当前位置：文档之家 › VIRTUAL CONNECTION TREE OVER MULTIPLE ACCESS TECHNIQUES FOR 3G WIRELESS COMMUNICATION SYSTE

VIRTUAL CONNECTION TREE OVER MULTIPLE ACCESS TECHNIQUES FOR 3G WIRELESS COMMUNICATION SYSTE

  • 格式：pdf
  • 大小：329.32 KB
  • 文档页数：26

VIRTUAL CONNECTION TREE OVER MULTIPLE ACCESS TECHNIQUES FOR 3G WIRELESS COMMUNICATION SYSTEMSA. Heath and R.A. CarrascoSchool of Engineering and Advanced Technology, Staffordshire UniversityPO BOX 333, Beaconside, Stafford ST18 0DF, Staffordshire, U.K.Emails: A.L.Heath@, R.A.Carrasco@Abstract: This paper evaluates a Virtual Connection Tree (VCT) algorithm for mobile Asynchronous Transfer Mode (ATM) handoff that offers service adaptability and efficient allocation of wired resources is applied to different multiple access techniques. This creates a more distributed system where decisions about traffic conditions in different areas can be evaluated at the Base Station (BS) level and not the Master Switching Centre (MSC) level.Keywords: 3G, VCT, ATM, Mobile Communications1IntroductionIn future third generation (3G) systems it is anticipated that wireless, wired and satellite communications will be integrated in one system where multimedia data will be transferred at bit rates up to 2Mbits/sec [1]. Data traffic is growing at a much faster rate than voice, so new and efficient mediums are required to transport this information [2]. A medium that can be used to integrate multimedia traffic is ATM technology, which is a wired infrastructure that provides excellent QoS [3-5]. This paper presents a way in which Mobile ATM can be used to improve the QoS for many users in a network.Extensive research has been conducted to determine the best multiple access technique for future mobile communication systems where CDMA, TDMA, PRMA, FDMA and combinations of these are employed [6-8]. This paper considers the advantages of applying the VCT algorithm developed in [9,10] to each of the aforementioned technologies. In the future it is thought that the MSC will be removed from the system model, as in ad-hoc networks and that Internet Protocol (IP) traffic may be transmitted over an ATM backbone [11], due to the QoS guarantees.It has been demonstrated in [12] that the service adaptable handoff algorithm can be applied to data rates of up to 2Mbits/sec and above without significant degradation of service. A solution to the mobile handoff problem was illustrated in [13] in which the MSC is not involved with the handoff but wired resources are wasted unlike the proposal in [12]. Using the Call Admission Control Algorithm which is presented in [9, 10, 12] and developed in this paper a more distributed system is created.Section 2 examines how the VCT can be applied to various multiple access techniques, while section 3 presents call/carrier communication algorithm. Section 4 details the simulations and a discussion of the results and finally section 5 is used to draw conclusions and suggestions of future work.2 Virtual Connection TreeVCT is an ATM oriented strategy that avoids the need to involve the MSC during handoffs [12]. The VCT consists of cellular BSs with radio transceivers connected to switching nodes thorough and ATM wired infrastructure and mobile stations (MS), which transmit information over the shared radio link.In order to apply the VCT to the multiple access scheme, at call set-up each MS connection is assigned at the Virtual Connection Identifier (VCI) in the VCT. Each VCI is uniquely associated to a carrier for time division duplex (TDD), or a pair of carriers for frequency division duplex FDD. The VCI-VPI combination represents the carrier and BS used at any moment by a given connection. The numbering structure is shown in Figure 1.Each BS is associated to a Virtual Path Identifier (VPI) and each mobile connection is assigned a group of VCIs, each VCI corresponding to a carrier. During a handoff the VPI changes, indicating a new BS and the VCI could change indicating a change in carrier.2n+3-vci 2n MS 1MS 2…MS m Carrier 1vci 1…Carrier 2…Carrier 3…….…………Carrier n …MS 1 → vpi 1-vci 4MS 2 → vpi 3-vci n+3MS 3 → vpi 2-vci 2n+10 (before H/O)MS 3 → vpi 3-vci 2n+5 (after H/O)vci 2vci 3vci nvci n+1vci n+2vci n+3vci 2nvci (m-1)n+1vci (m-1)n+2vci (m-1)n+3vci mnFigure 1 –a)VCT-CRDMA Integration, b) VCT, Carrier-map and tablesThe handoff procedure for MS 3 is illustrated in Figure 1. The VPI-VCI information allows the MSC to locate any MS at any time, cells are routed correctly given this information.By using the VCT with multiple access techniques no handoff processing is carried out at the MSC since all possible routes are pre-established. This implies a reduction in the amount of signalling and processing during a handoff, which improves the GoS. The traffic can be evaluated at the MSC since the VCNs provide the carrier frequency and BS information of every mobile without any additional signalling.3Carrier Communication AlgorithmIn [11] a carrier communication algorithm was presented. This involves passing in real-time, the information gathered at the MSC to all BSs in the VCT, such that a BS creates a ‘map’ of the carriers used in adjacent cells. Each BS has its table similar to that in CSMA, which contains information about its own and interfering cells. The size, S of this table, the carrier-map table, depends on the number of cells considered as interferers,B i as well as the maximum number of carriers/codes allowed in each BS, C, and is given by Equation 1.