Headroom Measurement
Protocol Design
Lily Lv1

To-Do List
• Ethertype for Qdt
 What EtherType should be used for the round trip delay?

• DCBX：PFC Configuration TLV format design Important not to let packet formats and perceived encoding efficiencies to drive the protocol design.

• Managed objects
 The effort, implementation cost, and purpose of statistic gathering and retention requires carefulconsideration• Timestamp point clarification
 Will (t3-t2) be impacted (variably) by queue delay?
 further specify t1, t4• Timestamp accuracy What is the accuracy of t1, t4?

Ethertype for Qdt
Reuse Qcz (CI) Ethertype 89-A2

Qcz definition

Subtype:This field, 4 bits in length, shall be transmitted with the value 0 to indicate an encapsulated CIM PDU. The Subtype fieldoccupies the least significant 4 bits of the first octet of the layer-2 CIM Encapsulation.

Qdt proposal
PDU Ethertype(89-A2)
VersionSubtype
Headroom Measurement
PDUOctet
133Length2
4 bits4 bits465-529

Subtype 0, CIM
Subtype 1, Headroom Measurement Message

Question:Is “65-529” too big for headroom measurement PDU?

PFC Configuration TLV format design (1/7)• Protocol design for capability notification.
• Augment DCBX by extending PFC configuration TLV
Phase 1: Capability notification-- If both sides support PFC HDRM, initiate PFC HDRM Measurement
Request, otherwise, stop the procedure.

PFC HDRM capability notificationt1

PFC HDRM Measurement Requestt2
PFC HDRM Measurement Responset4t3

Phase 1 answers:
 Which option(s) of measurement is supported?
 Which option of measurement will be used?
Should phase 1 answer
 What the compensation value is for each option?

PFC Configuration TLV format design (2/7)• DCBX mechanism
 DCBX has 3 types of attributes:
 Informational attributes

PFC configuration TLV
PFC configuration TLV “Shall be sent using Symmetricattribute passing”

 Asymmetric attributes
 Symmetric attributes

 PFC configuration TLV is sent using symmetricattributes passing.
 Symmetric attributes: “the passing of a attribute fromone port to its peer port with objective of both ports
utilizing the same attribute value.” ‘Willing’ is important in symmetric attribute passing.
 “A Willing port shall set its operational attribute to thatindicated in the received TLV if the received TLV has theW bit set to zero. If both the local port and remote port
are willing, then the attribute values of the port with thelower numerical MAC address shall take precedence.”

DCBX symmetric attributes

PFC Configuration TLV format design (3/7)• Non-PTP measurement required information from PFC configuration TLV• Non-PTP capability of remote port
• ( Compensation value is transmitted in response message)

Only capability is included in PFC configuration TLV.
Compensation value will be included in request-response procedure.

PFC Configuration TLV format design (4/7)• PTP-based measurement required information from PFC configuration TLV• PTP-based capability of remote• Compensation value (internal processing delay) of remote

PTP comp > 0 , PTP-based measurement is capable, compensation value equals to ‘PTP comp’
PTP comp = 0 , PTP-based measurement is incapable.

PFC Configuration TLV format design (5/7)• PTP-based measurement required information from PFC configuration TLVDoes it contradict the symmetric attribute passing rule?

Assuming below case.
Local para: W=0, PTP comp = ‘a’ (>0)
Remote para: W=1, PTP comp = ‘b’ (>0)
According to symmetric attribute passing rule, local operation parameter of PTP comp will still be ‘a’.
However, what local system really needs to calculate headroom is ‘b’.

PTP-based capability and PTP comp cannot be combined together in PFC configuration TLV.
• PTP-based capability is symmetric attribute• PTP comp is informational attributePFC Configuration TLV format design (6/7)• Proposal : PFC configuration TLV only includes ‘capability’
Question：if both non-PTP and PTP-based are capable, which will be used ?

Each bit indicates onecapability.

Option 1: Define priority of the 2 methods.

Option 2: Only one capability can be set in TLV.

Mode：00 non-capable
01 non-PTP
10 PTP based
11 reserved

PFC Configuration TLV format design (7/7)• Proposal : ‘PTP comp’ for PTP-based measurement passes to peer separately.
Option 1: Define a new informational TLV - PFC informational TLVDCBX informational attributes:“Informational attributes areexchanged via LLDP without
any participation in a DCBX
state machine.”

Compensation value for
PTP-based measurement

Option 2: Do not specify it in Qdt.
Mention the internal processing delay impact, but allow vendor specific way to implement.

Thanks

11