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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Figure 7-4 This damaged RBOC pedestal constitutes an SPOF on the network. Note 4 4s holding the structure up and plastic trash bags providing weather resistance.
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Figure 7-5 HA systems replicate all network elements, resulting in no SPOF . (Source: HewlettPackard)
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back office system
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active nodes management cluster
inactive nodes
active nodes management cluster
inactive nodes
application cluster application server
isolated computer rooms
application cluster application server application server
isolated computer rooms
management server
management server
management server
management server
application server
database server
database server
redundant WAN links
database server
database server
fibre channel links
fibre channel links
fibre channel links
fibre channel links
five 9s
disk array
CA-ESCON links
disk array
solution boundary
disk array
CA-ESCON links
disk array
primary site
standby / disaster recovery site
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Softswitch Is Just as Reliable as Class 4/5 Switches
Softswitch Is Just as Reliable as Class 4/5 Switches
software and hardware. A sound hot switchover design goes a long way toward making both of these possible. To update existing and running software while simultaneously running live traffic, it is necessary to switch over to the new software with no impact to service. To update hardware without service interruption, a hot swap is performed on the circuit packs. That is, one circuit pack is removed from the system without a negative effect on service. What Class 4 and Class 5 aficionados are referring to when they speak of five 9s is component reliability. System availability is a function of the reliability of the individual components. The best way to ensure a highly available system is to avoid failure in any component of a system. This is best accomplished using only the best quality parts with minimal failure rates. Network connectivity for a softswitch product includes interfaces to the Internet Protocol (IP) world and interfaces to the PSTN world. PSTN world connectivity is primarily through DS0 or higher types of interfaces, which are point to point and cannot be inexpensively replicated. Generally, for signaling, several parallel channels operate between the two network points through separate hardware interfaces and whenever one channel fails, traffic is diverted on to the parallel channels. Primarily, failing NICs or a lost network connection causes IP world connectivity failures. Floating IP and Floating Media Access Control (MAC), along with multiple points of connectivity to the IP cloud, are some of the concepts used for guarding against network failures. But problems with maintaining Transmission Control Protocol (TCP)/IP states across platforms require special handling in software. It is easier to handle failovers based on the User Datagram Protocol (UDP). Database failures can be caused by disk failures, disk controller failures, database corruption, and so on. Duplicating the hardware involved and replicating the database across multiple points protect against such database failures. Environmental and physical failures are difficult to predict and prevent. These include causes like fire and earthquakes, which can be protected against by geographical redundancy. ( Geographical redundancy refers to locating softswitch components at various locations around the country or around the world. In the event of a failure of one switch in New York City, for example, a back-up switch in Omaha, Nebraska, for example, would pick up the load of the New York-based failed switch.) It should be noted that since these systems work in parallel, a software bug in one system would also get replicated on the other side and lead to downtime.11
Hughes Software Corporation. Challenges in Building Carrier Grade Convergence Products. March 2001, pg. 7. This white paper is available online at www.hssworld.com/whitepapers/ voppapers.htm#5
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Softswitch Is Just as Reliable as Class 4/5 Switches
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Finally, reproducible quality dictates that strict operational controls are required to ensure that a supplier has predictable results with respect to the reliability of the systems produced. Such controls range from parts acquisition, components testing, system assembly, and the method of installation. A failure in operations can effectively eradicate the benefits provided by an elegant system design.12
Network Equipment Building Standards (NEBS)
In addition to five 9s, the other buzzword for reliability in the Class 4 market is NEBS. NEBS addresses the physical reliability of a switch. It is contained in Telcordia specification SR 3580, an extensive set of rigid performance, quality, safety, and environmental requirements applicable to network equipment installed in a carrier s central office. Most carriers in North America require that equipment in their central offices be NEBS compliant. NEBS testing includes electrical safety, immunity from electromagnetic emissions, lightning and power faulting, and bonding and grounding evaluations. Equipment must achieve standards including temperature, humidity, and altitude testing; fire resistance (usually by destructive burning); earthquake vibration resistance; and other rigid tests. NEBS compliance includes ensuring access to mirror sites, fire- and waterproof storage facilities for database and configuration backup information, and backing up electrical power in case of power failures. With five 9s and NEBS, the Class 4 and 5 vendors have developed, through decades of experience, a very reliable product that delivers superb uptime and rapid recovery capability. As a result, service providers are very reluctant to experiment with new technologies (see Figure 7-6).
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