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Understanding the network.pdf - Back to Home

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ATM private-class switches are comprised of <strong>the</strong> same architectural<br />

elements utilized by LAN/WAN switches:<br />

• Physical layer interface<br />

• Switch backplane<br />

• Switch logic controller<br />

Because ATM's founding premise was <strong>to</strong> provide transport over a<br />

large scaleable range of transmission speeds, a number of physical<br />

transmission media and interface types are available. Table 6.2 lists<br />

ATM's most commonly supported transmission media and <strong>the</strong>ir<br />

operating rates.<br />

Table 6.2. Common ATM Transport Implementations<br />

Transport Medium Operating Rate NNI or UNI Application<br />

ATM over DS1 (Cat 3) 1.544 Public<br />

ATM over UTP (Cat 3) 26.6 Private<br />

ATM over DS3 (Cat 3) 44.736 Public<br />

ATM over STP (Cat 3) 155.52 Private<br />

ATM over SONET (SMF/MMF) 155.52 Public/Private<br />

ATM over SONET UTP (Cat 3) 155.52 Private<br />

ATM over SONET UTP (Cat 5) 155.52 Private<br />

ATM over SONET (SMF) 622.08 Public/Private<br />

SMF = Single mode fiber<br />

MMF = Multimode fiber<br />

STP = Shielded twisted pair<br />

UTP = Unshielded twisted pair<br />

What makes ATM switch ports significantly different from <strong>the</strong>ir LAN<br />

counterparts is that <strong>the</strong>y only support one user <strong>network</strong> interface<br />

(UNI) or <strong>network</strong>-<strong>to</strong>-<strong>network</strong> interface (NNI) device per port.<br />

Commonly, ATM interface port densities are 8, 16, or 24 ports per<br />

switch or enterprise module, depending upon <strong>the</strong> supported port<br />

operating rate. It is also common for LAN switch manufacturers <strong>to</strong><br />

provide a single 155Mbps ATM-UNI interface module that can be used<br />

<strong>to</strong> interconnect <strong>to</strong> ano<strong>the</strong>r LAN switch or <strong>to</strong> an ATM switch backbone<br />

running LANE.

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