1. Introduction The optical core networks are based almost exclusively on optical transmission, because this technology pro- vides huge bandwidth: A single optical channel typi- cally carries data at a rate of 10 Gbps. In addition, the application of Wavelength Division Multiplexing (WDM) enables that a fibre can transmit more simultaneous sig- nals using parallel channels. Depending on the number of parallel channels we differentiate Coarse Wavelength Division Multiplexing (CWDM) and Dense Wavelength Di- vision Multiplexing (DWDM) systems. In DWDM systems more Tbps can be provided. In such DWDM networks connections between dis- tant nodes are realized using lightpaths that may be defined in advance or on-demand. Each lightpath is a sequence of wavelength channels and traffic enters and leaves it only through its endpoints, so these light- paths can be imagined as pipes laid in the network. The clear purpose of the operator in such networks is to use the available resources efficiently via properly configuring the lightpaths. The network operator faces two problems related to resource allocation: (1) the traffic demands have bandwidths by orders of magnitude lower than the size of a wavelength chan- nel, and (2) the traffic rate fluctuates, so it does not use the whole allocated band- width in the significant part of time. The first problem is sol- ved by the traffic grooming concept [2], while the second is by statistical multiplexing. The two areas have own considerable literature, but as far as we know the effects of joint application of these two solutions haven not been investigated in switched optical network, yet. We aimed this problem in our article. We illustrate the above problem through the follow- ing example. Figure 1. depicts a node with three ports and each port has two wavelength channels. The traf- fic arrives from three different sources while their desti- nations (or the next node along the paths) are the same. The traffic from three sources arrives on different wave- length channels. If wavelengths switching is allowed only (Figure 1.a), then only two of the three flows can be forwarded, thus, the third flow would be blocked at connection setup phase. If traffic grooming is supported, the traffic of all three sources could be combined to one channel. How- ever, the sum of the maximal bandwidths given by traf- fic descriptors exceeds the capacity of the outgoing wavelength channel; therefore, only two of the three flows can be groomed into one channel and a further channel will be defined for the third flow (Figure 1.b). Finally, if we allow that less than the sum of the maxi- mal bandwidth requirements is allocated – the exact method of how to calculate this value will be detailed later –, then all the three traffic flows can be carried in the same channel (Figure 1.c). VOLUME LXI.• 2006/7 17 Applying statistical multiplexing and traffic grooming in optical networks jointly ANDRÁS KERN, GYÖRGY SOMOGYI, TIBOR CINKLER, Budapest University of Technology and Economics, Dept. of Telecommunications and Media Informatics {kern, somogyi, cinkler}@tmit.bme.hu Keywords: dynamic optical network, GMPLS, traffic grooming, statistical multiplexing Multilayer optical core networks are able to provide huge bandwidth. With traffic grooming we can utilize more efficiently the available resources. The principle of grooming: if the routes of two different traffic flows (or demands) have common links, their traffic can be joined in to the same wavelength channel. Another well-known solution for increased efficiency of re- source usage is multiplexing the traffic. The statistical multiplexing does not allocate the maximal bandwidth for each traffic demand, but less than the maximal and more than the average. The aim of this article is to investigate the effects of applying both solutions. Figure 1. Joint application of grooming and statistical multiplexing based aggregation for switching a. Wavelength switching b. Traffic Grooming c. Grooming and aggregation Reviewed