RADIUS attribute from rfc2866

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Acct-Session-Time

This attribute indicates how many seconds the user has received
      service for, and can only be present in Accounting-Request records
      where the Acct-Status-Type is set to Stop.

   A summary of the Acct-Session-Time attribute format is shown below.
   The fields are transmitted from left to right.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |    Length     |             Value
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              Value (cont)         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      46 for Acct-Session-Time.

   Length

      6

   Value

      The Value field is four octets.

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