STARGATE

STARGATE

• 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

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

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

STARGATE

• 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

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

STARGATE

• Network architecture

STARGATE

• Optical bypassing

Wavelength sets– ΛOLT: Number of used wavelengths in a given WDM EPON in

both directions

– ΛAWG = P R: Number of used wavelengths to & from AWG, where R ≥ 1 denotes number of used FSRs

– ΛPSC = 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

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 ΛAWG

wavelength channels at each port

– Figure illustrates use of one FSR (R=1)

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 & ΛAWG

• Multiwavelength receiver operating on ΛAWG

STARGATE

• Node architecture– OLT in WDM EPON c is equipped with

• Array of c fixed-tuned transmitters & c fixed-tuned receivers operating on given ΛOLT downstream & ΛOLT 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 ΛAWG in order to avoid receiver collisions

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

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 ΛAWG wavelengths corresponding ONUs can be reached from a given AWG input port

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 ΛOLT

• One or more additional queue sets used to report bandwidth requirements on ΛAWG, including MAC address(es) of destina-tion ONU(s) in reserved field

STARGATE

• Operation– STARGATE MPCP message

• WDM extended GATE MPCPDU used to coordinate not only upstream transmissions on ΛOLT in each WDM EPON but also all-optical transmissions on ΛAWG 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

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 ΛAWG

STARGATE

• Operation– Access control on ring & PSC

• ONUs unable to access ΛAWG & 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

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

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

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

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 phases1. 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

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

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

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 ΛAWG

• 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 ΛAWG

• STARGATE provides high degree of connectivity => improved resilience & decreased number of required hops between nearby file-sharing peers