Low overhead aggregation at the physical layer
View Patent ↗A physical layer device distributes a high-speed packet data stream to multiple lower-speed physical channels, and reverses the process to receive a high-speed packet data stream that has been distributed across multiple lower-speed physical channels. The packet data is distributed by removing interpacket gap characters from between packets and using a different control character to delineate packets. Interpacket gap characters can then be used to delineate equal-length frames distributed to each of the multiple physical channels. Each frame consists of a concatenation of fixed-size blocks of packet data. By selecting a frame size larger than the average packet size, overhead on the multiple physical channels can actually be lower than the overhead on the single high-speed channel, allowing the aggregation to achieve line rate operation at the high-speed rate.
1. A method of transmitting packet data, the method comprising:
dividing a packet data stream into sequential packet data blocks, each packet data block is comprised of multiple packet data symbols, each packet data symbol is comprised of multiple bits;
removing interpacket gap symbols appearing in the packet data stream, tracking the net number of interpacket gap symbols removed from the packet data stream and not accounted for by adding characters to the parallel packet data substreams that did not appear in the packet data stream, and compensating for the net number of interpacket gap symbols removed by adding fill control characters following the end of a packet in a packet data block;
distributing the sequential packet data blocks among a plurality of parallel packet data substreams;
concatenating, among the plurality of parallel packet data substreams, multiple packet data blocks into a data frame without block delimiters; and
sending the concatenated data frame to a corresponding physical layer coder, each data frame concatenated among the plurality of parallel packet data substreams is delimited from a neighboring data frame by a control character sequence comprised of interpacket gap characters included in each of the parallel data frame substreams.
2. The method of claim 1 , wherein sending data frames from each parallel packet data substream to a corresponding physical layer coder comprises sending data frames to all physical layer coders at substantially the same time.
3. The method of claim 1 , wherein each frame further comprises a frame number.
4. The method of claim 1 , wherein packets in the packet data stream each comprise a packet preamble, and wherein dividing a packet data stream further comprises replacing at least one character in the packet preamble of each packet in the packet data stream with a packet start character.
5. The method of claim 4 , wherein dividing a packet data stream further comprises adding a packet terminate character at the end of each packet in the packet data stream.
6. The method of claim 1 , further comprising compensating for the net number of interpacket gap symbols removed by adding fill control characters to the beginning of a packet data block.
7. The method of claim 1 , wherein a standard frame length comprises a fixed number of fixed-length packet data blocks, the method further comprising compensating for the net number of interpacket gap symbols removed by terminating the frame prior to the standard frame length by transmitting, after a number of blocks less than the fixed number, control character sequences in all packet data substreams.
8. A physical layer aggregator comprising:
a first packet data interface having a first line rate;
a plurality of similar second packet data interfaces, having an aggregate line rate substantially equivalent to the first line rate;
a framing and blocking logic unit;
a first send buffer to receive packet data from the first packet data interface, to remove interpacket gap characters from the packet data received from the first packet data interface and mark packet endpoints with designated control characters, and supply packet data to the framing and blocking logic unit;
an idle character counter in communication with the first send buffer and the framing and blocking logic unit, the idle character counter tracking the net number of interpacket gap characters removed from the packet data supplied from the first packet data interface and not compensated for by other characters inserted in the packet data supplied to a plurality of second send buffers; and
the plurality of second send buffers to receive packet data from the framing and blocking logic unit and supply packet data to respective ones of the second packet data interfaces;
the framing and blocking logic unit dividing packet data from the first send buffer into sequential packet data blocks and distributing those packet data blocks to the plurality of second send buffers, the framing and blocking unit formatting the packet data blocks distributed to each of the plurality of second send buffers into data frames, each data frame is comprised of multiple packet data blocks concatenated in the plurality of second send buffers for transmission over respective second packet data interfaces, and delineating successive data frames from each other data frame in the buffer with a sequence of interpacket gap characters, wherein temporally corresponding data frames in the plurality of second send buffers are all of the same length.
9. The physical layer aggregator of claim 8 , the framing and blocking logic unit compensating for a net removal of interpacket gap characters by inserting fill control characters, different from the interpacket gap characters, into at least one of the packet data blocks distributed to the plurality of second send buffers.
10. The physical layer aggregator of claim 8 , the framing and blocking logic unit compensating for a net removal of interpacket gap characters by terminating all current frames after the current block of each current frame for each of the plurality of second send buffers.
11. The physical layer aggregator of claim 8 , further comprising:
a deskew and demultiplexing logic unit;
a first receive buffer to receive packet data from the deskew and demultiplexing logic unit and supply packet data to the first packet data interface;
a plurality of second receive buffers to receive packet data from respective ones of the second packet data interfaces and supply packet data to the deskew and demultiplexing logic unit, the packet data comprising data frames of fixed-length packet data blocks, wherein successive data frames received by each second receive buffer are separated by interpacket gap control character sequences;
the deskew and demultiplexing logic unit sensing frame boundaries in the packet data received from each second receive buffer and using sensed frame boundary information to align, with each other, data frames from the second receive buffers, the deskew and demultiplexing logic unit demultiplexing packet data blocks from the aligned data frames into a packet data stream supplied to the first receive buffer.
12. The physical layer aggregator of claim 11 , wherein the first receive buffer detects packet delimiter control characters in its received packet data stream and replaces the packet delimiter control characters with interpacket gap control characters, packet preamble characters, or combinations of interpacket gap control characters and packet preamble characters.