1 On the Interplay of Network Structure and Routing Strategies for Performance in Scale-Free Networks Walid. K. Ghamry, Khaled. M. F. Elsayed and Ameen M. Nassar Abstract— Network performance; characterized by the maximum end-to-end traffic flow the network is able to handle without overloading and has as short a route as possible between any two nodes while keeping the congestion in the network as low as possible; is an important issue in the design of Internet Service Provider’s topologies. In this paper, we examine how the structural characteristics of network topologies affect the network performance and examine the interplay between structural characteristics of network topologies and routing strategies. We consider routing strategies subject to practical constraints (router technology) and economic considerations (link costs) at layer 3. We propose two new routing methods suitable for implementation in large networks and examine various routing strategies (local, global, and hybrid) with tunable parameters and explore how they can enhance the network performance. We find that there exists an optimal range of values for the tunable parameters to achieve high network performance which depends on the structural properties of the network topology. We also show that our proposal routing scheme with the minimum local information achieves high network performance. Index Terms— Routing strategies, network throughput, network structure. I. INTRODUCTION ecently, there is increased interest in studying large- scale real-world systems which include the Internet, World-Wide Web (WWW), protein-protein reactions, and social networks. The most important complex network model is the scale-free network [1] in which the nodal-degree distribution is described as γ − ∝ k k P ) ( , (1) where denotes the fraction of nodes with degree k , ) ( k P γ is the exponent. There are levels of connectivity ranging from the physical layer up to the application layer. The physical connectivity at lower layer is more important for router- level related issues such as network performance. Also, the existence of routing protocols sitting on top of the raw router-level connectivity is important to provide a view of network performance. The efficient throughput for communication systems is affected by the ability of the system to be aware of congestion avoidance. Researcher Assistant, National Research Centre, e-mail: wghamry@yahoo.com . Deparment of Electronics and Communications Engineering, Faculty of Engineering , Cairo University, e-mail: khaled@ieee.org. Deparment of Electronics and Communications Engineering, Faculty of Engineering , Cairo University. It is thus of great interest to study the effects of routing strategies on traffic flow to find optimal strategies that achieve high network throughput and efficient distance communication. Ref. [2] evaluate several routing methods (min-hop, inv-cap, flow deviation method, and their proposed method) on the ISP router level topologies with different power-law degree distributions to assign link capacities and compute node loads based on these link capacities. Ref. [3] estimates the effects of variations of network structure and their proposed traffic awareness routing strategy on network capacity (total number of packets the network can handle at any given time). They build their network models using the model proposed by [4] to obtain various topologies structures with different power-law exponents. Ref. [5] investigates numerically the scale-free network of BA model through the use of various path finding strategies. A generalized diameter is introduced and a simple strategy is suggested to yield small-world behavior. Ref. [6] proposes a routing strategy to improve the transportation efficiency on complex networks. They give a generalized routing algorithm to find the so-called efficient path, which considers the possible congestion in the nodes along actual paths. Ref. [7] proposes a new routing strategy with a single tunable parameter which is only based on local information of network topology. They give an explanation why the delivering capacity of the network can be enhanced by choosing an optimal value for the tunable parameter. In this paper, it is the first time to study the effects of various routing strategies on network topologies having the same node degree sequence subject to practical considerations (router technology) and economic considerations (link costs) at layer 3. We analyze the effects of variations of network structure and routing strategies on network performance. Also, we attempt to answer the questions: how does the network throughput depend on the network topology and how does it vary with the interplay between routing strategies and network structure, and is there any relation between the efficacy of the routing strategy and network structure? We treat the nodes subject to their locations in the network topology: hosts, access routers, gateway routers, and backbone core routers. R