optical communications and networking · lecture 8: optical access networks. 朱祖勍. 7....
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Lecture 8: Optical Access Networks 朱祖勍1
Optical Communications and Networking
朱祖勍
Nov. 4, 2019
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Asymmetric Optical Access Networks
Point-to-point
Active Optical Network
Passive Optical Network(PON)
Cost
Bandwidth per U
ser
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Asymmetric Optical Access Networks
1-to-1 Delivery Broadcast-and-Select
Low Cost and Promising!
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PON Terminologies
OLT: Optical line terminal located at the service provider’scentral office
ONU: Optical network units located at/near end users
Upstream: Communication from ONU to OLT
Downstream: Communication from OLT to ONU
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History of PON Standards
Broadband PON (BPON)International Telecommunications Union (ITU)
622 Mb/s downstream, 155 Mb/s upstream
Gigabit PON (GPON)International Telecommunications Union (ITU)
Ethernet PON (EPON)IEEE Initiative
BPON, GPON and EPON are all TDM-PON, i.e., thebandwidth resources are allocated based on fixedtime-slots.
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TDM-PON Network Infrastructure
PON multiplexes upstream and downstream on a singlefiber using WDM
Upstream: 1310 nm (Why? Lowest loss in SMF)
Downstream: 1490 nm (Why? High-power transmitter isavailable and cheap.)
BPON, GPON and EPON have the same basicwavelength plan.
Two most important things to worry about in PON: Costand Power Budget.
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Communications in TDM-PON
Downstream (broadcast-and-select):OLT broadcasts data packets
ONU selects data packets according to the destination address
Upstream (request-and-grant):OLT ranges the ONUs
ONU sends requests and asks for transmission opportunities
OLT grants the requests by specifying a defined interval of timefor ONU’s upstream transmission.
ONU uses the time interval to transmit data packets.
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Upstream Bandwidth Allocation
ONU can lie at different distance from the OLT
OLT measures delay for synchronization.
OLT transmits grants to ONUs with MAPmessages.
The grant MAP is dynamically re-calculated everyfew msec.
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Upstream Bandwidth Allocation
Video/Audio traffic: fixed bandwidthallocation
Data traffic: dynamic bandwidth allocation(DBA)
GPON: status-reporting DBA, non-status-reporting DBA
EPON: status-reporting DBA
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Synchronous TDM
Advantages: fixed time slots, good fairness, easy control.
Disadvantages: low channel utilization, cannot adaptiveto user’s bandwidth.
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Asynchronous TDM
Advantages: high channel utilization, adaptive to users’bandwidth.
Disadvantages: more complicated.
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Multi-Point Control Protocol
Multi-Point Control Protocol (MPCP):a signalingprotocol between the OLT and the ONUs to facilitate adynamic timeslot allocation scheme.
MPCP consists of three functions:Discovery Processing: the OLT discovers and registers new ONUs.
Report Handling: the OLT handles the REPORT messages that includebandwidth requirements generated by ONUs to make bandwidthassignments accordingly .
Gate Handling: the OLT sends gate messages to ONUs to grant timeslots for them to transmit data.
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MPCP: Discovery Processing
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MPCP: Report Handling
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MPCP: GATE Handling
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Ranging Technology
The physical distances between OLT and ONUs are different.
Packets cannot arrive OLT in their pre-allocated time slots, resulting in
conflicted packets.
OLT cannot recognize the conflicted packets, resulting in high bit error rate
and sync loss.
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Timestamp Ranging
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Dynamic Bandwidth Allocation (DBA)
Status-Reporting DBAONU sends status of their input packet queue to OLT with the REPORTmessage.
OLT grants ONU transmission opportunities according to the service levelagreement with the GATE message.
Non-Status-Reporting DBAOLT continuously allocates a small amount of extra bandwidth to each ONU.
ONU transmits idle frames when there is nothing to send
If OLT observes a large number of idle frames, it will reduce the bandwidthallocation.
OLT increases bandwidth allocation when there is no idle frames from aONU.
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DBA Example
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WDM-PON
Each ONU gets a wavelength channel, and achievesdedicated bandwidth and guaranteed QoS.
Logical P2P network infrastructure to ensure protocol,data-rate transparency, and better security.
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Challenges for WDN-PON Systems
Colorless ONU is mandatory
To realize high-performance colorless ONU withlow cost is difficult
Tunable laser
Injection-locked Fabry-Perot laser
Reflective semiconductor optical amplifier
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TWDM-PON Basic Architecture
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TDM-based TWDM-PON
Main Advantages: improve downstream bandwidth capacity, compatible with
traditional TDM-PON and leverage network expansion and upgrade.
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WDM-based TWDM-PON
Main Advantages: simplify network control protocol, no need to coordinate
ONUs’ data transfer and perform load balancing.
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TDM-over-WDM TWDM-PON
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WDM-over-TDM TWDM-PON
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Hybrid Fiber-Coaxial (HFC) Networks
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TransportRing
HeadEnd RF HybridCoupler
DistributionHub
RF Amplifier
Optical Fiber
OpticalNode
CustomerHouse
Coaxial Cable
Hybrid Fiber Coax (HFC) Network
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Global Subscriber Growth
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Cisco CMTS: uBR10k
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Infrastructure of DOCSIS 3.0 HFC Network
Cable Modem Termination System
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What’s Channel-Bonding?
UpstreamChannels
DownstreamChannels
DOCSIS3.0 CM
PreDOCSIS3.0 CM
Bonding Group as one virtual channel
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Dynamic Bonding Change (DBC)
UpstreamChannels
DownstreamChannels
DOCSIS3.0 CM
Transmitter Channel Set(TCS)
Receiver Channel Set(RCS)
DBC_REPLACE
DBC_DELETE
DBC_ADD
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Channel-Bonding Technology
Boost access bandwidth and
user experience Increase power consumption
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Operation of Access Networks
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Performance
Power Consumption
Tradeoff