NC-SI


NC-SI is an electrical interface and protocol defined by the Distributed Management Task Force. NC-SI enables the connection of a Management Controller, also known as a Baseboard Management Controller to one or more Network Controllers or Network Interface Controller in server computer systems for the purpose of enabling out-of-band manageability. It allows the BMC to share the network connections of the NIC ports for management traffic and the host traffic.
The NC-SI defines a control communication protocol between the BMC and NICs. The NC-SI is supported over several transports and physical interfaces.

Hardware interface

The RBT interface defined by NC-SI is based on the RMII specification with some modifications allowing connection of multiple network controllers to a single BMC.
NC-SI can also operate over a variety of other electrical interfaces including SMBus and PCIe when used over the Management Component Transport Protocol.
RBT is made up of the following signals:
SignalDescription
REF_CLKA 50 MHz clock reference for receive, transmit, and control interface
CRS_DVCarrier Sense/Receive Data Valid for traffic sent from one of the NCs
RXDReceive Data
TX_ENTransmit Enable - Data Valid for traffic sent from the BMC
TXDTransmit Data
RX_ERReceive Error signal sent from the NC to the MC
ARB_INHardware Arbitration - input
ARB_OUTHardware Arbitration - output

Traffic types

NC-SI defines two fundamental types of traffic, pass-through and control traffic. Pass-through traffic consists of data exchanged between the BMC and the network via the NC-SI interface. Control traffic is used to inventory and configure aspects of NIC operation and control the NC-SI interface.
Control traffic is broken down into three sub-types:
When NC-SI is used over RBT, standard Ethernet framing is used for all traffic types. Control traffic is identified by using an EtherType of 0x88F8.
When NC-SI is used in conjunction with MCTP, MCTP provides the packetization methodology and traffic type identification.