Distribution of messages within a DS

4.5.2 Distribution of messages within a DS
4.5.2.1 Distribution
This is the primary service used by IEEE 802.11 STAs. It is conceptually invoked by every data message to
or from an IEEE 802.11 STA operating in an ESS (when the frame is sent via the DS). Distribution is via
the DSS.
Refer to the ESS network in Figure 4-11 and consider a data message being sent from STA 1 to STA 4. The
message is sent from STA 1 and received by STA 2 (the “input” AP). The AP gives the message to the
distribution service of the DS. It is the job of the distribution service to deliver the message within the DS in
such a way that it arrives at the appropriate DS destination for the intended recipient. In this example, the
message is distributed to STA 3 (the “output” AP) and STA 3 accesses the WM to send the message to
STA 4 (the intended destination).
How the message is distributed within the DS is not specified by IEEE Std 802.11. All IEEE Std 802.11 is
required to do is to provide the DS with enough information for the DS to be able to determine the “output”
point that corresponds to the intended recipient. The necessary information is provided to the DS by the
three association related services (association, reassociation, and disassociation).
The previous example was a case in which the AP that invoked the distribution service was different from
the AP that received the distributed message. If the message had been intended for a STA that was a member
of the same BSS as the sending STA, then the “input” and “output” APs for the message would have been
the same.
In either example, the distribution service was logically invoked. Whether the message actually had to
traverse the physical DSM or not is a DS implementation matter and is not specified by this standard.
While IEEE Std 802.11 does not specify DS implementations, it does recognize and support the use of the
WM as one possible DSM. This is specifically supported by the IEEE 802.11 frame formats. (Refer to
Clause 8 for details.) A mesh BSS might form an entire DS or a part of a DS using the WM, as shown in
Figure 4-8. Mesh services are used to form a mesh BSS and distribute messages. Clause 13 defines how
mesh BSSs are formed and how messages are distributed through a mesh BSS.