Alert Standard Format (ASF) Specification

Alert Standard Format (ASF) Specification v2.0 DMTF Document DSP0136
DSP0136 23 April 2003 Page 24 of 94
Contents Type Offset Value
Session ID 4 Bytes 2Ah
Sequence Number 4 Bytes 2Eh
RSP
Hdr
Version 1 Byte 32h 06h (ASF)
Reserved 1 Byte 33h
Sequence Number 1 Byte 34h
Class of Message 1 Byte 35h 06h (ASF)
RMCP
Header
IANA Enterprise Number 4 bytes 36h 4542 (ASF)
Message Type 1 Byte 3Ah
Message Tag 1 Byte 3Bh
Reserved 1 Byte 3Ch
Data Length 1 Byte 3Dh
Data Variable 3Eh
ASF RMCP Data
Pad Variable
Pad Length 1 Byte
Next Header 1 Byte
Inte
g
rit
y
Protected
Integrity Data Variable
RSP
Trailer
3.2.3.1 Header and Trailer Formats
An RSP header contains two fields: Session ID and Sequence Number. A Session ID is an
arbitrary number that is selected by each entity and exchanged using the RSSP Open Session
Request/Response messages (see 3.2.3.4). Session IDs are used to identify the particular
session state (algorithms, keys, etc) that is used to process a particular message.
Sequence Numbers are used along with a Sliding Receive Window (see 3.2.3.3.3) to provide an
anti-replay service for messages. For this specification, the size of the Sliding Receive Window is
32 messages. A Sequence Number is a unique monotonically increasing number inserted into
the header by the sender. When a session is created, the Sequence Number is initialized to zero
and incremented by one at the start of outbound processing for a given message. A new session
must be created prior to the Sequence Number wrapping around back to zero. These fields are
specified in the following table.
Contents Type Offset Value
Session ID 4 Bytes 00h The Session ID of the destination entity.
0000 0000h “Bypass” Session ID. This Session ID is used to
indicate that an unprotected RMCP, RSSP, or RAKP
message follows the RSP header and no RSP trailer
following the message’s Data field. When this Session
ID is present, the Sequence Number field is ignored.
This mechanism allows some messages (e.g.,
Presence Ping/Pong) to be received over the RMCP
security extensions UDP port prior to session
establishment. “Set”-type messages (e.g., Reset) shall
not be accepted under this Session ID.
All others Regular Session IDs
Sequence
Number
4 Bytes 03h The sender's Sequence Number for the message.
RSP Header
An RSP trailer contains four fields:
1. Pad provides DWORD alignment for the Integrity Data field within a protected RMCP
message. Some messages may not require padding if the messages already provide the
necessary alignment.
2. The Pad Length field defines the number of Pad bytes (0 to 3) present in the message. This
field is mandatory; if no Pad bytes are required, the Pad Length field is set to 00h.