HELPnet Fundamental Principles of Design: 1. No single link failure should take down a site 2. No single site failure should disrupt any other site Note and Additions to the Fundamental Principles: We have always acknowledged that the HELPnet design does not faithfully execute these rules in every case. There are the five main network centers -- Central Office, Bulkeley High School, Hartford Public High School, Milner Elementary School and Quirk Middle School -- the loss of any one of which would cripple part or all of the network. This weakness is imposed on us largely due to the layout of our fiber-optic cables. However, scrupulous application of these Principles where ever possible has produced a robust and stable network. One of HELPnet's most powerful features is the ability to deliver any VLAN anywhere. This credo may be the best candidate yet for a third Fundamental Principle. With the addition of edge sites fed by Gigabit Ethernet links connecting to non-redundant Ethernet switches, is becomes necessary to restate the first and second principles as No single link failure should take down a core network site, and No single core network site failure should disrupt any other core network site. Again, due to limitations of phusical fiber we must make exceptions to the Fundamental Principles. This creats a kind of second-class site whose attachment to, and proliferation within, HELPnet must be closely monitored. Careless creation of singly-linked edge sites can compromise the network's stability. Hartford Public Schools Information Technology Department | Updated 9-3-01