11 Replies Latest reply: Nov 26, 2010 1:45 AM by davidpalma RSS

ping to keep GPRS alive?

Newbie

Hi all..

 

I had some troubles in M2M system using Telit modems.

 

My modems are  acting like servers - is up to the IT to contact it and retrieve data when desired.

So it does not depend on my modem to establish a connection... it's up to the IT.

When for long inactive periods, the modem still has an IP, still reports a socket is listening in a specific port, but the network cannot reach it. I could not handle to specify how much it is a "long inactive time"... sometimes are a couple of hours, sometimes are a dozen.

 

From readings done, and from info here in M2M site, I found it's necessary to keep PDP context alive somehow.

I did it sending periodically a ping to the network and it works.

Do you find it reasonably?

Also can you tell me if pings are charged as normal traffic on mobile operators?

Or since it processes on different communications layer it's not charged? Already heard both versions.. already ask my mobile operator, but no answer up to now!

 

Regards

David Palma

  • Re: ping to keep GPRS alive?
    Harald Naumann Expert

    The modem is always the client for several reasons:

     

    - If the modem runs in trouble because:

    --> It hangs in a software loop

    --> It gots a power down reset

    --> It is on roaming and is registered to wrong GPRS operator

    --> GSM base station is on maintance

    --> ... and a lot of more

     

    then you have to take care to register to the GSM network and to GPRS again. Only the client=modem can detect the reson and act.

    • Re: ping to keep GPRS alive?
      Newbie

      Hi Harald...

       

      When I write "server" I mean that the modem has a socket listening.. it does not actively talk/connect to a IT. Is simply waiting from a connection from the IT.

      I monitor all the troubles you described, and try to solve them.. or by re-registing again on the network or on a worst case scenario making a complete reboot to the system.

       

      Concerning the other questions about:

      - does a ping command seems reasonbly to keep a GPRS context alive?

      - is ping charged as normal traffic on GPRS network?

      Any feeling about it?

       

      Regards

      David P.

      • Re: ping to keep GPRS alive?
        Harald Naumann Expert

        Hi David,

         

        - does a ping command seems reasonbly to keep a GPRS context alive?
        I am not sure. The client = modem should send a character to check is the connection is still alive. If not then the client has to activate the connection again.

         

        - is ping charged as normal traffic on GPRS network?
        You have to pay for any byte. There is no differece for Ping, protocol overhead in TCP/IP or data.

         

        regards

        Harald

  • Re: ping to keep GPRS alive?
    Novice

    Most operators don't want M2M devices to remain connected to the network (data session) if the device is not sending/receiving data. They don't like it when you use a ping to keep the session active. Operators would prefer that the device disconnects when its done with the session. The server can send an SMS to wakeup the device and have it connect again.

    There is a cost for SMS, but if your device is not sending/receiving often enough to hold the data session without a ping, then it doesn't make sense to keep it connected.

    -Tim R

    • Re: ping to keep GPRS alive?
      Newbie

      My modem in the field can will never take the attitude to connect to data center.

      It's the data center that will connect to the modem in the field, at any time it wants. It's a completeley asynchronously conection between the data center and the modem.

       

      So... either:

      - the modem is always listening  for a connection  from the Data center (that implies to have a PDP active, with no data beeing trasnmited),

      - or is sleeping and must find a way to wake it up. (SMS for instance)

       

      How come the first network  topologie - the modem in the field is a server listening for a connection - seems so odd for you people?

      Do you all work for mobile operators ?

       

      David

      • Re: ping to keep GPRS alive?
        Novice

        I don't work for an operator, but I work closely with many of them globally. (I understand that was a hypothetical question)

        Many operators are concerned about the traffic from iPhones, iPads, eReaders and tablets that are consuming lots of bandwidth on their networks. And since we have to rely on their networks, we have to play by their rules.

        Obviously operators make more money on smartphones using lots of data than they do on M2M devices using small amounts of data. They have to protect those high-ARPU devices.

        -Tim R 

      • Re: ping to keep GPRS alive?
        Harald Naumann Expert
        - the modem is always listening  for a connection  from the Data center (that implies to have a PDP active, with no data beeing trasnmited),

        - or is sleeping and must find a way to wake it up. (SMS for instance)

         

        How come the first network  topologie - the modem in the field is a server listening for a connection - seems so odd for you people?

        Do you all work for mobile operators ?

         

         

        SMS is a risk. It will be delivered worst case days later. I am using voice call or CSD call to trigger the client in the field.

        BTW, I am not working with a GSM operator as well, but I am working on economic hardware and software concepts all the time.

        If you device will have a fixed IP, then you can listen for connection. Anyhow, the client has to take care o register to the GPRS network again as soon the connection is lost for some reasons.

        The drawbacks

        - GPRS with fixed IP is more expensive

        - GPRS with fixed IP is not "green". It will charge 20 mA all the time. With GSM idle mode it is 1.5 mA only. The GSM idle mode will save energy or your money in your pocket or both, because the battery in your M2M device can be smaller

        - With smaller battery, you device will be smaller or with standard battery the standby time longer

        Regards
        Harald
        P.S.: I am independent and interested to share my 25 years in radio communication with you