Efficient routing strategies in scale-free networks with limited bandwidth

We study the traffic dynamics in complex networks where each link is assigned a limited and identical bandwidth. Although the first-in-first-out (FIFO) queuing rule is widely applied in the routing protocol of information packets, here we argue that if we drop this rule, the overall throughput of the network can be remarkably enhanced. We proposed some efficient routing strategies that do not strictly obey the FIFO rule. Comparing with the routine shortest path strategy, the throughput for both Barab'asi-Albert (BA) networks and the real Internet, the throughput can be improved more than five times. We calculate the theoretical limitation of the throughput. In BA networks, our proposed strategy can achieve 88% of the theoretical optimum, yet for the real Internet, it is about 12%, implying that we have a huge space to further improve the routing strategy for the real Internet. Finally we discuss possibly promising ways to design more efficient routing strategies for the Internet.

💡 Research Summary

The paper investigates traffic dynamics on complex networks where each link possesses a limited, identical bandwidth, a realistic constraint for many communication and transportation systems. Traditional routing protocols assume a strict first‑in‑first‑out (FIFO) queuing discipline at every node, which forces packets to be processed in order of arrival regardless of current link congestion. The authors argue that abandoning this rigid FIFO rule can dramatically increase the overall throughput of the network.

A simple model is adopted: every node acts both as a host and a router, each link can transmit at most one packet per time step (bandwidth B = 1), and at each step λ N new packets are generated with random sources and destinations. A node of degree k_i can forward up to k_i packets simultaneously, limited only by the availability of its incident links. The system’s state is characterized by the order parameter η, which is zero in the free‑flow phase and positive when congestion builds up. The critical packet generation rate λ_c (the value of λ at which η becomes non‑zero) serves as the primary performance metric.

Four routing strategies are proposed and compared against the conventional shortest‑path (SP) rule:

• Strategy A (FIFO + SP) – Strict FIFO is kept; each packet selects the shortest‑path neighbor among free links. This is essentially the baseline SP implementation with FIFO.
• Strategy B (FIFO + traffic‑aware distance) – Each link i ↔ ℓ carries a time‑delay counter τ_iℓ that increments whenever the link is used. A packet destined for node j evaluates an “effective distance” d_B(ℓ)=h·d_ℓj+(1−h)·τ_iℓ, where d_ℓj is the topological distance and h∈