# Highest Cost First-Based QoS Mapping Scheme for Fiber Wireless Architecture
## 4 Proposed QoS Mapping Schemes for FiWi Testbed  
The prime objective of this study was to investigate the performance issues arisen with the deployment of the FiWi access network based on the XGPON and fifth generation wireless local area  
Figure 3: A typical tree topology of the PON network. network (WLAN). Following the recommendations (i.e., G.987.x series) from the Full-Service Access Network (FSAN) group of International Telecommunication Union Telecommunication (ITU-T) [38] and IEEE Standard 802.11 ac [39], a comprehensive FiWi simulation testbed was designed in OMNET environment. Considering that both XGPON and 802.11 ac are quite complex standards, therefore, we have chosen a built-in 802.11 ac module of the INET4.2 framework [40] and used our own XGPON module designed in OMNET, reported in our earlier studies [41; 42], and implemented its proper connectivity, in compliance to respective standards, with the 802.11 ac module of INET4.2 for this study. Both XGPON and fifth generation WLAN support different traffic classes and require careful mapping of all the traffic classes to achieve service differentiation. The proposed architecture of FiWi with QoS traffic mapping is shown in Figure 4.  
The proposed architecture shows the QoS mapping between XGPON and fifth generation Wi-Fi/WLAN for their traffic aggregation. However, XGPON and 5G Wi-Fi/WLAN offer various types of services (ToS) with different delay and bandwidth requirements but they have some common properties and, thus, mapping is possible. For example, T-CONT 1 is similar to the voice (VO) type of WLAN because voice traffic is constant bit rate (CBR) traffic, and T-CONT 1 deals with CBR traffic in XGPON. T-CONT 4 is similar to best-effort (BE) traffic of WLAN. Figure 5a shows packet classification of the DCF model and EDCA mode of WLAN. The pre-specified QoS mapping scheme is done, where all data frames (DFs) are represented with one single FIFO queue (all-in-one mapping) using the DCF model in STA, and it ensures the provision of QoS in DCF mode. Access points (AP) are also configured with the same QoS configuration and STAs compete with the equivalent bandwidth in DCF mode. By mapping of a class of service (CoS) for each frame in this scheme, no packet classification is required for all frames in the STA and, thus, eliminates the associated overhead, as in FiWi. While, in the EDCA mode, each packet is marked with a user-priority (UP) value that has eight distinct values, i.e., 0 to 7. After marking the packet, it will then be sent to the ONU unit by an Ethernet link through an AP. For every access category or DSCP, packets are categorized and coupled with a right T-CONT type in each ONU, as shown in Figure 5b. Besides, the dynamic mapping of traffic classes is conducted using the highest cost first (HCF) algorithm inside the data frame arrival process block in the ONU. Algorithm 1 shows the pseudo-code  
Figure 4: Proposed FiWi architecture with QoS traffic indicators. Figure 5: (**a**) Packet classification of DCF and EDCA mode in STA. (**b**) Packet classification in ONU. of the highest cost first (HCF) algorithm. It is assumed that the highest categorical data packet involves the highest cost because the highest cost packets are delay-sensitive traffic in the network. T\({}_{\text{XGPON}}\) = {T1, T2, T3, T4} represents a set of transfer method of QoS queues in XGPON. We assume the STAs set priority (P) value at the data frame classifier (DFC) block before transmission of the data packet. The cost (J) is calculated according to the transfer method of data packets as per service requirements. Generally, we have J(T1, P) > J(T2, P) > J(T3, P) > J(T4, P). J(T1, P) needs a constant/fixed bandwidth, therefore, its transfer method has the highest priority. The algorithm of the highest cost first mapping dynamically assigns user traffic to the ONU queues according to the cost (J) value.