Frank, I do not see any conflict between the text that you have quoted and the figure. I do not understand how you can say using modulo arithmetic has no effect. For example, 1 - 2 = -1, but 1 - 2 modulo 2^24 is 2^24 - 1. The absolute value of the difference between local and received values can not be used as this would be the same at both ends, hence both would conclude to being the master (or both the slave). Best regards Mike Nilsson -------------------- Mike Nilsson Advanced Video Services

BTexact Technologies

Callisto House, B81 Room 102 pp14 Adastral Park, Martlesham Heath, Ipswich, IP5 3RE, UK Tel: +44 1473 645413 Mobile: +44 7808 635412 Fax: +44 1473 646589 Email: mike.nilsson@bt.com BTexact Technologies is a trademark of British Telecommunications plc Registered office: 81 Newgate Street London EC1A 7AJ Registered in England no. 1800000 This electronic message contains information from British Telecommunications plc which may be privileged or confidential. The information is intended to be for the use of the individual(s) or entity named above. If you are not the intended recipient be aware that any disclosure, copying, distribution or use of the contents of this information is prohibited. If you have received this electronic message in error, please notify us by telephone or email (to the numbers or address above) immediately.

-----Original Message----- From: frank.derks@philips.com [SMTP:frank.derks@philips.com] Sent: Thursday, May 03, 2001 3:23 PM To: mike.nilsson Cc: itu-sg16 Subject: RE: The use of statusDeterminationNumber in masterSlaveDeterminat ion

Mike,

the figure only partly solves the problem. The text that I referred to does not reflect what is in the figure, so this should be corrected.

Furthermore, since the values that statusDeterminationNumber can take on are in the range 0..(2^24-1). The "modulo operation" with 2^24 has no effect whatsoever.

It would seem that the real intent is that the _absolute_ value of the difference between the received statusDeterminationNumber and the locally generated statusDeterminationNumber determines which party is to become the master and which party is to becomes the slave. If the difference is smaller than 2^23 then the party that received the masterSlaveDetermination message becomes the master. Otherwise it becomes the slave. In the case that the two numbers are equal, the result is indeterminate.

Regards,

Frank

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mike.nilsson@bt.com on 03-05-2001 16:04:45 To: Frank Derks/HVS/BE/PHILIPS@EMEA2 cc: Subject: RE: The use if statusDeterminationNumber in masterSlaveDeterminat ion Classification:

Frank,

The answer is in Figure C.4(v) of H.245.

Best regards

Mike Nilsson

-------------------- Mike Nilsson Advanced Video Services

...

BTexact Technologies

Callisto House, B81 Room 102 pp14 Adastral Park, Martlesham Heath, Ipswich, IP5 3RE, UK Tel: +44 1473 645413 Mobile: +44 7808 635412 Fax: +44 1473 646589 Email: mike.nilsson@bt.com

BTexact Technologies is a trademark of British Telecommunications plc Registered office: 81 Newgate Street London EC1A 7AJ Registered in England no. 1800000

This electronic message contains information from British Telecommunications plc which may be privileged or confidential. The information is intended to be for the use of the individual(s) or entity named above. If you are not the intended recipient be aware that any disclosure, copying, distribution or use of the contents of this information is prohibited. If you have received this electronic message in error, please notify us by telephone or email (to the numbers or address above) immediately.

...

-----Original Message----- From: Frank Derks [SMTP:frank.derks@PHILIPS.COM] Sent: Thursday, May 03, 2001 1:51 PM To: ITU-SG16@MAILBAG.INTEL.COM Subject: The use if statusDeterminationNumber in masterSlaveDetermination

C.2.1.4/H.245 states the following:

"If the terminal type numbers are the same, the statusDeterminationNumbers are compared using modulo arithmetic to determine which is master

If both terminals have equal terminalType field values and the difference between statusDetermination field values modulo 2^24 is 0 or 2^23, an indeterminate result is obtained"

The first sentence states that "modulo arithmetic" must be used to compare the numbers. I would say that that's a rather vague way of describing how the comparison must be done. Furthermore it does not tell me what the result must be for a terminal to be determined to be the master!

According to the second sentence, I know how to obtain an indeterminate result. So any result that is not any of the two specified values is not indeterminate, but I still do not know what the meaning of the result is. "Modulo arithmetic" is, however, introduced, but it is not clear whether this is the modulo arithmetic referred to in the first sentence. Furthermore, what is the significance of a result of 2^23?

I assume that the same rules that apply to the comparison of the terminalType field apply (i.e. the terminal with the higher value becomes the master), but this is not stated explicitly.

Regards,

Frank

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