July 21st, 2007 — GSM/CDMA
Both are similar in many ways, but SS7 is more powerful and core to the network. PRI is a subset of SS7.
ISDN PRI link must directly be connected to switch. It has no capability to route the call intelligently. Using SS7 every node in the network can be accessed. Nodes need not be connected directly, SS7 has got built in intelligence to redirect packets to the correct destination.
ISDN PRI is divided into Transport (B) channels and signaling (D) channels. Voice/Data is transmitted through the B channels and the associated signaling information is transmitted through the D channel. T1 has 23B and 1D channels. E1 has 30B and 2D channels.
SS7 allows to access the telecom companies databases, like the subscriber data, and other configuration information. Now a days most of the call routing is based on database information about the customer and the destination number.
An example for this would be, the credit limit approaching message that we hear when our credit limit is about to expire. Whenever a call is placed, subsriber information is looked up from the database the appropriate message is played or routed to the destination.
SS7 is used to interconnect the switches. Its not a consumer end protocol. Modern day switches convert SS7 to PRI before giving it to a vendor or a consumer.
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June 20th, 2007 — GSM/CDMA
Where ever you hear the name gateway, assume that we are talking about external connectivity. SMS gateway is used to provide SMS connectivity to third parties or solve protocol incompatibilities.
The SMSC is a part of the operators SS7 network. The SMS gateway is connected to the SMSC. In most cases the SMSC has inbuilt gateways. Any external connection from a network other than the SS7 network is handled through the gateway.
One major advantage of a gateway is that it supports TCP/IP based SMPP protocol. So we can access an SMS gateway from an IP network like the internet. Bulk SMS providers setup their own gateways or get connectivity to already set up gateways.
The SMS gateways provides SMS connectivity to third parties via many protocols, which includes HTTP, SMPP and XML. This allows a normal programmer to access SMS services very easily without having to worry about the telephone network protocols. If he is using the HTTP protocol to connect to an SMS gateway, he can send an SMS by calling an http request.
The only limitation of HTTP is that the number of SMS that can be send per second is less than 10. For higher throughput we need to use SMPP protocol. Its a bit more complicated, but many open source libraries are available to make the task easier.
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June 5th, 2007 — GSM/CDMA
SS7, the backbone of mobile networks. It is the protocol and makes mobile telephony work. SS7 is the protocol that makes communication between network entities possible. SS7 network structure is very much similar to the TCP/IP network structure. As you can see from the picture SS7 protocol is also derived from OSI model and has got all the 7 different layers.
In TCP/IP you have Ethernet card as your hardware and in SS7 you have SS7 signalling cards. For TCP/IP you have IP addresses that gives a logical structure to the network. In SS7 you have point codes.
All the network elements like HLR, VLR, MSC, SMSC etc are connected to the SS7 network and has got point codes assigned to them. Its almost like having a database server, a web server, an ftp server etc connected to the internet.
You can create your own SMSC, MSC, VLR, HLR or any SS7 network element by using an SS7 signalling card and writing the appropriate software for it. Its like using TCP/IP to create your own web server or FTP server.
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June 5th, 2007 — GSM/CDMA
PSTN - Public Switched Telephone Network
GMSC - Gateway MSC
MSC - Mobile Switching Center
BSC - Base Station Controller
BTS - Base Transceiver Station
MSCs are the telephone exchanges of GSM networks. They route the calls based on the destination numbers current location. The BSCs and BTS are responsible to taking the call from the MSC to the handset. Those two components together handle the complications in the radio communication part.
The Gateway MSC is used to connect networks that follow different protocols. PSTN and GSM and connected via a GMSC which will take care of the signaling conversions. Old PSTN networks were analog networks, but now a days the internal network functions of a PSTN are digitally managed and uses the ss7 protocol. Only the end user connectivity is still maintained as analog.
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