This document provides an overview of IEEE 1588 precision time protocol (PTP). It describes IEEE 1588-2002 and 1588-2008 standards, including clock types, message types, best master clock algorithm, and synchronization methods. It also discusses message transport and some open source software implementations of PTP on Linux.

1. IEEE1588-v2 Introduction

2. AGENDA
•
•
•
•
•
•
Time Synchronization
IEEE1588-2002
IEEE1588-2008
Best Master Clock Algorithm
Message Transport
Implementation

3. Time Synchronization
• NTP/SNTP
– Application Layer
– Not accuracies(10~100 ms)
• GPS
– Expensive
• Precision Time Protocol (PTP)
–
–
–
–
Local area network
sub-microsecond (μs)
Measurement and control system
Master-slave architecture

4. IEEE1588-2002 Clock Type
• Ordinary Clock (OC)
– a single PTP port
– end nodes
• Boundary Clock (BC)
– multiple PTP port
– sync from one network to another
– switch & router
• Grandmaster Clock (GMC)
– stable & accuracies
• GPS or atomic clock
– Best Master Clock (BMC)  define GMC
– One GMC in local network

5. IEEE1588-2002 Clock Type
GPS
GMC
S
M
S
BC
M
S
OC
OC
M
S
BC
M
S
OC

6. IEEE1588-2002 Message type
• Sync (Offset)
– Master to Slave
– Timestamp (predict send out time)
– Send every 2 sec
• Follow up (Offset)
– Master to Slave
– Contain send sync timestamp
• Delay Request (Delay)
– Slave to Master
– Send every 4 ~ 60 sec
• Delay Response (Delay)
– Master to Slave

7. Synchronizing with Master and Slave
• Synchronizing
– Delay + Offset = t2-t1
– Delay - Offset = t4-t3
– Delay
• ((t2-t1) + (t4-t3)) / 2
– Offset
• ((t2-t1) - (t4-t3)) / 2
• Precision
– Software (ms)
– Software + Hardware (μs)

8. Synchronizing with Local Clock
• Drift
– Frequency is difference between master & slave
clock
• Solution
– Time stamp in hardware
– Follow-up message to adjust the frequency

9. IEEE1588-2008 Clock and Message
Type
• Transparent Clock (TC)
– Convey PTP message
– End-to-End (E2E) Transparent Clock
• forwards all messages on the network
• Add the switch “transit time” to “correction field” on SYNC &
DELAY_REQUEST message
• No “propagation delay”
– Peer-to-Peer (P2P) Transparent Clock
• Add “propagation delay” (upstream link delay)
• Add “transit time” + “upstream link delay” to “correction field”
• Message Type
– Pdelay_Req
– Pdelay_Resp
– Pdelay_Resp_Follow_Up

10. IEEE1588-2008 Clock and Message
Type
Sunc, Follow
_Up, Delay_R
eq, Delay_Re
sp
GPS
GMC
M
S
E2E TC
M
Pdelay_Req,
Pdelay_Resp,
Pdelay_Resq
_Follow_Up
GPS
GMC
S
M
S
P2P TC
OC
S
OC
S
M
S
OC
OC

11. Synchronizing with P2P TC
• Synchronizing
– Delay + Offset = t2-t1
– Delay - Offset = t4-t3
– Delay
• ((t2-t1) + (t4-t3)) / 2
– Offset
• ((t2-t1) - (t4-t3)) / 2

12. Best Master Clock Algorithm (BMC)
• Select the best candidate clock
– Identifier : MAC address
– Quality : timing deviation (GPS is highest quality)
• 1588-2002 : data field stratum
• 1588-2002 : clock accuracy & clock class
– Priority : help select a grandmaster
• 1588-2002 : boolean
• 1588-2008 : two 8-bit
– Variance

13. Message Transport
• Ethernet layer
– EtherType : 0x88F7
– Multicast address : 01:1B:19:00:00:00
– Peer Delay address[2008] : 01:80:C2:00:00:0E
• IP layer
– Multicast address : 224.0.1.129 & FF0x::181
– Peer Delay address[2008] : 224.0.0.107 & FF02::6B
• UDP
– Event Message : 319
• Sync, Delay_Req, Pdelay_Req, Pdelay_Resp
– General Message : 320
• Follow_Up, Delay_Resp, Pdelay_Resp_Follow_Up

14. Implementation
• Software on linux
– PTPd (BSD lisence)
• IEEE1588-2002, 2008 (OC)
• HW：Intel 82576 or 82580
– Ptpv2d (GPL)
• IEEE1588-2002, 2008 and IEEE802.1AS (OC)
• HW：Freescale MPC831x family
– Ptp4l (GPL)
• IEEE1588-2002, 2008 and IEEE802.1AS (BC, OC)
– Linux PTP Hardware Clock (linux kernel 3.0)
– SO_TIMESTAMPING (linux kernel 2.6.30)
• HW：Freescale eTSEC gianfar, National Semiconductor
DP83640, Intel IXP465