NC-SI

NC-SI ("Network Controller Sideband Interface") is an electrical interface and protocol defined by the Distributed Management Task Force (DMTF). NC-SI enables the connection of a Management Controller (MC), also known as a Baseboard Management Controller (BMC) to one or more Network Controllers (NCs) or Network Interface Controller (NICs) 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.[1][2]

Network Controller Sideband Interface
StatusPublished
Year started2010 (2010)
OrganizationDistributed Management Task Force (DMTF)
Base standardsPlatform Management Components Intercommunication (PMCI)
DomainOut-of-band management
AbbreviationNC-SI
Websitewww.dmtf.org/standards/pmci

Hardware interface

The RBT (RMII-Based Transport) 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 (MCTP).

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
RXD[1:0]Receive Data (from NC to MC)
TX_ENTransmit Enable - Data Valid for traffic sent from the BMC
TXD[1:0]Transmit Data (from MC to NC)
RX_ERReceive Error signal sent from the NC to the MC (optional)
ARB_INHardware Arbitration - input (optional)
ARB_OUTHardware Arbitration - output (optional)

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:

  • Commands, sent from the BMC to one of the NCs.
  • Responses, sent by the NCs as results of the commands.
  • AENs (Asynchronous Event Notifications), sent asynchronously by the NCs, equivalent to interrupts, upon the occurrence of the specified event.

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.


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See also

References
  1. OCP Mezzanine card V2.0-1.1 Specification (PDF) in Open Compute Project Server/Mezz
  2. OCP NIC 3.0 Specification 1.00 (PDF) in Open Compute Project Server/Mezz
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