PGW Design Considerations with CVP
Introduction
In many Hosted environments, particularly when the service provider is itself a PSTN carrier, all the actual call routing occurs via an ICM NIC. In that sense, these deployments are very much like Deployment Model #4 (i.e VRU Only with NIC Controlled Routing). The same situation applies if a PGW is being used to route calls using (typically) the ICM SS7 NIC.
PGW can be consider in such deployment models where a service provider is looking to support very high level of call volume. Such deployment could use the UCCE parent child model.
Features
PGW does support Geographic redundancy, call limiting, SIP virtual interfaces, etc; PGW can support SIP to SIP over 1000 call per second today, and has potential to double this performance. It is based on class-4 softswitch, and has powerful routing capabilities for both E.164 and FQDN-based routing. It is a full SIP B2BUA that also supports SIP proxy mode.
Call Control Traffic
Unified CVP is currently certified with three types of VoIP endpoints: Cisco IOS voice gateways, Cisco Unified Communications Manager (Unified CM), and the PGW (in either Call Control mode)
PGW as a Call Control Entity
Customers using Deployment Model #4 (VRU Only with NIC Controlled Routing) rely on call switching methods that do not involve Unified CVP. In these situations, all switching instructions are exchanged directly between a Unified ICM SS7 Network Interface Controller (NIC) and the PSTN via PGW. CVP just acts like a VRU (Queuing and Prompting) in such cases.
Terminology
The Service Provider side of terminology is little bit different than what we use in the enterprise world so it is important to understand it quickly here.
- Caller-A : Is a caller behind the PSTN makind inbound call into the Contact Center
- Agent-B : Is Transferring Agent (A level one agent that receives all calls before sending them to right agent)
- Agent-C : Is Transferred-To Agent (The final agent)
- ITNT: Is very much equivalent to DTMF based input method during the IVR session
- NBT: Is Network Based Transfer and can also be referred as GUI based transfer
- NCT: Network Consulting Transfer
- NCT After NCT: Is a transfer mechanism that solves the double transfer problem
PGW and CVP Design Comparison
- Like CVP, PGW will always remains in the loop
- PGW is also a call control entity more like CVP but it doesn't provide queuing and VRU type functionality
- In such deployments, the CVP will only be used as VRU and will not act like a call processing unit
- PGW only takes care of the Transferring Agent (Agent-B), rest is handled by CVP and ICM
- Before PGW, the ITP and MGX are required components
- ITP receives SS7 signaling traffic where MGX receives the bearer traffic
Call Flow 1
NOTE: In this flow, Agent-C is available to take the call and no IVR queuing and prompt required
- Call comes in from PSTN over SS7 network to ITP before hitting PGW
- Since SS7 is out of band call signaling mechanism, hence the bearer will establish using a different path via MGX that will be discussed later
- ITP will send the call to PGW
- PGW will make a INAP query to ICM
- ICM will receive such queries via SS7 NIC
- ICM will reply back with INAP-RESPONSE
- CVP will check the agent availability and will send call to Agent-B
- Agent-B will then do the final transfer
Call Flow 2
NOTE: In this flow, Agent-C is not available and VRU treatment and queuing is required at CVP.
This call flow would remain the same as Call Flow 1 till the point where call comes in to the Network. Once it is there the media will be terminated on the MGX gateway and signaling will be handled by CVP
Call Flow 3
NOTE: In this flow, Agent-B is not available and VRU treatment and queuing is required at CVP.
This call flow would remain the same as Call Flow 1 till the point where call comes in to the Network. Once it is there the media will be terminated on the MGX gateway and signaling will be handled by CVP.
Courtesy of Amir Raza
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