WDM EPON WDM EPON EPON upgrades At present

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WDM EPON

WDM EPON

WDM EPON • EPON upgrades – At present, single-channel TDM EPONs are considered attractive

WDM EPON • EPON upgrades – At present, single-channel TDM EPONs are considered attractive solution • Wavelength channel bandwidth is shared by nodes via TDM => Only one type of single-channel transceiver needed => Simplified network operation & maintenance – Given steadily increasing number of users & bandwidth-hungry applications, TDM EPONs need to be upgraded – EPON upgrades • Increase line rate of TDM EPON – Implies that all installed transceivers have to be replaced with higher-speed transceivers • Deploy wavelength division multiplexing (WDM) – WDM EPONs provide cautious upgrade path in that wavelength channels are added one at a time – Only nodes with higher traffic demands are WDM upgraded

WDM EPON • State of the art – Cost-effective WDM OLT & ONU structures

WDM EPON • State of the art – Cost-effective WDM OLT & ONU structures • WDM OLT consists of multicarrier generator supplying hundreds of optical carriers => greatly reduced number of required laser diodes • Each ONU is assigned separate pair of dedicated upstream & downstream wavelength channels • ONUs deploy no light source, but simply modulate optical carriers supplied by OLT for upstream transmission => remote modulation • Remote modulation used to realize wavelength-independent (colorless) ONUs • Colorless ONUs help reduce costs & simplify operation and maintenance of WDM EPONs

WDM EPON • State of the art – Wavelength-selection-free ONU transmitters • Design &

WDM EPON • State of the art – Wavelength-selection-free ONU transmitters • Design & feasibility study of cost-effective burst-mode ONU transmitters which can operate on any wavelength channel without requiring wavelength tuning => wavelength-selectionfree transmitters • Wavelength-selection-free transmitters require neither wavelength stability circuits nor network operators to stock spare transmitters for each wavelength channel (similar to colorless ONUs) => reduced costs

WDM EPON • State of the art – PON interconnection • Interconnection of multiple

WDM EPON • State of the art – PON interconnection • Interconnection of multiple PONs of arbitrary topology • PON interconnection is highly scalable & provides evolutionary upgrade path from TDM PONs to WDM PONs • Each ONU is assigned separate pair of dedicated upstream & downstream wavelength channels • Existing field-deployed PON infrastructures remain intact • Transmitters at OLT may be shared among all interconnected PONs • For upstream transmission, each ONU may have different node structure • For downstream transmission, receiver of each ONU has to operate on different wavelength band which cannot be used by more than a single ONU at any given time

WDM EPON • State of the art – WDM-DBA algorithm • In WDM EPON

WDM EPON • State of the art – WDM-DBA algorithm • In WDM EPON under consideration, all ONUs are equipped identically with an array of fixed-tuned transceivers, one for each upstream/downstream wavelength channel • So-called WDM IPACT with a single polling table (WDM IPACT-ST) dynamic wavelength allocation (DWA) algorithm – Multichannel extension of IPACT with online scheduling – Transmission windows assigned to ONUs in round-robin fashion allowing them to transmit on first available upstream wavelength channel • WDM IPACT-ST EPON outperforms single-channel TDM IPACT PON in terms of delay by maintaining short polling cycle

WDM EPON • State of the art – Integration of APON & EPON •

WDM EPON • State of the art – Integration of APON & EPON • So-called byte size clock (BSC) protocol is scalable in bandwidth assignment – Heavy users may be assigned a single wavelength – Light users may share a single wavelength • In BSC, time is divided into periodically recurring time frames – Each frame consists of dedicated reservation minislots, one for each ONU, and data slots – Data slots are assigned on demand after transmitting request packets in minislots in previous frame • Preallocation – Reservation overhead can be avoided by preallocating a number of dedicated data slots to certain ONUs • Delta compression – Only delta (difference) between packets is transmitted

WDM EPON • TDM to WDM EPON migration – WDM upgrade of single-channel TDM

WDM EPON • TDM to WDM EPON migration – WDM upgrade of single-channel TDM EPONs will likely occur over long periods of time in pay-as-you-grow manner – To fully capitalize on WDM, it appears reasonable to use an array of fixed-tuned transceivers at OLT, one for each operating wavelength channel – Evolutionary WDM upgrade of EPON should not impose any particular WDM ONU architecture & should let the decisions be dictated by • Economics • State of the art of transceiver manufacturing technology • Service provider preferences – Evolutionary WDM upgrade helps operators realize their survival strategy for highly cost-sensitive access networks – Legacy EPON channel should be used as common channel

WDM EPON • WDM extensions to MPCP – To guarantee compliance of evolutionary WDM

WDM EPON • WDM extensions to MPCP – To guarantee compliance of evolutionary WDM upgrade of EPON with IEEE 802. 3 ah, MPCP must be extended – WDM extensions to MPCP should enable OLT to schedule transmissions to & receptions from ONUs on any wavelength channel(s) supported by OLT & respective ONU – WDM extensions include • Discovery & registration • Upstream coordination • Downstream coordination

WDM EPON • WDM extensions to MPCP – Discovery & registration • For backward

WDM EPON • WDM extensions to MPCP – Discovery & registration • For backward compatibility, discovery & registration of ONUs take place on original TDM EPON wavelength channel • A discovered ONU conveys following information about its WDM architecture using reserved fields in REGISTER_REQ MPCPDU – TX_type & RX_type » No WDM, fixed-tuned, or tunable – TX_tuning_time & RX_tuning_time » Tuning time given as integer multiple of unit time – Wavelength_id_type » Two-level or flat encoding scheme – TX_waveband & RX_waveband » Supported waveband of transmitter & receiver – TX_supported_wavelengths & RX_supported_wavelengths » Bitmap of supported wavelengths of tansmitter & receiver

WDM EPON • WDM extensions to MPCP – Upstream coordination • Wavelength identifier is

WDM EPON • WDM extensions to MPCP – Upstream coordination • Wavelength identifier is issued along with every transmission grant by OLT using reserved fields in GATE MPCPDU – Downstream coordination • No appropriate MPCPDU exists to let OLT (re)configure receiving wavelength(s) of ONU • Two new recommended MPCPDUs – RX_CONFIG » Sent by OLT to (re)configure a given ONU’s receiver(s) – RX_CONFIG_ACK » Sent by ONU to acknowledge (re)configuration

WDM EPON • WDM extensions to MPCP

WDM EPON • WDM extensions to MPCP

WDM EPON • DWA – In WDM EPONs, dynamic bandwidth allocation (DBA) is done

WDM EPON • DWA – In WDM EPONs, dynamic bandwidth allocation (DBA) is done not only in time but also wavelength dimension => dynamic wavelength allocation (DWA) problem – DWA algorithms can be classified into • Online scheduling algorithms – OLT schedules upstream transmission as soon as it receives an individual REPORT message – Scheduling decisions are made without global knowledge • Offline scheduling algorithms – OLT schedules upstream transmissions after receiving REPORT messages from all ONUs – Scheduling decisions are made with global knowledge at expense of report-to-scheduling delay – Online scheduling DWA algorithms tend to lower packet delays than offline counterparts at medium to high traffic