Common channel signaling

The other way in which you can overcome the disadvantages of channel associated signaling protocols (see Disadvantages of channel associated signaling), is to use a common channel signaling (CCS) protocol. Common channel signaling avoids all these problems. Using short, fast messages that are sent (bidirectionally) down a single time slot of a trunk, the switch/network and the voice response unit can communicate much more efficiently than they can with a channel associated signaling trunk.

Blueworx Voice Response supports two types of common channel signaling protocol:

Integrated Services Digital Network (ISDN)
Signaling System 7 (SS7)

Blueworx Voice Response also supports the development of specialized common channel signaling protocols for intelligent network (IN) applications, through the use of the signaling interface.

Integrated Services Digital Network

In contrast to Signaling System 7, the ISDN primary rate interface (PRI) is designed as an access protocol, and is therefore also known as primary rate access (PRA).

Figure 1. ISDN as an access protocol
This diagram shows ISDN being used to connect a caller to a telephone switch, and to connect another switch to . The switches are connected to each other by voice circuits, and to a service control point through SS7.

This diagram shows ISDN being used to connect a caller to a telephone switch, and to connect another switch to . The switches are connected to each other by voice circuits, and to a service control point through SS7.

An ISDN trunk is a T1 or E1 trunk with one of the timeslots dedicated to signaling; this timeslot is called the D-channel. (The D-channel signaling protocol is based on the ITU-T Q.921 and Q.931 recommendations.) The remaining timeslots are used for voice and are called B-channels (see Figure 2). ISDN trunks are generally used between an external subscriber and a switch within a network. ISDN will eventually displace channel associated signaling (that is, T1 and E1 trunks) as the means by which primary-rate subscribers attach to SS7-controlled networks.

Figure 2. ISDN B-Channels and D-Channels. This example shows one digital trunk. An E1 trunk has 30 B-channels ; a T1 trunk has 23 B-channels.
A switch connected to by a single trunk, showing the separate D-channel for signalling and B-channels for voice.

A switch connected to by a single trunk, showing the separate D-channel for signalling and B-channels for voice.

Figure 3. Attaching Blueworx Voice Response as an intelligent peripheral in North America
used as an intelligent peripheral, connected to a switch by an ISDN link, within an advance intelligent network.

used as an intelligent peripheral, connected to a switch by an ISDN link, within an advance intelligent network.

In addition to being used as an access protocol, primary rate ISDN is used in the United States to attach intelligent peripherals within an operating company's advanced intelligent network (as shown in Figure 3). Blueworx Voice Response can either function as an intelligent peripheral, or provide voice processing function as part of a larger service node.

Advantages of ISDN

The usual reason for using ISDN is that it allows a single digital channel to be used for several different types of communication services, such as voice, X.25, video, and so on. However, for Voice Response Units such as Blueworx Voice Response, ISDN offers a further set of benefits, even if the Voice Response Unit is used only for voice:

Reliable call setup and clearing
Fast, reliable, delivery of called and calling number to the Voice Response Unit

ISDN protocols supported

The optional ISDN features support:

Primary rate interface (PRI) vendor-specific implementations
PRI switching and signaling capabilities
Calling number identification services for PRI

An optional feature of Blueworx Voice Response allows you to connect to the network over an ISDN primary rate interface that conforms to each of the following protocols:

Lucent 5ESS 5E8
Lucent 5ESS 5E9 National 1
Lucent TR41449/TR41459
Nortel DMS100 BCS34/36
Nortel DMS100 National 2 — NA015
Nortel DMS250 — IEC05
Lucent 5ESS 5E11–15 National ISDN2
INS Net Service 1500
Euro-ISDN
E1 ISDN QSIG ECMA 143 and international standard ISO/IEC 11572:2000

The National ISDN effort is being driven by Bellcore and the Corporation for Open Systems, on behalf of the operating companies and the North American ISDN Users Forum (NIUF).

The functions provided by each standard are summarized in Table 1 . Table 2 shows how Blueworx Voice Response supports ISDN protocols.

