## 2 Theoretical Background
### Logistics Operator in Multi-Channels  
A key component in assessing the effectiveness of physical distribution is the quality of logistics processes including, in particular, reliability [71]. Therefore, cooperative organisations in omni-channel systems seek to collaborate with LSPs, who add value by providing multiple complementary services, as well as sharing physical resources and information to streamline flows throughout the supply chain [7]. Retailers can, for example, shorten the lead time of orders mainly through picking services provided by LSPs [72]. Logistics issues in the context of multi-channel and omni-channel are most often concerned with the interaction in supply chains, warehouse operations and the design of warehouse management solutions, e-fulfilment, and logistics-related customer service issues [73]. Logistics is a critical aspect related to the success of e-commerce operations [74; 75], but also to the operation of other forms of distribution like multi-, cross-, and omni-channel [76]. The growth of the 3 PL market has been accelerated due to the e-commerce boom and the increase in return logistics operations. There has been a massive influx of third-party logistics to help maintain this highly complex supply chain, offering a wide variety of different services [77]. LSPs also have an impact on reducing environmental impact by increasing the use of environmentally friendly modes of transport, increasing delivery efficiency, and increasing delivery flexibility [78]. Alongside information technology, 3 PL is often recognised as one of the necessary elements to achieve rapid multi-channel business growth [79]. However, it is important to note that acquiring logistics operators is equated with a long-term financial decision [5]. For 3 PL operators, it is critical to have physical resources such as warehouses or transport fleets [1] which provide them with the ability to run flexible operations. An increasing number of logistics service providers are becoming actively involved in the multi-channel distribution of food products. One of the first logistics service providers to become actively involved in the multi-channel distribution of food products was DHL [80]. The concept of multi-channels and the concept of using an LSP entity to deliver logistics services are mostly separate issues in the literature [81]. This can be seen, among other things, in the development of models for integrating e-commercial platforms into the communication between manufacturer and customer, in which the LSP is treated as a separate entity that is not included in the information flow, but only performs the outsourced logistics services [82]. In our opinion, such an approach is not correct, especially if the distribution network is to fulfil the assumptions arising from omni-channelism and thus ensure the same level of customer satisfaction in each channel [83]. According to some authors, the inclusion of logistics operators in the flows increases the complexity of omni-channel systems [82]; however, the benefits of their use are so significant that their role in such distribution systems is constantly increasing. In multi-channel systems, it is essential to maintain and make rational use of the knowledge base of customers across channels [84]. End-customer satisfaction is a result of, among other things, the level of logistics service offered by LSPs to network participants [2]. LSPs offer logistics services, but they also provide access to a network of contacts for retailers to leverage their network of relationships to efficiently fulfil orders to customers. They can handle product returns or work with carriers for 'last-mile' deliveries [7]. Some authors place the greatest emphasis on last-mile delivery and see it as a critical point in the performance of multi-channel systems. They also note that systems not focused strictly on the last mile, even if LSPs are present, are less effective than those focused on last-mile optimisation [85].