cs 453 computer networks
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CS 453 Computer Networks. Lecture 23 Network Management and Performance. Performance Issues. Clearly, users of networks expect them to perform well… …and usually notice when they do not… … and expect the network management to fix the problems. Performance Issues. - PowerPoint PPT PresentationTRANSCRIPT
CS 453CS 453Computer NetworksComputer Networks
Lecture 23Lecture 23
Network Management and Network Management and PerformancePerformance
Performance Issues
Clearly, users of networks expect them to perform well…
…and usually notice when they do not…
… and expect the network management to fix the problems.
Performance Issues
Down routes – network routes fail or shutdown for a variety of reasons, network management software must be able to detect route or link failures, …
…and provide a means to resolve or work around the problem….
For example, rerouting traffic, until preferred routes are restored
Performance Issues
Congestion – Networks (particularly WANs) have multiple routes to provide end-to-end connectivity
There are usually one or more preferred routes… But these preferred routes often aggregate traffic from
multiple sources… Which can overload links and create congestion
(compounding problem) Network management systems should be able to—
Recognize congestion
…and shed traffic to other routes, if possible
Performance Issues
Low end processing hardware/software High performance networks connected to
old/slow hardware (routers, PCs) can cause performance problems
Messages arrive faster than the hardware can process them…
Messages are lost, and retransmitted,… And this problem can compound if the
overload is not transient
Performance Issues
Synchronous overloads – Suppose a bad message is broadcast to a
network of 10,000 machines…. …and each of these machines replies with an
error message… Result can be massive overload of the
network Broadcast Storm UDP protocol changes to inhibit error reports
for broadcast messages
Performance Issues
Synchronous Overloads- Imagine the simultaneous restart of all
machines/routers in a network… … like a regional power failure Every machine on the network will start and
may issue a DHCP Discovery request, simultaneously…
Routers will update their routes and configurations,
Network hosted software will reload And the network will come to it’s knees
Performance Issues
Synchronous Overloads- This is not far fetched Happens all of the time on a modest scale Recently, happened on a global scale… Due to a MS Windows automatic update Update required a restart Something like 6 million computers worldwide
restarted at the same time
Performance Issues
Tuning Insufficient buffer space in routers,
source/destination computers Scheduling algorithm giving too little priority to
processing incoming data, drops messages, causes retransmits
Timer settingsToo short – messages in-flight reported as lost
Too long – waste time waiting for lost messages
Performance Issues
Inefficient use of resources
For example, high performance network with low feed
Performance Issues
Jitter We want a short mean arrival time Also want small standard deviation for arrival
time Large standard deviation in arrival time is
called Jitter Jitter big problem with new services like
VoIPStreaming audioStreaming video
Can mitigate some
Network Management
More things to see http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/
snmp.htm http://en.wikipedia.org/wiki/Network_performance_management http://en.wikipedia.org/wiki/Snmp http://www.cotse.com/tools/netman.htm
TCP/IP http://www.redbooks.ibm.com/Redbooks.nsf/RedbookAbstracts/gg243376.html?Open