v.1.2 11/10/12 ∙ BIGR slide № 1 Time Distribution using IEEE 1588 v2 (PTP) Oscilloquartz SA
v.1.2 11/10/12 ∙ BIGR slide № 1
Time Distribution using IEEE 1588 v2 (PTP)
Oscilloquartz SA
v.1.2 11/10/12 ∙ BIGR slide № 2
ASZINKRON ÀTVITELI HÀLÒZATOK
SZINKRONIZÀCIÒS KÉRDÉSEI NAPJAINKBAN
v.1.2 11/10/12 ∙ BIGR slide № 3
Network synchronization
Node A
Node B
Node C
Node D
Reference
Clock
Distribution of frequency, phase and/or time
v.1.2 11/10/12 ∙ BIGR slide № 4
Frequency synchronization
Node A
t
t
Clock signal of node A
Clock signal of node B
Node B
TA = 1 / fA
TB = 1 / fB
fA = fB
v.1.2 11/10/12 ∙ BIGR slide № 5
Az idö mértékegysége
Általános Súly- és Mértékügyi Konferencia
(Conférence Générale des Poids et Mesures – CGPM)
1967-ben hozott döntése értelmében
A másodperc az alapállapotú cézium-133 atom két hiperfinom
energiaszintje közötti átmenetnek megfelelő sugárzás
9 192 631 770 periódusának időtartama.
v.1.2 11/10/12 ∙ BIGR slide № 6
Frequency source: atomic Cesium clock (Cs)
Example: OSA 3230B cs Clock
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Frequency source: atomic Cesium clock (Cs)
Magnetic Cesium Beam Tube
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Phase synchronization
Node A
t
t
Clock signal of node A
Clock signal of node B
Node B
! ! !
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Time synchronization (time-of-day)
Node A
t
t
Time signal of node A
Time signal of node B
Node B
14/01/00
08:34:56
14/01/00
08:34:57
14/01/00
08:34:55
14/01/00
08:34:55
14/01/00
08:34:56
14/01/00
08:34:57
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Time source: Global Navigation Satellite System (GNSS)
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Performance level: frequency
1 · 10 - 7
1 · 10 - 8
1 · 10 – 9
(1 ppb)
1 · 10 - 10
1 · 10 - 11
1 · 10 - 12
1 · 10 – 6
(1 ppm)
SDH, PSTN, MSC, MGW, BSC, RNC
Radio interface of BTS, Node B, eNode B
Femto Cell
Input of BTS, Node B, eNode B
Fractional (relative)
frequency accuracy [1]
LTE eNode B with Network MIMO
v.1.2 11/10/12 ∙ BIGR slide № 12
Performance level: phase & time
1 ms
100 μs
10 μs
100 ns
10 ns
10 ms
LTE with Location Based Service
Power Distribution: Synchro-phasor
IT Time-of-Day distribution
Phase or time
accuracy
1 μs
cdma2000
UMTS-TDD, LTE
v.1.2 11/10/12 ∙ BIGR slide № 13
Network Convergence
PSTN
(TDM)
PDCN
(Packet
Switched)
NGN (Packet
Switched)
CONVERGENCE
v.1.2 11/10/12 ∙ BIGR slide № 14
Time Distribution via the
Precision Time Protocol PTP (IEEE 1588 v2)
ETHERNET
Base Station Controller
PTP GRAND MASTER CLOCK
Base Station
Base Station
Base Station
Base Station
PTP SLAVE CLOCK
PTP SLAVE CLOCK
PTP SLAVE CLOCK
PTP SLAVE CLOCK
GPS Antenna
Oscilloquartz PTP IEEE 1588 v2 Equipment
v.1.2 11/10/12 ∙ BIGR slide № 15
PTP PRINCIPLES
Chapter 1
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SWITCH/
ROUTER
Typical Backhaul Network
RNC/BSC
GRANDMASTER
GRANDMASTER
SWITCH/
ROUTER
METRO TRANS.
NETWORK
AGGREGATION
NETWORK
SWITCH/
ROUTER BTS/NodeB
SLAVE
Phase : 1us
Frequency : 50ppb /16ppb
Primary
Secondary
v.1.2 11/10/12 ∙ BIGR slide № 17
IEEE standards
● IEEE 1588 (Precision Time Protocol) is standardized since 2002
● Version 1 of the protocol is used for applications in:
● Industries (e.g. Automation)
● Test and measurement
● Power networks
● Military and Avionic
● Version 2 is released since June 2008 and is made for applications in:
● Telecom
● Broadcasting
● Power and Utilities
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What’s new in PTP v2 ?
