Over the last few years we've seen a proliferation of IP
telephony standards. Where once we had just plain H.323,
we're now up to H.323 version 4. We also have to contend
with SIP, MGCP, and Megaco, all of which have emerged as
key standards. So what's the state of equipment
interoperability as the standards have proliferated? Is
it better than two or three years ago -- or is it worse?
To help answer that question, I interviewed Adam
Altman, who for the last two years has been responsible
for ConvergeNET
at the INTERNET
TELEPHONY� Conference & EXPO shows. I also
spoke to Jeff Dworkin, who's responsible for the
interoperability showcase at the Voice
on the Net shows. We'll get to their thoughts in a
moment. First, let's take an overview look at the
various standards.
ALPHABET SOUP
As you probably know, H.323 was the first IP telephony
call control standard -- available from the video
conferencing industry when the VoIP industry emerged,
since video conferencing used a LAN. Why reinvent the
wheel when there was already something that worked?
Actually, that thought process worked for about six
microseconds. As soon as Internet telephony started
taking off, the cry was heard for "better" standards. We
needed "lightweight" standards, like SIP. We needed "scalable"
standards that fit better with the telco distributed
architecture world, like Megaco/H.248. And, of course,
both the ITU and the IETF needed to stake a claim. H.323
was the ITU's answer; the IETF came up with SIP. And
both bodies worked together on Megaco/H.248. Not to be
left out, CableLabs came up with MGCP.
In the early days, the issue was simply whether one
vendor's H.323 implementation (or gateway) would work
with another vendor's H.323 gateway. It was (and still
is) well known that one vendor could implement H.323 and
call itself "H.323-compliant" but not work with the
H.323 gateway from another vendor -- which also, quite
rightly, marketed its product as "H.323 compliant." In
fact, ITXC came up
with the iNOW! (Interoperability NOW; currently overseen
by the IMTC) initiative to instruct vendors to implement
a "known" profile of H.323 so that interoperability
might be achieved. Further complicating the H.323
picture is the fact that there are four versions, each
more mature than the last. For example, the speed with
which vendors implemented version 2 compared to version
1 was a major inhibitor to interoperability.
But these are no longer the early days. The wide
variety of different call controls has led to
geometrically increasingly complexity. Since we don't
have a single call control, the potential exists for an
H.323 gateway to try to talk to both a Megaco
gateway and a SIP phone -- right? Well, sort of. In
fact, most networks have become H.323 networks, SIP
networks, MGCP networks, or H.248 networks -- solving
that problem automatically. And with the emergence of
softswitches, which can act as protocol converters
between the different call controls, this problem
thankfully hasn't been a major one for the industry. Or
maybe the softswitch vendors, who knew a hot revenue
opportunity when they saw one, saw this trend coming. I
remember the first softswitch companies, before they
were called softswitches, offering these protocol
converters.
So what do Adam and Jeff have to say about
same-call-control-to-same-call-control interoperability?
They have a unique vantage point since they manage
interoperability events and know what really goes on
behind the scenes. Both have seen improvements over the
last two years, although Adam is quick to point out, "Not
as much as I would have liked." He's really saying that
there is not as much interoperability as the industry
should have expected. For another viewpoint on this, I
interviewed a contact at a large Internet telephony
service provider, a major user of Internet telephony
vendor equipment. Her only comment for publication? "Impossible
dream." She's been personally frustrated by the slowness
of interoperability.
This raises an interesting point. Is the lack of
interoperability the vendor's fault? I've said in past
columns that interoperability isn't inevitable unless
service providers push the vendors by setting out
interoperability requirements in their RFPs. Vendors who
support open standards have led the interoperability
charge. But what about the others? Is deployment and
time to market more -- or less -- important than having
fully interoperable (and therefore exchangeable) systems
for service providers? I won't answer that question,
since both points of view are valid. But that's one
reason this issue is interesting.
At least we've seen improvements. Why? As Jeff points
out, H.323 has matured and the "wiggle room" in the
standard has been squeezed out through experience. "Experience"
is a key word, since it suggests that the service
providers are pushing the vendors to interoperate. I
believe this has forced them to gain experience and work
out the issues, driven by the potential for revenue.
Adam and Jeff also agree that the situation in the
SIP community is better, since SIP is a lighter protocol
and less complicated to implement. It's still not
perfect, though. There can still be device configuration
issues (for instance, one SIP device could use G.711,
another could use G.723.1, and the two wouldn't be able
to negotiate to a common codec).
But the bottom line is that we're getting there. It's
slower than the hope -- and hype -- but it is happening.
Finally, you may be wondering why I used "mania" in
the title of this column. Mania can mean two things
according to my handy-dandy, well-worn, decades-old
Webster's Collegiate Dictionary. One definition is, "excessive
or unreasonable enthusiasm;" another is, "excitement
manifested by disorganization of behavior." Which one
describes the state of interoperability? It all depends
on your point of view.
Jim Machi is Director, Product Management for the Intel
Telecommunication and Embedded Group. The Intel
Telecommunication and Embedded Group develops advanced
communications technologies and products that merge data
and voice technologies into a single network.
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