Modelling Contention Avoidance and Resolution in

Modelling Contention Avoidance and Resolution in Optical Networks Annie Gravey Networking Context Traffic Evolution Network Architecture ON classification Contention resolution within the ON

Modelling Contention Avoidance and Resolution in Optical Networks Annie Gravey

OPS OBS Doing without photonic contention resolution Lossy OPS Lossless OPS

Department of Computer Engineering Institut Mines Telecom Atlantique Bretagne Pays de la Loire

Workshop on Optical Networks at EURANDOM, 16-18 April 2018

Passive Optical Networks Modelling PONs PON perspectives Summary 1/49

Outline Modelling Contention Avoidance and Resolution in Optical Networks

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Networking Context Traffic Evolution Network Architecture ON classification

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Contention resolution within the ON OPS OBS

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Doing without photonic contention resolution Lossy OPS Lossless OPS

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Passive Optical Networks Modelling PONs PON perspectives

Annie Gravey Networking Context Traffic Evolution Network Architecture ON classification Contention resolution within the ON OPS OBS Doing without photonic contention resolution Lossy OPS Lossless OPS Passive Optical Networks Modelling PONs PON perspectives Summary

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Networking Context Traffic Evolution: driven by Internet traffic

Modelling Contention Avoidance and Resolution in Optical Networks Annie Gravey Networking Context Traffic Evolution Network Architecture ON classification Contention resolution within the ON OPS OBS Doing without photonic contention resolution Lossy OPS Lossless OPS Passive Optical Networks Modelling PONs PON perspectives

Traffic growth and optical networking: a chicken and egg problem

Summary 4/49

Networking Context Traffic Evolution: which access for user traffic demands?


A minority of the traffic is destined to mobile access! The fixed access network still carries most of the traffic to the users

Summary 5/49

Networking Context Traffic Evolution: serving user traffic demands


A majority of the traffic corresponds to content distribution! Traffic is more and more generated by cloud-based applications (typically video)

Summary 6/49

Networking Context Traffic Evolution: Data Center generated traffic


Data Center generated traffic is a major point to take into account within metro and backbone networks (and inside data centers!)

Summary 7/49


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Networking Context Network Architecture: segmenting the network


Different architectures for Access, Metro, Backbone Networks

Summary 9/49

Networking Context Network Architecture: segmenting the network and locating data centers


Network design should take account of content distribution!

Summary 10/49

Networking Context Network Architecture: definition of the Evolved Packet Core

Modelling Contention Avoidance and Resolution in Optical Networks Annie Gravey Networking Context Traffic Evolution Network Architecture ON classification Contention resolution within the ON OPS OBS Doing without photonic contention resolution Lossy OPS Lossless OPS Passive Optical Networks Modelling PONs PON perspectives Summary

Mobile traffic is tunnelled to Packet Gateways (PGW) Mobile data plane is getting more distributed as mobile data increases 11/49

Networking Context Network Architecture: the notion of a transport network


User traffic is generated within the electronic layer, and carried over optical fibres in the different network portions 12/49


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Networking Context ON classification: what is so special with Optical Networks?

Modelling Contention Avoidance and Resolution in Optical Networks Annie Gravey Networking Context Traffic Evolution Network Architecture ON classification Contention resolution within the ON OPS OBS Doing without photonic contention resolution Lossy OPS Lossless OPS Passive Optical Networks

Pros Optical fibres can support huge capacity demands Optical transport technology is mature, and is still progressing Optical switching is potentially more energy efficient than electronic switching Optical switching could also be faster than electronic switching

Cons Light cannot be stored, i.e. lack of optical random access memory (RAM) to serve as ”optical buffers” the optical granularity is rather coarse (wavelength, or grid based) Optical Packet Switching may still rely on custom optical components

