On Thu, Nov 26, 2009 at 4:20 PM, plug bert <[email protected]> wrote:
> Hi peeps,
>
> Can one use a layer 2 switch to extend ethernet over 100 feet?
>
> Ganito kasi: we are planning to get a new office unit, and from the looks
> of it the cabling will
> definitely be more than 100 feet. We plan to install around 10 cables in all.
>
>
> Can we just break up each cable, each representing a different subnet, then
> use a multiport
> switch, set up a layer 2 VLAN with two ports for each subnet, then connect
> the two
> segments to those ports?
hi,
you are talking two different things here - ethernet cable length
(layer 1 or physical layer) and vlan (layer 2 or data-link layer)...
for layer 1... the length of your ethernet depends on the IEEE 802.3
specification that you are going to use...
below are some examples of IEEE 802.3 specifications:
IEEE 802.3 (10base5) - 10 mbps baseband 500 meters coax cable length
IEEE 802.3a (10base2) - 10 mbps baseband 185 meters coax cable length
IEEE 802.3i (10baseT) - 10 mbps baseband 100 meters UTP cable length
IEEE 802.3u
(100baseTX) - 100 mbps baseband 100 meters UTP cable length
(100baseSX) - 100 mbps baseband 300 meters multimode opticla fiber
cable length
(100baseFX) - 100 mbps baseband 2 kilometers multimode optical
fiber cable length
IEEE 802.3ab (1000baseT) - 1000 mbps baseband 100 meters UTP cable length
take note that the metric used here are meters and not feet as what
you mentioned above...
since you didnt mention what kind of switch you have... ill discuss it
here so that you can design what is best for your setup...
there are two kinds of hub:
1. passive hub
2. active hub
assuming you just want to connect two PCs directly without the hub...
diagram below show you the distance:
for 100baseTX (100 meters):
PC <---------- 100 meters max ----------> PC
you need crossover cable for that...
for passive hub:
PC <------- distance A -------> passive hub <------- distance B -------> PC
<-------
distance C --------> PC
distance A + B is less than or equal to 100 meters
distance A + C is less than or equal to 100 meters
distance B + C is less than or equal to 100 meters
for active hub... this is called now a switch... an active hub or
switch has a repeater in it (unlike with passive hub which dont
have)... repeater belongs to layer 1 or physical layer...
function of a repeater is to extend network length... repeater receive
and decode data from a worst case noise, timing and signal amplitude
conditions.. it retransmits the data with the correct timing and
amplitude as well as transmitting a jam signal throughout the network
if a collision occurs...
there are two classes of repeater/switch... class 1 and class 2..
class 1 switch can connect two different signaling (eg. 100baseTX and
100baseSX)...
the diagram below show the distance depends on the 802.3 specification
that you use:
PC A <------- distance A ------> class1 switch <------- distance B -------> PC B
if PC A and B used 100baseTX (100 meters):
distance A + B is less than or equal to 200 meters but distance A
and B must not more than 100 meters
if PC A used 100baseTX (100 meters) and PC B used 1000baseSX (300 meters):
distance A is less than or equal to 100 meters
distance B is less than or equal to 300 meters
distance A + B is less than or equal to 400 meters but distance A
must not more than 100 meters and distance B must not more than 300
meters
class 2 switch cannot connect two different signaling but can connect
to another class 2 switch for additional ports...
the diagram below show the cable length if you are using 100baseTX (100 meters):
PC <-- distance A --> class 2 switch <-- distance C --> class 2 switch
<-- distance B --> PC
distance A and B must not more than 100 meters
distance C must not more than 5 meters
class 1 switch cannot connect to another class 1 switch... only one
class 1 switch and two class 2 switches in a given collision
domain....
take note.. in a given collision domain.. the above diagrams... its
maximum cable length and number of switches that you can connect are
all true if and only if your network topology have collisions...
normally you have collisions in your network if it is configured as
*half* duplex...
you are limited by the distance of the diagrams above because of
*round trip collision delay* that must conform with the 802.3
specification...
but good news.. everything changed when full duplex came... ethernet
is using carrier sense multiple access / collision detection or
CSMA/CD access method... CSMA/CD is not CSMA/CD anymore because there
is no more to sense the carrier before transmitting to avoid collision
and no collision anymore if it is under full duplex mode :->
with that.. under full duplex mode.. there is no more to worry about
round trip collision delay... so therefore... you can connect two or
more switches to extend your network as long as the maximum distance
cable used is within its distance specification and make sure that the
ports are configured in full duplex mode..
fooler.
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