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We're pleased to announce the availability of Asterisk: The Future of Telephony online!
The result of hundreds of hours of painstaking labour, this book represents the work of Jim Van Meggelen, Jared Smith, and Leif Madsen over the past year as part of the Asterisk Documentation Project.
Thanks to O'Reilly Media for publishing the book and agreeing to publish it under the Creative Commons license.

Asterisk Installation Guides and Supporting Applications:-

Free "Asterisk: The Future of Telephony" book in pdf format
Beginners and Linux Novices:- FreePBX
Recommended OS:- CentOS
Management:- FreePBX (Formerly known as AMP)
Installation Guides - AussieVoIP
General & Advanced Info - voip-info.org

Frequently Asked Questions

What is the correct FXS impedance for the UK ?
What is the Called ID Scheme in the UK ?
What is VoIP ?
What are the advantages of VoIP over analogue PSTN lines ?
What type of service and equipment are needed for VoIP deployment ?
Can I use dial-up for VoIP or do I need broadband ?
Do I need a computer to make/receive VoIP calls ?
Can I surf the web during VoIP calls ?
Should I use an ATA or an VoIP Phone ?
Can I use VoIP for all the phones in my home ?
How can I make/receive free VoIP calls to/from remote location ?
Can VoIP make and receive calls to/from PSTN lines ?
Can I keep my existing phone number when migrating to VoIP ?
What are VoIP Service Providers (VSPs) ?
Which VoIP Service Provider should I use ?
What are IP PBXs ?
What are VoIP Gateways ?
What are FXO and FXS ports ?
What are PSTN failover lines ?
Which VoIP signalling protocols are commonly used ?
Which voice codec should I use ?
What are Gatekeepers and Registrars ?

 
What is the correct FXS impedance for the UK ?
Answer:
The first value in Hz is the Frequency and the second value is the On - Off Sequence in seconds
CountryRing FrequencyDial ToneBusy ToneRing back Tone FXS ImpedanceCallerID MethodTX GainRX GainOnhook Voltage
Australia25 Hz
0.4 - 0.2 - 0.4 - 2.0
425 Hz
Continuous
400 Hz
0.375 - 0.375
400 Hz
0.4 - 0.2 - 0.4 - 2.0
220 + 820 Ohm || 120nF 0 dB-7 dB 
Austria50 Hz
1.0 - 5.0
420 Hz
Continuous
420 Hz
0.4 - 0.4
420 Hz
1.0 - 5.0
220 + 820 Ohm || 115nF 0 dB-7 dB 
Belgium    150 + 830 Ohm || 72nF    
Bulgaria    220 + 820 Ohm || 115nF    
Canada         
China20 Hz
1.0 - 4.0
350 + 440 Hz
Continuous
450 Hz
0.35 - 0.35
450 Hz
1.0 - 4.0 
200 + 680 Ohm || 100nF  0 dB0 dB 
Cyprus         
Czech Republic         
Denmark    400 + 500 Ohm || 330nF    
Estonia         
Finland         
France50 Hz
1.5 - 3.5
440 Hz
Continuous
440 Hz
0.4 - 0.4
440 Hz
1.5 - 3.5
180 + 910 Ohm || 150nF -2 dB-9 dB 
Germany125 Hz
0.25 - 4.0 -1.0 - 4.0
425 Hz Continuous425 Hz
0.48 - 0.48
425 Hz
0.25 - 4.0 - 1.0 - 4.0
220 + 820 Ohm || 115nF +3 dB-10 dB 
Germany225 Hz
0.5 - 4.0 - 1.0 - 4.0
425 Hz Continuous425 Hz
0.15 - 0.475
425 Hz
0.5 - 4.0 - 1.0 - 4.0
220 + 820 Ohm || 115nF 0 dB-7 dB 
Greece    600 Ohm    
Hungary         
Iceland         
India    370 + 620 Ohm || 310nF    
Italy25 Hz
1.0 - 4.0
425 Hz
0.2 - 0.2 - 0.6 - 1.0
425 Hz
0.5 - 0.5
425 Hz
1.0 - 4.0
600 Ohm 0 dB-7 dB 
Japan20 Hz
1.0 - 2.0
400 Hz
Continuous
400 Hz
0.5 - 0.5
400 Hz
1.0 - 2.0
600 Ohm 0 dB-9 dB 
Korea20 Hz
1.0 - 2.0
350 + 440 Hz
Continuous
480 + 620 Hz
0.5 - 0.5
440 + 480 Hz
1.0 - 2.0
600 Ohm 0 dB-9 dB 
Lithuania         
Luxembourg         
Latvia         
Malta         
Netherlands25 Hz
1.0 - 4.0
425 Hz
Continuous
425 Hz
0.5 - 0.5
425 Hz
1.0 - 4.0
600 Ohm 0 dB-7 dB 
New Zealand25 Hz
0.4 - 0.2 - 0.4 - 2.0
400 Hz
Continuous
400 Hz
0.5 - 0.5
400 + 450 Hz
0.4 - 0.2 - 0.4 - 2.0
370 + 620 Ohm || 310nF +3 dB-9 dB 
Norway    120 + 820 Ohm || 110nF     
Poland         
Portugal         
Rep of Ireland         
Romania         
Slovakia    220 + 820 Ohm || 115nF    
Slovenia    220 + 820 Ohm || 115nF    
South Africa    220 + 820 Ohm || 115nF    
Spain25 Hz
1.5 - 3.0
425 Hz
Continuous
425 Hz
0.2 - 0.2
425 Hz
1.5 - 3.0
600 Ohm 0 dB-7 dB 
Sweden    270 + 750 Ohm || 150nF     
Switzerland         
Turkey         
UK25 Hz
0.4 - 0.2 - 0.4 - 2.0
350 + 440 Hz
Continuous
400 Hz
0.375 - 0.375
400 + 450 Hz
0.4 - 0.2 - 0.4 - 2.0
370 + 620 Ohm || 310nFETSI-FSK with PR+3 dB-9 dB50v DC
 Note that some non BT exchanges in the UK may need you to specify CTR21 (270 Ohm + 750 Ohm || 150nF) for Impedance and Bellcore for CID
USA120 Hz
2.0 - 4.0
350 + 440 Hz
Continuous
480 + 620 Hz
0.5 - 0.5
440 + 480 Hz
2.0 - 4.0
600 OhmBellcore+3 dB-3 dB48v DC
USA220 Hz
1.0 - 4.0
350 + 440 Hz
Continuous
480 + 620 Hz
0.5 - 0.5
440 + 480 Hz
1.0 - 4.0
350 + 1000 Ohm || 210nFBellcore0 dB0 dB48v DC

