Crlsp Setup Procedure - HP FlexNetwork HSR6600 Configuration Manual

CRLSP setup procedure

As shown in
1. The ingress LSR generates a Path message that carries LABEL_REQUEST, and then forwards
the message along the path calculated by CSPF hop-by-hop towards the egress LSR.
2. After receiving the Path message, the egress LSR generates a Resv message carrying the
reservation information and the LABEL object. It forwards the Resv message to the ingress
LSR along the reverse direction of the path that the Path message traveled.
The Resv message advertises labels, reserves resources, and creates a reserve state on each
LSR it passes, so QoS can be guaranteed for services transmitted on the CRLSP.
3. When the ingress LSR receives the Resv message, the CRLSP is established.
Figure 44 Setting up a CRLSP
Ingress
Sender
RSVP refresh mechanism
Refresh messages
RSVP maintains resource reservation states on a node by periodically sending messages.
The resource reservation states include path states and reservation states. A path state is saved in a
path state block (PSB), and a reservation state is saved in a reservation state block (RSB). A PSB is
created by a Path message and saves the LABEL_REQUEST object. A RSB is created by a Resv
message and saves the LABEL object.
The path states and reservation states are refreshed periodically by Path and Resv messages. A
state is removed if no refresh messages for the state are received in a certain interval, and the
CRLSP established based on this state is also removed.
The Path and Resv messages for refreshing the resource reservation states are collectively referred
to as refresh messages. Refresh messages can also be used to recover from lost RSVP messages.
When multiple RSVP sessions exist on a network, a short refresh interval can cause network
degradation, but a long refresh interval cannot meet the requirements of delay sensitive applications.
To find an appropriate balance, you can use the summary refresh (Srefresh) and the reliable RSVP
message delivery features.
Srefresh
Srefresh is implemented by adding a Message_ID object to a Path or Resv message to uniquely
identify the message. To refresh Path and Resv states, RSVP does not need to send standard Path
and Resv messages. Instead, it sends an Srefresh message carrying a set of Message_ID objects
that identify the Path and Resv states to be refreshed. The Srefresh feature reduces the number of
refresh messages on the network and speeds up refresh message processing.
Reliable RSVP message delivery
An RSVP sender cannot know or retransmit lost RSVP messages. The reliable RSVP message
delivery mechanism is designed to ensure reliable transmission.
This mechanism requires the peer device to acknowledge each RSVP message received from the
local device. If no acknowledgment is received, the local device retransmits the message.
To implement reliable RSVP message delivery, a node sends an RSVP message that includes a
Message_ID object in which the ACK_Desired flag is set. The receiver needs to confirm the delivery
Figure 44, a CRLSP is set up by using the following steps:
Path
Resv
Egress
Path
Resv
Receiver
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