DOCSLIB.ORG

Local Area Networks

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Local Area Networks Local area networks Katia Jaffr`es-Runserand Gentian Jakllari fkjr,jakllarig-at-n7.fr Toulouse INP - ENSEEIHT D´epartement Sciences du Num´erique 1`ereann`ee INP ENSEEIHT T O U L O U S E 1SN - Local area networks 1 Lecture 1: Introduction to local area networks Central question for this class : How to create a network for devices that are relatively close to each other { a local network ? 1SN - Local area networks 2 Local area networks NOT a dedicated wire per communication It doesn't scale: for N devices, we need N(N − 1)=2 wires. 1 1 source: https://cedarandthistle.files.wordpress.com/2013/09/messy_cables.jpg 1SN - Local area networks 3 Local area networks Share the wire ! All devices have to share the same wire. I In this case, the communication is by nature ***in broadcast*** mode Each transmitted bit is received by all other nodes on the channel 1SN - Local area networks 4 Different situations may occur: I No one else is transmitting data for the complete transmission duration. ! The message is received properly by the destination . I Another device transmits a message during the transmission, ! The messages are superimposed (destructively) and can't be understood: there is a collision ! / Shared access networks What happens if a device sends its message whenever needed? 1SN - Local area networks 5 I Another device transmits a message during the transmission ! The messages are superimposed (destructively) and can't be understood: there is a collision ! / Shared access networks What happens if a device sends its message whenever needed? Different situations may occur: I No one else is transmitting data for the complete transmission duration. ! The message is received properly by the destination . , 1SN - Local area networks 6 Shared access networks What happens if a device sends its message whenever needed? Different situations may occur: I No one else is transmitting data for the complete transmission duration. ! The message is received properly by the destination . I Another device transmits a message during the transmission, ! The messages are superimposed (destructively) and can't be understood: there is a collision ! / 1SN - Local area networks 7 Using a Medium Access Control protocol a.k.a. MAC protocol. These are rules enforced so as to: I Avoid collisions or re-transmit data if a collision occurs, I Offer each node a fair access to the channel. Each device on the network gets a fair share of channel bandwidth on average. Bandwidth The amount of data that can be passed along a communication channel in a given period of time. Shared access networks Collisions Have of course to be mitigated. But how? 1SN - Local area networks 8 Bandwidth The amount of data that can be passed along a communication channel in a given period of time. Shared access networks Collisions Have of course to be mitigated. But how? Using a Medium Access Control protocol a.k.a. MAC protocol. These are rules enforced so as to: I Avoid collisions or re-transmit data if a collision occurs, I Offer each node a fair access to the channel. Each device on the network gets a fair share of channel bandwidth on average. 1SN - Local area networks 9 Shared access networks Collisions Have of course to be mitigated. But how? Using a Medium Access Control protocol a.k.a. MAC protocol. These are rules enforced so as to: I Avoid collisions or re-transmit data if a collision occurs, I Offer each node a fair access to the channel. Each device on the network gets a fair share of channel bandwidth on average. Bandwidth The amount of data that can be passed along a communication channel in a given period of time. 1SN - Local area networks 10 MAC protocol and channel access method MAC protocol Decides when each device can transmit its messages on the shared channel (or who speaks next). There are numerous MAC protocols available: I For wired networks: Ethernet, switched Ethernet, HDLC, Token Ring, Token Bus, CAN, AFDX, FDDI, etc... I For wireless networks: WiFi, Bluetooth, ZigBee, WiMax, GSM, LTE, etc... 1SN - Local area networks 11 MAC protocol and channel access method Channel access methods MAC protocols follow different approaches for sharing the channel. Each type is called a channel access method. 