Other systems implementing reliable multicast protocols often perform well when they repair occasional loss but they behave badly when they confront the massive loss of a crybaby receiver. A lossy receiver like this can easily push a source to spend all its efforts retransmitting, thereby sharply limiting or even stopping new message transmission. The symptoms of such behavior include abundant negative acknowledgments (NAKs) leading to its description as a NAK storm.
LBM sources monitor the rate of retransmissions and do not go beyond a configurable limit. This policy lets an administrator limit the extent to which lossy receivers can slow lossless receivers. The number of lossy receivers doesn't matter--they must all share the available retransmission rate limit.
LBM Benefits. Retransmission rate controls have eliminated concern about NAK storms occurring with reliable multicast. LBM networks continue stable operation under all traffic and loss conditions.
Other messaging systems are known to have problems when sources send faster than even the fastest receiver can receive. This situation is most common when a source is connected to a network with a faster port speed than all of its receivers. Sending in excess of the receivers' port speed triggers loss for all receivers causing them all to request retransmission and making more work for the source at a time when it already has a lot to do.
LBM sources monitor the rate that data is being sent and will not allow it to exceed a configurable limit. Sources have a choice of adding latency or having send requests fail until the data rate drops below the limit.
LBM Benefit. LBM sources never make more work for themselves and can operate with stability in any network configuration.
Other reliable multicast protocols were designed at a time when multicast worked only within a LAN. Design decisions that were made that did not anticipate the modern world where multicast routing is common and delivers many benefits. These messaging systems require gateway daemons using TCP connections to relay multicast between LANs. Such daemons are a common source of latency and administrative headaches.
LBM's reliable multicast protocol is designed with multicast routing in mind. It supports receivers on LANs at remote sites as well as receivers on the same LAN as the source.
LBM Benefit. Using WAN multicast routing lowers latency and provides better reliability.
See Section 7.7 for a description of a gateway bundled with LBM.
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