I've been looking for and wondering about an OpenSER book for quite some time...
Everyone knows Asterisk is king when it comes to anything open source VoIP or telephony. OpenSER rocks but it just seems so, well, hardcore.
I can't imagine anyone walking into a Borders or Barnes and Noble, grabbing a book about OpenSER and cuddling up in one of those comfy, over-stuffed chairs on a rainy afternoon for some reading. Ok, I don't know anyone that does that anyway, and certainly not anyone with a book about OpenSER. I don't know about you but my tech books always end up getting rammed into my carry on for reading during "electronics prohibited" periods of air travel. That's all the time I care to dedicate to dead tree reads. But hey, it beats SkyMall (Jim Gaffigan: "Hey buddy, I work for SkyMall and I don't appreciate you jabbing us").
Bringing this back into focus (and on topic), is there a market for an OpenSER book? I've worked with two publishing companies in the past doing various amounts of writing and technical reviewing. Mostly O'Reilly but lately another company: Packt Publishing. Well, Packt decided there was a market for an OpenSER book and they decided to publish one. It's called Building Telephony Systems with OpenSER.
I found out about this book and knew I had to read it. What would an OpenSER book look like? What OpenSER features would be explored? What would it cost? What would it smell like? Ok, I'm just kidding about that last one but I was very interested.
I happened to be working on a couple of Packt Publishing projects at the time. I thought I'd contact one of my editors to see if they could hook me up. Turns out the book had already gone to press but they were willing to send me one. Cool!
Before I go any further I need to tell you: I won't be bought and I'm not easily influenced. Just because I've worked with Packt in the past doesn't mean I'm going to spare them any criticism or cut them any slack. If anything I'll go a little harder on them because they usually know how to get good authors and reviewers (me). ;) (Kidding, of course).
So they sent me a book. It's 295 pages and written by Flavio E. Goncalves. Flavio is a Brazilian that runs VoIP training in Brazil. Florianopolis, to be exact. Florianopolis is gorgeous. If you ever go to Brazil check it out. Hey, while you're there take an OpenSER training class from Flavio and get your company to pay for the whole thing!
Anyways, this is where my criticism starts to come in... I'm not one of these American English Nazis (does that make any sense?) that stands in line at the grocery store and freaks out when someone speaks Spanish or any other foreign language. However, I do believe that language exists as a mechanism to effectively communicate between people and sometimes that can be a little tricky even between two speakers of the same language. How many misunderstandings have you had with your friends, relatives, strangers etc while speaking the same language?
Brazilians speak Portuguese and I love it. It's one of the best sounding languages around. Being Brazilian, Flavio's first language is of course, Portuguese. It's also the language this book (Building Telephony Systems with OpenSER) was originally written in. My understanding from reading the book is that the book was developed out of Flavio's original (Portuguese) training course work and later translated to English. This makes for some very interesting and (sometimes) difficult to understand English language usage. There are several instances in the book that are difficult to follow because the language is, well, awkward. It looks like there was a proofreader... Maybe his style is different from mine but I'm pretty sure most people agree with me.
Part of me feels like this criticism is unfair and I wrestled with even mentioning it. Here's my chance to elaborate on this and explain myself.
Neither the author, editor, nor reviewers are native English language speakers yet this is what the book was written in. That's amazing to me. These people, in addition to being remarkably talented in their respective fields (publishing, technology) can all speak multiple languages and work on a team, around the world (India, Romania, Brazil) in a second language. The world is flat, my friend.
I feel like I can barely work and speak English half the time. Most Americans are the same way. We're all lazy, fat, SUV driving slobs that grunt back and forth in something that resembles English (which is already pretty "ugly"). Ok it's not that bad but that's what it's often made out to be... Anyone ever seen Idiocracy?
So for a technical book, my main criticism is English language usage and that's not even that bad. So far they're doing pretty well! On to the technical stuff...
I thought the book did a great job explaining the use of various OpenSER modules and OpenSER scripting in general. I also like how Flavio introduced readers to the various (relevant) SIP RFCs along the way. In working with OpenSER and SIP in general I can't stress how important this is. Many SIP platforms isolate you from the RFCs as much as possible. Everything is taken care of and it magically works (even with Asterisk when compared to OpenSER). With OpenSER this is not the case. You better know your RFCs. You better know the difference between components in a SIP network (Proxy, UAC, UAS, B2BUA, etc). You better know some core aspects of RFC3261 (stateful vs. stateless, strict routing, loose routing, methods, dialogs, domains, etc). Flavio isn't afraid to present this to the reader and he does it in a way that doesn't come across as snobby. Depending on the situation I've been known to quote RFCs and sections before. I probably (almost always) end up looking like a jerk but sometimes, hey, it needs to be done!
While reading I was disappointed to see so much focus on MediaProxy. I don't like MediaProxy. It's written in Python. Yuck. Enough said. I kept reading and by the end of the book Flavio admitted the mistake of more or less ignoring RTPProxy and agreed it was mostly superior. Bravo! No one knows everything, not even the guys that write the books. It was refreshing to see this in print. Once again, well done.
A couple of specific (nit picky) problems... The Asterisk config for a PSTN gateway on pg. 147 is suspect. The type doesn't make it clear which file you are working in and I doubt anyone would really use that SIP configuration in production. There's also no Zaptel config. I know this isn't an Asterisk book (there are plenty of those, the best one is free) but there should at least be a pointer to an online resource for Asterisk/Zaptel configuration or something.
The same thing goes for the Cisco config. If you look closely you'll see the dial-peer uses sip-notify for dtmf-relay. No one uses this and we certainly haven't configured OpenSER for it. Again, it's nit picky but some user could end up pulling all of his hair out trying to get this to work.
I didn't go over the OpenSER script bracket by bracket but it looked pretty good. That's even tougher to comment on because it's practically a programming language and no programmer ever completely loves the way someone else wrote something. That's just how it goes.
Overall, this is a very good book and it deserves to do well, for Flavio, everyone at Packt, OpenSER and the community in general. People who should be running OpenSER aren't. Hopefully this book can help change that!
Thank you to Flavio, the OpenSER team, and everyone at Packt Publishing!