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NC-SI ("Network Controller Sideband Interface") is an electrical interface and protocol defined by the Distributed Management Task Force enabling the connection of a Baseboard Management Controller (MC) to a set of Network Interface Controller (NICs) in server computer systems for the purpose of enabling out-of-band remote manageability.
The NC-SI interface is based on the RMII interface with some modifications allowing connection of multiple network controllers to a single MC. It contains the following signals:
|REF_CLK||A 50 MHz clock reference for receive, transmit, and control interface|
|CRS_DV||Carrier Sense/Receive Data Valid for traffic sent from one of the NCs|
|RXD[1:0]||Receive Data (from NC to MC)|
|TX_EN||Transmit Enable - Data Valid for traffic sent from the MC|
|TXD[1:0]||Transmit Data (from MC to NC)|
|ARB_IN||Hardware Arbitration ring - input|
|ARB_OUT||Hardware Arbitration ring - output|
NC-SI traffic can be either:
- Pass Through traffic
- Control traffic
Both types of traffic are Ethernet frames. Pass through traffic consists of data exchanged between the MC and the network via the NC-SI interface. Control traffic includes frames used to configure and control of the NC-SI interface and is identified by an EtherType of 0x88F8. There are three types of control packets:
- Commands - Commands from the MC to one of the NCs.
- Responses - Response of the NC to the command.
- AENs (Asynchronous Events Notifications) - Notifications sent asynchronously by the NC. These are equivalent to interrupts.
- Management Component Transport Protocol (MCTP)
- Platform Management Components Intercommunication (PMCI)