[Wolves] I have just recieved my N+ first course book and have a query......

[Adam Sweet]

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James Dalley wrote:
>  From: davmor2 at gmail.com
>> To: wolves at mailman.lug.org.uk
>> Date: Sat, 26 Jan 2008 21:33:33 +0000
>> Subject: [Wolves] I have just recieved my N+ first course book and
> have a query......
>>
>> In the text it says a bus topology follows the 5-4-3 rule.
>> 5 network segments (what the hell is a segment? Is it just as simple
>> as 5 section where computers can be added)
>> 4 repeaters (these I understand improve the signal strength)
>> 3 of the 5 segments can have nodes. (why?)
>>
>> Help please it's thrown me and I know that your explainations will make
>> more sense than the course providers :)
>> --
>> Seek That Thy Might Know
> 
> 
>       5-4-3 Rule
> 
> A consideration in setting up a tree topology using Ethernet protocol is
> the 5-4-3 rule. One aspect of the Ethernet protocol requires that a
> signal sent out on the network cable reach every part of the network
> within a specified length of time. Each concentrator or repeater that a
> signal goes through adds a small amount of time. This leads to the rule
> that between any two nodes on the network there can only be a maximum of
> 5 segments, connected through 4 repeaters/concentrators. In addition,
> only 3 of the segments may be populated (trunk) segments if they are
> made of coaxial cable. A populated segment is one which has one or more
> nodes attached to it . In Figure 4, the 5-4-3 rule is adhered to. The
> furthest two nodes on the network have 4 segments and 3
> repeaters/concentrators between them.
> This rule does not apply to other network protocols or Ethernet networks
> where all fiber optic cabling or a combination of a fiber backbone with
> UTP cabling is used. If there is a combination of fiber optic backbone
> and UTP cabling, the rule is simply translated to 7-6-5 rule.
> 
> 
> http://www.teach-ict.com/as_a2/topics/networks/pages/chap5.htm

It is specific to non-switched networks, ie those using hubs and
repeaters. A hub is a multi-port repeater which sends all traffic
received out of every port except the one it was received on.

Networks using switches don't have to adhere to this rule. On a hub or
repeater, all devices contend for media access (ie to be able to
transmit) and have to back off for a random period if they transmit at
the same time (collide) before trying again. This makes transmission on
networks using hubs and 10BASE-T (10Mb) networks very slow compared to
switched 100BASE-TX (let alone 1Gb) networks.

(The number at the front in the name of an Ethernet standard is the
speed, usually in Mb unless it has a G after it. The characters at the
end denote the cabling type.)

100BASE-TX (100Mb ethenet over CAT-5, CAT-5e or CAT-6 cable), is not
only capable of 100Mb transmission at any one time, it is also able to
transmit and receive at the same time (full-duplex), which makes 200Mb/s
overall when a machine is sending and receiving data at optimum
performance. At this stage, only 4 of the 8 wires in the cable are being
used, 1Gb ethernet uses them all.

If anyone is using hubs or 10-BASE-T equipment out there, replace it
immediately if performance is even remotely important.

Regards,

Adam Sweet

- --

http://blog.adamsweet.org/

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