tag:blogger.com,1999:blog-13401748.post3396250085641477484..comments2024-03-25T10:55:14.348-04:00Comments on ARCANE RADIO TRIVIA: FDMA DAMA CSMA PAMA FAMAUnknownnoreply@blogger.comBlogger1125tag:blogger.com,1999:blog-13401748.post-50731418001990467332010-01-02T02:18:28.965-05:002010-01-02T02:18:28.965-05:00It should be observed that DAMA and TDMA both are ...It should be observed that DAMA and TDMA both are 100% collision-free, by definition.<br /><br />DAMA is, essentially, a token <b>tree</b> (versus token ring or bus) network, and like all token-passing networks, can achieve 90+% link utilization without collisions in normal operation. The only time a collision can occur is when multiple, mutually unaware nodes attempt to join the network concurrently. However, DAMA installations always have a slotted-ALOHA or CSMA slot in which to do this.<br /><br />TDMA works similarly to DAMA in that you often have a dedicated CSMA slot with which to announce network joins. The remaining bandwidth is managed by means of leased time slots; since all nodes on the network are aware of which slots are used, and by whom, no collisions can occur except via malicious hardware.<br /><br />TDMA depends on global wall-clock synchronization, while DAMA relies on relative timing. In nearly all other respects, they're operationally equivalent, and thus, it's no surprise that both can achieve jaw-dropping link efficiencies.<br /><br />Contrast this with a pure CSMA-CD or CSMA-CA implementation, which can get ONLY 38% to 50% link efficiency.<br /><br />BTW, the Ethernet link on the back of your PC is very likely to be 10-base, 100-base, or even 1G-base-T. These links <b>DO NOT</b> use CSMA, because they don't have to -- the <i>-T</i> means it's twisted-pair cabling, which by definition is point-to-point wiring. Since nobody else is on any given pair of wires, there's no need to listen first before sending. This is why contemporary Ethernet is faster than the 38% you'd expect from CSMA.<br /><br />In fact, modern Ethernet is architecturally more related to ATM and STS networks than they are to old-school CSMA Ethernet links.Samuel A. Falvo IIhttps://www.blogger.com/profile/11523132404727383627noreply@blogger.com