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Available bit rate
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<table><tbody><tr><th rowspan="2"><a href="/facts/Network_architecture/b9IWEJIU">Network architecture</a></th><th rowspan="2"><a href="/facts/Service_model/pIB42HaQ">Service model</a></th><th colspan="4">Guarantee ?</th><th rowspan="2">Congestion feedback</th></tr><tr><th><a href="/facts/Bandwidth_(computing)/lY6Tb4gX">Bandwidth</a></th><th>Loss</th><th>Order</th><th>Timing</th></tr><tr><td><a href="/facts/Internet/Xw1rVvJU">Internet</a></td><td>best effort</td><td>none</td><td>no</td><td>no</td><td>no</td><td>no (inferred via loss)</td></tr><tr><td><a href="/facts/Asynchronous_Transfer_Mode/SzA8ewFL">ATM</a></td><td><a href="/facts/Constant_bit_rate/UHHb5Wfg">CBR</a></td><td>constant rate</td><td>yes</td><td>yes</td><td>yes</td><td>no congestion</td></tr><tr><td><a href="/facts/Asynchronous_Transfer_Mode/SzA8ewFL">ATM</a></td><td><a href="/facts/Traffic_contract/3Cdwr1ST">VBR</a></td><td>guarantee rate</td><td>yes</td><td>yes</td><td>yes</td><td>no congestion</td></tr><tr><td><a href="/facts/Asynchronous_Transfer_Mode/SzA8ewFL">ATM</a></td><td><a href="/facts/Available_Bit_Rate/telIRSEP">ABR</a></td><td>guarantee minimum</td><td>no</td><td>yes</td><td>no</td><td>yes</td></tr><tr><td><a href="/facts/Asynchronous_Transfer_Mode/SzA8ewFL">ATM</a></td><td><a href="/facts/Traffic_contract/3Cdwr1ST">UBR</a></td><td>none</td><td>no</td><td>yes</td><td>no</td><td>no</td></tr></tbody></table> <p>Available bit rate (ABR) is a service used in <a href="/facts/Asynchronous_Transfer_Mode/SzA8ewFL">ATM</a> networks when source and destination don't need to be synchronized. ABR does not guarantee against delay or <a href="/facts/Data_loss/oGGosFHt">data loss</a>. ABR mechanisms allow the network to allocate the available <a href="/facts/Bandwidth_(computing)/lY6Tb4gX">bandwidth</a> fairly over the present ABR sources. ABR is one of five service categories defined by the ATM Forum for use in an ATM Network. </p><p>The <a href="/facts/Network_switch/CnvmhNYT">network switches</a> use locally available information to determine the explicit allowable rates or relative rate (increase/decrease) for the source. The newly calculated rates are then being sent to the sources using resource management records (RM-cells). RM-cells are generated by the source and travel along the data path to the destination and sent back. ABR sets a minimum cell rate (MCR) and a peak cell rate (PCR). When transfers exceed the PCR, cells are dropped. </p><p>Many implementers consider ABR to be overly complex, and its adoption has been modest. </p>