Requirements and viewpoints for
backhaul synchronization
draft-zhou-tictoc-ran-sync-req-00.txt
Angela Zhou, Xiaodong Duan
China Mobile
Outline
• Synchronization Requirements
• Mobile backhaul network
• Concerns on synchronization
Synchronization in 2G/GSM
• Current 2G/GSM Networks
• Future 2G/GSM Networks
MS
Ref.
clock
MS
E1
BSC
BTS
E1
Circuit
Emulation
E1
SDH
E1
Ref.
clock
PSN
MS
BTS
BSC
FE
IP BTS
• Sync Requirements in
current 2G/GSM Networks
–
–
–
SDH transport network need
frequency sync: +/- 50ppm
Base stations need frequency sync:
+/- 0.05ppm
Reference clock is distributed via an
explicit transport at the physical layer:
PDH/SDH
•
GE
IP BSC
Sync Requirements in future
2G/GSM Networks
–
Packet switching network do not need strict
synchronization
– Base stations need frequency sync: +/- 0.05ppm
– For base stations, Reference clock is distributed via
PSN, need physical synchronization support (e.g.
Sync Ethernet) or packet-based synchronization (e.g.
1588).
Note: Previous SDH transport network maybe still exist
for traditional base stations, sync requirement is the
same as before.
Synchronization in 3G/TD-SCDMA
• Current trail 3G/TD-SCDMA
Networks
• Future 3G/TD-SCDMA
Networks
Ref.
clock
NodeB
NodeB
SDH
PSN
ATM
GE
RNC
FE
RNC
ATM
NodeB
NodeB
• Sync Requirement in current
3G/TD-SCDMA Networks
–
–
–
–
SDH transport network need frequency
sync: +/- 50ppm
For transport network, Reference clock is
distributed via an explicit transport at the
physical layer: PDH/SDH
Base stations need frequency sync: +/0.05ppm, and phase sync: +/- 3us
For base stations, reference clock is
distributed via GPS
• Sync Requirement in future
3G/TD-SCDMA Networks
–
–
–
Packet switching network do not need
strict synchronization
Base stations need frequency sync:
+/- 0.05ppm, and phase sync: +/- 3us
For base stations, reference clock is
distributed via PSN, need physical
synchronization support (e.g. Sync
Ethernet) for frequency sync or
packet-based synchronization (e.g.
1588) for time/phase sync.
Synchronization in 4G/TDD-LTE/FDD-LTE
• Possible synchronization requirements in LTE
– Synchronization requirements in ALL-IP network
– Synchronization requirements in distributing Base Station
(mesh topology among base stations)
– Synchronization requirements in distributing BBU & RRU
– Synchronization requirements in radio interfaces
Note: synchronization requirement in LTE is under discussion.
eNB
eNB
eNB
Ref.
clock
PSN
eNB
AGW
eNB
eNB
eNB
Synchronization in different parts
• Requirements schematic diagram
Base
station
UE
UE
Radio
Interface
SYNC
Node
SYNC
Base
station
controller
Ref.
Clock
Network SYNC
Base
station
• Synchronization requirements in different positions
Layer
Sub Items
Frequency Accuracy
Phase Accuracy
Network Sync
E1
50ppm
-
STM-N
4.6ppm
-
PTN
Not so strict
-
Controller-Base
station
50ppb(If base station pick up
3us(if base station pick up time
time from base station controller) from base station controller)
Inter-Base station
50ppb(If base station pick up
time from other base station)
3us(If base station pick up time
from other base station)
GSM
50ppb
-
WCDMA
50ppb
-
TD-SCDMA
50ppb
3us
TDD LTE
50ppb
TBD
FDD LTE
50ppb
-
Node Sync
Radio interface
Outline
• Synchronization Requirements
• Mobile backhaul network
• Concerns on synchronization
Mobile backhaul
• Mobile backhaul could be based on
–
–
–
–
Carrier Ethernet (e.g. 802.1ad, PBB-TE)
IP/MPLS (e.g. PW, VPLS, L3VPN ,IP routing)
T-MPLS
Others
• Each transport technique can fit certain scenario
respectively, and they could be used in different network
layers (access/aggregation/core).
Mobile backhaul
• Mobile backhaul network
Base
station
Access
Aggr
Base
station
controller
802.1ad
Base
station
Base
station
PBT
Core
IP/MPLS
core
Base
station
controller
IP/MPLS
core
Base
station
controller
PON
DLS
Base
station
controller
Base
station
TMPLS
TMPLS
Base
station
TMPLS
Base
station
controller
Base
station
MPLS Access
MPLS AGG
VLL/VPLS
Base
station
802.1ad
IP/MPLS
core
Base
station
controller
SON & Self-backhauling
Ref.
Clock
• Self Organization Network
AGW 2
AGW 1
– Some BSs are
configured only by it’s
mother BS for both sync
and radio resource
• Self-backhauling
New BS
Join
– Using in-band connection
between BSs for
backhaul
Outline
• Synchronization Requirements
• Mobile backhaul network
• Concerns on synchronization
Concerns & Summary
•
The requirements for RAN is clear and urgent
– Radio Access Network is on the early stage of moving to IP transport
– Using GPS will affect the flexible deployment of BS, we really need a new
synchronization technology to substitute GPS, epically though a simple Ethernet
port
– How to distribute synchronization through packet based network? Can 1588
meet our requirements? Telecom profiles of 1588 should be standardized:
• network scale/ network load/ local clock accuracy
• Security
– The synchronization methods in next generation mobile network (LTE) and
MESH/SON network should be paid more attention.
•
At the same time, it is complex and more technologies in backhaul
– How to extend IEEE1588 or other synchronization technology so that it can be
used smoothly in PBN and complex backhaul.
– Features needed for Backhaul nodes to support 1588 for high accuracy
– Different layers shall collaborate to meet the sync requirements form end to end,
so what kind of mechanisms/protocols are need between different layer and
technologies in backhaul?
Thank you&
Any questions?