| 摘要 |
A system in which core information, for example in the form of a core block or blocks (C), is transmitted in a core packet (PC), and at least some enhancement information, for example, in the form of enhancement blocks (E), is transmitted in an enhancement packet (PE) which is separate from the core packet (PC) and is discardable to relieve congestion. Preferably, the core and enhancement packets have headers (H) which include a discard eligible marker (DE) to indicate whether or not the associated packet can be discarded. The enhancement blocks (E) may be distributed between the core packet and enhancement packet in accordance with congestion conditions, or the enhancement blocks may be incorporated only in the enhancement packet, and the actual number of enhancement blocks included are varied depending on congestion conditions. Preferably, the packets are transmitted in frame relay format and congestion forward (CF) and congestion backwards (CB) markers are used to feed back information of congestion conditions within a network to the packet assembler (7) forming the core and enhancement packets.
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