Modelling PONs PON perspectives Summary 14/49

Networking Context ON classification: Optical Circuits


Optical Circuits: point-to-point connections between electronic nodes DWDM networks, relying on wavelength switching and slow reconfiguration by ROADM current developments : ”flexible” networks (”flex-grid”). set-up/tear-down time: several tens/hundreds of milliseconds Performance evaluation for optical circuits Mostly a planning and dimensionning problem (not addressed in this talk!) technical issue: optimizing routing and wavelength usage (Routing and Wavelength Assignment, RWA), with blocking probability as performance indicator In ”flex-grid” networks, the technical issue morphs into Routing and Spectrum Assignment (RSA), avoiding Spectrum fragmentation

Summary 15/49

Networking Context ON classification: Sub-Lambda Photonically Switched Network (SLPSN)

Modelling Contention Avoidance and Resolution in Optical Networks Annie Gravey Networking Context Traffic Evolution Network Architecture ON classification Contention resolution within the ON OPS OBS Doing without photonic contention resolution

A Sub-Lambda Photonically Switched Network (SLPSN) presents an optical user plane and carries temporal slices of individual or multiple wavelengths [1] Packet Switching : information is carried in optical containers (”optical packet”) which are individually switched Burst Switching : fast set-up of an optical circuit, fully dedicated to a flow

Lossy OPS Lossless OPS Passive Optical Networks Modelling PONs PON perspectives Summary 16/49

Networking Context ON classification: How is contention resolution implemented ?

Modelling Contention Avoidance and Resolution in Optical Networks Annie Gravey Networking Context Traffic Evolution Network Architecture ON classification Contention resolution within the ON OPS OBS Doing without photonic contention resolution Lossy OPS Lossless OPS

A simple SLPSN classification : how does the Optical Network deal with the contention resolution issue? Contention resolution within the Optical Network Fibre Delay Lines Wavelength conversion Deflection (Hot Potato) routing

No Contention resolution within the Optical Network lossy optical network lossless optical network: contention resolution in edge nodes (implemented in electronics)


Networking Context ON classification: Classification of SLPSN

Modelling Contention Avoidance and Resolution in Optical Networks

A more complete classification

Annie Gravey Networking Context

a very large number of cases!

Traffic Evolution Network Architecture ON classification

many have been studied since the 1990’s


few can realistically be implemented (due to commercial availability of optical components)

Doing without photonic contention resolution Lossy OPS Lossless OPS Passive Optical Networks Modelling PONs PON perspectives

Figure: Classification of SLPSN [1]

Summary 18/49


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Contention resolution within the ON Optical Packet Switching: switch elements


control plane ”all optical” (uncommon) ”transparent”: control information synchronized with data, and electronically processed

data plane usually synchronous (slot time a few µs or less) relies on mux/demux, optical wavelength converters and delay lines

1997 ACTS project KEOPS “Keys for Optical Packet Switching” switch Limited FDL number FDL dedicated per input and shared per output

Summary 20/49

Contention resolution within the ON Optical Packet Switching modelling


KEOPS modelling [2] as an example! A KEOPS original feature: FDL present non consecutive delays Stage 1: the FDLs schedule packets in the future in case of contention (max delay=F ) Stage 2: contention is due sharing the M converters by all output lines Ad-hoc modelling approach non work-conserving system packets may be lost even if FDLs are available (stage 2!) state of system: number of packets in FDLs Bernoulli or Poisson arrivals : (approximate) Markovian models Ploss = A−S A Performance evaluation for OPS if M is small, and M = F : large Ploss . M < F allows to ensure a small Ploss 21/49


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Contention resolution within the ON Optical Burst Switching: How does it work?


