TCP/IP Tutorial and Technical Overview - IBM Redbooks

RSVP message format
An RSVP message basically consists of a common header, followed by a body
consisting of a variable number of objects. The number and the content of these
objects depend on the message type. The message objects contain the
information that is necessary to realize resource reservations, for example, the
flow descriptor or the reservation style. In most cases, the order of the objects in
an RSVP message makes no logical difference. RFC 2205 recommends that an
RSVP implementation should use the object order defined in the RFC, but
accepts the objects in any permissible order. Figure 8-9 shows the common
header of a RSVP message.
Figure 8-9 RSVP common header
Where:
Version 4-bit RSVP protocol number. The current version is 1.
Flags 4-bit field that is reserved for flags. No flags are defined
yet.
Message type 8-bit field that specifies the message type:
304 TCP/IP Tutorial and Technical Overview
– Path
– Resv
– PathErr
– ResvErr
– PathTear
– ResvTear
– ResvConf
RSVP vhecksum 16-bit field. The checksum can be used by receivers of an
RSVP message to detect errors in the transmission of this
message.
Send_TTL 8-bit field, which contains the IP TTL value with which the
message was sent.
RSVP length 16-bit field that contains the total length of the RSVP
message including the common header and all objects
that follow. The length is counted in bytes.