A radio interface is bandwidth constrained because it is bound to use limited spectrum. Although 3G networks claim to provide bit rates up to 2 Mbps, it is still a far cry from the 52.8 Mbps a Very high Data rate Digital Subscriber Line (VDSL) can offer on a single twisted-pair copper loop. Similarly, bit rate of 11 Mbps in WLAN is no comparison to 1 Gbps of the gigabit Ethernet (IEEE 802.3). Therefore, it is highly desired to use the available bandwidth as efficiently as possible, so as to give the user a decent performance for IP compared to the wired world. Cellular operators pay a significant amount of their deployment costs in acquiring a spectrum. Therefore, radio link efficiency is also highly desired for cost savings.

One approach to improving efficiency for some IP protocols is to use header compression. A problem with IP is namely its large header overhead.

Bandwidth efficiency can also be improved by performing compression on IP payloads. Sometimes IP payloads are already compressed (images, audio, video, “zipped” files) by the applications or are already encrypted above the IP layer. For payload compression the best bandwidth efficiency can be achieved if application-level compression techniques are used extensively. The challenge is to ensure that almost all the applications have a compression mechanism and are using them over wireless links.

Wireless IP networks can be similarly divided into several paging areas. The paging area information can be broadcast with the help of specific radio broadcast capabilities. The mobile node can remain idle within the paging area without needing to perform idle mobility procedures, thus saving power. The mobile node can switch to dormant mode by registering itself as a dormant node to a network element that handles dormancy and paging functions. It needs to wake up only when it crosses the paging area to update its new paging location.

Any downstream traffic toward the mobile node triggers a paging request to wake up the mobile node within that paging area.

The benefit of IP-level dormancy and paging is twofold. It offers these power-saving functions to wireless access technologies like WLAN that do not have such capabilities at the layer 2 level.

Although all cellular technologies do provide these functions, implementing IP-level dormancy offers transparency between the layer 2 functions and the layer 3 functions. Another incentive to IP-level dormancy and paging is due to its access network independence, as discussed in the previous section. Paging when combined with mobility management protocols can provide a very desirable solution for dormancy of mobile hosts in IP networks.

Some current wireless networks, 3G, and future cellular networks are capable of providing high rates over radio connections. Thus, they will have communication bandwidth capabilities similar to the fixed hosts and therefore will be capable of using voice over IP and digital audio and video streaming.

3G cellular networks have already defined QoS classes as part of the radio link layer, but these definitions are limited from the mobile node over the cellular radio up to some core network element that terminates these QoS levels. These networks employ native technology for QoS resource management and admission control to admit or reject any QoS requests from users based on subscription profile and available resources. Additionally, interworking between the QoS classes defined in terms of end-to-end service levels must be mapped to QoS classes over the radio.

The challenge of QoS is not introduced by wireless networks alone, but it was realized with the introduction of new high-bandwidth applications on the Internet. Normal IP data services, referred to as background or best-effort services, like email, Web browsing, FTP, and telnet sessions can work fine without a need for QoS. As new applications like voice over IP, multimedia streaming, and other bandwidth-hungry applications come into existence, the need to manage, control, differentiate, and guarantee the desired service levels has become an important issue. The user perception of quality is determined by end-to-end factors like latency, jitter, throughput, bit-error rate, and bandwidth.

The details of the mobility mechanisms in each of the cellular networks at the radio level and roaming across different networks are dependent on the protocols used for that specific cellular technology. Users can roam only to the networks that support the same cellular technology.

For example, GSM users can roam only to similar GSM networks. When other non-cellular access technologies (e.g., WLAN) are considered, it is even worse since currently there is no common network infrastructure and protocol exchange to support roaming between these access networks.

Cellular networks are operated by different service providers, and each service provider manages the network by dividing the network into manageable network areas in a hierarchical fashion, all the way down to the cell level. Mobile nodes are identified by location based on which cell the user is presently in.

Cellular networks perform location management by continuously tracking the location of mobile nodes with the help information received from the mobile nodes. The location information determines the cell (or a larger network area) where the mobile node is currently located. The location information is broadcast to all the mobile nodes in the network or cell area.

Mobility is an important feature in cellular networks and in any wireless network. Hence, it has been a key design element and an integrated part of current cellular network architectures. However, this is not the case with IP networks, and hence mobility can be considered as one of the biggest challenges for IP.

Without support for mobility, the applicability of IP to cellular networks is quite limited and may result in wireless-specific solutions to handle mobility.

Although IP and its application protocols are designed as link generic to accommodate a very wide range of data link networks, there was an implicit assumption in the designs that the network is a wired network.

Now that the wireless is adopting these protocols, it is realized that the radio links have their own characteristics, which impact the performance of the IP protocols.

These impacts are more significant in the case of Wireless Wide Area Networks (e.g. cellular networks) and Wireless Personal Area Network (e.g. Bluetooth), compared to the Wireless LAN (IEEE 802.11).

This is because WWAN and WPAN offer more latency and limited bandwidth. Thus the limitations of IP applicability to wireless networks are also based on the characteristics of radio links for IP.