2,200年前の高槻・安満遺跡「二重環濠」と西国街道の飛脚リレーは、なぜ現代のファイアウォールやTCP/IP通信と同じ構造なのか？

#![forbid(unsafe_code)]

#[derive(Debug, Clone, Copy)]
pub struct RelayHopSpec {
    pub hop_distance_km: f64,
    pub propagation_speed_km_h: f64,
    pub switching_handover_secs: f64, // Store-and-Forward header verification & relay delay
    pub payload_bytes: u64,
}

#[derive(Debug, Clone, Copy)]
pub struct NetworkPathMetrics {
    pub total_end_to_end_secs: f64,
    pub effective_throughput_bps: f64,
    pub bandwidth_delay_product_bits: f64,
}

/// Computes end-to-end Store-and-Forward latency and Bandwidth-Delay Product (BDP)
/// across a multi-hop relay backbone (applicable to both historical Hikyaku and packet hops).
pub fn analyze_multihop_backbone(hops: &[RelayHopSpec], in_flight_windows: u32) -> NetworkPathMetrics {
    if hops.is_empty() {
        return NetworkPathMetrics {
            total_end_to_end_secs: 0.0,
            effective_throughput_bps: 0.0,
            bandwidth_delay_product_bits: 0.0,
        };
    }

    let mut total_secs = 0.0;
    let mut min_hop_bps = f64::MAX;

    for hop in hops {
        let travel_secs = (hop.hop_distance_km / hop.propagation_speed_km_h.max(1e-6)) * 3600.0;
        let hop_total_secs = travel_secs + hop.switching_handover_secs;
        total_secs += hop_total_secs;

        let hop_bits = (hop.payload_bytes as f64) * 8.0;
        let hop_bps = hop_bits / hop_total_secs.max(1e-6);
        if hop_bps < min_hop_bps {
            min_hop_bps = hop_bps;
        }
    }

    let effective_bps = min_hop_bps * (in_flight_windows.max(1) as f64);
    let rtt_secs = total_secs * 2.0;

    NetworkPathMetrics {
        total_end_to_end_secs: total_secs,
        effective_throughput_bps: effective_bps,
        bandwidth_delay_product_bits: effective_bps * rtt_secs,
    }
}