Annex G & big messages (and TPKT and Annex E)

[Chip Sharp]

I agree with Gur.

The TPDU in RFC1006 (TPKT) and the equivalent message in Annex E are
"limited" (I don't think this is much of a limitation personally) to 64K
bytes (65536 bytes).  For Annex E, any message over 1500 bytes (actually
1500 bytes minus headers) must be sent over TCP since neither UDP nor Annex
E (nor RFC 1006) inherently provide a fragmentation and reassembly mechanism.

Since Annex E is really only defined for H.225 transport this shouldn't be
a problem.

Does anyone have an example of a real-world signaling message that exceeds
1500 bytes (much less 64K bytes)?  How about an imaginary one (with
probability of occuring greater than 0)?

I'd recommend that if you are transmitting messages larger than 64K bytes
over Annex E or G that you re-evaluate the protocols (or the
implementations) you are using.  Neither Annex E nor G are intended for use
as a general purpose Transport protocol over the Internet.

Chip

At 09:07 PM 5/4/99 +0600, Gur Kimchi wrote:
>Douglas , Espen:
>
>You are right, both TPKT and Annex E limit each segment within a message to
>a max of 64K bytes -
>and both allow you to aggregate - place multiple payloads, each sized at
>(or less) 64K in a single
>message - this is of course relevant only to Annex E over TCP (which is not
>really used as this time
>for anything).
>
>I don't see this is a serious limitation - unless the information exchange
>between GKs is going to
>contain many pictures... seriously, you will need to divide up your large
>transactions into 64K segments.
>
>If any of you think this is a real problem - speak up -
>
>- gur
>
>-------- On 05/04/99 09:15 AM GMT  Douglas Clowes <dclowes at OZEMAIL.COM.AU>
>wrote:
>
>
>
>
>No, I had reached the same conclusion - the packet size is, indeed, limited
>to 65K bytes. If the message size exceds the UDP MTU, it hould be sent by
>TCP. What I am still wondering is, will we exceed the 65K on TCP?
>
>Subtly, this raises a similar question for Annex E which has the same
>limitation. Should Annex E have a larger size field, and Annex G use Annex
>E for a larger message size?
>
>Does the TPKT size limitation affect anything else which uses it?
>
>Douglas
>
>At 09:35 1999-05-04 +0200, ETO wrote:
>>Hi all,
>>
>>When an Annex G message will exceed max packet size (typically a
>>DescriptorConfirm) on UDP,
>>a Reject might be sent, and the session is repeated on TCP.
>>
>>But, isn't our PDU size on TCP also limited? When using TPK, the max pdu
>>size is 65k too, as seen in RFC-1006....
>>
>>Hope I'm wrong here.
>>
>>Espen
>>
>>

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Chip Sharp                 voice: +1 (919) 851-2085
Cisco Systems              Consulting Eng. - Telco
Reality - Love it or Leave it.
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