter-cell handover measurement, paging procedure measurement, and assignment procedure measurement.
1.6.6 Special service measurement subset
The special service measurement subset is used to observe the traffic of other telecom services except the tele-service, such as short message, bearer service, supplementary service, thus to provide reference data for the network dimensioning & planning, cost and market survey and network management. Its measurement types include: Short message service (SMS) measurement and bearer service measurement.
1.6.7 BSSMAP measurement subset
The BSSMAP measurement subset is used to observe the major events that occur in the BSS equipment, thus enabling the user to see the BSS status from the NSS side and providing reference data for the network management, planning, and maintenance. Its measurement types include: BSC measurement
1.6.8 Signaling procedure measurement subset
The signaling procedure measurement subset is used to check the processing capability, effectiveness, and utilization of the signaling processing parts such as MTP, SCCP, TCAP, A interface, MAP, TUP, and ISUP to provide reference data for the network maintenance, management, and evaluation of the QoS. Its measurement types include: MTP signaling link (SL) measurement, MTP SL set measurement, MTP DSP state measurement, MTP adjacent signaling point state measurement, SCCP performance measurement, SCCP availability measurement, SCCP utilization measurement, TCAP availability measurement, TCAP component utilization measurement, A interface signaling procedure error measurement, MAP common service procedure error measurement, MAP signaling procedure error and timeout measurement, number of TUP messages, number of TUP exceptions, TUP node performance, TUP network performance, TUP circuit group performance, number of ISUP messages, number of ISUP exceptions, ISUP node performance, ISUP network performance, and ISUP circuit group performance.
1.6.9 Common part measurement subset
Common parts serve the call connection process, but do not join in a specific call processing after the call connection is established. Since common parts are shared by many calls, their quantity and performance may directly affect key indexes such as the call completion rate. Therefore, traffic and congestion times of common components can be measured to provide most basic information for improvement of the QoS of the exchange.
1.6.10 Control part measurement subset
The control part is the core of the switch. Its processing capability is directly related to the BHCA index. The measurement data about the load, congestion, and overload of the control part can serve a reference for network management and flow control.
1.6.11 VLR measurement subset
The VLR measurement includes subscriber data measurement inside the VLR, the CPU load of the VDP board, and the VLR basic service measurement. It reflects the signaling traffic processing of the VLR.
1.6.12 Call records
By recording the data at the key stages of the call proceeding, you can understand the operational performance and overhead of the switch and evaluate the grade of service and quality of service of the switch. Analyzing the sampled call records is very helpful in the maintenance personnel’s troubleshooting.
1.6.13 Intelligent service traffic measurement subset
The intelligent service traffic measurement subset includes the following measurement types: intelligent call traffic measurement, intelligent proportion measurement, intelligent session measurement, intelligent failure measurement, SRF resource measurement, INSM operation measurement, MAP intelligent service measurement, intelligent events measurement, and SSF call measurement.
Among them, the intelligent call traffic measurement again includes several types: intelligent to mobile calls, mobile to intelligent calls, intelligent to fixed calls, fixed to intelligent calls, intelligent to intelligent calls, calls of all subscribers to operator (presently only the 13800138000 call is available).
1.6.14 Location area and cell traffic model measurement subset
The location area traffic distribution measurement and the cell traffic distribution measurement can be used to measure the call traffic, call drops, location updates, and subscriber distribution of a location area or cell from the geographical perspective. By the above measurements, you can further analyze the geographical factors that lead to low call completion rate and low location update success rate, as well as the influence of user groups in different regions on the QoS of the switch.
1.7 Brief Analysis of the Completion Rate
1.7.1 Overview
I. Factors that may affect the toll call completion rate
There are several factors that may lead to the low toll call completion rate:
- Paging success rate
- Subscriber busy
- Wireless call loss (TCH assignment failure and SETUP failure).
- Forward clear (connection and paging expiry due to BSC and MSC parameter definition errors).
- Incomplete number
- Called onhook, or no answer
II. Methods for analyzing the completion rate
The completion rate is of concern to the users. The traffic measurement system provides preliminary measures to locate the causes that may lead to a low completion rate. They include:
- By failure cause measurement, you can know the failure causes and number of failures, and compare them with the previous data to see what leads to the drop of the completion rate.
- By digital mobile switch traffic measurement, you can know the call information of each flow direction and the major failure causes and judge which direction is abnormal.
- By the trunk traffic measurement of the office direction, you can select all the office directions and all the measurement entities to see the failure causes of each office direction and to tell which office direction is abnormal.
- By flexible use of the combination conditions object measurement, you can further tell the incoming call or outgoing call of which office direction has abnormal disconnect operation.
