Channel coordination (or supply chain coordination) aims at improving supply chain performance by aligning the plans and the objectives of individual enterprises. It usually focuses on inventory management and ordering decisions in distributed inter-company settings. Channel coordination models may involve multi-echelon inventory theory, multiple decision makers, asymmetric information, as well as recent paradigms of manufacturing, such as mass customization, short product life-cycles, outsourcing and delayed differentiation. The theoretical foundations of the coordination are based chiefly on the contract theory. The problem of channel coordination was first modeled and analyzed by Anantasubramania Kumar in 1992.Kumar, A.: Supply Contracts and Manufacturing Decisions, Graduate School of Industrial Administration, Carnegie Mellon University, Pittsburgh, PA, 15213, 1992.
Overview The decentralized decision making in supply chains leads to a dilemma situation which results in a suboptimal overall performance called double marginalization.Tirole, J.: The Theory of Industrial Organization. MIT Press, 1988. () Recently, partners in permanent supply chains tend to extend the coordination of their decisions in order to improve the performance for all of the participants. Some practical realizations of this approach are Collaborative Planning, Forecasting, and Replenishment (CPFR), Vendor Managed Inventory (VMI) and Quick Response (QR).
The theory of channel coordination aims at supporting the performance optimization by developing arrangements for aligning the different objectives of the partners. These are called coordination mechanisms or schemes, which control the flows of information, materials (or service) and financial assets along the chains. In general, a contracting scheme should consist of the following components:Li, X., Wang, Q.: Coordination Mechanisms of Supply Chain Systems. Invited Review. European Journal of Operational Research, 179(1), pp. 1-16, 2007.
local planning methods which consider the constraints and objectives of the individual partners, an infrastructure and protocol for information sharing, and an incentive scheme for aligning the individual interests of the partners.
The appropriate planning methods are necessary for optimizing the behavior of the production. The second component should support the information visibility and transparency both within and among the partners and facilitates the realization of real-time enterprises. Finally, the third component should guarantee that the partners act upon to the common goals of the supply chain.
The general method for studying coordination consists of two steps. At first, one assumes a central decision maker with complete information who solves the problem. The result is a first-best solution which provides bound on the obtainable system-wide performance objective. In the second step one regards the decentralized problem and designs such a contract protocol that approaches or even achieves the performance of the first-best.
A contract is said to coordinate the channel, if thereby the partners' optimal local decisions lead to optimal system-wide performance.Cachon, G.P.: Supply Chain Coordination with Contracts . In de Kok, A.G., Graves, S.C. (eds): Supply Chain Management: Design, Coordination and Cooperation. Handbooks in Operations Research and Management Science, 11, Elsevier, pp. 229-339, 2003. () Channel coordination is achievable in several simple models, but it is more difficult (or even impossible) in more realistic cases and in the practice. Therefore, the aim is often only the achievement of mutual benefit compared to the uncoordinated situation.
Another widely studied alternative direction for channel coordination is the application of some negotiation protocols.Stadtler, H.: A Framework for Collaborative Planning and State-of-the-Art. OR Spectrum, 31, pp. 5-30, 2009.Albrecht, M.: Supply Chain Coordination Mechanisms Springer, 2010. (). Such approaches apply iterative solution methods, where the partners exchange proposals and counter-proposals until an agreement is reached. For this reason, this approach is commonly referred to as collaborative planning. The negotiation protocols can be characterized according to the following criteria:
The initial proposal is most frequently generated by the buyer company which is called upstream planning. By contrast, when the initiator is the supplier, it is referred to as downstream planning. In several cases there already exists an initial plan (e.g., using rolling schedules or frame plans). There are also some protocols where the initial plan is generated randomly. In order to guarantee finite runtime, the maximal number of rounds should be determined. In addition, the protocol should also specify the number of plans offered in each round. When the number of rounds or plans is high, the practical application necessitates fast local planner systems in order to quickly evaluate the proposals and generate counter-proposals. Generally, the negotiation protocols cannot provide optimality, and they require some special conditions to assure convergence. The counter-proposals usually define side-payments (compensations) between the companies in order to inspire the partner deviating from its previously proposed plan.
An also commonly used instrument for aligning plans of different decision makers is the application of some auction mechanisms. However, “auctions are most applicable in pure market interactions at the boundaries of a supply chain but not within a supply chain″, therefore they are usually not considered as channel coordination approaches.