● PTPv2 meets accuracy for telecom applications
● High refresh rates up to 64 or 128 messages per second
● Correction field for asymmetric measurements
● Multicast and Unicast or Mixed are available
● Manual and Automatic Master Clock selection methods
v.1.2 11/10/12 ∙ BIGR slide № 19
ITU-T standards
v.1.2 11/10/12 ∙ BIGR slide № 20
Fact Sheet PTP v2
● PTP (Precise Time Protocol) is an IEEE standard:
● IEEE 1588 v1: for LAN applications
● IEEE 1588 v2: broader application space, incl. telecom
● Protocol for sub-microsecond synchronization of real-time clocks over frame and packet switched networks
● Uses ‘Two-way Time Transfer’ (TWTT) and ‘Hardware Assistance’
v.1.2 11/10/12 ∙ BIGR slide № 21
Fact Sheet PTP v2
● The main idea is to mitigate the protocol stack delay with appropriate electronic hardware and a modified TWTT protocol.
● A hardware « Precision Time Stamp Generator » measures the frame receive and transmit times at or close to the Physical Layer (Layer 1).
● The measured frame transmit times are communicated to the other end system with a second message.
● The TWTT calculation expoits the time values measured by the Precise Time Stamp Generator.
● The configuration of the clock hierarchy can be done manually or automaticaly using the Best Master Clock (BMC) algorithm.
v.1.2 11/10/12 ∙ BIGR slide № 22
PTP Clock
PTP Entity
e.g. Network Layer
e.g. Data Layer
Physical Layer
Precise Time Stamp
Generator
Physical Network Media
e.g. Tranport Layer
Low
er
Layers
of P
roto
col S
tack
EventPortGeneralPort
Local Clock
v.1.2 11/10/12 ∙ BIGR slide № 23
Elements of a PTP System
● Nodes
● Ordinary clocks:
● Communicate with other clocks over a single communication path
● Boundary clocks (optional):
● Communicate with multiple sets of clocks using distinct communication paths
● Administrative nodes (optional):
● For management purposes
● Communication paths
● Network segments that allow direct communication between clocks
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Master Clocks
● The Primary Reference source of time of the network
● Typically synchronized to GPS
● Very stable and accurate
● High-speed PTP time stamp processor
● Min 100 Base-T line speed
Grand Master
Clock
GMC
UTC Reference
LAN/WAN Packet
Switched Network
v.1.2 11/10/12 ∙ BIGR slide № 26
Slave Clocks
● Are slaves to the path containing the best clock they can see
● Reduce Jittter and Latencies of packet transit introduced by Network switches and router
● Give time, phase and frequency to the Network Element
Slave Clock SC
LAN/WAN
NE Network
Element
Packet Switched Network
v.1.2 11/10/12 ∙ BIGR slide № 27
The Simplest PTP Network
GMC SC
NE
MASTER SLAVE
GPS
Satellite
Network
Element
requiring sync
Packet Switched Network
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Boundary Clocks
● Are slaves to the path containing the best clock they can see
● Are masters to the clocks on all other paths
● Serve to implement time distribution trees
● Are required…
● …in gateways between different communication technologies
● …in network element which block PTP messages
● Are recommended in network elements which insert significant delay fluctuations
Boundary Clock BC
Packet Switched Network
Packet Switched Network
v.1.2 11/10/12 ∙ BIGR slide № 29
L1
L2
L3
L4
L5SYNCH
Precise Time
Stamp Generator
e.g. Ethernet Switch or IP Router
Precise Time
Stamp Generator
L1
L2
L3
L4
L5SYNCH
Boundary Clocks Principle
v.1.2 11/10/12 ∙ BIGR slide № 30
PTP Network Principle with Boundary Clock
SC
NE
GMC
BC
SC
NE
MASTER
SLAVE MASTER
