It is useful to define some mobility-related terms that are often used in the context of handover and optimization. In this appendix, we introduce a few of the relevant terms, including some from RFC 3753 (Manner and Kojo 2004) and ITU-T X.200 (ITU-T 2004), that are useful for handover optimization and have been used in various chapters of this book.
A mobile node may be either a mobile host (with no forwarding functionality) or a mobile router (with forwarding functionality). A mobile node can have multiple interfaces.
An interface identifier can be a layer 2 or layer 3 identifier depending upon the specific configuration. For example, a MAC address is defined to be a layer 2 identifier, whereas an IP address is a layer 3 identifier.
A typical device identifier could be the MAC address of an IP-based device or the electronic serial number (ESN) of a cellular device. If multiple interfaces are assigned to a device, each interface will have a unique MAC address.