The Vision: Ubiquitous Wireless Internet Access Overview of Wireless Networking Systems anywhere office, car, train, in the forest, or in a swamp anytime day or night anyone between two mobile users anywhere in the world any device pager, cell phone, pocket computer, wireless watch, sensor Infrastructured Networks Mobile wireless WANs Fixed wireless WANs Broadband Wireless Networks WLANs: the 802.11 family Infrastructureless Mobile Ad Hoc Networks (MANETs) Sensor Ad Hoc Networks (SANETs) any service Multimedia (voice, video, data) Hybrid Mesh Networks Page 1 Page 2 Types of Wireless Networks (1) 1. Cellular Networks (Mobile Wireless WANs) Infrastructured fixed networks Centralized base station controller Optimized for voice communications Large coverage Low data rates MSC PSTN MSC MSC Other MSC clusters A wireless channel: each mobile device assigned a distinct channel Generations in Mobile Wireless Service First Generation (1G) Mobile voice services Second Generation (2G) Primarily voice, some low-speed data (circuit switched) Generation 2½ (2.5G) Higher data rates than 2G A bridge (for GSM) to 3G A base station A mobile/wireless device Third Generation (3G) Seamless integration of voice and data Higher data rates, full support for packet switched data Page 3 Page 4 Evolution of Mobile Wireless (1) Evolution of Mobile Wireless (2) Advance Mobile Phone Service (AMPS) FDMA 824-849 MHz (UL), 869-894 MHz (DL) U.S. (1983), So. America, Australia, China Global System for Mobile communications (GSM) TDMA Different frequency bands for cellular and PCS Developed in 1990, >1B subscriber by end of 2003 European Total Access Communication System (E-TACS) FDMA 872-905 MHz (UL), 917-950 MHz (DL) Deployed throughout Europe IS-95 CDMA 800/1900 MHz Cellular/PCS U.S., Europe, Asia Page 5 Page 6 1
Evolution of Mobile Wireless (3) Evolution of Mobile Wireless (4) General Packet Radio Services (GPRS) Introduces packet switched data services for GSM Transmission rate up to 170 kbps Some support for QoS Universal Mobile Telecommunication Systems (UMTS) Wideband DS-CDMA Bandwidth-on-demand, up to 2 Mbps Supports handoff from GSM/GPRS Enhanced Data rates for GSM Evolution (EDGE) Circuit-switched voice (at up to 43.5 kbps/slot) Packet-switched data (at up to 59.2 kbps/slot) Can achieve on the order of 475 kbps on the downlink, by combining multiple slots IS2000 CDMA2000: Multicarrier DS-CDMA Bandwidth on demand (different flavors, up to a few Mbps) Supports handoff from/to IS-95 Page 7 Page 8 Types of Wireless Networks (1) Types of Wireless Networks (2) 1. Broadband Wireless Metropolitan Area Networks (WMANs) Mobile Broadband Wireless (IEEE 802.20) Specifies physical and medium access control layers Licensed bands below 3.5 GHz Optimized for IP-data transport Per user data rate > 1Mbps Supports vehicular speeds up to 250 km/h WiMAX (IEEE 802.16) Fixed Wireless Broadband Access (IEEE 802.16a) Specifies physical and medium access control layers Defines how wireless traffic will move between subscribers and core networks Addresses wireless last connectivity (e.g., alternative to traditional twisted pair) Licensed and unlicensed bands IEEE 802.16e (supports Mobile access) 2. WLANs Infrastructured fixed networks Centralized access point controller Small coverage High data rates Page 9 Page 10 WLANs: IEEE 802.11 Family Infrastructure Mode (1) 802.11 working group Specify an open-air interface between a wireless client and a base station or access point, as well as among wireless clients IEEE 802.11a Up to 54 Mbps in the 5 GHz band Uses orthogonal frequency division multiplexing (OFDM) IEEE 802.11b (Wi-Fi) 11 Mbps (with fallback to 5.5, 2 and 1 Mbps) in the 2.4 GHz band Uses DSSS IEEE 802.11g 20+ Mbps in the 2.4 GHz band Access Point Wired LAN Mobile Stations Basic Service Set (BSS) Access point serves as a local bridge Stations communicate through the access point, which relays frames to/from mobile stations Page 11 Page 12 2
