Different performance issues in network

• Performance Problems in Computer Networks
• Network Performance Measurement
• System Design for Better Performance
• Fast TPDU Processing
• Protocols for Gigabit Networks
Performance problems in computer networks
• Overloads Example 1: TPDU containing the bad parameter when broadcast may
clog the n/w results in broadcast storm due to error message
• synchronous overload due to power failure-DHCP contacted for booting
• Apart from this problems due to insufficient memory TPDUs lost
• Not setting the timeout correctly the TPDUs lost
• Gigabit n/w pose new problems
• The next figure explains this here the transmission line used only for .5msec

greatly reducing the efficiency
• The useful quantity is the Bandwidth-Delay product
• The product is the capacity of the pipe from sender to receiver and back to sender
in bits
• In the above example it is 40 million bits but the actual utilisation is only 1.25
percent of the pipe capacity
• therefore for good performance the receiver window must be at least as large as
the Bandwidth-Delay product
• Another performance problem could be jitter to avoid a small standard deviation
is used
The basic loop for improving network performance.
• Measure relevant network parameters, performance.
• Try to understand what is going on.
• Change one parameter
Precautions taken while measuring
• Sample size should be large enough
• Samples should be representative
• To be careful while using coarse grained clock
• Nothing unexpected going on while tests are conducted
• Caching problem
• Understanding the measurements
• Extrapolation of the result
System Design for Better Performance
Rules:
• CPU speed is more important than network speed.
• Reduce packet count to reduce software overhead.
• Minimize context switches.
• Minimize copying.
• You can buy more bandwidth but not lower delay.
• Avoiding congestion is better than recovering from it.
• Avoid timeouts.
Fast TPDU Processing
• TPDU processing overhead has two components
• one –overhead per TPDU
• other – overhead per byte
• Example take the sending side
 • first the sending side traps to kernel to SEND
• if it is a normal case then the state is ESTABLISHED and typically this path is
taken (fast path) shown in the figure below
The fast path from sender to receiver is shown with a heavy line.
The processing steps on this path are shaded.
Another example
• In the TCP header the fields that are same between consecutive TPDUs on a one
way flow are shaded
• All sending TCP entity has to copy from the prototype header into the output
buffer
• It handovers the header and data to the special IP procedure for sending a regular
max TPDU
• IP then copies its prototype header and makes the packet ready
the above figure
(a) TCP header. (b) IP header. In both cases, the shaded fields are taken from the
prototype without change.
Fast path processing at receiver side
• step 1: locating the connection record for the incoming TPDU
• The TPDU checked to see if it is normal case
• If all checks are met then a fast procedure is called
• Many TCP implementations use Header Prediction
• The other two areas where major performance gain are possible are
Buffer management
Timer Management
• The timer management done by the timing wheel
• There are some problems and the possible solution posed by the Gigabit protocols
• Problems
Sequence Numbers
Communication Speeds
Go back n protocol and its poor performance
gigabit lines are bandwidth limited
Results of new application

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