完成py_plan.md

sim/mac/reliable_mac.py

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+"""
+Reliable MAC layer with ACK and retransmission.
+
+Implements:
+- Send queue management
+- Random backoff before transmission
+- ACK等待 and retransmission
+- Maximum retry limit
+"""
+
+import random
+from typing import Optional, Dict
+from dataclasses import dataclass, field
+from collections import deque
+
+import simpy
+
+from sim.core.packet import Packet, PacketType
+from sim.radio import airtime as airtime_calc
+from sim import config
+
+
+@dataclass
+class PendingAck:
+    """Tracks a packet waiting for ACK."""
+
+    packet: Packet
+    dst: int
+    retry_count: int = 0
+    send_time: float = 0.0
+
+
+class ReliableMAC:
+    """
+    Reliable MAC layer with CSMA-like backoff and ACK.
+
+    Send flow:
+    1. Enqueue packet
+    2. Wait for random backoff
+    3. Transmit
+    4. Wait for ACK
+    5. Retry or success
+    """
+
+    def __init__(self, env: simpy.Environment, node_id: int):
+        """
+        Initialize MAC layer.
+
+        Args:
+            env: SimPy environment
+            node_id: This node's ID
+        """
+        self.env = env
+        self.node_id = node_id
+
+        # Send queue
+        self.queue: deque = deque()
+
+        # Pending ACKs {seq: PendingAck}
+        self.pending_acks: Dict[int, PendingAck] = {}
+
+        # Statistics
+        self.sent_packets = 0
+        self.received_acks = 0
+        self.retries = 0
+
+        # Channel access (set by node)
+        self.channel = None
+
+    def enqueue(self, packet: Packet, dst: int):
+        """
+        Add packet to send queue.
+
+        Args:
+            packet: Packet to send
+            dst: Destination node ID
+        """
+        self.queue.append((packet, dst))
+
+    def dequeue(self) -> Optional[tuple]:
+        """
+        Get next packet from queue.
+
+        Returns:
+            Tuple of (packet, dst) or None if queue empty
+        """
+        if self.queue:
+            return self.queue.popleft()
+        return None
+
+    def has_pending(self) -> bool:
+        """Check if there are packets to send."""
+        return len(self.queue) > 0
+
+    def calculate_backoff(self) -> float:
+        """
+        Calculate random backoff time.
+
+        Returns:
+            Backoff time in seconds
+        """
+        return random.uniform(config.BACKOFF_MIN, config.BACKOFF_MAX)
+
+    def calculate_ack_timeout(self, packet: Packet) -> float:
+        """
+        Calculate ACK timeout based on packet airtime.
+
+        Args:
+            packet: The packet waiting for ACK
+
+        Returns:
+            Timeout in seconds
+        """
+        if packet.is_data:
+            ack_time = airtime_calc.get_ack_airtime()
+        else:
+            ack_time = airtime_calc.get_hello_airtime()
+
+        return ack_time * config.ACK_TIMEOUT_FACTOR
+
+    def start_pending_ack(self, packet: Packet, dst: int):
+        """
+        Start tracking a packet waiting for ACK.
+
+        Args:
+            packet: The sent packet
+            dst: Destination node ID
+        """
+        self.pending_acks[packet.seq] = PendingAck(
+            packet=packet, dst=dst, retry_count=0, send_time=self.env.now
+        )
+
+    def ack_received(self, seq: int) -> bool:
+        """
+        Handle ACK received for a packet.
+
+        Args:
+            seq: Sequence number of acknowledged packet
+
+        Returns:
+            True if ACK was pending (success)
+        """
+        if seq in self.pending_acks:
+            del self.pending_acks[seq]
+            self.received_acks += 1
+            return True
+        return False
+
+    def should_retry(self, seq: int) -> bool:
+        """
+        Check if a packet should be retried.
+
+        Args:
+            seq: Sequence number
+
+        Returns:
+            True if should retry
+        """
+        if seq not in self.pending_acks:
+            return False
+
+        pending = self.pending_acks[seq]
+        if pending.retry_count >= config.MAX_RETRY:
+            # Max retries reached, remove from pending
+            del self.pending_acks[seq]
+            return False
+
+        return True
+
+    def increment_retry(self, seq: int):
+        """
+        Increment retry count for a packet.
+
+        Args:
+            seq: Sequence number
+        """
+        if seq in self.pending_acks:
+            self.pending_acks[seq].retry_count += 1
+            self.retries += 1
+
+    def get_retry_packet(self, seq: int) -> Optional[Packet]:
+        """
+        Get packet for retry.
+
+        Args:
+            seq: Sequence number
+
+        Returns:
+            Packet to retry, or None if max retries reached
+        """
+        if seq in self.pending_acks:
+            pending = self.pending_acks[seq]
+            if pending.retry_count < config.MAX_RETRY:
+                return pending.packet
+        return None
+
+    def get_pending_count(self) -> int:
+        """Get number of packets waiting for ACK."""
+        return len(self.pending_acks)
+
+    def get_queue_length(self) -> int:
+        """Get send queue length."""
+        return len(self.queue)
+
+    def reset_stats(self):
+        """Reset MAC statistics."""
+        self.sent_packets = 0
+        self.received_acks = 0
+        self.retries = 0
+
+    def record_send(self):
+        """Record a packet send."""
+        self.sent_packets += 1
+
+    def get_stats(self) -> dict:
+        """Get MAC statistics."""
+        return {
+            "sent_packets": self.sent_packets,
+            "received_acks": self.received_acks,
+            "retries": self.retries,
+            "pending_acks": len(self.pending_acks),
+            "queue_length": len(self.queue),
+        }