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An Overview of PON Technologies

Pu-Chen Mao3/21/2011

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Outline

• Background• G-PON• EPON• NG-PON• Future Studies• References

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Background (1/3)

• Access technologies– Wireless

• 802.11, 802.16, etc.• Low cost deployment• Insufficient capacity for high bandwidth (revenue) applications

such as IPTV

– Copper• DSL• Point-to-point architecture allows unshared bandwidth• Limited distance due to noise• Cost of deployment only slightly less than an all-fiber approach

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Background (2/3)

– Fiber• Low noise• Long reach• Topology

– Tree» More cost effective

– Point-to-point» Dedicated fiber plant from CO to subscriber

– Ring» Fault tolerant

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Background (3/3)

• Shared fiber architectures– Active Ethernet• Signals split by electronic equipment

– PON• Signals replicated passively by splitter• Higher reliability due to no electronic equipment in

outside plant• Signal format transparency• Can be more flexibly upgraded• Requires no electric power source

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G-PON

• Specified by ITU-T G.984 series• Began in FSAN consortium in 2001

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G-PON Layers

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G-PON Transmission Convergence (GTC) Layer

• Performs adaptation to the physical-medium-dependent (PMD) layer

• Adaption methods– ATM– G-PON encapsulation method (GEM)

• Preferred method• Ethernet adaptation• TDM adaptation

• MAC function– Coordinates interleaving upstream traffic from individual

ONUs

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GTC Layer

• Control functions– Defines protocols & procedures for registering &

performance monitoring of ONUs– Configuration of transport features• FEC• Encryption• Bandwidth allocation

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GTC Layer

• GTC framing sub-layer– Downstream frame format• 125 us• 8 KHz signal for ONU reference clock• Physical Control Block (PCBd)

– Framing, PHY operations, PLOAM fields– Message-based protocol for PMD & GTC mgmt.– Bandwidth map field for upstream transmission allocation

• Payload follows PCBd

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GTC Layer

• GTC framing sub-layer– Upstream frame format• Same as downstream 125 us• Physical layer overhead (PLOu) field

– Preamble & delimiter configurable by OLT– Dynamic bandwidth report (DBRu) field for DBA traffic

queuing reports from ONUs– PLOAM identical to downstream frame– DBRu & PLOAM are optional, requested by OLT

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GTC Layer

• GTC TC adaption sub-layer– GEM• Protocol independent connection-oriented

encapsulation for variable-sized packets• Virtual connection unit: GEM port• 5 byte header

– Port ID & frame size

• Frames may be fragmented• G.984 specifies transport of Ethernet & TDM over GEM

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GTC Layer

• T-cont– Each T-cont aggregates one type of traffic out of 5 classes– Composed of multiple virtual port connections

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Upstream Bandwidth Allocation

• Static method

• Dynamic Method (DBA)– Status reporting DBA• ONU reports via DBRu field

– Non-status reporting DBA• T-cont utilization monitored by OLT

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GTC Control Plane

• Operated via PLOAM message protocol and embedded OAM

• Management functions– PMD layer management

• Upstream config, PHY monitoring, generate stats

– GTC layer management• Framing, requesting PLOAM / DBRu, etc.

– ONU activation• Activate ONU, ranging protocol, optical power tuning

– Encryption management• AES, key exchange procedure

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G-PON Management

• G.984.4 specifies the ONT management and control interface (OMCI)

• OMCI– ONU management information base– ONT mgmt. control channel protocol (OMCC)• Conveys MIB info between ONU & OLT

– Models equipment configuration, port types, and service types

– QoS

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EPON

• Ethernet sub-layers

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EPON• 1 Gb/s bidirectional links• 1490 nm downstream• 1310 nm upstream• 1550 nm reserved for extensions• 802.3ah EPON

– Minimum 1:16 split ratio• Up to 1:64 commercially available

• 802.3 similarities– Standard inter frame gap (IPG)– Uses same MAC

• Multi-Point Control Protocol (MPCP) for P2MP connectivity– Uses standard Ethernet packets in MAC sub-layer

• Modified preamble

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EPON Downstream

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EPON Upstream

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EPON ONU Registration

• MPCP handshake– OLT broadcasts GATE message– Unregistered ONUs respond with REPORT and

REGISTER_REQ– OLT approves and replies with REGISTER– ONU responds with REGISTER_ACK

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EPON Operation

• OLT controls ONU transmission windows with GATE messages

• ONU responds queue status with REPORT• OLT calculates transmission window length

using DBA• Synchronized to PON clock with 16 ns

resolution counter in MPCP messages• OLT and ONU exchange timestamps to measure

RTT for upstream scheduling

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EPON Frame• Downstream preamble

– Logical link ID field specifies the destination ONU• ONU filters frames by LLID• ONU receives unique LLID assigned by OLT• Special value of LLID reserved for broadcast

• Upstream preamble– LLID marks the source ONU– Ensure preamble field integrity by CRC– One ONU may have multiple LLIDs (virtual ONU)

• FEC– Based on RS(255,239)– Frames encoded separately, parity bytes appended to end

• Encryption– AES-based

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EPON Management

• Link layer management– OLT remotely manages attached ONUs– Remote link monitoring

• OAM– Established after discovery process– Maintained by periodic messages– Remote failures conveyed in flags of OAM msgs.

• OAM using SNMP

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NG-PON

• Next-generation PON technologies to extend current bandwidth to 10 Gb/s

• XG-PON by ITU-T

• 10GE-PON by IEEE 802.3av

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NG-PON Direction

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10 Gb/s PON

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10 Gb/s PONs

• Similarities of XG-PON & 10GE-PON– L-band downstream 1575 – 1580 nm– O-minus band upstream 1260 – 1280– Mandatory FEC• RS(255, 223)

– Video overlay 1550 – 1560 nm

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10 Gb/s PONs

• Uniqueness– 10GE-PON• Conflict in EPON 1260 – 1360 nm and 1260 – 1280 nm

band used• Share overlapping spectrum using TDMA

– XG-PON• 32-bit word aligned framing• XGEM extension• PLOAM, DBRu, bandwidth allocation, ranging functions as

clients to XGEM system, with XGEM becoming the main protocol

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Future Studies

• System architecture, specifications of XG-PON and 10GE-PON

• Long-reach PON

• DBA comparison for EPON, GPON, and next-generation PON

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References

[1] Effenberger, F., et al., “An introduction to PON technologies,” IEEE Communications Magazine, Vol. 45, Issue: 3, 2007

[2] Effenberger, F., et al., “Standardization trends and prospective views on the next generation of broadband optical access systems,” IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 28, NO. 6, AUGUST 2010

[3] Paul E. Green Jr., “Fiber to The Home: The New Empowerment”, Wiley, 2006