With 100BASE-TX hardware, the raw bits (4 bits wide clocked at *25 MHz* at the MII) go through 4B5B <http://en.wikipedia.org/wiki/4B5B> binary encoding to generate a series of 0 and 1 symbols clocked at *125 MHz* symbol rate<http://en.wikipedia.org/wiki/Symbol_rate>. The 4B5B encoding provides DC equalization and spectrum shaping (see the standard for details)[*citation needed<http://en.wikipedia.org/wiki/Wikipedia:Citation_needed> *]. Just as in the 100BASE-FX case, the bits are then transferred to the physical medium attachment layer using NRZI<http://en.wikipedia.org/wiki/NRZI>encoding. However, 100BASE-TX introduces an additional, medium dependent sublayer, which employs MLT-3 <http://en.wikipedia.org/wiki/MLT-3> as a final encoding of the data stream before transmission, resulting in a maximum "fundamental frequency" of* 31.25 MHz*. The procedure is borrowed from the ANSI X3.263 FDDI <http://en.wikipedia.org/wiki/FDDI>specifications, with minor discrepancies. [3] <http://en.wikipedia.org/wiki/Fast_Ethernet#cite_note-mlt3-2>
Source: http://en.wikipedia.org/wiki/Fast_Ethernet Josh Luthman Office: 937-552-2340 Direct: 937-552-2343 1100 Wayne St Suite 1337 Troy, OH 45373 Those who don't understand UNIX are condemned to reinvent it, poorly. --- Henry Spencer On Thu, Jan 8, 2009 at 12:02 AM, Marlon K. Schafer <o...@odessaoffice.com>wrote: > So far all I can find on the internet is that ethernet is at either 12.5 or > 31.25mhz. NOT 350, that's gigE, not 10/100. > > Also, this tower is a 100' wooden pole. Can't move anywhere really. > marlon > > ----- Original Message ----- > From: "Adam Goodman" <a...@wispring.com> > To: "WISPA General List" <wireless@wispa.org> > Sent: Wednesday, January 07, 2009 9:15 AM > Subject: Re: [WISPA] FM radio station site strangeness > > > > It also sounds like there is a new leak in the waveguide. One more > > thing you might try is to move the cable from leg to leg on the tower > > so that you variable length sections that do not resonate at 350MHz or > > ~100MHz (FM transminssion). > > > > > > On Wed, Jan 7, 2009 at 11:16 AM, Adam Goodman <a...@wispring.com> wrote: > >> We also colocate with an FM transmitter. Only 1300W though. we also > >> had interference on our Ethernet lines. We solved it by moving radios > >> away from the FM antenna (3 feet or so on a 90' tower) We also > >> installed ferrits which helped (I actually used a conduit pipe). > >> Grounding the cat5 helped too. > >> > >> I would think that if you find that you need more shielding. put all > >> your cat5 cables in a conduit and install abreakout box at the top of > >> the tower. If your area is prone to electrical storms (where isn't > >> these days?!) you will at some point be very sorry you didn't grount > >> (and well!!) > >> > >> > >> > >> On Wed, Jan 7, 2009 at 10:47 AM, Marlon K. Schafer < > o...@odessaoffice.com> > >> wrote: > >>> Hi All, > >>> > >>> I think we finally have this all figured out. Now I just have to > figure > >>> out > >>> how to fix it. > >>> > >>> We've been up there for over 6 years now. It's certainly been a > >>> problematic > >>> site though. Constant channel changes (we have 3 competitors a mile > >>> away > >>> and pick up hundreds of ap's from in town) are the norm. > >>> > >>> This fall (a month or two ago) one of the tenants left the building. > >>> This > >>> cleared out most of the hardware that was in there. A little bit > before > >>> that I replaced an Inscape Data and a smartBridges combo with a single > >>> MT > >>> access point, using one of the cables that had been working for one of > >>> the > >>> other two. > >>> > >>> About a week ago things started to really act up. Multiple devices > were > >>> having trouble. I was able to catch it in the act finally. This time > >>> the > >>> problem wasn't a wireless issue, the devices were constantly > >>> disconnecting > >>> and reconnecting at the switch level. > >>> > >>> I pulled the Cisco switch out and dropped in a Netgear unit. That > >>> didn't > >>> fix it. Next I put in a Digital Loggers rack mount reboot device. > That > >>> wouldn't connect right either. > >>> > >>> I finally had to pull all of the hardware off of the shelf and set most > >>> of > >>> it on the floor (or just let it hang there) to get it working at all > >>> well. > >>> Still not perfect but better. > >>> > >>> I had by now hiked up there through sometimes knee deep snow 3 or 4 > >>> times. > >>> Next I took a motorbike with studded snow tires up and got permission > to > >>> turn down the power to the radio station. That didn't fix the problem > >>> either. > >>> > >>> Next I borrowed a snowmobile and hauled some help and my spectrum > >>> analyzer > >>> up. I was unable to see any signals that didn't belong. > >>> > >>> Next day, another hike up the hill. > >>> > >>> OK, maybe a cat 5 cable went bad and I'm getting backfeed through the > >>> switch. DC current or something. So I started testing the cables that > >>> run > >>> to the most problematic units. Well now, look at that. Bad cable. In > >>> fact > >>> there are three of