draft-ietf-ippm-checksum-trailer-04.txt   draft-ietf-ippm-checksum-trailer-05.txt 
Network Working Group T. Mizrahi Network Working Group T. Mizrahi
Internet Draft Marvell Internet Draft Marvell
Intended status: Experimental Intended status: Experimental
Expires: May 2016 November 9, 2015 Expires: May 2016 November 16, 2015
UDP Checksum Complement in OWAMP and TWAMP UDP Checksum Complement in OWAMP and TWAMP
draft-ietf-ippm-checksum-trailer-04.txt draft-ietf-ippm-checksum-trailer-05.txt
Abstract Abstract
The One-Way Active Measurement Protocol (OWAMP) and the Two-Way The One-Way Active Measurement Protocol (OWAMP) and the Two-Way
Active Measurement Protocol (TWAMP) are used for performance Active Measurement Protocol (TWAMP) are used for performance
monitoring in IP networks. Delay measurement is performed in these monitoring in IP networks. Delay measurement is performed in these
protocols by using timestamped test packets. Some implementations use protocols by using timestamped test packets. Some implementations use
hardware-based timestamping engines that integrate the accurate hardware-based timestamping engines that integrate the accurate
transmission timestamp into every outgoing OWAMP/TWAMP test packet transmission timestamp into every outgoing OWAMP/TWAMP test packet
during transmission. Since these packets are transported over UDP, during transmission. Since these packets are transported over UDP,
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on May 9, 2016. This Internet-Draft will expire on May 16, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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packets. packets.
The accuracy of delay measurements relies on the timestamping method The accuracy of delay measurements relies on the timestamping method
and its implementation. In order to facilitate accurate timestamping, and its implementation. In order to facilitate accurate timestamping,
an implementation can use a hardware based timestamping engine, as an implementation can use a hardware based timestamping engine, as
shown in Figure 1. In such cases, the OWAMP/TWMAP packets are sent shown in Figure 1. In such cases, the OWAMP/TWMAP packets are sent
and received by a software layer, whereas the timestamping engine and received by a software layer, whereas the timestamping engine
modifies every outgoing test packet by incorporating its accurate modifies every outgoing test packet by incorporating its accurate
transmission time into the <Timestamp> field in the packet. transmission time into the <Timestamp> field in the packet.
OWAMP/TWAMP-enabled Node OWAMP/TWAMP-enabled Node
+-------------------+ +-------------------+
| | | |
| +-----------+ | | +-----------+ |
Software | |OWAMP/TWAMP| | Software | |OWAMP/TWAMP| |
| | protocol | | | | protocol | |
| +-----+-----+ | | +-----+-----+ |
| | | | | | +---------------------+
| +-----+-----+ | | +-----+-----+ | / Intermediate entity |
| | Accurate | | | | Accurate | | / in charge of: |
ASIC/FPGA | | Timestamp | | ASIC/FPGA | | Timestamp | | /__ -Timestamping |
| | engine | | | | engine | | |-Updating checksum or|
| +-----------+ | | +-----------+ | | Checksum Complement |
| | | | | | +---------------------+
+---------+---------+ +---------+---------+
| |
|test packets |test packets
| |
___ v _ ___ v _
/ \_/ \__ / \_/ \__
/ \_ / \_
/ IP / / IP /
\_ Network / \_ Network /
/ \ / \
\__/\_ ___/ \__/\_ ___/
\_/ \_/
Figure 1 Accurate Timestamping in OWAMP/TWAMP Figure 1 Accurate Timestamping in OWAMP/TWAMP
OWAMP/TWAMP test packets are transported over UDP. When the UDP OWAMP/TWAMP test packets are transported over UDP. When the UDP
payload is changed by an intermediate entity such as the timestamping payload is changed by an intermediate entity such as the timestamping
engine, the UDP Checksum field must be updated to reflect the new engine, the UDP Checksum field must be updated to reflect the new
payload. When using UDP over IPv4 ([UDP]), an intermediate entity payload. When using UDP over IPv4 ([UDP]), an intermediate entity
that cannot update the value of the UDP checksum has no choice except that cannot update the value of the UDP checksum has no choice except
to assign a value of zero to the checksum field, causing the receiver to assign a value of zero to the checksum field, causing the receiver
to ignore the checksum field and potentially accept corrupted to ignore the checksum field and potentially accept corrupted
 End of changes. 4 change blocks. 
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