[Asterisk-biz] VoIP Suggested Reading?

[Nate Kapi]

Simple question....do any of you that operate VoIP companies have any
books you would recommend about VoIP technology, networks or soft
switches? I know there aren't really any advanced books out there
about Asterisk/IAX2 but I would like to read up on some more VoIP
carrier related material in general. Carrier Grade Voice Over IP by
Daniel Collins looks decent.

Thanks! I look forward to hearing your suggestions.