DOCSLIB.ORG

Chapter 6 Medium Access Control Protocols and Local Area Networks

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Chapter 6 Medium Access Control Protocols and Local Area Networks Chapter 6 Medium Access Control Protocols and Local Area Networks Part I: Medium Access Control Part II: Local Area Networks Chapter Overview z Broadcast Networks z Medium Access Control z All information sent to all z To coordinate access to users shared medium z No routing z Data link layer since direct z Shared media transfer of frames z Radio z Local Area Networks z Cellular telephony z High-speed, low-cost z Wireless LANs communications between co-located computers z Copper & Optical z z Ethernet LANs Typically based on broadcast networks z Cable Modem Access z Simple & cheap z Limited number of users Chapter 6 Medium Access Control Protocols and Local Area Networks Part I: Medium Access Control Multiple Access Communications Random Access Scheduling Channelization Delay Performance Chapter 6 Medium Access Control Protocols and Local Area Networks Part II: Local Area Networks Overview of LANs Ethernet Token Ring and FDDI 802.11 Wireless LAN LAN Bridges Chapter 6 Medium Access Control Protocols and Local Area Networks Multiple Access Communications Multiple Access Communications z Shared media basis for broadcast networks z Inexpensive: radio over air; copper or coaxial cable z M users communicate by broadcasting into medium z Key issue: How to share the medium? 3 2 4 1 Shared multiple access medium M 5 … Approaches to Media Sharing Medium sharing techniques Static Dynamic medium channelization access control z Partition medium Scheduling Random access z Dedicated allocation to users z Polling: take turns z Loose z Satellite z Request for slot in coordination transmission transmission z Send, wait, retry if z Cellular schedule necessary Telephone z Token ring z Aloha z Wireless LANs z Ethernet Channelization: Satellite Satellite Channel uplink fin downlink fout Channelization: Cellular uplink f1 ; downlink f2 uplink f3 ; downlink f4 Scheduling: Polling Inbound line Data fromData 1 from 2 Poll 1 Poll 2 Data to M Outbound line Host M computer 1 2 3 Stations Scheduling: Token-Passing Ring networks token Data to M token Station that holds token transmits into ring Random Access Multitapped Bus Crash!! Transmit when ready Transmissions can occur; need retransmission strategy Wireless LAN AdHoc: station-to-station Infrastructure: stations to base station Random access & polling Selecting a Medium Access Control z Applications z What type of traffic? z Voice streams? Steady traffic, low delay/jitter z Data? Short messages? Web page downloads? z Enterprise or Consumer market? Reliability, cost z Scale z How much traffic can be carried? z How many users can be supported? z Current Examples: z Design MAC to provide wireless DSL-equivalent access to rural communities z Design MAC to provide Wireless-LAN-equivalent access to mobile users (user in car travelling at 130 km/hr) Delay-Bandwidth Product z Delay-bandwidth product key parameter z Coordination in sharing medium involves using bandwidth (explicitly or implicitly) z Difficulty of coordination commensurate with delay-bandwidth product z Simple two-station example z Station with frame to send listens to medium and transmits if medium found idle z Station monitors medium to detect collision z If collision occurs, station that begin transmitting earlier retransmits (propagation time is known) Two-Station MAC Example Two stations are trying to share a common medium Distance d meters A tprop = d / ν seconds transmits AB at t = 0 B does not Case 1 transmit before A B t = tprop & A captures channel