TABLE OF CONTENTS We illustrate the use of the trading model through a congestion control scheme for a many-to-one (concast) service. The concast example shows capsules that trade brandwidth for memory when there is congestion.
The term "concast" has been defined in [CAL 00] as a many-to-one service, in opposition to multicast (one-to-many). Figure 3 illustrates this concept. While multicast copies information from one source to many destinations, concast merges information from several sources to one destination. A concast service can be used, for instance, to aggregate feedback in a reliable multicast service, to transmit reception statistics in a multimedia session, to merge information coming from several sources in an auction or tele-voting application, or to combine several real-time streams into one, e.g. to perform audio mixing from several audio sources.
The concast service is faced with the feedback implosion problem, that is, multiple simultaneous sources might congest the path to the single destination, if no congestion control is performed. This problem is aggravated by the fact that many concast flows are used as signalling to support a more robust protocol such as the aggregation of NACK feedback messages for a reliable multicast protocol. Flow control for such signalling messages is often neglected or oversimplified, since the signalling traffic is assumed to be kept small enough when compared to the data traffic. This might lead to poor performance when there is congestion in such a signalling...
