WDM ring networks WDM ring networks Unidirectional rings

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WDM ring networks

WDM ring networks

WDM ring networks • Unidirectional rings – Most WDM ring networks are based on

WDM ring networks • Unidirectional rings – Most WDM ring networks are based on unidirectional fiber ring carrying W wavelengths – Each of the N ring nodes deploys OADM to drop and add traffic – For N = W, each node has dedicated home channel for reception – For N ≥ W, system becomes scalable since number of nodes is independent of number of available wavelengths

WDM ring networks • Channel vs. receiver collision – Each ring node is equipped

WDM ring networks • Channel vs. receiver collision – Each ring node is equipped with • • i fixed-tuned transmitters (FT) j tunable transmitters (TT) m fixed-tuned receivers (FR) n tunable receivers (TR) – Node architecture described as FTi-TTj-FRm-TRn, whereby i, j, m, n ≥ 0 – Channel collision occurs when a node inserts packet on a given shared wavelength while another packet is passing by – Receiver collision (destination conflict) occurs when a node’s receiver is not tuned to wavelength of arriving packet – Channel & receiver collisions can be mitigated or completely avoided at node architecture and/or medium access control (MAC) protocol level

WDM ring networks • Categorization – WDM ring networks can be categorized with respect

WDM ring networks • Categorization – WDM ring networks can be categorized with respect to applied MAC protocol

WDM ring networks • Slotted ring w/o channel inspection – Simple way to avoid

WDM ring networks • Slotted ring w/o channel inspection – Simple way to avoid channel & receiver collisions is deployment of TDMA with static bandwidth assignment, whereby time is divided into slots equal to packet transmission time – Typically, slots are of fixed size & are aligned across wavelength channels – Well suited for uniform regular medium to high traffic loads – Low channel utilization under bursty & low traffic loads

WDM ring networks • MAWSON – Metropolitan area wavelength switched optical network (MAWSON) is

WDM ring networks • MAWSON – Metropolitan area wavelength switched optical network (MAWSON) is based on a FTW-FR or alternatively TT-FR node architecture – N=W nodes connected to ring via passive OADMs using fiber Bragg gratings (FBGs) for dropping different home channel at each node => no receiver collisions – With FTW-FR node structure, broadcasting & multicasting achieved by turning on multiple lasers simultaneously – Channel access is arbitrated by deploying so-called Request/Allocation Protocol (RAP)

WDM ring networks • RAP – Time divided into fixed-size slots aligned across all

WDM ring networks • RAP – Time divided into fixed-size slots aligned across all W wavelengths – Each slot further subdivided into header & data fields – Slots dynamically assigned on demand by using statically assigned N-1 TDMA Request/Allocation (R/A) minislots – Each minislot comprises one request & one allocation field

WDM ring networks • RAP – Node i ready to send variable-size data packets

WDM ring networks • RAP – Node i ready to send variable-size data packets to node j uses request field of its assigned R/A minislot on j’s home channel to make a request – After receiving request, node j allocates one or more data minislots to node i by using allocation field of its assigned R/A minislot on i’s home channel – After one RTT, node i transmits data packet using allocated data minislots but no more than M data minislots – Benefits of MAWSON & RAP • Simple node architecture & protocol (e. g. , no carrier sensing capabilities required) save costs • Due to in-band signaling, no separate control channel & control transceivers needed • Completely avoids channel & receiver collisions, achieves good throughput & fairness, at expense of overhead & delay

WDM ring networks • Slotted rings w/ channel inspection – Most slotted WDM rings

WDM ring networks • Slotted rings w/ channel inspection – Most slotted WDM rings avoid channel collisions by enabling nodes to check status (used/unused) of each slot – Generally, this is achieved by tapping off some power from fiber & delaying slot while status is inspected – Packet can be inserted in slot at unused wavelength – Typically, node maintains separate VOQs, either for each destination or for each wavelength – MAC protocol has to select appropriate VOQ according to given access strategy • A priori access strategy – Node selects VOQ prior to inspecting slot status • A posteriori access strategy – Node first checks status of slot & then selects VOQ

WDM ring networks • RINGO – Ring optical (RINGO) network uses FTW-FR node structure

WDM ring networks • RINGO – Ring optical (RINGO) network uses FTW-FR node structure – Each node has channel inspection capability built with commercially available components – Nodes execute multichannel empty-slot MAC protocol with a posteriori access strategy • Number of wavelengths equal to number of nodes • Each node has one FIFO VOQ for each wavelength • In tie situations, longest among selected VOQs is chosen – Single bit sufficient to identify status of a given slot => small overhead of empty-slot MAC protocol – No separate control channel & control transceivers required – Variable-size packets can be transmitted without segmentation & reassembly by deploying optical FDLs

