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Abstract

Data is compressed in an industry-standard local-area network (LAN) such as IEEE 802.2 or 802.3. Compression occurs at a low level, in the data link layer just above the physical layer. The data in the packet is compressed, but the source and destination addresses are not compressed. A type/length field which indicates the length of the data field is adjusted for the new compressed length, while a frame checksum which was calculated for the uncompressed data is re-generated for the compressed data. Thus the packet with the compressed data has the length and checksum adjusted for the newly compressed data so that the packet appears normal to other layers of the LAN protocol. A status byte may be added to the compressed data to disable compression on a remote LAN station. The compressed data packet is compatible with hubs to other LANs and bridges to WANs. The low-level compression is compatible with LANs that have older LAN stations that do not have compression capabilities, since the only packets compressed are those sent to LAN stations that support low-level compression. A destination address table is consulted which includes the compression capabilities of other LAN stations. Thus multi-point LANs can support data compression.

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