Upgrade and Optimization Scheme: GSM Intelligent Network to DestinationNetwork

Guo Zhong Xu Kai

（Jiangsu Branch of China United Telecommunications Corporation, Nanjing 210000, China）

Abstrac t:The networking of intelligent networks involves overlay network and destination network.Destination network triggers intelligent services by the CAMEL Subscription Information（CSI）,and it has broader applications than overlay network.Upgrade from existing network to destination network requires a multitude of preparations and tests.Cities and provinces upgrade their networks from the aspects of Service Control Point（SCP）,Home Location Register（HLR）,Mobile Switching Center（MSC）,Gateway Mobile Switching Center（GMSC）and subsciption information through different processes.In order to fully realize the destination network after upgrading the accounting systems,the bill collection have to be rebuilt while the value-added services have to be upgraded.However,many difficulties,such as the Originating-CAMEL Subscription Information（O-CSI）,the Terminating-CAMEL Subscription Information（T-CSI）,and the special access number optimization,which all needs a particular solution,exist in upgrading.

T he networking of intelligent networks involves overlay network and destination network.Overlay network triggers intelligent services by a special access number.Destination network triggers the intelligent services by the CAMEL Subscription Information（CSI）,and it has broader applications.This article introduces the practical upgrade construction experience of Jiangsu Unicom in GSM intelligent network to destination network,and discusses the way of smoothly upgrading the overlay network to destination network and the supporting scheme of various services after implementation.

1 Connection Principle of Destination Network

In the destination network,Originating/Terminating-CAMEL Subscription Information（O/T-CSI）are stored in the Home Location Register（HLR）.In case where the intelligent network subscriber initiates the call（A is assumed as the initiating party,Bis assumed as the terminated party,as shown in Figure 1）,the Mobile Switching Center（MSC）/Service Switching Point（SSP）receives the call and triggers services based on O-CSIof subscriber A in HLR.The Service Control Point（SCP）sends the Initial Detection Point（IDP）message,and the SCPa queries the initiating party's relevant information to determine the account balance,and acquires the area code of the visited location of initiating party from the LOCATION NUMBERin the IDP message.If the localcallis not supported,SCPa determines the charge rate in accordance with the originated call's home location,visited location and the terminated number,and sends messages including Request Report Basic Call State Model Event（RRBE）and Acknowledged Charge（AC）,and continues to accomplish the calling connection procedure of intelligent network［1］.

When an intelligent network user is in terminating mode（A is assumed as the initiating party,B is assumed as the terminated party,as shown in Figure 2）,MSCa/SSPreceives the call,sends Send Routing Information（SRI）to terminated HLR,and the subscription information T-SCIis returned.Once the terminated Global Title（GT）address of SCPb is obtained from T-CSI,MSCa/SSPwill send an IDPmessage to SCPb.When receiving the IDPinformation,SCPbanalyzes the account information,home location and roaming location related to the terminated party to determine the charge rate,and sends RRBE,AC,and Continue messages to MSCa/SSP.After receiving Continue,MSCa/SSPinitiates the second query to the terminated HLR to obtain the Mobile Station Roaming Number（MSRN）and conduct the connection［2］.

Figure 1.▶Call originating access flow chart of destination network.

◀Figure 2.Call terminating access flow chart of destination network.

2 Pre-test and Preparations for Destination Network Upgrade

（1）Test before Upgrade As the devices in legacy network are from different vendors,equipment versions for destination network upgrade are immature and equipment interoperability is complicated.As a result,the following tests should be conducted prior to upgrade:

·Each vendor's single subscription information loading test

This is to test if the HLRwill automatically update the subscriber information in Visitor Location Register（VLR）after subscription is loaded,and to check the loading rate and the verification of subscription information loading instructions.

·Co-existence test of MSC number segment triggering data and subscription information

This is to test the influence of the co-existence of two types of calldata,which serves as a reference for determining the scheme for upgrade at night.

·Test for various terminated numbers（access number,IP,dedicated service number and short code）

When upgrading to destination network,the transfer format of terminated numbers is commonly changed into numbers without prefix.Tests for IP,dedicated service number and short code should be specially noticed.