Characteristics of coordination schemes
There are several classifications of channel coordination contracts, but they are not complete, and the considered classes are not disjoint.Tsay, A. A., Nahmias, S., Agrawal, N.: Modeling Supply Chain Contracts: A Review. In: Tayur, S., Ganeshan, R., Magazine, M. (eds.): Quantitative Models for Supply Chain Management. International Series in Operations Research and Management Science, 17, Kluwer Academic Publishers, pp. 299-336, 1999. () Instead of a complete classification, a set of aspects are enumerated below which generalizes the existing taxonomies by allowing classification along multiple viewpoints.Egri, P.: Coordination in production networks. PhD Thesis, Eötvös Loránd University, Budapest, 2008.
Problem characteristics
Horizon Most of the related models consider either one-period horizon or two-period horizon with forecast update.Sethi, S.P., Yan, H., Zhang, H.: Inventory and Supply Chain Management With Forecast Updates. Springer, 2005. ( ) In the latter, the production can be based on the preliminary forecast with normal production mode or on the updated forecast with emergency production, which means shorter lead-time, but higher cost. Besides, the horizon can consist of multiple periods and it can be even infinite. The practically most widespread approach is the rolling horizon planning, i.e., updating and extending an existing plan in each period.
Number of products Almost all contract-based models regard only one product. Some models study the special cases of substitute or complementary products. However, considering more products in the general case is necessary if technological or financial constraints—like capacity or budget limits—exist.
Demand characteristic On one hand, the demand can be stochastic (uncertain) or deterministic. On the other hand, it can be considered static (constant over time) or dynamic (e.g., having seasonality).
Risk treatment In most of the models the players are regarded to be risk neutral. This means that they intend to maximize their expected profit (or minimize their expected costs). However, some studies regard risk averse players who want to find an acceptable trade-off considering both the expected value and the variance of the profit.
Shortage treatment The models differ in their attitude towards stockouts. Most authors consider either backlogs, when the demand must be fulfilled later at the expense of providing lower price or lost sales which also includes some theoretical costs (e.g., loss of goodwill, loss of profit, etc.). Some models include a service level constraint, which limits the occurrence or quantity of expected stockouts. Even the 100% service level can be achieved with additional or emergency production (e.g., overtime, outsourcing) for higher costs.
Parameters and variables This viewpoint shows the largest variations in the different models. The main decision variables are quantity-related (production quantity, order quantity, number of options, etc.), but sometimes prices are also decision variables. The parameters can be either constant or stochastic. The most common parameters are related to costs: fixed (ordering or setup) cost, production cost and inventory holding cost. These are optional; many models disregard fixed or inventory holding costs. There exist numerous other parameters: prices for the different contracts, salvage value, shortage penalty, lead-time, etc.
Basic model and solution technique Most of the one-period models apply the newsvendor model. On two-period horizon, this is extended with the possibility of two production modes. On a multiple period horizon the base-stock, or in case of deterministic demand the EOQ models are the most widespread. In such cases the optimal solution can be determined with simple algebraic operations. These simple models usually completely disregard technological constraints; however, in real industrial cases resource capacity, inventory or budget constraints may be relevant. This necessitates more complex models, such as LP, MIP, stochastic program, and thus more powerful mathematical programming techniques may be required.
As for the optimization criteria, the most usual objectives are the profit maximization or cost minimization, but other alternatives are also conceivable, e.g., throughput time minimization. Considering multiple criteria is not yet prevalent in the coordination literature.
Decentralization characteristics
Number and role of the players The most often studied dilemmas involve the two players and call them customer and supplier (or buyer-seller). There are also extensions of this simple model: the multiple customers with correlated demand and the multiple suppliers with different production parameters. Multi-echelon extensions are also conceivable, however, sparse in the literature. When the coordination is within a supply chain (typically a customer-supplier relation), it is called vertical, otherwise horizontal. An example for the latter is when different suppliers of the same customer coordinate their transportation.
Sometimes the roles of the participants are also important. The most frequently considered companies are manufacturers, retailers, distributors or logistic companies.
Relation of the players One of the most important characteristics of the coordination is the power relations of the players. The power is influenced by several factors, such as possessed process know-how, number of competitors, ratio in the value creation, access to the market and financial resources.
The players can behave in a cooperative or opportunistic way. In the former case, they share a common goal and act like a team, while in the latter situation each player is interested only in its own goals. These two behaviors are usually present in a mixed form, since the opportunistic claims for profitability and growth are sustainable usually only with a certain cooperative attitude.