CSNB314: Advanced Computer Networks Chapter 5 Wireless and Mobile Networks Introduction Wireless and mobile devices have been proliferating for the last 15 years. More such devices will come in the future. Wireless and mobile are actually two different concepts. Wireless: connection between device and network is done through wireless medium. Mobile: device can move around. Both have their own technical issues that need to be solved. Wireless technology is implemented in data link and physical layers. Introduction Introduction Two modes of wireless network: Infrastructure mode: hosts are associated with a base station. Ad hoc mode: hosts communicate with themselves, without the use of a base station. When a wireless device is also mobile, it may need to associate / disassociate with different base stations. This process is called handoff. Performing handoff can cause various technical issues. Different wireless standards are designed for different usage and environment. Introduction Personal Local Area Metropolitan Wide Area Area Network Area Network Network (LAN) Network (WAN) (PAN) (MAN) Bluetooth 802.11a/b/g/n 802.16 GSM Technology Ultra-wideband (a.k.a. Wi-Fi) (a.k.a. WiMAX) GPRS (UWB) WiGig W-CDMA HSPA LTE Low data rates (1 – High data rates (up Medium data rates Low to high data Data 2 Mbps) to 600 Mbps) (up to 37 Mbps) rates (10 Kbps – Transfer 300 Mbps) Very short range (3 Short range (100 Medium range (50 Long range Range meters) meters) km) (Global) Notebook to PC to Computer to LAN or computer to Smartphones and Connectivity peripheral devices computer and the high-speed wire other mobile to systems Internet line Internet devices to WANs and the Internet Introduction Wireless Transmission Media Wireless transmission is done by radiating electromagnetic energy. Frequencies of interest: Microwave frequency: 1Ghz – 40GHz Radio frequency: 30Mhz – 1Ghz Infrared: 3x1011 Hz – 2x1014 Hz Antenna is required to transmit and receive data. Wireless Transmission Media Antenna An electrical conductor used to radiate or collect electromagnetic energy. Electrical energy is converted into electromagnetic energy and vice versa. Different types of antenna is used for transmitting / receiving electromagnetic energy of different frequencies. Parabolic reflective antenna for microwave. A simple conductor for radio. Terrestrial Microwave Use parabolic dish antenna. Transmitting and receiving antenna needs to face each other. Both antennas need to have line of sight. Normally located at substantial heights above ground. To achieve long distance transmission, a series of antennas are used. Terrestrial Microwave - Applications Long haul telecommunications service. An alternative to coaxial cable or optical fiber. Commonly used for voice and television transmission. Short point-to-point links between buildings. Cellular systems. Terrestrial Microwave – Transmission Characteristics The higher the frequency used, the higher the potential data rate. Higher frequency has higher attenuation. Less useful for long distance transmission. Attenuation increases with rainfall. With increased number of users, signals may overlap and cause interference. Satellite Microwave A satellite is a microwave relay station. Used to link two earth stations that are located far apart. Satellite receives transmission on one frequency (uplink), amplifies or repeats it, and transmits it on another frequency (downlink). Satellite can both be used for point-to-point communication or broadcast communication. Satellite Microwave Satellite Microwave Satellite Microwave Communication satellites are normally geosynchronous orbit (GEO) satellites. Satellite remains stationary with respect to its position on Earth. This is achieved by placing the satellite at the height of 35,863 km at the equator. To avoid interference, two satellites using the same frequency cannot be put close together. This limits the number of satellites that can be put in the orbit. Satellite Microwave - Applications Television distribution. Very suitable due to broadcast nature of satellite. Example: ASTRO. Long-distance telephone transmission. Private business network. Satellite provider can lease some channels to business users. Satellite Microwave – Transmission Characteristics Frequency bands used in satellite communication: 4/6 GHz band 12/14 GHz