The survivability of optical/wireless communication Network in the Physical Layer module has been discussed with the help of Fiber Span Layout Demand Distribution in the previous chapter. The present chapter deals with Fiber Network User Service Survivability [FNUSS] in the Physical Layer Module.
Manonnet Singh et.al. discussed network connectivity parameters in optical networks, using the Hubbing Span Architecture as shown in the Fig. 3.1 and table 3.1. This architecture supports only the small demand cross connectivity of 1 X 5 node connectivity fiber optic facility links with single failure mechanism. Ondaria. J. et.al. extended the work of Manonnet Singh et.al. by introducing 1:1 restoration mechanism which is limited to a number of elements of fiber optic facility and demand distribution rate as shown in the Fig.3.2 and table 3.2. They suggested the possibility of other Restoration Schemes such as Automatic Protection Switching (APS), 1:1, 1+1, 1:N and Diverse Protection (DP) inorder to achieve better survivability. However they did not extend their work in these directions.
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The present discussions and simulations of Fiber Network User Service Survivability (FNUSS) are estimated for N X N node configuration in Point-to-Point Span Architecture with Survivable Protection switching System (SPSS) methodology. This type of architecture is presented for the first time in the literature (53) and is very much significant from the survivability point of view. This architecture not only measures the link survivability but also measures the network survivability. This architecture ensures protection against the failures at DS1 and DS3 levels also and enhances the demand distribution rate to as high a value of 86% compared to 20% earlier.
This program is implemented successfully to estimate the failures in network survivability in terms of Detection, Routing Selection, Rerouting and Return to Normal Mode at the DS1 and DS3 levels. The same has been extended to determine the integration of the Restoration Schemes in order to support the large number of demands of fiber optic facility links in Point-to-Point Span Architecture.
Through the proposed point-to-point Span Architecture, User Service Survivability demand distribution of a 8 X 8 node complex network has been configured and the related parameters like Demand Routing, Multiplexing and Restoral Schemes have been computed by using Fiber Network User Service Survivability (FNUSS) algorithm.
SURVIVABILITY PROTECTION SWITCHING SYSTEM (SPSS)
In the Survivable Protection Switching System (SPSS) notations like Automatic Protection Switching (APS), 1:1, 1+1, 1:N etc. are widely used in the context of survivability systems. 1+1 protection switching system denotes a dedicated standby arrangement in the working system by using a line signal in APS. The switching speed of 1:1 APS is, however, slightly slower than 1+1 because the transmitted signal is not bridged all times in the survivability aspect.
1:N APS denotes that N working systems share one standby protection system arrangement. The significance of a 1:N APS system is only to protect against single channel of fiber failures by using a standby channel within the system itself. The standby need not be diverse routed because there is no capability with 1:N APS to protect against a complete cable cut.
Network survivability can be accomplished by quick recovery from network failures and maintaining the required existing services in cluster mechanism. With the increasing sophistication of network technologies, survivability capabilities are becoming available at multiple layers, allowing for protection and restoration to occur in multiple layers of the network. Network survivability has become an issue of great concern for the internet community. As network technologies continue to improve converge, protection and restoration schemes are being developed with parameters like time-scale of operations, resource efficiency and etc.
FIBER NETWORK USER SERVICE SURVIVABILITY
The present work on Fiber Network User Service Survivability Ratio configurations are designed as shown in the Fig.3.3. It represents a global network to estimate the parameters like Restoration Link Demands (RLD), Demands and Survivability Ratio(%) with respect to different demand distributions.
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They are defined as
- Restoration Link Demands (RLD): It is defined as the total demands after link failure in a given network connectivity.
- Total Demands: Sum of the demands of individual links.
- Survivability Ratio (SR) (%) It is given by Restoration Demands to the Total Demands in a given network connectivity. SR (%) = Restoration Link Demands/ Total Demands [3.1]
Network survivability is measured based on the type of network such as switched and non-switched networks. The appropriate survivability measurement in general would be the percentage of the circuits lost due to a network component failure. For switched fiber networks, the measurement would be the average network blocking due to a failure or the average number of lost calls due to a failure. Non-switched survivability measurement can also be evaluated in a worst average case, depending upon the user's point of view . The average survivability measurement is the failure probability of each network component and the average restoration time from User Service Survivability configurations (USS) point of view.
