ESLEA Bits&Bytes, Manchester, 7-8 Dec 2006, R. Hughes-Jones Manchester1
Protocols
DCCP and dccpmon.
Richard Hughes-Jones The University of Manchester
www.hep.man.ac.uk/~rich/ then “Talks”
ESLEA Bits&Bytes, Manchester, 7-8 Dec 2006, R. Hughes-Jones Manchester2
UDPmon: The Measurements (1)
Latency Round trip times measured using Request-Response
UDP frames Latency as a function of frame size
Slope gives sum of individual data transfer rates end-to-endMem copy + pci + Gig Ethernet + pci + mem copy
Intercept indicates processing times + HW latencies
Histograms of ‘singleton’ measurements Tells us about:
Behavior of the IP stack The way the HW operates Performance of the LAN / MAN / WAN
ESLEA Bits&Bytes, Manchester, 7-8 Dec 2006, R. Hughes-Jones Manchester3
UDPmon: The Measurements (2)
UDP Throughput Send a controlled stream of UDP frames spaced at regular intervals Vary the frame size and the frame transmit spacing At the receiver record
The time of first and last frames received The number packets received, the number lost, number out of order The received inter-packet spacing is histogramed The time each packet is received provides packet loss pattern CPU load, Number of interrupts Packets in/out on each interface /proc/snmp IP and UDP counters
Use the CPU cycle counter for times and delay Few lines of user code – fast & precise
Tells us about: Behavior of the IP stack The way the HW operates Capacity and Available Throughput of the LAN / MAN / WAN
ESLEA Bits&Bytes, Manchester, 7-8 Dec 2006, R. Hughes-Jones Manchester4
UDPmon: The Works
How it works: The ‘Zero_stats’ request also provides an interlock against concurrent tests.
Zero stats / tsync OK done
●●●
Get remote statisticsSend statistics
Send data frames atregular intervals ●●●
Time to send Time to receive
Inter-packet time
Signal end of testOK done
n bytes
Number of packets
Wait timetime
ESLEA Bits&Bytes, Manchester, 7-8 Dec 2006, R. Hughes-Jones Manchester5
DCCP: The Application View Stephen & Richard with help from Andrea Ported udpmon to dccpmon
Some system calls don’t work
getsockopt(*soc, SOL_DCCP, DCCP_SOCKOPT_CHANGE_L, &dccp_features, &len); Had problems with Fedora Core 6 using kernel 2.6.19-rc1
DCCP data packets never reached the receiving TSAP ! Verify with tcpdump Using development “patches” kernel 2.6.19-rc5-g73fd2531-dirty
dccpmon tests Plateau ~990 Mbit/s wire rate No packet Loss Receive system crashed!
Iperf tests 940Mbps, back-to-back
Need more instrumentation in DCCP Eg a line in /proc/sys/snmp
zeus15-atb79_29Sep06
0100200300400500600700800900
1000
0 10 20 30 40Spacing between frames us
Rec
v W
ire r
ate
Mbi
t/s
800 bytes
1000 bytes
1200 bytes
1400 bytes
1424 bytes
ESLEA Bits&Bytes, Manchester, 7-8 Dec 2006, R. Hughes-Jones Manchester6
DCCP: Latest Kernel Kernel 2.6.19_pktd-plus - ~2 weeks old dccpmon tests
Receive system crashed even faster ! Just 1 or 2 1000,000 packet tests
Iperf tests OK short runs 940Mbps, back-to-back Hangs longer runs
ESLEA Bits&Bytes, Manchester, 7-8 Dec 2006, R. Hughes-Jones Manchester7
DCCP: dccpmon crash
ESLEA Bits&Bytes, Manchester, 7-8 Dec 2006, R. Hughes-Jones Manchester8
DCCP: ccid-VLBI Discussion Input from Haystack: Internet2 & Australia NRN view
Protect network from high bandwidth UDP flow DoS Concerns
VLBI view Want to send CBR data Don’t want to drop throughput if just lost a packet due to error
– tcpdelay results DO want to know it there is congestion / packet loss Don’t want SlowStart – DCCP RFC says use a ramp up phase
VLBI profile eg Ack Ratio =10No Send Ack Vector ?
API ?
ESLEA Bits&Bytes, Manchester, 7-8 Dec 2006, R. Hughes-Jones Manchester9
Any Questions?
ESLEA Bits&Bytes, Manchester, 7-8 Dec 2006, R. Hughes-Jones Manchester10
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