Chapter 15 Wireless LANs 15.# 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 15.# 1

Chapter6: Outline 15.1 INTRODUCTION 15.2 IEEE 802.11 PROJECT 15.3 BLUETOOTH 15.# 15.#

Wireless communication is one of the fastest-growing technologies. 15-1 INTRODUCTION Wireless communication is one of the fastest-growing technologies. The demand for connecting devices without the use of cables is increasing everywhere. 15.3 15.# 15.#

Figure 15.1: Isolated LANs: wired versus wireless 15.4 15.# 15.#

Figure 15.2: Connection of a wired LAN and a wireless LAN to other networks 15.5 15.# 15.#

15.15.3 Access Control An important issue concerning a wireless LAN is access control— Answering the question of how the wireless host can get access to the shared medium. The shared medium is free space for a wireless LAN. 15.6 15.# 15.#

15.15.3 Access Control The CSMA/CD algorithm does not work in wireless LANs for many reasons including these: Wireless signal amplitude degrades proportional to the inverse square of the distance. This makes relative amplitudes somewhat meaningless with wireless communication. The hidden station problem prevents collision detection. 15.7 15.# 15.#

Figure 15.3: Hidden station problem 15.8 15.# 15.#

15-2 IEEE 802.11 PROJECT IEEE has defined the specifications for a wireless LAN, called IEEE 802.11, which covers the physical and data-link layers. It is sometimes called wireless Ethernet. 15.9 15.# 15.#

15.2.1 Architecture The standard defines two kinds of services: BSS, the basic service set, and ESS, the extended service set (ESS). 15.10 15.# 15.#

Figure 15.4: Basic service sets (BSSs) 15.11 15.# 15.#

Figure 15.6: Extended service set (ESS) 15.12 15.# 15.#

15.2.2 MAC Sublayer Like wired Ethernet, IEEE 802.11 defines two sublayers within the data-link layer: LLC (logical link control) handles framing, error control, flow control. MAC (media access control) physical addressing 15.13 15.# 15.#

15.2.2 MAC Sublayer IEEE 802.11 defines two sublayers withing the MAC sublayer: DCF the distributed coordination function, and PCF and point coordination function. 15.14 15.# 15.#

15.2.2 MAC Sublayer DCF the distributed coordination function, and Uses CSMA/CA as the access method Implements a persistence strategy with exp-backoff Implements a DIFS after the media is idle. 15.15 15.# 15.#

15.2.2 MAC Sublayer DCF the distributed coordination function, and PCF and point coordination function. 15.16 15.# 15.#

Figure 15.6: MAC layers in IEEE 802.11 standard 15.17 15.# 15.#

DIFS & SIFS DIFS <= 50 microseconds SIFS <= 10 microseconds 15.#

Figure 15.7: Distributed Coordination Funcion: DCF 15.19 15.# 15.#

PCF Point Coordination Function, optional layer to allow for transmissions needing higher priority (quality of service) 15.#

Figure 15.8: Example of repetition interval 15.21 15.# 15.#

Figure 15.9: The frame format has 9 fields 15.22 15.# 15.#

Frame Format FC = Frame control D = duration SC = sequence control used for “fragmentation” Frame body up to 2312 bytes. FCS = CRC error detection 15.#

Table 15.1: Subfields in FC field 15.24 15.# 24

Figure 15.10: Control frames 15.25 15.# 15.#

Table 15.2: Values of subfields in control frames 15.26 15.# 26

15.2.3 Addressing Mechanism The IEEE 802.11 addressing mechanism specifies four cases, defined by the value of the two flags in the FC field. Each flag can be either 0 or 1, resulting in four different situations. 15.27 15.# 15.#

Table 15.3: Addresses 15.28 15.# 28

Figure 15.11: Addressing mechanisms 15.29 15.# 15.#

Figure 15.12: Exposed station problem 15.30 15.# 15.#

802.11-Physical Layer The unlicensed frequency bands in these three ranges 902–928 MHz, 2.400–4.835 GHz, and 5.725–5.850 GHz. Are known as the ISM bands, Industrial, Scientific and Medical. 15.31 15.# 15.#

Table 15.4: Specifications (DSSS = Direct Sequence...) 15.32 15.# 32

OFDM Orthogonal Frequency Division Multiplexing OFDM uses QAM for modulation. 15.#

15-3 BLUETOOTH Bluetooth is yet another wireless LAN technology requiring short distances between stations. 15.34 15.# 15.#

A Bluetooth LAN is an ad hoc network. The devices, (aka gadgets), find each other and make a network called a piconet. 15.35 15.# 15.#

15.3.1 Architecture Bluetooth defines two types of networks: piconet and scatternet. 15.36 15.# 15.#

Bluetooth Piconet Up to 8* stations One station is designated the primary The other stations are secondary 15.#

Bluetooth Piconet The secondary stations synchronize their clocks with the primary station. The secondary stations receive their hopping sequence from the primary station. 15.#

Bluetooth Piconet Communication is one-to-one or One-to-many. 15.#

Bluetooth Piconet While limited to seven “active” secondary stations. It is possible to put a station in a “parked state” to allow another station on the piconet. 15.#

Figure 6.17: Piconet 15.41 15.# 15.#

Figure 15.18: Scatternet 15.42 15.# 15.#

Bluetooth V1 1 Mbps bandwidth 2.4-2.483GHz (overlaps with 802.11b & g) FHSS – 1600 hops per second 79 frequency channels of 1MHz each FSK modulation 15.#

Bluetooth V2 3 Mbps bandwidth 15.#

Bluetooth V3 24 Mbps bandwidth Bluetooth establishes the link and uses 802.11 to achieve the 24Mbps data rate. 15.#

Bluetooth Range Power Class 1 20db ~100 m Power Class 2 4 db ~10 m Power Class 3 ~1 m 15.#

15.3.2 Bluetooth Layers Bluetooth uses several layers that do not exactly match those of the Internet model defined in the text book. Figure 15.19 shows these layers. 15.47 15.# 15.#

Figure 15.19: Bluetooth layers 15.48 15.# 15.#

Bluetooth Access Method Polling-select The primary poles the secondary stations on even clock cycles. If a secondary is polled, it transmits on the next odd clock cycle. 15.#

Figure 6. 21: Single-secondary communication (diagram error Figure 6.21: Single-secondary communication (diagram error!) microseconds, not milliseconds 15.50 15.# 15.#

Figure 6.22: Multiple-secondary communication 15.51 15.# 15.#

Figure 6.23: Frame format types 15.52 15.# 15.#

Bluetooth V1 Throughput 1-slot frames, 192-Kbps 3-slot frames, 596-Kbps 5-slot frames, 730.484 Kbps 15.#