Capture object.
      Packet and its sub-classes are Marshal compliant.
    Objectcaplen
Return captured length.
datalink
          Return an integer representing data-link type.
          (e.g. DLT_EN10MB)
        
ip?
          Return true if this packet is an instance of
          IPPacket or its sub-class.
        
len
length
size
Return total length of packet.
raw_data
          Return raw data of packet as String.
        
tcp?
          Return true if this packet is an instance of
          TCPPacket or its sub-class.
        
time
          Return timestamp as Time.
        
time_i
Return timestamp as integer.
udp?
          Return true if this packet is an instance of
          UDPPacket or its sub-class.