1.7.2 General approaches to improve the completion rate
Generally, you can take the follow steps to improve the completion rate:
I. Collection of the data about the completion rate
Method 1: Traffic measurement
Traffic measurement is the major means for collecting the information about the completion rate. It is very helpful to register the following traffic measurement tasks by the command line or user interface (UI): office direction incoming traffic measurement (bearer object traffic measurement task), office direction outgoing traffic measurement (bearer object traffic measurement task), trunk group incoming traffic measurement (bearer object traffic measurement task), trunk group outgoing traffic measurement (bearer object traffic measurement task), subscriber line group traffic measurement (bearer object traffic measurement task), global failure cause summarization (global traffic measurement task), called subscriber toll busy traffic measurement (extreme value traffic measurement task), maximum call loss subscriber traffic measurement (extreme value traffic measurement task), busy subscriber traffic measurement (extreme value traffic measurement task, and no-reply subscriber traffic measurement (extreme value traffic measurement task).
You will have a comprehensive understanding of the failure causes after you registered the above traffic measurement tasks and observed the traffic measurement results for a period of time. The features, applicability, and creation methods of the above measurement tasks are introduced in Chapter 3.
Method 2: Signaling analysis
You can conduct signaling tracing in the maintenance console and analyze the tracing results. The traffic measurement is intended to get the results. The signaling messages can reflect accurately in detail the signaling procedure of each call connection. You can use the signaling analysis tool to analyze the large amount of signaling tracing files and find out the failure causes for the unsuccessful calls and the details of the signaling procedure of the call connections, thus to determine the factors that affect the completion rate.
II. Analysis of the collected results
The traffic measurement results and the signaling analysis results record all the successful or unsuccessful calls of the switch and list the direct causes and times of failure. By analyzing the failure causes one by one, you will be able to take the corresponding measures to improve the completion rate.
The results of traffic measurement need to be analyzed item by item from the global traffic to local traffic. Sometimes the traffic measurement of a single task may not unveil the failure causes, in which case you need to register several traffic measurement tasks and make a comparative analysis. Sometimes short-term traffic measurement results may not unveil the problem, in which case you need to conduct measurement and observe for a long time. Sometimes the analysis of only the traffic measurement results may not unveil the problem, in which case you need to turn to the signaling analysis software for a solution.
The SS7 signaling analysis software is mainly used to analyze offline the signaling files obtained by tracing the links through the maintenance console, so as to find out the causes that may lead to unsuccessful calls and get the statistics data of the calling and called parties. However, at present only the GMSC version is available.
III. Handling of the problems and faults found out by analysis and location
After you find out the causes that lead to the problem, you can make remedies accordingly and take measures to improve the completion rate. The measures that you can take include modifying the data configuration, traffic grooming and traffic balancing , circuit expansion, and hardware replacement. After the problem is corrected, you still need to observe the effect and make sure that the problem will not repeat.
1.7.3 Basic measures to improve the system completion rate
I. Ensuring that the equipment, the trunks, and the signaling channels are intact
Make careful routine maintenance and check periodically to guarantee that the equipment works normally. For example, periodically make the dial test over each trunk and check the 2M interfaces/connectors to ensure that the trunks are intact and to lower the call loss; periodically check the antennas, feeders and the connectors and loss of the antenna & feeder system, the azimuth and pitch angle of the antenna to lower the call drops due to poor signaling quality; periodically check the BTS transmission quality and 2M interfaces/connectors to lower Abis call drops; periodically check the 13Mhz clock of the BTS MCK to guarantee the signal synchronization and improve the handover success rate.
II. Proper configuration of the load of each module of the MSC
The configuration principles for the trunks and links of a multi-module office:
1) Balance the traffic load between the modules.
2) Decrease the trans-module message packets.
Try to keep the speech channel and the corresponding priority link in the same module. Avoid the case where there is only the voice channel but not any link in a module. In case STP is involved, the speech channel should be allocated in the module that has links to that STP. In this way, not only the security of the module is protected, but also the load between modules is reduced, thus avoiding a large amount of forwarding of SS7 link messages between modules. Usually there are two local tandem offices in the peer-to-peer status to serve as the upper-level offices for an end office. You can converge the trunks and links to the two tandem offices into two modules. Or they may be two identical local LSTPs to provide links, and then you can converge the trunks into two modules by the office directions. The signaling to some office direction uses the link set in the module as the priority route.
3) Try to arrange the links in the same link set to have the same load.
When there are several SS7 signaling links in one office direction, the selection of links becomes a matter. Generally, there are two links, and you can use any of the bits of SLS for load sharing, preferably bit 1. There are two principles here: first, enough bits should be selected to differentiate the links. Second, the selected bit shall means that this link control N speech channels at a spacing of N speech channels:
N = bit 0*1 + bit1*2 + bit2*4 + bit3*8
1 for selecting the bit and 0 for not selecting the bit .
