In conventional infrastructure-based wireless systems, wireless transmit/receive units (WTRUs) that may wish to communicate with each other must communicate with each other through a base station, even if they could, in principle, communicate with each other directly. The result is an inefficient use of air interface resources as data that could be sent over the wireless medium once (from source to destination) is sent twice (from source to base station and then from base station to destination). There is also an inefficient use of network resources, including for example, base station bandwidth, power, bandwidth of the network backhaul links, and other related resources.
Direct link communications is an alternative means of communications that may be used between the WTRUs. In direct link communications, even though the WTRUs may belong to the network and maintain their connection with the base station, they also establish a communication link to send data back and forth to each other directly. This aspect of their communication may occur with or without involvement of the base station and may or may not be controlled or scheduled by the base station. For example, the direct link communications may occur in a different frequency range from that used by the base station.
In either case, the base station does not attempt to receive such communication. The key characteristic of a direct communication link is that a communication that is directly sent from one WTRU to another bypasses an infrastructure node, for example a base station or access point, that connects the localized wireless network to a larger “backbone” network. The direct link communication may be generalized to include a wireless relay.
Establishing and maintaining a properly secure connection in a direct link communication environment is problematic for several reasons. For example, security methods, such as Wi-Fi Protected Access-2 (WPA-2) in Institute Of Electrical and Electronics Engineers (IEEE) 802.11, require that the WTRUs access and communicate with base stations to establish security. The base station in these instances is only involved in facilitating a connection to some other network node such as a Remote Authentication Dial In User Service (RADIUS) or Authentication, Authorization, and Accounting (AAA) server. This network-enabled security approach is contrary to direct link communications which attempts to reduce or eliminate any need for the WTRUs to communicate with any network nodes.
In other approaches, the WTRUs establish a secure connection to a network node, such as a base station, to enable a simple key establishment process for security. Here, however, although secure links to network nodes (including the base station) may be established to protect against attacks on the communication links (especially on the WTRU-base station wireless links), the network nodes themselves (including the base station) may not be fully trusted. In particular, the WTRUs wishing to establish a direct link with each other may want to keep their direct link communication secure from the network. This is not possible using many current network-enabled approaches. Thus, a direct link key refresh mechanism may be desirable.
Moreover, a direct link may be established for various purposes with various security requirements. Therefore, it may be desirable to enable the WTRUs setting up such the direct link to select a security and key management method appropriate for each particular application. Current methods do not allow the WTRUs to select how the direct link is protected.