# Approximate Networking for Universal Internet Access
## 3 Context-Appropriate Approximate Networking Trade-Offs
### Open Questions  
While we have described the main trade=offs involved in approximate networking, the all-important question still remains to be addressed: _how can we effectively manage these approximate networking trade-offs?_ This bigger question is very much an open issue requiring more research. Some important more specific follow-up research questions regarding trade-offs are:  
1. _Which approximation to apply where in the hardware/software stack, and to which degree, such that the end-to-end QoS requirements are fulfilled?_
2. _How to estimate end-to-end error degradation due to approximations?_
3. _How do we quantify when our approximation is working and when it is not?_
4. _How to measure success in managing the service quality/ accessibility tradeoff?_
5. _How do we measure the cost of approximation in terms of performance degradation?_
6. _How to dynamically control the approximation trade-offs according to the network condition?_
7. _Can the degradation models for approximation errors and channel errors be consolidated?_  
In answering these questions, we can leverage the copious literature produced in the field of multi-objective optimization for some tradeoff-related questions, however, answering other questions related to approximate networking would require new and original future research investigations. It is also important to point out that computing the right tradeoff requires the incorporation of factors such  
Figure 4: Leveraging the extra degree of freedom of exploiting errors can improve performance while reducing cost.  
as the (1) the technology-focused concept of _quality of service_ (QoS), and (2) the user-focused concept of _quality of experience_ (QoE) [22]. While most QoS works have focused on objective measurable metrics such as delay, jitter, throughput, and packet loss, both the objective and the subjective quality measures are needed to provide a holistic multi-dimensional assessment. The subjective quality measures can incorporate factors such as the subjective user preferences; the subjective and objective user perception of the QoS [22]; and the objective application/ service's QoS utility.  
An open challenge in defining and managing context-appropriate trade-offs is to determine the right granularity of the conception of context-appropriate trade-offs, which supports network-level efficiency as well as the user-level and application-level needs. Since the network will likely be used by many users and applications, there is also the problem that instead of a single approximate networking trade-off, there will be multiple interacting approximate networking trade-offs that have to be harmonized. In such an environment, a holistic or systems-thinking based approach will be useful to model the interaction between the various approximate networking point solutions.  
Another challenge is to support applications with approximate networking that are intolerant of even small transmission errors. For instance, implementing encryption in an approximate setting is going to be challenging since encryption transforms even error-resilient applications (such as images, audio, video) to be error intolerant [18]. Other error-intolerant applications may also exist and more research is needed to investigate how such applications can be supported with approximate networking.