()C 1B S i +=(1)Another table is also required, the VCT active user table, in which all active users are registered relating to the MB ID number. The tables and the area they refer to are illustrated in Figure 1b. Both tables are immediately updated when changes such as new connections, handoffs and terminations occur within the VCT. The active user table is only affected by connection set-ups and terminations. The carrier-map can be updated in one of two ways; if the change is inside the cell, the BS directly updates its own table. If the changeoccurs outside its cell, the BS waits for the information from MSC. The set-up and termination processes are shown in Figure 2a) and The handoff process is illustrated in Figure 2b).Figure 2 – a) Set-Up and Termination Process b) Handoff ProcessEach change requires a different frame to be generated by the MSC, these are shown in Figure 3.n bitsb)Set up Frame Handoff FrameTermination Frame9 bits 15 bits 6 bits 15 bits BS to MS Frame64 bits9 bits a)b)Figure 3– a)TDMA, FDMA, PRMA CCA, b) CDMA FramesThe carrier/code communication algorithm introduces distributed dynamic channel allocation schemes (FDMA, TDMA, PRMA) can easily be implemented since information about frequency usage is provided so the amount of interference is reduced. The system is distributed since BSs store information gathered and administer call admission control. In CDMA this is also useful as the MS can use this information to cancel out the interference from these cells.4Evaluation, Results and DiscussionA combination of the VCT-multiple access technique and carrier/code communication algorithm is evaluated.The bandwidth required for the carrier communication algorithm is determined. A comparison between FCA and DCA for TDMA, FDMA and PRMA and the advantages in CDMA are then evaluated. The saved amount of signalling at the MSC is then evaluated, when calls are admitted/declined at BS level. A cellular system is used to simulate these situations, using the parameters according to Table 1.The signalling bandwidth was measured by adding the bandwidth for the carrier/code communication algorithm, set-ups, handoffs and terminations. The bandwidths are illustrated in Figure 4, where the peak values are worst case conditions.The peak bandwidth varies from 5.76kbits/sec (15 ATM cells/sec) for 25 BSs at 1 call/sec generated, to 26.88kbits/sec (70 ATM cells/sec) for 49 BSs at 10 calls/sec. The bandwidth demand is small considering the rates used in ATM networks (150Mbit/sec). This occupancy may be reduced if the signalling channel is shared with other control information.Figure 4 - MSC-BS Bandwidth.FCA and DCA are now compared in terms of failing probabilities for the VCT applied to different multiple access techniques. With FDMA a system consisting of 16BSs each with 50 channels is considered. For a given failing probability DCA allows a higher intensity of traffic than FCA, until about 4%, see Figure 5. Improvements with respect to FCA of 0.87, 0.63 and 0.48 Erlang/mile2 are shown for cluster sizes of 7, 3 and 4 respectively at a failing probability of 1%. DCA increases the capacity of the system, so more connections are admitted and less ongoing calls are dropped. If the cell size is reduced the traffic intensity can increase compared to that with FCA.Figure 5- Failing Probability –a) FDMA b) TDMAThe TDMA has 17 carriers with 3 slots for each of the 16 BSs. Again DCA is more efficient than FCA only up to a limit of 1.5% failing probability, this is not as efficient as FDMA see Figure 5b. For 0.5% the improvement in traffic intensity for DCA with respect to FCA is approximately 0.43, 0.2 and 0.12 Erlang/mile2 for clusters of 7, 3 and 4 respectively at a failing probability of 0.5%.This reduction in the efficiency is caused by when a channel is borrowed from an adjacent cell in TDMA three slots are locked, which can not be used by any interfering cells, whereas in FDMA only one carrier is provided.For PRMA the system consists 16 BSs with 5 carriers with 10 slots each, FCA shows higher traffic intensity for the same failing probability with respect to DCA. DCA techniques where carriers are borrowed from one BS to another do not work well with packet switching multiple access techniques, instead a dynamic slot selection technique is required.When applying the VCT to CDMA, the BER comparison for a conventional and Parallel Interference Cancellation (PIC) detectors is illustrated in Figure 6a. The curve referred to as ‘1 user (no interference)’represents a single BS with one user transmitting, and has the best performance obtainable in a given channel.The processing at the MSC can be reduced using the call admission control algorithm. A threshold value of traffic is set so that BS perform admission control. The signalling in an FDMA, FCA allocation model with different thresholds has been measured. The number of new connections in a centralised system would be infinite and this signalling may cause congestion problems. Figure 7a) illustrates the signalling that would be employed in a centralised system. In a distributed system, with threshold traffic values this congestion would be avoided at the cost of a higher call failing probability, as shown in Figure 7b).The call dropping probability with different thresholds is greatly reduced, since some channels are saved for handoffs. Using the threshold method, once a call is accepted it has less chance of failing, but less calls are accepted, the optimum threshold is approximately 0.75.Figure 7 – a) Signalling to Block New Connections (Centralised), b) Threshold Failing