In this section:
This section provides you with information about ISUP trunk management.
The following figure shows an example of the ISUP call flow and Figure ISUP Message Sequence shows the ISUP message sequence for the corresponding network configuration.
ISUP Call Flow (Example)
ISUP Message Sequence
The following table lists the node records that have been declared in the example illustrated in Figure ISUP Call Flow (Example)
Node Records Created in the Preceding Configuration Example
| Name | Public PC | Private PC |
|---|---|---|
| Public Gateway | 3.3.3 | - |
| Switch 11 | 2.2.2 | 2.2.2 |
| Switch 2 | - | 4.4.4 |
| Switch 3 | - | 5.5.5 |
1 It is highly recommended that you keep the public and private PCs the same (if feasible) for simplicity in the public node definition
The following table shows the trunk mapping table that has been declared for the example illustrated in Figure PCE Architecture and Figure ISUP Call Flow (Example)
Trunk Mapping Table
| Public Node Name | Public Gateway Name | Public CIC Min | Public CIC Max | Private Node Name | Private CIC Min | Private CIC Max |
|---|---|---|---|---|---|---|
| Switch 1 | Public Gateway | 1 | 100 | Switch 2 | 201 | 300 |
| Switch 1 | Public Gateway | 101 | 200 | Switch 3 | 1 | 100 |
ISUP Message Flow Process
- Switch 1 sends a message to the public gateway PC (3.3.3). This is the public representation of the private switches.
- The PCE looks up the trunk record on the public side of the trunk mapping table. This process allows the PCE to determine that the message must be sent to Switch 2 and that the Circuit Identification Code (CIC) value must be mapped.
The OPC is mapped, but remains the same as Switch 1 at Public PC and Private PC (see Trunk Mapping Table). This configuration is highly desirable, because this arrangement makes troubleshooting easier by eliminating the extra conversion. - Switch 2 responds back to the originator (using private 2.2.2).
- PCE again uses its trunk mapping record to look at the Originating Point Code (OPC), Destination Point Code (DPC), and CIC value to determine the appropriate values on the public network.
ISUP Management Message Handling
The ISUP Management feature is designed to manage the trunk mapping restrictions. ISUP management affects incoming traffic from the public network destined for the private network where the intended private remote PC is unavailable from all PCE processes (MTP_PAUSE received) or the message's CIC is undefined (no matching trunk mapping record is found).
For traffic from the private network destined to the public network, PC deregistration of the private gateway PC in the private network manages the unavailability of an associated public remote PC. The corresponding MTP3 VNode, with enabled Broadcast TFA, Broadcast TFP, and Broadcast TFR attributes, triggers the necessary SS7 PC notification [Transfer Allowed (TFA), Transfer Prohibited (TFP), and Transfer Restricted (TFR)] on PCE registration and deregistration to MTP3.
For traffic from the public network destined to the private network, an unavailable private remote PC notification cannot be broadcasted to the public network through a TFP, because the corresponding private gateway PC is not a one-to-one map with a specific private remote PC.
If the ISUP Management feature (refer to Configuring the PCE Configuration) is disabled and a message is destined for an unavailable private remote PC or for an unknown trunk mapping, the message is discarded.
On loss of availability from a private remote PC at all processes (or locally with enabled Mono Mode feature), the active PCE process generates corresponding Circuit Group Blocking (CGB) messages for the specific CIC range and forwards these messages to the relevant public remote switches. The CIC range minus one, divided by 32 for ITU and 24 for ANSI, plus one determines the number of CGB messages required to block the specific CIC range. For ANSI, each CGB message is sent twice according to SS7 specifications.
Note
- The Mono Mode feature ensures voice circuit management on unavailable private signaling points where a PCE process is down or is unreachable. Only recommended for long maintenance windows.
- A Boolean attribute is defined in the PCE Configuration object to enable or disable the CGB generation on the loss of availability from a private remote PC. The CGB generation feature is only enabled if the ISUP Management feature is also enabled.
