# Global IoT Mobility: A Path Based Forwarding Approach
## 4 Mobility over Path Forwarding Architectures  
MN movement within a single operator domain from one Network Attachment Point to another is known as micro mobility or in other words intra-domain mobility. On the other hand, MN movement across two different domains is known as macro mobility or inter-domain. To this end, micro mobility management using a path forwarding architecture is described in detail in [13], where interested readers are referred to. However, it forms the foundation of our macro mobility management solution introduced in this paper; therefore, a brief description is provided here.  
In the proposed path forwarding architecture, we consider four types of entities that take part in any mobility scenario: an MN, a network attachment point (NAP), a Path Computation Element (PCE), and a Forwarding Element (FW). The MN connects wirelessly to an NAP that provides interconnection with a wider distribution network. The PCE determines a path of communication through the network on behalf of a MN or NAP. Optionally, the PCE can also include an information naming function (INF) that provides a method of storing identities (e.g., services, names, and/or IP Addresses) and matching interests. This can help in identifying different services, flows, or bearers for communication. The FW simply forwards information from the MN to the destination using a specific Forward Identifier (FID) generated for this transmission. All the NAPs receive their specified FIDs and populate a local table containing the complete set of FIDs required to reach any other NAP in the network. The first link connecting the MN to the network, e.g., the Network Attachment Point (NAP), is based on the IP protocol, while the NAP serves as an entry point to the core network, which is forwarding based. In the proposed architecture, IP simply becomes a service enabled through the forwarding core, and IP addresses are translated into identifiers used directly for routing.  
The proposed handover process is described using the example shown in Figure 4 for MNs with IP stack and connectivity; however, the solution is equally applicable using any other identifiers. Initially, the MN attaches to NAP A (collocated with gNB A) and performs Link Layer Connectivity and IP Address Establishment. The MN can acquire a global IPv6 address using the Stateless or Stateful address auto configuration procedures (or even manual address configuration) as specified in [17]. NAP A then extracts the source and destination IP addresses from the first packet sent from the MN towards the corresponding node (CN). NAP A sends a forwarding path request including the identifiers (IP addresses) to the PCE. The PCE (or possibly the INF) keeps track of all MN identifiers in the network and links every identifier to its corresponding attachment NAP. Next, the PCE uses its knowledge of the network topology and end-user identifiers to calculate and send the required Forward Identifier (FID) to NAP A, which at this point is ready to forward packets to the CN at NAP B (Collocated at gNB B). The process described above is only for one side of the communication; therefore, the same should happen at the CN's side in order to forward packets from the CN towards the MN. Crucially, this process only happens once for new communication flows, and not for every packet.  
Upon handover, NAP A notifies the PCE of MN A's departure so the latter can expect the MN's connection from a different NAP. MN A then attaches to NAP C (collocated with gNB C) and re-establishes Link Layer Connectivity and IP Address allocation. This triggers NAP C (upon receiving the first IP packet from MN A) to extract the source and destination IP addresses, and send a forwarding path request including the identifiers (IP addresses) to the PCE. Then, the PCE can use its knowledge of the network topology and end-user identifiers to calculate and send the required Forward Identifier (FID) to NAP C which at this point is ready to forward packets to the CN at NAP B.