Download - 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
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
