[SoCoSA/discuss] Two 100BASE-TX over one cable

Fri Jun 3 11:42:37 PDT 2011

VLAN's will be more then sufficient for 100Mbps connections in most cases.  If you are using a VoIP hard phone that supports VLAN tagging and has a built in switch this is a simple and cost effective method for companies who do not tend to saturate 100Mbps links.  

Audio from G.711 ulaw, the most likely codec to be in use) only takes up 64Kbps.  Over Frame relay this turns out to be 82.8Kbps and over ethernet 87.2Kbps.  If you only look at the short haul of the ethernet segment and ignore the WAN side of the calls 1 call at its most expensive is less then 100Kbps.  A single 100Mbps is around 100,000Kbps, so around 1000 VoIP calls could traverse a 100BASE-TX connection.  So if you consider that voice would use less then 1/1000th of the bandwidth available, the audio has massive room to work with unless you are using 999/1000 of the circuit already.  

In the long run, from a cost perspective, if you have more then 5 phones/desks to setup you might be better of with VLAN's from the switch if the phones support the option.  If your switch does not support VLAN's (and/or QoS to provide a Voice priority VLAN) then the splitters might be a good way to go.  And I would suggest using the splitters for testing for the reasons you mentioned, time, effort and prewired drops that work are good to leave in working order, without a large enough service loop you could end up shortening the cable so it wont remount easily to the existing wall jack.

Trevor Benson
A1 Networks  |  Network Engineer
dCAA, dCAP, Network+, CLA, CNA, MCP, LPIC-1
DID (707)703-1041
Fax (707)703-1983 
tbenson at a-1networks.com

On Jun 3, 2011, at 11:18 AM, gandalf at sonic.net wrote:

> Thanks for the info. I only have two gigabit connections, the server and the book keepers workstation which by the way speeds up quickbooks quite a lot. Fortunately there are three network ports in the book keepers office. I could probably do a test by cutting some wires on a patch cord and see if a connection will still work with our equipment. 
> 
> I wouldn't think they'd be that expensive (I'd expect about half that price really), but thinking about it I could easily spend a couple hours building these by hand and messing up and redoing it and it probably makes good economic business sense to just buy some. I did find them a buck cheaper at global (aka tiger direct) who I've been ordering from for years:
> http://www.globalcomputer.com/applications/SearchTools/item-details.asp?EdpNo=6373260&CatId=435
> 
> I keep liking the idea of a physically separated network vs a logically separated one although logically it doesn't make a huge difference. By physically separating the networks it makes it impossible for the Voip network to be affected the slightest by whatever happens on the data network (even if someone torrents all the Star Wars movies). Theoretically with a logical separation there should be at most 3% interference (3mbps internet connection) from the other network, but it just feels so much cleaner to have no interference at all. 
> 
> (imagine a cute or dirty tagline here)
> 
> On Fri 03/06/11 10:22 AM , Trevor Benson tbenson at a-1networks.com sent:
>> If the links were stripped down both those items came from newegg.com, and
>> were found by searching RJ45 splitter.
>> Trevor Benson
>> A1 Networks  |  Network Engineer
>> dCAA, dCAP, Network+, CLA, CNA, MCP, LPIC-1
>> DID (707)703-1041
>> Fax (707)703-1983 
>> tbens
>> on at a-1networks.com
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> On Jun 3, 2011, at 10:17 AM, Trevor Benson wrote:
>> 
>>> Can definitely be done.  the JC used to run 1
>> CATx cable and split use it for ethernet, appletalk and FXS (phone station
>> ports) to each desk.> 
>>> For what you want to do there are custom
>> "splitters" you can buy.  They plug in like a phone splitter
>> giving 2 ports from a single port.  The splitter provides pins 1,2,3 and 6
>> are mapped to port 1 (pins 1,2,3 and 6), and 4,5,7 and 8 are mapped to the
>> second ports pin 1,2,3,6.  You need to implement these on BOTH sides of the
>> cable obviously.  > 
>>> Newer splitters have an ethernet cable built in
>> to extend the unit.  I suggest these units highly because otherwise the old
>> school splitters would be too dense to plug into a patch panel if cables
>> were above and below as well as on both sides. Making space for 2 ports
>> when you only took up 1 becomes difficult in high density patch
>> panels.> 
>>> Here are some examples around $10.  They used to
>> be much less expensive.> StarTech RJ45SPLITTER Cat 5/5E 2-to-1 RJ45
>> Splitter Cable Adapter - M/F StarTech RJ45SPLITTER Cat 5/5E 2-to-1 RJ45
>> Splitter Cable Adapter - M/F> CABLES TO GO 37133 5.9 in 2-Port RJ45
>> Splitter/Combiner Cable CABLES TO GO 37133 5.9 in 2-Port RJ45
>> Splitter/Combiner Cable> 
>>> WARNING:  Depending on your ethernet switch
>> model and speed as well as if the computer is equipped with a 1000Base-T
>> NIC you may have additional problems.  1000Base-T specification requires
>> all 4 pairs to be present, and some interfaces are very touchy about auto
>> negotiation (even at 10/100Base levels) if any of the pairs are missing. 
>> Depending on the card and/or switch you may require to hardcode the
>> connection link and duplex on both sides.  If the switch and the NIC in the
>> computers are both limited to 100Base-TX you are less likely to run into
>> issues with auto negotiation of link.  However I have seen issues of cards
>> refusing to come up in any way even when configured for 10Base-T Half
>> Duplex, so I would suggest testing this out with your equipment and
>> verifying NIC speeds for each desktop.  Testing the 1000Base-T NIC's first
>> with a pair of these would be prudent before spending money on a batch of
>> them and finding problems.  However the same goes for rewiring the
>> cab!le by hand to multiple RJ45 ports and skipping the splitters so test
>> thoroughly before you spend a bunch of money or time attempting to go this
>> route.> 
>>> Trevor Benson
>>> A1 Networks  |  Network Engineer
>>> dCAA, dCAP, Network+, CLA, CNA, MCP,
>> LPIC-1> DID (707)703-1041
>>> Fax (707)703-1983 
>>> tbens
>> on at a-1networks.com> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> On Jun 2, 2011, at 4:55 PM, Jordan Erickson
>> wrote:> 
>>>> I saw this kind of cabling job to simply
>> hook 2 PCs up to a Linksys>> router, so it is possible...
>>>> 
>>>> 
>>>> gandalf at son
>> ic.net wrote:>>> This doesn't sound impossible. I'd like
>> to run two different networks over the same cable. We've got a VOIP
>> solution that is proving to be clean bandwidth demanding. I'd like to move
>> it to our already existing backup internet connection. However some of the
>> offices only have a single CAT5 jack. So I was thinking a simple solution
>> would be to transmit both connections on the same cat5 connection to the
>> offices with only one plug and then split them off at both ends. A little
>> custom cabling should do it. Of course I couldn't run gigabit over this
>> setup, but most of our machines don't dabble in that anyway. >>> 
>>>>> Hmmm, another solution might be to just
>> use the internal network and then separate it in the phone room with the
>> VOIP phones configured on one network and the computers configured on
>> another, something like 198.162.0.1 and 198.162.0.2 with each aDSL
>> connection configured as a separate network. With the main infrastructure
>> running at 100mbps and each internet connection running at 3.0mbps or less
>> there shouldn't be any real fight for bandwidth until the actual gateway.
>>>>> 
>>>>> I understand that each phone connection
>> uses 64kbps but both upload and download meaning that a 384 u/l internet
>> connection can only theoretically support 6 simultaneous calls and probably
>> only really support 5. >>> 
>>>>> Questions? Comments?
>> Laughter?>>> 
>>>>> 
>>>>> (imagine a cute or dirty tagline
>> here)>>> 
>>>>> 
>>>>> 
>>>>> 
>> _______________________________________________>>> SoCoSA discuss mailing list
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>> cosa.org>>> Your address: jerickson at logicalnetworking.net>>> http://socosa.org/mailman/listinfo/discuss>>> http://socosa.org/mailman/options/discuss/jerickson@logicalnetw
>> orking.net>> 
>>>> 
>>>> -- 
>>>> Jordan Erickson - LNS
>>>> (707) 636-5678  - http://logicalnetworking.net>> 
>>>> 
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