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## Overview * the LE radio operates in the unlicensed 2.4 GHz ISM bannd. * The LE system employs a frequency hopping transceiver. * LE radio operation uses a shaped, binary frequency modulation to minimize transceiver complexity.

Overview

  • The mandatory data rates: 1Mbps.
  • May support 2Mbps.
  • LE employs two multiple access schemes:
    • Frequency division multiple access(FDMA)
    • time division multiple access(TDMA)
  • Forty (40) physical channels, separated by 2 MHz, are used in the FDMA scheme.
    • Three (3) are used as primary advertising channels.
    • 37 are used as secondary advertising channels and as data channels.

Physical Channel

  • The physical channel is sub-divided into time units known as events.
  • There are four types of events:
    • Advertising
    • Extended Advertising
    • Periodic Advertising
    • Connection

Device Role

  • advertisers.transmit advertising packets on the advertising PHY channels
  • scanners.receive advertising packets on the advertising channels without the intention to connect to the advertising device
  • initiators.listen for connectable advertising packets.
## Device Role * Once a connection is established, the initiator becomes the master device. * the advertising device becomes the slave device. * Connection events are used to send data packets between the master and slave devices.
## Connection Events * channel hopping occurs at the start of each connection event. * the master and slave alternate sending data packets using the same data PHY channel within a connection event. * the master initiates the beginning of each connection event and can end each connection event at any time.
## Connection Events ![03](/images/2017/2017061203.png)
## data hopping pattern * in the connection request sent by an initiating device, a field will determine the specific frequency hopping pattern. * The hopping frequency pattern can be adapted to exclude a portion of the frequencies.

Hierachy of links

  • the hiearchy above physical channels are:
    • physical channel
    • physical link
    • logical transport
    • logical link
    • L2CAP channel
## Restrictions of Physical Links * Within a physical channel, a physical link is formed between devices. * There is a physical link between each slave and master. * Slaves are permitted to have physical links to more than one master at a time.
## Restrictions of Physical Links * A device is permitted to be master and slave at the same time. * Physical links are not formed directly between the slaves in a piconet.
## Logical link * The physical link is used as a transport for one or more logical links that support asynchronous traffic. * Traffic on logical links is multiplexed onto the physical link.
## control protocol * carried over logical links * This is the link layer protocol (LL). * Devices that are active in a piconet have a default LE asynchronous connection logical transport. * The default LE ACL is the one that is created whenever a device joins a piconet.
## Link Layer * The Link Layer function uses the LL protocol to control the operation of devices * provide services to manage the lower architectural layers(PHY & LL)
## L2CAP layer * provides a channel-based abstraction to applications and services. * It carries out fragmentation and de-fragmentation of application data. * multiplexing and de-multiplexing of multiple channels over a shared logical link. * L2CAP has a protocol control channel that is carried over the primary ACL logical transport.
## Security Manager protocol (SMP) * reside on top of L2CAP. * uses a fixed L2CAP channel to implement the security functions between devices.
## Attribute protocol (ATT) * provides a method to communicate small amounts of data over a fixed L2CAP channel. * also used by devices to determine the services and capabilities of other devices. * may also be used over BR/EDR.

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