Classes of Service THE CONSTRAINED-BASED ROUTING LABEL DISTRIBUTION

THE RESOURCE RESERVATION PROTOCOL RSVP 171 Object contents 2 Bytes 1 Byte 1 Byte Length bytes Class-num C-Type Figure 7.21 The object format. The following object classes have been defined: • NULL : The contents of a NULL object are ignored by the receiver. • SESSION : Contains the IP destination address, the IP protocol id, and optionally a destination port. This object is required in every RSVP message. • RSVP HOP : Carries the IP address of the RSVP-capable router that sent this message. For messages sent from the sender to the receiver, the RSVP HOP object is referred to as the previous hop PHOP object; for messages sent from the receiver to the sender, it is referred to as the next hop NHOP object. • TIME VALUES : Contains the value for the refresh period used by the creator of the message. It is required in every Path and Resv message. • STYLE : Defines the reservation style plus style-specific information. It is required in every Resv message. • FLOWSPEC : Carries the necessary information in an Resv message to make a reserva- tion in a router. • FILTER SPEC : Defines which data packets should receive the QoS specified in the FLOWSPEC object. It is required in a Resv message. • SENDER TEMPLATE : Defines the sender’s IP address and perhaps some additional demultiplexing information, such as a port number. It is required in a Path message. • SENDER TSPEC : Contains the traffic characteristics of the sender’s data flow. It is required in a Path message. • ADSPEC : Carries the one-pass with advertising OPWA information. As discussed above, this information is gathered at each node along the path that is followed by the Path message. This information is delivered to the receiver, who can then use it to construct a reservation request or adjust an existing reservation appropriately. • ERROR SPEC : Specifies an error in a PathErr, ResvErr, or a confirmation in a Resv- Conf message. • POLICY DATA : Carries information that allows a router to decide whether a reservation is administratively permitted. It can appear in a Path, Resv, PathErr, or ResvErr message. One or more POLICY DATA objects can be used. • INTEGRITY : Carries cryptographic data to authenticate the originating node to verify the contents of this RSVP message. • SCOPE : Carries an explicit list of sender hosts towards the information in the message is to be forwarded. It can appear in a Resv, ResvErr, or ResvTear message. • RESV CONFIRM : Carries the IP address of a receiver that requested a confirmation. It can appear in a Resv or ResvConf message. Below, we describe the Path and Resv messages. 172 LABEL DISTRIBUTION PROTOCOLS

7.3.4 The Path Message

The Path message consists of the common header shown in Figure 7.20 followed by the objects: • INTEGRITY optional • SESSION • RSVP HOP • TIME VALUES • POLICY DATA objects optional • A sender descriptor consisting of SENDER TEMPLATE and the SENDER TSPEC • ADSPEC optional Each sender host sends a Path message for each data flow it wishes to transmit. The Path message is forwarded from router to router using the next hop information in the routing table until it reaches the receiver. Each router along the path captures and processes the Path message. The router creates a path state for the pair {sender, receiver} defined in the SENDER TEMPLATE and SESSION objects of the Path message. Any POLICY DATA, SENDER TSPEC, and ADSPEC objects are also saved in the path state. If an error is encountered a PathErr message is sent back to the originator of the Path message.

7.3.5 The Resv Message

When a receiver receives a Path message, it issues a Resv message which is sent back to the sender along the reverse path traveled by the Path message. Recall that the data packets follow the same path traveled by the Path message. The Resv message is a request to each node along the path to reserve resources for the data flow. It consists of the common header shown in Figure 7.20 followed by the objects: • INTEGRITY optional • SESSION • RSVP HOP • TIME VALUES • RESV CONFIRM optional • SCOPE optional • POLICY DATA objects optional • STYLE • A flow descriptor list The RSVP HOP contains the NHOP i.e., the IP address of the router that sent the Resv message. The presence of the RESV CONFIRM object in the Resv message is a signal to the router to send a ResvConf message to the receiver to confirm the reservation. The RESV CONFIRM carries the IP address of the receiver. The flow descriptor list is style dependent. For the wildcard-filter WF style the flow descriptor list consists of the FLOWSPEC object. For the fixed-filter FF and shared explicit SE styles, it consists of the objects FLOWSPEC and FILTER SPEC. As mentioned above, RSVP is not aware of the content of the RSVP objects that contain the traffic information used by the routers to reserve resources. This was done