Telecom Architectures: Voice Ports

Showing posts with label Voice Ports. Show all posts

Tuesday, September 8, 2009

Configuring ISDN PRI Voice Ports

We discussed the analog VICs modules such as the E&M, FXO, and FXS, but larger organizations that need higher-density interfaces to the PSTN or PBX typically use digital T-1/E-1 modules. The following is a list of digital voice interfaces and supported platforms:

Digital T-1/E-1 Packet Voice Trunk Network Module, NM-HDV (VWIC-1MFT and VWIC-2MFT) Cisco 2600 and 3600 series.
Digital voice interface card (DVM) Cisco MC3810.
Octal or Quad T-1/E-1/PRI feature card Cisco AS5300 universal access server.
Channelized trunk card and voice feature card Cisco AS5800 universal access server.
T-1/E-1 high-capacity digital voice port adapter Cisco 7200 and 7500 series.

As with analog, the VICs are inserted into the VNMs to create the digital T-1 voice module for the Cisco 2600 and 3600 series routers. The Cisco 1760 router can use the individual VWIC-2MFT-T-1 card as an interface to a PBX or PSTN for digital connectivity. The card uses a RJ-48 crossover cable for connection to a PBX. The pinouts are listed below:

Pin 1 RX ring
Pin 2 RX tip
Pin 4 TX ring
Pin 5 TX tip

The items needed for configuration of the controller settings are the following:

Line interface T-1 or E-1
Signaling interface FXO, FXS, or E&M and ISDN PRI or BRI—Q.SIG or CCS
Line coding AMI or B8ZS for T-1, and AMI or HDB3 for E-1
Framing format SF (D4) or ESF for T-1, and CRC4 or no-CRC4 for E-1
Number of channels

The controller configuration steps for an ISDN PRI connection to a PBX follow:

router# config terminal
router(config)# isdn switch-type basic-ni1
router(config)# controller T-1 1/0
router(config-controller)# framing esf
router(config-controller)# clock source internal
router(config-controller)# linecode b8zs
router(config-controller)# pri-group timeslots 1-24

This produces the following configuration:

(Partial Router configuration)
!
hostname router
!
memory-size iomem 15
voice-card 1
!
isdn switch-type ni1
!
controller T-1 1/0
framing esf
clock source line
linecode b8zs
pri-group timeslots 1-24
!
interface Serial1/0:23
no ip address
no logging event link-status
isdn switch-type primary-ni1
isdn incoming-voice voice
isdn T310 60000
no cdp enable
!
voice-port 1/0:23
!

Saturday, September 5, 2009

Configuring ISDN BRI Voice Ports

Cisco routers support several types of ISDN voice interface cards such as VIC-2BRI-S/T-TE and VIC-2BRI-NT/TE, which can provide connectivity to a PBX or PSTN. A benefit of using the ISDN BRI VIC rather than the analog VIC modules is the additional calling information that is passed.

Up to four calls are supported when the VIC-2BRI is installed in the NM-2V module. The BRI VIC needs to be installed in Slot 0 of the NM-2V for both ports to be active. If an additional VIC is installed in the second slot of the NM-2V, the second port on the first VIC will be disabled. This is based on the two ports of the BRI VIC requiring four DSPs. The VIC interface modules support both ISDN network and user-side configurations. The following are the steps necessary to configure ISDN BRI to a PBX:

Enter global configuration mode:
```
router# configure terminal
```
Set the global ISDN switch type. The only NT supported type is basic-net or basic-qsig:
```
router(config)# isdn switch-type switch-type
```
Set the ISDN BRI interface slot and port:
```
router(config)# interface bri slot|port
```
Ensure that no IP address is configured for the ISDN interface (voice only):
```
router(config-if)# no ip address
```