Case 2 B transmits before t = tprop A B and detects A detects collision soon collision at thereafter A t = 2 tprop B Efficiency of Two-Station Example z Each frame transmission requires 2tprop of quiet time z Station B needs to be quiet tprop before and after time when Station A transmits z R transmission bit rate z L bits/frame L 1 1 Efficiency = ρmax = = = L + 2t prop R 1+ 2t prop R / L 1+ 2a L 1 MaxThroughput = Reff = = R bits/second L / R + 2t prop 1+ 2a Normalized Propagation delay t prop Delay-Bandwidth a = Product L / R Time to transmit a frame Typical MAC Efficiencies Two-Station Example: 1 Efficiency = 1+ 2a z If a<<1, then efficiency close to CSMA-CD (Ethernet) protocol: 100% 1 Efficiency = z As a approaches 1+ 6.44a 1, the efficiency Token-ring network becomes low 1 Efficiency = 1+ a′ a΄= latency of the ring (bits)/average frame length Typical Delay-Bandwidth Products Distance 10 Mbps 100 Mbps 1 Gbps Network Type 1 m 3.33 x 10- 3.33 x 10- 3.33 x 100 Desk area network 02 01 100 m 3.33 x 1001 3.33 x 1002 3.33 x 1003 Local area network 10 km 3.33 x 1002 3.33 x 1003 3.33 x 1004 Metropolitan area network 1000 km 3.33 x 1004 3.33 x 1005 3.33 x 1006 Wide area network 100000 km 3.33 x 1006 3.33 x 1007 3.33 x 1008 Global area network z Max size Ethernet frame: 1500 bytes = 12000 bits z Long and/or fat pipes give large a MAC protocol features z Delay-bandwidth product z Efficiency z Transfer delay z Fairness z Reliability z Capability to carry different types of traffic z Quality of service z Cost MAC Delay Performance z Frame transfer delay z From first bit of frame arrives at source MAC z To last bit of frame delivered at destination MAC z Throughput z Actual transfer rate through the shared medium z Measured in frames/sec or bits/sec z Parameters R bits/sec & L bits/frame X=L/R seconds/frame λ frames/second average arrival rate Load ρ = λ X, rate at which “work” arrives Maximum throughput (@100% efficiency): R/L fr/sec Normalized Delay versus Load E[T]/X E[T] = average frame z At low arrival transfer delay rate, only frame transmission X = average frame time transmission time z At high arrival rates, increasingly longer waits to Transfer delay access channel z Max efficiency typically less than 100% 1 ρ ρ 1 Load max Dependence on Rtprop/L E[T]/X a′ > a a′ a Transfer Delay 1 ρ ρ′max ρmax 1 Load Chapter 6 Medium Access Control Protocols and Local Area Networks Random Access ALOHA z Wireless link to provide data transfer between main campus & remote campuses of University of Hawaii z Simplest solution: just do it z A station transmits whenever it has data to transmit z If more than one frames are transmitted, they interfere with each other (collide) and are lost z If ACK not received within timeout, then a station picks random backoff time (to avoid repeated collision) z Station retransmits frame after backoff time First transmission Retransmission Backoff period B t t -X t0 t0+X t +X+2t + B 0 t0+X+2tprop 0 prop Vulnerable Time-out period ALOHA Model z Definitions and assumptions z X frame transmission time (assume constant) z S: throughput (average # successful frame transmissions per X seconds) z G: load (average # transmission attempts per X sec.) z Psuccess : probability a frame transmission is successful S = GP success z Any transmission that begins during vulnerable period leads to collision z Success if no arrivals X X during 2X seconds Prior interval frame transmission Abramson’s Assumption z What is probability of no arrivals in vulnerable period? z Abramson assumption: Effect of backoff algorithm is that frame arrivals are equally likely to occur at any time interval z G is avg. # arrivals per X seconds z Divide X into n