Which of the following statements is true with regards to peer$-$to$-$peer $($P$2$P$)$ computer network systems?

a$.$ These systems involve laying cable underwater between docks

b$.$ P$2$P protocols only allow connections between identical classes of users

c$.$ In a P$2$P system, there are no fixed clients and servers

d$.$ Only TCP$/$IP protocols allow P$2$P connections

e$.$ P$2$P systems require a direct physical connection through SONET