band 20/30 GHz band There is a propagation delay of about ¼ second from the transmission from one earth station to the reception by another. Satellite microwave is a broadcast facility. Radio Wave Omnidirectional. Antennas need not be aligned. Does not require dish-shaped antennas. Suffers less attenuation than microwave. Applications: AM and FM radio. UHF and VHF television. Mobile phones. Walkie-talkie. Wireless networks (WiFi, WiMAX). Infrared Use transmitters / receivers that modulate noncoherent infrared light. Requires line of sight. Does not penetrate walls. Used in electronic devices: TV remote control. Device-to-device communication. For example: computer to mobile phone. Air Interface Techniques Refers to the way the radio spectrum is shared by multiple communications. A particular wireless technology is normally allocated a range of frequency (frequency spectrum). Need to share this frequency spectrum between multiple users at the same time. But need to prevent different communications from overlapping each other. Common techniques: FDM (frequency division multiplexing) TDM (time division multiplexing) CDMA (code division multiple access) FDM The frequency spectrum is divided into smaller frequency bands. Each band will be used by one communication channel. Example: Say that there is a radio spectrum from 20 to 32 KHz and that each channel uses 4 KHz. Channel 1: Use spectrum from 20 to 24 KHz. Channel 2: Use spectrum from 24 to 28 KHz. Channel 3: Use spectrum from 28 to 32 KHz. FDM TDM Time is divided into slots. Each communication channel is assigned one or more slots. Example: Say that a radio spectrum has a capacity of 1 Mbps and that there are 5 communication channels. Channel 1 transmits data during t = 0s until t = 0.2s. Channel 2 transmits data during t = 0.2s until t = 0.4s. Etc… Each channel effectively will have a data rate of 0.2 Mbps (200 Kbps). TDM CDMA All users share the same frequency spectrum at the same time. Each user is given a distinct sequence of bits called the chipping sequence. Data sent by the sender is encoded with the chipping sequence. The receiver can read the data sent by a particular sender by decoding the received signal (this signal contains data from multiple simultaneous senders) with the same chipping sequence used by the sender. CDMA WiFi: 802.11 Wireless LANs Several wireless LAN technologies were developed in the 1990s. Today, the only one being used is IEEE 802.11 wireless LAN (commonly known as WiFi). There are several 802.11 standards. 802.11a, 802.11b, 802.11g, 802.11n. They vary in terms of frequency range and data rate. Most WiFi devices support more than one standards. They all use the same medium access protocol (CSMA/CA) and the same frame structure. They all support both infrastructure and ad hoc modes. WiFi: 802.11 Wireless LANs Standard Frequency Band Data Rate IEEE 802.11b 2.4 GHz Up to 11 Mbps IEEE 802.11a 5 GHz Up to 54 Mbps IEEE 802.11g 2.4 GHz Up to 54 Mbps IEEE 802.11n 2.4 GHz or 5 GHz Up to 600 Mbps IEEE 802.11ac 5GHz Up to 1 Gbps 802.11 Architecture 802.11 Architecture Basic service set (BSS): Fundamental building block of the 802.11 architecture. Contains one or more wireless devices and a central base station known as access point. Access point (AP): Connect wireless devices to an interconnection device (switch or router) that leads to the Internet. AP and router can be integrated into one unit. Each AP and wireless device has a 6-byte MAC address stored in the firmware of its network interface card. 802.11 Architecture Stations can also group themselves together to form an ad hoc network. Connecting several stations using Wi-Fi without using an access point. Will create a small, isolated network connecting the stations together. Useful when we have several mobile devices and need to exchange data in the absence of an access point. Channels and Association Each wireless device need to associate with an AP before it can send / receive data. Each AP must be given an SSID (Service Set Identifier). Wireless devices identify an AP by its SSID. IEEE 802.11b/g operates in the frequency range of 2.4 GHz to 2.485 GHz. This 85 MHz band is divided into 11 partially overlapping channels. Any two channels are non-overlapping if they are separated by 4 or more channels. Bandwidth can be increased by installing more than