Resolving OPS contention in photonics relies on non commercially available components (in particular wavelength converters). OBS potentially requires less components. OBS consists in reserving an end-to-end light-path (one-way reservation) for a short duration (from several µs to several ms) proposals vary on how the offset time (OT) is defined e.g. Just P Enough Time (JET) OT = δ(i) (typically tens of µs) Class differentiation by varying the OT: the larger it is, the smaller is the blocking probability [3]

Summary 23/49

Contention resolution within the ON Optical Burst Switching: performance evaluation


Performance evaluation for OBS with no delay lines, and fast wavelength converters : Blocking given by the M/M/k/k queue

The supported load decreases with the target loss probability

with delay lines and fast wavelength converters : lower bound for blocking given by the M/M/k/N queue [4] a very elegant method for G burst size relies on level crossing analysis [5] OBS can differentiate between classes using a simple offset based mechanism

OBS is NOT adequate for transport networks (low blocking, reasonable load) [6] 24/49

Contention resolution within the ON Some references on ”classical” OPS and OBS


[1] IST STREP MAINS (Metro Architectures enablINg Subwavelengths). D1.6 “Standardization activities during the second half of the project”. Feb. 2013 [2] P. Cadro, A. Gravey, C. Guillemot and R. Marie. ”Performance Evaluation of the KEOPS Wavelength Routing Optical Packet Switch”. Feb. 2000, European Transactions on Telecommunications 11(1):125-132 [3] Myungsik Yoo, Chunming Qiao and S. Dixit, ”Optical burst switching for service differentiation in the next-generation optical Internet,” in IEEE Communications Magazine, vol. 39, no. 2, pp. 98-104, Feb 2001 [4] Myungsik Yoo, Chunming Qiao and S. Dixit, ”The effect of limited fiber delay lines on QoS performance of optical burst switched WDM networks,” 2000 IEEE International Conference on Communications. ICC 2000. Global Convergence Through Communications. Conference Record, New Orleans, LA, 2000, pp. 974-979 vol.2 [5] S. Tang and L. Tan, ”Analysis of Blocking Probability of Multi-Class OBS With General Burst Size Distribution,” in IEEE Communications Letters, vol. 20, no. 11, pp. 2153-2156, Nov. 2016. [6] P. Pavon-Marino and F. Neri, ”On the Myths of Optical Burst Switching,” in IEEE Transactions on Communications, vol. 59, no. 9, pp. 2574-2584, September 2011.

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Doing without photonic contention resolution Learning about contention


If the distance between source and contention is small, losses are quickly detected (propagation delay: 5ns/m), and re-transmission triggered !

Networking Context Traffic Evolution Network Architecture ON classification Contention resolution within the ON OPS OBS Doing without photonic contention resolution Lossy OPS Lossless OPS Passive Optical Networks Modelling PONs PON perspectives

Figure: from [8] Figure: from [7]

ACK carried by TCP

NACK carried by optical layer

These mechanisms can be used for Optical Switches deployed in datacenters

Summary 27/49

Doing without photonic contention resolution Modelling random backoff [8]


Architecture of the wavelength routed data center network

Annie Gravey Networking Context Traffic Evolution Network Architecture ON classification Contention resolution within the ON OPS OBS Doing without photonic contention resolution Lossy OPS Lossless OPS Passive Optical Networks Modelling PONs PON perspectives

The switch is time-slotted Random back-off (as in IEEE 802.11) for blocked packets

Flow level analysis packet level: with generalized Engset flow level : processor sharing works well with 80 wavelengths, 10 µs back-off time, 50% load

Summary 28/49

Doing without photonic contention resolution Modelling immediate retransmission [9]


Figure: Throughput versus offered load for different switch size

Packet level analysis

Time is slotted

fixed point analysis to derive input traffic (offered + re-transmissions)

Immediate retransmission of blocked packets

throughput derived from offered traffic

Packet level analysis with Bernoulli arrivals

works well if offered traffic less than 0.6

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Doing without photonic contention resolution Some references on Lossy OPS


[7] P. J. Argibay-Losada, K. Nozhnina, G. Sahin and C. Qiao, ”Using stop-and-wait to improve TCP throughput in fast optical switching (FOS) networks over short physical distances,” IEEE INFOCOM 2014 - IEEE Conference on Computer Communications, Toronto, ON, 2014, pp. 1312-1320. [8] T. Bonald, D. Cuda, R. M. Indre and L. Noirie, ”Building optical packet networks without buffering, signaling or header processing,” in IEEE/OSA Journal of Optical Communications and Networking, vol. 5, no. 4, pp. 294-304, April 2013. [9] S. Di Lucente, N. Calabretta, J. A. C. Resing and H. J. S. Dorren, ”Scaling low-latency optical packet switches to a thousand ports,” in IEEE/OSA Journal of Optical Communications and Networking, vol. 4, no. 9, pp. A17-A28, Sept. 2012.



