RSVP Common Header Format

  The common header considers of two 32-bit words of the following form:

       0             1              2             3
+-------------+-------------+-------------+-------------+
| Vers | Flags|  Msg Type   |       RSVP Checksum       |
+-------------+-------------+-------------+-------------+
|  Send_TTL   | (Reserved)  |        RSVP Length        |
+-------------+-------------+-------------+-------------+

Vers:

4 bits
The current protocol version number is currently 1.

Flags:

4 bits
0x01-0x08: Reserved
No flag bits are defined yet.

Msg Type:

8 bits
The current set of RSVP messages, comprises:  

• 1 = PATH
• 2 = RESV
• 3 = PATHERR
• 4 = RESVERR
• 5 = PATHTEAR
• 6 = RESVTEAR
• 7 = RESVCONF

RSVP Checksum:

16 bits
The one's complement of the one's complement sum of the message.

Send_TTL:

8 bits
The IP TTL value with which the message was sent.

RSVP Length:

16 bits
The sum of the lengths of the common header and all objects included in the message.