Rule-Based Topology Advertisement Supporting Generalized Protection János Szigeti, Tibor Cinkler High-Speed Networks Laboratory Department of Telecommunications and Media Informatics Budapest University of Technology and Economics Magyar tudósok krt. 2, H-1117 Budapest, Hungary E-mail: {szigeti,cinkler}@tmit.bme.hu Ricardo Romeral Department of Telematic Engineering Carlos III University of Madrid Leganés 28911, Spain Email: rromeral@it.uc3m.es Abstract—Routing in multilayer optical networks can be made efficient if Label Switched Paths are searched in a Wavelength Graph that represents the state and the switching facilities of the network devices very accurately. Maintaining the Wavelength Graph by using the conventional Link State Advertisement control mechanism leads to scalability problem. Much of the link state information is, however, redundant as the set of state changes triggered by a single resource allocation or release are in correlation. By introducing a rule-based topology advertisement and maintenance method, the amount of control messages can be significantly reduced without deteriorating the quality of routing. This paper proposes an extension to the method to be able to handle various protection schemes in the network simultaneously. Although the proposed method is primarily developed for optical networks and Wavelength Graphs it can be applied efficiently also onto pure MPLS networks. Index Terms—path computation, multilayer, topology adver- tisement, protection, shared risk link group I. I NTRODUCTION The communication networks keep growing and are getting more and more meshed. WDM (Wavelength Division Mul- tiplexing) or even DWDM (Dense WDM) systems displace single-wavelength optical transmission. Connections become rather automatically switched than permanently set up by the management plane. All this means a simultaneous growth of multiple factors; the operators of the current core and metro networks, and most of all the Control Plane (CP) of the networks, must cope with an increasing number of devices, fibers, wavelengths and connections together, that all lead to an increasing number of control messages calling for control channels with higher capacity. Much of the controlling overhead is generated by the Link State Advertisement (LSA) task of the Interior Gateway Pro- tocol (IGP). The LSA carries topology information necessary for routing. However, this topology information does not scale well as the network and the number of traffic demands grow, particularly in multilayer networks. There are several proposals on how to reduce the controlling overhead caused by the topol- ogy advertisement: a) we can use time- or bandwidth-based The work described in this paper was carried out with the support of the BONE-project (“Building the Future Optical Network in Europe”), a Network of Excellence funded by the European Commission through the 7 th ICT- Framework Programme. policy for triggering information update [1] with appropriate smart routing algorithms [2], [3], [4]; b) we can send the topology information directly to a dedicated network element instead of flooding it to all controllers in network – as the PCE- PCC (Path Computation Element/Client) model recommends [5]; and c) even in heterogeneous optical networks, we can ap- ply the Rule-Based Topology Advertisement and Maintenance method (RBTA) to exploit the redundancy in the link state information of the crossconnects [6]. Originally, the RBTA was introduced without any support for resilience 1 . Although by means of RBTA the amount of transmitted and stored topology information can be dramat- ically reduced, the lack of internal support of resilience has been a serious shortcoming of the mere RBTA. The current paper aims to eliminate this shortcoming by proposing the Rule-Based Topology Advertisement and Main- tenance with Protection (RBTA-P), an extension of RBTA to support various protection schemes. Taking into account that RBTA was intended to be quite general to describe any kind of opto/electric crossconnect, concerning resilience, RBTA-P also tries to be as general as possible being based on the concept of Generalized Protection Formula (GPF). The paper is organized as follows. In Sect. II we review the RBTA method, section III gives an overview of generalized protection formula. In Sect. IV we define how to extend the RBTA to support protection. In Sect. V we analyze the proposed model comparing it to the existing one by means of complexity and scalability. Finally, Sect. VI summarizes the benefits and requirements of applying RBTA-P. II. REVIEWING THE RULE-BASED TOPOLOGY ADVERTISEMENT Out of the numerous factors that influence the amount of topology information that the control channel has to carry, triggering policies and the PCE act in the dimensions of traffic intensity and network size, however, in an optical network, the 1 In fact, only failure-dependent switchings are not supported by the RBTA. However these involve not only the shared (link, segment or end-to-end path) protections, but also the 1:1 dedicated ones. For restoration and 1+1 kind of protections the mere RBTA is well-suited.