RADIUS attribute from rfc2865

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Framed-Compression

This Attribute indicates a compression protocol to be used for the
      link.  It MAY be used in Access-Accept packets.  It MAY be used in
      an Access-Request packet as a hint to the server that the NAS
      would prefer to use that compression, but the server is not
      required to honor the hint.

      More than one compression protocol Attribute MAY be sent.  It is
      the responsibility of the NAS to apply the proper compression
      protocol to appropriate link traffic.A summary of the Framed-Compression 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

      13 for Framed-Compression.

   Length

      6

   Value

      The Value field is four octets.

       0      None
       1      VJ TCP/IP header compression 
       2      IPX header compression
       3      Stac-LZS compression

        FreeRADIUS Vendor-Specific dictionary values:

                    0 - None 
                    1 - Van-Jacobson-TCP-IP 
                    2 - IPX-Header-Compression 
                    3 - Stac-LZS 
            

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