NC-SI
NC-SI, abbreviated from network controller sideband interface, is an electrical interface and protocol defined by the Distributed Management Task Force (DMTF). The NC-SI enables the connection of a baseboard management controller (BMC) to one or more network interface controllers (NICs) in a server computer system for the purpose of enabling out-of-band system management. This allows the BMC to use the network connections of the NIC ports for the management traffic, in addition to the regular host traffic.[1][2]
| Abbreviation | NC-SI |
|---|---|
| Status | Published |
| Year started | 2010 |
| Organization | Distributed Management Task Force (DMTF) |
| Base standards | Platform Management Components Intercommunication (PMCI) |
| Domain | Out-of-band management |
| Website | www |
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 RMII-based transport (RBT) interface defined by NC-SI is based on the RMII specification with some modifications that allow connection of multiple network controllers to a single BMC. The NC-SI can also operate over a variety of other electrical interfaces, including SMBus and PCI Express when used over the Management Component Transport Protocol (MCTP).
The table below sums up the signals comprising the RBT interface.
| Signal | Description |
|---|---|
| REF_CLK | 50 MHz clock reference for receive, transmit and control interface |
| CRS_DV | Carrier sense and receive data validity for the traffic sent from one of the NICs |
| RXD[1:0] | Receive data (from the NIC to the BMC) |
| TX_EN | Transmit enable and data validity for the traffic sent from the BMC |
| TXD[1:0] | Transmit data (from the BMC to the NIC) |
| RX_ER | Receive error signal, sent from the NIC to the BMC (optional) |
| ARB_IN | Input data hardware arbitration (optional) |
| ARB_OUT | Output data hardware arbitration (optional) |
Traffic types
The 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:
- Commands, sent from the BMC to one of the NICs
- Responses, sent by the NICs as results of the commands
- Asynchronous event notifications (AENs), sent asynchronously by the NICs and equivalently to interrupts, upon the occurrence of the specified event
When the 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 the NC-SI is used in conjunction with MCTP, MCTP provides the packetization methodology and traffic type identification.