WDM ring networks • SRR – Synchronous round robin (SRR) is another empty-slot MAC

WDM ring networks • SRR – Synchronous round robin (SRR) is another empty-slot MAC protocol for unidirectional WDM ring with fixed-size time slots & destination stripping – Each of the N nodes is equipped with one fixed-tuned receiver & one transmitter tunable across all wavelengths on a per-slot basis (TT-FR) – Each node deploys N-1 separate FIFO VOQs, one for each destination – SRR uses a priori access strategy

WDM ring networks • SRR node architecture

WDM ring networks • SRR node architecture

WDM ring networks • SRR protocol – In SRR, each node cyclically scans its

WDM ring networks • SRR protocol – In SRR, each node cyclically scans its VOQs in a roundrobin manner on a per-slot basis, looking for a packet to transmit – First (oldest) packet of selected VOQ is transmitted, provided current slot was sensed empty – If selected VOQ is empty, first packet from longest queue of remaining VOQs is sent – If current slot is occupied, next VOQ is selected for next transmission attempt in subsequent slot according to round-robin scanning of SRR – In doing so, SRR converges to round-robin TDMA under heavy uniform load conditions when all VOQs are nonempty

WDM ring networks • SRR performance – For uniform traffic, SRR asymptotically achieves a

WDM ring networks • SRR performance – For uniform traffic, SRR asymptotically achieves a bandwidth utilization of 100% – However, presence of unbalanced traffic leads to wasted bandwidth due to nonzero probability that a priori access strategy selects wavelength channel whose slot is occupied while leaving free slots unused – A posteriori access strategies avoid this drawback & achieve improved throughput-delay performance at expense of increased complexity – Benefits of SRR • Good performance requiring only local VOQ backlog information • Destination stripping allows for spatial reuse & increased capacity, but raises fairness control problems especially under nonuniform traffic

WDM ring networks • HORNET – Hybrid optoelectronic ring network (HORNET) is unidirectional WDM

WDM ring networks • HORNET – Hybrid optoelectronic ring network (HORNET) is unidirectional WDM ring using destination stripping – Nodes have a TT-FR structure – Similar to SRR, each node uses VOQs, one for each wavelength, and both a priori & a posteriori access strategies can be deployed – Nodes sense availability of each slot by monitoring subcarrier multiplexed (SCM) tones • SCM-based carrier-sensing scheme is more cost-effective than demultiplexing, separately monitoring, and subsequently multiplexing all wavelengths • Instead of wavelength demultiplexer, photodiode array, and wavelength multiplexer, HORNET channel inspection scheme needs only a single photodiode

WDM ring networks • CSMA/CA – Carrier sense multiple access with collision avoidance (CSMA/CA)

WDM ring networks • CSMA/CA – Carrier sense multiple access with collision avoidance (CSMA/CA) MAC protocols are used in HORNET • First CSMA/CA protocol – Multiple different slot sizes according to predominant IP packet size distributions (e. g. , 40 -, 552 -, and 1500 Byte long IP packets) circulate along the ring – Dedicated node controls size & number of slots • Second CSMA/CA protocol – Unslotted – A node begins to transmit a packet when a wavelength is sensed idle – Packet transmission is aborted when another packet arrives on same wavelength – Incomplete packet is marked by adding jamming signal – Aborted transmission is resumed after backoff time

WDM ring networks • CSMA/CP – A more bandwidth-efficient modification of unslotted CSMA/CA is

WDM ring networks • CSMA/CP – A more bandwidth-efficient modification of unslotted CSMA/CA is the so-called carrier sense multiple access with collision preemption (CSMA/CP) MAC protocol • In CSMA/CP, variable-size IP packets do not necessarily have to be transmitted in one single attempt • Variable-size IP packets are allowed to be transmitted & received as fragments by simply interrupting packet transmission • Thus, successfully transmitted parts of original IP packet are not retransmitted => higher channel utilization

WDM ring networks • A posteriori buffer selection schemes – For an empty-slot protocol

