# Tunnel-Free Distributed Mobility Management (DMM) Support Protocol for Future Mobile Networks
## 1 Introduction  
The advent of a huge plethora of wireless technologies have opened new opportunities besides the typical voice calling services. Wireless services and devices have seen a remarkable increase, especially since the introduction of smart phones. As reported in Sandvine [1], the population of mobile nodes now exceeds that of traditional wired nodes. With such an increase, the IP paradigm is now shifting from IPv4 to IPv6 as the IPv4 addresses are not enough. The current implementation of a mobile core network architecture is in a hierarchical and centralized manner. Therefore, the mobility management protocols, such as mobile IPv6 (MIPv6) and proxy mobile IPv6 (PMIPv6), have also been deployed in this manner [2; 3]. More devices need more IP addresses, which results in the need for network scalability. A scalability issue has been identified as one of the limitations of the current centralized and hierarchical network architecture [4; 5]. Other limitations include sub-optimal routing, central point of failure, and reliability problems. Distributed mobility management (DMM) [5] is often seen as a solution to the scalability, reliability, central failure point, and routing issues of the centralized network architecture since the DMM approach distributes the responsibility of providing connectivity and mobility by going toward a flat networkarchitecture. IP mobility support for such flat mobile network architectures is needed. Therefore, to address such architectural changes, the IETF (Internet Engineering Task Force) Distributed Mobility Management (DMM) working group was developed in March 2012 to manage the rapidly increasing mobile internet usage. IETF is making sure to deploy such DMM protocols that are not centrally deployed, but instead distributes mobile Internet traffic in an ideal way [6]. The problems and issues in centralized mobility management (CMM) can be overcome if effective mobility protocols are introduced in DMM. The IETF standardized mobility management schemes for IPv6 are different variations of MIPv6 [2], which are further divided into two categories: network-based mobility protocols and client-based mobility protocols. The client-based mobility methods maintain session continuity through tunneling using a home agent (HA) as a mobility anchor and a mobile node (MN) as a signaling agent, e.g. MIPv6 and Dual Stack MIPv6 [7]. In contrast, network-based mobility methods maintain session continuity with tunneling using a local mobility agent (LMA) as a mobility anchor and a mobile access gateway (MAG) as a signaling agent, e.g. Proxy Mobile IPv6 (PMIPv6) [3]. In both these approaches, there are centralized entities, i.e. HA/LMA, they anchor the IP addresses used by the MN, and are responsible for maintaining mobility management. Development of DMM faces some challenges as well [8]. The DMM approach allows an MN to keep more than one IP address simultaneously in the case of MN mobility. Hence, there is a need for proficient tunneling and IP address management. Second, additional IP addresses result in the increment of bi-directional tunnels, which in turn increases the signaling messages along with an additional registration delay. Another challenge regards network configuration and resource management since everything now has to be managed in a distributed fashion. Tunneling management is a big challenge for current DMM-based mobility protocols. This research will focus on this problem. In this research, a tunneling-free design for mobility in a DMM was proposed in order to ensure seamless session continuity for MNs. In this design, session continuity of an MN on the move is ensured by using a make-before-break (MBB) approach. To ensure Quality of Service (QoS) to users, handover is to be performed in an MBB fashion, i.e., a new path reservation is made for an ongoing connection before switching its whole traffic onto the new path and tearing down the old path [9]. The handover takes place when an MN is in the overlapping region of the two base mobility agents (BMAs).