IEEE 802.1 January 2023 Interim Session

Source Flow Control Design: Management
P802.1Qdw contribution

Jeremias Blendin
Contributors: Jeongkeun "JK" Lee, Yanfang Le, Paul Congdon

SFC High Level Concept

Today: 802.1Qbb - Priority-based Flow Control (PFC)
PFC
HoLB

PFC

PFC

PFC

HoLB

• Signal from switch directly to traffic source:
can allow for per-flow pausing

PFC§ Source Flow ControlCongestion

PFC• Removes head-of-line blocking from network

Proposed: Source Flow Control (SFC)
SFCM• Simplify deployments compared to PFC• Does not require complex buffer tuningCongestion• Remove risk of deadlocks

SFC Message(SFCM)

Congested Flow
Victim FlowIEEE 802.1 September 2022 Interim

SFCM

Figure source: https://mentor.ieee.org/802.1/dcn/21/1-21-0068-01-ICne.pdf

2SFC w/ ToR Proxy (SFC-P)§ SFC with ToR Proxy

Source Flow Control (w/ ToR Proxy)
SFCM• Works with today's RDMA NICs
• SFC proxy converts SFC message toPFC frame at sender ToR• Removes congestion from network

GenerateCongestion

Intercept

SFC Message (SFCM)

PFC• HolB possible at sender NICs but not in switchesSFCM

Not the focus of this presentation!
IEEE 802.1 September 2022 Interim

Congested Flow
Victim Flow

Figure source: https://mentor.ieee.org/802.1/dcn/21/1-21-0068-01-ICne.pdf

3Managed Objects

IEEE 802.1 September 2022 Interim

4Overview§ Goals• Minimize configuration to absolutely required parts• Separate base model for native SFC from SFC-P specific details§ Management hierarchy• SFC Entity (per bridge/end station)• SFC Instance (per VLAN/virtual network)• SFC Instance Port (per instance per port)• Multiple SFC Instance Port rows can exist per physical port

• SFC Queue (per queue)• One queue is assigned to zero or more SFC Instance Ports.

§ Open issues: SFC-P/caching options, counters
IEEE 802.1 September 2022 Interim

5Key Management Parameters
SFCM§ Enable/disable feature§ Proxy mode enablement

Congestion
SFC Message(SFCM)§ SFCM packet header fields• DSCP

Congested Flow

• UDP dst port

Victim Flow

SFCM

• Source IP address• IP connectivity requires configuration parameters
per-VLAN/virtual network

IEEE 802.1 September 2022 Interim

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SFC Entity Managed Row Elements
Name

Data typeOperationssupportedConformance

AutoCfg

sfcMainEnable

BooleanRWBENosfcSFCMSuppressionInterval

unsigned integer [0..1024]

RWBENosfcSFCMDestUDPPortUDP port number

RW

IETF RFC 798

NoIEEE 802.1 September 2022 Interim

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SFC Entity Managed Row Elements§ sfcMainEnable (Boolean)• Enable SFC feature globally on this device.

§ sfcSFCMSuppressionInterval (unsigned integer [0..1024])• Suppression interval in microseconds. The interval during which SFCM to thesame destination are suppressed, only one SFCM per destination per interval
will be sent.

§ sfcSFCMDestUDPPort (UDP port number)• Destination UDP address used for sending and accepting SFCM

IEEE 802.1 September 2022 Interim

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SFC Instance Managed Row Elements
Name

Data typeOperations
supportedConformance

AutoCfg

sfcEnable

Boolean

RW

BE

No

sfcSFCMTransmitDiffServCodePoint

unsigned integer [0..64]

RW

BE

No

sfcSFCMTruncationLength

unsigned integer [0..512]

RW

BE

No

sfcProxyMode

Enum (off, on, auto)

RW

B

No

Opt: sfcEnableCaching

TBD§ There does not seem to be a IETF standard on how to model therelation between IP networks, VLANs, and ports• This draft has expired: https://datatracker.ietf.org/doc/html/draft-ietf-netmodsub-intf-vlan-model-07
IEEE 802.1 September 2022 Interim

