WIRELESS LANs BLUETOOTH

Topics discussed in this section: 14-2 BLUETOOTH Bluetooth is a wireless LAN technology designed to connect devices of different functions such as telephones, notebooks, computers, cameras, printers, coffee makers, and so on. A Bluetooth LAN is an ad hoc network, which means that the network is formed spontaneously. Topics discussed in this section: Architecture Bluetooth Layers Baseband Layer L2CAP

BLUETOOTH Bluetooth name comes from Danish king Harald Blåtand (Bluetooth), Credited with uniting the Scandinavian people during the 10th century. The idea was that Bluetooth wireless technology would unite personal computing devices.

Bluetooth Bluetooth is a trademark owned by the Bluetooth SIG, Inc., USA. Bluetooth Special Industry Group (SIG) formed in winter of 1998 by Ericsson,IBM, Intel, Nokia, and Toshiba. Goals • low cost • low power • primarily a cable replacement (to connect mobile phones to headsets)

Bluetooth • There are those who believe it can be used as a Wireless Personal Area Network (WPAN), hence it was the basis for IEEE 802.15. Using: • short-range radio technology • ad hoc networking • dynamic discovery of other Bluetooth devices & the services they offer

Figure 14.19 Piconet

PICONET Can have up to 8 stations:- 1 primary only, the rest are called secondaries (max 7 stations). Communication between primary and secondary can be one to one or one to many. All the secondary stations synchronize their clocks and hopping sequence with the primary.

PICONET (cont..) Masters vs. Slaves Each Bluetooth device is a Master or Slave: • master initiates exchange of data and the slave responds to the master • in order to communicate devices must use same sequence of frequency hops, hence slaves synchronize to hop sequence of master

PICONET (cont..) • master assigns an Active Member address (AM_ADDR) to the slaves participating in active communications within the piconet Additional devices may be registered with the master and be invited to become active as necessary -- their state is called “parked” Devices not currently associated with any piconet are in stand-by mode.

Figure 14.20 Scatternet

SCATTERNET Combination of piconet. A secondary in Piconet can be the primary in another piconet. This station can receive messages from the primary in the first piconet and acting as a primary, deliver them to secondaries in the second piconet.

Figure 14.21 Bluetooth layers

BLUETOOTH LAYERS Radio layer equivalent to physical layer of internet model. BT devices- low power ;range =10m Band- 2.4GHz ISM(medical) band,79 channels (1MHzeach). BT uses FHSS to avoid interference. Type of modulation used- GFSK.

Physical Layer • Uses 2.4 GHz unlicensed Industrial, Scientific, and Medical (ISM) band (globally portions of this band are available) • many other systems using the same spectrum – interference to other systems – interference from other systems

Physical Layer (cont..) • 2.400-2.4835 GHz, i.e., 83.5 MHz divided into 79 channels with carrier frequencies f = 2402 +k MHz, k = 0, … , 78; Channel spacing is 1 MHz • Gaussian Frequency Shift Keying (GFSK) modulation with one bit per symbol • • uses fast (1600 hops/s) frequency hopping spread spectrum (FHSS) • 625 microsecond long time slots • one hop per packet, but a packet can be 1 slot, 3 slots, or 5 slots long

BLUETOOTH LAYERS Baseband layer- equivalent to MAC layer in LANs. The access method is TDMA. The primary and secondary communicate with each other using time slots. Single-Secondary Communication (SSC)- Simple operation, primary uses slots 0,2,4… and secondary uses slots 1,3,5… Operate in half duplex mode. Multiple-Secondary communication (MSC)- for more than one secondary in the piconet. All secondaries listen on even-numbered slots, but only one secondary sends in any odd-numbered slot.

Figure 14.22 Single-secondary communication

Figure 14.23 Multiple-secondary communication

PHYSICAL LINKS 2 types :– a) A sychronous connection oriented (SCO). Used when avoiding latency is more important than integrity eg: Real time audio b) An asychronous connectionless link (ACL) . Used when DATA integrity more important than avoiding latency, eg: ATM

Baseband Baseband controls the radio and is responsible for low level timing, error control, and management of link during a single data packet transfer Packet types: • SCO, ACL - carrying payload • ID packet consists of access code, used during re-connection • NULL packet consists of access code and header, used for flow control or to pass ARQ • POLL packet same structure as NULL packet, must be acknowledged • FHS (Frequency Hop Synchronization)

L2CAP-logical Link Control and Adaptation Protocol. Equivalent to LLC sublayer LANs . Used for data exchange on ACL link. Specific duties: Muxtiplexing,segmentation and reassembly,QoS and group management.

Figure 14.25 L2CAP data packet format

Topics discussed in this section: 15-1 CONNECTING DEVICES In this section, we divide connecting devices into five different categories based on the layer in which they operate in a network. Topics discussed in this section: Passive Hubs Active Hubs Bridges Two-Layer Switches Routers Three-Layer Switches Gateways

Figure 15.1 Five categories of connecting devices

A repeater connects segments of a LAN. Note A repeater connects segments of a LAN.

Figure 15.2 A repeater connecting two segments of a LAN

A repeater forwards every frame; it has no filtering capability. Note A repeater forwards every frame; it has no filtering capability.

A repeater is a regenerator, not an amplifier. Note A repeater is a regenerator, not an amplifier.

Figure 15.3 Function of a repeater

Figure 15.4 A hierarchy of hubs

A bridge has a table used in filtering decisions. Note A bridge has a table used in filtering decisions.

Figure 15.5 A bridge connecting two LANs

A bridge does not change the physical (MAC) addresses in a frame. Note A bridge does not change the physical (MAC) addresses in a frame.

Figure 15.6 A learning bridge and the process of learning

Figure 15.7 Loop problem in a learning bridge

Figure 15.8 A system of connected LANs and its graph representation

Figure 15.9 Finding the shortest paths and the spanning tree in a system of bridges

Figure 15.10 Forwarding and blocking ports after using spanning tree algorithm

Figure 15.11 Routers connecting independent LANs and WANs

Topics discussed in this section: 15-2 BACKBONE NETWORKS A backbone network allows several LANs to be connected. In a backbone network, no station is directly connected to the backbone; the stations are part of a LAN, and the backbone connects the LANs. Topics discussed in this section: Bus Backbone Star Backbone Connecting Remote LANs

In a bus backbone, the topology of the backbone is a bus. Note In a bus backbone, the topology of the backbone is a bus.

Figure 15.12 Bus backbone

In a star backbone, the topology of the backbone is a star; Note In a star backbone, the topology of the backbone is a star; the backbone is just one switch.

Figure 15.13 Star backbone

Figure 15.14 Connecting remote LANs with bridges

Note A point-to-point link acts as a LAN in a remote backbone connected by remote bridges.

Topics discussed in this section: 15-3 VIRTUAL LANs We can roughly define a virtual local area network (VLAN) as a local area network configured by software, not by physical wiring. Topics discussed in this section: Membership Configuration Communication between Switches IEEE Standard Advantages

Figure 15.15 A switch connecting three LANs

Figure 15.16 A switch using VLAN software

Figure 15.17 Two switches in a backbone using VLAN software

VLANs create broadcast domains. Note VLANs create broadcast domains.