Protocol Stack in .NET Attach Code 128 Code Set C in .NET Protocol Stack

How to generate, print barcode using .NET, Java sdk library control with example project source code free download: Protocol Stack generate, create code 128 code set b none for .net projects GTIN-13 The proposed standard i visual .net code 128 barcode s divided into the Link Layer Control (LLC), MAC, and its physical layer (PHY) (see Figure 9.17).

. Figure 9.17. IEEE 802.15.4 Protocol Stack < Day Day Up > < Day Day Up > 9.7 IEEE 802.15.4 Physical Layer The radio can operate a t the following frequencies: the 868 MHz band (e.g., in Europe), the 915 MHz band (e.

g., in the U.S.

), and the 2.4 GHz band (worldwide) (Figure 9.18).

At 868 MHz and 915 MHz, the transmission speed is 20 kbps using DSSS. 868 MHz band allows one channel while in the 915 MHz band there are 10 non-overlapping channels that is, up to 10 networks can coexist in the same area. The 2.

4 GHz band supports 250 kbps using DSSS, allowing 16 non-overlapping channels that is, up to 16 networks can coexist in the same area.. Figure 9.18. IEEE 802.15.4 Frequency Band < Day Day Up > < Day Day Up > 9.8 IEEE 802.15.4 Media Access Control IEEE 802.15.4 focuses o barcode 128a for .

NET n low-cost, low power consumption devices. This focus constrains the MAC protocol design to be rather simple with adequate functionalities to support the low rate applications mentioned earlier. Sophisticated functions (i.

e., QoS mechanisms) reside in the upper layers (above IEEE 802.15.

4 MAC) which are not included in the draft standard. Several techniques are proposed to minimize the amount of overhead in maintaining the communication link. The packet structure is designed to be simple.

IEEE 802.15.4 has three packet structures: beacon packet, data packet, and handshake packet (acknowledgment packet).

Besides the beacon, there is no explicit message or command originated from the MAC layer that provides peer communication between the MAC layers of the two devices. The draft standard also defines several service primitives (i.e.

, primitives between the LLC and MAC sublayers and primitives between the MAC sublayer and the PHY) via the service access point (SAP) as shown in Figure 9.19. For more details on the concept of service primitives, please refer to IEEE 802.

2. The MAC sublayer PAN information base (MAC PIB) is the MAC"s database which maintains the network configuration. The peer communication between the MAC sublayers of the two devices takes place indirectly through the upper layers and the service primitives as shown in Figure 9.

20.. Figure 9.19. MAC Sublayer Reference Model Figure 9.20. Example of Signaling Flow The proposed MAC utiliz es either CSMA/CA or TDMA protocols, or a combination of both. As shown in Figure 9.21, the channel is organized into superframes.

Each superframe starts with a network beacon, sent by the network coordinator. The superframe includes a beacon, a contention period, and guaranteed time slots (GTSs). The superframe duration varies depending on the active applications.

If there are no low-latency applications, the superframe consists of only the beacon and the contention period. On the other hand, if there are lowlatency applications, GTSs are present..

Figure 9.21. IEEE 802.15.4 Frame Structure In the beacon, the netw ork coordinator 1) synchronizes the DEVs, 2) describes the structure of the superframe, and 3) notifies the pending node messages. In the contention period, the DEVs can access the wireless media using the CSMA/CA mechanism. The CSMA/CA mechanism is similar to the one presented for the IEEE 802.

11 standard (see 4). Each time a DEV wishes to transmit packets, it needs to determine if the wireless medium is free. For this process, the MAC sends a clear channel assessment (CCA) request to the physical layer.

If the wireless medium is free, the packet is transmitted. If the wireless medium is busy, the DEV will back off for a random period before trying again. All data transmissions require a handshake or acknowledgment by the receiving DEV.

If an acknowledgment is not received at the sender within a pre-determined time, the sender will retransmit the packet. The DEVs must stop competing for channel access at the end of the contention period. The GTS is reserved for specific DEVs that need guaranteed bandwidth.

The network coordinator may decide not to allocate a GTS to a requesting DEV or to de-allocate an existing GTS at any time. The proposal also defines the following services required for LR-WPAN operation: network discovery by the network coordinator and DEV, network initiation by the network coordinator, network synchronization by the DEV, and network searching by the DEV. Network discovery is the process of finding out which networks exist close to the network administrator in order to be able to choose a unique network identifier and channel.

Network initiation is the process of establishing the network and its operation. Network synchronization is the process of listening to the network beacon to find out the availability of communication opportunities. Network searching is the process of finding the network beacon when network synchronization has been lost.

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