# A Next-Generation Core Network Architecture for Mobile Networks
## 7 Mobility  
Mobility management in today's cellular networks is a major component of the cellular infrastructure. In particular, the access network is split in Tracking Areas (TAs) and the MME keeps track of which UEs are in which TAs. Whenever a UE changes TA, it notifies the network which records the new TA for that UE. If a UE needs to be reached by the network (e.g., incoming call), the network pages the UE in the last known TA for that UE. This, together with handover management, makes mobility possible in the cellular network.  
One downside of this architecture is that, as the UE moves around, the signaling has to always reach the EPC infrastructure in the datacenter to which the UE is assigned. This means that, when  
Figure 17: CNN high-level architecture (SIP Proxy and Internet gateway are multi-homed).  
a user from New York goes to LA and makes a call, the signaling has to go all the way to the datacenter in New York and back to LA. This clearly introduces high delays and long Round Trip Time (RTT).  
In our new architecture, we propose a significantly different approach to mobility, borrowing concepts from Content Distribution Networks [25]. In particular, we try to deploy a VCN as close to the UE as possible in order to minimize latency and RTT. We distinguish between pre-call mobility and mid-call mobility.  
In pre-call mobility, the UE is in idle mode and notifies its SN of changes in TA. When this happens, the SN searches and selects the available hosting infrastructure closest to the UE's new location: if needed, the SN will deploy there a VCN. When the UE goes into active mode, the SN carries out this deployment.  
In mid-call mobility, the UE is in active mode (e.g., in the middle of a call) and, as the user moves, the UE changes TA. Because the UE is in active mode, it has already been re-directed to a VCN and, as such, notifies the VCN of the change in TA. On receiving this TA update (TAU), the VCN notifies its SN by forwarding the TAU to it. When the SN receives the TAU from the VCN, it searches and identifies a new hosting infrastructure as close as possible to the UE's new location. Once this infrastructure has been identified, the SN starts a live migration [26] of the VM hosting the UE's VCN to a VM hosted in the new infrastructure--all standard live-migration techniques can be applied [27; 28; 29]. At the MPLS layer, flow tables must be updated accordingly in order to enable routing to the VCN's new location. As mentioned in Section 6.2, this can be enabled by the SN acting as an SDN controller and leveraging protocols such as OpenFlow and RSVP-TE.  
The hosting infrastructure closest to the UE's new location (i.e., its new TA) can be discovered by relying on any of the existing protocols used for location-based services, such as Location-to-Service Translation (LoST) [30; 31] and DNS [32]. The identified hosting infrastructure can be either: a datacenter of the cellular operator; a specific eNodeB, provided that this has VM hosting capabilities (e.g., fog computing); or anything in between. In particular, for high-profile users (e.g., Government), VCNs can be hosted on private cloud infrastructures not operated by the network operator, hardened with their own security measures in order to achieve a higher level of privacy and security for the UE. For such private infrastructures, the network operator would only retain a control interface between SN and VCN in order to initiate and terminate VCN deployment. In particular, as described in Section 5.2, media is exchanged directly between VCNs and UEs with no SN involvement, thus preserving privacy and confidentiality.