Logical Channels in .NET Use Code 128A in .NET Logical Channels Logical Channels using none toassign none for web,windows application Java Projects Bluetooth de none none fines five logical channels used to transfer different types of information:. Link Control (LC) Channel: This channel carries low-level link control information such as flow control and payload characterization. Link Manager (LM) Channel: Typically it carries control information exchanged between the master"s LMs and the slaves. User Asynchronous (UA) Channel: It carries L2CAP transparent asynchronous user data.

These data may be transmitted in one or more baseband packets. User Isochronous (UI) Channel: It carries L2CAP transparent user isochronous data. These data may be transmitted in one or more baseband packets.

User Synchronous (US) Channel: It carries transparent synchronous user data. This channel is carried over the SCO link..

LC and LM ar none for none e used at the link control level and LM. UA, UI, and US are used to carry user information. The information on the LC channel is carried in the packet header, while the information for all other channels is carried in the packet payload.

The information for the US channel is carried only by the SCO link. The information for the UA and UI channels is normally carried by the ACL link; however, it can also be carried by the data portion of the combined data-voice packet on the SCO link. The information on the LM channel can be carried either by the SCO or the ACL link.

Figure 8.8 shows the flow of each logical channel..

Figure 8.8. Logical Channels Packet Format Figure 8.9 s hows the standard packet format, which includes the Access Code, LC header, and payload. .

Figure 8.9. Standard Packet Format There are th ree types of access codes:. Channel Acce none none ss Code (CAC): CAC is used to identify a piconet. CAC is determined by the device address of the piconet"s master. Therefore, CAC is unique in each piconet.

CAC is normally included in the user data packet.. Device Acces s Code (DAC): DAC is used to identify a device. DAC is uniquely determined by the device address. DAC is used for the paging procedures.

For example, in the paging procedure, the master will send the DAC of the slave with which it wants to establish a connection. Then, the slave responds back with its DAC. The DAC is included in the paging and paging response messages which include only the access code field (no header and payload).

Inquiry Access Code (IAC): IAC is used for the inquiry procedures. IAC is included in the inquiry message which includes only the access code field (no header and payload). The master sends inquiry messages to collect the device addresses of slaves in the transmission range.

. Figure 8.10 none none shows the packet format of the ACL and SCO links. An SCO packet contains the voice payload while an ACL packet contains the data payload.

Some SCO packets can also contain data payload. The LC can use either SCO or ACL packet with or without payload (i.e.

, NULL and POLL packets do not have data payload while frequency hop synchronization (FHS) packets include control information in the data payload). The LM includes its control information in the data payload..

Figure 8.10. SCO and ACL Packet Format 8.4.2 Link Control Before the m aster and slaves can communicate with each other, they have to establish the piconet using link control mechanisms based on link control states. Link control information is included in the link control header of the packet as shown in Figure 8.10.

. Link Control States A station ca n be in one of a number of link control states (see Figure 8.11). There are two major states: Standby and Connection.

In addition, there are substates with their associated procedures: page, page scan, inquiry, and inquiry scan. These procedures are used to establish a piconet or add new slaves to a piconet. The substates are transient states between the Standby and Connection states.

. Figure 8.11. Link Control State Diagram Standby State The station none for none default state is Standby state, which is a low-power consumption mode. The Standby stations are not associated with any piconets. Occasionally, the Link Controller may leave this state to scan for page or inquiry messages, or to page or inquiry itself.

If the station received such a message (i.e., page message, inquiry message), it will enter the Connection state and become a slave.

If the station itself transmits a successful page message or inquiry message, then it will enter the Connection state and become the master. Inquiry procedures (see Figure 8.12) are the interaction processes between the station in the inquiry substate (called inquiry station) and the station in the inquiry scan substate (inquiryscan station).

Inquiry is used where the destination"s device address is unknown to the source. The inquiry stations are the stations that want to discover which new stations are within their transmission range. The inquiry-scan stations are the stations that want to be discovered by other stations.

The inquiry station transmits the inquiry message (containing IAC) with a frequency that follows the inquiry frequency hopping sequence. The inquiry-scan station scans the inquiry message at a single hop frequency. The inquiry-scan stations can receive the inquiry message whenever the inquiry station transmits at the same frequency.

After receiving the inquiry message successfully, the inquiry-scan station will send to the inquiry station the response message that contains the device address and the clock. In summary, during this process, the inquiry station collects the device addresses and clocks of all stations that respond to the inquiry message. Based on this information the inquiry station can issue a page message to establish connection to known stations.

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