TCP 滑动窗口及 MTU

TCP 滑动窗口:



TCP的MTU(Maximum Transmission Unit)值是1460字节。MSS(Maximum Segment Size)是TCP报文段中的数据字段的最大长度。
mss加包头数据就等于mtu. 简单说拿TCP包做例子。 报文传输1400字节的数据的话,那么mss就是1400,再加上20字节IP包头,20字节tcp包头,那么mtu就是1400+20+20。

IP 包(包头最后加上数据)



TCP 包(包头最后加上数据)


upd包(包头加上数据)



### TCP Sliding Window Mechanism In network communications, the TCP sliding window mechanism plays a crucial role in managing data flow between two endpoints. The core function of this mechanism lies in controlling how much unacknowledged data can exist at any point during transmission[^1]. By adjusting the size of the transmit window dynamically based on current network conditions, it ensures efficient utilization while preventing potential overload. A key aspect involves rejecting duplicates via maintaining a sliding receive window which has a minimum required width of 32 units although systems generally prefer wider windows like those sized 64 or more depending upon specific requirements without notifying senders about these dimensions explicitly[^3]. For implementing congestion avoidance within such frameworks, various algorithms including Reno and CUBIC have been developed to optimize performance further under diverse scenarios using parameters controlled by `tcp_cong_avoid`. ### Fragmentation Handling Regarding fragmentation handling specifically related to TCP: - **Fragmentation**: Typically occurs when packets exceed Maximum Transmission Unit (MTU) limits imposed by underlying layers causing routers along paths from source towards destination breaking larger IP datagrams into smaller fragments. - **Reassembly**: Upon arrival at their final destinations, fragmented pieces get reassembled back together before being passed upwards toward higher-level protocols where they originated initially outside transport layer concerns directly addressed hereunder discussion points regarding only aspects pertinent strictly speaking inside boundaries defined around TCP operations themselves rather than entire OSI model stack interactions involved indirectly through interdependencies existing among different protocol suites working collaboratively across multiple abstraction levels simultaneously over time periods spanning beyond single connection lifetimes possibly involving complex state transitions requiring careful consideration especially concerning security implications potentially arising out there somewhere far away enough so as not immediately apparent unless one looks very closely indeed! ```python import socket def check_mtu(address): try: sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) sock.setsockopt(socket.IPPROTO_IP, socket.IP_MTU_DISCOVER, socket.IP_PMTUDISC_DO) sock.connect((address, 80)) mtu_size = sock.getsockopt(socket.SOL_IP, socket.IP_MTU) return mtu_size except Exception as e: print(f"Error occurred: {e}") ```
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