1SN - Local area networks 12 Channel access methods Random Access I Stations contend with each other without any centralized coordination I Collisions are the norm I A specific algorithm for resolving contention/reducing collisions once they happen I resolve collisions : detect a collision and do something to fix it I reduce collisions : reduce the odds for a collision to happen 1SN - Local area networks 13 Channel access methods Deterministic Access I There is no contention { stations agree in advance I There are no collisions I Different ways to agreeing, resulting in different MAC protocols : I Centralized : a unique entity decides on resource allocation I Distributed : nodes agree by exchanging messages 1SN - Local area networks 14 Channel access methods Deterministic Access I Different ways to executing the agreement I Circuit-like: TDMA, FDMA, ... I Packet based: Polling, Token passing I Remember from telephony: Either we share time (TDMA), frequencies (FDMA), time-frequency blocks (FTDMA), orthogonal codes (CDMA), or space (SDMA). 1SN - Local area networks 15 This course This course introduces *** the main channel access methods *** and illustrates them with *** state-of-the-art MAC protocols.*** 1SN - Local area networks 16 Outline for the rest of this class Lecture 1: Introduction to local area networks Part 1: Random channel access Lecture 2: Random channel access Lecture 3: Ethernet and switched Ethernet Lecture 4: WiFi - Distributed Coordination Function (DCF) Part 2: Deterministic channel access Lecture 5: WiFi (PCF) Lecture 6: Token Ring 1SN - Local area networks 17 Lecture 2: Random channel access. ALOHA Carrier Sense Multiple Access 1SN - Local area networks 18 ALOHA networks ALOHA: The origin of random access2 I Developed in the late 60's by Norman Abramson et al to allow the 7 campuses of the Univ. of Hawai'i, located on 4 different islands, to share computer resources on the main campus I The first user terminals went into operation in June 1971 I The communication protocol was implemented by a special-purpose piece of equipment { the terminal control unit (TCU) I Compare it to a wifi card... I A user terminal was attached to the TCU 2 N. Abramson, "The AlohaNet - surfing for wireless data [History of Communications]," in IEEE Communications Magazine, vol. 47, no. 12, pp. 21-25, Dec. 2009. 1SN - Local area networks 19 How to try again ? Re-send data after a random duration called the Backoff period I Avoids repeated collisions. I The way this random choice is made influences the overall performance. ALOHA networks ALOHA networks I Key decision: Use the direct form of transmitting user information in a single high-speed packet burst in a shared wireless channel I Driven by the need for a simple design; throughput computed several weeks after the decision I Cost of memory for a packet buffer of 88 bytes was about $300 I Channel access philosophy : let collisions happen, detect when they occur and then try again. I Any station can send data at any time I If, while transmitting, any data is received concurrently, then there is a collision { will need to try again. 1SN - Local area networks 20 ALOHA networks ALOHA networks I Key decision: Use the direct form of transmitting user information in a single high-speed packet burst in a shared wireless channel I Driven by the need for a simple design; throughput computed several weeks after the decision I Cost of memory for a packet buffer of 88 bytes was about $300 I Channel access philosophy : let collisions happen, detect when they occur and then try again. I Any station can send data at any time I If, while transmitting, any data is received concurrently, then there is a collision { will need to try again. How to try again ? Re-send data after a random duration called the Backoff period I Avoids repeated collisions. I The way this random choice is made influences the overall performance. 1SN - Local area networks 21 ALOHA networks Vulnerability period The message transmitted at time t experiences a collision if any other message overlaps partially with its transmission. Sender A Sender B Fail Sender C Success T t−T t t+T time Vulnerability period 2T If all messages have equal length T , then the vulnerability period is of size 2T . 1SN - Local area networks 22 ALOHA networks Throughput achieved by ALOHA It can be derived as follow: I Suppose that the number of transmission attempts per frame duration T follows a Poisson distribution of mean G. G k e−G Thus the probability of having k attempts during T is: k! I The probability of having no collision for the vulnerability period of 2T is given by e−2G I Thus, the throughput is the number G of attempts during T that don't experience any collision : D = G · e−2G 1SN - Local area networks 23 Throughput for ALOHA Maximum throughout is obtained for a load G = 0:5, that is D = 0:5=e ' 0:184. I Very low! Only 18% of frames don't collide at best. 1SN - Local area networks 24 Slotted ALOHA Increase the efficiency of ALOHA Idea: reduce the vulnerability period duration by synchronizing transmissions Sender A Sender B Fail Success Sender C Clock node Slot Vulnerability period T I All nodes are synchronized on a given slot duration of size T I A transmission can only start at slot begin. ! vulnerability period is reduced to T .