SLAVE
Packet Switched Network
Packet Switched Network
v.1.2 11/10/12 ∙ BIGR slide № 31
● Are typically contained in switching equipment
● Measure the time elapsed between Switch input and Switch output
● Are recommended in network elements which insert significant delay fluctuations
● Not recommended by ITU-T
End-to-end Transparent Clocks
Transparent
Clock
TC
Switch
Packet Switched Network
Packet Switched Network
v.1.2 11/10/12 ∙ BIGR slide № 32
Transparent Clock
L1
L2
L3
L4
L5SYNCH
Residence Time
Measurement
e.g. Ethernet Switch or IP Router
L1
L2
L3
L4
v.1.2 11/10/12 ∙ BIGR slide № 33
● Are typically contained in switching equipment
● Measure the time elapsed between Switch input and Switch output
● Measure time elapsed between two Transparent clocks
● Are recommended in network elements which insert significant delay fluctuations
● Not recommended by ITU-T
Peer-to-peer Transparent Clocks
Transparent
Clock TC
Switch
TC Transparent
Clock
Switch
Packet Switched Network
v.1.2 11/10/12 ∙ BIGR slide № 34
PTP COMMUNICATION
Chapter 2
v.1.2 11/10/12 ∙ BIGR slide № 35
Time Exchange between Master and Slave
L1
L2
L3
L4
L5
Packet Switched Network
PTP Slave side PTP Grandmaster side
Frequency, Phase and/or Time-of -day Reference
DATA + SYNC
Time Stamp
SYNC
L1
L2
L3
L4
L5
Time Stamp
SYNC
v.1.2 11/10/12 ∙ BIGR slide № 36
Two-Way Time Transfer (TWTT)
TIME
GMC SC
TIME
12:00 12:05
12:01 12:06
12:02 12:07
12:03 12:08
12:05 12:05
T1
T2
T3
T4
(T2-T1) – (T4-T3)
2 = 5 =
(12:06-12:00) – (12:03-12:07)
2
6 – -4
2 =
T Final
T Offset =
Mean Propagation Delay = TSC – T Offset = 12:10 – 5 = 12:05
v.1.2 11/10/12 ∙ BIGR slide № 37
PTP V2 Messages
● Announce:
● Entity the Master Clock
● Conveys clock propeties
● Typically sent every 2 sec.
● Sync messages:
● Conveys Master Clock’s time information (T1)
● Follow_up:
● Conveys Master Clock’s time information (T1) in 2-step mode
● Delay_Req messages:
● Used to measure and correct transmission delay
● Conveys estimate of transmit time
● Delay_Resp messages:
● In response to a Delay_Req message
● Used to measure and correct transmission delay
● Conveys precise time stamp of Delay_Req message’s receive time
v.1.2 11/10/12 ∙ BIGR slide № 38
Master Selection Methods
● Manual:
● Configured via management system; static.
● Semi-automatic:
● Acceptable master table:
● Configure slave ports to accept only clocks from the table as masters
● Fully automatic:
● Best Master Clock Algorithm (BMCA)
v.1.2 11/10/12 ∙ BIGR slide № 39
Best Master Clock Selection
GMC
LAN/WAN
GMC
GMC
SC GMC
GMC
Communication between GMC
GMC Selection
Loss of GMC
v.1.2 11/10/12 ∙ BIGR slide № 40
Acceptable Master Table - Redundancy
Master Clock Site
PTP
Grandmaster
GPS
Master Clock Site
GPS
Slave Clock Site
PTP
Slave
Slave Clock Site Slave Clock Site Slave Clock Site Slave Clock Site Slave Clock Site
PTP
Slave
PTP
Slave
PTP
Slave
PTP
Slave
PTP
Slave
PTP
Grandmaster
v.1.2 11/10/12 ∙ BIGR slide № 41
PTP PERFORMANCE
Chapter 3
v.1.2 11/10/12 ∙ BIGR slide № 42
Definition: Packet Delay δAB(k)
Packet switched
network
End
system
End
system
A B
1 2 k
t
1 2 k
t
Packets/frames received over interface B
Packets/frames sent over interface A
δAB(k)
Consider two interfaces A and B, which are traversed by a given packet flow.
v.1.2 11/10/12 ∙ BIGR slide № 43
TWTT (Two-Way Time Transfer ) is not perfect…
● Because of a packet delay asymmetry, the formula is affected by errors.
● In a packet network, the queuing part of the total packet delay is highly asymmetrical, except when there are very low traffic loads.
