1. Internet Traffic Patterns Learning outcomes –Be aware of how information is transmitted on the Internet –Understand the concept of Internet traffic –Identify the relationship between human activities and Internet traffic –Device a strategy to evaluate your Internet connection –Be able to explain and compare active and passive traffic measurement techniques

2. Internet traffic The little pieces of information are called packets All the packets from all the people around the world cause traffic Too much traffic causes queues and congestion Queues reduce speed, hence “the net is slow today”

3. Traffic is linked to people’s activities 21.3001.30 05.30 09.3013.3017.3021.30 01.30 05.30 09.3013.3017.3021.30

4. Effects of human activity Congestion occurs during heavy load periods leading to packet loss and retransmissions The best service would require an over sized network Companies have to optimise the relationship between customer service and resource utilisation That is why you do not get full broad-band speed at home

5. Traffic measurement Active measurement –Interferes with the traffic actively Passive measurement –Does not interfere with Internet traffic

6. Active traffic measurement Sending probes into the network in order to measure: –Packet loss –Delay –Delay variation –Available bandwidth estimation along defined paths –Host availability Common measuring tools: Ping, traceroute, ad hoc programs, ping plotter

7. Active traffic measurement Internet Probe packet Echo copy Originating computer 1. Send probe packet with timestamp & sequence number 2. Wait for reply 3. As echo copy arrives calculate delay 4. Compare sequence numbers for lost packets 5. Compare delay values for delay variation Echo server 1. Wait for probe packet 2. Extract originating address & content 3. Send echo copy

8. Active traffic measurement Main characteristics End-to-end metrics: –Delay:d i =return time – send time –Delay variation:  d=|d i+1 -d i | –Packet loss ratio (PLR): PLR= –Where N is the number of probe packets sent per trace

9. Active traffic measurement Main characteristics UDP is often used as a transport protocol The echo node is considered as a network node part of the path being probed so as to avoid clock synchronisation All packets must have the same length

10. Active traffic measurement Disadvantages Introduces extra traffic into the network, could potentially saturate paths with limited bandwidth Extra traffic may actually change the desired measurements Difficult to implement because of security issues QoS provision and different queueing policies may affect measurements Trace files require large storage space and data must be analysed as it is collected Packets may traverse different paths within one trace

11. Active traffic measurement Overcoming disadvantages Piggy backing of probes on real traffic (e.g. video) Configuration of secure measurement servers Planning collection times so that file sizes can be minimised and the probability of probing different paths is minimised

12. Active traffic measurement Advantages Easy to create ad hoc measurement programs Black box technique, does not involve knowledge about configuration of nodes Effective technique to evaluate resources on Internet paths and to identify bottleneck links Shows a cumulative view of network load

13. Active traffic measurement Sample applications Evaluation of services Available bandwidth estimation Characterisation of Internet paths Dynamic rate adaptation of non-TCP based applications Instantaneous, short & long term traffic characterisation

14. Active traffic measurement

17. Resources Internet traffic report: http://www.internettrafficreport.com/main.htm Traces available in the Internet Traffic Archive http://ita.ee.lbl.gov/html/traces.html CAIDA Internet Data -- Active Data Sources http://www.caida.org/data/active/index.xml

18. Summary Internet traffic patterns are dependant on human activity patterns Active traffic measurement –able to measure end-to-end packet delay, packet delay variation and packet loss –used to estimate instantaneous, short and long term patterns –however, modifies the traffic being measured

19. Passive traffic measurement Capturing actual Internet packets in order to measure: –Packet sizes –Traffic volumes –Application utilisation –Resource utilisation –Network monitoring –Traffic characterisation Commercial products and freeware software –HP openview, NetPredict, tcpdump