one AP that use non-overlapping channels. Channels and Association Passive scanning: AP periodically sends beacon frames. These frames include the AP’s SSID and MAC address. Wireless device scans the 11 channels to seek for beacon frames. If any AP is found, it can be selected for association. Active scanning: Wireless device broadcasts a probe frame to all APs within range. APs responds by sending a probe response frame. Wireless device can then choose an AP for association and sends an association request frame. Channels and Association After association is formed, the wireless device joins the subnet to which the AP belongs. IP address is typically obtained using DHCP. Access for association with an AP can be open or require authentication. Authentication can be done in several ways: Based on the MAC address of the device Using username and password based on security protocols such as: WEP WPA / WPA2 802.1x IEEE 802.11 Frame IEEE 802.11 Frame 802.11 frame shares many similarities with an Ethernet frame. Main differences: There are 4 address fields Address 1: MAC address of receiver Address 2: MAC address of sender Address 3: MAC address of router interface connected to the AP Address 4: Used in ad hoc mode when APs forward frames to each other IEEE 802.11 Frame Sequence number In wireless environment, bit corruption and frame lost can occur more easily. Each frame must be acknowledged by the receiver. Sequence number is used to distinguish between new frame and retransmitted frame. Duration 802.11 protocol allows a transmitting device to reserve a channel for a period of time. The reserved duration is included in this field. Frame control fields Contain various subfields that control various aspects of the 802.11 protocol and its security protocol. Mobility in the Same IP Subnet Mobility in the Same IP Subnet As a wireless device moves further from an AP, the signal gets weaker. The wireless device will then starts scanning for a stronger signal. If another AP with stronger signal is found: The device would then disassociate from its current AP and associate with the other AP. This association / disassociation is only at the link layer. Only possible if the two APs are connected to the same subnet (i.e. connected to the same switch). IP address and any ongoing TCP connections are maintained. Mobility in the Same IP Subnet With the change in AP, the switch must also update its forwarding table. Otherwise, any frame directed to the wireless device would still be sent to the first AP. Solution: the second AP sends an Ethernet broadcast frame to the switch with the wireless device’s MAC address just after association. This would cause the switch to update its forwarding table. What happen if the wireless device moves to a BSS that is attached to a different subnet? This is a more difficult problem since the device would now have to change its IP address. Can be handled using mobility protocol such as mobile IP. IEEE 802.15.1 – Bluetooth Bluetooth a cable replacement technology for interconnecting notebooks, peripheral devices and mobile phones. Designed to operate over a short range, at low power and at low cost. Operates in the 2.4 GHz – 2.4835 GHz unlicensed radio band in a TDM (time division multiplexing) manner. Can provide data rate of up to 2.1 Mbps (for Bluetooth 2.0). Bluetooth Classes Class Maximum Permitted Range Power (approximate) (mW/dBm) Class 1 100 mW (20 dBm) ~100 meters Class 2 2.5 mW (4 dBm) ~10 meters Class 3 1 mW (0 dBm) ~1 meter Bluetooth Applications Bluetooth can be used for communications between: A cell phone and a hands-free headset. A PC and its I/O devices (e.g. keyboard, mouse, printer). Two cell phones for transferring files, address book, etc. Devices within an entertainment system. Many, many others… Bluetooth Communication and Connection Bluetooth networks are ad hoc networks. No network infrastructure (e.g. an access point). When Bluetooth-capable devices come within range of one another, an electronic conversation takes place to determine whether they have data to share or whether one needs to control the other. This happens automatically without user intervention. Bluetooth Communication and Connection The information exchanged between devices are: Device name Device class List of services Technical information, for example, device