[VOIPSEC] 4G Issue Map: signaling complexity

[Simon Horne]

Brian

Customers don't care whether it's text or binary, they just care that it 
works and whether it can it deliver the solution to the customer 
requirements and that today includes PSTN integration, Security and NAT 
Traversal.  As SKYPE would say, arguing about which or what is better is 
just purely academic. Can you deliver the solution? The truth is after 10 
years with SIP we're all still scratching our heads.

Simon

At 06:00 AM 25/08/2006, you wrote:
>Paul
>
>Re: Text vs Binary.
>
>I was there.  I was the IETF editor for the first Megaco RFC.  The design
>was a compromise.  You can say, after the fact we could have done better,
>and no doubt that was true.  However, the text guys will tell you the same
>thing: if they could have ignored the binary guys, they could have done
>better.
>
>The only think I have heard that MAY have some validity is that the binary
>guys should have pushed PER instead of BER.
>
>I don't understand the compress SIP issue.   If you have a SIP device on a
>network with hundreds of kilobits or megabits or gigabits of bandwidth, then
>you can ignore compression; not worth it.  When you are on a device that has
>kilobits of signaling channel, then compression is a good idea.  SIP
>compresses well, without significant compute expense.  I don't think ASN.1
>would compress well.  I'm not sure I've actually seen anyone try, but many
>the normal compression tricks wouldn't work well except on the obvious
>repeated URI stuff, which is text always.
>
>What we have discovered about text encoding is that they are much easier to
>get right IN THE BIG PICTURE.  They are much, much easier to debug.
>
>The usual claimed ASN.1 advantage beyond message size is the automatic
>syntax correctness.  My personal experience with that is that it's true on
>the wire, but not in the implementation.  It takes more time to get an
>interoperable implementation with ASN.1, because it takes more time to get
>through the edit/compile/test loop, and it takes longer to diagnose.  Once
>you have the implementation working (and I mean interoperable) the
>correct-by-construction syntax advantage goes away.  The thing that
>surprised me the most was watching bakeoffs (sorry Pillsbury).  ASN.1 based
>bakeoffs are painful, text ones are much, much easier.  Total time clearly
>favors text in a bakeoff.  Syntax errors are easy to diagnose and fix.
>Semantic errors are much harder, and diagnosing them when you fumble with
>your decoding tools is hard.
>
>Also, of course, we're a whole lot better with our ABNF parser tools now.
>
> > > If we were to start over in the IETF, the golden rule would be: This
> > > protocol is NOT INTENDED to replace the PSTN, and any suggestion that a
> > > feature is needed because the PSTN has it, or does it some particular
> > way,
> > > is sufficient reason for outright rejection of the feature or method.
> >
> > :-)  Yes and no.  When the user attempts to call a remote party and a
> > recording says "the number you've dialed has been disconnected" is played,
> > that needs to be heard.  It's either that, or devices have to process a
> > lot
> > of different (and equivalent) error codes.
> >
> > I was once using a SIP phone that would not properly play in-band
> > announcements.  It was several days later (when I used my mobile phone)
> > before I discovered why the phone just kept ringing and ringing.
>Thank you.  Couldn't have picked a better example.
>
>The bell heads forced sip to implement early media, because they have a very
>broken billing system, that they insisted had to be copied.
>
>Your problem was your phone did not play early media.
>
>The sip mechanism is that the end device gives you your error; there are no
>announcements in audio form played by the far end.  What if you were calling
>someone with a text phone because you are deaf?  Your phone could text you
>the proper message, the far end can't.
>
>If you want media, complete the call.  That's because SIP is a session
>establishment protocol, and the media is the session.  If you want media,
>create a session.  That, in and of itself, is not the problem.  The problem
>is the BILLING.  They want the session to NOT be established, and yet they
>want (one way, if you please) media.
>
>Early media is a very, very bad idea, and has caused untold grief and
>complication in SIP.
>
>
>
>
>_______________________________________________
>Voipsec mailing list
>Voipsec at voipsa.org
>http://voipsa.org/mailman/listinfo/voipsec_voipsa.org