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802.16 IP Telephone Lab 1 One-Way Ping Dr. Quincy Wu, Associate Professor Graduate Institute of Communication Engineering National.

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Presentation on theme: "802.16 IP Telephone Lab 1 One-Way Ping Dr. Quincy Wu, Associate Professor Graduate Institute of Communication Engineering National."— Presentation transcript:

1 IP Telephone Lab 1 One-Way Ping Dr. Quincy Wu, Associate Professor Graduate Institute of Communication Engineering National Chi Nan University - Introduction to OWAMP

2 IP Telephone Lab 2 Number of computers attached to the Internet In 1998, the average rate of new computers being added to the Internet reached more than one per second –And has accelerated Growth of Internet Computer Networks and Internets, Douglas E. Comer, Pearson Prentice hall, 2004.

3 IP Telephone Lab 3 Plotted on a log scale The growth appears approximately linear –Exponential growth –The Internet has been doubling in size every nine to twelve months Growth of Internet (cont.) Computer Networks and Internets, Douglas E. Comer, Pearson Prentice hall, 2004.

4 IP Telephone Lab 4 Hosts & Routers LAN: Local Area Network

5 IP Telephone Lab 5 Probing The Internet Q: How do we know the number of computers attached to the Internet? In the early days when the Internet consisted of a dozen sites, this size could be determined manually. Now we use programs that test to see whether a computer is currently online. –ping is alive –ping is alive Certainly, this probing is not very precise, for two reasons.

6 IP Telephone Lab 6 Interpreting A Ping Response C:\>ping Pinging cswww.cse.yzu.edu.tw [ ] with 32 bytes of data: Reply from : bytes=32 time=14ms TTL=115 Reply from : bytes=32 time=11ms TTL=115 Reply from : bytes=32 time=10ms TTL=115 Reply from : bytes=32 time=11ms TTL=115 Ping statistics for : Packets: Sent = 4, Received = 4, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 10ms, Maximum = 14ms, Average = 11ms C:\>ping Pinging [ ] with 32 bytes of data: Reply from : bytes=32 time=6ms TTL=56 Ping statistics for : Packets: Sent = 4, Received = 4, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 6ms, Maximum = 6ms, Average = 6ms

7 IP Telephone Lab 7 Probing Packets

8 IP Telephone Lab 8 Round-Trip Time Client Server ms ms ms ms request reply request reply

9 IP Telephone Lab 9 Why Didnt We Measure One-Way Delay? Asynchronous system clocks would make the measurement result confusing. Receiver Sender 19:20:21 19:20:19 Delay = -1 sec ! 19:20:20

10 IP Telephone Lab 10 ICMP Packet Format RFC 792 – Internet Control Message Protocol

11 IP Telephone Lab 11 Why Do We Favor One-Way Delay? The path from a source to a destination may be different than the path from the destination back to the source ("asymmetric paths"). Even when the two paths are symmetric, the behavior of applications can be quite different: –File transfer –Web browsing –IPTV

12 IP Telephone Lab 12 Why Can We Measure 1-Way Delay Now? Available Time Source: –Cesium oscillator: Definition of time (subject to relativistic effects) –Rubidium oscillator: found in cell towers, very stable –GPS receiver: accuracy circa 10 ns –CDMA receiver: accuracy circa 10 μs The stratum of any NTP-synchronized device is the stratum of the device it is synchronized to, plus 1. –GPS receiver: stratum 0 –Computer connected to it by a serial line: stratum 1 –Client that gets the time from that computer: stratum 2 Stratum 1 Time Servers: –http://ntp.isc.org/bin/view/Servers/StratumOneTimeServers

13 IP Telephone Lab 13 Measuring One-Way Delay Receiver Sender 19:20:21 19:20:19 Delay = 1 sec 19:20:22 Synchronization 19:20:21

14 IP Telephone Lab 14 OWAMP Design Goals One-Way Active Measurement Protocol –RFC 4656, September Wide deployment of open servers would allow measurement of one-way delay to become as commonplace as measurement of RTT using ICMP tools such as ping.

