# A Novel Multipath Transmission Scheme for Information-Centric Networking
## 2 Related Work
### Multipath Transmission Mechanism of IP Networks  
According to the difference in design and deployment, the multipath transmission mechanism of the existing IP networks can be classified into the overlay method and the underlay method. The overlay method creates a virtual overlay topology on the underlying network and forms multiple end-to-end paths through logical links. The Resilient Overlay Network (RON) [13] is a typical example of the overlay method. RON periodically measures the status information of virtual links between overlay nodes, then distributes topology and path information to each neighbor node, and finally forwards traffic by building IP tunnels to avoid congested links. However, the overhead of periodic detection and information distribution is not conducive to large-scale deployment of RON. Based on RONs, some studies have proposed a multi-homing overlay network (MON) [14], which introduces the multi-homing characteristics of devices into overlay routing. Although the MON improves transmission benefits, the high overhead is still its fatal drawback. In order to improve the scalability of the overlay method, the authors in [15] proposed the One-Hop Source Routing (OHSR), which attempts to recover from congestion or failure by randomly selecting optional relay nodes for indirect routing. However, the random selection manner does not guarantee the status of the indirect path. In addition, Path Probing Relay Routing (PPRR) [16] uses a random search method to discover alternative detour paths and determines the path state by probing on demand. When serious congestion or failure occurs on the direct path of the underlying IP network, PPRR can quickly switch to an alternative path. Moreover, the Topology-Aware Reliable Overlay Multipath (TAROM) [17] can accurately find relay nodes based on global topology and routing information, but it is difficult to obtain dynamic internet topology and routing information timely and accurately. The underlay method uses a layer-2 or layer-3 routing and forwarding mechanism to ensure end-to-end multipath connectivity. ECMP is a classic multi-path routing protocol, which is widely used in Data Center Networking (DCN). ECMP distributes traffic equally over multiple available forwarding ports based on the diversity of the underlying physical paths. However, the traffic is equally distributed, which also determines that ECMP is difficult to apply to asymmetric networks. Therefore, researchers proposed Weighted Cost Multi-Path (WCOMP) [20] based on ECMP. WCOMP distributes traffic proportionally across paths based on link state. However, WCOMP is inflexible and cannot reroute flows based on congestion information. In [21], the authors proposed a dynamic acyclic multipath routing algorithm, which keeps multiple possible next hops and weights for one destination address, and the router assigns packets of the same destination address to multiple next hops according to the estimated weight ratio. Compared with the traditional IP routing protocol, Multi-Protocol Label Switching (MPLS) [22] provides a new network switching method, which maps IP addresses into short and fixed-length labels. MPLS uses label switching instead of IP routing table lookup to significantly improve forwarding efficiency. As a result of its high price and poor security, MPLS has been stretched under the condition of high bandwidth demand. In addition, researchers have proposed segment routing in the past few years. Segment routing [23] is a packet routing and forwarding mechanism based on source routing. The forwarding path is encoded in the packet header before sending. During the forwarding process, routers can determine who the next hop is according to the header address field. Segment routing has attracted much attention due to its flexible path selection and forwarding. For instance, the authors in [24] proposed an online and offline algorithm for path selection based on segment routing, and the experimental result showed that both methods are effective.