WDM ring networks • A posteriori buffer selection schemes – For an empty-slot protocol to be run on HORNET, certain rules must be given to select buffer or packet whenever more than one wavelength channel carries an empty slot – A posteriori selection processes are computationally more complex than a priori schemes – Possible a posteriori VOQ selection strategies • • • Random selection Longest queue selection Round-robin selection Maximum hop selection Channel-oriented TDMA (C-TDMA) selection – Each VOQ is allocated certain slot within a TDMA frame of size W (number of wavelengths) – Random & round-robin buffer selection schemes provide satisfactory compromise between performance & complexity

WDM ring networks • FT-TR rings – Unidirectional empty-slot WDM ring may also use

WDM ring networks • FT-TR rings – Unidirectional empty-slot WDM ring may also use source stripping and nodes with one fixed-tuned transmitter & one tunable receiver (FT-TR) => FT-TR rings • At each node, packets are buffered in single FIFO transmit queue • In applied source stripping, a sender must not reuse the slot it just marked empty => simple fairness mechanism that prevents node from starving entire network • However, destination stripping clearly outperforms source stripping in terms of throughput, delay, and packet dropping probability • Receiver collisions can be avoided in several ways – Recirculating packets on ring until receiver is free – Replacing TR with array of W fixed-tuned receivers – Using optical switched delay lines at destination node

WDM ring networks • Slotted rings with control channel – In some slotted rings,

WDM ring networks • Slotted rings with control channel – In some slotted rings, status of slots is transmitted on separate control channel (CC) wavelength – To this end, each node is typically equipped with additional transmitter & receiver, both fixed tuned to CC wavelength – Benefits of separate CC wavelength • Enables nodes to exchange control information at high line rates • Eases implementation of enhanced access protocols with fairness control & Qo. S support

WDM ring networks • Bidirectional HORNET – Original unidirectional TT-FR HORNET ring architecture can

WDM ring networks • Bidirectional HORNET – Original unidirectional TT-FR HORNET ring architecture can be extended to slotted bidirectional ring whereby SCM is replaced with CC wavelength, one for each direction – CC conveys wavelength availability information that allows nodes to “see” one slot into the future – On each ring, every node deploys one fast tunable transmitter & one fixed-tuned receiver for data, and one transceiver fixed-tuned to CC => CC-FT 2 -TT 2 -FR 4 system – Benefits of CC-based bidirectional dual-fiber HORNET • Preserves advantages of original unidirectional HORNET (e. g. , scalability & cost-effectiveness) • Provides improved fault tolerance against node/fiber failures & survivability – Bidirectional HORNET deploys so-called segmentation and reassembly on demand (SAR-OD) access protocol

WDM ring networks • SAR-OD – SAR-OD supports efficient transport of variable-size packets by

WDM ring networks • SAR-OD – SAR-OD supports efficient transport of variable-size packets by reducing number of segmentation & reassembly operations • Packet transmission from a given VOQ starts in an empty slot • If packet is larger than a single slot, packet transmission continues until it is complete or following slot is occupied • Packet is segmented only if required to avoid channel collision • Segmented packet is marked incomplete • Transmission of remaining packet segment(s) continues in next empty slot(s) on corresponding wavelength • SAR-OD reduces segmentation/reassembly overhead by approximately 15% compared to approach where all packets larger than one slot are segmented irrespective of state of successive slots

WDM ring networks • Segmentation/reassembly – Segmentation & reassembly of variable-size packets can be

WDM ring networks • Segmentation/reassembly – Segmentation & reassembly of variable-size packets can be completely avoided in CC-based slotted WDM rings – To achieve this, each node of unidirectional HORNET ring uses additional transmitter fixed-tuned to the node’s drop wavelength => CC-FT 2 -TT-FR 2 system – Additional transmitter used to forward dropped packets destined to downstream nodes sharing same drop wavelength – Furthermore, each node is equipped with two VOQs for each wavelength, one for short packets & one for long packets – Nodes deploy MAC protocol based on reservation frames

WDM ring networks • Reservation frames – Ring is subdivided into multiple reservation frames

WDM ring networks • Reservation frames – Ring is subdivided into multiple reservation frames with frame size equal to largest possible packet length – In these frames, multiple consecutive slots are reserved to transmit long packets without segmentation – Single reservation control packet containing all reservations circulates on CC – Each node maintains table in which reservations of all nodes are stored – When control packet passes, a node updates its table & is allowed to make a reservation – Additional fixed-tuned transmitter forwards packets concurrently with transmitting long packets – Short packets fitting into one slot are accommodated by means of immediate access of empty & unreserved slots

WDM ring networks • Wavelength stacking – Recall that wavelength stacking was used in