·Voice loading test

Before upgrading,only specific SSP may load the voice services of the intelligent network.After the upgrade,all end office SSPs should carry the intelligent network voice triggered by the end office;thus,the destination network must load voice and conduct detailed test for voice procedure.

·Test for subscription information suppression

Before the entire network is upgraded to the destination network,subscription information triggering is carried out independently in several provinces.When a subscriber with subscription information roams out of the province where the network has been upgraded to Mobile Application Protocol（MAP）PHASE 2+,exceptional location update and interrogation occur,and the subscriber will fail in completing a call as a result.

To comply with the specification,a subscription information suppression function is needed for HLR,and it can be implemented by adding“black list”or“white list”data,suppressing or not suppressing the subscription information of relevant end offices.In the case of suppression,after the subscription information subscriber logs on,O-CSIis not returned to the log-on initiated office when HLRreceives the Location Update request initiated by the suppression end office;when the suppression end office initiates Interrogation inquiry for subscription information pre-paid subscriber,T-CSIis not returned to the inquiry initiated office by HLR.And it is reversed in the case of not suppressing.

（2）Preparations before Upgrade

Preparation work involves network element topology,which includes the following:

·SCPs in the entire network are improved.

·HLRs in the entire network are improved to support subscription information suppression,loading and unloading functions.

·Accounting customer service system is improved to accept subscription information related command input.

·All vendors complete compatibility test on（G）MSC/SSPand comply with the specification.

·MAPversions of HLR,MSC,Gateway Mobile Switching Center（GMSC）are upgraded to MAPPHASE 2+［1］to support subscription information.

3 Major Steps and Contents of Destination Network Upgrade

Major steps and noticed items in destination network upgrade are listed in Table 1 and Table 2.

（1）SCP

·According to the terminated test contents mentioned above,the transfer methods of various terminated numbers in the destination network mode are determined as“86+number”,“area code without a zero+number”,“0086+number”,“area code with zero+number”,and data in“number”format with Table Mapping configuration［1］.In the overlay network,two-bit prefixes are used to substitute the data of multi-bit short code or IPprefix code;however,this method is no longer applicable in destination network mode.Thus,real prefix code data is adopted instead（as destination network co-exists with overlay network in the previous upgrade,the old data can not be deleted）.

·In the destination network,all end offices are not transferred to specific SSP for triggering;therefore,SCPshould be configured with data related to additional SSP.

▼Table 1. Steps and noticed items in local city upgrade

▼Table 2. Steps and noticed items in provincial upgrade

（2）HLR

·The MAPversion of HLRis upgraded to MAPPHASE 2+.If MAP PHASE 2+is not supported by relevant MSC,MAPversion between HLR upgraded to MAPPHASE 2+and corresponding MSC is still MAPPHASE 2,with no impact on original Overlay calling procedure.

·Translation data of Global Title（GT）related to nationwide SCPis added.

（3）MSC,GMSC

·The upgrade to MSC/SSPsupports CAMEL application protocol（CAP）PHASE 2.

·Load intelligent network record notification.

·Modify prefix data,which is implemented at the upgrading night after the subscription information is loaded,and which enables all provincial Pre-Paid Service（PPS）subscribers to trigger CAPprocedure via O/T-CSI,rather than overlay to specific SSP according to originated/terminated number analysis;when an out-of-province PPSsubscriber in his localnetwork is called,and an out-of-province PPSsubscriber roaming to the province initiates a call or is called,overlay to independent SSP according to number analysis to implement CAPprocedure triggering.On completion of nationwide upgrade of CAPPHASE 2,MAPPHASE 2+,and having determined that out-of-province PPSsubscribers use O/T-CSIto trigger CAPprocedure,the triggering procedure of these out-of-province subscribers may be modified.

·MAPversion of MSC is upgraded to MAPPHASE 2+.