Infrastructure Mode (2) Ad Hoc Mode Wired LAN Server Access Points Mobile Stations Extended Service Set (ESS) A set of infrastructure BSSs Access points communicate among themselves to forward frames between BSSs and to facilitate movement of stations between BSSs Mobile Stations Independent Basic Service Set (IBSS) or Peer to Peer Stations communicate directly with each other When no direct link is feasible between two station, a third station may act as a relay (multi-hop communications) Page 13 Page 14 Distribution Systems The architectural component used to interconnect BSSs is the distribution system (DS) DS enable mobile device support Address-to-destination mapping Seamless integration of several BSSs In practice, an access point implements DS services Bluetooth Characteristics Comparison with IEEE 802.11 Wired LAN Access Points Mobile Stations Page 15 Page 16 Introduction Characteristics Motivation: cable replacement in peripherals and embedded devices Named after Harald Blaatand Bluetooth II, king of Denmark 940-981 A.D. Estimated > 670 M Bluetooth-enabled devices by 2005 Operates in the ISM band (like 802.11b) Frequency hopping spread spectrum Up to 720 kbps data transfer with a range of 10 m Transmission rate decreases if interference from other devices is present Master/slave architecture A collection of master + slaves is called a piconet Up to 7 slave devices may communicate with a master Piconets can be linked together to form a scatternet Page 17 Page 18 3
Comparison with 802.11 Types of Wireless Networks (5) Characteristic Spectrum Max Data Rate Connections Frequency Selection Distance Bluetooth 2.4 GHz 725 kbps Point-to- Multipoint FHSS 10 meters IEEE 802.11b 2.4 GHz 11 Mbps Point-to-Point DSSS ~250 meters IEEE 802.11a 5 GHz 54 Mbps Point-to-Point OFDM ~150 meters 5. Mobile Ad Hoc Networks (MANETs) No wired backbone All nodes are capable of movement All nodes serve as routers (multi-hop routing) Dynamic topology Ease of deployment A link in the wireless fabric: all nodes communicate over a single channel. A mobile node: A router with hosts and wireless devices Page 19 Page 20 Types of Wireless Networks (6) Wireless Mesh Networks WLANs + MANET principles IEEE 802.11s Access point/router Mobile Station BSS BSS Gateway BSS Attributes of Wireless & Mobile Communication Systems Wireless limited bandwidth: frequencies have to be coordinated broadcast meduim: requires efficient access mechanisms variable link quality (noise, disconnection, interference) high latency, higher jitter (cellular) Security Mobility User and terminal is a dynamic system variable Speed of mobile impact wireless bandwidth Security Portability Limited battery capacity Limited computing Limited storage Small dimensions (user interface) Gateway BSS Page 21 Page 22 Our Focus Agents Involved in Communication The main focus of this course: IP stack over wireless WLAN Mesh and mobile ad hoc networks Basic differences between cellular and WLAN WLAN Designed for high bit-rate data transmission Internet Protocols oriented Low-scale mobility, small area coverage Use unlicensed ISM frequency bands Cellular Originally (2 nd generation) design for voice communication Limited bit-rate data transmission Large scale mobility and coverage (high speed, large cells) Operated over licensed frequency bands Applications Exchange data between computers (e.g., electronic mail) Computers Connected to networks Networks Transfers data from one computer to another Page 23 Page 24 4
The Need for a Protocol Architecture Protocols A set of layers and protocols is called a network architecture. Why the need for layers and protocols? There must be a path between source and destination. The source must activate a path or inform the communication network of the identity of the destination. Source must understand the capabilities of the destination. Data translations may be required Define the format and order of messages exchanged between two entities in the network Define the actions to be taken upon transmission or arrival of messages or some other event Examples: IP, HTTP, DHCP, TCP etc. A high degree of cooperation between source and destination is required. Better to implement logic into subtasks, implemented separately (in distinct layers). Hello! Hello! Changes