Preventing Calls from Being Transferred Through a Trunk and the IVR

It is recommended that you configure prefixes for intra-office, local, national toll, and international toll calls. By default, even if the national and international toll call prefixes are not configured, the system automatically determines whether a call is a local, national toll, or international toll call according to the number a user has dialed. If the user does not have the corresponding call rights, the system denies the call. If a user has the requirements to make national or international toll calls, configure the national (ddd) or international (idd) toll call rights.

The 214 control point enables or disables automatic determination and call restriction functions, and it does not affect the call restriction functions when national and international toll call prefixes are configured.

In the tandem scenario, if the outgoing prefix of PBX2 is the same as the country code prefix or area code prefix of PBX1, users under PBX1 need to dial the outgoing prefix (for example, 9) of PBX1, outgoing prefix (for example, 0) of PBX2, and then a user number, which is 90+user number, and one digit of the called number needs to be deleted on PBX1. Figure 2-11 shows the trunk tandem network. Assuming that the country code prefix is 00 and area code prefix is 0, if a user under PBX1 has only the right to make local calls, the user cannot make outgoing calls by dialing 90+user number. This is because PBX1 considers 0+user number as a toll call number. When the national and international toll call prefixes are not configured, configure the 214 control point so that the system will restrict calls not according to the calling parties' call-out rights. For details, see pbx number-parameter.

Figure 2-11 Trunk tandem network

If the 214 control point is configured for the system to restrict calls not according to the calling parties' call-out rights, toll fraud may occur. In this case, the national and international toll call prefixes must be configured to prevent toll fraud.

Mapping between the call prefix attribute and call-out rights for calls transferred over a trunk and the IVR:

Assume that the right for the inter-office call prefix between PBX1 and PBX2 is 1.

For the calling party whose incoming calls are made over a trunk, the default call-out right is the same as that for calls transferred over a trunk. If the call-out right for calling number discrimination is configured on the PBX, the call-out of the calling party is that configured for calling number discrimination. To prevent users from calling inter-office users after calls are connected over a trunk, configure the call-out right for calling number discrimination.

<Huawei> system-view [Huawei] voice [Huawei-voice] caller-change 0 [Huawei-voice-caller-change-0] callerprefix 7* [Huawei-voice-caller-change-0] outgoing-right
inter enable [Huawei-voice-caller-change-0] caller no-change [Huawei-voice-caller-change-0] called no-change [Huawei-voice-caller-change-0] save

Assume that the prefixes 9, 90, and 900 indicate the local calls, national toll calls, and international toll calls. Call prefix 9 is used as an example. For call prefixes 90 and 900, set attribute values to 2 and 3. For details, see Configuring a Call Prefix.

<Huawei> system-view [Huawei] voice [Huawei-voice] callprefix 9 [Huawei-voice-callprefix-9] prefix 9 [Huawei-voice-callprefix-9] call-type category basic-service attribute 1 [Huawei-voice-callprefix-9] digit-length 1 32 [Huawei-voice-callprefix-9] save

Call-out rights are classified into inter, local, ddd, idd, all. You can configure multiple call-out rights simultaneously. The default call-out rights for calls transferred through a trunk are inter and local. To enable the PBX not to forward incoming calls over a trunk, configure inter. If a user makes a call over a trunk and wants to call a local user, configure inter and local. If a user wants to make national or international toll calls, configure ddd or idd. For details on how to configure call-out rights, see Configuring Call Limiting Over a Trunk.

It is recommended that outgoing-right of the trunk between PBX1 and PBX2 be set to inter&local and outgoing-right of the trunk between the PBXs and the PSTN be set to inter.

<Huawei> system-view [Huawei] voice [Huawei-voice] trunk-group sippra [Huawei-voice-trunkgroup-sippra] outgoing-right local enable [Huawei-voice-trunkgroup-sippra] callroute 1 [Huawei-voice-trunkgroup-sippra] save

If a trunk has local right or more rights, a user can make a call over this trunk and calls inter-office users, which may cause a call fraud.

Assume that a 4-digit extension number is used. Set the second-dialing number length to 4 so that an inter-office user only needs to dial the IVR and extension number to call the intra-office user. If the second-dialing number length is larger than or equal to the inter-office number length, when inter-office call conditions are met, an inter-office user can dial the IVR and another inter-office user. As a result, a call fraud occurs. To prevent users from dialing the IVR and inter-office user's number, set the second-dialing number length to the intra-office number length. For details, see IVR Configuration.

Call-out rights are classified into inter, local, ddd, idd, all. You can configure multiple call-out rights simultaneously. The default call-out right is inter. By default, after a user dials the IVR, the user cannot call an inter-office user. If a user wants to dial the IVR and make outgoing calls, configure the call-out right.

<Huawei> system-view [Huawei] voice [Huawei-voice] callprefix 888 [Huawei-voice-callprefix-888] vuoutgoingright
local enable [Huawei-voice-callprefix-888] save

When the IVR has local right or more rights, a user can dial the IVR, hear the second-stage dialing tone, and dial the inter-office user's number, which may cause a call fraud.