them. Hmmm, kinda strange though. All three have > >>> the > >>> exact same fault! Oh well, better change them out anyway. I ran three > >>> new > >>> cable runs and just for kicks I tested one of them. What the heck????? > >>> The > >>> new cable has the EXACT same fault as the old one! Even though it > >>> didn't > >>> follow the exact same path as the old cables. > >>> > >>> Man, this is sure looking like a problem caused by the radio station. > I > >>> was > >>> using indoor cat5 and didn't run lightning protection or ground > >>> anything. > >>> Yeah I know, but remember that this has been there for a very long time > >>> like > >>> this. And as a guy with an electrical background I know that there are > >>> actually two ways to deal with stray electrical. Grounding is one. > >>> Insulating is another!!!! Anyway, I know it wasn't built to specs. > >>> > >>> I added some grounding and that didn't help at all. > >>> > >>> Yesterday I finally had one of the local wireless companies (Day > >>> Wireless) > >>> that mainly does VHF radios, backhaul etc. They also checked things > >>> with > >>> the spectrum analyzer but couldn't find anything amiss. I was able to > >>> duplicate the wiring fault for them (with my Ideal tester). But > >>> suddenly > >>> everything cleared right up! Stuff was looking good, no cable fault > >>> etc. > >>> Pings were looking good, devices were finally negotiating the > >>> connections > >>> right etc. > >>> > >>> I called the radio station to ask if I could try turning the power down > >>> again to see if we see any change on the spectrum analyzer. They said > >>> they > >>> thought that I'd already done that because the showed the power was way > >>> down. Turns out someone in the building had bumped a breaker and shut > >>> down > >>> part of the transmitter! Well, we got all of that figured out and > guess > >>> what. All of the problems came right back! I then turned the power > >>> back > >>> down and they cleared up. > >>> > >>> Tip for you guys, dropping an 18,000 watt system down by even 60% of > >>> it's > >>> normal output isn't always enough. We had to drop down to 10 to 20% to > >>> get > >>> the problems to clear up. The guys from Day Wireless had some small > >>> ferrite > >>> beads with them so we stuck them onto the cables. Put the beads on and > >>> the > >>> radios would negotiate at 100full. Take them off and they'd drop right > >>> back > >>> to 100 half. Duplicatable all day long. > >>> > >>> Soooo, current theory is that the radio station is screwing up my cat5 > >>> connections. The fact that the building has less hardware in it and we > >>> have > >>> more snow up there than normal has probably caused some different eddy > >>> currents or multipath. Or some other such strangeness. > >>> > >>> I have some shielded cable and connectors on the way. I have > permission > >>> to > >>> move my gear from one side of the building to the other side. I've got > >>> more > >>> high end ferrite beads on the way (one that is made for cat 5 and is > big > >>> enough for three wraps to go through it). Not the little $.50 ones, > >>> these > >>> are nearly $6.00 each. > >>> > >>> I also have a Fluke DTX on the way. > >>> > http://www.flukenetworks.com/fnet/en-us/products/DTX+CableAnalyzer+Series/ > >>> They rent for $650 per month from http://www.trs-rentelco.com/ List > is > >>> over > >>> $7000. If I like it I'll probably get one and add it to my two > spectrum > >>> analyzers and my bucket truck. grin > >>> > >>> Never ever forget that wireless is 50% science and 62% black magic! > >>> > >>> I am quite hopeful that the new cable, beads on bother ends of the > cat5, > >>> better grounding, and an equipment move will fix this site up nicely. > >>> If > >>> not, who wants to buy it? lol Seriously, this site and one of the > ones > >>> that it feeds cause nearly 80% of my trouble calls. With any luck it > >>> wasn't > >>> wireless trouble that I've been having all along. Shrug. > >>> > >>> Here's the really strange part to all of this. The hardware that cost > >>> the > >>> most has the most trouble! grrrr > >>> > >>> Also, the Day Wireless guy had some kind of wide band sensor. He could > >>> move > >>> it around and see where overall signal levels were unsafe for people. > >>> Right > >>> beside a 4" or so copper pipe that the radio station used as a wave > >>> guide > >>> was pretty bad. A couple of inches from it was ok. The next highest > >>> readings at the whole site? RIGHT a the BASE of the 100' wooden pole > >>> that > >>> everything is mounted on! And what did I do when I installed all this > >>> new > >>> gear a year ago? Yeah, I put the antennas up top and the radios right > >>> down > >>> at the base of the tower so I could get to them without having to rent > a > >>> lift. Dang the luck! > >>> > >>> Hope that this helps someone else out. > >>> marlon > >>> > >>> > >>> > >>> > >>> > >>> > -------------------------------------------------------------------------------- > >>> WISPA Wants You! 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