To notify us of corrections, additions or amendments to this information please click here

600c      600 Ohms complex
600r      600 Ohms real
900c      900 Ohms complex
900r      900 ohms real
complex1  220 ohms + (820 ohms || 115nF)
complex2  270 ohms + (750 ohms || 150nF)
complex3  370 ohms + (620 ohms || 310nF)
complex4  600r, line = 270 ohms + (750 ohms || 150nF)
complex5  320 + (1050 || 230 nF), line = 12Kft
complex6  600r, line = 350 + (1000 || 210nF)
see detailed doc


What is the Called ID Scheme in the UK ?
Answer:North America - Bellcore
Canada - CID
China - Bellcore
Brazil - DTMF
Denmark - DTMF
Finland - ETSI-DTMF or DTMF
France - ETSI-FSK
Germany - ETSI-FSK
Norway - ETSI-FSK
Sweden - DTMF or ETSI-DTMF
Taiwan - ETSI-FSK
UK - ETSI-FSK with PR (Note that some non BT exchanges in the UK, notably NTL/Telewest/Virgin may need you to specify CTR21)
ETSI-DTMF with PR
ETSI-DTMF after ring


see detailed doc

What is VoIP?
Answer:Voice over Internet Protocol (VoIP) - technology that enables one to make and receive phone calls through the Internet instead of using the traditional analogue PSTN (Public Switched Phone Network) lines.

What are the advantages of VoIP over analogue PSTN lines?
Answer:The primary main advantage of VoIP over PSTN lines is cost (it's cheaper!) Other advantages of VoIP are as follows: digital features not commonly available on PSTN lines such as voicemail, caller ID, conference, music-on-hold, etc.

What type of service and equipment are needed for VoIP deployment?
Answer:The following equipment and services are required for VoIP deployment: High-Speed Broadband connection, VoIP Phones (Softphones will require PC) or Analogue Telephone Adapters (ATAs) and VoIP Service Provider (terminate calls).

Can I use dial-up for VoIP or do I need broadband?
Answer:Dial-up can be used for VoIP when necessary or if its the only type of connection available. However, we recommend using broadband since certain VoIP codecs (e.g. G.711) require higher bandwidth.