Service survivability is measured similar to network survivability but is viewed from a user perspective and its flow chart is as shown in Fig.3.3 and the program is given in Appendix - B. Acceptable network survivability does not imply an acceptable user's service survivability. For example, if only a single path connects a customer and the serving CO and that single path fails, the customer will lose the service even if the network is protected on a 1:1 basis (i.e. 100 percent survivability). Hence 1:2/DP is employed and results are obtained
For example assuming du1=6 DS1s, du2=3 DS1s, and du3=4 DS1s, where dui is the DS1 demand requirement between user Cu and user Ci. For example, if DS1 demands between pair (Cu, C1) are routed through path cu-CO-1-CO-3-CO-2-C1 and If the link between CO-2 and CO-3 fails, it disconnects the path between customers Cu and C1. Now 3 DS1s can be restored as when a 1:2/DP system is engineered for the fiber span between CO-2 and CO-3. Thus, the service survivability from customer cu's point of view is 77 percent when the link fails because the total number of DS1s that are still intact from customers Cu's point of view is 10 (3+3+4) compared to a total of 13 DS1s earlier. However, a number of interesting problems and challenges arise in the domain of Physical Layer in network architectures, interworking with IP routing and resource management protocols.
The survivability networks are expected to meet a growing volume of requirements imposed by new applications such as multimedia streaming and video conferencing. In order to satisfy these requirements, a common approach is to use two disjoint paths between the source and the destination nodes, the first serving as a primary path and the second as a restoration path. Such an approach referred to as path restoration has several advantages, the major one being the ability to switch promptly from one path to another in the event of a failure. Since network resources are allocated along both primary and restoration paths, it improves the overall network performance. It also describes the fundamental problem of finding two disjoint paths that satisfying the constraints at an optimum level.
The simulation results for Network Survivability and Fiber Network User Service Survivability parameters are obtained for different types of traffic multi node-to-node connetivities like 3 X 3, 4 X 4, 5 X 5 and 8 X 8 by using 1:2/DP are as shown in the tables 3.1[a] USSR - 1 X 5 Node Connectivity PPSA, 3.1[b] SR parameters for 1 X 5 Node Connectivity, 3.2[a] USSR - 3 X 3 Node Connectivity- PPSA, 3.2[b] SR parameters for 3 X 3 Node Connectivity, 3.3[a] USSR - 4 X 4 Node Connectivity- PPSA, 3.3[b] SR parameters for 4 X 4 Node Connectivity, 3.4[a] USSR - 8 X 8 Node Connectivity- PPSA, 3.4[b] SR parameters for 8 X 8 Node Connectivity respectivitely.
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In the previous work Manonnet Singh et.al and Ondaria. J. et.al. worked the 1 X 5 node connectivity by using Hubbing Span Architecture and their results are as shown in tables 3.5 and 3.6.
However the Survivability Ratio (SR) factor in the network survivability was 20%.Using Point -to -Point Span Architecture, the parameters like Demand Connectivity in an integrated approach results in the SR factor is 86%.
The Hubbing Span Architecture Proposed by Manonnet Singh Group analyzed the User Service Survivability from a single user point of view. The connectivity is established from node-to-node for a simple network and also provides for a single link failure. The survivability of the Hubbing Span Architecture cannot be measured from multi user point of view.
The Ondaria.J. Group examined the network connectivity parameters by using restoration schemes such as APS, 1:1, 1:N and DP individually in Hubbing Span Architecture for limited number of demands. This architecture ensures a slightly better performance in single link failure mechanism.
The new Point-to-Point Architecture proposed overcomes the limitations of Hubbing Span Architecture. This architecture assures satisfactory parameters with multi node-to-node connectivities for multi link failures of complex networks.
It provides the computing paths with an integrated restoration mechanism from network survivability point of view. An effective FNUSSR algorithm has been proposed for the network survivability to compute the large number of demands for different types of survivable architectures in terms of Detection, Routing Selection, Rerouting and Return to Normal Mode at the DS1 /DS3 levels. It also measures the time-scale of operations, resource efficiency for multiple layers switching methodology. The FNUSSR algorithm has the potential to take into account different multi node configurations and to support integrated restoration topology, bridging primary and backup paths.
The introduction of Point-to-Point span Architecture is this justified, and the implementation of FNUSS algorithm provides the integrated approach for different types of survivability architectures with multiple connecitivities and performance characteristics.
Survivability parameters of User Service Survivability Ratio in the Physical Layer Module has been analyzed in this chapter, and the procedure is extended to compute the DS3 forming parameters of the optical networks in the next chapter.