## 4 QoS Provisioning Techniques for Future FiWi Networks
### Aggregation Techniques  
Bandwidth provisioning plays an important role to support QoS especially for wireless end-users of FiWi networks. In [53], we proposed and investigated advanced aggregation techniques for both next-generation WLAN and EPON networks. We note that the IEEE standard 802.3 ah does not specify any aggregation method for EPON. We introduced a novel integrated EPON-WLAN FiWi network architecture which consists of different ONU structures that enable existent EPON networks to evolve in a pay-as-you-grow manner while providing backward compatibility with legacy infrastructure and protecting previous investments. Fig. 9 depicts the functional block diagram of the CO and ONU-HT AP components. In this diagram, all depicted blocks are intended to be logical. For instance, the two logical OLT blocks are part of a single physical OLT. An ONU-HT AP provides the optical-wireless interface in our proposed FiWi network. Figure 9: Functional block diagram of CO and ONU-HT AP. It includes a software and hardware upgrade for aggregation and wireless extension, respectively. More specifically, it determines the type of aggregation (_i.e._, A-MSDU, A-MPDU, or two-level aggregation) for both optical and wireless segments. The ingress and egress traffic of the ONU-HT AP comes from and goes to optical subscribers. In the logical branch on the left-hand side, incoming optical traffic is first aggregated by the aggregation module and broadcast to the connected ONUs. The destination ONU-HT AP de-aggregates the received traffic, as shown in Fig. 9. The incoming packets are injected to the ONU and are subsequently divided into egress and WiFi traffic. The WiFi traffic in addition to the ingress traffic destined to WiFi are forwarded to the AP. The ingress traffic destined to EPON in addition to the traffic routed by the AP and WiFi control traffic are injected to the ONU and transferred by using aggregation. The WiFi control traffic consists of status updates of connected HT STAs and ONU-HT APs. The optical traffic and WiFi control traffic are received by the OLT, whereby a switch separates and forwards them to the AP Controller (APC). The APC controls, monitors, and configures the ONU-HT APs to facilitate their wireless operations, such as hand-over of high-speed mobile STAs. Moreover, it performs load balancing between the optical and wireless network segments. Specifically, an APC is able to mitigate traffic congestion at ONU-HT APs by means of WMN between them. The APC periodically monitors ONU-HT APs and establishes WMN links to decrease the optical traffic load, especially for delay-sensitive traffic. On the right-hand logical branch of Fig. 9, incoming and outgoing wireless traffic destined to another ONU-HT AP is received and transfered by using the aggregation unit. Note that while both EPON and next-generation WLAN in HCCA mode use the same eight traffic classes, the HT AP unit of ONU-HT AP performs traffic class mapping for the EDCA mode. The role of the CPU at the ONU-HT AP is to monitor and synchronize all the operational processes at the AP and ONU, including alarm management for congested traffic. The CPU at the CO monitors the OLT and APC to avoid traffic congestion. According to the pros and cons of single- and two-level aggregation schemes, we proposed and investigated various advanced aggregation techniques for our FiWi network. We applied A-MSDU in the optical segment since A-MSDU is able to achieve a higher throughput than A-MPDU for error-free channels [24]. A-MPDU is considered for the wireless network segment. For optical downstream traffic destined to HT STAs, two-level aggregation techniques are used to improve the throughput-delay performance. In EPON, the maximum size of an MSDU is restricted to 1500 octets. For the optical traffic, we set the maximum size of an A-MSDU frame to 7935 octets.