Specify incoming voice calls over ISDN:

router(config-if)# isdn incoming-voice voice

Shut down the interface. Configure the physical layer type. Enable interface with no shutdown:
- Enter user to configure the port as TE and to function as a clock slave. This is the default.
- Enter network to configure the port as NT and to function as a clock master.
```
router(config-if)# shutdown
router(config-if)# isdn layer1-emulate {user | network}
router(config-if)# no shutdown
```
Turn on or off the power supplied from an NT-configured port to a TE device:
```
router(config-if)# [no] line-power
```

Configure the Layer 2 and Layer 3 port protocol:

router(config-if)# isdn protocol-emulate {user | network}

Exit global configuration mode:
```
router(config)# end
```

Figure 1 illustrates a scenario with ISDN BRI connectivity to a PBX and PSTN. A partial configuration lists the commands pertaining to the PSTN and PBX interfaces.

Figure 1: ISDN BRI PBX and PBX Scenario

(Partial Cisco 1760 configuration)
!
hostname 1760
!
 isdn switch-type basic-net3
!
interface BRI 1/0
no shutdown
description connected to PBX
no ip address
 isdn switch-type basic-net3
 isdn incoming-voice voice
shutdown
isdn layer1-emulate user
no shutdown
isdn protocol-emulate user
!
interface BRI 2/0
no shutdown
description connected to PSTN
no ip address
 isdn switch-type basic-net3
 isdn incoming-voice voice
 isdn overlap-receiving
shutdown
isdn layer1-emulate network
no shutdown
isdn protocol-emulate network

Wednesday, August 26, 2009

Configuring Voice Ports

We have now discussed the basic hardware installation for VNMs and VICs. The next step is to configure the cards on the Cisco router IOS. Voice card configuration is covered in the following sections. Some basic configuration parameters must be set in order for a voice port to operate. To configure a voice port, complete the following steps.

Enter Privileged Exec mode:
```
router> enable
```
Check the DSP voice channel activity with the following command:
```
router# show voice dsp
```
Enter Global Configuration mode:
```
router# configure terminal
```
Enter Voice Card Configuration mode. On the router, the slot must be 0:
```
router(config)# voice-card slot
```

Enter the CODEC type for the voice card:

router(config-voicecard)# CODEC {med | high}

This series of steps sets the CODEC compression technique, which is either high or medium complexity. High complexity can handle fewer calls per DSP. This is due to the higher CPU utilization required for high CODEC complexity operation. High and medium complexity CODECs:

High complexity Specifies two voice channels encoded in any of the following formats: G.711ulaw, G.711alaw, G.723.1 (r5.3), G.723.1 Annex A (r5.3), G.723.1 (r6.3), G.723.1 Annex A (r6.3), G.726 (r16), G.726 (r24), G.726 (r32), G.728, G.729, G.729 Annex B, and fax relay.
Medium (default) complexity Specifies four voice channels encoded in any of the following formats: G.711ulaw, G.711alaw, G.726 (r16), G.726 (r24), G.726 (r32), G.729 Annex A, G.729 Annex B with Annex A, and fax relay.

Configuring FXO or FXS Voice Ports

All these parameters have default settings, and FXS and FXO port default configuration values are adequate for most situations. Therefore, user intervention is rarely needed. The following settings are mandatory to any FXS/FXO port configuration:

Signal type
Call progress tone
Ring frequency
Ring number
Dial type (FXO only)
PLAR connection mode
Music threshold
Description
Voice activity detection (VAD)
Comfort noise

Follow these steps to complete a basic setup for all FXS/FXO voice ports:

Enter Privileged Exec mode:
```
router> enable
```
Enter Global configuration mode:
```
router# configure terminal
```

Identify which port to configure on a 2600 and 3600 series router:

router(config)# voice-port nm-module/vic-module/port-number
router(config)# voice-port slot/port   (Cisco 175x/1760 and MC3810)

Select the appropriate signaling for the start of a call:

router(config-voiceport)# signal [loop-start|ground-start]

