# Reliable User Datagram Protocol as a Solution to Latencies in Network Games
## 2 Related Research
### The Characteristics of User Datagram Protocol (UDP) in Network Games  
User data protocol (UDP) has several notable characteristics compared to TCP:  
* Data is transmitted or received unilaterally without giving any consideration to its connection.
* Transmission data is transmitted by the packet unit.
* There are no special processing processes for the transmitted data.  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**User Datagram Protocol (UDP)** & **TCP** & **Reliable User Datagram Protocol (RUDP) (Ours)** \\ \hline Sometimes packet(s) may not be delivered. & Packet(s) will certainly be delivered. & Packet(s) will certainly be delivered. \\ \hline Packet sequence may change. & Packet sequence is guaranteed. & Packet sequence depends on implementation. \\ \hline Header size is small.28 bites including IP header. & Header size is large.40 bites including IP header. & Header size depends on implementation. \\ \hline Speedy processing speed. & Slow processing speed. & Slow processing speed. \\ \hline Likely to cause Network Address Translation (NAT) problem. & Unlikely to cause NAT problem. & Likely to cause NAT problem. \\ \hline \hline \end{tabular}
\end{table}
Table 1: Communication types.  
First, the fact that no thought has been given to the connection issue is its characteristic rather than its demerit. Nevertheless, considering that it is an element that burdens game programmers who need to consider or process connection problems, it could very well be a demerit.  
From the system's point of view, each connection does not use a separate port and, as there is neither buffer or information regarding the connection, the system uses less resources. Therefore, since taking a resource security approach would not mean much, it will be correct to say that this is a characteristic rather than a merit.  
Data are transmitted by the packet unit and their sizes are limited depending on the system settings such that this will not be a demerit for the games where mainly a small number of packet units are exchanged. Meanwhile, the fact that there are no processing processes for the transmission state or results is a notable characteristic.  
* Data can be transformed.
* The order can be changed.
* Delivery may not be successful.
* Delivery can be made several times.  
Although such characteristics are inherent to UDP, it would be more accurate to say that a network's intrinsic characteristics are as revealing as they are. Essentially, from the network level, it is also true that TCP will not be able to escape from such limitations but it does not need to bother with them as it compensates for these characteristics, whereas they will be burdensome to UDP users. Despite these demerits, the major strength of UDP is that it is faster than TCP as such error-correction processes are omitted. But, strictly speaking, the word 'faster' is somewhat incorrect.  
Even so, it is not entirely incorrect also because, as for TCP, the data following the preceding data lost during its transmission must be on standby at the buffer and this leads to an additional delay to unidirectional network latency when the processed data actually arrives at the client side. For example, there are 4 data (A, B, C and D) and if A has been lost and the others have been transmitted, UDP will deliver B, C and D through Application Program Interface (API) first but TCP will not do so until A has been delivered through re-transmission(s). The contribution of this study is that the OPNET simulations have been performed to apply advantageous characteristic(s) of UDP to games while partially improving its reliability.