WDM ring networks • Wavelength stacking – Recall that wavelength stacking was used in PSR networks – Wavelength stacking/unstacking allows a node to simultaneously send & receive multiple packets in one slot using only one transceiver – Wavelength stacking can be used to transmit multiple packets in one slot of CC-based slotted unidirectional WDM ring – Wavelength stacking • Time is divided into slots of duration Tp • Each node is equipped with one fast-tunable transmitter & one photodiode • Node starts transmission W time slots before its scheduled time slot, where W denotes number of wavelengths

WDM ring networks • Wavelength stacking

WDM ring networks • Wavelength stacking

WDM ring networks • Virtual circles with DWADMs – In unidirectional slotted ring WDM

WDM ring networks • Virtual circles with DWADMs – In unidirectional slotted ring WDM networks, each node may deploy a dynamic wavelength add-drop multiplexer (DWADM) – As opposed to tunable transmitter & receiver, the input & output wavelengths of a DWADM must be the same – As a consequence, a given node receiving on λi must transmit on same wavelength λi => virtual circles – DWADMs expected to be less expensive than tunable transceivers – However, wavelength utilization expected to be smaller than in TT-TR systems where TT & TR can be tuned to any arbitrary wavelength independently

WDM ring networks • Virtual circles with DWADMs

WDM ring networks • Virtual circles with DWADMs

WDM ring networks • Virtual circles with DWADMs – Virtual circles can be changed

WDM ring networks • Virtual circles with DWADMs – Virtual circles can be changed dynamically according to varying traffic demands – Operation • W data wavelength channels & a separate TDMA control wavelength channel • Nodes exchange (1) transmission requests and (2) acknowledgments over control wavelength channel • W+1 wavelengths divided into three periodically recurring cycles – In first cycle, a control packet sent by a server node collects transmission requests from all nodes – In second cycle, server node sends wavelength assignments/acknowledgments back to nodes – In third cycle, each node with assigned wavelength tunes its DWADM appropriately & starts data transmission

WDM ring networks • Multitoken rings – Slotted WDM ring networks have several advantages

WDM ring networks • Multitoken rings – Slotted WDM ring networks have several advantages • Easy synchronization of nodes even at high data rates • High channel utilization • Low access delay • Simple access schemes – However, variable-size packets are difficult to handle & explicit fairness control is needed – In contrast, variable-size packets can be transported in reasonably fair manner in (asynchronous) token rings • Access controlled by means of token circulating around the ring • Each node can hold token for a certain period of time during which the node can send packets • Due to limited token holding time fairness is achieved

WDM ring networks • MTIT – Multitoken interarrival time (MTIT) is a token-based access

WDM ring networks • MTIT – Multitoken interarrival time (MTIT) is a token-based access protocol for source-stripping unidirectional WDM ring with CC-FTW+1 -FRW+1 node structure

WDM ring networks • MTIT – CC used for access control & ring management

WDM ring networks • MTIT – CC used for access control & ring management – Channel access regulated by multitoken approach • Each channel is associated with one token that circulates among nodes on CC & regulates channel access • Token holding time controlled by target token interarrival time (TTIT) • Token interarrival time (TIAT) defined as time elapsed between two consecutive token arrivals at a given node • Upon token arrival, node is allowed to hold token for TTIT – TIAT • When token holding time is up, node must release token as soon as current packet transmission is completed (or earlier if no more packets are left for transmission) • Node may simultaneously transmit on distinct channels if two or more tokens are concurrently held at node

WDM ring networks • MTIT – MTIT avoids receiver collisions & allows each node

WDM ring networks • MTIT – MTIT avoids receiver collisions & allows each node for simultaneously using multiple data wavelength channels – MTIT achieves low access delay due to the fact that a node may grab a token more frequently than in conventional token rings where a node has to wait for one RTT for the next token – MTIT is able to self-adjust relative positions of tokens & maintain even distribution of them => low variance of token interarrival time & consistent channel access delay in support of high-priority traffic – At the downside, capacity of MTIT expected to be smaller than that of destination-stripping ring networks

WDM ring networks • Meshed rings – In unidirectional source-stripping WDM rings, capacity is

