# Performance Analysis of a Novel TCP Protocol Algorithm Adapted to Wireless Networks
## 1 Introduction  
The Transmission Control Protocol (TCP) was originally designed for wired networks, by interpreting packet loss (PL) as congestion consequence; meanwhile, in wireless networks, PL is also caused by issues in the communication channel, such as interference, multi-path fading, mobility, and reflections, which may produce a PL misinterpreting [1]. In order to avoid congestion, TCP employs cumulative Acknowledgments (ACK); in this sense, the receptor sends ACKs to indicate that a packet was successfully received and to specify that it is expecting the next one. If the transmitter undetected an ACK, the packets are re-sent or the connection is disrupted [2]. TCP can use four algorithms for Congestion Window (CWND) control: Slow Start, Congestion Avoidance, Fast Retransmit and Fast Recovery. These algorithms seek to achieve a high network performance and to avoid collapse by congestion. Slow Start increases exponentially the transmission bit rate until a packet loss is detected. From this point, the Congestion Avoidance algorithm increases the transmission bit rate linearly, and when three duplicate ACKs are detected, TCP reduces the transmission bit rate by half. Meanwhile, Fast Retransmit and Fast Recovery allow to resend packets immediately when three duplicate ACK (DUPACK) are detected. The transition from one algorithm to another occurs when PL is detected [3]. Although CWND control algorithms achieve their goal in wired networks, in wireless networks,unnecessary executions of the four algorithms occur frequently, which, in turn, causes low transmission bit rates, as seen in the results presented in [4]. TCP has different versions seeking CWND optimization by an ACK notification rate analysis. Two of the most popular TCP versions are TCP Reno and TCP Westwood. The first one reduces CWND by half after three DUPAC, while the second selects a Slow Start threshold (ssthresh) and a CWND consistent with the effective connection bit rate [5]. Several efforts to improve TCP protocol in wireless networks have been developed, for instance, Explicit Loss Notifications (ELN) which adds explicit bits to the packet as feedback to the TCP source to identify the loss cause. For example, in [6], ELN gives a superior throughput (\(\overline{\theta}\) ) than TCP Reno and TCP-Tahoe, reaching as high as 80 to 90% in an error free simulated scenario. Similarly, in [7], by using ELN, reduced response times of almost 30% were obtained for high error probability web traffic in a simulated scenario. Another proposal for wireless TCP improvement is the end-to-end coding approach [8], in which redundancy is added to the TCP packet to facilitate loss recovery, which outperforms in simulation TCP New Reno and TCP with the selective acknowledgment option (TCP SACK) over a range of loss probability and propagation delays. Additionally, other modification approaches exist for TCP functionality, such as the use of a fast end-to-end retransmission scheme [9]. This proposal avoids long pauses in communication during cellular handoffs. It requires minimal changes to end terminals and improves \(\overline{\theta}\)  values from 1400 to 1490 kb/s for non-overlapped cells with zero seconds between cells, and from 1100 to 1380 kb/s for non-overlapped cells with 1 second between cells. In [10], the Indirect TCP protocol (I-TCP) splits the network in a wired-cum-wireless connection by adding a Mobility Support Router, and then it attempts to alleviate mobility related performance problems by adapting the transport layer protocols on the wireless link, modifications are required only on the Mobile Host (MH). This solution achieved better \(\overline{\theta}\)  than TCP Reno for a local area network under a Bit Error Rate (BER) of up to \(2\times 10^{-6}\), and twice \(\theta\) for a wide area network under BER of up to \(5\times 10^{-6}\). In [11], a sender-only TCP modification based on dynamic bandwidth estimation in wired-cum-wireless networks is presented as TCP Prairie.