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3GTPL - Synchronisation
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RAN1254 Timing Over Packet (TOP)
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RAN1254 Timing over Packet Feature
Timing over Packet (ToP) provides the means to provide asynchronization reference for base stations in Ethernet/packettransport networks
No need for separate TDM links for providing a synchronization
reference for base stationsNo need for GPS based synchronization sources at the base
station sites
Applicable for Iub/IP and packet-based backhaul with Pseudowire
The Master Clock is implemented as a dedicated networkelement at the RNC site.
Slave Clocks are integrated into the Ethernet interface units of
the base stations ToP solution is based on the use of IEEE 1588 v2 protocol This protocol is also called Precision Time Protocol (PTP).
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ToP Solution Overview
At the RNC site there is a Master Clock
The Master Clock has a timing reference traceable to a Primary
Reference Clock (PRC) ToP can be used as synchronization alternative in packet networks havingno other possibility to synchronize the base station.
RNC can not be synchronised with ToP
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Timing over Packet Operating Principle
The Master Clock sends Sync messages to the Slave Clocks The Slave Clocks recovers the synchronization reference byusing the Sync messages received from the Master Clock The Master and Slave Clocks communicate by using IEEE1588 v2 protocol
Used is communication mode is unicast
Unicast discovery (preconfiguration
of slave clocks with the
address of the master clock) and unicast
negotiation are
supported
Sync messages and signaling messages are supported Sync messages are time stamped event messages Signaling messages are used for unicast negotiationsignaling messages are not time stamped
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ToP Messages
There are three types of Messages supported by NodeB:
Announce
Announce and Signaling messages are not time stamped, general
messages. Announce messages are needed for maintainingthesynchronization
hierarchy. A slave clock tries to lock to a master only
if it receives Announce messages from the master.
Signalling Signaling messages are used for unicast negotiation. Sync Sync messages are time stamped event messages. A slaveclockrecovers
the timing reference based on the Sync messages sent bythe master clock.
With the unicast options of IEEE 1588 v2, all slave clocks arepreconfiguredwith the address of the master clock. By using unicast negotiation, a slaverequests the master to send Announce or Sync messages. As a response,the master sends a grant in a signaling message, and after grant
it starts to
send Announce or Sync messages.
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ToP QoS Requirements Low network Utilisation
Low network utilization (< 50%)
it is possible to introduce ToP
without any additional measures in networks
with less than 50% bandwidth utilization even as BE traffic.
This Requires Maximum 50% link loading in the network No frame loss
Maximum queue length 10 frames (preferably 3 frames)
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ToP QoS Requirements High network Utilisation
High network utilization (< 90-95%) If the network utilization is larger than 50% it is necessary to use Classes ofServices (CoS) in the network to ensure proper Quality of Service (QoS) forthe ToP
packets.
The load on the CoS containing the ToP traffic needs to be lowerthan the whole network utilization The high load scenario is discused further in the slides belowin terms of
Priorisation Classification
Policing
Queuing
Scheduling and shaping
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ToP in High load network Classification
The classification function at the ingress of each networkelement identifies the received packet or frame and assign itto the correct flow and the corresponding CoS
for the further
handling in the network element. The ToP packets or frames are identified
UDP port plus the DSCP value
VLAN ID plus the user_priority
Note that the TP 5000 supports only 16 VLANS so a pure layer 2solution for Iub with VLANs needs a router for ToP master forcreating the VLANs.
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ToP in High load network Policing andBandwidth Assignment
Bandwidth has to be reserved for each connection with QoSguarantees in a network supporting QoS better than just BE.
The bandwidth needed per ToP
connections between
Master and Slave with 16 synch messages per second:
Direction from Master to Slave:
On IP level: 9.3 kbps per connection
On Ethernet level :
12.1 kbps per connection
Direction from Slave to Master: On IP level: 0.005 kbps per connection On Ethernet level : 0.006 kbps per connection Bandwidth can be reserved by CAC or by manualconfiguration depending on the network. Policing functions at networks boundaries may be necessary
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ToP in High load network Queuing
The support of ToP requires that the network is designed in such a waythat for ToP frames queues are only needed for rate adaptation betweeningress and egress.
Only short queues of less than 100 frames are needed for this purpose inthe ideal case it should be even less than 10 frames.
Queues for handling of traffic bursts and congestion requiring longerqueue length should be avoided for ToP flows. . A frame loss of < 2% is acceptable for ToP. Queues for ToP flows should be short even with the risk of slightlyhigher frame losses.
Tail Discard, RED or WRED do not make a difference to ToP
Sophisticated drop mechanism can lead to lower network loadbenefiting also ToP messages.
