USN Field in SSDP Search Response ?

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TheDecker
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USN Field in SSDP Search Response ?

Beitrag von TheDecker » 20. Dez 2007 08:45

How often and with which values must a device/service answer to a search request which it matches ?

Once for each possible USN (3 for devices/service + 1 for root devices) ? Only once with an USN matching the request ?

fernando
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Beitrag von fernando » 21. Dez 2007 15:27

Hello,

[font=Courier New] 1) How often and with which values must a device/service answer to a search request which it matches? [/font]

To answer, I'll refer to the Upnp Documentation (upnp Device Architecture 1.0 - Document revision date 20.07.2006)
About How Soon:
PAGE 14:
"Advertisements in the initial set should have comparable durations and the entire set should be sent as quickly as possible.", and then PAGE 15: "Devices should wait a random interval less than 100 milliseconds before sending an initial set of advertisements in order to reduce the likelihood of network storms"

About How often:
The notifications are set with a random duration (CACHE_CONTROL header), with a minimun of 1800 miliseconds. PAGE 14: "These messages must be sent out as a series with roughly comparable expiration times; order is unimportant, but refreshing or canceling individual messages is prohibited." After the first quick response (<100 miliseconds), the notifications are set with a random duration (CACHE_CONTROL header), with a minimun of 1800 miliseconds.

Which values must a device/service answer to a search request which it matches?
Please read pages 20, 21 (too long to paste it here). It follows the same pattern as the notifications (ssdp:alive), "except that the NT header there (NOTIFY, page 16) is an ST header here". (PAGE 20).
About the USN values, you can find them in the table in page 16.

[font=Courier New]2) Once for each possible USN (3 for devices/service + 1 for root devices) ? Only once with an USN matching the request ?[/font]
Table in page 21 has all the information.

Best regards,
Fernando

fernando
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Re: USN Field in SSDP Search Response ?

Beitrag von fernando » 9. Jan 2008 13:53

Hello,

A few details following another question from today's Q&A:
Response to an "ssdp:discover" event:
Answer is via unicast UDP, by sending it directly to the device that sent the M-SEARCH (for details on how to get that address see the other especific posting). Be careful that there are 2 cases:
1) if the ST field of the M-SEARCH request is <> "ssdp:all", then the ST header contains the same value as in the request.
2) If the ST field =="ssdp:all", then 3+2d+k response messages are sent, similar as with "ssdp:alive"

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