6.6 Summary

6.6 Summary

In this chapter we discussed the following:

  • Most organizations today require at least some measure of fault tolerance in their networks. The degree of resilience offered on any network is a compromise between risk and cost. For mission- or business-critical applications, such as a public network service provider's switching center, very high levels of availability will be required (say 99.99 percent or greater), as well as carrier class equipment.

  • Resilience is the best approach from the top down. Potential failures should be identified from the wide area circuit design down to component level. Once these failures are identified, a plan for resolving each failure, together with associated cost, should be devised.

  • Techniques such as multilink and multipath load sharing are important in the wide area, where backbone links are typically expensive, congested, and critical to the successful operation of the network.

  • Protocols such as VRRP and HSRP enable key devices such as routers and firewalls to be deployed in a fault-tolerant configuration, transparently to end users.

  • HA clusters and fault-tolerant systems both provide effective availability solutions. Each has specific advantages depending upon the environment and problems to be solved. In some cases, a combination of HA clusters and fault tolerance is appropriate.

  • Fault tolerance often goes hand in hand with performance scalability, since the use of parallel paths or multiple system, often has a performance benefit.


[1] K. Norvag, "An Introduction to Fault-Tolerant Systems," IDI Technical Report 6/99, Norwegian University of Science and Technology, July 2000.

[2] T. Kenyon, High-Performance Network Design: Design Techniques and Tools (Woburn MA: Digital Press, 2001)

[3] www.drj.com/special/stats/tari.htm88, information about recent disasters.

[4] www.fema.gov/library/lib01.htm. information about recent disasters.

[5] www.ibm.com, IBM home page.

[6] www.symantec.com, Symantec home page.

[7] J. Gray and A. Reuter, Transaction Processing: Concepts and Techniques (San Mateo, CA: Morgan Kaufmann Publishers, 1993).

[8] www.sra.org, The Society for Risk Analysis, home page.

[9] www.riskworld.com, Risk World home page.

[10] A. Kershenbaum, Telecommunications Design Algorithms (New York: McGraw-Hill)

[11] himalaya.compaq.com, Tandem home page (part of Compaq).

[12] www.stratus.com, Stratus home page.

[13] www.hp.com, Hewlett-Packard home page.

[14] www.microsoft.com, Microsoft home page.

[15] Virtual Router Redundancy Protocol, RFC 2338, April 1998.

[16] Cisco Hot Standby Router Protocol (HSRP), RFC 2281, March 1998.

[17] www.nokia.com, see security products.

[18] United States Patent Office, Patent Number: 5,473,599, Standby Router Protocol, December 5, 1995.

[19] www.cisco.com, Cisco home page. See links for HSRP.

[20] www.arcoide.com, Arco Computer Products, Inc., home Web page. Supplier of disk mirroring products.

[21] http://teak.wiscnet.net/linux-mirror-cookbook, Linux disk mirroring cookbook.

Data Networks. Routing, Seurity, and Performance Optimization
ActionScripting in Flash MX
EAN: 2147483647
Year: 2001
Pages: 117

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