Probability5 ConclusionApplying the VCT to all the different multiple access methods has proved advantageous, in the reduction signalling traffic. The peak bandwidth of the algorithm varies from 5.76kbits/sec to 26.88kbits/sec this issmall considering the rates used in ATM networks (150Mbit/sec). DCA for FDMA provided improvements of 0.87, 0.63 and 0.48 Erlang/mile2 are shown for cluster sizes of 7, 3 and 4 respectively at a failing probability of 1%. Next was TDMA with 0.43, 0.2 and 0.12 Erlang/mile2 for clusters of 7, 3 and 4 respectively at a failing probability of 0.5%. In CDMA interference was removed from signals, improving the BER curve. There is more work required for the packet switched applications and IP transport protocols The references [14-16] are a starting point for future work in this area, in which the system will be operated through an IP interface using the ATM technology. For all multiple access methods are more distributed system has been created, for FDMA the signalling saved was shown, this is similar for all the multiple access schemes.6References[1]Godara, L.C.; Ryan, M.J.; Padovan, N. ‘Third generation mobile communication systems:Overview and modelling considerations’Annales des Telecomms/Annals of Telecomms v 54, n 1, 1999, p 114-136[2]ITU Documentation on IMT-2000, available at http://www.itu.int/imt/.[3]Singh M., ‘3G Wireless with respect to IMT-2000 and beyond’, Telecom 99, Inter@ctive 99.[4]Cuthbert, L.G., Sapanello, G.C., ‘ATM: the broadband telecommunication solution’,IEE London.UK. 1993.[5]Yuan, R., Biswass, S.K. and Raychaudhuri, D., ‘A Signalling and Control Architecture forMobility Support in Wireless ATM Networks’ACM/Baltzer Mobile Networks and Applications, Vol. 1, No 3, December 1996.[6]Lee, W.C., ‘Overview of Cellular CDMA’, IEEE Transactions on Vehicular Technology, Vol. 40,No. 2, May 1991.[7]Gilhousen, K.S., Jacobs, I.M., Padovani, R., Viterbi, A.J., Weaver, L. A. and Wheatley III, C. E.,‘On the capacity of a Cellular CDMA System’, IEEE Transactions on Vehicular Technology, Vol.40, No. 2, May 1991.[8]Sourour, E. ‘Time Slot Assignment Techniques for TDMA Digital Cellular Systems’, IEEETransactions on Vehicular Technology, Vol. 43, No. 1, February 1994.[9]Larrinaga, F. and Carrasco, R.A., ‘Virtual Connection Tree Concept Application over CDMABased Cellular Systems’IEE Coll on ATM Traffic in the Personal Mobile Communications Environment, Savoy Place, London 11 Feb. 1997.[10]Larrinaga, F. and Carrasco, R.A., ‘Application of the VCT over Multiple Access Techniques usingFrequency Division’, submitted to IEEE Transactions. 2000.[11]Karim S.A., Hovell P., ‘Everything over IP - an overview of the strategic change in voice and datanetworks’, BT Technology Journal v 17, n 2, (1999), p 24-30.[12]Heath, A. and Carrasco, R. A., ‘Virtual Connection Tree Based Algorithms For 3G MobileCommunication Systems’PREP2000, University of Nottingham, 11-13 April 2000.[13]Acampora, A.S., Naghshineh, M., ‘An architecture and methodology for mobile-executed hand-offin cellular ATM networks’, IEEE Journal on Selected Areas in Communications, Vol: 12, Iss: 8, p. 1365-75, Oct. 1994, ISSN: 0733-8716.[14]Caceres R., Padmanabhan, V. N., ‘Fast and scalable wireless handoffs in support of mobile Internetaudio’, Mobile Networks and Applications v 3, n 4, (Jan 1999), p 351-363.[15]Balakrishnan H., Seshan S., Amir E., Katz R. H., ‘Improving reliable transport and handoff(TCP/IP) performance over wireless networks’, Proceedings of the Annual International Conference on Mobile Computing and Networking, MOBICOM, , (1995), p 2-11.[16]Balakrishnan H., Padmanabhan V. N., Seshan S., Katz, R. H., ‘Comparison of mechanisms forimproving TCP performance over wireless links’, IEEE/ACM Transactions on Networking, v 5, n 6, (Dec 1997), p 756-769.Alison HeathMEng, AMIEEA.L.Heath@andProfessor Rolando CarrascoBSc(Hons), PhD, CEng, FIEER.A.Carrasco@/personal/engineering_and_technology/alh2/School of Engineering& Advanced TechnologyVIRTUAL CONNECTION TREE OVER MULTIPLE ACCESS TECHNIQUES FOR 3GWIRELESS COMMUNICATION SYSTEMS18-20 July 2000Contentsl Introduction, to 3G communication systems l Background Theory–Multiple Access Techniques, ATM Modell VCT Service Adaptable Handoff Algorithm l VCT applied to multiple access techniques l CAC Algorithm–Fixed Channel Allocation/Dynamic Channel Allocationl Simulation Model and Results–Signalling BW, Failing Probability for FCA & DCA–BER for CDMA when PIC cancellation usedl Conclusions and Future WorkResearch Objectivesl Investigate the issues affecting the access to mobile ATM networksl Accommodate mixed types of information –Voice, data, images - Multimedia, and Mobilityl Reduce the amount of signalling, increase system capacityl Produce a more distributed systeml Simplify re-routing of information (handoffs)Backgroundl Accommodate mixed information types–with different QoS contracts l Allow Mobility and high BitRates with a finite Band Widthl Simplify the routing of information (handoffs)3GSystemsVoiceDataM3IMT-2000/UMTS cdma2000 WCDMAMultiple Access TechniquesCodeFrequencyTimeC h a n n e l 1C h a n n e l 2C h a n n e l 3C h a n n e l NFDMACodeFrequencyTimeCha nn el 1Cha nn el 2Cha nn el 3Cha nn el NT i m e Sl o t s TDMACodeFrequencyTimeChannel 1Channel 2Channel 3Channel NCDMAPRMApkt Npkt 1pkt 2pkt 3Asynchronous Transfer Mode (ATM)lDifferent types of services at different traffic rates using the same unique Universal Networkl Common Network Layer for all types of traffic lIntelligent Network that assures QoS lUMTS