features, manufacturer, Bluetooth specification, clock offset. Bluetooth Piconet If the devices figure out they need to communicate, they will create a personal area network called the piconet. In a piconet, there can be 8 devices connected simultaneously Can also contain 255 parked devices. One of the devices in the piconet is designated as the master. The rest become the slaves. Bluetooth Piconet Bluetooth Piconet The master node controls the piconet. Its clock determines time in the piconet. It can transmit in each odd number slot. A slave can transmit only after the master has communicated with it in the previous slots. Slave can only transmit to the master. Parked devices can be in the piconet, but cannot communicate with any other node. To communicate, the parked devices must first has its status changed from parked to active by the master node. Bluetooth Pairing To have a more secure communication, pairs of Bluetooth devices can perform pairing. Pairing is a trusted relationship where the communication between the two devices can be encrypted using a passkey. The passkey is normally entered by the user. The same passkey must be entered on the two devices to be paired. For a pair of device, the passkey only need to be entered when they are paired for the first time. The pairing information can be stored to be used during future pairing. IEEE 802.16 – WiMAX WiMAX stands for Worldwide Interoperability for Microwave Access. An evolution from the WiFi technology. Designed to deliver last mile broadband access as an alternative to DSL and cable modem technologies. The actual data rate varies depending on the WiMAX standard used and several other factors: Distance to base station. Number of users sharing the same base station. Ground speed (speed of the user). The bandwidth of a channel. WiMAX Standards 802.16d (Fixed WiMAX) Does not support mobility. Data rate: up to 75 Mbps in 20 MHz channel. 802.16e (Mobile WiMAX) The standard currently deployed by most service providers. Data rate: Up to 37 Mbps (downlink) in 10 MHz channel. 802.16m Also known as WiMAX 2.0. Fulfill the IMT-Advanced (a.k.a. 4G) requirements. Data rate: 1Gbps for fixed users and 100 Mbps for mobile users. WiMAX Architecture A WiMAX system consists of two parts: A WiMAX tower The WiMAX base station. Similar to a cell phone tower. Can provide a coverage of about 30 – 50 km for fixed stations and 5 – 15 km for mobile stations. A WiMAX receiver Also called the subscriber stations. Can be a small box, a USB dongle or built into the mobile device. WiMAX Architecture WiMAX Architecture WiMAX can provide two forms of wireless services: The non-line-of-sight service: Lower data rate, but can go around obstacles. Uses frequency between 2 GHz to 11 GHz. The line-of-sight service: Higher data rate but require line-of-sight (there should be no obstacles between the base station and the subscriber station). Uses frequency between 10 GHz to 66 GHz. Cellular Wireless Network Cellular network was primarily developed to provide mobile telephone. Designed to transfer voice. Use circuit switching technology. Over the time, the cellular network has evolved in the following ways: Use of digital data (voice data is digitized). Provide data transfer capability (this allows us to access the Internet). Cellular Wireless Network Architecture A cellular network is divided into a number of cells which are viewed as hexagons. This is the reason why a mobile phone is also called a cell phone. Each cell is allocated a band of frequencies and served by a base station. Adjacent cells are assigned different frequencies to avoid interference. However, cells sufficiently distant from each other can use the same frequency band. Cellular Wireless Network Architecture Cellular Wireless Network Architecture A base station consists of: An antenna. A controller. A number of transceivers for communicating on the channel assigned to the cell. Each base station is connected to a mobile switching center (MSC). This link can either be wired or wireless (normally wired). One MSC may be serving multiple base stations. The MSC is then connected to the public telephone network. Cellular Wireless Network Architecture An MSC performs the following tasks: Assign voice channel to each call. Perform handoffs. Monitors the call for billing information. There are two