Transcript Introduction to OWAMP

802.16 IP Telephone
Lab
- Introduction to OWAMP
One-Way Ping
Dr. Quincy Wu, Associate Professor
([email protected])
Graduate Institute of Communication Engineering
National Chi Nan University
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Growth of Internet
• 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
Computer Networks and Internets, Douglas E.
Comer, Pearson Prentice hall, 2004.
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Growth of Internet (cont.)
• Plotted on a log scale
• The growth appears
approximately linear
– Exponential growth
– The Internet has been
doubling in size every
nine to twelve months
Computer Networks and Internets, Douglas E.
Comer, Pearson Prentice hall, 2004.
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Hosts & Routers
LAN
LAN
router
LAN
router
router
LAN
LAN
router
router
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 Response
C:\>ping www.cse.yzu.edu.tw
Pinging 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=115
Reply from 140.138.144.172: bytes=32 time=11ms TTL=115
Reply from 140.138.144.172: bytes=32 time=10ms TTL=115
Reply from 140.138.144.172: bytes=32 time=11ms TTL=115
Ping 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, Average = 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
Reply from 140.113.209.41: bytes=32 time=6ms TTL=56
Reply from 140.113.209.41: bytes=32 time=6ms TTL=56
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 Time
Client
Server
request
0.000 ms
reply
9.952 ms
request
1006.122 ms
reply
1017.039 ms
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Why Didn’t We Measure One-Way Delay?
• Asynchronous system clocks would make the measurement result
confusing.
Sender
19:20:21
Receiver
19:20:19
19:20:20
Delay = -1 sec !
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ICMP Packet Format
• RFC 792 – Internet Control Message Protocol
0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
Code
Type
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
Synchronization
Sender
19:20:21
Receiver
19:20:19
19:20:21
19:20:22
Delay = 1 sec
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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
OWAMP-Test
Session Receiver
Server
OWAMP-Control
Control-Client
OWAMP-Control
Fetch-Client
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Commonly Implemented Model
Session-Sender
OWAMP-Test
Control-Client
OWAMP-Control
Session-Receiver
Server
Fetch-Client
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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
0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
Sequence Number
Timestamp (8 octets)
Error Estimate
Packet Padding
• 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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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
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http://weathermap.grnoc.iu.edu/abilene.png
owping
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$ 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: fef1505dc8e1a459016511e87b0e310c
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]:52896 --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
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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 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: 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.
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