WhichVoIP Blog

There has been a lot of publicity recently on Asterisk for your business telephony needs. 

What is Asterisk?

Asterisk is known as the open source IP PBX.  Basically, rather than using traditional PBX equipment or Cisco VoIP platform equipment, such as their Call Manager IP PBX, some businesses and universities are utilizing Linux based servers to handle their telephone calls using VoIP.  No expensive PBX equipment needed and no Cisco license fees as part of their call manager network.

The linux servers are normally found in such environments anyway in order to handle the data network for a facility so adding voice is a case of installing asterisk and connecting your phones to the server.  Analog phones will need some form of conversion to digital (e.g. using Cisco VGC gateway devices), but if you have IP phones, simple, just connect the Ethernet cables from the phone to the server.  The voice traffic will simply follow the same path as the data does now over the T1 interfaces. 

There is some downside of course.  The technical support has gone, although so has the expense   So long as you are comfortable running your voice and data network with Linux servers and have some expertise in this area so you can handle the administration, the cost savings are substantial.  Recent University studies suggest that moving from a Cisco call manager license based system to Asterisk can reduce your telephone costs by over 65%.

Asterisk is definitely one for us all to watch.
http://www.asterisk.org/

Andy

If you have ever searched for Business VoIP or have been serious about using any business telecom service then you will have come across the term T1. Over the course of the next few weeks we’ll endeavour to explain what a T1 is and delve down into the details of it for you techies out there.

So what is a T1? Well a T1 really defines 4 things.

1. The physical medium used.
2. The bandwidth or clock rate.
3. The type of signaling and encoding used.
4. The format or frame the data is transferred in. 

With a T1 there are two physical mediums. One is 100 Ohm shielded twisted pair and the other is 75 Ohm Coaxial cable. Typically inside patch panels the 100 Ohm twisted pair is used as it is cheap and flexible but for transmission to the outside world a balun is used to match to 75 Ohm Coaxial cable which is typically used to connect to the ISP or PBX.

The bandwidth of a T1 is 1.544Mbits/sec that’s for one direction, one of the advantages of a T1 is that you get this dedicated bandwidth in both the uplink and downlink directions.

T1 uses a signal encoding called B8ZS which stands for Binary 8-zero Substitution - quite a mouthful. Without going into too much detail just now, this type of encoding allows data and a clock to be sent across the same cable - vital for synchronous data transfer.

Finally the format - Each T1 is split into 24 channels referred to DS0’s. Each channel is 8 bits wide and the frame is sent on a 8KHz boundary. The data capacity is therefore 24×8x8000 = 1.536Mbits/sec. Didn’t I say earlier that a T1 was 1.544Mbits/sec? Well there is something called a framing bit, this is 1 bit every frame that a receiver on the other end can lock onto to ensure that whatever equipment is there can extract the correct DS0’s in the correct order. This framing bit makes for an extra 8000 bits/sec giving a grand total of 1.544Mbits/sec.

T1’s are essential a for any business that employs more than about ten people at the one site. They are very reliable and give you a guaranteed bandwidth.

If you are starting a business or you already own a  business and are planning on expanding, fill out this form for a quote on how much a T1 is - you maybe pleasantly surprised.

Next week or when we have time we’ll explain how the 8KHz frame rate came about and how we get 8 bits in a DS0.

WhichVoIP team

http://www.whichvoip.com

Every so often we’ll pick a topic that is relevant to VoIP and explain in detail how it works. Hopefully we can explain it well enough that even my wife can follow it and there will be enough detail out there for you techies. The first subject for this will be “What is a T1″

If you have any topics you would like explained drop us an email at customerservice@whichvoip.com or leave a comment and we’ll get round to it. I hope you all find this enjoyable as well as educational.

The WhichVoIP team

http://www.whichvoip.com