In this paper, we investigate and analyze for the first time the
stability properties of heterogeneous networks, which use a
combination of different universally stable queueing policies for
packet routing, in the Adversarial Queueing model. We
interestingly prove that the combination of SIS and LIS policies,
LIS and NTS policies, and LIS and FTG policies leads to
instability for specific networks and injection rates
that are presented. It is also
proved that the combination of SIS and FTG policies, SIS and NTS
policies, and FTG and NTS policies is universally stable.
Furthermore, we prove that FIFO is non-stable for any $r \geq
0.749$, improving significantly the previous best known bounds of
\cite{2,10}, by using new techniques for adversary construction
and tight analysis of the packet flow time evolution.