Lecture 10: Wireless Network PDF

# Lecture 10: Wireless Network ## Objectives * Understand the electromagnetic spectrum. * Understand radio frequency ranges. * Differentiate between 2.4 GHz and 5 GHz bands. * Recognize the elements of a wireless network. * Understand wireless modulation. * Differentiate between active and passiv...

# Lecture 10: Wireless Network ## Objectives * Understand the electromagnetic spectrum. * Understand radio frequency ranges. * Differentiate between 2.4 GHz and 5 GHz bands. * Recognize the elements of a wireless network. * Understand wireless modulation. * Differentiate between active and passive scanning. * Define Wi-Fi: 802.11 wireless LANs * Understand wireless frame addressing. * Understand personal area networks. * Understand cellular network components and technology. ## Overview of Wireless Network ### What is a wireless network? * A wireless network refers to a computer network that makes use of radio frequency (RF) connections between nodes in the network. * The number of wireless (mobile) phone subscribers now exceeds the number of wired phone subscribers (5-to-1). * The number of wireless internet-connected devices equals the number of wireline internet-connected devices. * Two important (but different) challenges: * **Wireless:** communication over a wireless link. * **Mobility:** handling the mobile user who changes the point of attachment to a network. ### Electromagnetic Waves A diagram depicting the electromagnetic spectrum, its wavelengths and frequency, and its corresponding usage for example: * Radio * Television * Microwave * Infrared * Visible Light * Ultraviolet * X-rays * Gamma rays ### Why do we use RF waves for communication? * **The Ionosphere:** * It is an electrified region within the upper atmosphere that contains large concentrations of ions (charged particles) and free electrons. * It prevents UV, X-rays, and gamma rays from passing to the earth. * **RF Waves:** * RF waves are not harmful to humans. * Since the ionosphere reflects RF waves (E and F layers), RF waves can bounce between Earth's surface and the ionosphere many times for many 1,000s of kilometers. This is known as **Skywaves**. * **Microwaves** are used to communicate with satellites or anything outside of Earth's atmosphere. This is known as **Space Waves**. * **Ground Waves** are low and medium frequency waves that propagate over Earth's surface. They are used for TV/AM/FM broadcast. ### Types of RF Waves | Frequency Band Name | Frequency Range | Wavelength Range | Application | |-----------------------|-----------------|------------------------------------------|-----------------------------------------------| | Extremely Low Frequency (ELF) | 3-30 Hz | 100,000 to 10,000 km | Underwater communication | | Super Low Frequency (SLF) | 30-300 Hz | 10,000 to 1,000 km | AC power | | Very Low Frequency (VLF) | 3-30 kHz | 100 to 10 km | For navigation alarms | | Low Frequency (LF) | 30-300 kHz | 10 to 1 km | AM radio | | Medium Frequency (MF) | 300-3,000 kHz | 1 km to 100 m | Aviation | | High Frequency (HF) | 3-30 MHz | 100 to 10 m | Shortwave radio | | Very High Frequency (VHF) | 30-300 MHz | 10 to 1 m | FM radio | | Ultra-High Frequency (UHF) | 300-3,000 MHz | 1 m to 10 cm | Television, mobile phones, GPS | | Super High Frequency (SHF) | 3-30 GHz | 10 cm to 1 cm | Satellite; wireless communication | | Extremely High Frequency (EHF) | 30-300 GHz | 1 cm to 1 mm | Remote sensing; astronomy | ### Other Electromagnetic Waves: * **Infrared** comes from the heat and thermal radiation and is not visible to the naked eye. It is used for medium and short-range communication, such as TV remote control, robot control system, cordless microphones, headsets, modems, and other peripheral devices. * **Visible Light** is the light we can see. It is used in **fiber-optic communication**, where coded pulses of light travel through glass fibers from a source to a receiver. * **Ultraviolet** has hazardous effects on the human body. It is not used for communication. Instead, it is used in