and Wireless ATM (Mobile )Physical &ConvergenceLayerATM Layer ATM Adaptation LayerHigher LayersHigher LayersControl PlaneUser Plane Management Plane ATM Protocol Reference ModelService Adaptable Handoff AlgorithmHandoff requestat BSWireless bw available?Type of service ?VCT with extendedcell sequencing AlgorithmBlocked ConnectionStandard VCT AlgorithmTransmission from new BS (VPI)Delay SensitiveCell Loss SensitiveNoYesBS 2BS 1MSCFixedNetworksEndpointObjectives •Test Algorithm Performance •Compare to Simple Virtual Connection Tree (VCT)Conditions •Diff. Call Rates •Diff. Services •MobilityMeasurements •Cell Loss •Cell mis-orderring •Cell Error Rate •Cell Delays8Cell Error Rate &Mean End-to-End Cell DelayCell Error Rate for ATM Handoff System0.000010.00010.0010.010.1500100015002000Transmission RateC e l l E r r o r R a t eStd Alg (Const)Std Alg (Var)Ext Alg (Const)Ext Alg (Var)Mean End-to-End Cell Delay2004006008000500100015002000Transmission Rate (kbits/sec)T i m e (µs )Std Alg (Const)Std Alg (Var)Ext Alg (Const)Ext Alg (Var)Variable traffic largermean delay than constant trafficHigher CER, bursty sources max = 0.085dtransmitte cells of no.errorsg sequencin of no. cells lost of no.CER +=9VCT applied tomultiple access techniquesVCT - CRDMA IntegrationBS 3BS 2BS 1MSCBS 1MSC 123VP switchesReserve PVP for BSs3vpi 1vci 4vci 2n+10vci n+3vci 2n+5vpi 2vpi 3BS 2BS 3MS VPI 11423n+3322n+10before h/o 332n+5after h/oVCI MS 1MS 2MS 3…MS m 11n+12n+1…(m-1)n+122n+22n+2…(m-1)n+233n+32n+3…(m-1)n+3…………nn 2n 3n …m nVCI Carrier10Carrier Communication (CAC) AlgorithmlPassing in real time information gathered at MSC to all BSs in VCT.()C1B S i +=MB IDCodeMB IDCodeMB IDCodeMB IDCodeMB IDCodeMB IDCodeMB ID CodeBS EBS CBS D BS G BS F BS A BS B REFMB ID…….Service TypeRate…….…….MAP at BS AActive User TableSize of MAP11CAC Algorithm ProcessesSet-up. Req.VCISet-up Frame BroadcastMSCAccess BSMSOther BS in VCTTable UpdateTable UpdateTermination. Req.Connection endedTermination Frame BroadcastTable UpdateTable UpdateMMMMSet-up & Termination ProcessChann . Req .Chann.+VCNDetect HandoffTable UpdateTable UpdateTable UpdateATM flow from/to MS (old BS)First ATM cells from MS in New BSHandoff Frame Broadcast ATM flow from/to MS (new BS)MSCOld BSNew BSMSOther BS in VCTHandoff ProcessCAC FrameslAllows 215(32768) users, 29(512) BSs and 211(2048)Carriersl Allows DCA schemeslSystem becomes distributedSet up FrameMB ID Number Ref. Number New BS Carrier ??bits15 bits9 bits11 bitsHandoff FrameNew BS Ref. Number New Carrier 9 bits15 bits11 bitsTermination Frame15 bitsRef. Number ServiceRate n bits51015202530k b i t s /s e c253649Number of BSs in VCTBandwidth Avg. 1 calls/sec Avg. 5 calls/sec Avg.10 calls/secPeak 1 calls/secPeak 5 calls/secPeak 10 calls/secBW Saved with CACSimulation Modell Band Width and Signalling in fixed network for CAC Algorithm l Comparison between FCA & DCA for TDMA, FDMA and PRMAlCAC at BS levelArea (M)77.94 miles2No. of BS16Call gen rate (avg, µ)1, 5, 10 call/sec Simulation Duration 500 3600 secChannels per BS 50Cluster sizes 3, 4 and 7FDMA 50; 1TDMA 17; 3PRMA 5; 10Speed 20 - 70 miles/h Length 30 - 240 sec.Directions (max)8No. channels and slots14Call Failing Probability,FDMA & TDMADCA allows higher traffic intensity of traffic than FCA until 4%DCA more efficient than FCA up to 15%Call Failing Probability, TDMA 16BS1234568.58.7599.259.59.751010.2510.510.7511Traffic Intensity/mile2%FCA Cluster 3Cluster 4Cluster 7Call Failing Probability, FDMA 16BS01234568.58.7599.259.59.751010.2510.510.7511Traffic Intensity/mile2%FCA Cluster 3Cluster 4Cluster 7FDMA more efficient than TDMA15CDMACall Failing Probability CDMA123416253649Number of BSs%510Adjacent Cell Interference (7*3)-3.5-3-2.5-2-1.5-1-0.5002468101214Own Cell cancellation 3 Cell Cancellation One Cell 7 users 3 Cells (No Cancellation)1 user (no interference)As the number of BSs increase the probability of a call failing decreasesWith cancellation gives >0.5db improvement at SNR of 12dBSNR (dB)B E R (d B )Call Failing Probability510152025308.669.029.419.8410.3110.83Traffic Intensity / mile2%FCA FCA (0.85)FCA (0.75)FCA (0.65)Call Dropping Probability0.511.522.58.669.029.419.8410.3110.83Traffic Intensity / mile 2%FCA FCA (0.85)FCA (0.75)FCA (0.65)Call dropping probability increases as threshold is reducedProbability of a call failing is dramatically reduced as the threshold is increased.(Optimal threshold of 0.15)Call Failing Probability (DCA)51015202530358.669.029.419.8410.3110.83Traffic Intensity / mile2%Cluster 7DCA Cluster 7 (0.85)DCA Cluster 7 (0.75)DCA Cluster 7 (0.65)Call Dropping Probability (DCA)0.511.522.58.669.029.419.8410.3110.83Traffic Intensity / mile2%Cluster 7DCA Cluster 7 (0.85)DCA Cluster 7 (0.75)DCA Cluster 7 (0.65)• Call dropping probability reduces to very small value at thresholds of 0.25, 0.35 for DCA • Call failing probability less for DCA than FCA.