intervals of duration Δ=X/n z p = probability of arrival in Δ interval, then G = n p since there are n intervals in X seconds Psuccess = P[0 arrivals in 2X seconds] = = P[0 arrivals in 2n intervals] G = (1- p)2n = (1− )2n → e−2G as n → ∞ n Throughput of ALOHA −2G S = GPsuccess = Ge z Collisions are means -2 for coordinating 0.2 e = 0.184 0.18 access 0.16 z Max throughput is 0.14 0.12 ρmax=1/2e (18.4%) S 0.1 z Bimodal behavior: 0.08 0.06 Small G, S≈G 0.04 Large G, S↓0 0.02 0 z Collisions can 5 5 0 2 2 5 5 5 5 .5 1 2 4 1 6 2 2 2 .2 0 8 5 1 6 .1 0 snowball and drop 7 1 3 .0 0 0 .0 .0 0 .0 0 0 0 throughput to zero G Slotted ALOHA z Time is slotted in X seconds slots z Stations synchronized to frame times z Stations transmit frames in first slot after frame arrival z Backoff intervals in multiples of slots Backoff period B t (k+1)X t +X+2t kX 0 prop t0 +X+2tprop+ B Time-out Vulnerable period Only frames that arrive during prior X seconds collide Throughput of Slotted ALOHA S = GPsuccess = GP[no arrivals in X seconds] = GP[no arrivals in n intervals] G = G(1− p)n = G(1− )n → Ge−G n 0.4 0.368 0.35 0.3 S 0.25 Ge-G 0.2 0.184 0.15 0.1 0.05 Ge-2G 0 1 2 4 8 0.5 0.25 0.125 0.0625 0.01563 0.03125 G Application of Slotted Aloha cycle . Reservation X-second slot mini-slots z Reservation protocol allows a large number of stations with infrequent traffic to reserve slots to transmit their frames in future cycles z Each cycle has mini-slots allocated for making reservations z Stations use slotted Aloha during mini-slots to request slots Carrier Sensing Multiple Access (CSMA) z A station senses the channel before it starts transmission z If busy, either wait or schedule backoff (different options) z If idle, start transmission z Vulnerable period is reduced to tprop (due to channel capture effect) z When collisions occur they involve entire frame transmission times z If tprop >X (or if a>1), no gain compared to ALOHA or slotted ALOHA Station A begins transmission at t = 0 A Station A captures channel at t = tprop A CSMA Options z Transmitter behavior when busy channel is sensed z 1-persistent CSMA (most greedy) z Start transmission as soon as the channel becomes idle z Low delay and low efficiency z Non-persistent CSMA (least greedy) z Wait a backoff period, then sense carrier again z High delay and high efficiency z p-persistent CSMA (adjustable greedy) z Wait till channel becomes idle, transmit with prob.
Load more

Recommended publications
  • Implementing MACA and Other Useful Improvements to Amateur Packet Radio for Throughput and Capacity
    Implementing MACA and Other Useful Improvements to Amateur Packet Radio for Throughput and Capacity John Bonnett – KK6JRA / NCS820 Steven Gunderson – CMoLR Project Manager TAPR DCC – 15 Sept 2018 1 Contents • Introduction – Communication Methodology of Last Resort (CMoLR) • Speed & Throughput Tests – CONNECT & UNPROTO • UX.25 – UNPROTO AX.25 • Multiple Access with Collision Avoidance (MACA) – Hidden Terminals • Directed Packet Networks • Brevity – Directory Services • Trunked Packet • Conclusion 2 Background • Mission County – Proverbial: – Coastline, Earthquake Faults, Mountains & Hills, and Missions – Frequent Natural Disasters • Wildfires, Earthquakes, Floods, Slides & Tsunamis – Extensive Packet Networks • EOCs – Fire & Police Stations – Hospitals • Legacy 1200 Baud Packet Networks • Outpost and Winlink 2000 Messaging Software 3 Background • Mission County – Proverbial: – Coastline, Earthquake Faults, Mountains & Hills, and Missions – Frequent Natural Disasters • Wildfires, Earthquakes, Floods, Slides & Tsunamis – Extensive Packet Networks • EOCs – Fire & Police Stations – Hospitals • Legacy 1200 Baud Packet Networks • Outpost and Winlink 2000 Messaging Software • Community Emergency Response Teams: – OK Drills – Neighborhood Surveys OK – Triage Information • CERT Form #1 – Transmit CERT Triage Data to Public Safety – Situational Awareness 4 Background & Objectives (cont) • Communication Methodology of Last Resort (CMoLR): – Mission County Project: 2012 – 2016 – Enable Emergency Data Comms from CERT to Public Safety 5 Background &
