VLAN parameter meaning

Dear All,

Could you help me expain these words for me ("total headroom inc","total encap on xmit" ,INGRESS priority mappings,  EGRESS priority mappings.

[root@ibapp network-scripts]# cat /proc/net/vlan/bond0.117
bond0.117  VID: 117      REORDER_HDR: 1  dev->priv_flags: 1
         total frames received         6165
          total bytes received       453605
      Broadcast/Multicast Rcvd         1952

      total frames transmitted         2806
       total bytes transmitted       265508
            total headroom inc            0
           total encap on xmit            0
Device: bond0
INGRESS priority mappings: 0:0  1:0  2:0  3:0  4:0  5:0  6:0 7:0
 EGRESS priority mappings:
 
 Thank you.