in one layer should not require changes in other layers. Peer layers communicate using a protocol by means of formatted blocks. How are you? Fine, thanks! Page 25 Page 26 Layering OSI Model Start with services provided by the hardware, then add a sequence of layers, each providing services to the layer just above it Why? Decomposes the very complex problem of providing networked communications into more manageable pieces More modular design (easier to add a new service or to modify the functionality of a layer) Example of protocol layering HTTP (for web browsing) uses services from TCP (for instance, reliable delivery of packets), which uses services provided by IP (for instance, globally unique addressing) Reliable delivery, error recovery, congestion control Addressing, medium access, error control End System Application Presentation Session Transport Network Data link Physical Application-specific exchange of messages Routing, segmentation and reassembly, network-wide addressing Voltage swing, bit duration, connector type, etc. Page 27 Page 28 Encapsulation Communications Networks M Layer 5 Protocol M H4 M H3 H4 M1 H3 M2 Layer 4 Protocol Layer 3 Protocol H4 M H3 H4 M1 H3 M2 Layer Application Application Protocol (http, ftp, telnet, etc.) Data unit Exchanged Application APDU H2 H3 H4 M1 T2 Layer 2 Protocol H2 H3 H4 M1 T2 H2 H3 M2 T2 H2 H3 M2 T2 Layer 1 Protocol Page 29 Page 30 5
IP Protocol Suite IP Protocol Stack Why so successful? Many protocols run over IP. IP runs over everything. Architectural principles Minimalism, autonomy Best effort service Stateless routers Decentralized control Application Transport Internet Physical + Data Link e.g. TELNET, FTP, SNMP, DNS, HTTP, etc. TCP, UDP IP e.g. Ethernet, 802.11, SONET, ATM, etc. Page 31 Page 32 OSI and the IP suite Essential Characteristics of IP Source: Introducing TCP/IP, by FindTutorials.com Connectionless Each IP datagram is treated independently and may follow a different path Best effort No guarantees of timely delivery, ordering, or even delivery Globally unique 32-bit addresses Usually expressed in dot-decimal notation: 128.17.75.0 Each interface has its own IP address Later, we will see that there are ways to use non-unique addresses Typical IP datagram contains payload + a 20-byte header with control information (addressing, redundant bits for error detection, etc.) Page 33 Page 34 Issues in WLAN, Mobile Ad Hoc, & Mesh Networks Physical Layer How to resist to the wireless link limitations? multiple error control coding schemes Medium Access Layer Transmission scheduling and coordination of nodes Dealing with wireless limitations (medium sensing and collisions detections) Network Layer How to maintain the routing tables in the context of highly mobile nodes (multi-hop routing)? Transport Layer TCP is optimized for congestion avoidance how to extend to error control Application Layer How to satisfy the application requirements (delay, throughput)? How can the application adapt to the channel? Resource conservation Power-consumption, bandwidth optimization Self-configuration for multi-hop ad hoc networks The Data Link Layer Page 35 Page 36 6
Data Link Layer Design Issues Functions of the Data Link Layer Services Provided to the Network Layer Framing Error Control Flow Control Provide service interface to the network layer Dealing with transmission errors Regulating data flow Slow receivers not swamped by fast senders Page 37 Page 38 Functions of the Data Link Layer (2) Services Provided to Network Layer Relationship between packets and frames. (a) Virtual communication. (b) Actual communication. Page 39 Page 40 Services Provided to Network Layer (2) Data Link Layer Design Issues Placement of the data link protocol. Framing Character counts Byte/Bit stuffing Error detection Error correction Page 41 Page 42 7
