Circuit Switched Data Call

Innovation Name: Circuit Switched Data Call

Intent : To establish connection between two PCs without Internet at just rate of local call.

Context:  GSM provides Fax and data call service since long time. Generally people use GPRS, 3G and now LTE etc PS service only for data connectivity and Internet. This idea describes how to exploit basic CS Data call service. Nowadays Internet is omnipresent and wireless data rate is also decreasing. The local call rate for CS voice call is even cheaper in India.

  • This application can provide IP connectivity using GSM network, across the globe between a pair of computer.
  • No need of Internet.
  • Provide minimum 9.6kbps dedicated link.
  • With HSCSD one can get upto 38.4 kbps speed. 
  • In case of wireless Internet by GPRS and 3G, the radio resources are shared among all the active user cover by a single cell. So the Internet bandwidth will be low, if more users are accessing the network. The CSD call provides dedicated link, so the Internet bandwidth does not depend upon presence of other active users in the same cell.  

Two PCs and two mobiles


Each mobile can be connected to one PC over USB interface. Here mobile acts as modem. So mobile handsets obeys the AT commands. The application can be built using AT commands to initiate CSD call at one PC and to receive CSD call at another PC. Once the call is establish, the both PCs are connected over serial interface. One can use any application like chat, file transfer, etc over serial interface.

The more sophisticated application can be built using IP connectivity. The CSD call originator can be client and CSD call receiver can be server. The server will run PPP demon over Linux. It will also acts as DHCP server. Over windows RAS (Remote Access Server) can be configured. The server waits for incoming CSD call. The client will establish CSD call. The Linux client will run PPP client script and acquire IP address. The Windows client can run any dialer application and acquire IP address. The PPP protocol will use IPCP protocol to exchange the initial IP addresses. After successful CSD call and PPP negotiation, both PCs are connected to ad-hoc LAN network with IP address. So any kind of networking applications can be run.

The simple serial interface, without PPP will be simpler and more efficient. There will be no overhead for PPP framing and IP, TCP, UDP headers.

Known Uses:

The possible usage can be as follows. 
  • In the Machine to Machine (M2M) communication, CSD (Circuit Switch Data) call can be more economical in some countries.
  • It can be useful by media to report image/video etc in case of Internet backbone is destroyed.
  • It is useful for individual also to share photos, videos etc.
  •  CSD call can be useful to transfer periodic images surveillance purpose.
  • CSD can be used for telemedicine and remote health care.
  • This can be also used to share network resources like printer, fax etc across the geographical boundary. 
  • One can also his Internet connection over this CSD call, then wireless Internet can be much chipper. 
  • The data rate is very slow. Just 9.6 kbps
  • The GSM coverage is required.  
Future Scope

With proper usage, marketing and killing applications, GSM CSD can be popular in developing countries like India

Related Solution 

CDMA technology may also provide such CSD facility. I am not sure. 
If any two PCs are connected over Internet, then they can use many applications for screen sharing, video chat, etc etc. However, CSD call can be done without Internet. 


·         3GPP standard TS 27.007



Nitin Agarwal said...

Nice post...
I will be more interested in making a testing setup using CSD.
Is the service still available in India ?
And, can you share the details with me on how to setup a csd call ?

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