The transit cache is divided into three parts: transit cache state
block, transit head area and transit block area. In the process of
transit cache initialization, transit heads are set from the end of
transit cache state block which is in the low-end of cache area
and their corresponding transit blocks are divided in the high-end
of cache area at the same time. All the transit blocks form the
transit block area, while all the transit heads form the transit
block area. Every transit head links its corresponding transit
block to form a transit unit. There are two kinds of transit units:
network transit unit which is made up of a network transit head
and a network transit block, and local transit unit which is made
up of a local transit head and a local transit block. The transit
cache structure