RESERVED BANDWIDTH
When traveling would you book a room at a hotel if all you could get was a promise that it is very likely you will have a room when you arrive? High quality A/V streams or critical control streams require a reservation, just like individuals require a hotel reservation. The IEEE created Stream Reservation Protocol (SRP) to provide those reservations, because simple preferential treatment that existing reservation techniques could provide was not good enough. In a dynamic system, devices request network resource needs with SRP and the entire network path is configured to provide the bandwidth needed. This bandwidth is allocated to the stream data and all other traffic may use the remaining bandwidth. This protection along with the traffic shaping provided by the AVB Credit-Based Shaper prevents network congestion that could result in packet loss and delivery delays. SRP establishes loss-less bounded latency reservations across multiple network topologies and automatically configures the associated hardware queues, packet forwarding and VLAN configuration. In addition, should the bandwidth not be available for the new stream, error reporting is sent back to the requester so that the system operator can diagnose any issued. In the unfortunate event of an emergency situation such as a 911 phone call or a fire/health safety announcement the “network” will automatically remove other reservations so the emergency announcements can be made immediately, without requiring the time-consuming delays associated with negotiations among all the non-emergency end stations to make bandwidth available on the network.
AVB/TSN networks can provide these reservations dynamically with as described above with SRP or statically. In a static system the switched are pre-configured at boot up with the reservations. While this loses some flexibility, it can speed startup time and can be useful for non-varying systems like automotive or industrial.
Detailed Features
1. No congestion loss: ensures no congestion loss because of SRP built-in admission control and the direct mapping of reserved traffic onto higher priority hardware egress queues that only process reserved traffic. SRP was created because the simple preferential (optimized) stream treatment provided by existing reservation protocols was determined to be not good enough. SRP ensures delivery and maximum latency. Qav shaper replaces strict priority shapers so congestion does not occur in the network core, and the Qav shaper will enforce the reservation’s bandwidth usage. End stations don’t need big buffers to solve congestion problems.
2. Reserved traffic protection: Protects AVB-cloud by remapping non-AVB traffic that tries to use AVB priorities onto non-AVB priorities. This makes sure non-AVB traffic do not end up in the Bridge’s AVB hardware egress queues.
3. Simple configuration: No bridge configuration required to achieve this high level of QoS. SRP discovers the path and configures the hardware, all via a simple Talker and Listener packet exchange. This hardware configuration includes shaper setup as well as packet forwarding and VLAN configuration.
4. Diagnostic information: SRP also provides diagnostic information when a reservation cannot be created (i.e. when admission is denied).
5. Packet identification: The three-bit PCP code in the 802.3 header along with the stream destination address is all that is required for no congestion loss packet forwarding.
6. Multiple network technology support: SRP is a single protocol that works across wired, wireless and MoCA.
7. Emergency traffic: The “network” is allowed to tear down existing reservations so an emergency stream (think 911 phone call or safety announcement) can be immediately established.
8. Automatic network configuration
