This is a front-end SIP proxy configuration for the xlab1 project
See for more details: https://txlab.wordpress.com/tag/xlab1/
The configuration requires Kamailio version 3.3.x

This work is licensed under a Creative Commons Attribution 3.0 License
Author: Stanislav Sinyagin <ssinaygin@k-open.com>



In this configuration, Kamailio serves as a pass-through proxy,
dispatching everything to the back-end servers: all SIP messages
including registration, and also RTP is proxied. This allows to keep
only a minimal set of public IP addresses, and build as large
infrastructure at the back-end as needed.

The Dispatcher and Domain modules are used for SIP routing. They both
use a text-based database for the list of domains and routing
destinations. A text database is chosen for two reasons: 1) no SQL
dameon is required; 2) the database content can be managed by Git and
replicated on multiple front-end servers.

The domain table maps domain names to DID (domain ID):

############### /opt/sipfe/etc/kamailio_db/domain ######
id(int,auto) domain(string) did(string,null) last_modified(int)
1:sip.customer01.com:1:0
2:sip.customer02.com:2:0
######


The domain attributes table assigns a route set number that is used by
Dispatcher:

############### /opt/sipfe/etc/kamailio_db/domain_attrs ######
id(int,auto) did(string) name(string) type(int) value(string) last_modified(int)
1:1:routeset:0:1:0
2:2:routeset:0:2:0
######


The dispatcher table matches each routeset into the internal server's IP
address. The initial idea was to use DNS names, but Kamailio queries A
records regardless if the initial SIP call was received over IPv4 or
IPv6. So, explicit addresses have to be specified. For each routeset,
4000+N is used for IPv4, and 6000+N for IPv6. The "attrs" field cannot
be empty, so I added a dummy attribute which does not play any role.

############### /opt/sipfe/etc/kamailio_db/dispatcher  ######
id(int,auto) setid(int) destination(string) flags(int) priority(int) attrs(string) description(string)
1:4001:sip\:10.100.0.17\:5060:0:1:backend=be011:"be011 default"
2:4002:sip\:10.100.0.18\:5060:0:1:backend=be021:"be021 default"
3:6001:sip\:[2001\:DB8\:8\:100\:\:17]\:5060:0:1:backend=be011:"be011 default"
4:6001:sip\:[2001\:DB8\:8\:100\:\:18]\:5060:0:1:backend=be021:"be021 default"
######


The configuration is tested with Kamailio version 3.3.x. Also it
requires the rtpproxy daemon to be running on the same or an additional
server. Rtpproxy can also be scaled to utilize multiple cores, so the
design is fully scalable. Two or more such servers can be running in
parallel.

After changing the database files, simply restart kamailio daemon. As
it's completely stateless, no SIP running sessions would be harmed.