III. Trying to use No. 7 signaling trunk and pay attention to the trunk selection
For SS7 signaling circuits, the national standards of China provide two line selection modes: big number-small number/small number-big number and master/slave (LIFO/FIFO). The master/slave mode has a higher priority. Some switches, such as 5ESS, may use the big number-small number/small number-big number mode. You should note at this time that one of the two interconnected exchanges should select circuits with the biggest CIC first and the other should select circuits with the smallest CIC first. But the circuit selection of MSC is implemented via the internal trunk code. You should pay attention to the mapping relationship between the CIC and internal trunk code to make correct data configurations. As SS7 signaling circuits are bi-directional, contention may arise. To avoid this, we predefine that the two interconnected switches control half of the circuits respectively, so that when contention occurs, the slave party will release the circuit and initiate the call again in another idle circuit. The switch whose signaling point code is bigger controls the circuits with even CICs and the other switch whose signaling point code is smaller controls the circuits with odd CICs. When the traffic is comparatively large, circuit contention may affect the completion rate to a certain content, so it should be avoided.
IV. Proper configuration of the data and radio parameters
1) Configuring the prefix data reasonably
In a toll call, automatic paging, or special number call where the called subscriber requests the calling number, it is preferable that the calling number be sent voluntarily to reduce the number of inter-office message packets and ensure that the local exchange can send the calling type voluntarily in the case of interworking between CAS and SS7 signaling. If the calling number is not sent voluntarily,, there will be GRQ/GSM message in the SS7 link, thus increasing the load and the internal messages in the SS7 link and putting a heavy load on the MSC. The prefix of a local call must be complete in the outgoing prefix table, otherwise call loss will arise in the outgoing trunk due to incorrect prefix. For example, assume that the prefix of a local net is 2 and the office number is 211, if in the prefix table the prefix is conFigured as 2, all the numbers 2XXXXXX with the prefixes of 22-29 and 212-219 (the number sending takes the group mode for mobile calling) will occupy the outgoing trunk, and thus lead to call loss.
2) Configuring the number of SDCCHs reasonably
By adjusting the base station configuration and allocating the number of SDCCHs reasonably, you can reduce the drop of wireless completion rate due to failure in assigning the SDCCH to the mobile station at the normal call origination, location update, inter-cell handover and short messages.
3) Adjusting the base station parameters and distributing the traffic reasonably
For example, you can adjust the minimum signal level for the mobile station to access the neighboring cell and the cell reselection parameter C2 (i.e., adjust CRO to adjust the C2 value of each cell), so that the mobile stations at the cell borders stay in the cell where the traffic is relatively low.
V. Advertising the application of new services
For example, you can offer new services to the subscribers like CFB. If the subscriber has several communication tools (e.g. pager and telephone), he/she can set CFB to other communication tools such as the voice mailbox or secretary station.
VI. Using traffic measurement to find out problems and solve them on time
You can use the traffic measurement in the routine data statistics to offer data for the GSM network planning and management. You can also use the traffic measurement’s large capacity and wide coverage features to do many tasks. The traffic measurement data will help you find out the causes for call loss. For example, if the traffic in the cell is too large, you can increase the number of TRXs or the micro-cells to alleviate the traffic.
VII. Maintaining the equipment timely
1) Timely solve the transmission and peer office problems to recover the trunks quickly.
2) Analyze the SS7 message to guarantee the integrity of the signaling links.
The following are some causes for the link message that may affect the completion rate:
Causes that lead to SEC:
1. Failure in applying for the internal resources like CR and CCB
2. Unstable inter-module links, which lead to call disconnect.
3. Failure in applying for the forward resources
4. Failure in applying for HW resources
Causes of CFL: when the switch fails to connect a call, other messages are inappropriate to express the failure reasons, so CFL will be sent. For example, an incoming trunk is used by the local exchange as a semi-permanent connection and the peer exchange has a call that occupies this trunk, then the incoming and outgoing calls in this trunk will be restricted, and CFL will be sent.
Causes of LOS: it is a backward signal sent in the fixed network when the called subscriber line does not work or is faulty. For example, if the telephone is not well on hook for a long time, the telephone will be locked, and if there are calls to this telephone, LOS will be returned. In a mobile network, when the called party is a mobile subscriber, MSC will send LOS if the called party cannot be paged due to the damage of the equipment in BSS.
Note: There is a chapter later to describe how to improve the completion rate in more detail. What is described here serves as an overview only.
1.8 Troubleshooting for Traffic Measurement
Problem 1: an office changes the period of a measurement report task (permanent) from 15 minutes to 60 minutes at 10:20. From 10:00 – 11:00 there is no report result.