Types of Data Link Protocols Stop and wait Sliding window Go-back-N Selective repeat Medium Access Control Page 43 Page 44 Wireless Medium Access Channel access methods for cellular networks Why Medium Access Control (MAC)? How to allocate a single broadcast channel among multiple competing users? Is MAC required in wired networks? Issues in wireless networks Bandwidth availability Reliability Collision detection (for random access networks) Two classes of MAC Protocols? Mobile cellular Random (for data networks) Contention-based Collision-free Hybrid Voice-oriented access methods assumes relatively long conversations several MB of data exchanged in both directions uses a separate signaling channel call set-up, reserve resources, termination the network will assign a slot time a portion of frequency a specified code Three basic methods FDMA, TDMA, CDMA What are the tradeoffs? Page 45 Page 46 Access for Voice Oriented Cellular Networks FDMA vs. TDMA FDMA single channel shared among multiple users by assigning each user to an exclusive frequency band within the channel TDMA A number of users share the same frequency band by taking assigned turns in using the channel. GSM, IS-136 CDMA IS-95, IMT-2000 Frequency-division multiplexing (FDMA) Takes advantage of the fact that the useful bandwidth of the medium exceeds the required bandwidth of a given signal Time-division multiplexing (TDMA) Takes advantage of the fact that the achievable bit rate of the medium exceeds the required data rate of a digital signal Page 47 Page 48 8
Forward and Reverse Channels Forward link (downlink: communication between the base station and mobile) Reverse link (uplink: communication between the mobile and base station) TDD forward and reverse channels use same frequency band forward and reverse channels use alternating time slots FDD Forward and reverse channel use different carrier frequencies Figure 1: (a) FDMA/FDD (b) FDMA/TDD (c) TDMA/FDD with multiple carriers (d) TDMA/TDD with multiple carriers Page 49 Page 50 Frequency Division Multiple Access Example: FDMA in AMPS with FDD All users transmit simultaneously Must address the Near-Far Problem have frequencies in each cell as far apart as possible employ power control techniques to ensure all signals from the mobiles within a given cell arrive at the base of the cell with equal power. to maximize the total user capacity to minimize the consumption of transmitted power of portable unit Forward and reverse channels use different carrier frequencies 30kHz channels in 25MHz of spectrum 395 channels for voice traffic use guard bands to reduce adjacent channel interference Page 51 Page 52 Example: FDMA in CT-2 with TDD Forward and reverse channels take turns via alternating time slots 4 MHz 40 carriers each with 100 khz of bandwidth Page 53 Page 54 9
Time Division Multiple Access A number of users share the same frequency band by taking turns using the channel Transmit controller assigns time slots to users Time slot is held by user until user releases it Example TDMA in GSM 8-slot TDMA scheme Forward and reverse channels use separate carrier frequencies (FDD) 13kbps per user 124 frequency carriers (FDMA) 100 khz guard band at each edge Receiver must synchronize to the TDMA signal frame Receiver extracts time slot designated for that user Page 55 Page 56 Code Division Multiple Access Can accommodate various users with different bandwidth requirements Multiple users use the same band at the same time Page 57 Page 58 Code Division Multiple Access CDMA Code Division Multiple Access The user is differentiated by a code. Codes are selected so that when they are used at the same time in the same band a receiver knowing the code of a particular user can detect that user among all the received signals. (a) Binary chip sequences for four stations (b) Bipolar chip sequences (c) Six examples of transmissions (d) Recovery of station C s signal Page 59 Page 60 10
WLANS, MESH, Ad hoc Networks Random channel access methods Random medium access control Multi-hop routing over mesh and ad hoc networks TCP over Wireless Networks Data-oriented access methods designed for burst of data no separate signaling channel each packet carries signaling information destination address source address packet priority MAC Protocols for WLANs, Mesh, Ad Hoc Networks ALOHA-based Carrier SenseIEEE 802.11 ALOHA MAC-SCC Page 61 Page 62 11