Allworx 24X Manual de usuario descargar pdf (Pagina 27)

VoIP White Paper

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trademarks or registered trademarks of their respective owners.

Revised: February 8, 2007

Page 24

traffic routing difficulties. When two dual interface devices are hooked together in parallel, both with a common

routable path between networks, difficulties can arise. The most common case of this is when Allworx and

some other router/firewall are hooked up with both the LAN and WAN interfaces between the same pair of

networks (logically, the two WAN interfaces and the two LAN interfaces are connected together). This

configuration causes a problem because some routing decision optimizations are done between layers two and

three of the network protocol stacks. Because the same MAC address is reachable from two different

interfaces and both devices have visibility to both paths to that address, neither device can determine the

correct routable interface to use to reach the intended destination.

To prevent this from becoming a problem, you must configure the network so that the devices do not have

visibility to both interfaces of the other. Generally, the easiest solution is to avoid the above configuration – or if

it must be used, configure the WAN sides of these devices to be on different VLANs so that they cannot see

each other’s traffic. Assuming a hypothetical 3-port switch, put one device on port 1 (VlanId=1), the other

device on port 2 (VlanId=2), and the Internet router on port 3 (VlanId=1&2).

14.4 DTMF digits not passed during live calls

Negotiation of how DTMF number key digits pass during live calls is the least standardized and most

problematic aspect of doing VoIP telephony with SIP. With Allworx equipment, this will not be a concern, but it

does often create a problem when operating with ITSPs. The most typical symptom is that PSTN phone calls

coming in from an ITSP will not be able to operate the Allworx auto-attendant or voicemail applications. The

reverse may also be a problem – where Allworx system phones will not be able to operate phone applications

out on the PSTN. These problems happen because during call setup negotiations, the service provider may

not have indicated correctly how it plans to send and receive DTMF digits.

Allworx products expect all SIP parties to negotiate DTMF out-of-band so that DTMF can work correctly with all

coder types (including G.729). If you are having these problems, the default negotiation settings can be

controlled in the advanced settings tab of the Allworx server SIP Proxy and Gateway configuration pages of the

administrative Web site. You can control the default RTP type and whether padding of RTP payloads should

be applied.

14.5 Music On-Hold sound quality is poor

Some voice coders are specifically designed to compress human voice signals – and NOT arbitrary audio

content. This is case for G.729 and its variants that take full advantage of human vocal tract properties to get

such levels of high-quality compression. However, when transmitting audio that is not speech (such as music)

through these compressed streams, the resulting audio is distorted. Configure the system to use only the

G.711 coder if this is a concern.

14.6 Calling Auto Attendant

When a user reports problems with calls to or from a particular station, or when calling a particular party, it is

usually best to let the Allworx auto-attendant assist with troubleshooting. If a station has correct connectivity to

the Allworx server, dialing extension 400 should always return your own familiar auto-attendant outgoing

greeting in short order. If there are delays in connecting to the auto-attendant or a fast busy congestion signal

is returned, then there are connectivity or connection problems that must first be addressed. Additionally, once

the auto attendant is reached successfully, dialing ‘#7’ will have the auto-attendant report back audibly which

station it thinks you are calling from – so your station identity can be confirmed. Additionally, once you hang up

(per the auto-attendant instructions), the system will automatically place a call back to your station to confirm

return connectivity to your location. If the system is properly configured and good connectivity exists, this auto-

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