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Voice Network Switching (VNS) release 3.0 also supports the VNS CAS 2.2 feature. CAS 2.2 is QSIG protocol variation that works in conjunction with the IGX's Universal Voice Module (UVM) with Model B or higher firmware to provide a way for PBXs using Channel Associated Signaling (CAS) to take advantage of Voice Network Switching. The UVM with Model B firmware is supported in Switched Software Release 8.5. With this feature, IGX switches with UVM cards will convert CAS signals to QSIG protocol messages that can be interpreted by the VNS. The VNS then switches voice or data calls from the CAS PBX, just as if they supported the QSIG protocol.
This appendix contains the following sections:
The UVM card on the IGX switch converts CAS signaling and dual-tone multi-frequency tones to common channel signaling (CCS), that is, QSIG protocol, messages. The VNS subsequently routes the calls from the PBX over a Cisco WAN switching network, using voice switched virtual circuits (SVCs) under the control of a VNS.
Figure I-1 illustrates a simple CAS-to-QSIG VNS network. The two PBX's are CAS signaling. Both of their T1 trunks terminate in a UVM on an IGX switch. The UVM converts the CAS signaling to QSIG messages and routes these messages to the VNS. The VNS never sees the CAS signaling. In Figure I-1, the signaling links are shown as dashed lines; the voice or data connections (the bearer channels), which are setup and maintained by the signaling connection, are indicated by the solid line connecting the two PBX's.
There are two modes of signaling prevalent in T1 and E1 digital trunk interfaces. In the CCS mode, a single DS0 channel is dedicated to carrying signaling information for all the DS0 bearer channels. Moreover, the signaling information is carried in a message format (packets or frames). This is the mode used in T1- and E1-based ISDN trunks, and hence is the mode supported by the VNS.
In the CAS mode of signaling, DS0 channel states are encoded in bits and transmitted on the trunks in two possible ways. For CAS T1 trunks, a technique called robbed-bit signaling (RBS) is used. A single bit in every DS0 bearer channel is "stolen" from every 6th frame and used to carry signaling information. The robbed bit in frames which are odd-multiples of 6 (6th, 18th, 30th,...) is termed the `A' bit, whereas the robbed bit in frames which are even multiples of 6 is termed the `B' bit. In CAS E1 trunks, TS16 (timeslot 16) is used to carry the signaling bits for all channels, but in a bit-to-channel mapped format. Each frame, except the first, carries a 4-bit signaling payload for 2 DS0s. It thus requires 15 frames to deliver the signaling information for the 30 DS0 bearer channels.
To enable connections on CAS trunks to be switched through a Cisco WAN switching network using the VNS, the CAS signaling information must be translated into near-equivalent CCS messages. This "gateway" function is performed by the UVM interfaces on the IGX switch that terminate the digital CAS trunks. Once the CAS signaling is converted to CCS signaling messages, they may be forwarded to and processed by the VNS.
With the CAS feature, the CCS protocol is operating between the IGX's UVM card and the VNS. The UVM always performs the master role in channel allocation protocol, so the VNS must be set to slave.
Since all 24 DS0s (timeslots) of the CAS T1 interface are used to carry signaling and user information, the UVM CAS-to-QSIG conversion process creates a pseudo channel, DS0 25, to carry signaling messages to the VNS. DS0 25 is a logical channel that exists only between the UVM and the VNS. So, for CAS-to-QSIG UNI ports, the UNI Channel field of the Port Information menu must be configured as 25. The UNI Channel field is described in Chapter 7, Understanding the VNS Configuration Interface in the section, Port Information.
First you rack mount the VNS with its co-located IGX switch as described in Chapter 4, Rack Mounting the VNS. Next you connect power to the VNS as described in Chapter 5, Connecting Power to the VNS. Then you connect the VNS interfaces to the node as described in Chapter 6, VNS Interface Connections. Then you connect the CAS BPX to the IGX UVM as described in the Cisco IGX 8400 Series Installation manual and Cisco IGX 8400 Series Reference document for Release 8.5 in the section, Connecting the UVM to T1 Lines. The Cisco Command Reference for Release 8.5 also contains general procedures for setting up circuit lines and configuring voice connections.
When connecting the CAS PBX to the UVM for Voice Network Switching, however, there are some special configuration procedures that must be performed. For CAS-to-QSIG conversion, configure the UVM as follows:
Step 1 Use upln to activate a circuit line in the slot containing the UVM.
