Signaling protocols

In addition to the voice signals that are sent to and from the caller, other signaling information is also sent to and from the switch, to enable such functions as:

Call control (call setup and clearing)
Detection and notification of caller hangup
Provision of call information such as the caller's telephone number
Call-transfer and message-waiting information

A variety of signaling protocols provide some or all of these functions. Functions that are supported by T1 protocols are listed in Table 1, and functions that are supported by E1 protocols are listed in Table 2. Before deciding on or configuring a specific protocol, you must ensure that your central office switch, PSTN, PABX, or channel bank can also support the required functions. More information about the protocols is given in the Blueworx Voice Response for AIX: General Information and Planning information.

Table 1. Functions provided by T1 protocols.
For each T1 protocol, this table shows if it is a trunk-side or a line-side protocol, whether or not PSTN, PABX, and channel bank connectivity are supported, and also whether or not answer detection, call transfer, far-end disconnect, ANI, and DID or DNIS are supported.
Protocol	Type ⁹	Connectivity			Function
		PSTN	PABX	Channel bank	Answer detection	Call transfer	Far-end disconnect	ANI	DID or DNIS
E&M¹	Trunk	Yes	Yes	Yes²	Yes	No³	Yes	Yes	Yes
FXS Loop Start ¹	Line	Yes	Yes	Yes²	No	Yes	No⁴	No⁵	No ⁵
SAS Loop Start	Line	Yes	Yes	Yes	No	Yes	No⁴	No⁵	No ⁵
FXS Ground Start ¹	Line	Yes	Yes	Yes ²	No	Yes	Yes	No ⁵	No ⁵
ISDN (5ESS 5E9)	Trunk	Yes	No	Yes⁶	Yes	No	Yes	Yes	Yes
ISDN (5ESS 5E12)	Trunk	Yes	No	Yes⁶	Yes	No	Yes	Yes	Yes
ISDN (T1 National 2)	Trunk	Yes	No	Yes⁶	Yes	No	Yes	Yes	Yes
ISDN (DMS100 BCS34/36)	Trunk	Yes	No	Yes⁶	Yes	No	Yes	Yes	Yes
ISDN (TR41449/41459)	Trunk	No	Yes	Yes ⁶	Yes	No	Yes	Yes	Yes
ISDN NA008 (DMS National)⁷	Trunk	Yes	No	Yes⁶	Yes	No	Yes	Yes	Yes
ISDN IEC05 (DMS250)⁸	Trunk	Yes	No	Yes⁶	Yes	No	Yes	Yes	Yes
ISDN(INS Net Service 1500)	Trunk	No	Yes	Yes⁶	Yes	No	Yes	Yes	Yes
In the Type column, Trunk means “trunk-side protocol” and Line means “line-side protocol” Note: For both 2-bit AB (SF) format and 4-bit ABCD (ESF) format, as defined in TIA/EIA 464-B. A channel bank for 4-bit (ESF) format CAS signaling must support extended superframe (ESF) line framing. Yes, if the switch offers a release link trunk. Yes, if a disconnect clear signal is provided. Some PABX and ACD systems send number identification by sending DTMF digits before or after the call is answered. A channel bank for ISDN must support extended superframe (ESF) line framing. Supports RLT call transfer and two B-channel transfer. Supported RLT call transfer.