• Optimal threshold value of 0.15Signalling SavedAmount of Signalling (FCA)20040060080010001200140016008.669.029.419.8410.3110.83Traffic Intensity / mile2b i t /s e cFCA (0.85)FCA (0.75)FCA (0.65)Amount of Signalling (DCA cluster 7)20040060080010001200140016008.669.029.419.8410.3110.83Traffic Intensity / mile2b i t /s e cDCA Cluster 7 (0.85)DCA Cluster 7 (0.75)DCA Cluster 7 (0.65)The amount of signalling saved increases with traffic intensity and with a reduction of threshold, which reduces the processing at the MSCConclusionsl Applying the VCT to all the different multiple access methods has proved advantageous, in the reduction signalling traffic.l The peak bandwidth of the algorithm varies from 5.76kbits/sec to 26.88kbits/sec this is small considering the rates used in ATM networks (150Mbit/sec).l DCA for FDMA provided improvements of 0.87, 0.63 and 0.48 Erlang/mile2 are shown for cluster sizes of 7, 3 and 4 respectively at a failing probability of 1%. Next was TDMA with 0.43, 0.2 and 0.12 Erlang/mile2 for clusters of 7, 3 and 4respectively at a failing probability of 0.5%.l In CDMA interference was removed from signals, improving the BER curve.l There is more work required for the packet switched applications and IP transport protocolsl For all multiple access methods are more distributed system has been created, for FDMA the signalling saved for FCA & DCA was illustrated, this is similar for all the multiple access schemes.Future Workl Investigate reasons for cell sequence errors at high speeds l Implement similar Algorithm for TCPl Implement a packet switched B-ISDN system to run on top of IPl Investigate multiple access schemes such as cdma2000, WCDMA, TDMA, FDMA。

合集下载

swi-ov

swi-ov

Chapter7Overview of Layer2 SwitchingIntroduction ................................................................................................... 7-2Switch Ports ................................................................................................... 7-2Enabling and Disabling Switch Ports ........................................................ 7-2Autonegotiation of Port Speed and Duplex Mode .................................... 7-3Port Trunking .......................................................................................... 7-3Link Access Control Protocol (LACP) ........................................................ 7-3Packet Storm Protection .......................................................................... 7-3Port Mirroring ......................................................................................... 7-3Port Security ............................................................................................ 7-4Virtual Local Area Networks (VLANs) .............................................................. 7-4Creating VLANs ....................................................................................... 7-5Summary of VLAN tagging rules .............................................................. 7-6VLAN Interaction with STPs and Trunk Groups ......................................... 7-6Generic VLAN Registration Protocol (GVRP) .................................................... 7-6Quality of Service ........................................................................................... 7-7Spanning Tree Protocol (STP) .......................................................................... 7-8Spanning Tree and Rapid Spanning Tree Port States ................................. 7-8Multiple Spanning Tree Protocol (MSTP) ................................................... 7-9IGMP Snooping ............................................................................................. 7-9Triggers .......................................................................................................... 7-97-2AlliedWare OS Software ReferenceSoftware Version 2.9.1C613-03126-00REV AIntroductionThis chapter outlines the Layer 2 and IP switching features on the switch, andhow to configure some of them. For more detail, see:■Chapter 8, Switching ■Chapter 40, Quality of Service (QoS) on Switch PortsSwitch PortsEach switch port is uniquely identified by a port number. The switch supportsa number of features at the physical level that allow it to be connected in avariety of physical networks. This physical layer (layer 1) versatility includes:■Enabling and disabling of ports.■Auto negotiation of port speed and duplex mode for all 10/100 BASE ports.■Manual setting of port speed and duplex mode for all 10/100 BASE ports.■Link up and link down triggers.■Port trunking.■Packet storm protection.■Port mirroring.■Support for SNMP management.Enabling and Disabling Switch PortsAn switch port that is enabled is available for packet reception andtransmission. Its administrative status in the Interfaces MIB is UP. Disabling aswitch port does not affect the STP operation on the port. Enabling a switchport will allow the port to participate in spanning tree negotiation. A switchport that has been disabled by the Port Security feature cannot be enabledusing the ENABLE SWITCH PORT command.To enable or disable a switch port, use the commands:ENABLE SWITCH PORT={port-list |ALL}DISABLE SWITCH PORT={port-list |ALL}Resetting ports at the hardware level discards all frames queued for receptionor transmission on the port, and restarts autonegotiation of port speed andduplex mode. Ports are reset using the command:RESET SWITCH PORT={port-list |ALL} [COUNTER]To display information about switch ports, use the command:SHOW SWITCH PORT[={port-list |ALL}]Overview of Layer2 Switching7-3Software Version2.9.1 C613-03126-00REV A Autonegotiation of Port Speed and Duplex ModeEach of the switch ports can operate at either 10 Mbps or 100 Mbps, in either full duplex or half duplex mode. In full duplex mode a port can transmit and receive data simultaneously, while in half duplex mode the port can either transmit or receive, but not at the same time. This versatility makes it possible to connect devices with different speeds and duplex modes to different ports on the switch. Such versatility also requires that each port on the switch know which speed and mode to use.Port TrunkingPort trunking, also known