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WiMAX Vendor Specific Attribute (VSA) Format


To support the length of WiMAX attributes, Steel-Belted Radius Carrier natively supports structured attributes. These WiMAX RADIUS VSAs are transported in a RADIUS VSA. Each attribute format contains the following bit definitions:

  • The RADIUS attribute format is:

  • The RADIUS VSA format is:

  • The WiMAX VSA Payload format is:

    The Continuation field of the WiMAX VSA format is:

    If the WiMAX VSA value is larger than 246 bytes, then the value must be fragmented into a series of WiMAX VSAs. The C-bit of the Continuation field indicates whether a WiMAX attribute is fragmented.

    • When the C-bit=0, the WiMAX attribute is not fragmented.

    • When the C-bit=1, the WiMAX attribute is fragmented. The next WiMAX VSA of the same WiMAX type is appended to this attribute.

      A fragmented WiMAX attribute has its C-bit set to 1 for all of its fragments except for its last fragment. To indicate that the fragment is the last fragment of the attribute, its C-bit is set to 0.

      When using XML to specify the structured attribute format, the hasContinuationFlag=true attribute represents the C-bit. This element indicates that the attribute starts with a continuation octet, where the payload of the attribute may be split over multiple VSAs.

      The r-bits are reserved for future use. They are set to 0 by the sender and are ignored by the receiver.

Structured Attributes

Structured Attributes

SBR Carrier natively supports structured attributes that contain subattributes. Subattributes like normal RADIUS attribute-value pair (AVPs), consist of the raw encoding of a type field (such as 1 for WiMAX-Release, within the WiMAX-Capability VSA) followed by a length value (such as 5) followed by the value of the attribute (such as 1.2).

Subattributes are values in a RADIUS packet that are not stored as a RADIUS AVP, or vendor-specific-attribute (VSA), but rather are packed with other subattributes into a RADIUS VSA. In a RADIUS packet, multiple RADIUS VSAs might contain subattributes. The RADIUS VSA, which consists of multiple subattributes, is sometimes referred to as a structured attribute because it contains structured data.


You specify structured attributes using the “.” notation. For example:


Where attribute “A” is a group attribute containing a sequence subattribute “b”, which contains a simple attribute “c”.

Structured attributes are addressable only by their full pathname, which must include all interim group or sequence attributes.

You do not need to add every subattribute in a tree. Steel-Belted Radius Carrier handles partially defined trees by automatically supplying subattributes that have a default value specified in the .jdict definition files. Additionally, if a subattribute is added that does not have a suitable parent or group defined, Steel-Belted Radius Carrier automatically creates one.

For information about specifying structured attributes, see the section on Attribute Processing Files of the SBR Carrier Reference Guide.