[colug-432] protocols (Re: SSH)

[Rob Funk]

On Tuesday, March 08, 2011 07:35:25 pm Jeff Frontz wrote:
> Take a look at SIP over TCP (SIP is one of my oldest and bestest
> text-based frenemies); it's what everyone is moving toward (if not
> already using) for telephony (be it traditional phone calls or
> "presence") and the big boys are using it over TCP (for reliability).
> There is no away a priori to know how big of a buffer you're going to
> need to slurp an INVITE.  You have to do byte-by-byte inspection to
> know when you can stop

Yeah, SIP is a weird protocol. "Let's add voice capability to HTTP 1.1!"

> Compare that to, say H.323 or SS7/MTP -- or TCP or IP or UDP -- you
> know exactly how big the message will be and can pre-allocate buffers
> accordingly (and you know exactly where to look for screening/routing,
> etc.).

There are two major differences here. (Warning, I'm making broad 
generalizations.)

First is design by telephony people vs design by internet people. The 
telephony people are more hardware and low-level oriented, while the internet 
people are more oriented toward software that has been parsing textual 
protocols for years. 

The other is the level of abstraction being dealt with, once the internet 
people are in charge. To them, an internet voice protocol is an application 
layer running on top of the lower-level TCP or UDP stuff, and therefore has no 
need to care about bits or byte-counting the way the lower levels do. And 
again, they've been dealing with textual protocols for decades, so it's no big 
deal to them.

Of course, the internet people are more used to working with full-blown 
computers when working with those textual protocols, rather than working with 
telephones. On the other hand, today's telephones are often more capable than 
the full-blown computers of 20 years ago.

> Similarly, I don't think anyone would want to use "web services" to do
> their disk I/O, whether it's over the LAN or across the bus.  Heaven
> help us if (when?) there would ever be an IETF RFC purporting to be a
> "replacement" for USB! <shudder>

Ever heard of iSCSI (RFC 3720)?
http://en.wikipedia.org/wiki/iSCSI