为什么802.11确认帧没有源MAC？ [英] Why do 802.11 Acknowledgement Frames have no source MAC?

问题描述

谁知道为什么802.11确认帧没有源MAC地址？当我使用监视模式和混杂模式驱动程序从Linux捕获TCPDUMP或Wireshark的数据包时，看不到它。如果帧中没有源MAC地址，接入点如何区分ACK帧与不同的802.11客户端？

Anyone know why 802.11 Acknowledgement Frames have no source MAC address? I don't see it when I capture the packets from TCPDUMP or Wireshark from Linux with a monitor-mode and promiscuous-mode driver. How does the Access Point distinguish ACK frames from different 802.11 clients if there is no source MAC addresses in the frame?

我从所有捕获中都可以看到ACK立即出现在发送帧后（大约10到30微秒），但是仅凭这一点还不足以区分信号源吗？也许每个帧都有某种唯一的标识符，而ACK帧内部有这个ID？既然WLAN使用WPA-PSK模式，也许在加密的有效载荷中就有识别信息？

I can see from all the captures that the ACK comes immediately after the frame is sent (around 10 to 30 microseconds) but that alone can't be enough to distinguish the source can it? Maybe each frame has some kind of unique identifier and the ACK frame has this ID inside it? Maybe there is identifying information in the encrypted payload since the WLAN uses WPA-PSK mode?

推荐答案

不，没有任何内容802.11 MAC ACK帧。

No, there is nothing encripted in 802.11 MAC ACK frames.

802.11是基于竞争的协议。即，在时间上，媒体都由在相同频道[频率]中工作的不同STA和AP共享。想要传播的人争夺媒介，获得媒介的胜利者开始传播。

802.11 is a contention based protocol. ie the medium is shared by different STA's and AP's who all are working in the same channel [frequency] in terms of time. Those who wants to transmit are competing for medium , winner who gets medium starts transmitting.

根据802.11规范。 ，一帧播出后，下一个 SIFS时期的介质应该是免费的。即没有人被允许发送。
在SIFS的末尾，单播帧的接收方应发送ACK。这是规则。

As per 802.11 spec. , once a frame is on air, the next "SIFS" period medium should be free. ie no one is allowed to transmit. At the end of SIFS, the reciever of unicast frame should transmit ACK. This is the rule.

对于基于OFDM的802.11实现[802.11 G，A]，802.11中的SIFS [短帧间空间]约为10微秒。对于802.11b，如果我的内存正确，则约为20微秒。这就是为什么您在TX和ACK之间看到10或30微秒的原因。

SIFS [Short Interframe space] in 802.11 is ~10 microseconds for OFDM based 802.11 implementations [802.11 G,A]. For 802.11b its ~20 microseconds if my memory is correct. Thats why you are seeing 10 or 30 microseconds in between TX and ACK

因此，每个人都知道谁在发送ACK，以及谁要发送ACK。因此，无需包括源地址，它是有效的。

So, everyone knows who is transmitting the ACK and whom the ACK is to. So no need to include source address, its implecit.

为什么不包括源地址？
减小帧大小，以达到相同的功率。

Why Source address not included? To reduce the frame size and so to same power.

希望它会有所帮助。如果您对此有更多疑问，请随时

Hope it helps. If you got more questions on this, please feel free

这篇关于为什么802.11确认帧没有源MAC？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！