Lucent 5ESS 5E8: 5ESS 5E8 is a custom protocol implemented by Lucent Technologies on 5ESS central office switches in the U.S. It provides 23B+D channels over a T1 facility.
Lucent 5ESS 5E9 National 1: 5ESS 5E9 is a custom protocol implemented by Lucent Technologies on 5ESS central office switches in the U.S. It provides 23B+D channels over a T1 facility.
Lucent TR41449/TR41459: TR41449 and TR41459 are the custom protocols implemented by Lucent Technologies on the Definity PABX and 4ESS switch for use with T1 facilities.
Nortel DMS100 BCS34/36: DMS100 BCS34 and BCS36 are custom protocols implemented by Nortel on DMS100 central office switches in the U.S. They provide 23B+D channels over a T1 facility.
Nortel DMS100 National 2 NA015: DMS100 National 2 NA015 is a custom protocol implemented by Nortel on DMS100 central office switches in the U.S. It provides channels over a T1 facility.
Nortel DMS250 IEC05: DMS250 IEC05 custom protocols implemented by Nortel on DMS250 central office switches in the U.S. It provides channels over a T1 facility.
Lucent 5ESS 5E11–15 National ISDN2: National ISDN2 is a common ISDN standard developed for use in the U.S. It provides 23B+D channels over a T1 facility. National ISDN-2 is supported on the Summa Four PBX switch and on the Lucent 5ESS switch with 5E12 protocol.
INS Net Service 1500: INS Net Service 1500 is an ISDN standard developed for use in Japan. It provides 23B+D channels over a T1 facility.
Euro-ISDN: Euro-ISDN is a common European ISDN standard that provides 30B+D channels over an E1 facility. Euro-ISDN services are available in seventeen countries in Europe (including France, Germany, and the U.K.). Most of these countries provide Euro-ISDN services for production use; in a few countries, only pilot services are available. In some European countries, ISDN is already the generally-accepted method of connecting telephony equipment to the public network when multiple lines are required (and is tariffed accordingly).
Note: In some countries, a Euro-ISDN switch may send multiple channels in the Channel ID Information element of a RESTART message. If this occurs, Blueworx Voice Response only acknowledges the RESTART message if all the channels in the relevant trunk have had their operating status set to inservice. If the switch is configured in this manner, the Blueworx Voice Response ISDN Signaling system parameter Send RESTART on Channel Enable must be be set to No (refer to the Blueworx Voice Response for AIX: Configuring the System information for details).
E1 QSIG: E1 QSIG is specified by the ECMA-143 (International Standard ISO/IEC 11572), which defines the signalling procedures and protocol at the Q-reference point between Private Integrated Network Exchanges (PINXs) within a Private Services Network (PISN). The physical connection must be an E1 telephony trunk.
Blueworx Voice Response is intended to be used either as the originating PINX or the terminating PINX and provides functionality to become a transit PINX.
Blueworx Voice Response QSIG also supports ECMA-242, which provides control for a Message Waiting Indicator (MWI) over the signaling D-Channel. MWI control can be invoked using the signaling library SL_STATION_SET_MWI_REQ primitive and supports the following states: SL_MWI_ON and SL_MWI_OFF. Refer to the Blueworx Voice Response for AIX: Programming for the Signaling Interface information for further information.

Table 1. Functions provided by ISDN protocols.
For each ISDN 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	Connectivity			Function
In the Type column, Trunk means ‘trunk-side protocol’ and Line means ‘line-side protocol’.		PSTN	PABX	Channel bank	Answer detection	Call transfer	Far-end disconnect	ANI	DID or DNIS
Lucent 5ESS 5E8	Trunk	Yes	No	Yes¹	Yes	No	Yes	Yes	Yes
Lucent 5ESS 5E9 National 1	Trunk	Yes	No	Yes¹	Yes	No	Yes	Yes	Yes
Lucent TR41449/ 41459	Trunk	No	Yes	Yes¹	Yes	No	Yes	Yes	Yes
Nortel DMS100 BCS34/36	Trunk	Yes	No	Yes¹	Yes	No	Yes	Yes	Yes
Nortel DMS 100 National 2 NA015	Trunk	Yes	No	Yes¹	Yes	Yes² Yes³	Yes	Yes	Yes
Nortel DMS 250 IEC05	Trunk	Yes	No	Yes¹	Yes	Yes² Yes³	Yes	Yes	Yes
Lucent 5ESS 5E11–15 National ISDN2	Trunk	Yes	No	Yes¹	Yes	Yes²	Yes	Yes	Yes
INS Net Service 1500	Trunk	Yes	Yes	Yes¹	Yes	No	Yes	Yes	Yes
Euro-ISDN	Trunk	Yes	Yes	–	Yes	Yes⁴	Yes	Yes	Yes
E1 QSIG	Trunk	No	Yes	No	No	Yes⁴	Yes	Yes	Yes
Note: A channel service unit (CSU) for ISDN must support extended superframe (ESF) line framing. Bellcore 2B channel transfer feature RLT transfer Single step transfer

