# QoS-Aware Resource Management in 5G and 6G Cloud-Based Architectures with Priorities
## 3 Transmission Waiting Time FIFO Queue
### Packet Segmentation Analysis  
The 5G, and subsequently forthcoming 6G, packet transmission in Layer 2 Radio protocol stack (i.e., PDCP, RLC, MAC protocols) is based on IP packet formation [24; 25]. According to 3 GPP TS 36.321 standards, the packets to be transmitted all the way down from PDCP to the RLC and MAC layers are controlled by the MAC scheduler decision on the UE's radio link quality. The MAC layer will inform RLC about the requested packet length (in bits) and the RLC will accommodate the PDCP IP packets from the proper buffer and apply segmentation functionality to fit them into the MAC request. As a general justified service statement, the average number of TCP/UDP IP bits per packet, \(M_{I}\), is considered for most applications to be 1500 bytes. Relying on 3 GPP MAC layer uplink mapping, \(\lceil M_{I}/M_{mac}\rceil\) could be estimated considering also that MAC payload carried in one slot during an uplink RB and scheduled in a Time Transmission Interval (TTI) will vary depending on the coding and modulation scheme selected from the Link Adaptation algorithm. The corresponding data rate at the MAC layer is defined precisely by 3 GPP. Let us consider then a TCP/UDP IP packet of MI variable bits per packet that is framed in such a way that the resulting MAC packets of variable length Mmac (bits per packet) contain a fixed number of Moverhead bits per packet [24]. In such a model, then, one MI packet will be segmented into MI/Mmac number of MAC packets. Considering that this division will rarely allocate an integer number, then one extra MAC packet will be needed in most of the cases to accommodate the remaining bits out of the division. The total number of transmitted bits then will be \(M_{I}+[M_{I}/M_{mac}]M_{over}\), where the factor \([M_{I}/M_{mac}]M_{over}\) indicates the overhead created by the MAC layer for the MI size TCP/UDP IP packet transmission. Considering ideal radio channel conditions (no retransmissions), the expected whole TCP/UDP IP packet transmission time is  
\[T_{delay}=\frac{M_{I}+\left\lceil\frac{M_{I}}{M_{mac}}\right\rceil\cdot M_{ over}}{M\cdot N\cdot n_{TTI}}T_{s}+\overline{\pi}T_{s} \tag{11}\]  
where \(n_{TTI}\) is the number of transmitted bits per scheduled block (TTI duration varies accordingly in the discrete time domain range of (1 ms, 0.5 ms, 0.25 ms, 0.125 ms) based on the sub-carrier spacing (SCS) of the network configuration and bounded in the frequency domain in the fixed bandwidth of 180 kHz) which depends on the Link Adaptation Modulation Scheme, N is the average allocated number of 180 kHz radio block (RB) units of bandwidth per TTI considering also the constraint that \(0\leq\) N \(\leq\) BW where BW is the allocated configured bandwidth during cell planning (minimum 5 MHz up to maximum 100 MHz for sub6 GHZ or 400 MHz for mmW) and M is the number of antenna ports (in the case of MIMO implementation). In this analysis, then, and for average N 180 kHz-allocated RB, it is considered that (N \(\cdots\)\(n_{TTI}\)) bits out of the total are transmitted simultaneously in a TTI scheduled interval. If spatial multiplexing (SMUX) of M \(\times\) M in a typical massive MIMO (mMIMO) solution is also considered, then (M \(\cdots\) N \(\cdots\)\(n_{TTI}\)) bits are expected to be transmitted simultaneously in a scheduled TTI interval. Finally, (\(\overline{\pi}\)\(\cdots\) T) is the average non-scheduled period of time for the service, where \(\overline{\pi}\) is an integer value to indicate the average number of slots (Time Transmission Intervals) that one MAC service packet is not scheduled by the scheduler in a total scheduling period T. Remember that \(\overline{\pi}\) for downlink scheduling decisions depends mainly on the QoS Guaranteed Bit Rate (average) GBR parameter, on Channel Quality Index CQI measurement report, and also on UE transmitter mean-packet waiting time on the buffer. The average transmission delay is expected to be increased due to MAC HARQ retransmission functionality [25].