Modem Traffic Calculation

The Software of the Modem (the KMMidlet) tries to establish a TCP connection with one of the Servers and to keep this open. For this purpose it has to send data packages across the connection even if there are no requests or alarms. Different carriers use different values for the maximum time a TCP Socket is kept open without any data traffic. Common values for this time are:

• 30 minutes, e.g. KPN, Jasper
• 20 minutes, e.g. Beeline
• 15 minutes, e.g. Vodafone NZ, Eplus Germany,
• 10 minutes, e.g. Vodafone AUS
• 5 minute, e.g. Vodafone UK

To keep a TCP Socket (Connection) alive the Modem can send two types of messages:

• a ping(), this call gets an answer on application level
• a plonk(), this is a notification (one way message) only

Payload is 15 Byte for the request and 7 Byte for the response. Each request or response generates also a TCP-ACK packet. The modems are able to work with two different TCP variants, the default variant has an TCP/IP Header of 52 Bytes, the other the minimum of 40 Bytes. This means (number in brackets is for the 40 Byte TCP/IP variant):

• one ping() costs 230(182) Bytes of traffic
• one plonk() costs 119(95) Bytes of traffic

The Midlet Version 3XX will generate the following numbers:

• 30 minutes: 14 pings(), 44 plonks() -> 8456(6728) Bytes a day, 248(198) kBytes a month
• 20 minutes: 16 pings(), 50 plonks() -> 9630(7662) Bytes a day, 283(225) kBytes a month
• 15 minutes: 16 pings(), 83 plonks() -> 13557(10797) Bytes a day, 398(317) kBytes a month
• 10 minutes: 17 pings(), 133 plonks() -> 19737(15729) Bytes a day, 579(461) kBytes a month
• 5 minutes: 17 pings(), 298 plonks() -> 39372(31404) Bytes a day, 1154(921) kBytes a month

This is just the traffic to keep a Socket open and alive, each successful opening of a TCP Socket costs a payload of 161 Bytes for authentification and 3 TCP/IP packets (SYN, SYN-ACK and ACK). These are 317(281) Bytes for each successful reconnect.

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Accounted traffic may be very different from these calculations

• Carriers use many different accounting models
• Nearly every accounting model uses rounding blocks (1kByte, 10 KByte, 100 KByte)
• These rounding are done on different conditions like:
  • new gprs session (new IP address), this is very common
  • on time limits (one day, one hour, 15 minutes)
  • sometimes extra fees are billed for every day with traffic or even new gprs sessions

So the accounting/billing model is the most important part. Please use the above mentioned real traffic values for negotiations with your carrier/provider