as port bundling or link aggregation, allows a number of ports to be configured to join together to make a single logical connection of higher bandwidth. This can be used where a higher performance link is required, and makes links even more reliable.Link Access Control Protocol (LACP)The Link Access Control Protocol (LACP) follows the IEEE Standard802.3-2002, CSMA/CD access method and physical layer specifications. It enables trunk groups, called aggregated links, to be created automatically. LACP operates where systems are connected over multiple communication links. It constantly monitors these links and automatically adds or removes them from trunk groups.Packet Storm ProtectionThe packet storm protection feature allows you to set limits on the reception rate of broadcast, multicast and destination lookup failure packets. The software allows separate limits to be set for each port, beyond which each of the different packet types are discarded. The software also allows separate limits to be set for each of the packet types. Which of these options can be implemented depends on the model of switch hardware.Port MirroringPort mirroring allows traffic being received and transmitted on a switch port to be sent to another switch port, the mirror port, usually for the purposes of capturing the data with a protocol analyser. This mirror port is the only switch port that belongs to no VLANs, and therefore does not participate in any other switching. Before the mirror port can be set, it must be removed from all VLANs except the default VLAN. The port cannot be part of a trunk group.7-4AlliedWare OS Software ReferenceSoftware Version 2.9.1C613-03126-00REV APort SecurityThe port security feature allows control over the stations connected to eachswitch port, by MAC address. If enabled on a port, the switch will learn MACaddresses up to a user-defined limit from 1 to 256, then lock out all other MACaddresses. One of the following options can be specified for the action takenwhen an unknown MAC address is detected on a locked port:■Discard the packet and take no further action,■Discard the packet and notify management with an SNMP trap,■Discard the packet, notify management with an SNMP trap and disable the port.Virtual Local Area Networks (VLANs)A Virtual LAN (VLAN) is a logical, software-defined subnetwork. It allowssimilar devices on the network to be grouped together into one broadcastdomain, irrespective of their physical position in the network. Multiple VLANscan be used to group workstations, servers, and other network equipmentconnected to the switch, according to similar data and security requirements.Decoupling logical broadcast domains from the physical wiring topologyoffers several advantages, including the ability to:■Move devices and people with minimal, or no, reconfiguration ■Change a device’s broadcast domain and access to resources withoutphysically moving the device, by software reconfiguration or by moving itscable from one switch port to another■Isolate parts of the network from other parts, by placing them in differentVLANs■Share servers and other network resources without losing data isolation orsecurity■Direct broadcast traffic to only those devices which need to receive it, toreduce traffic across the network■Connect 802.1Q-compatible switches together through one port on eachswitch Devices that are members of the same VLAN only exchange data with eachother through the switch’s switching capabilities. To exchange data betweendevices in separate VLANs, the switch’s routing capabilities are used. Theswitch passes VLAN status information, indicating whether a VLAN is up ordown, to the Internet Protocol (IP) module. IP uses this information todetermine route availability.The switch has a maximum of 255 VLANs, ranging from a VLAN identifier(VID) of 1 to 4094. When the switch is first powered up, a “default” VLAN iscreated and all ports are added to it. In this initial unconfigured state, theswitch will broadcast all the packets it receives to the default VLAN. ThisVLAN has a VID of 1 and an interface name of vlan1. It cannot be deleted, andports can only be removed from it if they also belong to at least one otherOverview of Layer2 Switching7-5Software Version2.9.1 C613-03126-00REV A VLAN. The default VLAN cannot be added to any STP, but always belongs to the default STP. If all the devices on the physical LAN are to belong to the same logical LAN, that is, the same broadcast domain, then the default settings will be acceptable, and no additional VLAN configuration is required. Creating VLANsTo briefly summarise the process of creating a VLAN:1.Create the VLAN.2.Add tagged ports to the VLAN, if required.3.Add untagged ports to the VLAN, if required.To create a VLAN, use the command:CREATE VLAN=vlan-name VID=2..4094Every port must belong to a VLAN, unless it is the mirror port. By default, all ports belong to the default VLAN as untagged ports.To add tagged ports to a VLAN, use the command:ADD VLAN={vlan-name|1..4094} PORT={port-list|ALL}FRAME=TAGGEDA port can be tagged for any number of VLANs.To add untagged ports to a VLAN, use the command:ADD VLAN={vlan-name|1..4094} PORT={port-list|ALL}[FRAME=UNTAGGED]A port can be untagged for zero or one VLAN. A port can only be added to the default VLAN as an untagged port if it is not untagged for another VLAN. A port cannot transmit both tagged and untagged frames for the same VLAN (that is, it cannot be added to a VLAN as both a tagged and an untagged port). To remove ports from a VLAN, use