# Proxy-Based Adaptive Transmission of MP-QUIC in Internet-of-Things Environment
## 2 Related Works on QUIC and MP-QUIC  
QUIC has been designed to solve a number of transport-layer and application-layer problems that have been experienced by modern Web applications. QUIC is similar to TCP + TLS + HTTP/2 but implemented on top of UDP. The key advantages of QUIC over TCP + TLS + HTTP/2 include the connection establishment with low latency, the stream multiplexing to alleviate the head-of-line blocking problem, and the connection migration to solve the rebinding issue of network-address-translator (NAT).  
The QUIC has been developed based on the previous works on SPDY [7]. However, the QUIC can provide distinctive features over SPDY in the viewpoint of the connection establishment process and connection migration. During the connection establishment, QUIC can support 0-RTT or 1-RTT data transmissions, whereas the conventional TCP + TLS scheme requires a 3-RTT handshaking process for connection setup. In the meantime, QUIC connections are identified by a 64-bit connection ID. In contrast, TCP connections are identified by a 4-tuple of source address, source port, a destination address, and destination port. This means that if a client changes IP addresses (for example, by moving out of Wi-Fi range and switching over to cellular) or ports (if a NAT box loses and rebinds the port association), any active TCP connections are no longer valid. With the help of the connection migration functionality, the QUIC data transmission can be continued seamlessly, even though the IP address or port number is changed.  
The Multipath QUIC (MP-QUIC) has recently been proposed and discussed [12]. MP-QUIC is an extension of QUIC in which a QUIC connection can utilize two or more network paths concurrently for data transmission between client and server. This multipath transmission can be used for traffic load balancing and also throughput enhancement in the networks. In MP-QUIC, a Path ID is used to identify a specific path in connection with multiple paths. Each client needs to determine the path to be used for data transmission among the candidate paths available in the network. One simple rule to determine the path is a _round-robin_ policy in which all available paths will be used for data transmission sequentially in rotation for load balancing.  
On the other hand, some works have been made to deploy QUIC into mobile communication networks, such as 3G, LTE, and 5G. The Cross-layer QUIC (C-QUIC) scheme was proposed to use QUIC for next-generation mobile networks [13]. In C-QUIC, the authors propose a variety of policies to determine the network path between cellular link and Wi-Fi link by using the underlying link-layer information, whereas the conventional QUIC uses the 'Wi-Fi First' policy. This approach may be useful to reduce the power consumption of mobile phones and also to enhance the transmission throughput. The authors argue that C-QUIC can provide better performance than the conventional QUIC by 20%, TCP by 36%, MP-TCP by 17%.  
Another study is being progressed so as to integrate MP-QUIC into the 3 GPP mobile network system, named the Access Traffic Steering, Switching, and Splitting (ATSSS) system [14]. The ATSSS system provides network support for multihomed devices to select a path for transmission (steer), move traffic from one path to another (switch), or use multiple paths simultaneously (split). 3 GPP has discussed how to enable ATSSS for non-TCP traffic, based on the use of QUIC.  
Until now, we have investigated the existing works for QUIC enhancement, which include MP-QUIC. From the observations, it is noted that there has not been enough works on how to effectively use QUIC or MP-QUIC in the Internet-of-Things (IoT) environment with a lot of IoT devices/sensors. In addition, the works on efficient QUIC transmission by considering dynamic network conditions have not been made enough in the networks where transmission delays or packet loss rates are changed dynamically.