ork keys. Data encryption Optional 128-bit AES using link keys between devices or a common network key. Frame integrity check Check to ensure that data transmitted within a frame has not been modified Sequential freshness A sequentially updated freshness value that allows the check network controller to check for and reject any replayed data frames. and data integrity, as shown in Table 11-8. Specific security implementations can then be developed using these services. Two security modes are defined in the ZigBee standard, commercial and residential. The full access control functionality of the network co-ordinator, or trust centre is only available in the commercial security mode. In residential mode the network co-ordinator controls device access to the network but does not establish or maintain keys, in order to reduce the memory cost of the trust centre device. IrDA Security The IrDA standard does not include a specification of link level security as the short range and line-of-sight requirements provide an inherent low level security. Any threat of unauthorised access to data through an active port, for example when using an IrDA enabled laptop in a public setting, can be easily countered by disabling the IrDA port when not in use and by ensuring that sensitive data is only transferred in a private environment. Additional security measures, such as authentication and encryption, are implemented at the application level. One such example is the IrDA OBEX authentication mechanism, which requires a user-entered OBEX password to be stored on both devices before an OBEX connection Chapter Eleven can be made. This password is then used by both devices for authentication when the link is established. Summary of Part IV In common with wireless LANs, wireless PAN implementation can also benefit from a systematic approach to establishing requirements and selecting the most appropriate technology. Pilot testing can also be a valuable implementation stage, particularly if the WPAN is being deployed for a large and diver