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Revision 3 as of 2005-12-08 10:22:23
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Revision 5 as of 2005-12-15 14:18:37
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XXX - add a brief description of UDP-Lite history Wireless links typically have lower bit rates and higher error rates when compared to wired links. Applications such as audio/video streaming can use error-resilient codecs, but are delay-sensitive. Hence retransmission do to checksum errors in less important
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    Checksum: 0x4620 [correct]     Checksum: 0x4614 [correct]
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XXX - Add a simple example capture file to the SampleCaptures page and link from here (see below). Keep this file short, it's also a good idea to gzip it to make it even smaller, as Ethereal can open gzipped files automatically.  * attachment:SampleCaptures/udp_lite_full_coverage_0.pcap If coverage=0, the full packet is checksummed over.
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 * attachment:SampleCaptures/udplite.pcap  * attachment:SampleCaptures/udp_lite_illegal_1-7.pcap Coverage values between 1..7 (illegal).

 * attachment:SampleCaptures/udp_lite_normal_coverage_8-20.pcap Normal ones with correct checksums (legal).

 * attachment:SampleCaptures/udp_lite_illegal_large-coverage.pcap Three traces with coverage lengths greater than the packet length.

 * attachment:SampleCaptures/udp_lite_checksum_0.pcap Checksum 0 is illegal.

Lightweight User Datagram Protocol (UDP-Lite)

The Lightweight User Datagram Protocol (UDP-Lite) ([http://www.ietf.org/rfc/rfc3828.txt RFC 3828]), which is similar to the User Datagram Protocol (["UDP"]) ([http://www.ietf.org/rfc/rfc768.txt RFC 768]), but can also serve applications in error-prone network environments that prefer to have partially damaged payloads delivered rather than discarded. If this feature is not used, UDP-Lite is semantically identical to UDP.

History

Wireless links typically have lower bit rates and higher error rates when compared to wired links. Applications such as audio/video streaming can use error-resilient codecs, but are delay-sensitive. Hence retransmission do to checksum errors in less important

Protocol dependencies

  • ["IP"]: Typically, UDP-Lite uses ["IP"] as its underlying protocol. The assigned protocol number for UDP-Lite is 136.

Example traffic

{{{Frame 1 (60 bytes on wire, 60 bytes captured) Ethernet II, Src: 00:60:97:a0:e3:7e (00:60:97:a0:e3:7e), Dst: 00:04:75:c7:87:49 (00:04:75:c7:87:49) Internet Protocol, Src: 139.133.204.185 (139.133.204.185), Dst: 139.133.204.176 (139.133.204.176)

  • Version: 4 Header length: 20 bytes Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00) Total Length: 40 Identification: 0xb651 (46673) Flags: 0x04 (Don't Fragment) Fragment offset: 0 Time to live: 64 Protocol: UDPlite (0x88) Header checksum: 0xd387 [correct] Source: 139.133.204.185 (139.133.204.185) Destination: 139.133.204.176 (139.133.204.176)

Lightweight User Datagram Protocol, Src Port: 1024 (1024), Dst Port: 1234 (1234)

  • Source port: 1024 (1024) Destination port: 1234 (1234) Checksum coverage: 8 Checksum: 0x4614 [correct]

Data (12 bytes)

0000 68 65 6c 6c 6f 20 77 6f 72 6c 64 0a hello world.}}}

Ethereal

The UDP-Lite dissector is in development as of December 2005. It rides with the ["UDP"] dissector, using an additional field for checksum coverage length.

Preference Settings

  • Ignore checksum coverage (default:TRUE) - Ignore the fact that the checksum coverage value is invalid and the datagram should be dropped.

Example capture file

  • attachment:SampleCaptures/udp_lite_full_coverage_0.pcap If coverage=0, the full packet is checksummed over.
  • attachment:SampleCaptures/udp_lite_illegal_1-7.pcap Coverage values between 1..7 (illegal).
  • attachment:SampleCaptures/udp_lite_normal_coverage_8-20.pcap Normal ones with correct checksums (legal).
  • attachment:SampleCaptures/udp_lite_illegal_large-coverage.pcap Three traces with coverage lengths greater than the packet length.
  • attachment:SampleCaptures/udp_lite_checksum_0.pcap Checksum 0 is illegal.

Display Filter

A complete list of UDP-Lite display filter fields can be found in the [http://www.ethereal.com/docs/dfref/protofirstletter/proto.html display filter reference]

  • Show only the UDP-Lite based traffic:

     udplite 

Capture Filter

  • Capture only the UDP-Lite traffic:

     ip proto 136 

Discussion

Lightweight_User_Datagram_Protocol (last edited 2008-07-22 16:07:03 by GeraldCombs)