Abstract: A dynamic Retransmission Timeout (RTO) algorithm: DRTO (Dynamic RTO) for solving the TCP packets out-of-order caused by LTE network handover was proposed. The essence of DRTO was to use the TCP packet sequence number to distinguish the old and the new packets. Hence the multiplicative factor calculated in the past traditional RTO could be replaced by the difference of the serial number. The algorithm did not need to modify the handover mechanism, which can solve the packet out-of-order between the first part of packets (the packets transferred from source eNB to target eNB) which was transferred before handover process and the second part of the packets (the packets sent by server) which was transferred after handover process. Finally, the DRTO algorithm was compared with the traditional RTO algorithm on NS-2 simulation platform. The simulation results show the DRTO algorithm is better than the traditional RTO algorithm in terms of throughput, the number of retransmission packets and latency.

Key words: Transmission Control Protocol (TCP), Long Term Evolution (LTE), Retransmission Timeout (RTO), handover

摘要： 针对长期演进(LTE)网络中切换引起的TCP数据包乱序问题，提出了一种动态超时重传计时器(RTO)算法——DRTO。DRTO算法的核心是利用TCP数据包的序号来区分新旧数据包，通过新旧数据包序号的差值来取代以往计算传统RTO时很难确定的乘积因子。该算法不需要对切换机制进行修改，就可以解决用户切换完成前接收的数据包(源基站接续转发的数据包)与切换完成后接收的数据包(服务器发送的数据包)的乱序问题。最后，在NS-2仿真平台下，分析比较DRTO算法与传统RTO算法。仿真结果表明，在吞吐量、重传数据包个数和时延三个性能指标上，DRTO算法均优于传统RTO算法。

关键词: 传输控制协议, 长期演进, 超时重传计时器, 切换