Table 2. How Blueworx Voice Response supports ISDN protocols.
This table describes for each ISDN Feature, the support for specific ISDN protocols.
ISDN Feature	5ESS 5E8	5ESS 5E9 National 1	TR41449/ TR41459	DMS100 BCS34/36	DMS100 National	DMS250 IEC05	5ESS 5E11–15 National 2	INS 1500	Euro-ISDN	E1 QSIG
Network or User Side	User Side only	User Side only	User Side only	User Side only	User Side only	User Side only	User Side only	User Side only	User Side only	Endpinx User Side only
3.1 KHz Audio Bearer Capability	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes
64 kbit Speech-Bearer Capability	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes
Called and Calling Party Number¹	Bway²	Bway	Bway	Bway	Bway	Bway	Bway	Bway	Bway	Bway
User-to-User signaling	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	No
Restart message support	Bway²	Bway	Bway	Bway	Bway	Bway	Bway	Bway	Bway	Bway
B-channel Service Message Support	–	–	Yes	No	Yes	Yes	Yes	No	–	No
ETSI 300-062 to 064 Direct Dial In (DDI)	–	–	–	–	–	–	–	–	Yes	–
ETSI 300-050 to 052 Multiple Subscriber Number (MSN)	–	–	–	–	–	–	–	–	Yes	–
ETSI 300-367 to 369 Explicit Call Transfer (ECT)	–	–	–	–	–	–	–	–	No	No
ECMA-300 Single Step Call Transfer Supplementary Service (SSCT)	–	–	–	–	–	–	–	–	Yes	Yes
Bellcore GR- 2865 2 B-channel transfer	–	–	–	–	Yes	Yes	Yes	–	–	No
Release link trunk (RLT) transfer	–	–	–	–	Yes	Yes	–	–	–	No
Non-Facility Associated Signaling (NFAS)	–	Yes	Yes	Yes	Yes	Yes	Yes	Yes	–	No
D-channel backup	–	No	Yes	No	Yes	Yes	Yes	No	–	No
Bellcore TR-1268 Call by Call service selection	No	No	No	No	No	No	No	–	–	No
Note: Call information is transferred through the use of system variables SV541 and SV542. For details refer to the Blueworx Voice Response for AIX: Application Development using State Tables information. "Bway" is an abbreviation for "Bothway" A hyphen indicates that the feature is not applicable for that protocol.

Non-Facility Associated Signaling

Blueworx Voice Response supports Non-Facility Associated Signaling (NFAS) on T1 systems. In the normal ISDN configuration, each T1 trunk has 23 bearer channels (B-channels) carrying voice traffic, and 1 signaling channel (D-channel) carrying signaling traffic. (23B+D).

In an NFAS configuration, the ISDN trunks are grouped into NFAS groups. You can define up to four NFAS groups on each pSeries computer with a maximum of 10 trunks in each group. The signaling traffic for all the trunks in a group is carried on one D-channel. The trunk that carries the signaling information on its 24th channel is called the primary trunk.

For some switches and line signaling protocols, you can also set aside a channel on another trunk in each group to act as a backup for the signaling channel. The backup D-channel does not carry voice and will automatically take over the signaling traffic if the primary D-channel goes out of service. The trunk that has its 24th channel on standby to carry the signaling information is called the backup trunk.

Table 3 shows the switch types and line signaling protocols that have NFAS D-channel backup enabled and the custom server needed for each. These switches and signaling protocols also support the use of service messages to take indiviual channels in and out of service.

Table 3. Switch types and line signaling protocols that can be used with D-channel backup..
This table describes for each switch type the line signaling protocol that can be used with D-channel backup and the custom server import file required.
Switch type	Line signaling	Custom server
Avaya (Lucent) 4ESS	TR41449	sigproc_att_tr41449.imp
Avaya (Lucent) 5ESS – 2000	ISDN National 2	sigproc_t1_nat.imp
Avaya (Lucent) Definity G1/G2/G3	TR41449	sigproc_att_tr41449.imp
NT DMS 100	ISDN National	sigproc_dms_nat.imp
NT DMS 250	ISDN_IEC05	sigproc_dms250.imp
Summa Four	ISDN National 2	sigproc_t1_nat.imp
Summa Four	TR41449	sigproc_att_tr41449.imp

To illustrate the concept of non-facility associated signaling, Figure 4 and Figure 5 show how many voice channels you get with four E1 or T1 trunks. Figure 6 shows how many channels you get with four T1 trunks using NFAS. Figure 7 shows how many channels you get with four T1 trunks using NFAS with D-channel backup.

