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Thread: Capacity Max- Preferred Sites can cause roaming issues

  1. #1
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    Default Capacity Max- Preferred Sites can cause roaming issues

    Team,
    If working on CapMax, be aware that adjusting the Site Preference number from default can cause some issues. This is a result of when a radio sees a site with a higher preference level than than the one it is on AND it can see that site above the ACCEPTABLE THRESHOLD (-108 typical), then it will roam to that site. It will then stay on that site until it cannot hear the site above this threshold.

    The issue I see several times a month is that the default Acceptable Level (-108) is a poor value for portable subscribers to be sitting on an RF site. Typically, MOTOTRBO radios will have poor inbound audio around -100 to -105 as measured from the radio in RSSI mode. I want my portables to start looking for adjacent sites at -95 or sooner. Typically, people try to use Preferred Site to drive radios from sites of lower RF resources to that of more RF resources (i.e. more repeaters at the site). Once this behavior is understood, the first reaction may be to change the Acceptable Level from -108 to -105/-103/-100. The issue is that the Acceptable Threshold sets the threshold where the radio will not allow you to key up on an RF site weaker than this value. Typically, adjusting this value causes a reduction in coverage as noticed by users in the field.

    I would like to recommend that instead of Site Preference, use different site RSSI Roaming Thresholds at each site. The site where you want radios to most land could be set to -100/-103/-105 and the site where you want radios to keep away from could be set to -50/-60/-70/etc. The would result radios not looking to roam away from the site where you want them spend the most time until they hit a weak RSSI. The radios would then roam to a site that was at least 6dB stronger than their current site. On the site where you want the radios to be at least, they would start looking at adjacent at a relatively strong value and would roam as soon as they found a site 6dB stronger. In effect, the radios will end of lingering/grouping at the sites with weaker RSSI roaming levels.

    Hope this helps, as there are many mis-configured systems that I come across. Also, a certain manufacturer is making a big push to upgrade Connect Plus systems to CapMax. FB
    Obviously NOT a radio professional!!


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  3. #2
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    Wayne published a nice article today along this train of thought --

    https://cwh050.blogspot.com/2020/05/...his-wrong.html

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    He still at a relatively high level, sometimes you gotta beat it into the folks who think 100w is always better than 25w (it may be, but it also may not be). And also those who think a 12dB gain antenna is always better than a 2dB gain antenna (it may be, but it may also not be). Same kind of folks who turn off all of the attenuation on their multicouplers......... FB

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    On the topic of Capacity Max roaming, is there a setting in the System Set to hold off site roaming to avoid constant "flapping" between sites when a subscriber radio is in a fringe area between sites which are near the roaming RSSI threshold?
    In Astro25 it's the "RFSS Debounce Timer" but in MotoTRBO RM there's a whole different set of terminology used to describe similar system timer settings. Searching for "Debounce" only refers to the context of GPIO pins and the other timers seem to concern loss of control channel sync or loss of payload channel sync.

    Also, is there a way for the system to announce to subscribers a dynamic preference of sites based on current traffic loading or payload timeslot capacity? I have a mixture of sites with more physical repeaters than the others and significant overlap. Since static preference isn't a good way to tell the subscriber to use one site over another if both are relatively similar RSSI, there's a chance a subscriber might roam to a site with lower capacity and miss calls (if there are no remaining available timeslots to grant) or get busies when it could be registered to the "better" site for that given geographical location, with lots more traffic capacity. I looked into the "centralized distribution" toggle which maybe seems like what I'm thinking of (the documentation refers to the "bandwidth" of a site which I'm assuming is the total aggregate of active repeaters that can carry traffic, not literally the RF signal occupied bandwidth). I kind of run into a similar thing on P25 systems but the subscriber automatically tries to location register and request channel on another usable adjacent site if it receives a queue_rsp on the site it was originally on. I don't see the MotoTRBO subscriber radios do that though, if the site is actually busy it will just bleep busy and sit on the same site's control channel and not immediately try another site to see if it can carry that voice group call request. The other use case for this would be for sites that have statically affiliated talkgroups in the case of VRC-connected dispatch audio or for the benefit of subscriber "scan" (RX group list) functions. If the radio roams over to a lesser-preferred site where there are no (other) affiliations to a given talkgroup that it is not itself affiliated with, but is on the scan/RX group list, it would still never unmute to that traffic that was not being carried on that site (but might be carried on another site, the subscriber wouldn't know about).

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    The big thing to prevent flapping is to not use defaults and have a sizable difference in RSSI threshold between the RF sites. There is no way to have the radio move around based on site resources. Many people use Site Preference, but it causes many issues. The cleanest way I have seen to control site loading is to have a lower RSSI threshold (-85) for sites where you want less traffic and a higher threshold (-95) were you want users to remain. This is not a perfect scenario. My speech to Astro folks is to change their expectations from about 5ft off the floor to about 2ft off the floor. Astro is about 10-15 times the price, so there will be a functionality difference.

    Audio in Cap Max is peer-to-peer. Centralized Distribution is for low bandwidth sites is a setting where ALL audio traffic is sent back to the CMSS for distribution to all sites involved in the call. This preventing overloading an RF site's backhaul where it would have to sent out a bunch of streams to many different sites.

    CapMax is ALL START, which means that all sites involved in the call must have resources available or you will start getting weird messages. PARTY BUSY being one of my favorite.

    Most of what you are wanting to be done can be controlled by the RSSI roaming value and it will take some work to get values you are looking for.

    You can setup the radio to drag scan list members over to RF site. In fact, I use it to overwhelm small capacity sites all the time in testing. FB
    Obviously NOT a radio professional!!