WDM ring networks • Meshed rings – In unidirectional source-stripping WDM rings, capacity is limited by aggregate capacity of all wavelengths – Capacity can be increased by means of destination stripping & resultant spatial wavelength reuse • For uniform traffic, mean distance between source & destination is half the ring circumference => two simultaneous transmissions on each wavelength => capacity 200% larger than that of unidirectional source-stripping rings – In bidirectional rings with shortest path routing, mean distance between source & destination is one quarter of ring circumference => capacity increased by 400% on each directional ring compared to unidirectional sourcestripping => total capacity increase of 800% – Capacity further increased in so-called meshed rings

WDM ring networks • SMARTNet – Scalable multichannel adaptable ring terabit network (SMARTNet) based

WDM ring networks • SMARTNet – Scalable multichannel adaptable ring terabit network (SMARTNet) based on a bidirectional slotted ring network with shortest path routing & destination stripping – Each node connected to both rings, for each deploying a FT WFRW structure – All wavelengths are divided into fixed-size slots whose length is equal to transmission time of fixed-size packet & header for indicating slot status – Medium access governed by means of empty-slot protocol – In addition to N ring nodes, K equally spaced wavelength routers, each with four pairs of input/output ports, are deployed to provide short-cut bidirectional links (chords) – For uniform traffic, SMARTNet (K=6, M=2) increases capacity by 720% compared to unidirectional source-stripping rings

WDM ring networks • SMARTNet – Chords provide shortcuts to the two M-th neighboring

WDM ring networks • SMARTNet – Chords provide shortcuts to the two M-th neighboring routers – Routers r(k+M) mod K and r(k-M) mod K are said to be the M-th neighboring routers of router rk, where k = 0, 1, …, K-1

WDM ring networks • SMARTNet – Each wavelength router characterized by a wavelength routing

WDM ring networks • SMARTNet – Each wavelength router characterized by a wavelength routing matrix that determines to which output port each wavelength from a given input port is routed – Wavelength routing matrix chosen such that average distance between each sourcedestination pair is minimized with a minimum number of required wavelengths

WDM ring networks • Fairness control – In unidirectional WDM rings, each wavelength can

WDM ring networks • Fairness control – In unidirectional WDM rings, each wavelength can be considered a unidirectional bus terminating at a certain destination – In an empty-slot access protocol, upstream nodes have a better-than-average chance to receive an empty slot while downstream nodes have a worse-than-average chance => starvation & fairness issues

WDM ring networks • MMR – Multi-Meta. Ring (MMR) fairness algorithm can be superimposed

WDM ring networks • MMR – Multi-Meta. Ring (MMR) fairness algorithm can be superimposed to SRR in order to enforce fairness – MMR algorithm adapts a mechanism originally proposed for Meta. Ring high-speed electronic MAN • In Meta. Ring, fairness is achieved by circulation of control message, termed SAT (standing for SATisfied) • Nodes are assigned a quota/credit (maximum number of packets) to be transmitted between two SAT visits • SAT is delayed at each un. SATisfied node until either the node’s packet buffer is empty or number of permitted packet transmissions is achieved • Each SATisfied node forwards the SAT on the ring

WDM ring networks • MMR-SS vs. MMR-MS – MMR Single SAT (MMR-SS) • A

WDM ring networks • MMR-SS vs. MMR-MS – MMR Single SAT (MMR-SS) • A single SAT regulates transmissions of all nodes on all wavelength channels • Each node can transmit at most K packets to each destination since the last SAT visit • Each SATisfied node forwards the SAT to the upstream node => SAT logically rotates in the opposite direction with respect to data (but physical propagation is co-directional) – MMR Multiple SAT (MMR-MS) • One SAT is used for each wavelength • Similar to MMR-SS, each SAT circulates together with data packets & is addressed to node upstream of node that emits the SAT • MMR-MS represents better extension of Meta. Ring fairness control scheme to WDM ring

WDM ring networks • M-ATMR – M-ATMR is an extension of asynchronous transfer mode

WDM ring networks • M-ATMR – M-ATMR is an extension of asynchronous transfer mode ring (ATMR) fairness protocol to WDM ring • In M-ATMR, each node gets certain number of transmission credits for each destination • A node gets into inactive state when it has used all its credits or has nothing to send • For credit reset, each active node overwrites so-called busy address field in header of every incoming slot with its own address • A node receiving a slot with its own busy address assumes that all other nodes are inactive • Last active node generates a reset immediately after its own transmission • Reset causes all nodes to set their credits to predefined values

WDM ring networks • DQBR – Distributed queue bidirectional ring (DQBR) fairness protocol is

