Summary over basic IP forwarding flow of NE20
The basic IP forwarding flow of NE20 refers to the forwarding of packets among NPs, RPU forwards the packets to NPU, and NPU to RPU.
1. High-speed to high-speed LPU forwarding (forwarding among NPs): the flow control is based on the hardware of NP.
2. High-speed to low-speed LPU forwarding( NPU to RPU forwarding): the flow control is finished through back pressure signals sent by CP to NP.
3. Low-speed to high-speed LPU forwarding (RPU to NPU forwarding): the flow control is finished by advertising receiving disable to the bottom layer by CP. It is finished by shutdown of terminal or disconnecting the connection to interface.
4. Forwarding between low-speed LPUs:
(1) including the forwarding from NPU to RPU, and that from RPU to NPU;
(2) the forwarding of low-speed LPUs has internal command lines, and it makes the forwarding of low-speed LPU bypass the NP, which is effective for locating if the packet loss in forwarding is resulted from NP.