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RSVP Resource Reservation Protocol

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RSVP, which stands for Resource Reservation Protocol, is a network signaling protocol used to reserve and manage network resources for real-time applications in IP-based networks. It was developed by the Internet Engineering Task Force (IETF) to enable quality of service (QoS) guarantees for applications such as voice and video conferencing, multimedia streaming, and interactive online gaming.

RSVP operates at the network layer (Layer 3) of the OSI model and works in conjunction with the IP protocol. It allows hosts to request specific QoS parameters, such as bandwidth, delay, jitter, and packet loss, from the network infrastructure, which then reserves and allocates the required resources to fulfill these requests.

Here's a step-by-step explanation of how RSVP works:

  1. Session initiation: A host that wants to establish a real-time session (e.g., a video conference) sends an RSVP PATH message to the network. This message contains information about the session, including the desired QoS parameters.
  2. Path reservation: The PATH message travels through the network towards the destination, signaling the intermediate routers and switches about the session requirements. Each node along the path checks its available resources and determines if it can accommodate the requested QoS parameters. If a node cannot satisfy the requirements, it sends a PATH ERR message back to the sender.
  3. Reservation establishment: When the PATH message reaches the destination, the destination host or the last node in the path sends an RSVP RESV message back towards the sender, confirming the reservation of network resources. This message carries the same QoS parameters requested in the PATH message.
  4. Resource allocation: As the RESV message traverses the network, each intermediate node reserves and allocates the necessary resources to ensure the requested QoS for the session. The resources can include bandwidth, buffer space, processing capacity, and other relevant parameters.
  5. Session data flow: With the reservation established, the real-time session can begin. The hosts involved in the session can exchange data packets according to the reserved resources and QoS parameters.
  6. Resource release: Once the session ends or the host releases the reservation explicitly, an RSVP TEARDOWN message is sent to tear down the reservation and release the allocated resources.

RSVP operates in two modes: reservation mode and wildcard mode. In reservation mode, hosts explicitly request and reserve resources along the entire path. In wildcard mode, hosts request resources only from the local node, and subsequent nodes along the path make their own resource reservation decisions based on the request.

It's important to note that RSVP is a soft-state protocol, meaning that it relies on periodic refresh messages to maintain the reservation. If the refresh messages are not received within a specified time, the reservation is released, and resources are made available for other sessions.

Overall, RSVP enables end-to-end resource reservation and QoS guarantees for real-time applications in IP networks, allowing them to function reliably and predictably in environments where network resources may be limited or congested.