WDM ring networks • DQBR – Distributed queue bidirectional ring (DQBR) fairness protocol is adaptation of DQDB for CC-based HORNET • In each CC frame, request bit stream of length W follows the wavelength-availability information • A node receiving a packet in VOQ w notifies upstream nodes by setting bit w in request bit stream in the CC that travels upstream with respect to packet direction • Upon reception, each upstream nodes increments request counter (RC) of wavelength w • Each time a packet arrives at VOQ w, the node stamps value in RC w onto packet & then clears RC w • Stamp is called wait counter (WC) • After reaching the head of VOQ, packet must allow frame availabilities on wavelength w to pass by as indicated by WC • WC is decremented for each availability passing by node • Packet can be transmitted when WC equals zero

WDM ring networks • Qo. S support – Many applications (e. g. , multimedia

WDM ring networks • Qo. S support – Many applications (e. g. , multimedia traffic) require quality -of-service (Qo. S) with respect to throughput, delay, and jitter – For Qo. S support, networks typically provide different service classes such as CBR or VBR • In general, traffic with stringent throughput, delay, and jitter requirements is supported by means of circuit switching via resource reservation => guaranteed Qo. S • To efficiently provide Qo. S to bursty traffic, network nodes process & forward packets with different priorities while benefitting from statistical multiplexing => statistical Qo. S

WDM ring networks • SR 3 – Synchronous round robin with reservations (SR 3)

WDM ring networks • SR 3 – Synchronous round robin with reservations (SR 3) is derived from SRR & MMR protocols – SR 3 allows nodes to reserve slots & thereby achieve stronger control on access delays • In SR 3, time is divided into successive reservation frames • Each reservation frame comprises P SRR frames • Each node can reserve at most one slot per destination per SRR frame • SAT messages used to broadcast reservation information – Each SAT contains reservation field (SAT-RF) which is subdivided into N-1 subfields – Each subfield is assigned to a particular node for reservations

WDM ring networks • SR 3 – If node i needs to reserve 1

WDM ring networks • SR 3 – If node i needs to reserve 1 ≤ h ≤ P slots per reservation frame on wavelength channel j, it waits until it receives j -SAT – Node i then forwards reservation request by setting the i-th SAT-RF subfield to value h – When node i receives j-SAT again, all network nodes are aware of the request of node i & reservation becomes effective – Benefits of SR 3 • Guarantees throughput-fair access to each node • Unreserved bandwidth can be shared by best-effort traffic • For multiclass traffic, SR 3 achieves very good separation of different traffic classes

WDM ring networks • Connection-oriented Qo. S support – To enable connection-oriented Qo. S

WDM ring networks • Connection-oriented Qo. S support – To enable connection-oriented Qo. S support in packetswitched WDM ring for real-time services, ring is divided into so-called connection frames – Real-time connections are established by reserving equally spaced slots within successive connection frames – Best-effort traffic is supported by using unreserved & empty slots – Pros & cons • Qo. S approach is able to meet delay requirements almost deterministically • However, it allows for reserving only one fixed-size slot (i. e. , only fixed-size packets are supported)

WDM ring networks • VOQ-based Qo. S support – In addition to W normal

WDM ring networks • VOQ-based Qo. S support – In addition to W normal VOQs, each of the N ring nodes has W real-time VOQs – Packets in real-time VOQs are transmitted via connections in equally spaced reserved slots – On each wavelength, ring is subdivided into frames each consisting of N/W slots, one per destination receiving on that wavelength – A single reservation slot carries connection set-up field & connection termination field, each consisting of N bits sent on a subcarrier – Connection set-up & termination fields are used by a given node to make & release reservations, respectively – Each node keeps track of reservations by maintaining table that is updated when reservation slot passes node

WDM ring networks • MTIT – Qo. S with lightpaths – MTIT protocol can

WDM ring networks • MTIT – Qo. S with lightpaths – MTIT protocol can be extended to support not only packet switching but also circuit switching with guaranteed Qo. S • Solution allows for all-optical transmission of packets with source stripping & circuits via tell-and-go establishment of point-to-point lightpaths with destination stripping • In the latter case, on-off switches at both source & destination nodes of corresponding lightpath are set in off state => spatial wavelength reuse • For all active lightpaths, each node maintains so-called local lightpath table (LLT) that is updated when token passes • So-called token lightpath table (TLT) is sent in each token to broadcast changes of lightpath deployment on wavelength associated with token • Each token has add & delete lists for lightpath set-up & tear-down • A source node holding a token sets up & tears down a lightpath by making an entry in the add list & delete list, respectively