## 3 Network Sliced Distributed Learning
### DL-as-a-Service for IoV Applications
#### 3.2.3. DLaaS Challenges  
Though the proposed DLaaS method can have many advantages, several challenges must be considered while performing slice function deployments. These challenges can be based on application requirements, user-side demands, network restrictions, etc. The following key challenges should be considered in the proposed DLaaS method for proper benefits.  
**Learning Function placement:** The DL functions can have specific requirements in terms of communication, computation, storage resources, and hardware dependencies.  
Figure 1: Distributed learning as a service over NS for IoV applications.  
Figure 2: Multi-layer Federated Learning as a slice for IoV scenarios.  
When placing the functions, it is also important to take into account the functional dependencies to avoid excess costs; for example, DPrF and DAF should be placed together to avoid the communication burden. The mobility of VUs, application requirements, and limited edge resources can add additional challenges. Thus, several of these issues can make the placement of the slice functions quite challenging, and improper placement of the functions can lead to an inefficient learning environment.  
**Network Resource Allocations:** Learning slices can be data-intensive, computation-intensive, or communication-intensive based on their higher demands for storage, computing, and communication resources, respectively. Edge nodes can have a limited set of available resources that can change over time with various demands. Additionally, each node may host several learning functions from different DL slices. Additional constraints, such as mobility, unstable communication environments, and application requirements, can make the network resource allocation problem quite challenging.  
**Multi-slice Implementations with Specific Demands:** DL slices are characterized by different function chains, requirements, etc., and implementing them over a common infrastructure can be challenging. Each slice can have an impact on other slices' performance as a result of resource sharing. Multiple communication links enabled through a different set of slices can increase issues like noise, interference, etc.  
**Security Threats:** Due to the presence of multiple DL slices with different user groups, the overall threat to data security can be elevated. Some slices/users can be more vulnerable to outside attacks and can end up impacting and compromising the security of other learning processes.  
**High-Speed Distributed Computing and Communication Environment:** The challenge of resource management in a high-speed distributed computing and communication environment is crucial for the efficient functioning of the DLaaS framework. As vehicular networks operate in dynamic and high-speed environments, ensuring optimal resource allocation for fast-paced distributed computing becomes a significant challenge [57]. The need to manage resources such as computation, communication, and storage in real-time, considering the rapid movement of vehicles and the evolving nature of network conditions, adds complexity to the DLaaS implementation.  
Thus, several of these challenges need to be properly addressed in order to have the additional benefits of DL as a Slice concept over a distributed vehicular networking environment.