Data management methods for use in a network system including at least first, second and third network terminal devices and traversal server are disclosed. First and second network terminal devices can traverse at least one NAT router and/or firewall to establish a connection channel between each other for data access through traversal server. The method includes the steps of: receiving first packet with first protocol format from first network terminal device; determining whether to perform protocol conversion operation; if so, obtaining a list of available network terminal devices, assigning first network terminal device from obtained list, converting first packet with first protocol format into second packet with second protocol format that is decodable by second network terminal device, and sending second packet to second network terminal device such that second network terminal device can obtain content of first packet by decoding second packet upon reception of second packet.