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Fault Recovery in Carrier Ethernet, Optical and GMPLS Networks

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Fault Recovery in Carrier Ethernet, Optical and GMPLS Networks Journal of Communication and Computer 11 (2014) 508-523 doi: 10.17265/1548-7709/2014.06.005 D DAVID PUBLISHING Fault Recovery in Carrier Ethernet, Optical and GMPLS Networks George Tsirakakis Department of Computer Science, University of Crete, Heraklio, Greece Abstract: The trend in the current multiple technology network environment is to reduce the number of network technology layers and form a dual layer, packet over circuit architecture. Carrier Ethernet (for the packet layer), optical networks (for the circuit layer) and GMPLS, are dominant enablers in this scenario. Survivability and robustness will be of critical role for the accomplishment of a transport class of network. This paper describes the fault recovery functionalities in optical, Carrier Ethernet and GMPLS networks, considering the role of GMPLS in each scenario. We overview the currently standardized schemes and published research, evaluate different cases and comment on unresolved issues and required extensions. Key words: Fault restoration, carrier ethernet, PBB, WDM, GMPLS. 1. Introduction Section 4 presents the existing fault recovery extensions in MPLS/GMPLS and its OAM standards. Future networks are going to provide connections Multilayer fault recovery benefits, enabling of high bandwidth and for this reason, survivability technologies and research done are explained in will be a standard requirement. Survivability has been Section 5. studied for many years on different technologies. Optical network survivability is discussed in 2. Optical Network Survivability Section 0 to include all optical networks and the new There are two types of optical networks, photonic requirements they impose, the digital wrapper or all optical (OOO) where no processing of the signal standard (G.709), optical ring, mesh and linear fault is done in the electronic domain and opaque or recovery, the application and the present extensions of semitransparent optical networks (optical electrical GMPLS for optical networks, the main principles of optical), where processing of the signal at nodes is the ASON (automatically switched optical network) done by converting the signal in electronic form. OEO framework and how this could be used for fault networks have the advantage of being more flexible as recovery and finally, fault recovery issues on the smaller granularity traffic channels can be reorganized upcoming OBS (optical burst switching) technology. (separated, monitored, rerouted, merged) after being Section 3 describes current developments in Carrier converted to electronic form. However, they are not Ethernet including OAM standards and fault recovery scalable, since each fibre duct may have thousands of based on this, GMPLS and the new requirements for wavelength channels (to be converted in electrical its introduction in Carrier Ethernet networks, PBB-TE form) and we need one transponder for each (provider backbone bridge-TE) and PLSB (provider wavelength channel. OOO networks have the link state bridging) with possible fault recovery disadvantage that it is difficult to perform fault schemes and packet ring topologies fault recovery. localization or other essential functions for Corresponding author: George Tsirakakis, Ph.D., research survivability (such as performance monitoring) of the fileds: carrier networks, fault recovery, multilayer networks, data signal. They also require a dedicated channel network management & control. E-mail: [email protected]. Fault Recovery in Carrier Ethernet, Optical, and GMPLS Networks 509 (possibly a separate wavelength) for the indicators, tandem signal performance monitoring etc. control/management and the OAM signals, as these The new FTFL (fault type and fault location) bytes need to be processed in electrical form and finally can carry fault information at section or tandem end they are prone to signal degradation in the absence of points to help the system localize the fault. Each regeneration. OEO have their control and OAM wavelength has this type of overheads applied to the channels transported along with the data signal (in information that it carries and is added to the user overhead bits) and can make use of the already information as this enters the optical layer. available survivability framework of SDH/SONET In addition to the GCC overheads and after the (ITU G.782). These facts make a direct impact on the signals are converted in optical form, all wavelengths survivability processes. are supported by overheads in the OSC channel, All optical networks are not going to be out-of-band. This type of overhead can be processed commercially popular for some years ahead. In the in all optical networks. The advantage of this out of mean term, optical signals are going to be processed band OSC channel arrangement is that only this in electronic form. In any case, we need to administer channel may be processed (by converting it to the light paths in the WDM network either if it