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SFC Instance Managed Row Elements§ sfcEnable (Boolean)• Enable SFC feature in general. Masks all other configuration parameters if false§ sfcSFCMTransmitDiffServCodePoint (unsigned integer [0..64])• DiffServ Code Point (DSCP) to use in IP header of SFCM

§ sfcSFCMTruncationLength (unsigned integer[0..512])• Length to which the original packet in the SFCM is truncated to§ sfcProxyMode (Enum (off, on, auto))• Defines the proxy mode behavior: off, on to override automatic configuration
and auto to accept negotiation from DCBXIEEE 802.1 September 2022 Interim

10SFC Instance Port Managed Row Elements
Name

Data typeOperations
supported

Conformance

AutoCfg

sfcSFCMSourceAddressIPv4

IPv4 address

RW

IETF RFC 791,BEOpt

sfcSFCMSourceAddressIPv6

IPv6 address

RW

IETF RFC
8200, BEOpt

sfcAdminPortMode

Enum (disable, native, proxy-mode,auto)

RWBENosfcOperPortMode

Enum (disable, native, proxy-mode)

RBEYesIEEE 802.1 September 2022 Interim

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SFC Instance Port Managed Row Elements§ sfcSFCMSourceAddressIPv4/6 (IPv4/IPv6 address)• IP address to use a source address for the SFCM. The IP address of the port ofthe congested queue should be used as source if available, the VLAN/VRF portotherwise.

§ sfcAdminPortMode (Enum (disable, native, proxy-mode, auto))• Configures the port mode
• disable: no send/accept SFCM or translate PFC messages, no DCBX override• native: do send/accept native SFCM, no DCBX override• proxy-mode: do send/accept PFC and translate to/from SFCM, no DCBX override. Only valid ifsfcProxyMode in the SFC Instance is enabled. If any SFC instance is in this mode on a port,
all SFC instances must use this mode on this port.
• auto: allow any port mode through DCBX and subject to sfcProxyMode, disable port by default.
IEEE 802.1 September 2022 Interim

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SFC Instance Port Managed Row Elements§ sfcOperPortMode (Enum: disabled, native, proxy-mode)• Displays the port’s mode:• disabled: no send/accept SFCM or translate PFC messages• native: do send/accept native SFCM
• proxy-mode: do send/accept PFC and translate to/from SFCM.

IEEE 802.1 September 2022 Interim

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SFC Queue Managed Row Elements
Name

Data typesfcMonitorQueue

BooleanOperations
supportedConformance

RW

BE

AutoCfg
No§ sfcMonitorQueue (Boolean)• Monitor and send SFCM for traffic of the associated VLANs in this queue• For native SFC, the flow classification and traffic class -> priority -> queue
mapping is not relevant.
• SFC requires that all traffic assigned to a monitored queue is part of an SFCenabled VLAN
• It is the task of the queueing system to specify when a queue is congested andfor how long senders should be paused to alleviate the congestion.
IEEE 802.1 September 2022 Interim

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Operational Model for SFC
SFCM§ Bridges use SFC to control congestion§ SFC operates between a congested
bridges and senders of congesting flows• End stations must adhere to SFCM pause
specificationCongestion
SFC Message(SFCM)

Congested Flow
Victim Flow

SFCM

• There are no SFC parameter interactions
between congested bridges• The SFC trigger mechanism and pause duration
calculation is specific to a bridge• Not required to be part of the specification, although it might be beneficial to do so.
IEEE 802.1 September 2022 Interim

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Conclusion§ We proposed a managed object model for native SFC• Key features and fundamental structure is in place§ Future topics• Yang model of L3 (virtual) networks to L2 port mapping• This seems to be an open issue• Configuration of queue to DSCP mapping for generating SFCM
• SFC-P• Caching• Configuration of other caching-related parameters
IEEE 802.1 September 2022 Interim16

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