  Driven by the primary requirement of emerging 5G mobile services, the demand
for concurrent multipath transfer (CMT) is still prominent. Yet, multipath
transport protocols are not widely adopted and TCP-based CMT schemes will still
be in dominant position in 5G. However, the performance of TCP flow transferred
over multiple heterogeneous paths is prone to the link quality asymmetry, the
extent of which was revealed to be significant by our field investigation. In
this paper, we present a performance analysis model for TCP over multiple
heterogeneous paths in 5G scenarios, where both bandwidth and delay asymmetry
are taken into consideration. The evaluation adopting parameters from field
investigation shows that the proposed model can achieve high accuracy in
practical environments. Some interesting inferences can be drawn from the
proposed model, such as the dominant factor that affect the performance of TCP
over heterogeneous networks, and the criteria of determining the appropriate
number of links to be used under different circumstances of path heterogeneity.
Thus, the proposed model can provide a guidance to the design of TCP-based CMT
solutions for 5G mobile services.