other industrial fields. * **X-rays and gamma rays** are very harmful to the human body, causing the mutation of genes. They are not used in communication; instead, they are used widely in medical purposes. ## 2.4 GHz Band * The 2.4 GHz frequency band divides into 14 fixed frequency channels, each 20 MHz wide. * Channels 12 and 13 are allowed for worldwide use, but only the USA allows them with a "low power" mode. * Channel 14 is banned in the USA and throughout most of the world, but it is allowed in Japan. * 2.4 GHz Wi-Fi offers a better signal over long distances and through solid objects. **Cons:** * Narrow band * Interference from other devices * More congestion and noise. ## 5 GHz Band * The 5 GHz frequency band dives into 24 non-overlapping channels, each 20 MHz wide, organized as U-NII-1 (Unlicensed National Information Infrastructure), U-NII-2A, U-NII-2C (U-NII-2 extended), U-NII-3, and ISM (Industrial, Scientific, and Medical) * 5 GHz Wi-Fi covers less distance and is not as good as penetrating through solid objects as 2.4 GHz Wi-Fi. ## Elements of a Wireless Network * **Wireless Hosts:** * Laptop, smartphone, IoT * Run applications * May be stationary (non-mobile) or mobile * Wireless does not always mean mobility. * **Base Station:** * Typically connected to a wired network. * Relay - responsible for sending packets between a wired network and wireless host in its "area". * For example - Cell Towers and 802.11 access points. * **Wireless Link:** * Typically used to connect mobile(s) to a base station. Also used as a backbone link. * Multiple access protocol coordinates link access. * Various transmission rates and distances, frequency bands. ### Infrastructure Mode * Base station connects mobiles into a wired network. * Handoff: mobile changes base station, providing connection to a wired network. ### Ad-hoc Mode * No base stations. * Nodes can only transmit to other nodes within link coverage. * Nodes organize themselves into a network: route amongst themselves. ## Wireless Network Taxonomy A table representing the wireless network taxonomy, based on whether the network is infrastructure-based, has single or multiple hops, and includes the example of each configuration. | Network | Single Hops | Multiple Hops | |------------------------|--------------------------------------------------|------------------------------------------------------------| | Infrastructure (e.g., APs) | Host connects to the base station (Wi-Fi, | Host may have to relay through several wireless nodes to connect | | | cellular) which connects to a larger internet. | to a larger internet: mesh network. | | No Infrastructure | No base station, no connection to larger internet | No base station, no connection to larger internet. May have to relay | | | (Bluetooth, ad hoc nets). | to reach another a given wireless Node MANET, VANET. | ## Wireless Links and Network Characteristics ### Important Differences From Wired Link * **Decreased Signal Strength:** radio signals are weaker when they travel through matter. This is called path loss. * **Interference from Other Sources:** wireless network frequencies (e.g., 2.4 GHz) are shared by many devices (such as Wi-Fi, cellular, motors), leading to potential interference. * **Multipath Propagation:** radio signals reflect off objects like the ground, arriving at a destination at slightly different times. This can make communication across a wireless link much more difficult. ### SNR: Signal-to-Noise Ratio * **Larger SNR:** easier to extract a signal from a noisy environment. * **SNR vs BER Tradeoffs:** * **Given Physical Layer:** Increase power results in an increase in SNR and a decrease in BER. * **Given SNR:** choose a physical layer that meets the BER requirements, resulting in the highest throughput. * **SNR can Change With Mobility:** dynamically adapting a physical layer (modulation technique, rate) can improve this. ### An Overview of Wireless Modulation A diagram is provided for visual illustration that depicts the process of modulating a carrier wave with a