while (off < tot) {
            int fragSize = tot - off;
            if (24 + fragSize > this.max_xmit) {
                // need fragementation
                msg.flags &= ~DCERPC_LAST_FRAG;
                fragSize = this.max_xmit - 24;
            } else {
                msg.flags |= DCERPC_LAST_FRAG;
                msg.alloc_hint = fragSize;
            }

            msg.length = 24 + fragSize;