In sections 7.3.2.104-107, 7.4.18.3-7, 9.9a.3 of the known IEEE 802.11s Draft Standard for WLAN Mesh Networking, version D5.0, a deterministic access mechanism for wireless mesh networks called MCCA (Mesh Coordinated Channel Access) is described.
The time between subsequent DTIM Beacons (Delivery Traffic Indication Message) is divided into a fixed number of MCCA time slots. These time slots can be reserved between neighboring mesh stations. An MCCA reservation, hereinafter also referred to as channel reservation, contains periodic definition of so-called MCCAOPs (MCCA opportunities). An MCCAOP is a continuous set of MCCA time slots that can be used for transmission. The initiator of such a reservation is called the MCCAOP owner, and has the right to transmit during the MCCAOP. The receiver is called the MCCAOP responder.
Due to a distributed nature of a wireless mesh network and due to its shared transmission medium it is necessary that each mesh station distributes its MCCA reservations at least in its 2-hop neighborhood. This is done with MCCAOP advertisements, which contain the MCCA reservations of the sending mesh station and the MCCA reservations of its neighboring mesh stations.
The MCCAOP advertisement which is defined as an information element in section 7.3.2.106 of said draft standard as an MCCAOP advertisements element.
Such an MCCAOP advertisements element is included in different frame types such as an MCCAOP advertisement frame, a beacon frame or a probe response frame. The former MCCAOP advertisement frame exclusively includes one single MCCAOP advertisements element whereas the latter beacon frame and the probe response frame may contain one single MCCAOP advertisements element in addition to an extensive amount of payload additionally included in the beacon frame or in the probe response frame.
According to the draft standard the size of an information element is restricted to a length of 255 octets. Due to the definition of an MCCAOP advertisements element as a general information element this restriction is a major drawback leading to a maximum of 62 MCCA reservations to be advertised by an MCCAOP advertisements element.
Although this number of reservations might be sufficient in the majority of situations, it is easily imaginable that there are situations which could require an advertisement exceeding this limit of 62 MCCA reservations.