Design Rules for 10Mbps Ethernet
Remember that interconnecting devices can be done through wire or wireless
media. It is also important to remember that these media have their
in-built limitations. For example, avoiding bends in fiber optics,
avoiding twisted pair cabling that is so long the signal degrades
Most of this page will present tables that summarize scalability constraints on particular transmission media when used in different network protocols such as Ethernet, Token Ring and FDDI. First we will start with design rules for Ethernet interconnectivity.
Ethernet Cabling Design Rules. The following table relates to provisioning networks based on the IEEE 802.3 for Ethernet specifications. The cabling characterizations exist on the following link for cabling specifications.
|Maximum Segment Length (meters)||500||185||100 from hub to station|
|Maximum Number of Attachments per Segment||100||30||2
(hub - station)
(hub - hub)
|Maximum Collision Domain||2500 meters of 5 segments and 4 repeaters. Only 3 segments can be populated||2500 meters of 5 segments and 4 repeaters. Only 3 segments can be populated||2500 meters of 5 segments and 4 repeaters. Only 3 segments can be populated|
|The 100 Mbps Ethernet has much more severe distance
limitations than does the 10 Mbps Ethernet. For example, the rule of
thumb is that for unshielded twisted pair, 100 Mbps Ethernet has a maximum
diameter of 205 meters as opposed to 2500 meters for 10 Mbps Ethernet.
Another very significant design rule for Ethernet has to do with the round trip propagation delay. If it is too great then the probability of collisions increases way too much. The rule is that the delay cannot exceed 512 bit times. The following table summarizes this.
|Bit Times||Round Trip Propagation Delay|
10 Mbps Ethernet
|0.1 microseconds||(512)(0.1) = 51.2 microseconds|
100 Mbps Ethernet
|0.01 microseconds||(512)(0.01) = 5.12 microseconds|
|This can prove to be a very serious limitation and it
needs to be considered in all network designs.
Now we will get into more detail about 10 Mbps and 100 Mbps Ethernet designs.
10 Mbps Fiber Ethernet Design Rules. The following table gives a summary of design rules for fiber optic cabling in 10 Mbps Ethernets. 10BaseF is based on the FOIRL - fiber optic inter-repeater link which includes 10BaseFP, 10BaseFB, 10BaseFL, and a revision of FOIRL. The new FOIRL allows DTE - Data Terminal Equipment or end node connections, rather than just the repeaters allowed in the older FOIRL.
|10BaseFP||10BaseFB||10BaseFL||Old FOIRL||New FOIRL|
|Topology||Passive Star||Backbone or Repeater Fiber Systems||Link||Link||Link or Star|
|Allow DTE Connections||Yes||No||No||No||Yes|
|Maximum Segment Length (meters)||500||2000||1000 or 2000||1000||1000|
|Allow Cascaded Repeaters||No||Yes||No||No||Yes|
|Maximum Collision Domains (meters)||2500||2500||2500||2500||2500|