question about persistent connection between caches

[fantacywall]

when i read the two lines below(line 1098 in http.c),i have a question 
about persistent connection between caches
else if (p->stats.n_keepalives_sent < 10)
        httpState->flags.keepalive = 1;
   else if ((double) p->stats.n_keepalives_recv / (double) 
p->stats.n_keepalives_sent > 0.50)
        httpState->flags.keepalive = 1;
why we have to keep the rate about n_keepalives_recv and 
stats.n_keepalives_sent .and why we need to keep n_keepalives_sent < 10? 
someone can tell me the reason? thanks