    [Show full text]
  • Lecture 10: Switching & Internetworking
    Lecture 10: Switching & Internetworking CSE 123: Computer Networks Alex C. Snoeren HW 2 due WEDNESDAY Lecture 10 Overview ● Bridging & switching ◆ Spanning Tree ● Internet Protocol ◆ Service model ◆ Packet format CSE 123 – Lecture 10: Internetworking 2 Selective Forwarding ● Only rebroadcast a frame to the LAN where its destination resides ◆ If A sends packet to X, then bridge must forward frame ◆ If A sends packet to B, then bridge shouldn’t LAN 1 LAN 2 A W B X bridge C Y D Z CSE 123 – Lecture 9: Bridging & Switching 3 Forwarding Tables ● Need to know “destination” of frame ◆ Destination address in frame header (48bit in Ethernet) ● Need know which destinations are on which LANs ◆ One approach: statically configured by hand » Table, mapping address to output port (i.e. LAN) ◆ But we’d prefer something automatic and dynamic… ● Simple algorithm: Receive frame f on port q Lookup f.dest for output port /* know where to send it? */ If f.dest found then if output port is q then drop /* already delivered */ else forward f on output port; else flood f; /* forward on all ports but the one where frame arrived*/ CSE 123 – Lecture 9: Bridging & Switching 4 Learning Bridges ● Eliminate manual configuration by learning which addresses are on which LANs Host Port A 1 ● Basic approach B 1 ◆ If a frame arrives on a port, then associate its source C 1 address with that port D 1 ◆ As each host transmits, the table becomes accurate W 2 X 2 ● What if a node moves? Table aging Y 3 ◆ Associate a timestamp with each table entry Z 2 ◆ Refresh timestamp for each
    [Show full text]
  • 802.11 BSS Bridging
    802.11 BSS Bridging Contributed by Philippe Klein, PhD Broadcom IEEE 8021/802.11 Study Group, Aug 2012 new-phkl-11-bbs-bridging-0812-v2 The issue • 802.11 STA devices are end devices that do not bridge to external networks. This: – limit the topology of 802.11 BSS to “stub networks” – do not allow a (STA-)AP-STA wireless link to be used as a connecting path (backbone) between other networks • Partial solutions exist to overcome this lack of bridging functionality but these solutions are: – proprietary only – limited to certain type of traffic – or/and based on Layer 3 (such IP Multicast to MAC Multicast translation, NAT - Network Address Translation) IEEE 8021/802.11 Study Group - Aug 2012 2 Coordinated Shared Network (CSN) CSN CSN Network CSN Node 1 Node 2 Shared medium Logical unicast links CSN CSN Node 3 Node 4 • Contention-free, time-division multiplexed-access, network of devices sharing a common medium and supporting reserved bandwidth based on priority or flow (QoS). – one of the nodes of the CSN acts as the network coordinator, granting transmission opportunities to the other nodes of the network. • Physically a shared medium, in that a CSN node has a single physical port connected to the half-duplex medium, but logically a fully-connected one-hop mesh network, in that every node can transmit frames to every other node over the shared medium. • Supports two types of transmission: – unicast transmission for point-to-point (node-to-node) – transmission and multicast/broadcast transmission for point-to-multipoint (node-to-other/all-nodes) transmission.
