Put simply, bridging your Grandstream HT502 ATA disables the devices higher level networking functions (Routing/NAT/DHCP).
Bridge mode can be useful if you are putting the ATA infront of other networking devices (such as a router), and may be necessary to obtain your full speed on packages above 25Mbps.
  1. Connect a PC directly to the LAN port of the ATA using an Ethernet cable.
  2. Navigate to the ATA's web interface. (http://192.168.2.1)
  3. Log into the ATA using the User password. (The default user password is 123)
  4. Click on the BASIC SETTINGS tab.
  5. Scroll down to the section titled NAT/DHCP Server Information & Configuration and set the Device Mode field to Bridge
  6. Click Apply