VoIP, SIP, and Trixbox

PBX



•
What is a PBX?

•
(Private Branch Exchange)

•
A small telephone switch owned
by an organization, which would
allow a reduction in total phone
lines needed by that organization.

•
Without a PBX, a company would
have to lease a phone line for
each phone.

•
Historically, switching was done by
hand.

•
Automated systems replaced old
manually systems



Operators switching calls, Madrid Telecommunications
Museum, Madrid, Spain.

PBX
–

Asterisk




•
Software implementation of PBX called
Asterisk

was
created

•
Allowed all standard PBX features plus some

•
Created in 1999 by
Digium

•
Released under the GNU General Public License.

•
Allowed for the for PCI cards to attach telephones,
telephone lines, T1’s and E1’s.

•
Many features have been added to it over the years.



VoIP in General




•
Advantages:

•
Same phone number anywhere

•
Easily implement services such as IVR, caller ID, etc. that you
normally pay for

•
Cost effective

•
Disadvantages

•
911 service

•
Power (not through telephone)

•
Reliability of internet

•
Security/encryption

Connecting with VoIP



•
VoIP phones

•
Looks like a normal phone, but connects to an Ethernet cable

•
Has some obvious other internal functions, such as a DHCP client

•
Sometimes has Power over Ethernet (PoE) capabilities

•
~$90 and up (PoE more expensive)

Power over Ethernet (
PoE
)


•
PoE sends power down an ethernet cable

•
This is somewhat comparable to current POTS technology which
does the same thing

•
Does not require any changes in the twisted pair

•
This
does

require special equipment to put power into the cable.

•
A switch with powered ports (much more expensive than the
equivalent switch without powered ports)

•
Buy a PoE injector (~$50)

•
Specified by 802.3af

•
Other possible uses besides VoIP phones include PoE adapters to
inject where there is a power outlet and take it out at the end to
plug into the device, such as a wireless router where there is no
power present

Connecting with VoIP

•
Analog Telephone Adaptor (ATA) device

•
Connects any normal phone to an IP network

•
~$30.00

•
Softphones

•
Software IP phones that you install on a computer

•
Popular phone is X
-
lite

•
These require speakers and a microphone.

•
Purchase Equipment: http://www.ipphone
-
warehouse.com


SIP
(Session Initiation Protocol
)

•
What is SIP

•
It is a text based protocol used to set up, maintain, and
tear down multimedia communications such a voice
and video calls over the internet.

•
RFC 2543, RFC 3261

•
Runs over
tcp

or udp, typically on port 5060

•
De facto standard

•
No security built into it

•
Ex. Cisco uses proprietary protocol but it can use SIP as
well.




Trixbox

•
Trixbox is a custom installation of CentOS.

•
Trixbox comes with a working installation of:

•
Asterisk

•
FreePBX administration tool

•
Other custom administration tools for a machine dedicated to
acting as a PBX

•
Trixbox CE is completely free and open source.

•
Trixbox Pro is for commercial call centers, independently
managed and operated.

Trixbox

FreePBX

features

•
Asterisk does not come with any built in programming, you have
to edit config files first.

•
FreePBX offers much pre
-
programmed functionality with an
excellent web based interface

•
Unlimited voicemail boxes

•
“Follow Me” functionality

•
Ring groups with call confirmation (so voicemail doesn’t stop the
other phones from ringing)

•
Unlimited conferences

•
Music on Hold

•
Call queues

•
Much more

•
LAMPA: Linux Apache MySQL PHP Asterisk

Trunks

•
To call out, you must add trunks.

•
Dial out a POTS line using a FXO card (cannot use a normal
modem).

•
SIP trunks:

•
You connect your PBX to these places through the SIP protocol,
who will then route your calls out over a POTS line if necessary

•
They can also give you DID numbers (incoming numbers)

•
Callcentric
,
voipstreet
, and les.net are 3 examples of such
services

•
Callcentric

prices: $0.0198/minute

•
DID number: $1.95/month


ZAP Trunks




•
Zaptel

compatible devices (interface

drivers)

•
FXO card

(Foreign Exchange Office)

•
A card that allows you to plug in a phone line to your
PBX box.

•
T1 card





•
Creates a zap channel for each phone line

•
If you use a SIP trunk the company you connect to will
have to have someway of connecting to phone lines.


Sources



•
http://www.tech
-
faq.com/pbx.shtml

•
http://www.packetizer.com/ipmc/sip/papers
/understanding_sip_voip/

•
http://en.wikipedia.org/wiki/Session_Initiation
_Protocol