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Lossless OPS Implementation options


Ensuring a lossless data plane by storing information at the edge of the optical network, and controlling its insertion Packets ”containers” filled by multiple electronic packets carried over a single (OBT, POADM, TWIN) or multiple wavelengths (WSADM)

Network Topology Slotted Rings and Bus Slotted Optically Passive Tree

Medium Access opportunistic insertion scheduler based insertion static scheduler token ring based dynamic scheduler (similar to PONs)

Summary 32/49

Lossless OPS Optical Packet Rings and Bus


unidirectional or bi-directional (for protection) slotted operation dynamic [10], reservation based/opportunistic [11], [12] unicast and multicast support

a single control channel and multiple data channels packet carried over a single channel ([10], [11]) or split over multiple channels [12] 33/49

Lossless OPS Packet level models for lossless OPS [12]

Annie Gravey Networking Context Traffic Evolution Network Architecture ON classification Contention resolution within the ON OPS OBS Doing without photonic contention resolution Lossy OPS Lossless OPS Passive Optical Networks Modelling PONs PON perspectives

Assuming Poisson arrivals of packets (PDU): γj (x) = e −Λx (Λx) j!

j

π is derived by solving πP = π Distribution of sojourn time before insertion on the ring FIFO electronic queue relies on memory-less property of the Poisson process

opportunistic insertion : ”Bernoulli” availability Reservation : 1 reserved every R slots

140 Opportunistic Insertion Channel Reservation Slot Reservation

120 Mean Sejourn Time (in µs)


100 80 60 40 20 0 0

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10

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Number of Wavelength Channels K

Summary 34/49

Lossless OPS Supporting Metro Networks


The Metro Ethernet Forum has set performance objectives for different network spans, including Metro (< 250km) Loss 10−4 0

Annie Gravey

MEF 23.2 WSADM PDU level

Networking Context Traffic Evolution Network Architecture ON classification Contention resolution within the ON

Passive Optical Networks Modelling PONs PON perspectives Summary

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Allocated Ressources

Lossy OPS Lossless OPS

Jitter 3ms 0.25ms insertion

WSADM for Metro networks simple models for complex systems

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OPS OBS Doing without photonic contention resolution

Delay 10ms 2.5ms (propagation) 0.25ms (insertion)

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WSADM quite efficient for delivering good performance

0.8 0.6 0.4 Opportunistic Insertion Channel Reservation Slot Reservation

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Offered Traffic

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the number of channels depends mostly on technology and traffic demands (not on performance) 35/49

Lossless OPS Static versus Dynamic Resource allocation in TWIN

Modelling Contention Avoidance and Resolution in Optical Networks Annie Gravey Networking Context

TWIN (Time-domain Wavelength Interleaved Networking) [13] also supports lossless OPS

Simulation based study using a real Metro level trace [14]

Traffic Evolution Network Architecture ON classification Contention resolution within the ON OPS OBS Doing without photonic contention resolution Lossy OPS Lossless OPS Passive Optical Networks Modelling PONs PON perspectives

Technical issue: schedule packet emission to avoid collision: Management Plane (slow) versus Control Plane (dynamic)

Summary 36/49

Lossless OPS Other use cases for lossless OPS


Intra data-center interconnections [15]

Annie Gravey Networking Context Traffic Evolution Network Architecture ON classification Contention resolution within the ON OPS OBS Doing without photonic contention resolution Lossy OPS Lossless OPS

