Phone System

Asterisk

Building Asterisk from source
Asterisk needs to be built from source so that it can be patched to enable Presence Subscriptions. A non-root build environment needs to be configured, and the Source RPM downloaded.
The CentOS Wiki provides general instructions.

As root

yum install rpm-build
useradd rpmbuild
su rpmbuild

As rpmbuild - create the build environment

cd
mkdir -p ~/rpmbuild/{BUILD,RPMS,SOURCES,SPECS,SRPMS}
echo '%_topdir %(echo $HOME)/rpmbuild' > ~/.rpmmacros

Fetch the src.rpm - use the current version

wget http://yum.freepbxdistro.org/pbx/SRPMS/asterisk/11/asterisk11-11.13.0-1.shmz65.1.31.src.rpm

Extract the rpm - this will likely show a list of packages that need to be created

rpmbuild --rebuild asterisk11-11.13.0-1.shmz65.1.31.src.rpm

Extract and patch the source - this gives us something to test the ASTERISK-13145 patch on

cd rpmbuild/SPECS/
rpmbuild -bp --without misdn asterisk11.spec 

Test the patch downloaded from the ASTERISK-13145

cd ../BUILD/asterisk-11.13.0/
patch --dry-run -p1 < ../../../gareth-11.13.0.patch

If the patch is ok, then copy it to the SOURCE directory, and add it to the SPEC file - it needs to bee added under the list of Patch1, Patch2, etc, and also under the %patch1, $patch2, etc.
For example, in Asterisk 11.13, it was added as Patch13, and %patch13 needed flags "-p1 -F2"
The Release field also has to be updated, in this case "1%{dist}.1.31_13145%{?_without_optimizations:_debug}"

cp ../../../gareth-11.13.0.patch ../../SOURCES/
cd ../../SPECS/
vim asterisk11.spec

And build

rpmbuild -bb --without misdn asterisk11.spec 

To install, you need to be root. List all the asterisk RPMs already installed, and the upgrade them (The oldpackage flag may be needed if rpm thinks the compiled version is older).

cd /home/rpmbuild/rpmbuild/RPMS/x86_64
rpm -qa | grep asterisk11 | sort

rpm -Uvh --oldpackage <rpm>

Presence configuration
First, to enable subscriptions for the extension, /etc/asterisk/sip_custom_post.conf needs to be modified.
Note: Due to a possible bug in the presence patch, the subscription seems to be doing greedy matching, which then causes another subscription not to register.
eg. Extensions 301 and 1301 - adding a subscription for 301 will cause 1301 not to register. The work around is to add a subscription for 1301 only.

; Enables 326 to subscribe to presence notifications for 325 and 1000
[326](+)
cisco_usecallmanager=yes
subscribe=325
subscribe=1000

; Enables 1301 to subscribe to presence notifications for 152 - see notes above
[1301](+)
cisco_usecallmanager=yes
subscribe=152

It's also necessary to add the following to the lines tag for the phone configuration

<line button="4">
  <featureID>21</featureID>
  <featureLabel>James</featureLabel>
  <speedDialNumber>325</speedDialNumber>
  <featureOptionMask>1</featureOptionMask>        <!-- If you want the line to cause an epileptic fit when it's ringing -->
</line>
<line button="5">
  <featureID>21</featureID>
  <featureLabel>Test</featureLabel>
  <speedDialNumber>1000</speedDialNumber>
</line>

Converting WAV to PCM:
Asterisk can't play mu-law files, so they need to be converted to PCM

ORIG=<ulaw file>
PCM=$(echo "$ORIG" | sed 's/ulaw/pcm/')
sox "$ORIG" -r 8000 -c 1 -e signed $PCM

Digium

Digium cards are picky when it comes to IRQs and Frame Buffers:

Oct 16 19:21:01 pbx1 kernel: wcte13xp 0000:01:00.0: Underrun detected by hardware. Latency bumped to: 4ms
Oct 16 19:21:01 pbx1 kernel: wcte13xp 0000:01:00.0: IO error reported by firmware.
Oct 16 19:21:01 pbx1 kernel: wcte13xp 0000:01:00.0: Underrun detected by hardware. Latency bumped to: 5ms
Oct 16 19:21:01 pbx1 kernel: wcte13xp 0000:01:00.0: Underrun detected by hardware. Latency bumped to: 6ms
Oct 16 19:21:01 pbx1 kernel: wcte13xp 0000:01:00.0: Underrun detected by hardware. Latency bumped to: 7ms

Check out these links if the PRI card is spamming the logs Dahdi Interface Flapping
How to disable the Linux framebuffer if it's causing problems

CentOS

RPM Command: 15 Examples to Install, Uninstall, Upgrade, Query RPM Packages
http://wiki.centos.org/HowTos/RebuildSRPM