Home networking with IEEE 802.15.4 – LR-WPAN

Source :
Home networking with IEEE 802.15.4 : A developing Standard for low-rate wireless personal are networks.
Ed callaway et all
IEEE Communications Magazine

This article presents the IEEE 802.15.4 draft stndard and its home networking applications. The main features of the standard are network flexibility, low cost, and low power consumption.

The Data Link Layer :
The MAC sublayer provides two services to higher layers that can be accessed through two service access points (SAPs). The MAC data service is accessed through the MAC common part sublayer (MCPS-SAP), and the MAC management services are accessed through the MAC layer management entity (MLME-SAP). These two services provide an interface between the SSCS or another LLC and the PHY layer.

The General MAC Frame Format :
The MAC frame is called te MAC protocol data unit (MPDU) and is composed of the MAC header (MHR), MAC service data unit (MSDU), and MAC footer (MFR). The first field of the MAC header is the frame control field. It indicates the type of MAC frame being transmitted, specifies the format of the address field, and controls the acknowledgment. In short, the frame control field specifies how the rest of the frame looks and what it contains.
The size of the address field may vary between 0 and 20 bytes.
The payload field is variable in length, however , the complete MAC frame may not exceed 127 bytes in length. the data contained in payload dependent on the frame type. The IEEE 802.15.4 has four frame types. These are the beacon frame, data frame, acknowledgment frame and MAC command frame. data and beacon frames contain information sent by higher layer, the acknowledgment and MAC command frames originate in MAC.

MAC features :

Depending on network configuration, an LR-WPAN may use one of two channel access mechanisms. In a beacon-enabled network with superframes, a slotted carrier sense multiple access with collision avoidance (CSMA-CA) or In network without beacon, unslotted.
While a device wishes to transmit in a non-beacon-enabled network, it first checks if another device is currently transmitting on the same channel. If so, it may backoff for random period, or indicate a transmission failure if unsuccessful after some retries.
In a beacon-enabled network, any device wishing to transmit during the contention access period waits for the beginning of the next time slot and then determining if another device transmit data in the same slot. If another device is transmitting data in the slot, the device backs off for a random number of slot or indicates a transmission failure after some retries.

The IEEE 802.15.4 draft standard provides for three levels of security : no security of any type, access control list (noncryptographic security), and symetric key security, employing AES-128.

this article is useful for understanding the beginning concept of network layer, data link layer, general MAC frame format, Superframe structure, MAC features and the physical layer for low rate wireless personal area networks. I think the physical layer is the most difficult.

Reference :
Home networking with IEEE 802.15.4 : A developing Standard for low-rate wireless personal are networks.
Ed callaway et all
IEEE Communications Magazine

Note : This resume is created for self-learning only. Author and Publisher hold copyrights

may Allah SWT always love both of you wherever you are

February 09 2008
,
Taipei City
High Speed Network Lab

Udin Harun

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