November 05, 2004

Not Much Good in VoIP

So it would seem from an article written by two well known researchers from Bell Labs/Lucent and published in ACM Queue. (To be sure that is not their claim, but one could come to that conclusion after reading that paper.) It was recently slashdotted and also widely bookmarked at the community bookmark site de.icio.us. Given the wide visibility given to the article, it is worth taking a closer look at it.

The article repeats the oft stated claim that VoIP will enable new revenue generating services. (Given the anticipated benefits, the resulting apocalypse and the fact that it is fashionable to make fun of the name VoIP, probably we should rename it Kalki.) The article further declares that many engaging services are already available, even though they do not give many examples. Interestingly, Pulver periodically admonishes the industry to come up with some innovative services. One example they talk about is click-to-dial. But it is not clear how VoIP facilitates it. Indeed, the description contained in the paper, the resultant call is a PSTN call.

The article suggests that limited signaling mechanism of PSTN makes it “awkward” to invoke services in PSTN. If so, then the article fails to pint out to VoIP industry that its reliance on ATA, which implies the same limited signaling mechanism, is going to limit VoIP to the same extent as well. The article points out the lack of industry wide effort in addressing the feature interaction problem. Feature interaction is one of the major reasons why PSTN has been slow to introduce new features; the article suggests that this problem is compounded in a distributed environment envisioned for VoIP. But it omits to point out that the limited signaling mechanism further aggravates this issue and this is another reason to revisit ATA based deployments.

One of the issues that stumped ISDN that VoIP is also finding it difficult to address is the transmission of DTMF tones. Whereas ISDN had two means of transporting DTMF (signaling message or on the bearer channel), VoIP provides three ways – encoded along with the speech, RFC 2833 and signaling message. Each method is appropriate for a given scenario, while none is satisfactory for all. The paper touches on this point but fails to point out that a terminal with richer interface can overcome this problem because the user will be able to specify the appropriate mode of transport.

The following sentence is found in their description of SIP: “If one SIP node knows the address of another node, the first may invite the second to join a SIP session.” If so, then how come a whole industry is developing around “helping end-points find one another”? The article does not say.

Ostensibly, the article would like to claim many great things for VoIP. In my opinion it does not make a case for it; it also fails to point out how current terminal architecture is holding back deployment of new and exciting features.

Posted by aswath at November 5, 2004 02:56 AM
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