We propose a packet-switched WDM slotted ring network with destination release. The total bandwidth of each channel is divided into a fixed number of equal-sized slots. The nodes are equipped with fixed transmitters and tunable receivers. Control information, which is transmitted on a specific wavelength, is electronically processed at every node while the payload is kept in the optical domain. This reduces packet-delay and provides protocol and bit-rate\ud
transparencies. Among other issues involved in the design of such a network, we discuss a node

Dey, D.

Koonen, A.M.J.

Salvador, M.R.

English

We propose a packet-switched WDM slotted ring network with destination release. The total bandwidth of each channel is divided into a fixed number of equal-sized slots. The nodes are equipped with fixed transmitters and tunable receivers. Control information, which is transmitted on a specific wavelength, is electronically processed at every node while the payload is kept in the optical domain. This reduces packet-delay and provides protocol and bit-rate transparencies. Among other issues involved in the design of such a network, we discuss a node architecture that takes into account multicasting and problems related to fiber dispersion

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Network architecture of a packet-switched WDM LAN/MAN

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Network Architecture of a Packet-switched WDM LAN/MAN

 	 !!"#$%'&()* ,+.-0/)123547688894;:<* =>2,4?%/)A@BC2C/)D* 1)	Network Architecture of a Packet-switched WDMLAN/MAND. Deya, A.M.J. Koonenb and M.R. Salvadoraa Centre for Telematics and Information Technology (CTIT), University of Twente, Netherlandsb Bell Labs, Lucent Technologies, Huizen, NetherlandsE-mails: a{dey, salvador}@cs.utwente.nl; bkoonen@lucent.comWe propose a packet-switched WDM slotted ring network with destination release.The total bandwidth of each channel is divided into a fixed number of equal-sizedslots. The nodes are equipped with fixed transmitters and tunable receivers.Control information, which is transmitted on a specific wavelength, iselectronically processed at every node while the payload is kept in the opticaldomain. This reduces packet-delay and provides protocol and bit-ratetransparencies. Among other issues involved in the design of such a network, wediscuss a node architecture that takes into account multicasting and problemsrelated to fiber dispersion.1. IntroductionWith the successful deployment of Wavelength Division Multiplexing (WDM) in corenetworks, access networks are the next bottleneck. The advantages of successfuldeployment of WDM accompanied by packet switching in local area networks (LANs)and metropolitan area networks (MANs) are incontrovertible. One very promisingattribute is efficient usage of network resources. Time-slotting may be considered as oneof the techniques useful in realizing a packet-switched network.Conceptually time-slotting is similar to time-division multiplexing (TDM). In time-slotting bandwidth of each channel is split into equal number of time-slots of fixed length(duration). A lot of work has been done on similar architecture, some of which include[1], [2], [3] and [4].In this paper we present architecture of a WDM LAN/MAN that goes beyondthese works by incorporating aspects such as fault tolerance and multicasting. We alsodeliberate upon issues that need to be considered in the successful design of such anetwork.2. Network ArchitectureWe consider a slotted multi-channel WDM network laid out as a ring. The nodes areinterconnected with fiber carrying W channels. Bandwidth of each of the channels isdivided in time domain into equal and constant number of mini-slots of fixed length thatcirculate around the ring. One of the W channels is reserved for carrying controlinformation and the header. We call a mini-slot on the control/header channel a headermini-slot. The remaining W-1 channels are used to carry the payload (i.e., data). We callthe mini-slots on these channels payload mini-slots.  The basic structure is as shown in figure 1a. The network consists of segmentrings connected to a backbone ring via optical cross-connects (OXCs). Nodes in segment6EF@BC2 0 >/ 23C2C   =01  71)C2D	 % 23/)	 : #%@0"%@rings are add-drop multiplexers (ADMs in figure 1a). Their function is either to drop apayload destined to it or to add a payload if a mini-slot is empty.Each node on the ring is able to transmit on a fixed wavelength but is able toreceive at any wavelength. This is shown in figure 1b. A fixed wavelength channel, λc, isreserved for transmitting the header and other control information. Except for the headermini-slot on λc, payload mini-slots on the other W-1 wavelength channels aresynchronized such that they reach each node all at the same time. The header mini-slot issynchronized with the payload mini-slots such that the header mini-slot arrives a littleahead of the payload mini-slots.The header mini-slot contains information about the payloads that are carried bythe payload mini-slots on each wavelength. The header-information tells each node if thepayload on any wavelength is or is not destined for that node. It also tells the node if themini-slot on its transmitting wavelength is empty.One of the major issues that we need to deal with in such a network is dispersion.As a result of dispersion, different channels may suffer from varied delay times. Thus, themini-slots on the various channels may lose their synchronization. In the followingsection, we design a node that is capable of dealing with this issue and thereby maintainthe required level of synchronization.OXCOXCOXCADMOXCADMADMADMADMADMBackbone SegmentN0N7 N1N5N6 N2N4N3w0w3SlotsFigure 1a - Multi-ring WDM network Figure 1b - Segment ring; W=4; N=83. Node ArchitectureThe node architecture is as shown in figure 2. The incoming data