Network Synchronization Technologies Poster
Synchronization Standards
PTP/IEEE 1588v2
1588v2 General Flow State
ITU-T ETSI
PRC G.811 EN 300 462-6-1
SSU/BITS G.812 EN 300 462-4-1
SONET/SDH Equipment Clock G.813 EN 300 462-5-1
Types of Synchronization
Time synchronization Devices synchronized to the same time
information
Frequency synchronization Devices having the same number of bits
over a period of time
Phase synchronization Devices will shift exactly at the same
time from one clock pulse to another
AcronymsBITS Building integrated timing supplyEEC Ethernet
equipment clock ESMC Ethernet synchronization
messaging channel
GPS Global positioning system MTIE Maximum time interval
errorPRC Primary reference clockPRS Primary reference source PTP
Precise time protocol
SEC SONET/SDH equipment clockSSU Synchronization supply
unitSyncE Synchronous EthernetTDEV Time deviationTIE Time interval
error
TIE Measurement Measures the phase of
a clock with respect to a reference clock
Measures over long periods (hours or days)
Uses raw data to calculate MTIE and TDEV
MTIE Measurement Measures the maximum
phase deviation over a measurement window
Predicts clock frequency stability over time
PTP is a synchronization scheme that provides high clock
accuracy in a packet network by continuously exchanging packets
with appropriate timestamps.
A grandmaster clock is a very precise clock source that
generates timestamp announcements and responds to timestamp
requests from boundary clocks and slave clocks.
Slave/client clocks are clocks that receive synchronization from
the grandmaster clock.
MTIE Performance Masks
Round-Trip Delay RTD = (T2 T1) + (T4 T3)
Offset (slave clock error and one-way path delay) OffsetSYNC =
T2 - T1 OffsetDELAY_REQ = T4 - T3
Assuming path symmetry, therefore One-Way Path Delay = RTD Slave
Clock Error = (T2 - T1) - RTD Notes
1. One-way delay cannot be calculated exactly, but there is a
bounded error.
2. The protocol transfers TAI (Atomic Time). UTC time is TAI +
leap second offset from the announce message.
Sw
itch/Router Laser
Master Clock
t1
Slave Clock Data atSlave Clock
Leap second offset
T2 (and T1 for 1-step)
T1, T2
T1, T2, T3
T1, T2, T3, T4
The process is repeated up to 128 times per second. Announce
rate is lower than sync rate.
Time
Announce
Sync (t1)
Follow-up (t1)
Delay_reques
t
Delay_response (t4)
Time
t4
t2
t3
xiTimeDelay
MTIE (S) = max max (xi) min (xi)
0 1 2
j
i
j + n 1
T (N 1) o
N n+1 n+j1
i=j i=jj=1
n+j1
S (n 1) 0
t i o
x
x (t)
ppj
N
3
Signal Under Test
TIEMeasurementDevice
Reference Signal
MTIE
(0.275 x 10-3 + 0.025) s for 0.1s < 1000 s
(10-5 + 0.29) s for > 1000 s
Synchronous Ethernet SSM Format (ITU-T G.8264/Y.1364)
Synchronous Ethernet (SyncE)SyncE is the scheme that transports
frequency at the Ethernet physical layer
MAC
100 ppm
4.6 ppm 4.6 ppm
Ethernet
SyncE
Line card
NE
Line cardClock card Clock cardLine card
NE NE
PHY
SSU
Direction of clock path
SSU
MAC PHY MACPHY
MAC
100 ppm
Line card
NE
PHY
EEC EECSyncE
processorSyncE
processor
Octet Number Size Field
1-6 6 octets Destination address = 01-80-C2-00-00-02 (hex)
7-12 6 octets Source address
13-14 2 octets Slow protocol Ethertype = 88-09 (hex)
15 1 octet Slow protocol subtype = 0A (hex)
16-18 3 octets ITU-OUI = 00-19-A7 (hex)
19-20 2 octets ITU subtype
21 4 bits Version
1 bit Event flag
3 bits Reserved
22-24 3 octets Reserved
25-1532 36-1490 octets
