Thread Links Date Links
Thread Prev Thread Next Thread Index Date Prev Date Next Date Index

Ambiguity in the stated PMD objectives

 
The intent of my proposal to revisit the PMD objectives was to clearly resolve any ambiguity in the objective statements in
regards to application-space media-distances and the usage of the word "installed" to represent MMF fiber performance.
 Although the ambiguity allowed for flexibility in the PMD implementations proposed it continues to be a source of confusion
in the reflector threads and beyond.
 
The task group needs to remove any ambiguity in the stated objectives in order for 802.3 voters to make informed decisions
 in regards to the PMD selection. It’s obvious from the discussions in the reflector threads that there are some number of 802.3
 voters who need unambiguous information on the PMD objectives and the proposed solutions before they can make informed
 decisions on the PMD implementations.
 
To help, I offer my understanding of the origin of certain aspects of the MMF objectives.
At the time the multimode physical layer objectives were agreed to the intent was establish two distance targets for
In-building cabling. And, to leave the MMF fiber type somewhat vague in order to allow for flexibility in PMD implementations.
The usage of the word "installed" in the 100 meter objective was to identify the MMF with the MMF currently referenced in 802.3z.
 The omission of the word "installed" was to implicitly allow for the new higher bandwidth MMF fiber. This allowance would be based
on careful evaluation of the PMD proposals to meet the distance objectives and cost considerations.
 
The following applies to the current implicit differences in the MMF distance objective and fiber types.
 
+++++Installed MMF – MMF as referenced in 802.3z.
+++++MMF – Either installed MMF or the Next Generation MMF fiber specifications
currently proposed in both TIA and ISO or both. The development for the Next Generation MMF
fiber specifications was supported in a Liaison letter issued from IEEE.
 
Chris Di Minico
Cable Design Technologies (CDT) Corporation
Director of Network Systems Technology
Phone: 800-422-9961 ext:333
e-mail: cd@xxxxxxxxxxxxxx