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Scheduling and shaping
Scheduling mechanisms ToP or voice are sensitive to delay and jitter but these connectionstypically have low bandwidth requirements compared to other services. These services should be served with highest strict user priority. WRR or WFQ may suit the other traffic in the interface better so anoptimal scheduler is a combination of WRR/WFQ and Strict Priority.
Shaping ToP load is relatively constant and quite low Shaping is not necessary as compared to e.g. TCP/IP data traffic
Shapers introduce additional delay and also under some
circumstances additional jitter and this is harmful for ToP messages.
AXC & FTM
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Timing over Packet Parameters
AXC C5.0FTM C5.0
AXC & FTM
FTM
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ToP ParametersFTM
Timing over Packet the
only choice if there is onlyEthernet interface activated
Check this box to activateToP(License needed)
FTM
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ToP: DSCP and PHBFTM
DSCP and PHB for ToP
DSCP -
46 and
PHB -
EF recommended
FTM
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Activating ToPFTM
In the rare
case that theToP Masteris in adifferentnetwork than
the Transportinterface, it isnecessary toconfigureroutes under
BTS Routing,not underBTS Routing.
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Master clock options (aligned with RU10)
Option 1: dedicated master / slave
Symmetricom TimeProvider 5000
New product based on NSN requirements formobile backhaul
Cost efficient solution for RNC sites and hub sites
Dual power supply, dual I/O card,1:1 node redundancy
Option 2: upgrade of existing SSU
Symmetricom SSU2000, large installed base
Can be upgraded with an IEEE1588v2 blade
Fully redundant node with various I/O options
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Master clock options (aligned with RU10)
Release 1.0
IEEE 1588v2 GM
GPS and/or E1 Inputs
10MHz/1pps Outputs
The RNC supports 2.048 MHz, 2.048Mbit/s
and 1.544 MHz external
synchronization interfaces
VLAN Support (up to 16 VLANs)
SNMP and CLI Management
One IOC interface module
2 x 100/1000Base-T SFPs
More than 10 000 Timing packets persecond
Rel 1.1 will have optional IOC slotgiving two additional Ethernet ports
Supports VLAN p-bits and DSCPmarking
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RAN1708 BTS Synchronous Ethernet
BTS S h Eth t
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BTS Synchronous Ethernet
The main advantage of Synchronous Ethernet is that it can provide a high
quality synchronization reference for base stations - the quality iscomparable to that of SDH
Contrary to packet based synchronization techniques (e.g. ToP) the
stability of the recovered frequency does not depend on network load ornetwork impairments like delay variation
BTS S h Eth t
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BTS Synchronous Ethernet
BTS Synchronous Ethernet (SyncE) provides a mechanism for timingsynchronization over Ethernet of Flexi/Ultra
BTS with Primary Reference
Clock according to ITU G.8261spec
The Ethernet transport interface of a BTS shall be SyncE capable SyncE as specified in RAN1708 is considered as an alternative to Timingover Packet (ToP) BTS synchronization, as specified in RAN1254
BTS S h Eth t
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Impact to UTRAN Transport dimensioning:
IP-based Iub dimensioning requires a selection of the synchronization
type: SyncE, ToP, none.
SyncE contributes with an additional capacity on IP-based Iub atthe BTS side (Iub last mile), due to SSM message flow terminatedat BTS. Bandwidth requirement of the SSM flow is around 6.4kbps. Note: this is specified only in the Ethernet layer, and not in the
IP layer.
BTS Synchronous Ethernet
BTS S nchrono s Ethernet
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BTS Synchronous Ethernet
The
basic principle of Synchronous Ethernet (SyncE) is that at transmitting side
Ethernetphysical layer signal is timed by using a network reference
At receiving side the clock signal is recovered from the physical layer signal, in thisway SyncE
is capable of carrying network synchronization reference from one
network element to another
BTS Synchronous Ethernet
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BTS Synchronous Ethernet
Interdependencies between features:
BTS Synchronous Ethernet can only be used for IP enabled Flexi orUltraSite
WCDMA BTS. One of the following features is a prerequisite:
RAN74: IP based Iub for Flexi WCDMA BTS
RAN1634: IP based Iub for UltraSite
WCDMA BTS
RAN1142: ATM over Ethernet (only with Flexi WCDMA BTS)
RAN1449: Dual Iub for Flexi WCDMA BTS
RAN1633: Dual Iub for UltraSite WCDMA BTSSystem Impact:
Iub requires 1Gb SyncE
capable interface card
2 Alarms SSM* mismatch; SSM missing 2 Parameters SSM enbling flag; SSM message timeout*) -
Synchronization Status Message
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