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12 March 2001
Ethernet PON (EPON) Protocol
By Edward Beili<ebeili@onepathnet.com>
12 March 2001IEEE 802.3 EFM working group2
EPON tutorial
Outline
l FTTx Services
l PON Networkl Point to Multipoint EPON Protocol
l EPONP building blocks
l Ranging
l Bandwidth Allocation
l PON Network Discovery
l Conclusion
12 March 2001IEEE 802.3 EFM working group3
EPON tutorial
FTTx services
l Data– Speed: 100/1000Mbps; Symmetric/Asymmetric – QoS: Latency, Min/Max Rate– Security
l Video– Analog/Digital streaming
l Voice– Low jitter & latency– Constant delay– Business vs. Residential (Life-line)
12 March 2001IEEE 802.3 EFM working group4
EPON tutorial
Passive Optical Network (PON)
OLT
ONU
ONU
ONT
ONU
PassiveOpticalSplitter/
Combiner
CO CPPON
12 March 2001IEEE 802.3 EFM working group5
EPON tutorial
PON Challenge
l Only the OLT is able to detect collisionsl Upstream channel separation methods:
– TDMA– WDM– RF sub-carrier– Phase etc.
l TDMA issues:– Burst-mode Transceiver– Downstream traffic isolation (privacy)– Frame Segmentation to achieve small latency
12 March 2001IEEE 802.3 EFM working group6
EPON tutorial
TDMA PON Protocols
l FSAN ATM-PON – ITU-T G.983+ Well defined, Field tried, Industry Standard
l Accepted by major ILECs: BT, FT, NTT, BellSouth, GTE, SBC, QUEST
l Supporting Vendors: Alcatel, Lucent, Terawave, QuantumBridge, Nortel…
+ Inherent 8Khz clock, QoS, Bandwidth allocation– Expensive & Complicated (Intermediate ATM layer)– Off-the-shelf components are scarce
l Ethernet PON+ Native IP+ Simple & Cheap off-the-shelf components– Non-standard technology– Complicated Telephony, QoS, Bandwidth allocation
12 March 2001IEEE 802.3 EFM working group7
EPON tutorial
EPON – The need for standard
Goals:l Multi-vendor interoperability between OLT &
ONU
l Standard solutions acceptance by service providers
l Cost reduction due to availability of standard components (larger volumes, broader deployment)
l More bandwidth to the end user for less $$
12 March 2001IEEE 802.3 EFM working group8
EPON tutorial
Ethernet PON (EPON) Protocol
l Using standard Ethernet frames
l OLT “broadcasts” Ethernet Frames to its ONUsl Each ONU transmits in turn using grants
issued by the OLT
l OLT regulates the amount of up-stream B/W given to each ONU by controlling the window size
l EPONP control frames are exchanged in-bandl Ranging is used to minimize inter-window gaps
12 March 2001IEEE 802.3 EFM working group9
EPON tutorial
EPON transport – Requirements
l Reliable & Secure transport
l Voice requirements:– Constant delay– Low latency– Low jitter– Life-line
l Bandwidth Allocation (Static/Dynamic)
12 March 2001IEEE 802.3 EFM working group10
EPON tutorial
EPON transport – Main functions
l Transmission grants
l ONU discovery/ID assignmentl Periodic sanity check (who is alive)
l Bandwidth allocation
l Security
l Error handling
12 March 2001IEEE 802.3 EFM working group11
EPON tutorial
EPONP - Overview
l 100/1000BaseFX Phy is used at both ends
l Full duplex, 100/1000Mbps statically configured
l Flow-control (back-pressure) is turned off at both ends
l Frames are not segmented
l Short (64 byte) control frames (grants and messages) are periodically exchanged between LC and ONUs
12 March 2001IEEE 802.3 EFM working group12
EPON tutorial
EPONP – Overview (2)
l Downstream– Ethernet traffic is broadcasted from OLT to all of its ONUs– OLT periodically sends a Start message containing grants for
1..N full cycles to its subtending ONUs– Each grant contains:
l Window_Size and Window_Offset per ONU
l Cycle_Sizel Number_of_Cycles
l Upstream– Each ONU buffers the upstream LAN traffic and sends it to the
OLT when its window is open.– Upstream B/W is controlled by the window size per ONU
12 March 2001IEEE 802.3 EFM working group13
EPON tutorial
EPONP – Parameters
Window_Size_ONU1
ONU1
ONU2ONU3
ONU4
IWG - Inter Window Gap
Window_Offset_ONU1Start_of_Cycle
Cycle_Size
Number_of_Cycles
12 March 2001IEEE 802.3 EFM working group14
EPON tutorial
EPONP - Parameter Limitations
EXAMPLE (100Mbps symmetric, 16 ONUs, no segmentation):
l (voice_frame + ctrl_frame + max_frame) <= Window_Size <= max Cycle_Size/16
l 2.5ms (16 x min Window_Size) <= Cycle_Size<= 20ms (max (max latency, max Voice_Delay)
l 0.96µs (IFG) <= IWG <= 4µs
12 March 2001IEEE 802.3 EFM working group15
EPON tutorial
EPONP – Ranging
l Ranging procedure to minimize the guard time, using echo messages sent from OLT to ONUs:– OLT measures round trip delay for each ONU– OLT notifies each ONU of equalization delay: Te
– ONU adjusts transmission phase to Te
l Adjust the delay periodically to compensate for temperature changes, component aging etc.
12 March 2001IEEE 802.3 EFM working group16
EPON tutorial
Bandwidth Allocation (BA)
l Upstream– Controlled by the OLT protocol state machine– Window size based – equal delay– Window rate based – variable delay
l Downstream– Rate limiting in the OLT or ONU
12 March 2001IEEE 802.3 EFM working group17
EPON tutorial
BA – Upstream
Upstream Static BA (window size based)
Upstream Dynamic BA
ONU4 -> LifeLine
ONU1
ONU2ONU3
ONU4
Start
ONU1
ONU2ONU3
ONU4 ONU1
ONU2
ONU3
ONU4
ONU1
ONU2ONU3
ONU4
Start
ONU1
ONU2
ONU3
ONU4
12 March 2001IEEE 802.3 EFM working group18
EPON tutorial
ONU discovery & ID assignment
l Static assignment– E.g. manual provisioning during ONU installation– …
l Auto-discovery– Binary Tree– Hashing (MAC) + Mask– Raffle– …
12 March 2001IEEE 802.3 EFM working group19
EPON tutorial
Conclusion
l Topics to work on:– Building blocks / Parameters– Ranging– BA– PON discovery
12 March 2001IEEE 802.3 EFM working group20
EPON tutorial
Acronyms
l CO Central Officel FTTB/C/Cab/H Fiber-To-The-
Business/Curb/Cabinet/Homel FSAN Full-Service Access Networkl OLT Optical Line Terminall ONT Optical Network Terminatorl ONU Optical Network Unitl PON Passive Optical Networkl POTS Plain Old Telephone Service
12 March 2001IEEE 802.3 EFM working group21
EPON tutorial
References
l ITU-T G.983.1, “High Speed optical access systems based on Passive Optical Network (PON) techniques”
l ITU-T G.983.2, “The ONT Management and Control Interface Specification”
l ITU-T G.983.3, “A broadband optical access system with increased service capability by wavelength allocation“
l ITU-T G.959.1, “Optical transport network physical layer interfaces”.
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