Assessment of packet latency on the 4G LTE S1-U interface: Impact on end-user throughput

4th Generation Long Term Evolution (4G LTE) networks are about to become the standard in mobile communications. These networks' backhaul transport for the LTE user and signaling traffic needs to operate in various environments and over a wide variety of networks built on a mix of technologies and equipments. All network elements of such a network are interconnected over other wired and wireless network technologies, each with performance characteristics of their own - and performance issues which will often be translated into issues seen on the overall LTE network performance. It is important to understand this behavior and the interdependencies in order to understand how to optimize and eventually predict performance of 4G LTE networks. Since 4G LTE itself is a full IP-based network, this means understanding and assessing the effect of IP impairments on LTE and its transport links. In this paper, we analyze the impact of backhaul packet delay (latency) on the LTE S1-U interface, which provides user plane transport between the Core Network and the Evolved NodeBs. We emulate different packet delays on the S1-U interface, measuring the impact on end-user throughput and discussing the results. We use a custom, self-built IP Impairment Tool: its flexible, cost-effective and mobile concept allows quick and easy integration and testing even on live commercial-grade LTE networks.