© 2009 Avaya Inc. All rights reserved.1 Chapter Eight, Troubleshooting Module Three – Global Assistance Calls

© 2009 Avaya Inc. All rights reserved.2 Overview It is likely that any fault on a network, regardless of the cause, will be reported as a degradation in the quality of VoIP calls. This module provides some items to consider: – End-to-End Matching Standards: VoIP depends upon the support and selection of the same voice compression, header compression and QoS standards throughout all stages of the calls routing. The start and end points must be using the same compression methods. All intermediate points must support DiffServ QoS. – Avoid Hubs: Hubs introduce echo and congestion points. If the customer network requires LAN connections beyond the capacity of the IP Office Unit itself, Ethernet switches should be used. Ethernet switches are recommended as they allow traffic prioritization to be implemented for VoIP devices and for other device such as the Voic Server PC.

© 2009 Avaya Inc. All rights reserved.3 Voice Compression Calls to and from IP devices often require conversion to the audio codec format being used by the IP device. For IP Office systems this conversion is done by voice compression channels on a Voice Compression Module (VCM). IP Office VCMs support the common IP audio codecs: – G711 – G723 – G729a For IP400 control units channels can be added by fitting IP400 Voice Compression Modules (VCMs). For the IP500 control units, channels can be added using IP500 VCM cards and licenses or IP400 Voice Compression Modules.

© 2009 Avaya Inc. All rights reserved.4 When VCM Channels are Used In order to minimize quality issues with IP audio due to VCM utilization it is important to understand when VCM channels are used. – IP device to non-IP device Also includes MOH, voic access, conference resources, etc. – IP device to IP device Short code confirmation, ARS camp on and account code entry tones require a voice compression channel If the IP devices use differing audio codecs Note: T3 IP devices must be configured to 20ms packet size for the above conditions to apply. If left configured for 10ms packet size, a voice compression channel is needed for all tones and for non-direct media calls.

© 2009 Avaya Inc. All rights reserved.5 When VCM Channels are Used - continued – SIP Line Call to/from Non-IP Devices – Incoming SIP Line Call to IP Device (Voice compression channel reserved until call connected.) T38 Fax Calls IP Office 5.0+ supports T38 fax on SIP trunks and SIP extensions. Each T38 fax call uses a VCM channel. – Within a Small Community Network, an T38 fax call can be converted to a call across across an H323 SCN lines using the IP Office Fax Transport Support protocol. This conversion uses 2 VCM channels. – In order use T38 Fax connection, the Equipment Classification of an analog extension connected to a fax machine can be set Fax Machine. Additionally, a new short code feature Dial Fax is available.

© 2009 Avaya Inc. All rights reserved.6 VCM Configuration Options Echo is typically generated by impedance mismatches when a signal is converted from one circuit type to another, most notably from analog to IP. To resolve this issue, an estimated echo signal can be created from one output and then subtracted from the input to hopefully remove any echo of the output. The System | VCM form in the Manager application allows adjustment of the operation of VCMs installed in the IP Office control unit.

© 2009 Avaya Inc. All rights reserved.7 Automatic Codec Preference The setting in Manager on the System | Telephony tab is used by all IP lines and extensions where the Compression Mode has been set to Automatic Select. The codec selected here will be the first codec the line or extension uses for codec negotiation. Note that the G.711 codecs are treated as a pair, so if one is selected as the first preference, the other will be second in the list.

© 2009 Avaya Inc. All rights reserved.8 VoIP Settings for IP Endpoints / IP Lines There are common VoIP settings on all IP extensions (H.323 / SIP) and IP Lines (H.323 / SIP / SES) for: – Compression Mode – VoIP Silence Suppression – Allow Direct Media Path

© 2009 Avaya Inc. All rights reserved.9 Compression Mode This field defines the compression mode (codec) or modes offered during call setup. Automatic Select – For pre-IP Office 5.0 systems, Automatic Select uses the codecs in the order of preference G729a, G711 ALAW, G711 ULAW and G – If required, a specific codec can be selected. – If negotiation for a specific codec fails during call setup, the IP Office will fallback to using Automatic Select.

© 2009 Avaya Inc. All rights reserved.10 VoIP Silence Suppression The VoIP Silence Suppression option will detect periods of silence on a call and will not send any data during those silent periods. This feature is not used on IP lines using G.711 between IP400 and IP500 systems. A typical voice conversation consists of 40 to 50 percent silence. Since there is not any voice going through the network for 40 percent of a voice call, some bandwidth can be saved by deploying Silence Suppression. There is a trade-off. There is a small amount of time before the codecs detect speech activity following a period of silence which may result in the clipping of received audio.

© 2009 Avaya Inc. All rights reserved.11 Allow Direct Media Path This settings controls whether H323 calls must be routed via the H323 gatekeeper (the IP Office) or can be routed alternately if possible within the network structure. If enabled, H323 calls can take routes other than through the IP Office and removes the need for a voice compression channel. – Both ends of the calls must support Direct Media. If Disabled (not selected) – On pre-4.0 calls between IP devices using the same audio codec require a voice compression channel. – On IP Office 4.0 and higher with RTP relay support, calls between devices using the same audio codec do not require a voice compression channel.

© 2009 Avaya Inc. All rights reserved.12 Line | Analog Options IP Office has configuration options to address echo generated by impedance mismatches on the Line | Analogue Options form. The Impedance field is only available for certain system locales; Brazil, Korea and the United States. The Quiet Line setting may be required to compensate for signal loss on long lines. (North American locales only) The Automatic Balance Impedance Match option can be used to test the impedance of a line and display the best match resulting from the test. (North American locales only)