    [Show full text]
  • ISDN LAN Bridging Bhi
    ISDN LAN Bridging BHi Tim Boland U.S. DEPARTMENT OF COMMERCE Technology Administration National Institute of Standards and Technology Gaithersburg, MD 20899 QC 100 NIST .U56 NO. 5532 199it NISTIR 5532 ISDN LAN Bridging Tim Boland U.S. DEPARTMENT OF COMMERCE Technology Administration National Institute of Standards and Technology Gaithersburg, MD 20899 November 1994 U.S. DEPARTMENT OF COMMERCE Ronald H. Brown, Secretary TECHNOLOGY ADMINISTRATION Mary L. Good, Under Secretary for Technology NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY Arati Prabhakar, Director DATE DUE - ^'' / 4 4 ' / : .f : r / Demco, Inc. 38-293 . ISDN LAN BRIDGING 1.0 Introduction This paper will provide guidance which will enable users to properly assimilate Integrated Services Digital Network (ISDN) local area network (LAN) bridging products into the workplace. This technology is expected to yield economic, functional and performance benefits to users. Section 1 (this section) provides some introductory information. Section 2 describes the environment to which this paper applies. Section 3 provides history and status information. Section 4 describes service features of some typical product offerings. Section 5 explains the decisions that users have to make and the factors that should influence their decisions. Section 6 deals with current ISDN LAN bridge interoperability activities. Section 7 gives a high-level summary and future direction. 2.0 ISDN LAN Bridging Environment 2 . 1 User Environment ISDN LAN bridge usage should be considered by users who have a need to access a LAN or specific device across a distance of greater than a few kilometers, or by users who are on a LAN and need to access a specific device or another network remotely, and, for both situations, have or are considering ISDN use to accomplish this access.
    [Show full text]
  • Solutions to Chapter 2
    CS413 Computer Networks ASN 4 Solutions Solutions to Assignment #4 3. What difference does it make to the network layer if the underlying data link layer provides a connection-oriented service versus a connectionless service? [4 marks] Solution: If the data link layer provides a connection-oriented service to the network layer, then the network layer must precede all transfer of information with a connection setup procedure (2). If the connection-oriented service includes assurances that frames of information are transferred correctly and in sequence by the data link layer, the network layer can then assume that the packets it sends to its neighbor traverse an error-free pipe. On the other hand, if the data link layer is connectionless, then each frame is sent independently through the data link, probably in unconfirmed manner (without acknowledgments or retransmissions). In this case the network layer cannot make assumptions about the sequencing or correctness of the packets it exchanges with its neighbors (2). The Ethernet local area network provides an example of connectionless transfer of data link frames. The transfer of frames using "Type 2" service in Logical Link Control (discussed in Chapter 6) provides a connection-oriented data link control example. 4. Suppose transmission channels become virtually error-free. Is the data link layer still needed? [2 marks – 1 for the answer and 1 for explanation] Solution: The data link layer is still needed(1) for framing the data and for flow control over the transmission channel. In a multiple access medium such as a LAN, the data link layer is required to coordinate access to the shared medium among the multiple users (1).
    [Show full text]
  • Reservation - Time Division Multiple Access Protocols for Wireless Personal Communications
    tv '2s.\--qq T! Reservation - Time Division Multiple Access Protocols for Wireless Personal Communications Theodore V. Buot B.S.Eng (Electro&Comm), M.Eng (Telecomm) Thesis submitted for the degree of Doctor of Philosophy 1n The University of Adelaide Faculty of Engineering Department of Electrical and Electronic Engineering August 1997 Contents Abstract IY Declaration Y Acknowledgments YI List of Publications Yrt List of Abbreviations Ylu Symbols and Notations xi Preface xtv L.Introduction 1 Background, Problems and Trends in Personal Communications and description of this work 2. Literature Review t2 2.1 ALOHA and Random Access Protocols I4 2.1.1 Improvements of the ALOHA Protocol 15 2.1.2 Other RMA Algorithms t6 2.1.3 Random Access Protocols with Channel Sensing 16 2.1.4 Spread Spectrum Multiple Access I7 2.2Fixed Assignment and DAMA Protocols 18 2.3 Protocols for Future Wireless Communications I9 2.3.1 Packet Voice Communications t9 2.3.2Reservation based Protocols for Packet Switching 20 2.3.3 Voice and Data Integration in TDMA Systems 23 3. Teletraffic Source Models for R-TDMA 25 3.1 Arrival Process 26 3.2 Message Length Distribution 29 3.3 Smoothing Effect of Buffered Users 30 3.4 Speech Packet Generation 32 3.4.1 Model for Fast SAD with Hangover 35 3.4.2Bffect of Hangover to the Speech Quality 38 3.5 Video Traffic Models 40 3.5.1 Infinite State Markovian Video Source Model 41 3.5.2 AutoRegressive Video Source Model 43 3.5.3 VBR Source with Channel Load Feedback 43 3.6 Summary 46 4.
