Nettalk Voiceline - Technical Support


 1. Can you get Caller ID for Call Waiting?

This is also known as "off-hook" Caller ID or Type 2 Caller ID. A standard for Call Waiting ID (CWID) was added to SIN 227 ages ago, but BT quietly introduced it on some exchanges in summer 1998 after an announcement in SIN 274 (now SIN 354). Unfortunately, very few devices support it. I know that the Relate 1500 and CD60 do, and no doubt there will be many more coming, but it's a very good reason to consider one of these if you are getting a Caller ID phone/box in the near future - I try to highlight CWID capability on my phones and boxes pages. Some Nortel Powertouchs and Maestros support it outside the UK. I think the same holds for another extension of Caller ID, Analogue Display Services Interface (ADSI), which allows data to be sent to the screen while you are on the phone - I think this is how the BT Easicom phones tell you that you have email waiting.. The one disadvantage of Call Waiting ID is that it is much more vulnerable to hacking.

 1. Problem: Echo

Echo is often due to a mismatched hybrid (2 to 4 wire convertor) on the analog part of a telephony connection. Another source of echo is acoustic feedback from speaker to microphone of a telephone handset.

Echo becomes a problem when combined with a significant amount of delay. For example, if an IP phone was connected over wide area IP network to a VoIP Gateway then the delay would be large – echo that occurred on the trunk side of the Gateway would be audible in the IP Phone. If a user reports an echo problem then the source of this problem is likely to be on the other end of the connection.

Talker echo occurs when some proportion of the "talker's" voice is echoed back to the talker - i.e. the person speaking hears their own voice.

Listener echo occurs when some proportion of the talker's voice is echoed from the listener's end of the connection and then a second echo occurs which causes some proportion of this signal to be reflected back to the listener. This results in the listener hearing an echo of the talker's voice.

Sources of echo

There are several points in the above system where echo can be introduced.

From the Caller's perspective, these are:

• Within the caller's telephone; a certain amount of the signal from the microphone is fed straight back to the earpiece. This is often done by design, and in any case, is not a problem here - more on why later. A particular special-case of this is a poorly-configured analogue (eg TDM400P) card - for example, the default (FCC) is not suitable for the UK.
• At the hybrid at the callee's end. An improperly balanced hybrid won't correctly filter out all of the transmitted signal, and will reflect some of it back down the other half of the trunk. Imbalance may be from poor design (common) or unpredictable impedance conditions on the POTS line (very common). The latter includes factors such as:
  • wet or damaged POTS cable
  • bridge-taps (something done by the telco, seldom seen any more)
  • cheap analog phones attached to the local line
  • some expensive analog phones on the local line
  • use of lengthy untwisted wire within the subscriber's premises
• At the handset at the callee's end. If the callee isn't holding the handset against his head, or if the handset is poorly designed, it's possible for the microphone to pick up the sounds coming from the earpiece, and reflect the audio back down the line.

It's worth noting that each of these points only introduces echo in one direction; each distinct echo-introducing component will only produce echo for one user - which, as can be seen from the list above, may or may not be the nearest user. It's also worth noting that not all of the above sources are necessarily bad - see the next section.

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Nettalk Voicelione VoiceMail System Guide