TIM
E
GMC SC
TIM
E
12:00 12:05
12:01 12:06
12:02 12:07
12:03 12:09
12:05 12:05
T1
T2
T3
T4
T Final
v.1.2 11/10/12 ∙ BIGR slide № 44
Factors impacting performance
● Objective: ITU-T G.823 Network Limit for PDH synchronization interfaces
● Performance is impacted by …
● Packet Delay Variation (PDV)
● Packet Delay Asymmetry (PDA)
● PDV and PDA depend on …
● the number of switching / routing nodes
● the traffic load
● QoS mechanisms
v.1.2 11/10/12 ∙ BIGR slide № 45
Definition: PDV (Packet Delay Variation) VAB(k)
0
0.1
0.2
0.3
0.4
0.5
0 200 400 600 800 1000k
DA
B(k
) [s
]
DMIN
VAB(k)
NODE NODE NODE A B
VδAB(k)
VδBA(k)
v.1.2 11/10/12 ∙ BIGR slide № 46
Overview of Stand-Alone Products
● Compact 1U / 19’’ rack-mountable units
● PTP Grandmasters
● OSA 5331 PTP Grandmaster – High Performance
● PTP Slaves
● OSA 5320 PTP Slave – Telecom
● OSA 5320 PTP Slave – Broadcasting
● OSA 5320 PTP Slave – Power & Utilities
v.1.2 11/10/12 ∙ BIGR slide № 47
OSA 5331 PTP Grandmaster Front Panel
5-BUTTON PAD LCD DISPLAY FRONT LEDs
v.1.2 11/10/12 ∙ BIGR slide № 48
OSA 5331 PTP Grandmaster - Rear Panel
Power supply B
Alarm Relay
E1 / 2.048 MHz / T1 / 75 ohms output
E1 / 2.048 MHz / T1 / 75 ohms output
10 MHz 50 ohms output
1PPS Output
Local
Mgmt
Remote
Mgmt
PPS Input
10 / 2.048 MHz Input
DC Power A
GPS input
ToD Output (NMEA 0183) ToD Input (NMEA 0183)
E1 / T1 / 75 ohms input
FE/GbE PTP Port
SFP PTP Port
v.1.2 11/10/12 ∙ BIGR slide № 49
TCC-PTP FOR OSA 5548C
Plug-in card
v.1.2 11/10/12 ∙ BIGR slide № 50
TCC-PTP (Time Code Card – PTP)
● Plug-in card for the OSA 5548C SSU/TSG
● Enhances PTP v2 Grandmaster function
● Fits into any Output card slot
● OSA 5548C SSU-E60 : up to 6 TCC-PTP cards
● OSA 5548C SSU-E200 : up to 20 TCC-PTP cards PTP Hub
OSA 5548C SSU-E60 OSA 5548C SSU-E200
v.1.2 11/10/12 ∙ BIGR slide № 51
OSA 5548C “PTP HUB”
CAPACITY (20 GM blades per shelf) in Unicast or Multicast
● with TCC-PTP GM
● More than 2’500 slaves per shelf
● with TCC-PTP II GM *
● More than 5’000 slaves per shelf
* Available in 2013
v.1.2 11/10/12 ∙ BIGR slide № 52
TESTING
v.1.2 11/10/12 ∙ BIGR slide № 53
Test Case 13 - Sudden large and persistent changes in
network load
● Test Case 13 models sudden large and persistent changes in network load. It demonstrates stability on sudden large changes in network conditions, and wander performance in the presence of low frequency PDV.
v.1.2 11/10/12 ∙ BIGR slide № 54
Test case 13 - Results
v.1.2 11/10/12 ∙ BIGR slide № 55
Test Case 14 - Slow change in network load over an
extremely long timescale
● Test Case 14 models the slow change in network load over an extremely long timescale. It demonstrates stability with very slow changes in network conditions, and wander performance in the presence of extremely low frequency PDV.
v.1.2 11/10/12 ∙ BIGR slide № 56
Test case 14 – Results with Traffic model 1
v.1.2 11/10/12 ∙ BIGR slide № 57
Test case 14 – Results with Traffic model 2
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Network Traffic Model 1 (majority of traffic is Voice)
Network Traffic Model 2 (majority of traffic is Data)
Network Traffic Models
● The access traffic is composed of conversational (voice), streaming (audio-video), interactive (http) and background (sms, e-mail):
● 80% of the load must be minimum size packets
● 15% of the load must be maximum size packets
● 5% of the load must be medium size packets
● Maximum size packets will occur in bursts lasting between 0.1 s and 3 s.
● 60% of the load should be based on packets of maximum size, and 40% on packets with a mix of minimum and medium size:
● 60% of the load must be maximum size packets
● 30% of the load must be minimum size packets
● 10% of the load must be medium size packets
● Maximum size packets will occur in bursts lasting between 0.1 s and 3 s.
v.1.2 11/10/12 ∙ BIGR slide № 59
NETWORK EXAMPLES
Chapter 5
v.1.2 11/10/12 ∙ BIGR slide № 60
Egy élö példa
v.1.2 11/10/12 ∙ BIGR slide № 61
Egy europai példa
v.1.2 11/10/12 ∙ BIGR slide № 62
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