The amount of trust required depends on the kind of information/resource that is to be shared. Sharing processor cycles requires less substantial trust then the sharing of personal information and commercial information can require another level of trust establishment altogether. There are systems currently in operation that can provide a certain amount of trust like the public key infrastructure that makes use of certificates; now often used in web based email systems, and Kerberos. Resource discovery Before any resource on a device in the grid can be utilized, those resources that are available must be discovered; all the devices that make up the grid and the resources they possess have to be identified. When a client enters the grid, such as a PDA, it has to be able to communicate to the other users that it is a PDA and it has a camera, GPS capabilities, a telephone function and various office applications such as a text editor. Protocols like UPnP and zeroconf can detect a new node in the network when it enters. When detected, other users can send a query to the new device to find out what it has to offer. Commercial service providers can 'advertise' the resources they have to offer through IP multicasts. Within large grids containing thousands of nodes, a kind of 'friend of a friend' mechanism can be used. There is a myriad of standards that include resource description protocols. Standards as IETF's zeroconf, Microsoft's UPnP, the Grid Resource Description Language (GRDL), the Web Services Description Language (WSDL) for describing various specific web services and parts of QoS that describe bandwidths all offer devices a way to describe and publish their specific resources and needs. There are also various systems currently available that can gather these resource descriptions and structure them for other devices to use. The OpenGrid Services Architecture (OGSA) uses a Web service-style IndexService. The Web services community has defined UDDI which can makes a database of services that are available on the network, and JXTA uses zeroconf to identify resources in a network. However, the problem with using these in wireless grids is that no stable publisher of these descriptions may exist. Resource description For any device to be able to use any resource, a way to identify and describe the resource has to be agreed on by all available devices. If, for instance, storage capacity is to be shared,