Figure 4. Using E1 ISDN trunks
A switch connected to a system over 4 E1 ISDN trunks, giving 120 voice channels in total

Figure 5. Using T1 ISDN trunks without NFAS
A switch connected to a system over 4 T1 ISDN trunks, giving 115 voice channels in total

Figure 6. Using T1 ISDN trunks with NFAS
A switch connected to a system over 4 T1 ISDN trunks, using NFAS, giving 119 voice channels in total

Figure 7. Using T1 ISDN trunks with NFAS and D-channel backup
A switch connected to a system over 4 T1 ISDN trunks, using NFAS with D-channel backup, giving 118 voice channels in total

A switch connected to a system over 4 T1 ISDN trunks, using NFAS with D-channel backup, giving 118 voice channels in total

Key facts about ISDN support

Blueworx Voice Response supports ISDN connectivity, giving customers the benefits of common channel signaling, such as very fast call setup and teardown, reliable network signaling, and the delivery of called and calling number information.
Blueworx Voice Response supports voice calls on the B-channels, by using the speech and 3.1kHz bearer capabilities.
Blueworx Voice Response protects customer investment in applications by allowing existing state tables to run unchanged over ISDN.
Blueworx Voice Response supports a maximum of 480 concurrent voice channels with ISDN on E1 on PCI-based hardware.
Blueworx Voice Response supports a maximum of 380 concurrent voice channels with ISDN on T1 on PCI-based hardware.
Blueworx Voice Response supports up to four Non-Facility Associated Signaling (NFAS) groups on T1 systems, with a primary and a backup D-channel for up to 10 trunks in each group.
Blueworx Voice Response supports the use of service maintenance messages to take individual channels out of service on T1 systems.
Blueworx Voice Response supports the coexistence of ISDN trunks and channel associated signaling trunks in the same system for ease of migration.
Blueworx Voice Response supports a number of key supplementary services.
Blueworx Voice Response operates in Terminal Equipment (TE) mode.

Signaling System 7

Note: In previous releases of Blueworx Voice Response, SS7 support was provided through the separately-orderable SS7 Call Manager feature with the SS7 PRPQ. These features are replaced in version 4.2 with a single new PRPQ that supports the same hardware, and provides similar functionality, but uses a new software stack. For details of the functionality provided by this solution, and its availability, please contact your IBM representative.

Signaling System 7 (SS7) is the common channel signaling protocol that is used internally in telephone operators' digital communication networks. SS7 is not an access protocol, by which terminal equipment attaches to the network, but is used to attach voice response units, such as Blueworx Voice Response.

The SS7 protocol is implemented to ISUP specifications, which Blueworx Voice Response supports. The higher levels of the protocol have many local variations.

Figure 8. Attaching Blueworx Voice Response in a telephone network
A schematic of a public telephone network, with ISDN being used to connect the caller to the switch, and SS7 used to connect the switches both to the service control point and to the Blueworx Voice Response system.

A schematic of a public telephone network, with ISDN being used to connect the caller to the switch, and SS7 used to connect the switches both to the service control point and to the Blueworx Voice Response system.

Figure 9. Attaching multiple Blueworx Voice Response systems in a telephone network
Building upon the previous figure, this graphic shows multiple instances of connected to the switch by voice circuits, with a separate SS7 link to a SS7 server.

Building upon the previous figure, this graphic shows multiple instances of connected to the switch by voice circuits, with a separate SS7 link to a SS7 server.

SS7 links and network components

SS7 uses discrete messages to exchange information. Packet-switched data links are used to send the messages between switches and the other end points. There are two types of connections in a telephony network:

Packet switched links that are used for SS7 messages (but not voice data).
Circuit switched links used for voice data (but not SS7 messages).

The SS7 protocol stack

SS7 is structured in a multi-layered stack that corresponds closely to the layers of the standard OSI model, although some SS7 components span several layers. SS7 supports the Integrated Services User Part (ISUP), which spans the presentation, session, and transport layers.

The ISUP handles the setup and tear-down of telephone calls and provides functions that are available with primary rate ISDN. These include called and calling number notification (or suppression), the ability to control billing (charging) rates, advanced telephony functions such as transfer, and control over whether the voice channel is used for voice, fax, or data.

ISUP messages flow only during the setup and tear-down phases of a call.

Communication between your SS7 switch and SS7 Server is determined by the existence of point codes. These are addresses that each side uses to send messages to the other. Each side has a concept of a Source Point Code (SPC) and a Destination Point Code (DPC). The SPC of your switch is the DPC of the SS7 Server; the SPC of SS7 Server is the DPC of your switch.