    [Show full text]
  • Logical Link Control and Channel Scheduling for Multichannel Underwater Sensor Networks
    ICST Transactions on Mobile Communications and Applications Research Article Logical Link Control and Channel Scheduling for Multichannel Underwater Sensor Networks Jun Li ∗, Mylene` Toulgoat, Yifeng Zhou, and Louise Lamont Communications Research Centre Canada, 3701 Carling Avenue, Ottawa, ON. K2H 8S2 Canada Abstract With recent developments in terrestrial wireless networks and advances in acoustic communications, multichannel technologies have been proposed to be used in underwater networks to increase data transmission rate over bandwidth-limited underwater channels. Due to high bit error rates in underwater networks, an efficient error control technique is critical in the logical link control (LLC) sublayer to establish reliable data communications over intrinsically unreliable underwater channels. In this paper, we propose a novel protocol stack architecture featuring cross-layer design of LLC sublayer and more efficient packet- to-channel scheduling for multichannel underwater sensor networks. In the proposed stack architecture, a selective-repeat automatic repeat request (SR-ARQ) based error control protocol is combined with a dynamic channel scheduling policy at the LLC sublayer. The dynamic channel scheduling policy uses the channel state information provided via cross-layer design. It is demonstrated that the proposed protocol stack architecture leads to more efficient transmission of multiple packets over parallel channels. Simulation studies are conducted to evaluate the packet delay performance of the proposed cross-layer protocol stack architecture with two different scheduling policies: the proposed dynamic channel scheduling and a static channel scheduling. Simulation results show that the dynamic channel scheduling used in the cross-layer protocol stack outperforms the static channel scheduling. It is observed that, when the dynamic channel scheduling is used, the number of parallel channels has only an insignificant impact on the average packet delay.
    [Show full text]
  • 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]
  • A Survey on Aloha Protocol for Iot Based Applications
    ISSN: 2277-9655 [Badgotya * et al., 7(5): May, 2018] Impact Factor: 5.164 IC™ Value: 3.00 CODEN: IJESS7 IJESRT INTERNATIONAL JOURNAL OF ENGINEERING SCIENCES & RESEARCH TECHNOLOGY A SURVEY ON ALOHA PROTOCOL FOR IOT BASED APPLICATIONS Shikha Badgotya*1 & Prof.Deepti Rai2 *1M.Tech Scholar, Department of EC, Alpine Institute of Technology,, Ujjain (India) 2H.O.D, Department of EC, Alpine Institute of Technology, Ujjain (India) DOI: 10.5281/zenodo.1246995 ABSTRACT With the emergence of IoT based applications in industries and automation, protocols for effective data transfer was the foremost need. The natural choice was a random access protocol like ALOHA which could be incorporated in the ultra narrowband ISM band framework because of its simplicity and lack of overhead. Pure ALOHA faced the limitation of greater rate of collisions among the packets of data and also there was higher level of frame delays. Slotted ALOHA overcame these limitations to some extent in which the transfer of data takes place after channel polling. Though the drawbacks of PURE ALOHA are somewhat resolved in Slotted ALOHA, still some redundant transmissions and delay of frames exist. The present proposed work puts forth an efficient mechanism for Slotted ALOHA which implements polling of channel that is non persistent in nature to reduce the probability of collisions considerably. Further it presents a channel sensing methodology also for prevention of burst errors. Interleaving serves to be useful in case of burst errors and helps in preserving useful information. The survey should pave the path for IoT based applications working on an ultra narrowband architecture.