Table 2. Functions provided by E1 protocols.
For each E1 protocol, this table shows if it is a trunk-side or a line-side protocol, whether or not PSTN, PABX, and channel bank connectivity are supported, and also whether or not answer detection, call transfer, far-end disconnect, ANI, and DID or DNIS are supported.
Protocol	Type¹²	Connectivity			Function
		PSTN	PABX	Channel bank	Answer detection	Call transfer	Far-end disconnect	ANI	DID or DNIS
E&M¹	Trunk	Yes	Yes	Yes	Yes	No²	Yes	Yes	Yes
FXS Loop Start	Line	Yes	Yes	Yes	No	Yes	No³	No⁴	No⁴
EL7/CAS	Line	No	Yes⁵	No	Yes	Yes	Yes	No⁶	No⁶
Italy	Trunk	Yes	No	No	Yes	No	Yes	No	Yes
R2⁷	Trunk	Yes	Yes	Yes	Yes	No	Yes	Yes	Yes
R2MFC^{8, 9}	Trunk	Yes	No	No	Yes	No	Yes	Yes	Yes
RE	Line	No	No	Yes	No	Yes	No	No	No
SL¹⁰	Line	Yes	No	No	Yes	No	Yes	No	No
TS003¹¹	Trunk	Yes	Yes	Yes	Yes	No	Yes	Yes	Yes
UK Callstream	Trunk	Yes	No	No	Yes	No¹²	Yes	No	No
UK Exchange	Trunk	Yes	No	No	Yes	No	Yes	No	No
UK Tie/DDI	Trunk	Yes	No	No¹³	Yes	No¹²	Yes	Yes	Yes
ISDN	Trunk	Yes	Yes	No	Yes	No	Yes	Yes	Yes
SS7 ISUP	Trunk	Yes	No	No	Yes	No	Yes	Yes	Yes
In the Type column, Trunk means “trunk-side protocol” and Line means “line-side protocol” Note: For connection to Siemens Hicom 300 switch. Yes, if the switch offers a release link trunk or an ACL exchange data link is available. Yes, if a disconnect clear signal is provided. Some PABX and ACD systems send number identification by sending DTMF digits before or after the call is answered. Unique protocol for Ericsson MD110. Yes, if a VMS exchange data link is available on the MD110. R2 digital line signaling as specified by ITU-T Q.421. Korean only R2MFC uses R2 for line signaling Subscriber Loop, used in France. Multifrequency compelled (MFC) is not supported. Yes, to support ”inverted“ E&M. “Mid-call diversion” is supported.

Two classes of signaling protocol exist: channel associated signaling (CAS) and common channel signaling (CCS). In addition, an exchange data link (EDL) can be used with a CAS protocol to provide additional signaling functions.

Channel associated signaling

When channel associated signaling protocols, such as E&M wink start, or FXS loop start, carry the signaling information for a particular channel, they carry the information on either of the following:

The voice channel.
A signaling channel that is permanently associated with the voice channel.

This signaling information enables call control (call setup and clearing), but other functions, such as far-end hang up detection, are not necessarily provided by all channel associated signaling protocols.

Exchange data link

If your CAS protocol does not provide all the signaling functions that you need, you might be able to use an exchange data link; that is, a link from the switch to the pSeries computer on which Blueworx Voice Response runs. This link can carry additional signaling information to enable:

Detection and notification of caller hangup (far-end hangup)
Provision of call information, such as called and calling telephone numbers
PABX-like functions, such as call transfer and message waiting indication

Exchange data link signaling protocols, such as ACL, SMDI, SMSI, and VMS, are typically used with trunks that use a channel associated signaling protocol for call control.

Alternatively, you can use CallPath Server to send additional information to and from the switch, including called and calling number, message waiting indication (MWI), and far-end hangup detection. The CallPath_SigProc signaling process that is used to communicate with CallPath Server is registered as an exchange data link, and needs to be configured in a similar way.

Note: Some switches restrict use of CallPath to trunks that use line-side protocols instead of trunk-side protocols (as shown in Table 1 and Table 2). Ask your switch manufacturer to verify that CallPath is supported.

Common channel signaling

Common channel signaling protocols, such as Signaling System Number 7 (SS7) and Primary Rate Integrated Services Digital Network (ISDN), carry allthe signaling information for many voice channels over a single, dedicated signaling link. The common channel signaling link can provide:

Call setup and clearing
Detection and notification of caller hangup (far-end hangup)
Provision of call information, such as the caller's telephone number

The signaling link is usually one 64 Kbps channel on a T1 or E1 trunk. Most common channel signaling protocols are based on the OSI reference model (X.200), and work by exchanging predefined messages.