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Old Pages/Old Wiki/JeeMesh.md

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+JeeMesh is a mesh protocol in development at HacDC to extend the
+[JeeNode](http://cafe.jeelabs.net/lab/jn5/)
+[RF12](http://cafe.jeelabs.net/sw/library_-_rf12/) low power wireless
+protocol for mesh routing, packet fragmentation, and (more) reliable
+delivery.
+
+RF12 has the following limitations:
+
+- up to 30 nodes (typically 26 nodes and 4 servers/gateways)
+- MTU 66 bytes
+- range of about 30' to 50' at 915mhz
+
+We intend to extend these limits somewhat:
+
+- MTU 1023 bytes
+- range up to 200' by routing through up to four nodes on a mesh
+
+A 16 bit header is added using the first two bytes of the RF12 packet
+data as follows:
+
+- 5 bits for original source node
+- 5 bits for final destination node
+- 2 bits for ttl
+- 4 bits for fragment sequence
+
+This allows us to reconstruct 1024 byte JeeMesh packet from 16 64-byte
+packet fragments. We further add another 8 bit header to the first
+packet fragment, reducing the MTU to 1023 bytes:
+
+- 4 bits number of fragments
+- 4 bits packet type
+
+[Category:Previous_Projects](Category:Previous_Projects "wikilink")