Design Rules for 10Mbps Ethernet


Background.  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 irretrievably.

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.


  10Base5 10Base2 10BaseT
Topology Bus Bus Star
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