A 24 byte fixed length cell is significantly smaller than ATM's 53 byte fixed length cell. However, 24 bytes is sufficient for reliable signaling, voice communication, slow-scan video and encapsulation of other network protocols. Furthermore, 24 bytes after 4B5B (or suchlike) bit stuffing is 240 bits. With the addition of a 16 bit cell frame marker, we have 256 bits. So, 24 bytes get encoded as 32 bytes. Over high speed networking, this can be implemented with an eight bit binary counter. Over low speed networking, multiple channels can be bit-banged in parallel.
There exists a low overhead method for bit stuffing. There exists a cell frame marker which always violates bit stuffing. Therefore, nothing in payload can immitate a frame marker. Therefore, the system is fairly immune to packet-in-packet attack without further consideration.
Addressing may be performed with a routing tag within each cell and a source address and/or destination address within each packet. Partial decode of the bit stuffing allows cells to be routed without decoding or encoding contents in full. Combined with techniques such as triple-buffering, each channel requires no more than 96 bytes excluding pointers and one common decode buffer. Eight channels require less than 1KB including pointers and common state. Therefore, it may be possible to implement cell networking on very basic hardware. This includes an eight bit micro-controller with less than 1KB RAM. Furthermore, it is possible to perform routing of packets which exceed 1KB via such a device.
However, more resources are required to perform security functions. In particular, key exchange and hash verification is very likely to require fields which exceed a 24 byte cell. Therefore, secure end-to-end communication with a leaf node requires a device which can unpack a payload which spans multiple cells. It remains desirable to implement triple-buffering at this level but it is also desirable to have an MTU which greatly exceeds 1KB. This is in addition to cryptography state, entropy state and application state. Despite these constraints, it is possible for a system with 64KB RAM to provide secure console and graphical services which are extremely tolerant to packet loss.
Cells Versus Packets, Part 2
(This is the 21st of many promised articles which explain an idea in isolation. It is hoped that ideas may be adapted, linked together and implemented.)
It is possible to tunnel arbitrarily long packets over fixed length cell networks. This works with conventional error detection and error correction schemes. Even if you dispute this, I'd like to describe my preferred, concise implementation.
A 24 byte fixed length cell is significantly smaller than ATM's 53 byte fixed length cell. However, 24 bytes is sufficient for reliable signaling, voice communication, slow-scan video and encapsulation of other network protocols. Furthermore, 24 bytes after 4B5B (or suchlike) bit stuffing is 240 bits. With the addition of a 16 bit cell frame marker, we have 256 bits. So, 24 bytes get encoded as 32 bytes. Over high speed networking, this can be implemented with an eight bit binary counter. Over low speed networking, multiple channels can be bit-banged in parallel.
There exists a low overhead method for bit stuffing. There exists a cell frame marker which always violates bit stuffing. Therefore, nothing in payload can immitate a frame marker. Therefore, the system is fairly immune to packet-in-packet attack without further consideration.
Addressing may be performed with a routing tag within each cell and a source address and/or destination address within each packet. Partial decode of the bit stuffing allows cells to be routed without decoding or encoding contents in full. Combined with techniques such as triple-buffering, each channel requires no more than 96 bytes excluding pointers and one common decode buffer. Eight channels require less than 1KB including pointers and common state. Therefore, it may be possible to implement cell networking on very basic hardware. This includes an eight bit micro-controller with less than 1KB RAM. Furthermore, it is possible to perform routing of packets which exceed 1KB via such a device.
However, more resources are required to perform security functions. In particular, key exchange and hash verification is very likely to require fields which exceed a 24 byte cell. Therefore, secure end-to-end communication with a leaf node requires a device which can unpack a payload which spans multiple cells. It remains desirable to implement triple-buffering at this level but it is also desirable to have an MTU which greatly exceeds 1KB. This is in addition to cryptography state, entropy state and application state. Despite these constraints, it is possible for a system with 64KB RAM to provide secure console and graphical services which are extremely tolerant to packet loss.