Cause: after the task period is reset, the host will calculate the result creation time based on the start time (0:00 for permanent task), current time, and the new period. The value of the counter at the start of the period must be saved and is subtracted from the current value of the counter at the end of the period to get the result of the current period. If the period is changed at 10:20, the value of the counter at 10:00 cannot be obtained, hence at 11:00 you cannot get the difference, nor the traffic measurement result and the report.
Solution: try not to set the period during the busy hour.
Problem 2: after a TUP office direction is added to the office direction table, the trunk traffic measurement task that measure all the office directions fails to include the new office direction.
Cause: the traffic measurement result is stored in the BAM. After a new record is added, to save the measurement result of that record, BAM needs to adjust the structure of task result storage. This will cause the loss of the previous measurement data. To guarantee the integrity of the previous measurement data, the task will be not added with the new record.
Solution: register another trunk traffic measurement task that measure all the office directions.
Problem 3: a task produces no result in some period under some circumstances. (Or the result is all 0s).
Cause: check the operation logs and it is found that some table data was once set. According to the design of traffic measurement, when the parameters of a task in the data management console is set, to guarantee the correctness of the current data, the measurement data corresponding to the set time will be discarded and the BAM will turn the result of the current period into 0s when it is obtaining the result of the next period.
Solution: try not to set data at the time when you need to observe the traffic measurement results, especially during the busy hour.
Problem 4: under the Originating Traffic Discrimination & Duration Measurement, some sample records show that the “exchange egress” data is measured and the “call attempt moment at the exchange egress” is not measured, while some other
sample records show that “call attempt moment at the exchange egress” is measured but the “exchange egress” data is not measured.
Cause: for calls to the fixed network, the data at the “exchange egress” is measured after the called number analysis is finished and DB returns the routing information (success or not), while the “call attempt moment at the exchange egress” is measured when the SETUP message is sent to TUP. If the routing fails, the data at the “exchange egress” will be recorded but the “call attempt moment at the exchange egress” will not.
For calls to the mobile network, the “call attempt moment at the exchange egress” is recorded when the paging information is fetched from the VDB, while the data at the “exchange egress” is recorded after the call is confirmed. If the paging receives no response, the above problem will occur. This is normal.
Solution: normal phenomenon, which does not need any processing.
Problem 5: the office-direction incoming trunk traffic measurement shows that number of connections is far greater than answer times plus releases while ringing plus no reply times plus call failures after connection.
Reason: ”Release while ringing” means the cases where the call is released while ringing really takes place, it does not include the cases where the call is released upon failure tone, which is included in the number of connected calls instead. Hence the inequality arises.
Solution: normal phenomenon, which does not need any processing.
Problem 6: a call sampled from the QoS measurement task is an effective call but the failure cause is “end point failure”.
Cause: the disconnect cause is reported from the bottom layer to the call processing module. This problem occurs when abnormal on-hook takes place due to call drops.
Solution: normal phenomenon.
Problem 7: the traffic measurement does not produce any result.
First you need to determine if none of the traffic measurement tasks can produce any result, or only part of them produce no results; If the no-result case lasts for only the recent one to two weeks, or all the time; If there is no result at all, or the result is all 0s. By querying and viewing the data operation logs and maintenance logs in the operation review of the data management console, you can check what operations were performed before and after the no-result period, such as the modification/setting of data, the switchover time and the adjustment time.
The following cases may lead to the problem of no results in the traffic measurement console:
1) Interruption of communication between BAM and GMPU.
2) Check the information of the task that produces no result to see if it is a limited period task, or a task that produces results by time segments, or a task whose number of tasks is limited by the QoS or traffic distribution. If it is a limited period task that has been terminated or one that produces results at certain time segments, naturally you will not be able to see the results.
3) After some tables are set, such as the office direction table, the called number analysis table, the BSC table, and the MTP table, it will lead to failure in producing results in the current period. This is not a bug, but a protection mechanism provided by the traffic measurement module to avoid abnormal traffic measurement result from occurring in this period after modification of the data.
4) Manual or automatic switchover will lead to failure in producing results for one or several periods.
5) Because of the BAM protection mechanism, if the system time is changed substantially, no result will be produced, in which case you need to delete the previous traffic measurement results for the new results to be produced.
If you have determined the cause, you can make remedies accordingly. The following are some measures:
1) Check the network cables and HUB to see if the communication between GMPU and BAM is normal. Check the data operation logs and alarms to see if there are any abnormal operations or alarms.
2) Set the corresponding tables: for example, if the office-direction measurement task produces no result, you can set the office direction table (without any need to modify the data). This is because after the table is set, the traffic measurement module will perform refresh operations. So you should re-measure the items such as traffic volume to check if there is any result at the next period.
3) Register a new task to see if it can produce results normally.
4) Save the previous results and then delete them to see if the result can be produced at the next period.
5) Restart BAM to see if the result can be produced.
