1. STARGATE

2. WDM EPON – what’s next? –WDM EPONs are expected to become mature in the near term –Key tasks of cost reduction & design of colorless ONUs will be addressed successfully in the near term –Research focus will shift to evolutionary upgrades & further cost reductions of WDM EPONs and their all- optical integration with WDM upgraded RPR networks –Resultant Ethernet-based optical access-metro area network is called STARGATE

3. STARGATE Opaque PON interconnection –Research on interconnection of (E)PONs has begun only very recently, e.g., Multiple PONs of arbitrary topology may be connected to common CO whose transmitters are shared for downstream transmission among PONs Alternatively, collector ring may interconnect multiple PONs with CO whose transmitters are used for both downstream & upstream transmissions In both PON interconnection models, inter-PON traffic has to undergo OEO conversion at CO (i.e., PONs are not interconnected all-optically) => opaque interconnection of PONs

4. STARGATE Islands of transparency –RPR can easily bridge to Ethernet networks such as EPON & may also span into MANs and WANs –As a result, layer 2 switching from access networks far into backbone networks becomes possible –End-to-end Ethernet networks may turn out to be practical –On the other hand, end-to-end optical islands of transparency are not feasible & are expected to be of limited geographical coverage due to Physical transmission impairments Other issues such as management, jurisdiction, and billing issues –However, islands of transparency with optical bypassing capability are key in MANs for Easy support of various legacy & future services Cost reduction

5. STARGATE –STARGATE all-optically integrates Ethernet based access & metro networks following three principles Evolutionary downstream SDM upgrades –IEEE 802.3ah supports both P2P & P2MP links –STARGATE deploys additional P2P or P2MP downstream fiber link (none in the upstream direction) Optical bypassing –All wavelengths on downstream P2P/P2MP fiber link optically bypass OLT –Optical bypassing avoids OEO conversion & additional transceivers at OLT => transparency & cost savings Passive optical networking –STARGATE lets low-cost PON technologies follow low- cost Ethernet technologies into metro networks –Passivity leads to simplified management & lower costs

6. STARGATE STARGATE vs. TWIN –Passive optical networking in all-optical wavelength- routing WDM networks has recently been studied in so- called time-domain wavelength interleaved networking (TWIN) concept In TWIN, fast TDM switching & packet switching are emulated through use of fast tunable lasers at network edge TWIN require network-wide scheduling of transmissions TWIN-WR allows only for optical multihop communication –Unlike TWIN, STARGATE Supports extensive spatial wavelength reuse while providing optical single-hop communication among all ONUs Requires only local scheduling of transmissions Does not require any time-of-day synchronization Targets access-metro networks with regular topologies

7. STARGATE Network architecture

8. STARGATE Optical bypassing Wavelength sets –Λ OLT : Number of used wavelengths in a given WDM EPON in both directions –Λ AWG = P  R: Number of used wavelengths to & from AWG, where R ≥ 1 denotes number of used FSRs –Λ PSC = 1 + H + (P-1): One control channel, 1 ≤ H ≤ P-1 home channels for hot-spot CO, and P-1 home channels for other COs

9. STARGATE Wavelength routing –Athermal AWG eliminates need for temperature control & wavelength shift monitoring –AWG is a wavelength routing device that allows for spatial reuse of all Λ AWG wavelength channels at each port –Figure illustrates use of one FSR (R=1)

10. STARGATE Node architecture –Regular CO is equipped with Two separate fixed-tuned transceivers, one for each direction of dual-fiber ring One transceiver fixed tuned to control channel of star subnetwork One receiver fixed tuned to its assigned PSC home channel One transmitter tunable over (P-1) + H home channels –Hot-spot CO is equipped with Two separate fixed-tuned transceivers, one for each direction of dual-fiber ring One transceiver fixed tuned to control channel of star subnetwork 1 ≤ H ≤ P-1 receivers fixed tuned to its PSC home channels H transmitters tunable over (P-1) home channels & Λ AWG Multiwavelength receiver operating on Λ AWG

11. STARGATE Node architecture –OLT in WDM EPON c is equipped with Array of c fixed-tuned transmitters & c fixed-tuned receivers operating on given Λ OLT downstream & Λ OLT upstream wavelength channels, respectively –ONU STARGATE does not impose any particular WDM node structure on ONUs except for ONUs which receive data over AWG Those ONUs must be equipped with a multiwavelength receiver operating on Λ AWG in order to avoid receiver collisions

12. STARGATE Operation –STARGATE uses WDM extensions to EPON’s MPCP messages –Operation of STARGATE involves following procedures Discovery & registration of ONUs Piggyback REPORT MPCP message STARGATE MPCP message STARGATING service Access control on ring & PSC

13. STARGATE Operation –Discovery & registration In each WDM EPON, an ONU sends REGISTER_REQ MPCPDU with WDM extensions to OLT for its discovery & registration REGISTER_REQ MPCPDU contains MAC address & detailed information about WDM node structure of ONU OLT learns about MAC address & WDM node structure of each of its attached ONUs After registration, all OLTs exchange via PSC the MAC addresses of their attached ONUs that are able to receive data over AWG As a result, OLTs know –Which MAC addresses can be reached via AWG –To which AWG output ports corresponding ONUs are attached –On which of the Λ AWG wavelengths corresponding ONUs can be reached from a given AWG input port