binary signal and its corresponding output, along with the description of the modulation schemes: * **ASK (Amplitude Shift Keying):** One bit per symbol. * **PSK (Phase Shift Keying):** * **FSK (Frequency Shift Keying):** ### Quadrature Phase Shift Keying (QPSK) * Allows for twice as much data to be carried as PSK. * Two bits per symbol. * Data is encoded as one of four phases. A diagram showcasing the QPSK modulation process. It illustrates the encoding of two-bit data into one of four phases (45°, 135°, 225°, 315°) that are transmitted using a carrier wave with a constant amplitude. ### Quadrature Amplitude Modulation (QAM) * It is an advanced modulation scheme widely used in Wi-Fi communication systems. It combines **phase modulation** and **amplitude modulation**. * A diagram showcasing the QAM-16 modulation process. It illustrates the encoding of four-bit data into one of 16 phases (45° intervals within 360°). The amplitude of the carrier wave varies according to the data being modulated. ### Modulation Rate * When devices move further away from a source in a more challenging RF environment, the modulation rate is a factor in achieving the desired BER. A diagram displaying the modulation schemes used in a wireless network, such as BPSK, QPSK, 16QAM, and 64 QAM, is provided. ### Problems With Multiple Wireless Senders and receivers * **Hidden Terminal Problem:** * Stations B and A hear each other. * Stations B and C each other. * Stations A and C cannot hear each other, which means they are unaware of their interference at station B. * **Signal Attenuation:** * Stations B and A hear each other. * Stations B and C hear each other. * Stations A and C cannot hear each other, resulting in their interference at station B. ## Wi-Fi: 802.11 Wireless LANs ### IEEE 802.11 Standards A table displaying the various 802.11 standards, their associated Wi-Fi versions, year of release, maximum data rate, range, and frequency. | IEEE 802.11 Standard | Wi-Fi Version | Year | Max Data Rate | Range | Frequency | |-----------------------|---------------|------|---------------|-------|------------------------| | 802.11a | Wi-Fi 2 | 1999 | 54 Mbps | 70m | 5 GHz | | 802.11b | Wi-Fi 1 | 1999 | 11 Mbps | 30m | 2.4 GHz | | 802.11g | Wi-Fi 3 | 2003 | 54 Mbps | 30m | 2.4 GHz | | 802.11n | Wi-Fi 4 | 2009 | 600 Mbps | 70m | 2.4, 5 GHz | | 802.11ac | Wi-Fi 5 | 2013 | 1.3 Gbps | 70m | 5 GHz | | 802.11ax | Wi-Fi 6 | 2019 | 10 Gbps | 70m | 2.4, 5 GHz | | 802.11af | | 2014 | 35-560 Mbps | 1 km | Unused TV bands (54-790 MHz) | | 802.11ah | | 2017 | 347 Mbps | 1 km | 900 MHz | All use CSMA/CA for multiple access and have base-station and ad-hoc network versions. ### 802.11: How Devices Associate With an AP * **Wireless Host**: communicates with a base station. * Base station = access point (AP) * **Basic Service Set (BSS)** (aka “cell”) in infrastructure mode contains: * Wireless hosts. * Access point (AP): base station. * Ad hoc mode: hosts only. * **Arriving Host:** must associate with an AP. * **Scans channels:** listens for beacon frames containing the AP's name (SSID) and MAC address. * **Selects AP:** to associate with. * **Authentication:** may then be performed, and DHCP is used to get an IP address in the AP's subnet. ### 802.11: Passive vs Active Scanning A diagram representing the passive and active scanning process for an 802.11 device to connect to a wireless network. * **Passive Scanning:** * Beacon frames sent from APs. * Association Request frame sent: H1 to the selected AP. * Association Response frame sent from the selected AP to H1. * **Active Scanning:** * Probe Request frame broadcast from H1. * Probe Response frames are sent from APs. * Association Request frame sent: H1 to the selected AP. * Association Response frame sent from the selected AP to H1. ### 802.11: Avoiding Collisions A diagram is presented to visually illustrate the RTS-CTS exchange mechanism used for collision avoidance in 802.11 networks. It shows that the sender first transmits a small "request-to-send" (RTS) packet to the access point (AP) to reserve the channel for the upcoming data frames. The AP responds with a "clear-to-send" (CTS) packet, which signals that the channel is available. The sender then transmits the actual data frame and receives an acknowledgement (ACK) once the data is successfully received. This mechanism reduces the likelihood of collisions during data transmissions on the wireless medium. * **Sender reserves the channel** for data frames using small reservation packets. * **Sender first transmits** a small "request-to-send" (RTS) packet to the base station (BS) using CSMA * RTS packets may collide with each other. * **BS broadcast a "clear-to-send"** CTS packet in response to the RTS packet. * **CTS heard by all nodes** * Sender transitions data frame. * Other stations defer transmission. **Collision Avoidance: RTS-CTS Exchange:** A diagram demonstrates the flow of communication between two devices (A and B) and the access point (AP). It illustrates a scenario where both devices attempt to send data frames to the AP, resulting in a reservation collision between their RTS packets. It shows that the AP only responds to one device (A) with a CTS packet, allowing device A to transmit its data frame. Device B is forced to defer its transmission until a later time. ### 802.11 Frame: Addressing A diagram of an 802.11 network frame, depicting its structure, different fields, and their corresponding functionality. A detailed description of each field is provided, focusing on its content, purpose, and how it contributes to the overall communication process within the network. ### 802.11: Mobility Within the Same Subnet * H1 remains in the same IP subnet and its IP address remains the same. * **Switch:** which AP is associated with H1? * **Self-learning switch:** will see the frame from H1 and remember which switch port to reach H1. ### Power Management * **Node-to-AP:** "I am going to sleep until the next beacon frame." * AP knows not to transmit frames to this node. * Node wakes up before the next beacon frame. * **Beacon Frame:** contains a list of mobiles with AP-to-mobile frames waiting to be sent. * Node will stay awake if AP-to-mobile frames need to be sent; otherwise, it will sleep again until the next bacon frame. ## Personal Area Networks: Bluetooth * Based on IEEE 802.15. * Less than 10 meters in diameter. * Replacement for cables (mouse, keyboard, headphones). * Ad hoc: no infrastructure. * 2.4-2.5 GHz ISM radio band, up to 3 Mbps. ### Bluetooth: Master/Slaves * **Slaves:** request permission to send (to master) * **Master:** grants requests. A diagram shows a piconet configuration with a master device, client devices and parked devices. ### Bluetooth: TDM, FDM, Parked Mode, and Bootstrapping * **TDM (Time Division Multiplexing):** 625 microseconds per slot. * **FDM (Frequency Division Multiplexing):** Sender uses 79 frequency channels in a known FHSS (Frequency Hopping Spread Spectrum). * Other devices/equipment not in the piconet only interfere in some slots. * **Parked Mode:** clients can "go to sleep" (park) and later wake up (to preserve battery). * **Bootstrapping:** Nodes self-assemble (plug and play) into a piconet. ## Ethernet vs Wi-Fi A table comparing ethernet and Wi-Fi, covering various aspects, such as: | Attribute | Ethernet | Wi-Fi | |----------------------|--------------------------------------------------------|--------------------------------------------------| | IEEE Standard | 802.3 | 802.11 / 802.15 | | Topology | BUS, Star, Ring, Hybrid (Star-BUS) | Fully meshed, Point to multiple points | | Medium | TP (UTP or STP), Fiber, and Coaxial | Air (RF waves) | | Collision | CSMA/CD | CSMA/CA, ALOHA | | Frame | Ethernet frame | Management (Association, dissociation, | | | | probe, beacon), control (RTS, CTS), data | | | | Source MAC (SA), Transmit MAC (TA), Receiver | | | | MAC (RA), and Destination MAC (DA) | | Layer 2 Devices | Switch | Access Point | | Multiplexing | TDM, FDM | Frame aggregation (MSDU, MPDU), OFDM | ### Think Hard: Does the Access Point (AP) Equivalent to Switch