1. Check update density to see whether it is correct.
2. Based on that, set up a density threshold.

1. move paper.

1. Exponential backoff.
2. Get rid of probing.
3. Review papers.

1. Bump the MSG_MAX_HDR_SIZE from 512 to 2048
2. Shrink both greedy and perimeter mode ip option
3. Expand ip_max_header in network/ip.h
4. remove application/application.cpp's abort for wrong app protocol.