Load more

Recommended publications
  • Physical Layer Overview
    ELEC3030 (EL336) Computer Networks S Chen Physical Layer Overview • Physical layer forms the basis of all networks, and we will first revisit some of fundamental limits imposed on communication media by nature Recall a medium or physical channel has finite Spectrum bandwidth and is noisy, and this imposes a limit Channel bandwidth: on information rate over the channel → This H Hz is a fundamental consideration when designing f network speed or data rate 0 H Type of medium determines network technology → compare wireless network with optic network • Transmission media can be guided or unguided, and we will have a brief review of a variety of transmission media • Communication networks can be classified as switched and broadcast networks, and we will discuss a few examples • The term “physical layer protocol” as such is not used, but we will attempt to draw some common design considerations and exams a few “physical layer standards” 13 ELEC3030 (EL336) Computer Networks S Chen Rate Limit • A medium or channel is defined by its bandwidth H (Hz) and noise level which is specified by the signal-to-noise ratio S/N (dB) • Capability of a medium is determined by a physical quantity called channel capacity, defined as C = H log2(1 + S/N) bps • Network speed is usually given as data or information rate in bps, and every one wants a higher speed network: for example, with a 10 Mbps network, you may ask yourself why not 10 Gbps? • Given data rate fd (bps), the actual transmission or baud rate fb (Hz) over the medium is often different to fd • This is for
    [Show full text]
  • 6.02 Notes, Chapter 15: Sharing a Channel: Media Access (MAC
    MIT 6.02 DRAFT Lecture Notes Last update: November 3, 2012 CHAPTER 15 Sharing a Channel: Media Access (MAC) Protocols There are many communication channels, including radio and acoustic channels, and certain kinds of wired links (coaxial cables), where multiple nodes can all be connected and hear each other’s transmissions (either perfectly or with some non-zero probability). This chapter addresses the fundamental question of how such a common communication channel—also called a shared medium—can be shared between the different nodes. There are two fundamental ways of sharing such channels (or media): time sharing and frequency sharing.1 The idea in time sharing is to have the nodes coordinate with each other to divide up the access to the medium one at a time, in some fashion. The idea in frequency sharing is to divide up the frequency range available between the different transmitting nodes in a way that there is little or no interference between concurrently transmitting nodes. The methods used here are the same as in frequency division multiplexing, which we described in the previous chapter. This chapter focuses on time sharing. We will investigate two common ways: time division multiple access,orTDMA , and contention protocols. Both approaches are used in networks today. These schemes for time and frequency sharing are usually implemented as communica­ tion protocols. The term protocol refers to the rules that govern what each node is allowed to do and how it should operate. Protocols capture the “rules of engagement” that nodes must follow, so that they can collectively obtain good performance.
    [Show full text]
  • Multiple Access Techniques for 4G Mobile Wireless Networks Dr Rupesh Singh, Associate Professor & HOD ECE, HMRITM, New Delhi
    International Journal of Engineering Research and Development e-ISSN: 2278-067X, p-ISSN: 2278-800X, www.ijerd.com Volume 5, Issue 11 (February 2013), PP. 86-94 Multiple Access Techniques For 4G Mobile Wireless Networks Dr Rupesh Singh, Associate Professor & HOD ECE, HMRITM, New Delhi Abstract:- A number of new technologies are being integrated by the telecommunications industry as it prepares for the next generation mobile services. One of the key changes incorporated in the multiple channel access techniques is the choice of Orthogonal Frequency Division Multiple Access (OFDMA) for the air interface. This paper presents a survey of various multiple channel access schemes for 4G networks and explains the importance of these schemes for the improvement of spectral efficiencies of digital radio links. The paper also discusses about the use of Multiple Input/Multiple Output (MIMO) techniques to improve signal reception and to combat the effects of multipath fading. A comparative performance analysis of different multiple access schemes such as Time Division Multiple Access (TDMA), FDMA, Code Division Multiple Access (CDMA) & Orthogonal Frequency Division Multiple Access (OFDMA) is made vis-à-vis design parameters to highlight the advantages and limitations of these schemes. Finally simulation results of implementing some access schemes in MATLAB are provided. I. INTRODUCTION 4G (also known as Beyond 3G), an abbreviation of Fourth-Generation, is used for describing the next complete evolution in wireless communications. A 4G system will be a complete replacement for current networks and will be able to provide a comprehensive and secure IP solution. Here, voice, data, and streamed multimedia can be given to users on an "Anytime, Anywhere" basis, and at much higher data rates than the previous generations [1], [2], [3].