14. STARGATE Operation –Piggyback REPORT MPCP message REPORT MPCPDU can carry one or more queue sets, each with up to eight queues First queue set used to report bandwidth requirements on Λ OLT One or more additional queue sets used to report bandwidth requirements on Λ AWG, including MAC address(es) of destina- tion ONU(s) in reserved field

15. STARGATE Operation –STARGATE MPCP message WDM extended GATE MPCPDU used to coordinate not only upstream transmissions on Λ OLT in each WDM EPON but also all-optical transmissions on Λ AWG across star subnetwork => STARGATE MPCP message Based on MAC addresses of destination ONUs, OLT of source WDM EPON uses STARGATE MPCP message to grant source ONUs a time window on wavelengths which AWG routes to destination ONUs according to DBA algorithm in use at OLT

16. STARGATE Operation –STARGATING service Similar to EPON, STARGATE is not restricted to any specific DBA algorithm However, DBA algorithms for STARGATE should be able to dynamically set up transparent all-optical circuits across AWG at wavelength & subwavelength granularity with predictable QoS Each OLT uses its DBA module to provide gated service across AWG-based star network => STARGATING service STARGATING enables dynamic set-up of low-latency circuits on Λ AWG

17. STARGATE Operation –Access control on ring & PSC ONUs unable to access Λ AWG & RPR ring nodes send data on tree, ring, and/or PSC along shortest path in terms of hops Channel access on ring is governed by RPR protocols Channel access on PSC –Time is divided into periodically recurring frames –On control channel, each frame consists of P control slots, each dedicated to a different CO –Each CO stores data packets to be sent on PSC in FIFO queue with look-ahead capability to avoid HOL blocking –For each stored packet CO broadcasts control packet »Destination address & length of data packet –All COs build common distributed schedule for collision- free data packet transmission on home channel of destination CO at earliest possible time

18. STARGATE Applications –Providing end users with advanced broadband access & growing body of content and applications has significant impact on their everyday lives –Subscribers of advanced access networks increasingly use Internet as “destination resort” –Two applications become increasingly popular in optical access networks among subscribers spending their free time Online gaming Peer-to-peer (P2P) file sharing

19. STARGATE Applications –Online gaming Traffic characteristics –Most online games are based on client-server paradigm where server keeps track of global state of game –Online game traffic consists of information sent periodically back & forth between all clients (players) and server –Online gaming requires low-latency point-to-point up- stream communication & low-latency directed broadcast downstream communication –Workload consists of large bursts of very small packets sent every 50 or 100 ms in up- & downstream direction »Upstream packets have extremely narrow length distribution centered around mean size of 40 bytes »Downstream packets’ length is spread between 0 and 300 bytes

20. STARGATE Applications –Online gaming Impact –Game server farms must be provided with a means to efficiently realize directed broadcasting –Online gaming introduces a significant downward shift in packet size => electronic processing bottleneck –Networking devices will suffer from packet loss or per- sistent packet delay & jitter –Optically bypassing electronic access network devices alleviates bottleneck by exploiting high predictability of online gaming traffic –Low latency & good scalability are the two most important network design aspects –Peer-to-peer design of scalable game architectures utilizes clients’ computing resources

21. STARGATE Applications –P2P file sharing Use of P2P applications for sharing large audio/video files & software has been growing dramatically P2P traffic represents now largest amount of data traffic in today’s operational access networks, clearly surpassing web traffic File sharing process can be divided into two phases 1.Signaling »By using specific (proprietary) P2P protocol a host identifies one or more target hosts from which to download the file 2.Data transfer »Requesting host downloads file from a selected target host

22. STARGATE Applications –P2P file sharing Traffic characteristics –Major P2P application exhibits a nearly constant traffic pattern over time, independent of number of subscribers –Vast majority of upstream traffic is generated by a small number of hosts, for both weekday & weekend »Top 1-2% of IP addresses account for more than 50% & top 10% of IP addresses account for more than 90% of upstream traffic –A few hot-spot servers with popular content originate most of P2P upstream traffic => resembles conventional client- server paradigm –Similarly, a few heavy hitters with long on-times are responsible for high percentage of P2P downstream traffic –Most queries can be solved locally by finding nearby peers

23. STARGATE Applications –P2P file sharing Impact –High volume & good stability properties of P2P traffic give rise to use of simple yet highly effective capacity planning & traffic engineering techniques –The fact that individual hot-spot servers & heavy hitters with long on-times generate huge traffic volumes & most queries can be resolved locally can be exploited at architecture & protocol level –Future P2P-friendly optical access networks must be designed to meet requirements of P2P applications

24. STARGATE Applications –STARGATE is well suited to meet requirements of online gaming & P2P file sharing All-optical subwavelength circuits may be used to carry periodic low-latency game traffic & high volumes of stable P2P traffic Directed broadcasting can be realized by letting hot-spot CO transmit packets on different wavelengths of Λ AWG ONUs sending or receiving large amounts of traffic may deploy additional transceivers STARGATE scales well –Additional EPON tree networks may be attached to RPR ring nodes & may be later connected to star subnetwork –Additional FSRs of AWG may be used to increase Λ AWG STARGATE provides high degree of connectivity => improved resilience & decreased number of required hops between nearby file-sharing peers