Figure: Typical electronical data center network [15]

Figure: Multiple POADM rings interconnected as a Torus [16]


Fronthaul networks

Summary 37/49

Doing without photonic contention resolution Some references on Lossless OPS


[10] J. Kim, M. Maier, T. Hamada and L. G. Kazovsky, ”OBT: Optical Burst Transport in Metro Area Networks,” in IEEE Communications Magazine, vol. 45, no. 11, pp. 44-51, November 2007. [11] D. Chiaroni et al., ”Cost and performance issues of a Packet-Optical Add/Drop Multiplexer technology,” 2009 International Conference on Photonics in Switching, Pisa, 2009, pp. 1-2. [12] A. Gravey, D. Amar, P. Gravey, M. Morvan, B. Uscumlic and D. Chiaroni ”Modelling packet insertion on a WSADM ring”. ONDM 2018 [13] Widjaja, I, Saniee, I., Giles, R. and Mitra, D., ”Light core and intelligent edge for a flexible, thin-layered, and cost-effective optical transport network”, Communications Magazine, IEEE, 2003, 41, S30-S36. [14] J. Pesic, A. Triki and A. Gravey, ”Adapting the EPON MAC protocol to a metropolitan burst switching network,” 2015 20th European Conference on Networks and Optical Communications - (NOC), 2015. [15] C. Kachris and I. Tomkos, ”A Survey on Optical Interconnects for Data Centers,” in IEEE Communications Surveys and Tutorials, vol. 14, no. 4, pp. 1021-1036, Fourth Quarter 2012. [16] Y. Pointurier et al., ”Green optical slot switching torus for mega-datacenters,” 2015 European Conference on Optical Communication (ECOC), Valencia, 2015, pp. 1-3. 38/49


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Passive Optical Networks Different types of PONs


A PON is usually build on a tree: the root is the OLT (Optical Line Termination) and the leaves (10s to 100s) are the ONUs (Optical Network Unit). Downstream traffic is broadcast to all ONUs, upstream traffic is time multiplexed Upstream traffic is buffered in ONUs till the ONU is allowed to send it The OLT allocates a transmission period to each ONU; technical issue: ”efficient” scheduling of upstream capacity Performance indicators: fairness, throughput, latency, jitter GPON uses 125µs frames, EPON does not rely on framing [17]

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Passive Optical Networks Modelling PON performance


Multiple upstream Bandwidth Allocation (BA) strategies: no standard for OLT allocation policy ”Status Reporting” (SR) BA rely on reports by ONUs, ”Non Status Reporting” BA rely on an estimation process made by the OLT Some SR mechanisms are well known: many variants of IPACT for EPON have been modelled PON Modelling a PON is a polling system each ONU impacts the others: most studies are simulation based! [17] Processor Sharing between ONUs is a good first order modelling of PON resource allocation [18]

Summary 41/49

Passive Optical Networks EPON mean delay performance


EPON mean queueing delay derivation ”pseudo-conservation” law [20] holds

Networking Context Traffic Evolution Network Architecture ON classification Contention resolution within the ON OPS OBS Doing without photonic contention resolution Lossy OPS Lossless OPS Passive Optical Networks Modelling PONs PON perspectives

Figure: Typical GATE and REPORT exchange in EPON [19]

distance between OLT and ONUs (deported buffers) cycle time between REPORT and corresponding GATE

not the typical G/G/1 queue with reservation [19], however.... Mean Value Analysis [21] can simplify derivation for mean queueing delay [22]

for the ”gated” service : TWi (n) = Qi (n − 1)