the command:DELETE VLAN={vlan-name|1..4094} PORT={port-list|ALL} Removing an untagged port from a VLAN will return it to the default VLAN, unless it is a tagged port for another static VLAN. An untagged port can only be deleted from the default VLAN if the port is a tagged port for another static VLAN.Ports tagged for some VLANs and left in the default VLAN as untagged ports will transmit broadcast traffic for the default VLAN. If this is not required, the unnecessary traffic in the switch can be reduced by deleting those ports from the default VLAN.To change the tagging status of a port in a VLAN, use the command: SET VLAN={vlan-name|1..4094} PORT={port-list|ALL}FRAME=TAGGEDTo destroy a VLAN, use the command:DESTROY VLAN={vlan-name|2..4094|ALL}7-6AlliedWare OS Software ReferenceVLANs can only be destroyed if no ports belong to them.To display the VLANs configured on the switch, use the command:SHOW VLAN[={vlan-name|1..4094|ALL}]To view packet reception and transmission counters for a VLAN, use thecommand (see Chapter11, Interfaces):SHOW INTERFACE=VLAN n COUNTERSummary of VLAN tagging rulesWhen designing a VLAN and adding ports to VLANs, the following rulesapply.1.Each port, except for the mirror port, must belong to at least one staticVLAN. By default, a port is an untagged member of the default VLAN.2. A port can be untagged for zero or one VLAN. A port that is untagged fora VLAN transmits frames destined for that VLAN without a VLAN tag inthe Ethernet frame.3. A port can be tagged for zero or more VLANs. A port that is tagged for aVLAN transmits frames destined for that VLAN with a VLAN tag,including the numerical VLAN Identifier of the VLAN.4. A port cannot be untagged and tagged for the same VLAN.5.The mirror port, if there is one, is not a member of any VLAN.VLAN Interaction with STPs and Trunk GroupsVLANs may have ports in more than one STP, when the ports belong tomultiple VLANs. VLANs can belong to multiple STPs.All the ports in a trunk group must have the same VLAN configuration: theymust belong to the same VLANs and have the same tagging status, and canonly be operated on as a group.Generic VLAN Registration Protocol(GVRP)The GARP application GVRP allows switches in a network to dynamicallyshare VLAN membership information, to reduce the need for staticallyconfiguring all VLAN membership changes on all switches in a network. Fordetailed information see Chapter10, Generic Attribute Registration Protocol(GARP).Software Version2.9.1C613-03126-00REV AOverview of Layer2 Switching7-7Software Version2.9.1 C613-03126-00REV A Quality of ServiceQuality of Service (QoS) enables you to prioritise traffic and/or limit the bandwidth available to it. The concept of QoS is a departure from the original networking protocols, which treated all traffic on the Internet or within a LAN the same. Without QoS, every different traffic type is equally likely to be dropped if a link becomes oversubscribed. This approach is now inadequate in many networks, because traffic levels have increased and networks transport time-critical applications such as streams of video data. QoS also enables service providers to easily supply different customers with different amounts of bandwidth.Configuring Quality of Service involves two separate stages:1.Classifying traffic into flows, according to a wide range of criteria.Classification is performed by the switch’s packet classifier. It is described in Chapter39, Generic Packet Classifier.2.Acting on these traffic flows.Approaches, methods and commands for this are described Chapter40, Quality of Service (QoS) on Switch Ports.Rapier i Series switches include full QoS functionality, including■policies, to provide a QoS configuration for a port or ports■traffic classes, for bandwidth limiting and user prioritisation■maximum bandwidth limiting on a traffic class■flow groups within traffic classes, for user prioritisation■control of the egress scheduling algorithm■priority relabelling of frames, at Layer 2, by replacing the VLAN tag User Priority field■class of service relabelling of frames, at Layer 3, by replacing the DSCP (DiffServ Code Point) or the TOS precedence value in the IP header’s Type of Service (TOS) fieldT able 7-1: The different QoS-type controls available on the switchCommand set Use for Do not use forQoS Bandwidth limiting of classified traffic flows.Priority queuing of classified traffic flows.Replacing TOS or DSCP byte of IP header.Replacing User Priority in VLAN tag header.Providing a coordinated QoS solution for a port orports, using the QoS policy model.Configuring a DiffServ domain.Limiting total bandwidth on a port, unless other QoS controls are also required.7-8AlliedWare OS Software Reference Software Version 2.9.1C613-03126-00REV ASpanning Tree Protocol (STP)The Spanning Tree Protocol (STP) makes it possible to automatically disableredundant paths in a network to avoid loops, and enable them when a fault inthe network means they are needed to keep traffic flowing. A sequence ofLANs and switches may be connected together in an arbitrary physicaltopology resulting in more than one path between any two switches. If a loopexists, frames transmitted onto the extended LAN would circulate around theloop indefinitely, decreasing the performance of the extended LAN. On theother hand, multiple paths through the extended LAN provide the opportunityfor redundancy and backup in the event of a bridge experiencing a fatal errorcondition.The spanning tree algorithm ensures that the extended LAN contains no loopsand that all LANs are connected by:■Detecting the presence of loops and automatically computing a logicalloop-free portion of the topology, called a spanning tree . The topology isdynamically pruned to a spanning tree by declaring the ports on a switchredundant, and placing the ports into a ‘Blocking’ state.