[ns] packet sending direction

[Gary Leung <kfleung@eee.hku.hk>]

Hi,

I am trying to send a ACK back to sender before the packet reach the
dest.

the header command which located in packet.h has the following elements:

struct hdr_cmn {
    enum dir_t { DOWN= -1, NONE= 0, UP= 1 };
        ...
    dir_t direction_;
    //Monarch extn begins
 nsaddr_t prev_hop_;     // IP addr of forwarding hop
 nsaddr_t next_hop_; // next hop for this packet
 int      addr_type_;    // type of next_hop_ addr
 nsaddr_t last_hop_;     // for tracing on multi-user channels

...
}

can you please tell me what is the meaning of the element "direction_"?
Should I set it as :

HDR_CMN(p)->direction() = hdr_cmn::UP;

Pls help!! thanks inadvance.

-Gary