- The ISUP Management feature is not applied, even if enabled, in the rare event that a PCE process is defined [through the Layer Distribution Library (LDL) file] but unavailable. This precaution is required, because of the possibility of the PCE process having an active link to a paused destination on the local system. CGB initiation on the local system would be conflicting. The Mono Mode feature is available to identify a lost PCE process down for maintenance.
- Unblocking of the circuits is the responsibility of the private remote switch and not generated by the PCE to avoid race conditions.
The following table provides you with the expected behavior on incoming traffic from the public network.
Incoming ISUP Traffic Management (Public Network)
| Message | Unavailable PC | Undefined CIC1 |
|---|---|---|
Address Complete Message (ACM) | Discard | Discard |
| Answer Message (ANM) | Discard | Discard |
| Blocking Acknowledgement Message (BLA) | Discard | Discard |
| Blocking Message (BLO) | Return BLA. | Return UCIC. |
| Connect Message (CON) | Discard | Discard |
| Circuit Group Blocking (CGB) | If CIC range overlaps with the CIC Mapping record, discard. Else, return CGBA. | Discard |
| Circuit Group Blocking Acknowledgement Message (CGBA) | Discard | Discard |
| Circuit Group Unblocking Message (CGU) | If CIC range overlaps with the CIC Mapping record, discard. Else, return CGUA. | Discard |
| Circuit Group Unblocking Message (CGUA) | If CIC range overlaps with the CIC Mapping record, discard. Else, return CGB with same range. | Discard |
| Circuit Group Query (CQM) | If CIC range overlaps with the CIC Mapping record, discard. Else, return CGB with same range followed by a CQR with all circuit states set to transient. | If CIC range overlaps with the CIC mapping record, discard. Else, return CQR with all circuit states set to unequipped. |
| Circuit Group Query Response (CQR) | Discard | Discard |
| Circuit Group Reset Acknowledgement (GRA) | Return BLO and RLC. | Discard |
| Circuit Group Reset (GRS) | If the CIC range overlaps with the CIC Mapping record, discard. Else, return GRA. | Discard |
| Initial Address Message (IAM) | Return BLO. | Return UCIC. |
| Release Message (REL) | Return RLC. | Return UCIC. |
| Release Complete Message (RLC) | Discard | Discard |
| Reset Circuit Message (RSC) | Return BLO and RLC. | Return UCIC. |
| Unblocking Message (UBL) | Return UBA. | Return UCIC. |
| Unblocking Acknowledgement Message (UBA) | Return BLO. | Discard |
| User Part Test (UPT) | Discard | Discard |
| Default (all other messages) | Discard | Discard |
1 A Boolean attribute is defined in the PCE Configuration object to enable or disable the Unequipped Carrier Identification Code (UCIC) message support. If the UCIC support is disabled, the incoming message is discarded. For more information, refer to Initial PCE Configuration Tasks.
The following table provides you with the information on the PCE-generated ISUP messages.
PCE Generated ISUP Messages
| Message | Attribute | Description |
|---|---|---|
| BLA | N/A | |
| BLO | N/A | |
| CGB | Range and Status CGSupMsgTypeInd1 | The Range is based on the SS7 Variant. The Status bits are set to 1 (blocking) and CGSupMsgTypeInd is set to 0x00 (maintenance-oriented). |
| CGBA | Range and Status CGSupMsgTypeInd1 | The Range is based on the SS7 Variant. The Status bits are set to 1 (blocking ack) and CGSupMsgTypeInd is set to 0x00 (maintenance-oriented). |
| CGUA | Range and Status CGSupMsgTypeInd1 | The Range is based on the SS7 Variant. The Status bits are set to 1 (unblocking ack) and CGSupMsgTypeInd is set to 0x00 (maintenance-oriented). |
| CQR | Range and Status Circuit State Indicator | The Status field is not included. The CSI length is the Range value + 1, where all indicator octets are set to 0x00 (transient). |
| GRA | Range and Status | The Range is based on SS7 Variant. The Status bits are set to 1 (blocked for maintenance reasons). |
| RLC | N/A | |
| UBA | N/A | |
| UCIC | N/A |
1 Circuit Group Supervision Message Type Indicator.
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