15 IP Telephone Lab 15 OWAMP Logical Model Session SenderSession Receiver Server Control-ClientFetch-Client OWAMP-Test OWAMP-Control

16 IP Telephone Lab 16 Commonly Implemented Model Session-Sender Control-Client Fetch-Client Session-Receiver Server OWAMP-Control OWAMP-Test

17 IP Telephone Lab 17 OWAMP-Test Transport Protocol: –UDP Sender/Receiver IP and port numbers: –Negotiated by OWAMP-Control message OWAMP-Test does not run on a fixed port –To prevent some devices may assign higher priorities to these measurement packets

18 IP Telephone Lab 18 OWAMP-Test Packet Format Sequence: start with 0; incremented by 1 Timestamp: RFC1305 format Padding is random, but users have an option to configure it to consist of all zeros. Minimum data length: 14 octets

19 IP Telephone Lab 19 OWAMP Errors Preliminary Findings: –Min error estimates look to be in the usec range. –Serialization Delay: ~5usec x 2 –Get Timestamp: ~15usec x 2 –Additional error is: Time from userland send to 1 st byte hits the wire Time from kernel has packet to userland recv returns Potentially recv process data processing before calling recv

20 IP Telephone Lab 20 Internet2 OWAMP deployment 2 overlapping full meshes (IPv4 & IPv6) –11 measurement nodes = 220 ongoing tests –UDP singletons singleton: a single observation of one-way delay –Rate: 10 packets/second –Packet size: 32-byte payload –Results are continuously streamed back to Measurement Portal for long-term archive and data dissemination (Near real-time)

21 IP Telephone Lab 21 Weather Map

22 IP Telephone Lab 22 owping $ owping -c 5 nms4-nycm.abilene.ucaid.edu --- owping statistics from [2001:e10:6840:20:20f:eaff:fe56:ea22]:52711 to [nms4-nycm.abilene.ucaid.edu]: SID: fef1505dc8e1a e87b0e310c 5 sent, 0 lost (0.000%), 0 duplicates one-way delay min/median/max = 138/138/147 ms, one-way jitter = 8.6 ms (P95-P50) Hops = 10 (consistently) no reordering --- owping statistics from [nms4-nycm.abilene.ucaid.edu]:64338 to [2001:e10:6840:20:20f:eaff:fe56:ea22]: SID: fe56ea22c8e1a4591f6c8b43d56f48c2 5 sent, 0 lost (0.000%), 0 duplicates one-way delay min/median/max = 112/112/113 ms, one-way jitter = 0.8 ms (P95-P50) Hops = 7 (consistently) no reordering

23 IP Telephone Lab 23 Captured OWAMP Packets

24 IP Telephone Lab 24 R&D Issues Design a system to scale (eliminate centralizations) How to discover OWAMP servers –DNS SRV, –DHCP option, –Multicast address How to insert On-Demand tests into regularly-scheduled test set Balance centralization and distributed database requirement Dynamically allocated AES key –Currently, the shared secret between sender and receiver is statically assigned

25 IP Telephone Lab 25 Security Considerations Protecting Your OWAMP Testing Traffic –To make it impossible for an attacker to tamper with test results. –To make it hard for a party in the middle of the network to make results look "better" than they should be. Preventing Third-Party Denial of Service Covert Information Channels Requirement to Include AES in Implementations Resource Use Limitations –Disk, Memory, Bandwidth Use of Cryptographic Primitives in OWAMP –TLS Stream-based. Not suitable for OWAMP-Test. –DTLS Duplication and reordering information are missing –IPSec Few deployments –SSH 2-4% –HTTPS: % –IPsec: 0.05%

26 IP Telephone Lab 26 HW 3 Install OWAMP client/server on your own hosts. Try to test the one-way delay. Your host may possess a public IP address. If this is not the case for IPv4, at least you know how to get a public IPv6 address. Show me your measurement, and the OWAMP packets which you captured.


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