An example would be a Gateway that could translate from Ethernet to Token-Ring so that the payload was intact and not altered.
A routing on the other hand can only transfer payloads between similar networks and Bridging only if the same Network Address method is used.
Gateway generally implies the Payload is not altered or even Observed. If the Payload is Observed then the Network device is considered a Proxy. Gateway SHOULD NOT need to determine the URI Scheme, for example, of the payload