is an electronic form) in the all optical network, without OOO or an OEO network. If we were going to depend having to process data in each wavelength. Fig. 1 on SDH/SONET overhead and OAM functionalities, shows such an arrangement. OSC overhead then all signals that enter the optical network need to information is per OCh (wavelength), per OMS be in SDH/SONET format. To avoid this limitation, (between multiplexers) and per OTS (fibre level). In ITU G.709 recommendation [1] defines the signal [3 Section 6.2] recommendations for the OTN OAM structure between WDM optical nodes, and the new are given, for each of the three (OCh, OMS, OTS) overhead information in this signal, to manage this optical layers. multi-wavelength optical network and the light paths OSC can be used to carry signal traces, defect in it. Among others, it defines a new set of overheads, indicators and APS messaging. One of the which are going to be processed in electronic form, to disadvantages of using an out of band channel like guarantee the signal integrity. Its architecture is quite OSC, is that if per wavelength functions need to be similar to that of SDH/SONET but extended (e.g., applied, some mechanism has to exist to enable Enhanced FEC and six levels of flexible operator wavelength identification. An alternative to OSC for defined Tandem Connection Monitoring). G.709 carrying overhead information is subcarrier refers to the OTN (optical transport network), an modulation on each wavelength frequency. Out of optical network which will be able to transport any band OAM will allow support of any client signal type of client signals (e.g., SDH or Ethernet) and this such as gigabit Ethernet, ESCON, cable video signals is possible by avoiding the dependence on the etc., as overhead format is now independent of the SDH/SONET frame format as explained. G.709 defines seven layers of overheads for network administration, four in band (in the GCC— General Communications Channel) and three out-of-band (in the OSC — Optical Supervisory Channel) [2 Section 9.5.7], [1]. GCCs are used to enable APS, FEC, transfer of GMPLS or other ASON (Section 0) signalling, backward and forward defect Fig. 1 OSC channel processing. 510 Fault Recovery in Carrier Ethernet, Optical, and GMPLS Networks data format. reduce this phenomenon while the existence of a As the hardware technology for optical nodes is still coordination mechanism could provide more optimal developing, the techniques for survivability will also reroutes. In Ref. [8] a scheme is explained for adapt accordingly. For example, it is expected that improving contentions of wavelength reservations future optical nodes will be able to do signal during distributed rerouting. processing in the optical domain by using optical logic While light paths are operational, backup resources gates and optical flip-flops [4], performance should be preferably used, if not needed for backup. monitoring [5] by measuring the spectrum and employ Wavelength numbers are reserved (to be used when all optical regenerators. A review of technologies for the backup is needed) but are not allocated (no cross optical network devices is given in Ref. [2]. At connections are made) in order to be used in normal present, reconfigurable optical nodes such as network conditions by extra traffic. ROADM and the use of tuneable lasers facilitate the Ring protection schemes are classified according to introduction of dedicated control plane such as whether they reroute individual channels (paths) or GMPLS by which recovery functions can be enforced. spans, and if resources in the ring can be shared (more In the optical layer, rerouting is done either per bandwidth efficient) or not. Path switched rings allow optical wavelength (OCh), per waveband (set of per path choice of recovery, with the possibility for wavelengths), or per fibre (optical multiplex section— this path recovery to be combined with another (e.g., a OMS). Waveband routing [6] combines the switching client) recovery scheme. Rings can be interconnected port savings of per fibre routing and the flexibility of in a hierarchical or flat architecture and be connected the smaller (to fibre routing) granularity, of by dual homing with an OXC or OADM. In Ref. [9] wavelength routing. an optical APS protocol is proposed for optical rings, In optical networks, an additional constraint is which is implemented as an IP lightweight protocol naturally presented in the rerouting process, that of the over OSC. ITU G.873.2 specifies ring protection but wavelength continuity. The wavelength (frequency) of is still under development. More information on the light has to be the same in all links along the path. transparent optical rings can be found in Ref. [10]. The use of wavelength converters can remove this while Ghani and Guo [11] provided description of constraint, and can allow bandwidth on the network to issues related to optical ring protection. be used more efficiently, but they also have a very Linear protection in optical networks is specified in high cost (at present they require conversion to ITU G.873.1 recommendation.
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