# C-RAN Traffic Aggregation on Latency-Controlled Ethernet Links
## 2 Related Works
These types of traffic are given absolute priority and, since it is QoS sensitive, their delivery must be guaranteed. The other traffic category is less delay sensitive and is in the packet format that will be transported through packet switches. This separation of different priorities of traffic in the network is accomplished by employing Statistical Multiplexing (SM). This type of hybrid network is demonstrated to offer improved performance at a lower cost, compared to a pure circuit or pure packet switched networks. Integrated Hybrid Optical Networks (IHONs) is a further evolution of the primary concept of hybrid node which was introduced in [18]. This new node architecture merges the circuit and packet network in the same wavelength to enable the circuit quality transport of demanding services with higher granularity than wavelengths and enabling statistical multiplexing for the throughput efficiency of packet networks. They used the same principle of dividing the traffic between priority and non-priority as mentioned before and demonstrate experimentally that priority traffic will have absolute transfer guarantees with no packet loss, low packet delay, and ultra-low PDV. Any capacity not utilized by the priority traffic is identified as idle time gaps which can be used by lower priority traffic. Implementation based on Ethernet has been demonstrated in C-RAN [19], assuming CPRI traffic transparently transported by a wavelength and using the leftover capacity for BH traffic. However, to prevent the FH traffic from PDV caused by BH traffic insertion, IHON adds a fixed delay, corresponding to the maximum duration of a BH frame, to all FH packets. An extension of the IHON concept was proposed and evaluated in [20] for possible application in data center by considering three different QoS levels and the possibility of pre-emption for priority traffic. The priority scheduling of three different service profiles was investigated to maximize data center traffic throughput while guaranteeing time transparency for delay-sensitive services and zero loss/fixed delay for guaranteed connections. The idea to use the integrated hybrid concept in C-RAN requires consideration of C-RAN traffic characteristics. In C-RAN, the interconnection between RRH and BBU Hotel is based on CPRI [21]. CPRI is nowadays the most common protocol to transport data in the FH segment of C-RAN between radio sites and baseband hotels/mobile edge computing. Being a Time Division Multiplexing (TDM)-based protocol, it poses strict capacity, latency and latency variation requirements on the transport network. Recently, packet-based functional splitting protocols, such as eCPRI [21], have been released, while splits proposed by 3 GPP [22] are on their way to being standardized. However, so far, the majority of the proposed splits concern the radio physical layer and do not relax the strict delay requirements on the FH transport. The utilization of Ethernet in this architecture is considered as a way for improving reconfigurability and efficiency in terms of both capital and operational expenditures. Since C-RAN is mainly dimensioned based on the peak traffic, it requires large capital expenditures. Moreover, implementing custom-made CPRI switches which enable reconfigurability to C-RAN adds extra costs to the network. In the work referenced in [23], authors focus on an FH solution encapsulating CPRI frames into Ethernet frames and implementing dynamic CPRI line bit rate reconfiguration. In their study, CPRI over Ethernet encapsulation/decapsulation is assumed to be performed at both the RRH and BBU Hotel. The encapsulation is performed as a size-based burst assembly and the minimum granularity of CPRI data to be encapsulated into an Ethernet frame is the CPRI basic frame. Performance evaluation results show that dynamic CPRI link bit rate reconfiguration is achieved within about one millisecond after rate reconfiguration triggering.