types of channels available between a mobile unit and the base station. Control channels: used to setup and maintain calls and also establish relationship between the base station and the mobile unit. Traffic channels: used to carry voice or data connection. Cellular Standards and Technologies Cellular technologies are classified into several “generations”: 1G, 2G, 3G, etc. These generations may differ in terms of: Data rate Capacity Signal quality Applications and services that can be offered 1G systems are pretty much extinct. Most cellular networks today use 2G technologies and above. First Generation (1G) Designed to carry only analog voice. The data is analog (voice), similar to the public telephone network. Uses FDMA (Frequency Division Multiple Access) technology for allocating channels to users. Each user is given one channel. The most popular 1G technology is AMPS (Advanced Mobile Phone Service) Used in the early 1980s. Other 1G technologies: NMT, C-Nets, TACS. Second Generation (2G) The second generation systems are developed to provide: Higher quality signals. Higher data rates to support digital services. Higher capacity. The main difference between 1G and 2G is that 2G systems send digital data. Voice is digitized before it is sent. But transmission is done using analog signal (all wireless signal is analog). Allows for services such as SMS. 2G Technologies IS-136 TDMA (Time Division Multiple Access) A combined FDM/TDM system that evolved from 1G FDMA technology. Widely deployed in North America. GSM (Global System for Mobile Communications). Uses combined FDM/TDM. Started off in Europe in the early 1990s. Also used in Asia and North America. IS-95A CDMA (Code Division Multiple Access). Also knows as CDMAOne. As the name suggests, it uses the CDMA technology. Widely deployed in North America and Korea. 2G Technologies Since 2G technologies convert voice to digital data before transmission, they can also be used to carry data (i.e. application data). They can act as a modem. Although it works, this is not an effective method for data transmission. Circuit switching is used – highly inefficient for bursty traffic. Data rate is very slow. GSM – 9.6 kbps CDMA – 14.4 kbps Transition from Second to Third Generation (2.5G) The 2G systems are optimized for voice service and not well adapted for data communication. In the 1990s, standard organizations have started developing 3G cellular technology targeted to carry both voice and data. Since 3G deployment may take many years, companies developed interim standards that enable data transmission over existing 2G infrastructures. 2.5G Technologies GPRS (General Packet Radio Services) Evolved from GSM and uses the underlying GSM network. A number of slots are set aside for data communications. Mobile device can use more than one time slot within a given channel in an on-demand basis. Slots are dynamically allocated to mobile device when there is data to send. Maximum data rate: 115 kbps. Typical data rate: 40 to 60 kbps. 2.5G Technologies EDGE (Enhanced Data Rates for Global Evolution) Increase the capacity of GSM/GPRS network. Achieve higher data rates by replacing GSM’s modulation scheme with a more powerful scheme. Maximum data rate: 385 kbps. Typical data rate: 144 kbps Some books / web sites categorize EDGE as 3G, and some categorize it as 2.75G. 2.5G Technologies CDMAOne (IS-95B) This is basically an enhanced version of CDMAOne (IS-95A) to support 2.5G capabilities. Requires very minor upgrades in CDMAOne (IS- 95A) networks. Maximum data rate: 115 kbps. Average data rate: < 64 kbps. Third Generation (3G) 3G wireless communication technologies are designed to provide fairly high-speed wireless communication to support multimedia, data and video in addition to voice. Referred to as IMT-2000 by ITU-R. Among the required 3G capabilities include: Voice quality comparable to public-switched telephone network. 144 kbps at driving speeds. 384 kbps for outside stationary or walking speeds. 2 Mbps for office use (indoor). 