[Seamoby] DoCoMo Implementation Issues with CTP

"James Kempf" <kempf@docomolabs-usa.com> Tue, 17 February 2004 22:25 UTC

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Message-ID: <059c01c3f5a4$63e9e360$936015ac@dclkempt40>
From: "James Kempf" <kempf@docomolabs-usa.com>
To: <seamoby@ietf.org>
Cc: "Raghu Dendukuri" <dendukuri@docomolabs-usa.com>
Date: Tue, 17 Feb 2004 14:21:29 -0800
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Subject: [Seamoby] DoCoMo Implementation Issues with CTP
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DoCoMo is in the process of implementing CTP, and we came up with the
following list of issues in the spec. Since none of them seem particularly
large, Allison suggested that we simply update the current version of the
document (which is now under review by the ROHC WG) in place, without reving
the document to a new version. She will make the changes.
Below, a list of the issues and suggested changes to the document to address
them.

Any comments? Please let me know by March 6.

            jak

-------------------------------------------

1) Section 2.5.1, pg. 10; Section 2.5.2, pg. 11; Section 2.5.3, pg. 12;
Section 2.5.4, pg. 13; Section 2.5.6, pg. 15 - 'V' flag

The spec allows CTP messages to carry both IPv4 and IPv6 addresses, but as a
practical matter in the implementation, a CTP message will be sent to the
IPv4 or IPv6 address of a router. Processing the address of the opposite
version in the stack is complicated. Suggestion is to only allow IPv4 or
IPv6 addresses, but keep the flag field size at 2 bits in case further
experience shows that there are reasons why both might be sent. The router
can issue separate messages if both addresses must be changed,  Suggested
change in text:

Replace: "When set to '10', indicate presence of both IPv6 and IPv4 Previous
(New) addresses."
With: "Values of '10' and '11' are reserved".

2) Section 2.5.3, pg. 12 - Length of Algorithm field in CTD message block.

The length of the algorithm field in the CTD message block is shown as 17
bits. It should be 16.

3) Section 2.5.1, pg. 10; Section 2.5.2, pg. 11; Section 2.5.3, pg. 12;
Section 2.5.4, pg. 13; Section 2.5.6, pg. 15 - Length field.

The size of the message length field is currently 8 bits, and the units for
the length are in 8 octet words. This allows a maximum of 2048 octets, which
might not be enough for bundling large amounts of context if padding is
required. Suggestion is to increase the size of the field and make it be
units of octets, for a total of 65535 octets. This would only involve moving
the flags into the Reserved field, and would not otherwise modify the
message.

Replace: In message diagram blocks, move Length to be 16 bits rather than 8.

Replace: "Length    message length in units of 8 octet words"
With: "Length    message length in units of octets"

4) Section 2.5.1. pg. 9; Section 2.5.2, pg. 11; Section 2.5.3, pg. 12;
Section 2.5.4, pg. 13; Section 2.5.5, pg. 14; Section 2.4.6, pg. 15 - IP
address field size.

The message block diagrams show the size of the IP address fields as 4
octets, but if the IP address is for IPv6, it will be 16.

Replace: In the message block diagrams, replace the final "|" with a "~" to
indicate a variable length field. Indicate variable length field by putting
"(4 or 16 octets)" after the text in the field.

5) Section 2.5.3, pg. 12 - Key field in message diagram

Only 4 bytes are shown for the key field, but the key size field allows
65535. The message diagram needs to be changed.

Replace: In the message diagram, replace the final "|" with a "~" to
indicate a variable length field. Indicate the variable length field by
putting "(variable)" after the text in the field.



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