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This Concept Map, created with IHMC CmapTools, has information related to: ch3 performance issues, Performance Issues for Distributed Networks are quality of service Metrics have been established to measure the reliability and bandwidth of networks. These often focus on throughput or bandwidth adjusted for possible failures and expressed as a minimum acceptable quality of service and a desired level., Performance Issues for Distributed Networks are reliability The original DARPANET, from which the Internet evolved, was designed as a military network to survive a nuclear attack. A key concern was reliability, in this case the ability to continue to transfer messages in the event of failures on the network. Error tolerant and error free communications are key reliability concerns., Performance Issues for Distributed Networks are latency on large networks Switching delays at routers and the time required to find and set up a communication path can cause latency delays on large networks such as the Internet that are several orders of magnitude larger than local area networks. Most of us are familiar with the Internet 404 errors that occur when the time to access information is longer than the timeout allowed for searching. Some of this is from latency delays, although most of it is from busy hosts or missing nodes, Performance Issues for Distributed Networks are multicasting Most networks are designed for point to point transfer of information between two nodes. There may also be a requirement for one-to-many communication, and some networks are designed to do this in an efficient manner., Performance Issues for Distributed Networks are mobility Personal Digital Assistants, Lap Top Computers and cellular phones are examples of mobile devices that may need access to a network at different locations. Networks must be designed to allow this to occur in an efficient, secure and productive manner., Performance Issues for Distributed Networks are scalability As a network grows in the number of nodes, it is a severe challenge to maintain performance. Bottlenecks and complexity often degrade throughput. Scalability refers to the ability of a network to grow in size without substantial loss of performance., Performance Issues for Distributed Networks are security Networks are also concerned with protection from unauthorized use, loss or compromise of data and with external threats to the ability to transfer messages or the integrity of messages. These topics are the subject of future lectures on distributed system security., Performance Issues for Distributed Networks are network speed The time required to transmit a message is: transmission time=latency+length/data transfer rate The total system bandwidth is a way of measuring the capacity or throughput of a network. It refers to the volume of traffic that can be transferred across the network in a period of time, usually 1 second. It is frequently expressed in millions or billions of bits per second, as Mbps or Gbps.