## 3 DDoS Attacks' Impact on LTE-M  
LTE-M is a standardized technology launched in the 13 th release by the 3 GPP organization to enhance the performance of Low-Power Wide-Area Networks (LPWANs). The objective of M2M communication is to achieve cost-effectiveness, energy efficiency, simplicity, and broad geographical reach [34]. LTE-M networks are limited in terms of bandwidth networks to 1.4 Mbps. In September 2016, a spree of massive DDoS attacks temporarily crippled the Krebs organization to enhance the performance of LPWAN. The initial attack exceeded 600 Gbps in volume, and it was among the largest ones [35]. Additionally, on 26 April 2017, Persirai Botnet [36] was discovered on 64% of the IP cameras Trend Micro was monitoring, which is more than twice as many as Mirai [37]. Now, with an LTE-M limited bandwidth along with a huge attack speed, can LTE-M networks scale to afford the huge amount of data generated by DDoS attacks? To answer this question, we study and evaluate the LTE-M data-rate.  
In order to explore the bandwidths and constraints of Long-Term Evolution-Advanced (LTE-A is a 4G standard) and LTE-M, we analyze the time-frequency resources and their relationship with data rates for M2M communication. In LTE, time-frequency resources are subdivided, as shown in Figure 1.  
Figure 1: Limited bandwidth of LTE-M carrier in LTE-A carrier with a Resource Element (RE) and Resource Block (RB).  
In LTE, the most significant temporal unit is the radio frame with a duration of 10 milliseconds (ms). This radio frame is further divided into ten equal sub-frames. Each sub-frame consists of two slots, and each slot has a duration of 0.5 ms. Each time slot consists of seven Orthogonal Frequency Division Multiple Access (OFDMA) symbols [4].  
* A Resource Element (RE) refers to a narrow channel with a spacing of 15 KHz in frequency domain and 0.5/7 ms in the time domain.
* A Resource Block (RB) consists of 15 KHz \(\times\) 12 sub-carriers = 180 KHz in frequency domain and 0.5 ms in the time domain.
* A Physical Resource Block (PRB) is the smallest allocation block that could be assigned to a single User Equipment (UE) for scheduling purposes. It consists of 15 KHz \(\times\) 12 sub-carriers = 180 KHz in frequency domain and 0.5 ms \(\times\) 2 = 1 ms in the time domain.  
A basic mathematical computation is employed:  
(6 RB \(\times\) 2 \(\times\) 12 Sub-carriers \(\times\) 7 OFDMA symbol \(\times\) 2 bits per RE)/1000 \(\approx\) 2 Mbps.  
Since there are separate channels designated for upload and download in the LTE-M network due to its half-duplex nature, the bandwidth is determined to be 1 Mbps for the upload stream and 1 Mbps for the download stream.  
Finally, to recall, LTE-M uses limited bandwidth (1.4 MHz) with a low data rate of 1 Mbps, and it is expected that DDoS attacks will flood the network with huge data (for example, the Krebs attack speed is about 600 Gbps). So, it is expected that LTE-M networks will be overloaded in a split second when facing a DDoS attack.  
If we know that DDoS attacks can target any type of network or device that is connected to the Internet, including LTE-M networks, many research questions might arise regarding the impact of DDOS attacks on LTE-M networks:  
* How may we detect and predict the occurrence of DDoS attacks?
* How can we analyze the behavior of the network during a DDoS attack?
* What are the impacts of a DDoS attack on M2M traffic?