On real-time delay monitoring in software-defined networks

Transcription

1 On real-time delay monitoring in software-defined networks Victor S. Altukhov Lomonosov Moscow State University Moscow, Russia Eugene V. Chemeritskiy Applied Research Center for Computer Networks Moscow, Russia

2 Motivation Huge number of network applications and services request advanced end-to-end requirements for the connection; Network hardware doesn t support necessary functionality to allow QoS issues; Most QoS metrics can t be easily calculated. IPTV VoIP File transfer Gaming

3 Motivation VoIP Delay sensitive Many network services and applications are delay sensitive; Delay measurement in asynchronous distributed system is hard. IPTV Delay sensitive Gaming Delay sensitive

4 Rationale Packet switch fabric F Output port queue Switch packet analyzer А F А Queuing delay can t be accurately measured without a regard to network load

5 Rationale Measured value consist of two parts: Real end-to-end delay for target route (effective part); Transmission delay between controller and switch (measurement overhead). SDN Controller Measurement will be accurate if: effective part overhead Target route

6 Loop-based method Allow to measure average target route RTT over n iterations; Measurement results include switch to controller jitter. SDN Controller Problems: Huge number of rules; Measure RTT, not one-way delay. Target route

7 Header loops Use header fields to decrease number of rules; Require to install modification rules; 1000 iterations cycles and 3 header fields require 30 modification rules. Iteration First field Second field Third field

8 Weighted method of RTT separation Allow to derive one-way delay from RTT; Can be used with one-hop RTT; Requires switch statistics. For a given RTT and time interval T, one-way delay can be estimated as following: (RRRRRR + max XX CC TT, 0 max (YY CC TT, 0) )/2 X, Y number of bytes, transmitted through switches output queues. T measurement time interval, C link bandwidth.

9 Delay map Network delay map structure, that contains all one-hop delays. Delay for a random route can be calculated as sum of one hop delays; Delay map can be construct with weighted method of RTT separation, but this approach generates big controller load;

10 Loops aggregation Number of PacketIn messages depend on number of iterations and loop s length; Bigger loops decrease controller load loops 2 PacketIn per 1 period loop 1 PacketIn per 2 periods Weighted method of RTT separation can be used only with one-hop loops

11 How to obtain one-way delays without weighted method?

12 Network delay map construction algorithm Idea: Construct a system of linear equations from a set of aggregated loops. Constraints: Loops in the aggregated set must be independent; Each one-way link must be include in at least one loop; Number of loops must be equal to number of one-way links.

13 Network delay map construction algorithm 1 Start from basic set of network cycles Number of cycles in basic is equal to cyclomatic number; Basic set is linear independent; Set of aggregated cycles from basic set is independent; But this is not enough

14 Network delay map construction algorithm Extend set of aggregated cycles to number of one-way links Find missing one-way links in set of aggregated cycles; Use weighted method of RTT separation to obtain missing one-way delays. 1 Use measurement results to solve system of linear equations and create network delay map

15 Experiments results Tested on hybrid SDN switch NEC PF5200 POX controller User traffic generation delay vary from 0 to 10 µs User traffic packet size vary from 64 to 1500 byte

16 Experiments results User traffic generation delay vary from 1 to 10 µs User traffic packet size vary from 64 to 250 bytes

17 Experiments results User traffic generation delay vary from 100 ns to 1 µs User traffic packet size vary from 250 to 750 bytes

18 Experiments results User traffic generation delay less then 100 ns User traffic packet size vary from 1000 bytes

19 Experiments results Tested on network, simulated by Mininet POX controller With weighted method of RTT separation: 5 one-hop loops 5 PacketIn messages in a second

20 Experiments results Tested on network, simulated by Mininet POX controller With set of aggregated cycles: 7 cycles with 36 hops 3,78 PacketIn messages in second.

21 Result Out method of end-to-end delay measurement has the following features: Per-flow delay measurement; Precise enough to cover the mutual flow influence; Work in SDN with general switching hardware; Update results up to several times in a second.

22 Questions?