Performance monitor for all-optical networks based on homodyne spectroscopy

9:45am-I0:00am TuC4 Cross - Connection Management Specialisation for WDM - OTN's Albert Rafel (l), Josep Prat, Jaume Comellas, and Gabriel Junyent Polytechnical University of Catalonia (UPC), Campus Nord D4-SlO8, Jordi Girona 1-3, 08034 Barcelona, Spain. Tel./Fax :+34 93 401 6441/+34 93 401 7200. (1) E-mail address: [email protected] 1. Introduction Future WDM Optical Transport Networks (WDM-OTN) will use new all-optical nodes that will perform functions such as routing, restoration and protection directly in the optical domain, using wavelength as a new network resource. They will require new levels of management and supervision to ensure its proper operation and the quality of payload delivery. A key word in future Om's is evolution, both in terms of traffic growth and technology availability. Hence, networks' topology and nodes' architecture will need careful design in order to meet operator's requirements regarding adaptability, scalability, modularity and transparency. Several European funded projects such as MEPHISTO and MOON have addressed the needs for OTN Management Systems Support, proposing layered management object information models for standardisation [ 11, [2]. This paper presents a new approach for the Optical Cross-connect (OXC) routing operation that takes into account a diminished connection capability. 2. New class definition Connection capability of an OXC may be diminished mainly for three reasons. The fmt one is external to the OXC and comes from the impossibility of certain output optical links to carry specific client signals due to e.g. PMD. The second reason is internal and arises from a component's failure thus precluding a number of connections. The third reason is also internal and results from the connection nature of the OXC structure, which is not strictly non-blocking (strictly nonblocking means that an input channel can always reach any output channel). When managtng an OXC with diminished connection capability, attainable output ports depend on both the number and the way the existing connections have been established. Hence an updated list with idle/available connections between inputloutput ports becomes necessary, which can be represented in a matrix format, and shall be called Node Status Matrix (NSM) from where the real internal OXC capabilities can be clearly and easily seen. Figure 1 shows an example where two connections have been established in a 4x4 OXC with 4 channels per fibre. The first sub-index indicates the input fibre and the second the input wavelength number. The NSM depicted in Figure 1 shows a connection between h3,2 + I,, precluding any connection between h3.1, h3,3, h3.4 -+ h1.3, h3.1, h4.2. An analogous case is shown for connection between h4.3 -+ To manage this matrix we propose a specialisation of the cross-connection fragment new class is derived from the generic object classfubn'cR1, which itself derives fromjbbn'c. 3. OXC routing functional description Relation between inputloutput channels can be described through the Wavelength Transfer Matrix (WTM) [4]. The knowledge of the WTM allows the systematic and simple resolution of the controls and their operation to establish any connection. The list of these controls can be written in a matrix format, which we call Routing Control Matrix (RCM). It is architecture depexident showing all physical paths f?om any input to any output port. Since there may exist more than one path between inputloutput ports, each RCM element is a vector every element of which is one out of n possible routing paths between input and output (i.e. [PI, P2, . . . , Pn]). In general, the dimension of all vectors in the RCM will be the same. However, there are cases where the OXC architecture may not be symmetric for every input channel and thus vector dimensions might be different. The network node agent uses the RCM to efficiently perform dynamic routing, connection rearrangement, and Node Status Matrix (NSM) updates. NSM is an abstraction of the RCM and, while the latter is implementation dependent, the NSM is implementation independent. 