Step 2 Use cnfln to configure the line to match the CAS PBX.
Step 3 Use cnfcassw (configure CAS switching) to configure the CAS-to-QSIG feature. This command will bring a menu similar to the following:
vnsigx8 TN StrataCom IGX 16 8.5.B0 Sep. 15 1997 23:59 PST
Line 8.1 CAS Switching Parameters
CASSW mode [PBX-END] Parm 11 [00] (H)
CCS Type [ 1] (D) Parm 12 [00] (H)
CAS Type [ 1] (D) Parm 13 [00] (H)
Conn Type [a24 ] Parm 14 [00] (H)
Country code [00] (H) Parm 15 [00] (H)
Interdigit TO [05] (H) Parm 16 [00] (H)
Tone level [00] (H) Parm 17 [00] (H)
DTMF duration [0C] (H) Parm 18 [00] (H)
Idle pattern [7F] (H)
Parm 6 [00] (H)
Parm 7 [00] (H)
Parm 8 [00] (H)
Parm 9 [00] (H)
Parm 10 [00] (H)
Last Command: cnfcassw 8.1
Next Command:
The cnfcassw command is used only for configuring CAS switching on the IGX's UVM. Only the first 9 fields of this screen are used at this time. Parm 6 through Parm 18 are reserved for future use. The first 8 fields and their possible values are:
Step 4 Use the VNS Configuration Interface to configure Voice Network Switching. The VNS Configuration Interface is described in Chapter 7. CAS-to-QSIG configuration is almost transparent to the VNS. For CAS switching, you must set the following parameters:
In addition to cnfcassw (configure CAS switching), other IGX commands that relate to CAS-to-QSIG conversion are:
IGX commands are fully documented in the Cisco WAN Switching Command Reference for Release 8.5.
The IGX display card (dspcd) for Release 8.5 will indicate in CAS switching is supported on the UVM card. The following example screen shows a UVM which supporting CAS switching:
vnsigx8 TN StrataCom IGX 16 8.5.B0 Sep. 16 1997 00:01 PST
Detailed Card Display for UVM in slot 8
Status: Active (Front Card Supports CAS-switching)
Revision: BC05
Serial Number: 336840
Integrated Echo Canceller
Channels: 24
Backplane Installed
Backcard Installed
Type: T1-2
Revision: AB
Serial Number: 289389
Last Command: dspcd 8
Next Command:
The configure channel utilization (cnfchutl) command for Release 8.5 permits the configuration of the CCS signaling channel (that is, the pseudo DS0 25) between the UVM and the VNS. This DSO 25 is not part of the T1 interface between the CAS PBX and the IGX UVM. The cnfchutl screen display is the same as the dspchcnf, shown in the example below. This example shows the configuration of connection vnsigx8.8.1.25. For a standard T1 interface, without the CAS-to-QSIG conversion on the UVM, slot.line.25 would not be configurable.
vnsigx8 TN StrataCom IGX 16 8.5.B0 Sep. 16 1997 00:03 PST
From % Adaptive Gain (dB) Dial Interface OnHk Cond
8.1.25 Util Voice Fax In Out Type Type A B C D Crit
8.1.25 40 Enabled Disabled 0 0 Inband Unconfig ? ? - - a
8.2.25 40 Enabled Disabled 0 0 Inband Unconfig ? ? - - a
Last Command: dspchcnf 8.1.25
Next Command:
In Release 8.5, the configure line command (cnfln) permits the setting of µ-law (Mu-law) for encoding the T1 line. It also displays the status of CAS switching. The dsplncnf command shows whether these parameters have been configured. The following example screen illustrates a T1 circuit line with µ-law encoding and CAS switching turned on. CAS-Switching with PBX-END indicates that CAS switching was turned on with the cnfcassw command.
vnsigx8 TN StrataCom IGX 16 8.5.B0 Sep. 16 1997 00:04 PST
LN 8.1 Config T1/24 UVM slot: 8
Loop clock: No
Line framing: ESF cnfg: External
coding: B8ZS slot.line: --
CRC: -- CAS-Switching: PBX-END
recv impedance: --
E1/J1 signaling: --
encoding: u-LAW
T1 signaling: ABAB
cable type: ABAM
length: 0-133 ft.
56KBS Bit Pos: msb
pct fast modem: 20
Last Command: dspclncnf 8.1
Next Command:
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