（4）Loading subscription information and opening it locally

As it takes a long time to load subscription information,according to previous single subscription information loading test results of various vendors,the HLRthat does not automatically update VLRdata after subscription information is loaded in the case of subscription information suppression,is loaded in advanced in the case of subscription information suppression.As for the HLRthat can automatically update VLRdata after subscription information is loaded in the case of subscription information suppression,the vendors can be coordinated to implement loading the subscription data of current equipment mirror disk,and to replace the mirror disk with the master disk at the night when the subscription information is opened.It's necessary to communicate with the accounting system before loading the subscription information to modify subscriber's applying/replacing card procedures.Also,the modification time must be determined to prevent the subscriber from applying/replacing a card between the start time of loading the subscription information and the modification time.

Major work in opening local subscription information involves:

·Modifying the number triggering data（prefix data）of the end office

·HLRopening the subscription information to the local end office

·The local end office initiating corresponding restarts,updating the location of the logon subscriber,and enabling VLRto obtain the subscription information.

·Conducting call test and verifying charges for each end office.

（5）Opening subscription information to the whole province

After the local subscription information is opened to all cities in the province,subscription information should be opened between cities.Below are three available schemes:

·All HLRin the province open subscription information of all end offices,and all end offices perform corresponding restarts.This scheme can be quickly implemented.However,it is not recommended due to too much end offices that must be restarted,high risk,and difficulties in personnel arrangement.

·All cities are divided into different regions.Subscription information is firstly opened inside the region,and is then gradually opened to the whole province.This scheme is a compromise from scheme 1,and should be adopted only in case of urgency.

·All provincial HLRs open the subscription information to allcities,and only one（or above）end office restarts at night.Compared to the former two schemes,this scheme has a low workload and equipment risk,but takes longer time for implementation.It may be adopted in the case of labor shortage or sufficient time.

4 Other Improvements on Upgraded Destination Network

The destination network targets eliminating the restriction on number segment,and enables mutual transformation between common subscriber and intelligent network subscriber.So far,as mentioned above,the upgrade and improvement of the switched network element have been accomplished.However,in order to fully realize the destination network,the following two aspects should be improved:

（1）The accounting system,especially the bill collection,should be improved.

The billing department acquires the revenue of intelligent network services from statistics of SCPbills while filtering and eliminating the intelligent network bills from the end office.Because a special number segment is used in the overlay network,the intelligent network number segment can be filtered via number segment judging.As mutual transformation between common subscriber and intelligent network subscriber is realized in the destination network,it can only use the special field in the bill for filtering.Take China Unicom,which applies Call Reference Number（CRN）to filter bills,for example.Their billing department is required to improve the bill collection program as a result of using CRN.

（2）Value-added services should be upgraded

As all PPSsubscribers in the intelligent network apply short message and customized information for real-time charge,the short message gateway and short message center should implement destination network upgrade to realize mutual transformation between common subscriber and intelligent network subscriber.Hence,it can judge whether to implement the charging procedure of the common subscriber or the intelligent network subscriber by the subscription information obtained from HLR.

5 Solutions to Destination Network Upgrade Difficulties

（1）O-CSI

According to GSM specifications,when originating subscription information is loaded for PPSsubscriber in HLR,O-CSIis transferred directly to MSC/VLR.Only when the subscriber re-initiates location update,will the suppression list in HLRreact to eliminate O-CSIof the subscriber.However,in such case,it is difficult to thoroughly clear all PPSsubscribers in a short period,especially when there are only one or two MSCs in the city,thus leading to O-CSIleakage in a certain period of time.

In order to erase the adverse effects on network during loading,it is recommended that the following routine should be done besides loading the originated subscription information（taking Siemens'instructions as an example）:

·Before loading,entire network suppression should be completed.

·Before loading,store the subscription information triggering the database INTRIG of local/provincial switches and major adjacent provinces,including the INTINTGTaddressing data of all SCPs.As O-CSIand the triggering database of calling digital analysis and functional control（DPFC）can co-exist,there is no impact on the local/provincial PPSsubscriber services.

·When daily instructions are loaded,switches in the city and adjacent provinces perform ACTHLRUPD instruction in HLR.

