Following is a list of documents originally on www.invisiblenet.net/i2p/ and rescued via the Wayback Machine. They are quite dated and may or may not be accurate. However, the I2CP and I2NP documents in particular have some good information.

Index of /i2p

Name                    Last modified       Size

I2CP_spec.pdf           03-Sep-2003 12:49   119k  
I2NP_spec.pdf           03-Sep-2003 12:49   356k  
datastructures.pdf      03-Sep-2003 12:49   149k  
i2p_philosophy.pdf      03-Sep-2003 12:52   126k  
polling_http_transpo..> 03-Sep-2003 12:49   189k