    [Show full text]
  • Time Division Multiple Access in Clustered Wireless Networks
    International Journal of Computational Engineering Research||Vol, 03||Issue, 12|| Time Division Multiple Access in Clustered Wireless Networks Srinivas.S1, M.Shashikala2 1m.Tech In Cse Dept ,Sr Engineering College,Warangal, Andhra Pradesh, India 2assistant Professor In Cse Dept, Sr Engineering College, Warangal, Andhra Pradesh, India ABSTRACT Time division multiple access (TDMA) is a channel access method for shared medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots. The users transmit in rapid succession, one after the other, each using its own time slot. This allows multiple stations to share the same transmission medium (e.g. radio frequency channel) while using only a part of its channel capacity. Based on the network-wide flow distribution calculated from the optimization model and transmission power on every link, we then propose an algorithm for deriving the TDMA schedules, utilizing the slot reuse concept to achieve minimum TDMA frame length. Numerical results reveal that our proposed solution reduces the energy consumption and delay significantly, while simultaneously satisfying a specified reliability objective. KEY WORDS: Wireless Sensor Networks (WSN), TDMA I. INTRODUCTION TDMA is a type of Time-division multiplexing, with the special point that instead of having one transmitter connected to one receiver, there are multiple transmitters. In the case of the uplink from a mobile phone to a base station this becomes particularly difficult because the mobile
    [Show full text]
  • Fundamentals of Telecommunications - Khaled M
    TELECOMMUNICATION SYSTEMS AND TECHNOLOGIES – Vol. I - Fundamentals of Telecommunications - Khaled M. Fouad Elsayed FUNDAMENTALS OF TELECOMMUNICATIONS Khaled M. Fouad Elsayed Cairo University, Giza, Egypt Keywords: Telecommunication networks, circuit-switching, packet-switching, multiplexing, protocol layering, the OSI model, telephony networks, the Internet Contents 1. Introduction 2. Types of Telecommunication Networks Procedure 2.1. Circuit-Switched Networks 2.2. Packet-Switched Networks 2.2.1. Virtual-Circuit Packet Switching 3. Multiplexing Techniques 3.1. Frequency-Division Multiplexing 3.2 Time-Division Multiplexing 3.3. Statistical Multiplexing 4. Network Protocol Layering 4.1. The OSI Model 4.1.1. The Application Layer 4.1.2. The Presentation Layer 4.1.3. The Session Layer 4.1.4. The Transport Layer 4.1.5 The Network Layer 4.1.6. The Data Link Layer 4.1.7. The Physical Layer 5. Telephony and Internet-oriented Technologies 5.1. Telephony/TDM 5.1.1 Architecture of the Telephone Network 5.1.2. Signaling in the Telephone Network 5.2. The Internet and IP-based Networks 5.2.1. The Internet Protocol Model 6. Future OutlookUNESCO – EOLSS Glossary Bibliography Biographical Sketch SAMPLE CHAPTERS Summary Telecommunications is one of the most dynamic industries that builds upon advances on networking, computing, electronics, and manufacturing. In this article, we provide an overview of the basics of telecommunications and concentrate the discussion on fundamental concepts and technologies in telecommunications. The coverage includes telephony networks and the Internet. Future outlook and a discussion of the on-going convergence between these two separate networks are included. ©Encyclopedia of Life Support Systems (EOLSS) TELECOMMUNICATION SYSTEMS AND TECHNOLOGIES – Vol.
