Response to "SIP Rules!"
From: Paul E. Jones [mailto:paulej@packetizer.com] Folks,
I have heard a lot of negative comments made about H.323
I have heard many claims that H.323 is complicated and that the protocol
specifications are too vast. To an extent, those claims are true. However,
H.323 is not the culmination of unnecessary complexity. Rather, it
represents a level of protocol maturity.
Some people begin their comparison of SIP and H.323 at the level of message
encoding: binary versus ASCII. There are some who believe that ASCII is the
right way to go, because it's "easy". The assertion is that it's easy to
write the code to encode and it is easy to identify encoding errors, since
everything is clearly visible as text. This argument makes sense when one
is developing a single protocol like SIP. However, as soon as one decides
to implement the next, different ASCII-based protocol, all of the
"low-level" work must often be done from scratch again. That is one of the
main reasons why protocols such as H.323 use ASN.1-- to prevent having to do
this work over and over again for every new protocol. While ASN.1 PER
encoding is not nearly as trivial as ASCII encoding, the work only has to be
done once and the tools to do that are available commercially. An
additional benefit of H.323 comes as new features are added to the protocol.
Again, the software developer is spared from having to change the code at
the lower layers that performs the encoding and decoding of messages.
Once we get passed encoding, I often hear arguments that H.323 is complex
because it requires support for multipoint audio/video conferencing. H.323
supports multipoint data conferencing with the use of the T.120-series of
protocols, which some say lends to the increased complexity. People look at
the size of H.323, H.225.0, and H.245 alone as enough reason to declare that
the protocol is too complex. People then look at supplementary services
based on the H.450-series protocols, which they believe does nothing but
continue to add to the complexity of the protocol.
The truth is that any mature system has a certain level of complexity that
is necessary in order to provide the services that service providers need in
order to meet customer demands. There are many things in H.323 that are
completely optional to implement, such as decentralized multipoint
conferencing, data conferencing, and all supplementary services. All of
those and many other features exist as options because people need them. So
on the surface, H.323 appears more complex than it is when one only needs
minimal functionality.
The interesting thing to note is that, while SIP is simpler in some ways,
the same complexity found in H.323 is creeping into SIP. If one examines
the architectural models of the SIP implementations and network designs of
various vendors and service providers, one will see a common theme: there is
a convergence toward the H.323 architecture. Yes, there are differences,
but I often see more similarities than differences. Just examining the
Internet Draft documents submitted for the last IETF
Another misconception I often hear is that SIP can take advantage of the
Internet in ways that H.323 cannot-- that simply is not the case. The
article " SIP Rules!
I often say that the real complexity of any system actually lies above the
protocol layer. The application often contains much more complexity than
the protocol under it. This is true for both SIP and H.323 equipment. One
can build a simple H.323 or SIP device, just as one can build complex
devices. Almost without exception, the complexity in any IP telephony
system usually has very little to do with the protocol used for signaling.
Now, I know that some may disagree with that statement, but as third-party
call control and various supplementary services are added to the SIP
protocol and as SIP proxies are connected to other network elements to
provide services, such as address resolution, authorization, billing, etc.,
I believe that those people will share the same opinion.
On the whole, I believe that there is a big misconception about H.323 in the
SIP community. At a recent IETF meeting, a comment was made that the SIP
folks know more about H.323 than the H.323 folks know about SIP. As editor
of H.323 and one who has also implemented SIP, I don't believe that to be
the case. Each protocol has its strengths and weaknesses, but I often hear
more uninformed bias than anything else. I believe this recent article in
Computer Telephony is the pinnacle of articles containing gross
misconceptions and disparaging remarks about H.323. H.323 is a strong
protocol and is widely deployed throughout the world. You will never hear
me make such negative comments about SIP: I respect the protocol and the
engineers who have worked to create it. It is unfortunate that some
advocates for SIP can be so disrespectful of technologies not created in
their own circles and that some startup companies feel compelled to use
"protocol bashing" as a technique for bolstering support for their young
company. Worse, I am disappointed that a magazine like Computer Telephony
would condone such antics.
Best Regards,
PS: SIP stands for "Session Initiation Protocol" and not "Session Interface
Protocol", as was stated in the article.
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