The IEEE 802.11 based Wireless LANs (WLANs) have emerged as a viable technology for supporting real-time applications such as voice over IP (VoIP). Even the personal digital assistants and Smartphones are being equipped with WLAN, leading such devices to operate in dual-mode with the WLAN and WAN (wide area network) radios capable of supporting IP communication. This development enables applications such as VoIP to roam or handover freely across the two networks. Seamless handover of VoIP between such networks poses two challenges: the call must persist in spite of mobility across networks, and the LAN and WAN must support the delay and packet loss requirement bounds for VoIP calls. In this paper, we present an experimental study of best-effort VoIP handovers across WLAN and the CDMA EVDO networks, using Skype as the VoIP application. The objectives of our study were: to understand and evaluate the mobility events and actions taking place in a handover; to evaluate the feasibility of running VoIP over WLAN and CDMA EVDO in the process of understanding mobility; and to provide insight into further research in this area. Our study shows that EVDO link acquisition latency and downlink scheduling, and IP mobility procedures contribute towards VoIP call failures. These results provide crucial input to the design of best-effort real-time applications as well as mobility protocols.

With the wireless and mobile access to the Internet growing, compression of Internet protocol (IP) headers is seen as crucial to maximally utilize scarce wireless bandwidth. The traditional IP compression schemes rely on consistent per-flow state in order to perform header compression. While these approaches focus on compression gain, i.e., the reduction in the number of header bytes as a percentage of the total packet size, the overhead is the cost of managing state per each unidirectional flow. In this document, we present a new header compression scheme with the emphasis on reducing or even eliminating the state, perhaps at the cost of reduced compression gain compared to the existing methods. We make use of existing route table information in order to achieve the state reduction. The net result is that significant compression gain can be achieved at a greatly reduced cost of maintaining and managing per-flow state information. This could be especially beneficial for short-lived flows.

Privacy when using IP communication has become an important problem. It is a challenging problem that spans multiple layers in the OSI reference model with various constant identifiers that can be profiled. This leads to user privacy concerns. Location Privacy, on the other hand, is primarily concerned with revealing a user’s identity as a function of mobility. When a user visits a new network and uses a fixed identifier, such as a Mobile IPv6 Home Address for communication, on-lookers can determine that the user has roamed. We address this problem of location privacy and provide a Privacy-Tag for use in place of a fixed identifier to protect user privacy. Our method is readily implementable using the Mobile IPv6 Return Routability [2] protocol and the Binding Update procedure.

The use of bandwidth constrained links in wireless networks necessitates the use of bandwidth saving header compression schemes. In these schemes, a compressor and a decompressor collaborate to encode bulky IP headers into streamlined compressed headers. Intuitively, the gain from compression is the average compressed header length divided by the uncompressed header size. In this paper, we show that this is not true in many situations: this does not account for the cost introduced by the variability of the header sizes during compression context initialization. First, we provide analytical basis for cost of compression context creation and compare the relative costs of establishing contexts with an optimistic approach and with an acknowledgement-based approach. We conclude that the optimistic approach can be used as an upper bound in our analytical model. Second, we evaluate the impact of header compression on traffic patterns in terms of bandwidth allocation, in order to accommodate the burst introduced by compression context initialization. We compute the actual compression ratio, that is the actual number of users of IP header compression that can be multiplexed onto a given link. We show this number is significantly different from the one computed by dividing the link bandwidth by the average rate of a compressed flow. Our results provide a formal basis for context management especially during handovers in mobile networks. For example, our result indicates that there is significant benefit to relocate compression contexts (from one network node to another) rather than to re-establish them each time during handovers.

No abstract available.