first goes through aslowly tunable λ-drop. This separates the header wavelength channel from the payloadwavelength channels. The payload mini-slots are then delayed in a fiber delay line. Thisdelay should equal the header processing time. The payload slots then go through aslowly tunable λ-drop, which selects the wavelength channel (λx in figure 2) that is to beused for transmitting data (provided the slot is already empty or will become empty atthis node). The remaining wavelength channels are de-multiplexed. According to theinformation contained in the header, the tri-state switch (switch A in figure 2) is either inthe bar, split or cross-states. The availability of switches operating in three states (cross,bar, split) enables all-optical multicasting of data-packets. The remaining wavelengthchannels are sent through a coupler, which drops 10% of the power to each of the6E6 	 !!"#$%'&()* ,+.-0/)123547688894;:<* =>2,4?%/)A@BC2C/)D* 1)	receivers. The remaining 90% of the power is allowed to pass through and thewavelength channels are then multiplexed. Based on the header information it is decidedwhether the 10% of the dropped power (at the couplers) is or is not meant for the node.If it is not it is simply discarded. The concept not only allows optical multicasting, but isalso important for simultaneous reception of multiple wavelengths. The input wavelengthchannels and the header wavelength channel are then consecutively added using a slowlytunable λ-add.As mentioned earlier the header mini-slot and the payload mini-slots aresynchronized such that the header mini-slot is slightly ahead of the payload mini-slots.This is to take into account the switching time after the header information is processed.Here it is important to note that the switching time is different from the header-processing time. For the header-processing time we make use of fiber-delay lines,whereas, for the switching-time (that is required after the header is processed) we allowthe header mini-slot to arrive at the node slightly ahead of the payload mini-slots.As mentioned in section 2, one of the drawbacks of such a network is dispersionbecause of which the slots on different wavelength channels may lose synchronization.This is however taken care of in our node architecture. Every time a node generates datait sends a regenerated signal whose time of transmission can be controlled within adesired level of accuracy. Such regeneration occurs at least once in one completerevolution around the backbone ring. This is because destination-release leads to slot-reuse. The time of transmission of the new payload mini-slot can be controlled such thatthe new payload mini-slot is generated exactly some fixed amount of time after theheader mini-slot is transmitted from the node.Figure 2. The node architecture6E @BC2 0 >/ 23C2C   =01  71)C2D	 % 23/)	 : #%@0"%@It is important to realize that in the event of a failure of the transmittingwavelength channel of a node, the node is not able to communicate at all. Therefore, weneed to take some measures to deal with this problem and to provide some faulttolerance. A close look at figure 2 indicates that the wavelength converter along withslowly tunable add-drops deal with this problem. The wavelength converter is able tomatch any incoming wavelength (carrying the data to be added in the node) to thespecific add wavelength of this node. In the event of a failure of the wavelength channelλx, the wavelength-converter can convert to a reserved wavelength channel fortransmitting data, in which case the slowly tunable λ-drop and λ-add can also tune toadd or drop this newly selected wavelength channel. The other pair of slowly tunableadd-drop takes care of a possible failure of the header channel, λc.ConclusionWe have designed a packet-switched WDM LAN/MAN. The network is fault-tolerant inthat it can switch to a reserved wavelength channel in the event of a failure in the control(header) channel or a channel at which a node is transmitting. We have also dealt withthe problem of dispersion, which is a dominant factor in such types of networks. Ournode architecture enables multicasting in the optical domain. The tri-state switch (switchA in figure 2) has to be fast enough to achieve high bit-rates. The payload is always keptin the optical domain. This is important in achieving bit-rate transparencies.AcknowledgementsThis research is supported by the Dutch Technology Foundation STW, applied sciencedivision of NWO and the technology program of the Ministry of Economic Affairs of theNetherlands.References[1] J. Fransson, M. Johansson, M. Roughan, L. Andrew and M. Summerfield, "Design of amedium access control protocol for a WDMA/TDMA photonic ring network," Proc. ofGlobecom ’98, (Sydney, Australia), pp. 307-312, November 1998.[2] I. Chlamtac, V. Elek, A. Fumagalli, and C. Szaba, "Scalable WDM access networkarchitecture based on photonic slot routing," IEEE/ACM Transactions on Networking, vol.7, no. 1, pp. 1-9, 1999.[3] S. M. Gemelos, K. Shrikhande, D. Wonglumsom, I. White, T. Ono, and L. G. Kazovsky,"HORNET: A packet-switched WDM metropolitan area network," Proc. CNIT ’99(Portofino, Italy), pp.260-276, 1999.[4] C. -S. Kang, B. -S. Park, J. -D. shin, and J. -M. Jeong, "A broadband ring network:Multichannel optical slotted ring," Computer Networks and ISDN systems, vol. 27, pp.1377-1398, 1995.6E 

Dey, D

Koonen, AMJ Ton

Salvador, MR

Repository TU/e

A broadband ring network: Multichannel optical slotted ring,&quot;

Design of a medium access control protocol for a WDMA/TDMA photonic ring network,&quot;

HORNET: A packet-switched WDM metropolitan area network,&quot;

Scalable WDM access network architecture based on photonic slot routing,&quot;

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Network architecture of a packet-switched WDM LAN/MAN

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