Software
Introduction to the SIP Protocol
http://isoc.nl/activ/2005-ENUMSIP/2-Mierla-SipTutorial.pdf
Session Initiation Protocol (SIP)
http://www.cs.columbia.edu/sip/
NIST Security Considerations for Voice Over IP Systems
http://csrc.nist.gov/publications/nistpubs/800-58/SP800-58-final.pdf
SIP and NAT - Good introduction to the problem on page one, but: Milkfish != Mediaproxy
http://download.dns-hosting.info/MediaProxy/NATtraversal-BestPractices.pdf
REFER RFC 3515
http://www.ietf.org/rfc/rfc3515.txt
Klaus Darilion's bookmarks - Voice over IP and related technologies
http://www.pernau.at/kd/voip/index.html
Introduction to Speech Codecs
http://www-mobile.ecs.soton.ac.uk/speech_codecs/
Introduction to the SIP Express Router
http://voip.internet2.edu/meetings/slides/200310/SIP_Express_Router.pdf
Security Engineering - A Guide to Building Dependable Distributed Systems by Ross Anderson
http://www.cl.cam.ac.uk/~rja14/book.html
SER - The SIP Express Router by iptel.org
http://iptel.org/ser/
Linksys' GPL Code Center
Link
Official DD-WRT Website
http://www.dd-wrt.com/
Official OpenWRT Website
http://openwrt.org/
Busybox uClinux embedded environment
http://busybox.net/
Animated Busybox Tutorial
http://www.linuxdevices.com/files/article018/
Enhanced OpenWRT User Interface
http://x-wrt.org
Windows-based Firewall Configuration Tool
http://www.fwbuilder.org/
Hardware
An application close to Milkfish hard- and software capabilities
http://www.hpl.hp.com/techreports/2005/HPL-2005-115.pdf
Doozy Milkfish hardware manufacturers website
http://www.mycable.de/