The Open Network Lab (Part 2)

Transcription

1 The Open Network Lab (Part ) Ken Wong pplied esearch Laboratory Computer Science and Engineering Department kenw@arl.wustl.edu (ONL) National Science oundation NI-0386, CNS-05565, EL Example sndr rcvr sndr UDP traffic NP. NP Ken Wong Oct 008

2 3 - Ken Wong Oct 008 Example (Modified) NP. NP NP. NP..5 0 Traffic» Max size pkts = 500 bytes» np starts 0 sec after np» np: = 67 pps» np: = 67 pps Port Capacities» port /:» port /3:» port /: Queueing ates» port /:» port /3:» port /:» Capacity: 00,000» Overflows in sec - Ken Wong Oct 008 Example (Modified) NP. NP NP. NP..5 0 Traffic» Max size pkts = 500 bytes» np starts 0 sec after np» np: = 67 pps» np: = 67 pps Port Capacities» port /: = 8 pps» port /3: 0 = 80 pps» port /:.5 = 6 pps Queueing ates» port /: - =» port /3: 0» port /: (+)-.5 = 0.3 n 0.3 = 37,500 ps = 5 pps» Capacity: 00,000 = 67 pkts» Overflows in 67/5 =.7 sec

3 Example (ack-to-ack Traffic) NP. NP..5 0 Different Traffic» back-to-back UDP pkts from np and np» both flows start at the same time» np: 00 max-size pkts (500 bytes each)» np: 00 max-size pkts (500 bytes each) What queues must be changed so that no pkt drops occur? 5 - Ken Wong Oct 008 NP. NP Ken Wong Oct 008 Example.5 Different Traffic» back-to-back UDP pkts from np and np» both flows start at the same time» np: 00 max-size pkts (500 bytes each)» np: 00 max-size pkts (500 bytes each) What queues must be changed so that no pkt drops occur? Transmission Volumes»bytes from each source»pragmatics: ONL UDP pkts n 8-byte UDP hdr, 0-byte IP hdr n 70-byte UDP payload n actual pkt size = 98 bytes ile transfer time

4 NP. NP Ken Wong Oct 008 Example.5 Different Traffic» back-to-back UDP pkts from np and np» both flows start at the same time» np: 00 max-size pkts (500 bytes each)» np: 00 max-size pkts (500 bytes each) What queues must be changed so that no pkt drops occur? Transmission Volumes»bytes from each source n 50,000 bytes = 00x500»pragmatics: ONL UDP pkts n 8-byte UDP hdr, 0-byte IP hdr n 70-byte UDP payload n actual pkt size = 98 bytes (NP.)»Capacity (for flows) n 300,000 bytes = 00 pkts Port /, Datagram Queue»Capacity (for flow) n 50,000 bytes = 00 pkts ile transfer time».6 sec = (.+.)/ Ken Wong Oct 008 Example 3 (orward Delay) Effect of 50 msec delay along forward path?» arrival of first pkt to np» finish time Interpacket Times» port /:» port /3:» np: andwidth-delay Products» np-np:» np3-np: NP. 0 NP. D.5

5 9 - Ken Wong Oct 008 Example 3 (orward Delay) NP. 0 NP..5 Effect of 50 msec delay along forward path?» arrival of first pkt to np n delayed by 50 msec» finish time n 50 msec longer than without delay Interpacket Times» port /: /(8 pps) =.9 msec» port /3: /(800 pps) = 0.9 msec» np: /(6 pps) = 7.93 msec andwidth-delay Products» np-np: x 50 msec = 50 Kb = 33.3 pkts» np3-np: 0 x 50 msec = 500 Kb = 333 pkts D Example (CK Delay) NP. 0 NP. D.5 Suppose»Small CK pkt returned along reverse path for each data pkt T = L/( ) T = L/ T3 = T T = T 0 - Ken Wong Oct 008

6 ONL Issues Port rate»integer multiple of n e.g.,.6 eceiver socket buffer size»default: 8 K»void ignoring incoming pkts for too long»use setsockopt() to increase buffer size n = 500 * 500; // 500 max-size pkts rc = setsockopt( sockfd, SOL_SOCKET, SO_CVU, &n, sizeof(n)); C/C++ code examples (onlusr:~kenw/src/)»pkt-pair/»xstcp/ - Ken Wong Oct 008 The Meaning of Port ate - Ken Wong Oct 008

7 Queue Table Port ate 7 x tokens b Controlled by a token bucket model» : long-term average link rate (LI parameter) n 5 Kbps granularity» b: maximum bucket depth (000 bytes)» : physical link rate ( ) Effect» avg output rate is» peak rate is Operational definition» fill token bucket at rate» transmit pkt when #tokens length of pkt at head of queue Link regulator model, NOT link emulator 3 - Ken Wong Oct 008 packets The Packet-Pair Problem interpacket time two 000-byte, back-to-back packets sndr, 50 msec rcvr CK Keshav s idea cvr receives the two pkts at times t0 and t»what will the interpacket time t-t0 be?»average interbit time? ONL Experiment: sndr rcvr - Ken Wong Oct 008

8 ONL Packet-Pair Experiment () link capacity Sndr cvr Ideal: T = L/ T = L/ ONL: T = L/.6 note initial burst Ken Wong Oct 008 ONL Packet-Pair Experiment () Puts $np, etc. into Linux bash environment rcvr: np #pkts: 7 0-byte IP hdr 8-byte UDP hdr 70-byte payload 6 - Ken Wong Oct 008