[ns] hello (ZRP)

[Batbold Toiruul]

Dear ns users,
from zrp.cc code, Could anyone explain below piece of code to me, please?

if (hdrc->ptype() == PT_ZRP) {
    jem =  hdrip->ttl();
    hdrip->ttl() -= 1;
    assert(jem == (hdrip->ttl() + 1) );
    if (hdrip->ttl() < 0) {
      zdrop(p, DROP_RTR_TTL);
      return;
    }