Since I have a few Cisco phones around here, I’ve played with XML apps. I have written a timezone calculator, an LDAP phone directory lookup utility (which hooks into the “external directory” function of the phones), an app that uses Qantas’ WAP interface to get flight arrival/departure information, and the obligatory RSS reader. They work, in some cases very well, but the inconsistency of the XML interface between different levels of the Cisco firmware makes it a trying exercise.
My latest exercise was an update to the RSS reader I’ve used for ages. I found RSS2Cisco ages ago and have used it quite successfully, but I’ve never really been satisfied with its way of displaying the whole feed in one text page. It works well for news feeds, where all you get is a headline and a teaser, but for things like blogs it’s not suitable (you’re lucky to get through one posting before hitting the limit of a Cisco XML text page). I wanted an interface like a “normal” RSS reader, where it lists the items in the feed in a menu and you then choose an item to be displayed.
Sounded simple, and wasn’t too hard to hack rss2cisco around to make it do my bidding (it’s not optimal yet as every time you read an item it pulls down the entire feed again). The problem I faced was in making the thing work consistently between the 7960 phones and the 7970s.
All my phones are running fairly recent SIP code, but for some reason the 7960 has an ancient XML parser. By ancient, I mean that the level of the XML SDK it supports is tied back to Call Manager 3.0. The 7970s, on the other hand, have support for a much more recent SDK and support some of the fancy operations that you can’t do on a 7960 unless you’re running SCCP firmware. At first I thought that there might have been a hardware limitation and that Cisco couldn’t fit the extra smarts of a client for later SDKs, but the SCCP code can’t be that much simpler than SIP that they’d have more room to fit a better XML browser and all the other features the SCCP code has over SIP…
So the SIP firmware for 7960 has a junk XML browser. You’d think, then, that the 7970 was easier to work with than the 7960… Wrong! Valid XML that worked quite happily on the 7960 would fail with a cryptic “XML Error[4]: Parse Error” message. It took quite a bit of time and quite a bit of trial-and-error to work out some of the dependencies (32 seems to be a magic number, folks…).
Call Manager XML (CMXML) is supposed to be really simple, but I can only imagine how complex it might get to deliver an app with a consistent interface if you had a number of different phone models to support — I have only two, and I’m looking at two different versions of my app!
In their defence, Cisco have provided a way for the phone to identify itself and its SDK level when it makes a request. A set of HTTP headers identify the device, and one specifically states the SDK version supported by the phone client. Reading these headers would allow a developer to adjust the output of their app to cater for the various phones — one app, but multiple output capabilities.
It strikes me though as a heck of a lot of work for limited return. These are phones intended for corporate installations, so it’s almost a given that there will be a full-function computer at the same desk. Why would a company invest that much effort developing and supporting an internal application for a single platform that’s tied to desks, when they could write it as a web app and deliver it practically anywhere? I’m starting to see why the Internet is not exactly awash with sites selling CMXML apps…
Having said that though, I love my timezone calculator. With three button presses I can find out the time in any of my six favourite timezones, and I can find any timezone in the world with only a few more presses. An application somewhere on the web couldn’t be anywhere near that speedy for me, and a desktop app would have to be some kind of widget already running and configured (or be the KDE Clock applet, all it takes is a mouseover… shame I’m stuck with GNOME for my work desktop).
So I’m not too keen to apply much development effort to my XML apps. I will stick them on my development site some time soon, but I don’t think it’s worth the effort to keep them functional. The Qantas one, for instance, is totally dependent on the URL and query format of the Qantas WAP application, which is obviously subject to change at any time. I wonder sometimes if a WAP-XML gateway would be useful, but then I think about the effort of writing a system to translate pages delivered over a dying protocol to an interface that never got off the ground…
In case you’re curious what the RSS reader looks like:
and something a bit more voluminous from my blog:
Yes, I am a bit proud of it, even though it’s rubbish… 😉
Crossed Wires 