## 3 Literature Review  
This section includes a literature review of the following: video latency measurement, packet switch network, time sensitive networking and secure video. Video latency measurement: This work is based on our previously published work [12] which focused on the measurement of glass-to-glass video delays [17]. In Ref. [12], a comprehensive review of state-of-the-art techniques for measuring latency of the video were covered. Here, some techniques and tools of video latency measurement are listed and a short description is provided. The first tool is called AvCloak [18] and is intended to be used mostly in conference call applications. The tool is able to provide OWD (one-way delay) measurements [19], with two ends synchronised to generic NTP servers. A tool with similar technique and target application is called vDelay [20]. Both tools focus on capturing timestamps as part of video data on one end and decoding of the information for calculating the difference on the opposite end. The VideoLat [21] tool measures the RTD (round-trip delay) of the video. This tool does not require any form of time synchronization while timestamp information is embedded into the video signal in the form of QR codes. Authors in Ref. [22] investigate the effects of video latency in augmented reality applications while in Ref. [23] novel latency reduction algorithm are presented. In these two papers, an LED was used as the source for the visual event. It is worth noting that none of the cited papers investigated video latency measurement with and without encryption. In addition, there is no detailed analysis of the network latency component within the glass-to-glass video latency, which becomes particularly interesting if the video is transferred over a packet-switched network, which is the case for this paper. Packet switch network: A characteristic of packet-switched networks is that they do not guarantee delivery of packets within a bounded time. The end-to-end delay of a network packet consists of the following delays: processing, egress and ingress delay [24], packets queuing delay [25] and transmission and propagation delays [26]. Successful packet delivery depends on the transport layer protocols (TCP or UDP) used. The TCP protocol guarantees that all packets will be delivered to the destination. There is a possibility that some packets will be delayed and retransmitted several times  
Figure 1: Target application system with integrated encryption and latency measurement system. before the acknowledgement receipt by the receiving end [27]. On the other hand, the UDP protocol does not guarantee the packet delivery, but it also does not negatively impact end-to-end delays [28]. All mentioned delay factors make transfer of the video in real-time over a network a challenging task. The evaluation metrics for the QoS (quality of service) in real-time is mandatory for certain applications like controlling a robot based on the video feedback over the Internet/LAN, which is the target application of this paper. The capabilities of data transfer speeds on Ethernet, excellent electromagnetic compatibility [29] and low cabling costs of Ethernet are encouraging factors for this application. The main goal is to enable guaranteed transfer of video data in real-time. Time sensitive networking: In recent years huge effort has been put into development of deterministic communication capabilities between devices connected over standard Ethernet. The most valuable progress, which resulted in a set of networking standards, was made by the TSN (time sensitive networking) task group which is a part of the IEEE 802.1 working group. The TSN was formed from the AVB (audio video bridging) task group which was dealing with real-time transport of audio and video over Ethernet [30]. The resulting solutions are defined by four main IEEE standards: 802.1 AS, 802.1 Qat, 802.1 Qav and 802.1 BA [31]. Guaranteed delivery with minimum bounded latency, low jitter and packet loss are the main goals or achievements aimed for by the TSN standards [32].