By the question above I am referring to how a Wi-Fi radio-wave works in terms of the data that it carries. For example, I know that routers use CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance), which allows only one node to "speak" to the router at a time. I am wondering if when the router responds to the device/node connected, do the radio-waves emitted by the Wi-Fi chip-set contain data for that specific node it was talking to earlier until the device acknowledges that it received the data, or can the router send multiple data for multiple devices? I know it's a quick process where even if every signal emitted by the Wi-Fi radio was sequential for every node, you would not be able to tell. I am just unsure if the Wi-Fi signals are simultaneous (meaning, one Wi-Fi radio-wave can carry data for multiple devices), or if the Wi-Fi signal sends data sequentially for every device/node in the network. Thanks in advance!
2 Answers
wifi transport protocols are a science-in-process, as newer protocol structures are coming online every year or two..
As to your specific question, YES, a packet response from a router TO a sender DOES carry target-specific ID info. (ie., a device (or STA, as it is generally referred to) sends a query or packet to the AP (router/access point), and the AP replies with an ACK (acknowledgement) to that STA, which contains the STA ID# and 'address'..
essentially every packet of data 'in flight' carries a small header which advise wheere it is from, where it's going, and who should care..
This becomes a bit more complicated on secure/encrypted network, but in essence the process still contains data as to who it's going to..
as to the 'multiple device' question: yes, routers may(or may not) elect to wait for a reply (thereby holding up other network traffic while waiting for a response).
Much of this depends on what mode of data transport is in process: multi-cast or unicast..
multicast (MC) traffic is a single packet that's 'broadcast' out for anyone who happens to have subscribed to that particular packet address or address group.
unicast (UC) traffic is to/from a single specific STA...
MC traffic does NOT generally expect any sort of acknowledgement from the STA that it has received the AP's packet transport.
UC traffic generally DOES expect to have an ACK reply from the STA upon receipt..
Many times ACKs are a hardware function, such that they are instantaneous, so as to minimize network delays...
a further evolution in the wifi is that many newer APs now contain 2,3, or 4 radios, and each of these radios is handling a section of traffic, in essence allowing multiple 'overlapping' traffic patterns (albeit on different channels/frequencies)..
It is technically speaking practically impossible for two unique data packets to 'fly' on the same exact frequency at the same exact time period, due to collision likelihood.. Therefore most wifi network structures are designed to prevent simultaneous traffic on the same channel or frequency.
Data are sent on the medium in discrete packets called frames. Each frame is addressed to a node, a broadcast address (all nodes), or a multicast address (multiple nodes interested in a multicast group), and, in general, frames are sent one at a time, to one address at a time.
The newest, and up and coming, Wi-Fi standards attempt to do something about this. 802.11ac Wave 2 is the latest Wi-Fi standard to be certified by the IEEE. Its main claim to fame is MU-MIMO (Multi-User Multiple-Input Multiple-Output. Using that, manufacturers can build WAPs that talk to multiple devices at the same time. 802.11ax has yet to be approved, but it will allow nodes to share the same channel at the same time.
