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3. Extended Report Block Framework

3. Extended Report Block Framework​

Extended report blocks are stacked, one after the other, at the end of an XR packet. An individual block's length is a multiple of 4 octets. The XR header's length field describes the total length of the packet, including these extended report blocks.

Each block has block type and length fields that facilitate parsing. A receiving application can demultiplex the blocks based upon their type, and can use the length information to locate each successive block, even in the presence of block types it does not recognize.

An extended report block has the following format:

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|      BT       | type-specific |         block length          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
:             type-specific block contents                      :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

block type (BT): 8 bits

  • Identifies the block format. Seven block types are defined in Section 4. Additional block types may be defined in future specifications. This field's name space is managed by the Internet Assigned Numbers Authority (IANA), as described in Section 6.2.

type-specific: 8 bits

  • The use of these bits is determined by the block type definition.

block length: 16 bits

  • The length of this report block, including the header, in 32-bit words minus one. If the block type definition permits, zero is an acceptable value, signifying a block that consists of only the BT, type-specific, and block length fields, with a null type-specific block contents field.

type-specific block contents: variable length

  • The use of this field is defined by the particular block type, subject to the constraint that it MUST be a multiple of 32 bits long. If the block type definition permits, it MAY be zero bits long.
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