    [Show full text]
  • UNIT II MEDIA ACCESS & INTERNETWORKING Medium Access Control
    UNIT II MEDIA ACCESS & INTERNETWORKING Medium access control: In telecommunications and computer networks, a channel access method or multiple access method allows several terminals connected to the same multi-point transmission medium to transmit over it and to share its capacity. Examples of shared physical media are wireless networks, bus networks, ring networks and half-duplex point-to-point links. A channel-access scheme is based on a multiplexing method, that allows several data streams or signals to share the same communication channel or physical medium. Multiplexing is in this context provided by the physical layer. Note that multiplexing also may be used in full-duplex point-to-point communication between nodes in a switched network, which should not be considered as multiple accesses. A channel-access scheme is also based on a multiple access protocol and control mechanism, also known as media access control (MAC). This protocol deals with issues such as addressing, assigning multiplex channels to different users, and avoiding collisions. The MAC-layer is a sub-layer in Layer 2 (Data Link Layer) of the OSI model and a component of the Link Layer of the TCP/IP model. Frequency Division Multiple Access (FDMA) The frequency-division multiple access (FDMA) channel-access scheme is based on the frequency-division multiplexing (FDM) scheme, which provides different frequency bands to different data-streams. In the FDMA case, the data streams are allocated to different nodes or devices. An example of FDMA systems were the first-generation (1G) cell-phone systems, where each phone call was assigned to a specific uplink frequency channel, and another downlink frequency channel.
    [Show full text]
  • Multiplexing Space-Division Multiplexing
    Multiplexing In telecommunication and computer networks, multiplexing (also known as muxing) is a method by which multiple analog message signals or digital data streams are combined into one signal over a shared medium. The aim is to share an expensive resource. For example, in telecommunications, several telephone calls may be carried using one wire. The multiplexed signal is transmitted over a communication medium communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the high-level communication channel into several low-level logical channels, one for each message signal or data stream to be transferred. A reverse process, known as DE multiplexing, can extract the original channels on the receiver side. A device that performs the multiplexing is called a multiplexer (MUX), and a device that performs the reverse process is called a de-multiplexer (DEMUX). Types of multiplexing Multiplexing technologies may be divided into several types, all of which have significant variations: Space division multiplexing (SDM) Frequency division multiplexing (FDM) Time division multiplexing (TDM) Code division multiplexing (CDM) Space-division multiplexing In wired communication, space-division multiplexing simply implies different point – to - point wires for different channels. Examples include an analogue stereo audio cable, with one pair of wires for the left channel and another for the right channel, and a multi pair telephone cable. In wireless communication, space-division multiplexing is achieved by multiple antenna elements. Frequency-division multiplexing When the carrier is frequency, FDM is used. FDM is an analog technology. FDM divides the spectrum or carrier bandwidth in logical channels and allocates one user to each channel.
    [Show full text]
  • Switching Techniques in Data Acquisition Systems for Future Experiments
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by CERN Document Server Switching techniques in data acquisition systems for future experiments. M. F. Letheren CERN, Geneva, Switzerland. Abstract An overview of the current state of development of parallel event building techniques is given, with emphasis on future applications in the high rate experiments proposed at the Large Hadron Collider (LHC). The paper describes the main architectural options in parallel event builders, the proposed event building architectures for LHC experiments, and the use of standard networking protocols for event building and their limitations. The main issues around the potential use of circuit switching, message switching and packet switching techniques are examined. Results from various laboratory demonstrator systems are presented. 1 Introduction A high energy physics experiment is usually composed of several different multi-channel detectors, each of which is equipped with its own specific modular front-end and readout electronics. Whenever an event trigger occurs, readout controllers each read the data from a local group of channels and format it into an event fragment in a local front-end memory. The various event fragments belonging to an event are scattered over these front-end memories, and they must be brought together1 before the event can be processed on-line using algorithms operating on the global event data, or before the event data can be recorded to mass storage. The process of collecting together the distributed event fragments is called event building. Figure 1(a) shows the architecture of a generic data acquisition system that includes a processor farm for on-line software triggering and uses a shared-medium interconnect to perform event building by moving event fragments from the sources (front-end buffers) into the destinations (members of the processor farm).
