Will a 60-foot run of CAT-5 ethernet cable work?

[Lennart Sorensen]

On Wed, May 12, 2010 at 04:05:19PM -0400, James Knott wrote:
> Lennart Sorensen wrote:
>> On Wed, May 12, 2010 at 07:36:45AM -0400, James Knott wrote:
>>    
>>> Dave Cramer wrote:
>>>      
>>>> Ethernet is spec'd well past 60 feet, something in the neighourhood of
>>>> 1000 feet, so 60 should not bother it.
>>>>        
>>> It's 100M or 330' max over CAT 5 or 6.  The original 10base5, 10 Mbit
>>> ethernet would go about 500M over coaxial cable (Thicknet).  Much
>>> greater distances are possible with fibre.
>>>      
>> And 10base2 (the coax everyone actually used) was allowed 200m.  The base#
>> indicated how long the cable run could be in hundreds of meters.
>>
>>    
> Now, do you know the maximum distance allowed?  Many people confuse this  
> with cable length.
>
> Back in the days of coax or hubs, collisions were likely.  To properly  
> handle collisions, they had to occur within 64 bytes or 512 bits.  This  
> works out to about 50 uS (actually, 51.2).  That is also round trip  
> time.  In 50 uS, light will travel 15 Km.  Divide by 2 for round trip =  
> 7.5 Km.  After allowing for cable velocity factor, you're down to about  
> 5 Km end to end.  Of course, repeaters etc. also consume time and reduce  
> that distance, but it is reachable with fibre.  However all those  
> concerns disappeared with full duplex switches, as collisions do not  
> occur with them.

With hubs, the maximum in a chain I believe was 5.  So from one client to
another at most 5 hubs could be in between, with whatever cable length
in between each device depending on the cable technology (so 200m for
10base2, 100m for 10baseT/100baseTX, 500m for 10base5).  To go further
requires a switch or router, not a hub.

5 might be wrong, it might be 4.  Hubs really aren't interesting anymore.

-- 
Len Sorensen
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