ieee 1588 ptp

IEEE Standard 1588Precision Timing Protocol - PTP

許勝倉@NCU 2008/March/08

Why Timing Sync

• Time Division Multiplexing - TDM

• Circuit Emulation over Packet - CESoP

• Time Division Multiplexing - TDMoIP

• Wireless Backhaul

• Building Integrated Timing Supplies - BITS

Clock Source to Sync

• Global Positioning System- GPS

• Network Time Protocol - NTP

• Adaptive clock Recovery - ACR

• Precision Timing Protocol - PTP

• Building Integrated Timing Supplies - BITS

• Clock from Loop

• Atom Clock Source

Timing Requirements

• 8.4us over 900 seconds

• 18us over 24 hours

T1 Standard, Maximum time variation

T1 Standard, Maximum time Interval error at sync

• 1us over 2000 seconds

• 2us over 100000 secondsMobile station frequency accuracy

• 50 Parts Per Billion (ppb)

Timing protocols problems

• ACR - Expensive oscillate source

• GPS - Weak signal indoor

• NTP - Not meet 50ppb

• BITS - Price too high

• Loop Clock - Can’t over Packet Network

• Atom Clock Source - Price very high

PTP Master

BITS/SSU

PSTN

Internet

PSTN Switch PTP Slave

ADSL

Ethernet

T1/E1

Access Node

DS1

Synchronizing TDM

How PTP work

Preamble SFD SRC MAC DST MAC Length/Type Data CRC

10101011 IP Header UDP Header PTP Message

Clock NetworkMaster

SlaveMaster Master Master

Salve Salve Salve

Salve

SalveMaster Master Master

Ordinary Clock (Best Master)

Boundary Clock (Ethernet Switch)

Clock Source

Ordinary ClockSalve

Boundary Clock (Ethernet Switch)

PTP Messages Type

Message ValueSYNC 0

DELAY REQUEST 1

FOLLOW UP 2

DELAY RESPONSE 3

MANAGEMENT 4

Reserved 5-255

PTP in Software

• PTP define in IANA Multicast address 224.0.1.129-224.0.1.132

• Use UDP port 319 for Event message

• Use UDP port 320 for general message

• Packet size less than 300 bytes

• Header length less than 40 bytes

SRC IP 224.0.1.1290x0800

PTP vsersionOrigin TimeStemp in

SecondsOrigin TimeStemp in

Nano Seconds

Port 319 PTP protocolSYNC

UDP

Message Type

PTP vsersionOrigin TimeStemp in

SecondsOrigin TimeStemp in

Nano Seconds

Port 320 PTP protocolFOLLOW UP

Message Type

PTP vsersionOrigin TimeStemp in

SecondsOrigin TimeStemp in

Nano Seconds

Port 319 PTP protocolDELAY REQUEST

Message Type

Estimated Master Variance

Estimated Master Drift

PTP vsersionDelay Receipt in

secondsDelay Receipt in Nano Seconds

Port 320 PTP protocolDELAY RESPONSE

Message Type

Sync

Follow-up

Delay request

Delay response

Sync T1

Follow-up

T1

T4

T3

T2

Sync

Follow-up

Master SlaveNetwork

Sync

Follow-up

Delay request

Delay response

T1

T4

T3

T2

Master Slave

Offset

Delay

Delay

Offset

Delay and Jitter

PTP

UDP

IP

Driver

MAC

PHY

Network

PTP

UDP

IP

Driver

MAC

PHY

Master Slave

Delay andJitter

ProtocolStack

Application

Driver

MII

Delay and Jitter Network

Precision time stamping in hardware

Microprocessor Ethernet MAC Ethernet PHY

Time Stamping Unit

(TSU)

LAN/WAN

Hardware for Time Stamp

Open Source PTPDhttp://ptpd.sf.net

Conclusion

• PTP require addition hardware to reduce processor and software’s delay and jitter for more precision clock.

• PTP is cheaper than Atom clock source.

• PTP could meet 50 ppb requirement of TDM network.

• With PTP, TDM could over Packet Switch Network without sync clock loss.

Reference

• IEEE Standard 1588-2002 Version 2

• IEEE 1588 Precision Timing Protocol, Jeremy Bennington, Symmetricom

• High Precision clock Synchronization according to IEEE 1588 Implementation and Performance Issue, Hans Weibel, Zurich Univ.

• PTPD for Linux http://ptpd.sf.net

• IEEE Standard 802.1AS Draft