·If the localnetwork is small with only one or two MSCs,and the HLR loading can be completed in one night,it is recommended to restart the switch.With this scheme,the calling subscription information of all PPSsubscriber can be cleared thoroughly.

Especially for subscribers roaming out of the province,once they are attached with the calling subscription information and go into the places without condition for calling subscription information triggering,the subscriber is unable to initiate a call,but is able to receive calls.When such problem occurs,the subscriber can be deleted from the current VLRin HLR,and is forced to initiate location update.

（2）T-CSI

It mainly targets the SSPwhere number segment triggering data and subscription information triggering data cannot co-exist,as exemplified by Siemens switch.

In Siemens HLRworking mechanism,suppression of terminated subscription information is controlled by the originated black/white list（RAT）.Opening the originated subscription information will influence the corresponding terminated subscription information service.

As for the development of terminated subscription information,the DPFC-related databases should be deleted once terminated subscription information is opened,because the terminated subscription information cannot co-exist with terminated DPFC triggering database.There are two schemes:

（1）Deleting DPFC-related databases before the terminated subscription information is opened.

Advantage:smooth transition of terminal PPSsubscriber service if the phone line is not disconnected during the opening process.

Disadvantage:when the terminal PPS subscriber makes a phone call during the short period before the opening of subscription information,it is unable to implement real-time charging,but only manual charging by SCPafter being processed by the background billing software.

（2）Deleting the DPFC-related databases after the terminated subscription information is opened.

Advantage:no charge is lost.

Disadvantage:during the short period before the DPFC-related databases are deleted,the PPSsubscriber called will lead to call failure due to a secondary triggering,thus harming the benefits of the terminal subscriber.

In general,the two cases mentioned above have only little impact on the network,and can be adopted according to actual situations.A combination of both schemes is applied in specific implementation project in Jiangsu province.

（3）Optimization for special number

The“Improvement specification of switched sub-system for China Unicom GSM Color Ring Back Tone service（V1.0）”says that,in order to reduce unnecessary CAPtraffic and save network resource,the following stipulations are made for dedicated services:

·For a charged dedicated service,it is necessary for SSPto trigger the dedicated service number to SCP.However,a free-of-charge dedicated service number can directly reach the provincial or local office,rather than being triggered to SCP.

·Refer to relevant provisions of China Unicom and its provincial branches for charge of dedicated services.

As for free dedicated service codes such as 110,119,120,122,the originated subscription information suppression of SSPshould be initiated to avoid the originated subscription information directly triggering such a call to SCP.Then,the originated handle is transferred to CODE=110,ORIG1=99,which can use number segment database（CPT）to send the call to the local office.If the user is permitted to dial local area code+110,or country code+local area code+110 locally,the corresponding suppression and access databases should be added.

It should be noted that the suppression of the originated subscription information will result in the calling DPFC triggering database working if the DPFC triggering database in the switch has not been cleared.In China Unicom's pre-paid live network,it means that the originated handle is transferred to CODE=C110,ORIG1=99.

The CPTdatabase has accordingly to be used for sending C110 to the local office.

For dedicated service code,which is free of charge for local calls and charges for long-distance calls,as exemplified by 10010,the originated subscription information suppression of SSPshould be initiated to avoid the originated subscription information in local MSC/VLRto directly trigger the call to SCP.But in GMSC/TMSC,a localarea code+1001 that comes from other cities and provinces should be transferred to SCP.

If some special numbers,such as PHSnumbers with head segment of 86,necessitate the suppression of originated subscription information triggering in the SSP,terminated special numbers should be modified and triggered to the SCPfor access.In this case,if SCPis unable to identify the special numbers,SSPwould conduct the suppression.

6 Conclusion

The upgrade process of China Unicom's GSM intelligent network,from the original overlay network to the destination network,is complicated.During the actual upgrade process,the upgrade scheme was continuously optimized based on the lessons gained in the upgrade experience.The intelligent network has smoothly been transformed to the destination network.In addition,the upgrade experience will serve as a guide for future nationwide intelligent network upgrade.