or Router? A diagram of a Linksys access point is presented, asking the reader to think about whether the access point's functionality is closer to that of a switch or a router. ## Cellular Networks ### Components of Cellular Network Architecture * **Cell:** * Covers a geographic region * **Base Station (BS):** * Analogous to an 802.11 AP * Mobile users attach to the network. * **Air-Interface:** * Physical and link layer protocol between the mobile and BS. * **MSC (Mobile Switching Center):** * Connects cells to a wired telephone network. * Manages calls. * Handles mobility. A diagram is displayed that illustrates a cellular network topology, depicting a collection of interconnected hexagonal cells, each with a base station. ### Cellular Networks: The First Hop * **Two Techniques for Sharing Mobile-to-BS Radio Spectrum:** * **Combined FDMA/TDMA:** Divide a spectrum into frequency channels and divide each channel into time slots. * **CDMA (Code Division Multiple Access):** A diagram is shown for visual representation that showcases the time division multiplex (TDM) technique employed in cellular networks. It explains that each channel is divided into discreet time slots, with each mobile phone using a distinct time slot for transmission to the base station. ### 2G (Voice) Network Architecture A diagram depicts the components and connections within a 2G (voice) cellular network architecture. It includes the following elements: * Base Transceiver Station (BTS): * Base Station Controller (BSC): * Mobile Switching Center(MSC): * Public Telephone Network: * Mobile Subscribers: ### Cellular Networks: 4G and 5G #### Elements of 4G LTE Architecture * **Mobile Device:** * Smartphone, tablet, laptop, IoT * 4G LTE radio. * International Mobile Subscriber Identity (IMSI) is stored on the Subscriber Identity Module (SIM) card. * User Equipment (UE) * **Base Station:** * At the “edge” of a carrier’s network. * Manages wireless radio resources, mobile devices in its coverage area. * Coordinates device authentication with other elements. * Similar to a Wi-Fi AP but… * Active role in user mobility. * Coordinations with nearby base stations to optimize radio use. * eNode-B * **Mobility Management Entity (MME):** * Device authentication (device-to-network, network to device) coordinated with mobile home network HSS. * Mobile device management: * Device handover between cells. * Tracking/paging device location. * Path (tunneling) setup from a mobile device to the P-GW * **Home Subscriber Service (HSS):** * Stores info about mobile devices, for which the HSS’s network is their “home network”. * Works with MME in device authentication. * **Serving Gateway (S-GW) and PDN Gateway (P-GW):** * Lie on the data path from mobile to/from the internet. * **P-GW:** gateway to a mobile cellular network. * Looks like any other internet gateway router. * Provides NAT services. * **Other Routers:** extensive use of tunneling. A diagram is shown that depicts the interconnected elements of a 4G LTE network. It illustrates how these components work together to support various cellular services. ### LTE: Data Plane Control Plane Separation * **Control Plane:** * New protocols for mobility management, security, and authentication. * **Data Plane:** * New protocols at the link, physical levels. * Extensive use of tunneling to facilitate mobility. A visual illustration of a 4G LTE architecture, emphasizing the separation of the control plane and data plane. ### 5G Cellular Network Overview * **Goal:** 10x increase in peak bitrate, 10x decrease in latency, 100x increase in traffic capacity compared to 4G. * **5G NR (New Radio):** * Two frequency bands: FR1 (450 MHz-6 GHz) and FR2 (24 GHz-52 GHz): millimeter wave frequencies. * Compatible with 4G. * **MIMO (Multiple-Input Multiple-Output):** multiple directional antennas, with a smaller antenna size for higher frequencies. * Higher frequencies carry more data than lower frequencies. ## Thank You A graphic illustration of a chalkboard is displayed, with the words "The End" written on it.