Do I need a computer to make/receive VoIP calls?
Answer:The answer depends on whether or not you will be using a softphone with your VoIP integration. VoIP does not require any computer to make/receive phone calls (only ATA devices or VoIP Phones). If softphones are used instead of physical phones or ATA devices, then computers are needed.

Can I surf the web during VoIP calls?
Answer:Yes, VoIP allows web surfing while making and receiving VoIP calls simultaneously. It shares the bandwidth connection with other LAN computers and prioritizes voice.

Should I use an ATA or an VoIP Phone?
Answer:It depends on your preference and budget. An ATA will allow you to use analogue phones for VoIP. While this might save money, they do not have one touch feature keys (e.g. transfer, hold, etc). On the other hand, using VoIP Phones will provide more features that are similar to digital phones.

Can I use VoIP for all the phones in my residence?
Answer:Definitely, VoIP can replace every single phone in your residence. Both ATA devices and VoIP Phones can be used instead of regular analogue phones. This setup requires an account with a VoIP provider.

How I can make/receive free VoIP calls to/from remote location?
Answer:Making and receiving free VoIP calls can be made possible by signing up with VoIP Service Providers such as Free World Dialup (FWD) that allow unlimited VoIP calling. These providers will sometimes allow making/receiving free VoIP to PSTN calls (and vice versa). In addition, VoIP end user devices such as ATAs and VoIP Phones can be set up to make point to point VoIP calls between one another.

Can VoIP make and receive calls to/from PSTN lines?
Answer:Absolutely! VoIP users can definitely make and receive calls to/from PSTN lines. Any type of calls (e.g. local, long distance, international, etc.) are allowed. This requires an account with VoIP Service Providers that provide termination.

May I keep my existing phone number when migrating to VoIP?
Answer:Most VoIP Service Providers will allow you to keep your existing PSTN phone number for VoIP. However, you will need to check with the provider since not all of them offer this service. A signed "Letter of Authorization" may be required by the provider when keeping your number.

What are VoIP Service Providers (VSPs)?
Answer:VoIP Service Providers (VSPs) are the next generation telcos that provide interconnection between VoIP and PSTN networks. They allow call origination and termination between these two networks.

Which VoIP Service Provider should I use?
Answer:VoIP Service Providers can be selected based on the services and calling plans that they provide. The features they offer can greatly differ based on the price of the calling plan that you choose. Rates vary between providers and their pricing ranges from per minute charges to flat monthly bills. Choosing the right calling plan should be based on your monthly phone usage and company budget. The list shows current available VoIP Service Providers

What are IP PBXs?
Answer:IP PBXs (Private Branch Exchanges) are complete phone systems that provide advanced telephony features and services between VoIP and PSTN networks. Common features and services include: call transfer, conference, voicemail, music-on-hold, auto-attendant, and auto call routing.

What are VoIP Gateways?
Answer:VoIP gateways are devices that take analogue voice signals and convert them to IP for transport over the LAN or WAN.

What are FXO and FXS ports?
Answer:Foreign Exchange Office (FXO) ports are interfaces used to connect with the central office or PSTN analogue lines. Foreign Exchange Station (FXS) ports are interfaces used to connect with end user devices (e.g. phone or fax).

What are PSTN failover lines?
Answer:PSTN (Public Switched Phone Network) failover lines are used as backup connections in the event your VoIP or Internet connection goes down. These are optional ports on ATA devices or VoIP Phones that connect directly to the analogue PSTN lines coming from the phone company. This setup requires having both regular analogue phone lines and an account any VoIP Service Provider.

Which VoIP signaling protocols are commonly used?
Answer:VoIP signaling protocols are used to setup and tear down calls, carry the required information to locate end users, and negotiate device capabilities. The following list shows the most common VoIP signaling protocols available: SIP (Session Initiation Protocol), H.323, Cisco SCCP (Skinny Client Control Protocol), IAX (Inter-Asterisk Exchange), and MGCP (Media Gateway Control Protocol).

Which VoIP codec should I use?
Answer:VoIP codecs convert analogue voice signals to their digital encoded version. Codecs vary in size, sound quality, bandwidth and computation requirements. The most common VoIP codecs currently available are: G.711 (alaw & ulaw), G.723, G.726, G.729, GSM, and iLBC.

What are Gatekeepers and Registrars?
Answer:Gatekeepers and Registrars are gateways that provide authentication, authorization, call control and call routing, and session invites for end user devices.

 

 

 
 
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