Select the appropriate country codes for call progression signaling. The default is northamerica:
```
router(config-voiceport)# cptone country-code
```
Configure the voice port connection mode type. If the connection will be to a PBX, use the tie-line option. If the connection will be for private line automatic ringdown (PLAR), use the plar option. If the connection will be for PLAR off-premises extension (OPX), use the plar-opx option.
```
router(config-voiceport)# connection {tie-line | plar | plar-opx} string
```
Assign the appropriate out-dialing dial type (FXO only):
```
router(config-voiceport# dial-type{dtmf | pulse}
```
Configure the frequency in Hertz of ringing for the system that is attached on a Cisco 1750, 2600, and 3600 series router (FXS only):
```
router(config-voiceport)# ring frequency [25| 50]
router(config-voiceport)# ring frequency [20| 30] 
```
Configure the maximum number of rings allowed before answering a call (FXO only):
```
router(config-voiceport)# ring number number
```
Specify an existing pattern for ring tone or define a new one (FXS only). Each pattern specifies a ring-pulse time and a ring-interval time:
```
router(config-voiceport)# ring cadence {[pattern01 | pattern02 … pattern12]
[define pulse interval]}
```
Specify the termination impedance, which needs to match the specifications of the PBX it is attaching to:
```
router(config-voiceport)# impedance [600c|600r|900c|complex1|complex2]
```
Configure the threshold in decibels for hold music:
```
router(config-voiceport)# music-threshold number
```
(Optional) Configure a text string to the configuration that describes the connection for this voice port:
```
router(config-voiceport)# description string
```
Configure background noise generation for the comfort of a user when there is no noise:
```
router(config-voiceport)# comfort-noise
```
(Optional) Enable voice activity detection:
```
router(config-voiceport)# vad
```

Configuring E&M Ports

E&M default settings are usually not sufficient to enable voice transmissions over IP. This is because E&M ports are designed to connect directly to a PBX and therefore must match the particular PBX's specifications. The following settings are mandatory to implement an E&M port:

Signal type
Call progress tone
Operation
Type
Impedance

The following commands complete a basic setup for all E&M voice ports:

Enter Privileged Exec mode:
```
router> enable
```
Enter Global Configuration mode:
```
router# configure terminal
```

Identify which port to configure on a 2600 and 3600 series router:

router(config)# voice-port nm-module/vic-module/port-number
router(config)# voice-port slot/port (Cisco 175x/1760 and MC3810)

Select the appropriate signaling for the interface:

router(config-voiceport)# signal [wink-start|immediate|delay-dial]

Select the appropriate country codes for call progression signaling. The default is us. The northamerica keyword is for the Cisco MC3810 multiservice concentrator for versions prior to Cisco IOS Release 12.0(4)T and for ISDN PRI:
```
router(config-voiceport)# cptone country code
```

Define cabling scheme operation:

router(config-voiceport)# operation [2-wire|4-wire]

Select the appropriate E&M interface type:

router(config-voiceport)# type [1|2|3|5]

Specify the termination impedance, which needs to match the specifications of the PBX the port is attaching to:
```
router(config-voiceport)# impedance [600c|600r|900c|complex1|complex2]
```

Some optional configurations for the E&M port are not required for operation. As with the FXS/FXO ports, the following configurations are used for optimization and usability:

Connection mode
Music threshold
Description
Comfort tone (VAD-activated only)

Use the following commands to adjust any of these optional configuration parameters for E&M ports:

Enter Privileged Exec mode:
```
router> enable
```
Enter Global Configuration mode:
```
router# configure terminal
```

Identify which port to configure on a 2600 and 3600 series router:

router(config)# voice-port nm-module/vic-module/port-number
router(config)# voice-port slot/port (Cisco 175x/1760 and MC3810)

Specify that the port configured for PLAR

router(config-voiceport)# connection plar string

Define the threshold in decibels for hold music:

router(config-voiceport)# music-threshold number

Specify a description field for port:

router(config-voiceport)# description string

Set comfort noise to generate background noise for the user when there is no sound on the line:
```
router(config-voiceport)# comfort-noise
```