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Download at Boykma.Com generate, create none none with none projectsqr code generating 10 . Bar Code Types Connecting Asterisk to mobile networks There are times w none for none hen you will want to connect to Asterisk to a wireless network. This can range from the simplicity of adding a standard wireless access point to the Ethernet network (so that wireless devices can connect to the network, and therefore to Asterisk), to the somewhat more esoteric area of giving Asterisk a direct connection to a mobile network. As the addition of a wireless access point is really standard networking practice, and not specific to VoIP, it will not be covered in this chapter.

. Why connect to mobile networks Before we look at none none the two options for connecting Asterisk directly to mobile networks, let"s examine the reason for doing it, which is usually "cost". In a lot of countries, it is fixed landline to mobile calls which are the most expensive and this is due to the interconnect charges made by the mobile operators to the landline telco, and the profit margin of that telco. The following diagram depicts this situation:.

Mobile Users GSM Cell GSM Cell Mobile Telephone Switching Office PBX FXO/ISDN PSTN This high-cost si tuation is in sharp contrast to rates of mobile to mobile calls, which are often included in mobile charging plans (for example, 500 minutes per month), or are sometimes totally free between SIMs on the same mobile network.. [ 197 ]. Download at Boykma.Com Integrating Asterisk with Wireless Technologies This fact has not been left unnoticed by the creative telephony community, and for some time now, devices called GSM gateways have been available. These devices usually have an external aerial and a cut down mobile phone circuit into which you install a SIM for access to a given mobile network. Until recently, the connection to the PBX was an analog line, which would work with Asterisk, but would need the introduction of an analog interface in addition to the GSM gateway.

More recently, not only have these GSM gateways been enhanced to give direct SIP connectivity, but another hardware option has emerged in the form of GSM cards that are installed in the PC. Here is a revised version of that previous diagram, showing the most cost-effective way of calling mobiles from the PBX. Although this diagram shows a GSM gateway box, the principle applies to the GSM card implementation too.

. Mobile users GSM cell GSM cell VoIP GSM gateway SIP/H.323 PBX FXO/ISDN PSTN IP phones Having looked at the concept, we can now evaluate the two types of implementation. The GSM gateway (box). Although the conc ept of the GSM gateway box has been explained previously, the actual equipment available varies from single SIM to multiple SIMs, connecting via an FXO line, PRI connections, or SIP (there may even by some H.323 models out there)..

[ 198 ]. Download at Boykma.Com 10 . Here are some examples:. Single SIM FXO Single SIM SIP Multiple SIM PRI Because these uni ts are designed to use up the "free" minutes included within the monthly plan for the SIMs, it is common to find more SIMs than radio circuits. The presence of this situation means that there is undoubtedly embedded software somewhere that allows the user to enter the number of included minutes for each SIM, and then, when the unit determines that the 500 minutes, say, from SIM "A" have been used up, it will seamlessly switch over to SIM "B". Of course, to get a reasonable return on investments for such (multi SIM) systems really requires that your customer currently has quite a heavy fixed-to-mobile call volume.

Even at the single user end of the market, money can be saved, and not only by routing outbound fixed-to-mobile calls straight into the mobile network using one of these (single SIM) devices. Keep an eye out for my "neat money saving tricks" further in this chapter..

Advantages none for none Not platform dependent Connect via FXO, SIP, or PRI for large scale deployments Easily scalable just add more boxes No special drivers required Disadvantages Lots of wires Antenna Power Connection to Asterisk. Care needed to ensure inclusive minutes are used effectively The GSM card The alternative t o a GSM gateway box is a GSM card. PCI cards are still the dominant type available, but there are sure to be PCIe versions around too, which will become dominant as the PCs of today have either one or no PCI slots..

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