3G Technologies W-CDMA (Wideband CDMA) Also known as UMTS (Universal Mobile Telecommunications Service). Used by GSM networks to upgrade to 3G. Uses a CDMA technique called Direct Sequence Wide CDMA (DS-WCDMA). Maximum data rate: 2 Mbps Typical data rate: 144 to 384 kbps. 3G Technologies CDMA2000 Used by CDMAOne networks to upgrade to 3G. There are several variants of CDMA2000: 1xRTT (Radio Transmission Technology) and 3xRTT. 1xEV-DO (Evolution – Data Only) 1xEV-DV (Evolution – Data Voice). TD-CDMA (Time Division CDMA) Intended to be used by TDMA networks to upgrade to 3G. Use unpaired spectrum. A single channel is used for both uplink and downlink, but each uses different slots. Very suitable for Internet data. Maximum data rate: 3.3 Mbps 3G Technologies What Can You Do With a 3G- enabled Devices? A 3G-enabled devices can act like a PC connected to the Internet. You can: Browse the Web using a Web browser. Read and reply emails. Chat using instant messaging application. Perform file transfer (FTP). Play online games. Watch live TV (or other streaming videos). Make a video call. Pre-4G Refers to intermediate technologies between 3G and 4G. Sometimes marketed as 3GX, 3G+, Turbo 3G. Provides higher data rates compared to 3G technologies. Done by improving the modulation scheme and refining the protocols between mobile phones and base stations. Some of the standards may also provide all-IP network and QoS support. Standards categorized under this category: HSPA (High Speed Packet Access), LTE (3GPP Long Term Evolution ), WiMAX 802.16e. Pre-4G Technology: HSPA An upgrade to W-CDMA. HSDPA (High-speed Downlink Packet Access) Designed to have faster downlink compared to uplink. Maximum downlink data rate: 14.4 Mbps. Maximum uplink data rate: 384 Kbps. HSUPA (High-speed Uplink Packet Access) Designed to have faster uplink compared to downlink. Maximum uplink data rate: 5.76 Mbps HSPA+ (Evolved HSPA) The latest revision of HSPA+ can achieve a data rate of up to 672 Mbps (downlink) and 168 Mbps (uplink). Pre-4G Technology: LTE Provides an all-IP network. Peak data rate of 300 Mbps (downlink) and 75 Mbps (uplink). Provides QoS provisioning that allows for RTT less than 10 milliseconds. Provides seamless handover between older technologies such as GSM and W-CDMA. For many LTE implementations, GSM or W- CDMA is still used for voice transmission. Fourth Generation (4G) – Beyond 3G Referred to as IMT-Advanced by ITU-R. According to ITU-R, among others, a 4G network must include the following features: A data rate of 100 Mbps when client is moving at high speed in relative to the base station. A data rate of 1 Gbps when device and base station are in relatively static position. Smooth handoff across heterogeneous network. Seamless roaming / connectivity across multiple networks. High QoS support for next generation multimedia (e.g. real time audio, HDTV video content, mobile TV, etc). An all IP, packet-switched network. Fourth Generation (4G) – Beyond 3G Standards that fully comply with the ITU-R specified 4G definition are yet to be released. However, the following pre-4G standards are commonly advertised as 4G: LTE (3GPP Long Term Evolution) IEEE 802.16e (Mobile WiMAX) The following standards are currently being developed to fully with comply with the 4G definition: LTE Advanced (Long Term Evolution Advanced) IEEE 802.16m Ad-hoc Networks In addition to infrastructure-based network technologies, ad-hoc network technology is gaining more interest these days. There are many situations where the use of infrastructure-based network is not possible. After natural disaster. During war. When network infrastructure is controlled by an opposing group. Ad-hoc networks will make communication possible in these situations. Ad-hoc Networks In an ad-hoc network, a host will also take the role of a routing node. Hosts need to have routing capability. Data is transmitted by being forwarded from one host to another. A host may join or leave the network at any time. This makes routing slightly more difficult. This can also cause a number of security issues. Examples of routing protocols designed for ad-hoc networks: Ad-hoc On-demand Distance Vector (AODV) Optimized Link-state Routing Protocol (OLSR) Ad-hoc Networks There are several different types of ad-hoc networks. Examples: Mobile ad-hoc network (MANET) Vehicular ad-hoc network (VANET) Many aspects of ad-hoc networks are being widely studied by researchers. However, a number of ad-hoc networks have already been deployed and seen real use. Search and rescue mission after natural disaster. Military operations.
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