architecture for IP/WDM networks
B.3 Performance evaluation
Some results on the performance of the unified control plane model, in terms of sub-lambda restoration, are presented in this section. The network parameters used for this analysis are the same as the ones used for the evaluation of the hybrid provisioning techniques in Section3.4.2.
Figure3.12compares the optical layer-based restoration capability of the uni-fied model (restoring sub-lambdas using the LOG-HYB-RWAsequence) with that of the conventional path-based restoration (restoring full lambdas) [24].
The fault is a link cut that brings down all four fibers in the trunk (a maximum of 16 wavelength channels can fail). The results in Figure3.12show the percent-age of restored bandwidth for the two approaches, and demonstrate that when the granularity of the restoration is on a per-call basis, much more percentage of the bandwidth affected can be restored. It is interesting to note the oscillations that the conventional path-based lightpath restoration exhibits when the network operates at higher loads. This is because the load increase is a feedback factor
The optical control plane 67
500 1000 1500 2000
10 20 30 40 50 60 70 80 90
Load (erlangs)
% BW restored
OTN call restoration OTN lightpath (conventional) restoration
Figure 3.12 Optical layer-based sub-lambda restoration. (From [24], Figure 2.
Copyright 2003 IEEE. Used by permission of The Institute of Electrical and Electronics Engineers Inc.)
in the restorability of the network. When the network is highly loaded, then the fiber cut causes more lightpaths to fail, leading to more network resources being freed. These resources could, in turn, be reused to restore some of the affected lightpaths. This can effectively, in some cases, provide a network with higher restoration capability at higher loads.
C. GigE/WDM network infrastructure
Afurther advantage is that this unified model is not confined to IP-over-WDM networks but could also be applied, for example, to GigE/WDM network infras-tructures where native Ethernet frames are mapped directly over WDM [28]. Uti-lizing the unified optical layer-based control plane to manage both GigE switches and OXCs can allow for the transport of native Ethernet (layer-2 MAC frame-based) end-to-end (from the access network through the metro and core networks to another access network), bypassing unnecessary translation of the Ethernet data traffic (the majority of enterprise data traffic) to some other protocol and then back to Ethernet at its destination. Such a network will diminish the role of SDH/SONET, and will combine the simplicity and cost effectiveness of Ethernet technology with the ultimate intelligence of WDM-based optical transport layer, to provide a seamless global transport infrastructure for end-to-end transmission of native Ethernet frames.
68 G. Ellinas, A. Hadjiantonis, A. Khalil, N. Antoniades, and M. A. Ali
3.5 Conclusions
This chapter presented an overview of the Generalized MPLS that has been widely viewed as the basis for the control plane for optical networks and then pre-sented a new unified optical layer-based control plane for the IP/WDM networks.
This model uses IP/MPLS-aware, non-traffic bearing OXC controller modules located within the optical domain to manage both routers and optical switches.
Utilizing this model, the optical layer can provide lambda/sub-lambda routing, signaling, and survivability functionalities, and can also enable the end-to-end management of the network (from the access network through the metro and core networks to another access network), across multiple ASs. A further advantage is that this model is not confined to IP-over-WDM networks but could also be applied, for example, for GigE/WDM network infrastructures where native Eth-ernet frames are mapped directly over WDM. This infrastructure will combine the simplicity and cost effectiveness of Ethernet technology with the ultimate intelligence of the WDM-based optical transport layer.
Clearly, any implementation of an optical control plane will depend primarily on its interoperability with legacy infrastructure. Furthermore, ease of use and reliability is critical for network operators who manage these types of networks.
The optical control plane implementation will depend on the choice of a design that can show improved decisions for provisioning, restoration, and overall effi-cient management of network resources, which will ultimately lead to reduced network operational expenses [43].
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