he Internet is currently experiencing a transition from point-to-point best effort (BE) communications toward a multiservice network that supports many types of multimedia applications, with potentially high bandwidth demand. Thanks to the rapid development of communication network hardware, adding physical resources (fast-speed switching and routing elements, high-capacity network links, etc.) to the existing Internet has become relatively cheap in recent years. Typically, the advent of

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... ingly high-speed links has offered opportunities for IP network providers (INPs) to adopt a strategy of bandwidth overprovisioning in their networks. Nevertheless, this approach is currently only applicable to the core network, and the demand from sharply growing customer traffic over the global Internet still cannot be satisfied. The measurement results presented in [1] indicate that bottlenecks of the Internet backbone are not only located at interdomain links between autonomous systems (ASs), but also within individual domains. Given this information, it is essential for INPs to perform efficient resource optimization both intra-and interdomain so as to eliminate these bottlenecks. Internet traffic engineering (TE) is the process of performing this task. In [2] TE is defined as large-scale network engineering for dealing with IP network performance evaluation and optimization. A more straightforward explanation of TE is also given in [3]: "to put the traffic where the network bandwidth is available." Therefore, the nature of TE is effectively a routing optimization for enhancing network ABSTRACT Traffic engineering is an important mechanism for Internet network providers seeking to optimize network performance and traffic delivery. Routing optimization plays a key role in traffic engineering, finding efficient routes so as to achieve the desired network performance. In this survey we review Internet traffic engineering from the perspective of routing optimization. A taxonomy of routing algorithms in the literature is provided, dating from the advent of the TE concept in the late 1990s. We classify the algorithms into multiple dimensions: unicast/multicast, intra-/interdomain, IP-/MPLS-based and offline/online TE schemes. In addition, we investigate some important traffic engineering issues, including robustness, TE interactions, and interoperability with overlay selfish routing. In addition to a review of existing solutions, we also point out some challenges in TE operation and important issues that are worthy of investigation in future research activities.