Transcript White Rabbit – The Protocol

Pedro Moreira
CERN
BE-CO-HT
WHITE RABBIT
WHITE RABBIT

Agenda

Requirements

White Rabbit Protocol

IEEE 1588 (PTP)

White Rabbit Control Message Protocol (WRCMP)

Q&A
WHITE RABBIT

Requirements
 Synchronize
up to 2000 stations with subnanosecond accuracy (jitter < 100ps)
 Bidirectional links
 Timing and Data Traffic
 3 layers based protocol (Physical, Data Link,
Network)
WHITE RABBIT - OVERVIEW
OSI MODEL
White Rabbit
Application
Presentation
Session
PowerLink ?
Not
Specified
LXI ?
EtherCat ?
Transport
Network
PTP | WRCMP
DataLink
White Rabbit
MAC
Physical
Synchronous
Ethernet
WR
Specification
WHITE RABBIT – NETWORK TOPOLOGY
White Rabbit Network
GPS
WR Switch
Timing
Receiver
Timing
Receiver
White Rabbit
Master
...
...
Data Traffic
Timing Traffic
WR Switch
Timing
Receiver
...
WR Switch
Timing
Receiver
WHITE RABBIT – THE PROTOCOL

Its is the set of (layer 2) standard rules for data
representation, signaling and error detection
required to send information over the Ethernet
channel.

Objectives
 To
tailor Ethernet to be used as real-time
communications network
 Keep it Simple, Stupit!
WHITE RABBIT – THE PROTOCOL

The Ethernet Frame

The Medium Access Control (MAC)


CSMA/CD (not used in switched Ethernet)
Problem

High Latency
WHITE RABBIT – THE PROTOCOL

High Priority Packet (HP)





Ethertype: 0xA0A0
Higher priority
Critical control messages
Fixed low latency
Standard Priority Packet (SP)



Ethertype: 0xA0A1
Lower priority than HP same as standard Ethernet traffic
Non-critical control messages (management, diagnostic)
WHITE RABBIT – THE PROTOCOL

High Priority Packet (HP)

Preemption
 If there is a frame being transmitted the node stops its
transmission, store the frame, and start the transmission
of the incoming HP packet.
 Fix Latency
WHITE RABBIT – THE PROTOCOL

High Priority Packet (HP)
For further discussions ( Layer 2+ issues)
WHITE RABBIT – THE PROTOCOL

Standard Priority Packet (SP)
For further discussions ( Layer 2+ issues)
WHITE RABBIT – IEEE 1588

IEEE 1588 - Precise Time Protocol (PTP)
 Standard
for time distribution over package based
networks
 Present benchmarks
 1μs
for topologies with no more than 30 consecutive
slaves
 IEEE
802.1 AS
 Timing
and Synchronization for Time-Sensitive
Applications in Bridged Local Area Networks
 Standard for IEEE 1558 over Ethernet for Audio, Video
Broadcast
WHITE RABBIT – IEEE 1588

IEEE 1588 - Precise Time Protocol (PTP)
 White
Rabbit Master/Slave – Ordinary Clocks
 White
Rabbit Switch – Boundary Clock
 No
Transparent Clocks
 The
use of synchrounous ethernet reduces the phase
noise accumulated in the cascades clocks
WHITE RABBIT – IEEE 1588

Synchronization
WHITE RABBIT – IEEE 1588

PTP Header
Correction Field :
Resolution:
152 fs.
Max Value
2s
Used for transparent clocks
to calculate the travelling
time in the transparent
clocks.
In White Rabbit it‘s used for
phase and link delay
compensation
It doen‘t break the standard
does it?
WHITE RABBIT – WRCMP

WRCMP – White Rabbit Control Message Protocol

WR network configuration/diagnostic

Connection of WR node




Connection of non-WR PTP node




Sends WRCMP INVITE
Receives WRCMP INVITE RESPONSE
Setup the PTP Daemon
Sends WRCMP INVITE msg
Timeout for WRCMP INVITE RESPONSE
Setup PTP Daemon for non-white rabbit node
PTP configuration

Sends WRCMP_PTPCONF



Interval sync
Phase Interval
WR management and network control
WHITE RABBIT
Thank You !
Q&A