4. Example of RCM and NSM usage The OXC structure depicted in Figure 2 is link modular where the routing mechanism consists of Wavelength Converters (W-C) followed by Arrayed Waveguide Gratings (AWG). nfferent modules are then interconnected through Star Couplers (SC) to the output fibres. This structure is rearrangeably non-blocking, (i.e. any connection can be established re-configuring 0-7803-5947-xl00/$10.0002000 IEEE 167 pre-estabiished connections), therefore some connection requests may be rejected because pre-established connections cannot be interrupted unless for protection purposes. Connection requests are considered successfully established when the input channel can be routed to the requesfed output fibre no matter at which wavelength. Blocking probability is defined as the ratio between rejected and total requests. To demonstrate the usage and show the usefulness of the RCM and NSM, we evaluate the blocking probability as a function of active channels. We will compare the blocking probability applying two different routing algorithms. The input traffic is considered uniformly distributed. 100 so. - Bbcking (Random) -B&hing (EM sltategy) -Total Blocldng (R”) -Total Blockhg (ESM st-) so. 2040 w) 60 m so m im ktiw Channels (n) Figure 3. Block probability using two routing approaches. Figure 2.4~4 OXC arch. with 8 wavelengths per fibre. To simulate the OXC operation, we randomly generate connection requests, with equal probability, from a list of idle input/output OXC channels. If the connection is not available it is blocked and registered, and then we generate a different request. Otherwise, we look at the RCM to find all possible paths and the controls to be operated. Following a routing algorithm, we choose one path, update the NSM and then register the connection. The blocking probability is calculated and another request can be processed. When the NSM is 111 (no more connections are available) it is reset and a new iteration begns. Tlus process is continued until the blocking probability value is stabilised for each active channel. Simulations address two different routing approaches. The frst approach randomly chooses an available path from the RCM. The second approach applies a routing strategy we call Emptiest Status Matrix (ESM). This strategy evaluates every NSM after each possible path is tried, and chooses that precluding less unused connections, which is the option that leaves more free elements in the matrix. If there are more than one most effective option, the choice is made at random. Results are drawn in Figure 3 showing a sensible improvement when the ESM has been applied. A blocking of 10% is reached for 66% and 80% of active channels with and without routing strategy respectwely. The peak values are 70% and SOYO reached at 90% and 94% of active channels respectively. A drawback of this structure is that it becomes completely blocked, i.e. no more connections are possible even when there are idle input/output OXC ports and the NSM becomes completely full. Usable OXC without total blocis 88% of active channels and 94% when ESM has been applied. Besides, the peak total blocking is 91% and 67% respectively (see Figure 3). NSM is an abstraction of the RCM and hence the node element agent must update it. Nonetheless, the implementation independence and the binary nature of the NSM ease the OXC manageability what represents a clear advantage for the Configuration and Protection Manager. Moreover, new threshold parameters can be defined in the NSM to deal with traffic capacity exhaust, what can be used by the Performance Manager. 5. Discussion A new object class has been proposed for the cross-cohection fragment of the Information Model what represents a specialisation for routing sub-networks in WDM transport networks. This class allows the manager to operate crossconnecting nodes with diminished connection capabilities. Using a new notation methodology to describe an OXC routing bctionality (WTM), the Routing Control matrix (RCM) can be found. WTM and RCM are a clear way to describe completely the architecture and operation of the cross-connecting sub-network. A new matrix called Node Status Matrix has been defined from a Management point of view that relaxes the processing and memory requirements and minimises messaging information. This Matrix along with the RCM allows a pro-active management approach from the Network Element Level. To demonstrate all these advantages, we have evaluated the internal blocking probability (as a function of active channels) of an OXC structure used as an example, which is not strictly non-blocking. Definition of the NSM has allowed us to apply a simple routing strategy that has lead to a sensible decrease in the OXC internal blocking probability. 6. References [l] S.Tomic, et al., ACTS MOON Deliverable, No. A231.P01.120.DS.P.022.b1, December 1998. [2] L.Berthelon, et al, ACTS MEPHISTO Deliverable, No. AC0209/UPC/TSC/GCO/P/Ol7/bl, June 1999. [3] ITU-T Recommendation M.3100, July 1995. [4] K.Oguchi, J. of Light. Tech., Vol. 14, no. 6, pp. 1255-1263, June 1996. 168