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© Cortina Systems, Inc. 2012 All Rights Reserved Proprietary and Confidential
October 12, 2013
GPON Introduction
Chengcheng Huang
Driver Team
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Outline
Standards overview
System architecture
Framing and MAC
Activation method
OMCI overview
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ITU-T Rec.
G.984.1: general characteristics
Bit rate
Logical / Physical reach
Split ratio
etc.
G.984.2: PMD layer specification
Line code
Wavelength
etc.
G.984.3: TC layer specification
TC layer framing
PLOAM
ONU activation
etc.
G.984.4/G.988: OMCI specification
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GPON vs. EPON
ITEM GPON EPON
OAM Mandatory eOAM/PLOAM/OMCI
Optional and private
MAC Layer Service Ether/TDM/SDH/etc. Ether
Frame GEM frame Ethernet frame
Physical Layer Bit rate Down: 1.25G, 2.5Gbps Up: 1.25Gbps
Down and Up: 1.25Gbps
Distance 10 / 20 km (Logical: 60 km)
10 / 20 km
Split ratio 1:64 (Logical: 128) 1: 16 or over
Line code NRZ 8B/10B
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GPON Multiplexing
ONU-ID ONU
Alloc-ID T-CONT
GEM-ID GEM Port
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ONU Identifier
ONU-ID is a 8-bit identifier
Assigned by OLT during activation using the PLOAM messaging channel
Used in PLOAM
Equal to default Alloc-ID
Assignable range: 0..253
Broadcast ONU-ID: 255
used in broadcast PLOAMd or by unassigned ONU in PLOAMu
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T-CONT
Basic upstream container
Associated with one Alloc-ID
Each T-CONT has a traffic profile
DBA report and grant based on it
Fixed number discovered via OMCC (ANI-G)
OMCC is mapped to Default Alloc-ID
Five types
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Alloc-ID
Identify a traffic-bearing entity that is a recipient of upstream bandwidth
allocations
Represented either by a T-CONT or by the upstream OMCC channel
Default Alloc-ID
implicitly assigned
equal to ONU-ID
used to carry the upstream PLOAM and OMCC traffic
range: 0..253
Additional Alloc-IDs
assigned explicitly using the “Assign_Alloc-ID” PLOAM message
range: 256..4095
Broadcast Alloc-ID
=254
used by OLT in a serial number request event
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GEM Port
A GEM port represent an traffic flow
Globally unique
Each GEM port bears one kind of service traffic ( i.e. a T-CONT type )
Scheduling via GEM port to T-CONT mapping
Mapping of T-CONTs to Alloc-IDs is performed via the OMCC
GEM Port-ID range: 0..4095
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Protocol stack
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GTC frame structure
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Downstream GTC frame
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PSync state-machine
The recommended value for M1 is 2.
The recommended value for M2 is 5.
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IDENT field
FEC Ind: Indicate whether FEC is being used in downstream.
Superframe counter:
ONU load it into local counter in Hunt state, and compare it when in Pre-sync and Sync
states.
employed by the encryption system
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PLOAM
ONU activation
OMCC establishment
Encryption configuration
Key management
Alarm signaling
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Plend field
Blen: Number of allocation, granted in 125us, up to 4095
Blen==0 means empty BWmap
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BWmap fields
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Allocation fields
Alloc-ID: Indicate a particular T-CONT or OMCC
Flags field:
Bit 10:Indicate whether the ONU shall send an PLOAMu
Bit 9:Inicate whether FEC parity shall be inserted during this allocation
Bit 8 and 7:Indicate DBRu (mode)
00: Do not send DBRu at all.
01: Send the "Mode 0" DBRu (two bytes).
10: Send the "Mode 1" DBRu (three bytes).
StartTime: 16-bit number that indicates the starting time of the allocation
measured in bytes
not include the PLOu
StopTime: 16-bit number that indicates the stopping time of the allocation
points to the last valid data byte associated with this allocation
within the frame in which the allocation began
CRC field
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Upstream GTC burst
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Upstream overhead
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PLOu fields
Preamble
Delimiter
BIP: bit error rate estimation
ONU-ID: assigned ONU-ID or 255
Ind:
Bit 7 (MSB): Urgent PLOAMu waiting
Bit 6: FEC status
Bit 5: RDI status
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DBA methods
Status reporting (SR)
based on explicit buffer occupancy reports
Traffic monitoring (TM)
based on OLT's observation of the idle GEM frame
DBRu modes
Mode 0: One-octet coding of total amount of data
Mode 1: Two one-octet coding. First is the data marked as “yellow” and the second is
the data marked as “green”
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GEM frame format
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GEM header fields
PLI: indicate the length of the payload
Port-ID: GEM port ID
PTI: indicate the content type of the payload
000: User data fragment, not the end of a frame
001: User data fragment, end of a frame
100: GEM OAM, not the end of a frame
101: GEM OAM, end of a frame
others: Reserved
HEC: provides error detection and correction for the header
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GEM frame delineation
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GEM user frame fragmentation
A user data fragment cannot straddle a GTC frame boundary
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MAC example
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Activation - Process
Three Phases
Parameter Learning (used in the upstream transmission)
pre-assigned delay
number of preamble bytes
optical power level
Serial Number Acquisition (assigns the ONU-ID)
Ranging (compute the EqD)
Exchange of upstream and downstream PLOAM messages
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Activation - ONU State Machine
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Timing of serial number acquisition
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Equalization delay measurements
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OMCI overview
A dedicated bidirectional virtual connection (OMCC GEM port)
PDU has fixed 48-bytes in length
Packet format
Transaction correlation identifier: avoid ambiguous responses
Message type
Bit 6: AR, require an ack or not
Bit 5: AK, is an ack message or not
Bit 4..0: MT, message type
create, delete, set, get, MIB upload, start software download, etc.
Device identifier: 0x0A for baseline OMCI message; 0x0B for extended
OMCI message
Message entity identifier: class-ID + instance-ID
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MEs relationship example
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Reference
ITU-T Recommendation G.984.1, 2008.
ITU-T Recommendation G.984.2, 2008.
ITU-T Recommendation G.984.3, 2008.
ITU-T Recommendation G.984.4, 2008.
GPON Technology and iROS™ Development, Charles Chen, 2007