Summary 42/49

Passive Optical Networks Some references for EPON performance analysis


[17] T. Orphanoudakis et al., “Performance Evaluation of GPON vs EPON for Multi-Service Access,” Int’l. J. Commun. Sys. 2009, vol. 22, pp. 187–202. [18] Y. Wang, M. Zukerman, R. G. Addie, S. Chan and R. J. Harris, ”A priority-based processor sharing model for TDM passive optical networks,” in IEEE Journal on Selected Areas in Communications, vol. 28, no. 6, pp. 863-874, Aug. 2010. [19] A. Dixit, B. Lannoo, D. Colle, M. Pickavet and P. Demeester, ”Delay models in ethernet long-reach passive optical networks,” 2015 IEEE Conference on Computer Communications (INFOCOM), Kowloon, 2015. [20] Boxma, O. J., and W. P. Groenendijk. ”Pseudo-Conservation Laws in Cyclic-Service Systems.” Journal of Applied Probability 24, no. 4 (1987): 949-64. doi:10.2307/3214218. [21] E. Winands, I. Adan, and G. van Houtum, ” Mean value analysis for polling systems”, Queueing Systems, Vol. 54, No. 1, pp. 35-44, Sep 2006. [22] Ngo, M.T., Gravey, A. and Bhadauria, D. Telecommun Syst (2011) 48: 203.

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Passive Optical Networks PON reality check and perspectives


PON reality check ! EPON deployed in some Asian countries GPON deployed in most developed countries, for residential broadband access mostly Best Effort, with fixed BA ! PON perspectives WDM PONs to increase available resources Fixed Mobile Convergence (FMC) to mutualise the fibre access network between fixed and mobile networks


Passive Optical Networks PON perspectives: providing backhaul to small cells


NG-PON considered to support the multiplication of radio cells Replace the legacy methods linking antenna and aggregation network

Networking Context Traffic Evolution Network Architecture ON classification Contention resolution within the ON OPS OBS Doing without photonic contention resolution Lossy OPS Lossless OPS Passive Optical Networks Modelling PONs PON perspectives Summary

Mobile access network is heterogeneous

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Passive Optical Networks PON perspectives: supporting fronthaul and backhaul


NG-PON considered to support the splitting radio access network functions compromise between complexity at antenna and fronthaul rate

Networking Context Traffic Evolution Network Architecture ON classification Contention resolution within the ON OPS OBS Doing without photonic contention resolution

Figure: Fronthaul and Backhaul for mobile traffic [23]

Lossy OPS Lossless OPS

GPON for backhaul is OK

Passive Optical Networks

BA should be revisited for fronthaul [23]

Modelling PONs PON perspectives

specific issues: latency and jitter [24], [25] mathematical models yet to be developed !

Summary 47/49

Passive Optical Networks Some references for PON perspectives


[23] N. P. Anthapadmanabhan, A. Walid and T. Pfeiffer, ”Mobile fronthaul over latency-optimized time division multiplexed passive optical networks,” 2015 IEEE International Conference on Communication Workshop (ICCW), London, 2015 [24] A. M. Mikaeil, W. Hu, T. Ye and S. B. Hussain, ”Performance evaluation of XG-PON based mobile front-haul transport in cloud-RAN architecture,” in IEEE/OSA Journal of Optical Communications and Networking, vol. 9, no. 11, pp. 984-994, Nov. 2017 [25] S. Zhou, X. Liu, F. Effenberger and J. Chao, ”Low-latency high-efficiency mobile fronthaul with TDM-PON (mobile-PON),” in IEEE/OSA Journal of Optical Communications and Networking, vol. 10, no. 1, pp. A20-A26, Jan. 2018.


Summary Modelling Contention Avoidance and Resolution in Optical Networks Annie Gravey Networking Context Traffic Evolution Network Architecture ON classification Contention resolution within the ON OPS OBS Doing without photonic contention resolution Lossy OPS Lossless OPS Passive Optical Networks

There are many types of optical networks; traffic profiles and QoS requirements should be taken into account. To lose or not to lose information within the optical layer ? is still an open question Many proposed solutions rely on non commercially available optical components; but technology constantly progresses. Disclaimer The area is so rich that what has been presented is a personal sample of the State Of Art Details of the mathematical models are available in the bibliography

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