PSTN stands for a public switched telephone network. A PSTN gateway is hardware components that third parties use to translate signaling.
The specifications for a PBX Phone systems can vary depending on the computer, things to be taken into consideration are, operating environment, PSTN Signalling, Management, Concurrent capacity, voIP signalling.
You will need a media gateway in order to connect a GSM network to PSTN lines without the need for a PBX or key system.
H.323 gateway. network + page 561
MGC or MEDIA Gateway Controller, it handles the connection to the PSTN (telephone system) from the computer VOIP side.
By the way, call from VOIP can be received by pstn modem. But pstn cannot make a call to VoIP number.
disadvantage of in-band signalling
Answer B H.323 gateway (A device that provides translation between network devices running H.323 signaling protocols and devices running other types of signaling protocols (for example, ss7 on the PSTN). Page 548
A normal MSC will connect BSC to the PLMN/PSTN Network directly. Meaning to say it will need to do the call connections and management from BSC all the way to PLMN/PSTN network. Once the network expands, the MSC will face congestion and therefore a solution needed. GMSC - Gateway MSC, as the name implies, will in this case serve as an interconnection between MSC and PLMN/PSTN Network. Thus this free up the resources of the MSC itself need to perform all the originally tasks.
ISDN is dial up lines and PSTN is a broadband line.
Cellular Signalling was created in 1989.
There is no such thing as GSM gateway fraud. It is the cell phone carriers who are calling it as a gateway fraud. There is a gadget that is called a GSM gateway, which is basically a cellphone (GSM module), that can connect to the internet. What it does is to help you save international long distance calls, by using the internet. Of course the cell phone carriers are not happy about it since they can no longer earn money from your international long distance calls. That is why cell phone carriers will say that it is a "GSM gateway fraud". If it is true that GSM gateway calls are fraud, then internet is also a fraud, VOIP calls are also fraud, since they bypassed the international gateways of local carriers, that includes cell phone carrier and PSTN carriers.