802.16 IP Telephone Lab 1 One-Way Ping Dr. Quincy Wu, Associate Professor ([email protected])...

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802.16 IP Telephone Lab

One-Way Ping

Dr. Quincy Wu, Associate Professor

([email protected])

Graduate Institute of Communication Engineering

National Chi Nan University

- Introduction to OWAMP

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• 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.

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• 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.

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Hosts & RoutersLAN

LAN

LAN

LAN

router

router

router

router

router

LAN

LAN

LAN: Local Area Network

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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 www.80216.com.ncnu.edu.tw• www.80216.com.ncnu.edu.tw is alive

– ping 163.22.24.102• 163.22.24.102 is alive

• Certainly, this probing is not very precise, for two reasons.

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Interpreting A Ping ResponseC:\>ping www.cse.yzu.edu.twPinging cswww.cse.yzu.edu.tw [140.138.144.172] with 32 bytes of data:Reply from 140.138.144.172: bytes=32 time=14ms TTL=115Reply from 140.138.144.172: bytes=32 time=11ms TTL=115Reply from 140.138.144.172: bytes=32 time=10ms TTL=115Reply from 140.138.144.172: bytes=32 time=11ms TTL=115Ping statistics for 140.138.144.172: Packets: Sent = 4, Received = 4, Lost = 0 (0

% loss),Approximate round trip times in milli-seconds: Minimum = 10ms, Maximum = 14ms, Averag

e = 11ms

C:\>ping www.csie.nctu.edu.tw

Pinging www.csie.nctu.edu.tw [140.113.209.41] with 32 bytes of data:

Reply from 140.113.209.41: bytes=32 time=6ms TTL=56




Ping statistics for 140.113.209.41: Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),

Approximate round trip times in milli-seconds: Minimum = 6ms, Maximum = 6ms, Average = 6ms

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Probing Packets

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Round-Trip TimeClientServer

0.000 ms

9.952 ms

1006.122 ms

1017.039 ms

request

reply

request

reply

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Why Didn’t We Measure One-Way Delay?

• Asynchronous system clocks would make the measurement result confusing.

ReceiverSender 19:20:21 19:20:19

Delay = -1 sec !

19:20:20

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ICMP Packet Format• RFC 792 – Internet Control Message Protocol

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Type Code Checksum

unused

Identifier Sequence Number

Data

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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

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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

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Measuring One-Way Delay

ReceiverSender 19:20:21 19:20:19

Delay = 1 sec

19:20:22

Synchronization

19:20:21

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OWAMP Design Goals

• One-Way Active Measurement Protocol– RFC 4656, September 2006.

• 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.

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OWAMP Logical Model

Session Sender Session Receiver

Server

Control-Client Fetch-Client

OWAMP-Test

OWAMP-ControlOWAMP-Control

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Commonly Implemented Model

Session-Sender

Control-Client

Fetch-Client

Session-Receiver

ServerOWAMP-Control

OWAMP-Test

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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

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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

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Sequence Number

Timestamp (8 octets)

Packet Padding

Error Estimate

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OWAMP Errors

•Preliminary Findings:–Min error estimates look to be in the 55-60 usec range.–Serialization Delay: ~5usec x 2–Get Timestamp: ~15usec x 2–Additional error is:

• Time from userland “send” to 1st byte hits the wire• Time from kernel has packet to userland “recv” returns• Potentially recv process data processing before calling “recv”

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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)

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Weather Map

http://weathermap.grnoc.iu.edu/abilene.png

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802.16 IP Telephone Labowping

$ 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]:64337 ---

SID: fef1505dc8e1a459016511e87b0e310c5 sent, 0 lost (0.000%), 0 duplicatesone-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]:52896 ---

SID: fe56ea22c8e1a4591f6c8b43d56f48c25 sent, 0 lost (0.000%), 0 duplicatesone-way delay min/median/max = 112/112/113 ms, one-way jitter = 0.8 ms (P95-P50)Hops = 7 (consistently)no reordering

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Captured OWAMP Packets

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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

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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 l

ook "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: 0.2-0.6%– IPsec: 0.05%

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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.

802.16 IP Telephone Lab 1 One-Way Ping Dr. Quincy Wu, Associate Professor ([email protected])...

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