vb.net barcode generator Softswitch Is Just as Reliable as Class 4/5 Switches in Software

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Softswitch Is Just as Reliable as Class 4/5 Switches
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Softswitch Is Just as Reliable as Class 4/5 Switches
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How Availability Is Calculated
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Availability indicates the system uptime from an operation perspective. System availability is a function of aggregate component reliability; thus, availability is likewise measured in terms of time. Calculating Availability and Unavailability The availability of a hardware/software module can be obtained by the following formula where A is availability. A MTBF/MTBF MTTR
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In the following formula, U is unavailability: U MTTR/MTBF 1 MTTR
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The product of the formula gives the percentage of up time for the system, that is the amount of time for which it is available. This is how availability is expressed. The target for a telephone network is 99.999 percent up time availability. This is known as five 9s of eliability. Annual Failure Rate The hours per year are 8760. AFR 8760/MTBF
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The greatest requirement for availability is for NEs, such as a circuit switch, which are generally required to provide 99.999 percent availability or 0.001 percent unavailability.5 Such a system is termed Highly Available (HA). The previous equations apply to each individual component on a network. How is availability determined for a network that has hundreds or thousands of components Figure 7-3 illustrates how different components on a network may have different levels of downtime or unavailability. In order to determine the availability of a network, it is necessary to add up the availability of all components on a network.
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Convergent Networks. Understanding Carrier-grade Reliability and Availability. www.convergentnetworks.com.
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Softswitch Is Just as Reliable as Class 4/5 Switches
Figure 7-3 System availability is a function of the availability of all the components.
Network Unavailability (.00023%)
7
Server
Unavailability (.00031%)
Unavailability (.00015%)
Application
Unavailability (.00014%)
Operator
Unavailability (.00013%)
Total Unavailability = .00096% or 99.99904% Availability
How Does a Switch, PSTN or Softswitch, Achieve Five 9s
Selling against the reputation of the Class 4 for reliability is the most difficult problem for softswitch vendors. Where are the five 9s of reliability is the inevitable question service providers pose to vendors. Although a number of softswitch vendors claim to achieve five 9s, much skepticism exists among service providers that the five 9s of the new technology have the same experience as a Class 4. If the heavy iron of a Class 4 switch can achieve five 9s, then how does a software-based product like softswitch achieve five 9s in reliability A service provider s confidence is further challenged by softswitch platforms that are not NEBs compliant. Given the cost of downtime, as discussed earlier in this chapter, long-distance service
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Softswitch Is Just as Reliable as Class 4/5 Switches
Softswitch Is Just as Reliable as Class 4/5 Switches
providers, for example, will insist that the components on their network provide five 9s. Achieving five 9s is mostly a matter of engineering. If softswitch vendors can engineer out SPOFs and engineer in redundancy and other measures that Class 4 and 5 switch vendors have used for years to ensure reliability, then they, like the Class 4 and 5 switch vendors, can also advertise five 9s of reliability. Softswitch vendors can also engineer their platforms to be NEBS compliant. These measures enable softswitch to match five 9s of reliability demonstrated by Class 4. A number of softswitch solutions have achieved five 9s. HA is simply a matter of good engineering. The main components of engineering a Class 4 or 5 switch for HA are redundancy, no SPOF, a hot switchover, a preservation of calls, in-service upgrades, component reliability, reproducible quality, and NEBS compliance. The same is true for a softswitched network. HA is enhanced when each component is replicated in a system. This is called redundancy. If one unit fails, its replicated unit takes over. Redundant configurations are expressed by the notation m:n, where m represents the number of standby units and n represents the number of active units supported by the standby units. A typical configuration is 1:1 where there is one active unit for every active unit, or 1:6 where there is one standby unit for 6 active units. Usually, the smaller the n, the greater the protection and cost. Given the highly reliable nature of today s components, a carrier may determine that configurations greater than 1:1 provide sufficient availability. In a PSTN configuration, 1:n redundancy schemes are employed on the access side (a Class 5 switch, for example) where an outage affects a smaller number of subscribers. Class 4 and 5 switches are more likely to use a 1:1 redundancy model because the effect of a failure is more expensive. The effect of Moore s Law, where computing power doubles while computing cost halves every 18 months, makes redundancy less expensive as time goes by.6 In an HA system, two or more systems are loosely coupled together with each other, with the help of redundancy software. The reliability provided can be further classified as asymmetric or symmetric based on whether the systems act as active/standby (idle) or run in a parallel load-sharing/balancing mode. In an Active/Standby type of system, further categories exist, such as 1 1 redundancy or N K redundancy based on the number of active nodes and standby nodes that are available. Cluster mode is another
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