Local area networks (LANs) are computer and communications networks which users may access at different access points (APs). One type of LAN is a wireless local area network (WLAN) in which user's equipment may be mobile and connects with an access point by means of a wireless link. A well known operating standard for WLANs is IEEE 802.11.
Mobile user equipment in a WLAN is usually referred to as a mobile node (MN). Some examples of an MN are a mobile telephone with a WLAN interface, a laptop computer with a WLAN interface, and a personal data assistant (PDA) with a WLAN interface.
When a MN moves, a requirement can arise for the MN to be handed over from one AP (which may be called the “initial” or “old” AP) to a “new” AP. Handover is controlled by a handover protocol. In the case of a WLAN operating according to IEEE 802.11, the handover protocol is typically the Inter Access Point Protocol (IAPP), which applies across the “initial” and the “new” AP.
The IAPP provides a means for transferring so-called “context” from the old AP to the new AP. The term context is used to describe information relating to the MN and its operation that is required at an AP for the AP to provide service to the MN. Such information may include security information such as authentication information, quality of service (QoS) information, and so on. However, in typical WLANs, and operating standards thereof, handover causes a break in service before the new AP takes over serving the MN. This may be disadvantageous, particularly when the MN is running a real-time application, e.g. a real-time multi-media application such as receiving and displaying real-time video.
In some WLANs, and operating standards thereof, so-called soft handover processes (in which two or more APs effectively serve the MN at the same time) have been applied in an attempt to alleviate the disadvantages of a break in service due to handover.
However, in many WLANs, or operating standards thereof, soft handover is not possible and/or not desirable. This is the case for WLANs operating under the IEEE 802.11 standard, in which adjacent APs typically operate in different frequency bands.
Also, a problem related to QoS provision may arise with handover of real-time applications in WLANs. In particular, where details of operating standards are based upon standards designed originally for fixed networks, a process of requesting and obtaining a required QoS level, using so-called reservation paths, tends to be problematic in WLANs where a user is allowed to change access points, essentially due to the need for re-establishing reservation paths after handover. For example, an Integrated Services (IntServ) framework, as standardized by the Internet Engineering Task Force (IETF) and discussed in R. Braden et al., “Integrated Services in the Internet Architecture: an Overview,” RFC 1633, June 1994, provides a means for requesting and obtaining QoS per flow. IntServ uses Resource ReserVation Protocol (RSVP), as described in R. Braden et al., “Resource ReSerVation Protocol (RSVP)—Version 1 Functional Specification,” RFC2205, September 1997, for implementing signalling associated with this. However, having been designed originally for fixed networks, RSVP is an example of a process which tends to be problematic in WLANs. In particular, depending on the distance between the peers, considerable delays can arise, deteriorating the network performance during handovers, especially for real-time applications.
Considerations such as those discussed above with respect to WLANs also apply to wireless wide area networks (WWANs). WLANs and WWANs may be considered to be two types of wireless access networks, and in this specification the term “wireless access network” is to be understood to include at least WLANs and WWANs, as well as any other access networks whose characteristics are able to benefit from the following invention.