    [Show full text]
  • Communication Networks: Sharing and Switches
    MIT 6.02 Lecture Notes Last update: November 3, 2012 CHAPTER 16 Communication Networks: Sharing and Switches Thus far we have studied techniques to engineer a point-to-point communication link to send messages between two directly connected devices. These techniques give us a com­ munication link between two devices that, in general, has a certain error rate and a corre­ sponding message loss rate. Message losses occur when the error correction mechanism is unable to correct all the errors that occur due to noise or interference from other concurrent transmissions in a contention MAC protocol. We now turn to the study of multi-hop communication networks—systems that connect three or more devices together.1 The key idea that we will use to engineer communication networks is composition: we will build small networks by composing links together, and build larger networks by composing smaller networks together. The fundamental challenges in the design of a communication network are the same as those that face the designer of a communication link: sharing for efficiency and relia­ bility. The big difference is that the sharing problem has different challenges because the system is now distributed, spread across a geographic span that is much larger than even the biggest shared medium we can practically build. Moreover, as we will see, many more things can go wrong in a network in addition to just bit errors on the point-to-point links, making communication more unreliable than a single link’s unreliability.2. The next few chapters will discuss these two challenges and the key principles to overcome them.
    [Show full text]
  • A Survey of ATM Switching Techniques
    A Survey of ATM Switching Techniques Sonia Fahmy < [email protected]> Abstract -Asynchronous Transfer Mode (ATM) switching is not defined in the ATM standards, but a lot of research has been done to explore various ATM switch design alternatives. Each design has its own merits and drawbacks, in terms of throughput, delay, scalability, buffer sharing and fault tolerance. By examining the features of the basic switch designs, several conclusions can be inferred about the design principles of ATM switching, and the various tradeoffs involved in selecting the appropriate approach. Table of Contents 1. Introduction 2. Switching Functions 2.1 User Plane 2.2 Control Plane 2.3 Management Plane 2.4 Traffic Control Functions 3. A Generic Switching Architecture 3.1 Switch Interface 3.1.1 Input Modules 3.1.2 Output Modules 3.2 Cell Switch Fabric 3.3 Connection Admission Control (CAC) 3.4 Switch Management 4. The Cell Switch Fabric 4.1 Concentration, Expansion and Multiplexing 4.2 Routing and Buffering 4.2.1 Shared Memory Approach 4.2.2 Shared Medium Approach 4.2.3 Fully Interconnected Approach 4.2.4 Space Division Approach 4.2.4.1 Banyan Networks 4.2.4.1.1 Delta Networks 4.2.4.1.2 Blocking and Buffering 4.2.4.2 Multiple-Path Multistage Interconnection Networks (MINs) 5. Switch Design Principles 5.1 Internal Blocking 5.2 Buffering Approaches 5.2.1 Input Queuing 5.2.2 Output Queuing 5.2.3 Internal Queuing 5.2.4 Recirculating Buffers 5.3 Buffer Sharing 5.4 Scalability of Switch Fabrics 5.5 Multicasting Page 1 of 23 5.5.1 Shared Medium and Fully Interconnected Output-Buffered Approaches 5.5.2 Shared Memory Approach 5.5.3 Space Division Fabrics 5.5.3.1 Crossbar Switches 5.5.3.2 Broadcast Banyan Networks 5.5.3.3 Copy Networks 5.6 Fault Tolerance 5.7 Using Priorities in Buffer Management 5.7.1 Preliminaries 5.7.2 Cell Scheduling 5.7.3 Cell Discarding 5.7.4 Congestion Indications 6.
    [Show full text]