RADIUS attribute from rfc4679

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Access-Loop-Encapsulation

This Attribute describes the encapsulation(s) used by the
      subscriber on the DSL access loop.  It MAY be present in both
      Access-Request and Accounting-Request packets.

   A summary of the Access-Loop-Encapsulation 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Vendor-Type  | Vendor-Length |                    Value
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    Value (cont'd) |
   +-+-+-+-+-+-+-+-+

   Vendor-Type

      144 (0x90) for Access-Loop-Encapsulation

   Vendor-Length

      5

   Value

      This field is a string 3 bytes in length, logically divided into
      three 1-byte sub-fields as shown in the following diagram:

       0                   1                   2
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Data Link   |    Encaps 1   |    Encaps 2   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Valid values for the sub-fields are as follows:

      Data Link

         0x01 AAL5
         0x02 EthernetEncaps 1

         0x00 NA - Not Available
         0x01 Untagged Ethernet
         0x02 Single-Tagged Ethernet

      Encaps 2

         0x00 NA - Not Available
         0x01 PPPoA LLC
         0x02 PPPoA Null
         0x03 IPoA LLC
         0x04 IPoA Null
         0x05 Ethernet over AAL5 LLC with FCS
         0x06 Ethernet over AAL5 LLC without FCS
         0x07 Ethernet over AAL5 Null with FCS
         0x08 Ethernet over AAL5 Null without FCS

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