Data and padding
Last 4 4 octets FCS
Clock Message SSM Code
EEC1 QL-EEC1 1011
EEC2 QL-EEC2 1010
Organizational Unique Identifier 0x0019A7
Slow Protocol Subtype 0x0A
8 bits Type: 0x01
16 bits Length: 0x04
4 bits 0 (unused)
4 bits SSM code
IEEE Assigned OUI and SPS QL TLV Format
ESMC PDU Format SSM Message for SyncE
IEEE-1588v2 ArchitecturesDelay Request-Response Model The master
and slave(s) exchange messages directly
The slave is the only one that calculates the clock offset:
- Mean Path Delay = [ [ T2-T1] + [ T4-T3] ] / 2
- Clock Offset = [T2-T1] Mean Path Delay
Peer-to-Peer Model Each node in the network measures the
port-to-port propagation time (i.e., the link delay
between two communicating ports that support the peer delay
mechanism)
The sum of all path delays is added to the sync message
Master
Sync
Delay_req
Delay_req
Sync, Follow-up, Delay_resp
Delay_resp
T1, tagged
T2, tagged / T1, received
T3, tagged
T4, received
(T1), received
Follow-up
T4, tagged
Slave
Delay_req
Sync, Follow-up, Delay_resp
T2, tagged / T1, received
T4, received
(T1), received
Sync, Follow-up, Delay_resp
Each node in the network measures the port-to-port propagation
time (i.e., the link delay
M
S
M
S
Sync: T1m, (link delays)
T1m
Pdelay_req
Pdelay_req
Pdelay_req
Pdelay_req
Pdelay_resp
Pdelay_resp
Pdelay_resp
Pdelay_resp
T2s
P1
P1
Clock offset = [T2s-T1m] - (link delays)in the sync message
Applies toeach leg
P2
P2
Port 1
Pdelay_req
PDelay_resp
PDelay_resp_follow-up
T1p tagged
T2p tagged
T3p tagged
T4p tagged(T3p-T2p) Received
(T3p) Received
Port 2
Port 1
Pdelay_req
PDelay_resp
PDelay_resp_follow-up
T2p tagged
T3p tagged
T1p tagged
T4p tagged(T3p-T2p) received(T3p) received
Port 2
Applies toeach leg Pdelay_respPdelay_respPdelay_resp
P1
Sync: T1m, (link delays)Pdelay_req
Pdelay_req
T2s
Pdelay_req
Pdelay_reqPdelay_req
Pdelay_respPdelay_respPdelay_respPdelay_respPdelay_respPdelay_resp
Pdelay_resp
P1
T3p tagged
T1p tagged
Pdelay_respPdelay_respPdelay_respPdelay_respPdelay_respPdelay_resp
Pdelay_reqPdelay_req
Pdelay_respPdelay_respPdelay_resp
Pdelay_req
Pdelay_resp
Pdelay_req
Pdelay_respPdelay_respPdelay_respPdelay_respPdelay_respPdelay_respPdelay_respPdelay_resp
Pdelay_reqPdelay_req
Pdelay_respPdelay_resp
Pdelay_reqPdelay_req
Pdelay_respPdelay_respPdelay_respPdelay_resp
P2P2P2P2
Clock offset = [T2s-T1m] - (link delays)
P2P2P2P2
Pdelay_reqPdelay_reqPdelay_reqPdelay_reqPdelay_reqPdelay_reqPdelay_req
Pdelay_respPdelay_resp
P1
M
S
M
S
BitsNumber of Bytes Offset
7 6 5 4 3 2 1 0
transportSpecific messageType 1 0
reserved versionPTP 1 1
messageLength 2 2
domainNumber 1 4
reserved 1 5
flagField 2 6
correctionField 8 8
reserved 4 16
sourcePortIdentity 10 20
sequenceID 2 30
controlField 1 32
logMessageInterval 1 33
1000
100
10
1
0.1
0.010.01 1 100 10000 1000000 1E+08
Observation Period (s)
MTIE (s)
MTIE (s)(log scale)
0.10.1 1 10 100 1 K
Types II, III
Type I
T1313260-98/d03
1010 m50 m 7,5 20 280
400
0.3
0.751
2
5
10
100
Observation Interval (s)(log scale)
MTIE (s)
T1306500-95
10
5.0
2.0
1.0
0.25
0.10.1 1.0 2.5 10 20 100 400 1000
Observation Interval (s)
MTIE Limit (s) Observation Interval (s)
0.75 0.1 < 7.5
0.1 7.5 < 20
2 20 < 400
0.005 400 < 1000
5 1000 < 10 000
MTIE Limit (s) Observation Interval (s)
0.25 0.1 < 2.5
0.1 2.5 < 20
2 20 < 400
0.005 400 < 1000
G.812-Input Wander Tolerance (MTIE) for Type I Node Clock
G.813-Input Wander Tolerance (MTIE) for Option 1