    [Show full text]
  • Data Link Layer
    Data link layer Goals: ❒ Principles behind data link layer services ❍ Error detection, correction ❍ Sharing a broadcast channel: Multiple access ❍ Link layer addressing ❍ Reliable data transfer, flow control: Done! ❒ Example link layer technology: Ethernet Link layer services Framing and link access ❍ Encapsulate datagram: Frame adds header, trailer ❍ Channel access – if shared medium ❍ Frame headers use ‘physical addresses’ = “MAC” to identify source and destination • Different from IP address! Reliable delivery (between adjacent nodes) ❍ Seldom used on low bit error links (fiber optic, co-axial cable and some twisted pairs) ❍ Sometimes used on high error rate links (e.g., wireless links) Link layer services (2.) Flow Control ❍ Pacing between sending and receiving nodes Error Detection ❍ Errors are caused by signal attenuation and noise. ❍ Receiver detects presence of errors signals sender for retrans. or drops frame Error Correction ❍ Receiver identifies and corrects bit error(s) without resorting to retransmission Half-duplex and full-duplex ❍ With half duplex, nodes at both ends of link can transmit, but not at same time Multiple access links / protocols Two types of “links”: ❒ Point-to-point ❍ PPP for dial-up access ❍ Point-to-point link between Ethernet switch and host ❒ Broadcast (shared wire or medium) ❍ Traditional Ethernet ❍ Upstream HFC ❍ 802.11 wireless LAN MAC protocols: Three broad classes ❒ Channel Partitioning ❍ Divide channel into smaller “pieces” (time slots, frequency) ❍ Allocate piece to node for exclusive use ❒ Random
    [Show full text]
  • OSI Data Link Layer
    OSI Data Link Layer Network Fundamentals – Chapter 7 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 1 Objectives Explain the role of Data Link layer protocols in data transmission. Describe how the Data Link layer prepares data for transmission on network media. Describe the different types of media access control methods. Identify several common logical network topologies and describe how the logical topology determines the media access control method for that network. Explain the purpose of encapsulating packets into frames to facilitate media access. Describe the Layer 2 frame structure and identify generic fields. Explain the role of key frame header and trailer fields including addressing, QoS, type of protocol and Frame Check Sequence. © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 2 Data Link Layer – Accessing the Media Describe the service the Data Link Layer provides as it prepares communication for transmission on specific media © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 3 Data Link Layer – Accessing the Media Describe why Data Link layer protocols are required to control media access © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 4 Data Link Layer – Accessing the Media Describe the role of framing in preparing a packet for transmission on a given media © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 5 Data Link Layer – Accessing the Media Describe the role the Data Link layer plays in linking the software and hardware layers © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 6 Data Link Layer – Accessing the Media Identify several sources for the protocols and standards used by the Data Link layer © 2007 Cisco Systems, Inc.
    [Show full text]
  • OSI Model and Network Protocols
    CHAPTER4 FOUR OSI Model and Network Protocols Objectives 1.1 Explain the function of common networking protocols . TCP . FTP . UDP . TCP/IP suite . DHCP . TFTP . DNS . HTTP(S) . ARP . SIP (VoIP) . RTP (VoIP) . SSH . POP3 . NTP . IMAP4 . Telnet . SMTP . SNMP2/3 . ICMP . IGMP . TLS 134 Chapter 4: OSI Model and Network Protocols 4.1 Explain the function of each layer of the OSI model . Layer 1 – physical . Layer 2 – data link . Layer 3 – network . Layer 4 – transport . Layer 5 – session . Layer 6 – presentation . Layer 7 – application What You Need To Know . Identify the seven layers of the OSI model. Identify the function of each layer of the OSI model. Identify the layer at which networking devices function. Identify the function of various networking protocols. Introduction One of the most important networking concepts to understand is the Open Systems Interconnect (OSI) reference model. This conceptual model, created by the International Organization for Standardization (ISO) in 1978 and revised in 1984, describes a network architecture that allows data to be passed between computer systems. This chapter looks at the OSI model and describes how it relates to real-world networking. It also examines how common network devices relate to the OSI model. Even though the OSI model is conceptual, an appreciation of its purpose and function can help you better understand how protocol suites and network architectures work in practical applications. The OSI Seven-Layer Model As shown in Figure 4.1, the OSI reference model is built, bottom to top, in the following order: physical, data link, network, transport, session, presentation, and application.
    [Show full text]