Unity SIP : Quick Definition
Unity SIP integrations are reliant on SIP for communications and is also reliant on a SIP Proxy Server and a SIP Gateway.
Call Manager/SCCP forward to Unity
When a call is forwarded by Call Manager to Unity, the following information are included:
- The called party’s extension
- The calling party’s extension or external phone number
- The reason that the call was forwarded to Unity (Busy, No-Answer, Inconditional)
So with these information, Unity is able to route the call to the correct mailbox.
Cisco Unity : Quick Definition
Cisco Unity provides voice mail and unified messaging capabilities for many thousands of users.
Unity can be integrated with the following products:
- Call Manager
- SIP
- Circuit-switched (traditional PBX)
- Circuit-switched via Intel PIMG
Signaling System 7 – SS7
SS7 is a Common Channel Signaling (CSS) system used in the PSTN that enables functionalities including call control, databases queries, network operations and transactions.
Also on SS7 networks, the redundancy must be a high statement
T1/E1 CAS
CAS stands for Common Associated Signaling and the signaling operates by “robbing” the least significant bits of information from voice channels and using this to send clocking and framing information. CAS is also known as robbeb bit signaling.
At the opposite of the ISDN, T1/E1 CAS uses in-band signaling which are:
- Loop-start
- Ground-start
- E&M wink-start (Feature group B, FGB)
- E&M wink-start (with acknowledge)
- E&M double wink (Feature group D, FGD)
- E&M Feature Group D Exchange NA, FGEANA
- E&M immediate-start
E&M signaling is often the preferred optino for CAS because it avoids glare, it provides answer/disconnect supervision and it can receive Automatic Number Identification (ANI) with FGD and send ANI with FGD-EANA. In other words, you can have 1 channel-group for incoming calls and 1 channel-group for outgoing calls.
ISDN (BRI/PRI)
ISDN is a digital transport service that can support both Data and Voice over existing telephone wires. There are 2 types of ISDN:
- Basic Rate ISDN – BRI : This provides 2 x 64 Kbps bearer channels and a 16 Kbps signaling channel. It represents then (2B+1D) channels , so 144Kbps
- Primary Rate ISDN – PRI : this provides 23 or 30 x 64 Kbps beare channels depending on whether it is delivered as a T1 or an E1. It represents then (23B+1D) channels for a T1 and (30B+1D) for an E1
At Layer2, ISDN signaling is provided by the Link Access Procedure on the D channel (LAPD) which is relying on Q920/921 messages.
At Layer3, ISDN call control signaling and access to service are specified by the Q931/932 messages suchg as Setup, Alerting, Connect ,…
Now as the network is not end-to-end all the time, you can encounter that you don’t receive anymore busy tone after the destination is busy. It is normal as once the ISDN network has sent the busy tone to the IP Phone, it iniatiates a normal call clearing so a disconnect, then you can fix this on the your side by setting the following command voice call convert-discpi-to-prog to force the gateway to send the busy tone on the IP end even if the ISDN side is torn down