■Automatically recovering from a switch failure that would partition theextended LAN by reconfiguring the spanning tree to use redundant paths,if available.Spanning Tree and Rapid Spanning Tree PortStatesIf STP is running in STANDARD mode, then each port can be in one of fiveSpanning Tree states, and one of two switch states. If STP is running in RAPIDmode, then each port can be in one of four states. The state of a switch port isHardware packet filters Priority queuing of classified traffic flows.Replacing TOS or DSCP byte of IP header.Replacing User Priority in VLAN tag header.Forwarding a flow that is marked to be dropped (forexample, because bandwidth allocation is exceeded).Specifying actions for packets which match the ingressand egress ports of a classifier (if set), but do not matchthe classifier’s other parameters.Configuring a simple DiffServ domain.Bandwidth limiting.Configuring most DiffServ yer 3 switch filters Priority queuing of up to 16 distinctly different types of traffic flow.Replacing TOS or DSCP byte of IP header.Replacing User Priority in VLAN tag header.QoS for non-IP traffic (e.g. IPX).QoS based on VLANs.Bandwidth limiting.SET SWITCH PORT Limiting total ingress and/or egress bandwidth onports.Limiting bandwidth of particular types of traffic.Limiting egress bandwidth if priorityqueuing is also required.T able 7-1: The different QoS-type controls available on the switch (cont.)Command set Use for Do not use forOverview of Layer2 Switching7-9Software Version2.9.1 C613-03126-00REV A taken into account by STP. To be involved in STP negotiations, STP must be enabled on the switch, the port must be enabled on the switch, and enabled for the STP it belongs to.Multiple Spanning Tree Protocol (MSTP)Multiple Spanning Tree Protocol (MSTP) was developed to address limitations in the existing protocols, Spanning Tree Protocol (STP) and Rapid Spanning Tree Protocol (RSTP). These limitations apply mainly to networks that use multiple VLANS with topologies employing alternative physical links. MSTP is defined in IEEE Standard802.1Q 2003.For detailed information, see “Multiple Spanning Tree Protocol (MSTP)” on page9-13 of Chapter9, Spanning Trees.IGMP SnoopingIGMP (Internet Group Management Protocol) is used by IP hosts to report their multicast group memberships to routers and switches. IP hosts join a multicast group to receive broadcast messages directed to the multicast group address. IGMP is an IP-based protocol and uses IP addresses to identify both the multicast groups and the host members. For a VLAN-aware devices, this means multicast group membership is on a per-VLAN basis. If at least one port in the VLAN is a member of a multicast group, by default multicast packets will be flooded onto all ports in the VLAN.IGMP snooping enables the switch to forward multicast traffic intelligently on the switch. The switch listens to IGMP membership reports, queries and leave messages to identify the switch ports that are members of multicast groups. Multicast traffic will only be forwarded to ports identified as members of the specific multicast group.IGMP snooping is performed at Layer 2 on VLAN interfaces automatically. By default, the switch will only forward traffic out those ports with multicast listeners, therefore it will not act as a simple hub and flood all multicast traffic out all ports. IGMP snooping is independent of the IGMP and Layer 3 configuration, so an IP interface does not have to be attached to the VLAN, and IGMP does not have to be enabled or configured.IGMP snooping is enabled by default. To disable it, use the command: DISABLE IGMPSNOOPINGFor more information, see Chapter27, IP Multicasting.TriggersThe Trigger Facility can be used to automatically run specified command scripts when particular triggers are activated. When a trigger is activated by an event, global parameters and parameters specific to the event are passed to the script that is run. For more information, see Chapter60, Trigger Facility.7-10AlliedWare OS Software ReferenceThe switch can generate triggers to activate scripts when a fibre uplink portloses or gains coherent light. To create or modify a switch trigger, use thecommands:CREATE TRIGGER=trigger-id MODULE=SWITCHEVENT={LIGHTOFF|LIGHTON} PORT=port [AFTER=hh:mm][BEFORE=hh:mm] [DATE=date|DAYS=day-list] [NAME=name][REPEAT={YES|NO|ONCE|FOREVER|count}] [SCRIPT=filename...][STATE={ENABLED|DISABLED}] [TEST={YES|NO|ON|OFF}]SET TRIGGER=trigger-id PORTS={port-list|ALL} [AFTER=hh:mm][BEFORE=hh:mm] [DATE=date|DAYS=day-list] [NAME=name][REPEAT={YES|NO|ONCE|FOREVER|count}][TEST={YES|NO|ON|OFF}]The following sections list the events that may be specified for the EVENTparameter, the parameters that may be specified as module-specific-parameters,and the arguments passed to the script activated by the trigger.Event LINKDOWNDescription The port link specified by the PORT parameter has just gone down.Parameters The following command parameter(s) must be specified in the CREATE/SETTRIGGER commands:Parameter DescriptionPORT=port The port on which the event will activate the trigger.Script Parameters The trigger passes the following parameter(s) to the script:Argument Description%1The port number of the port which has just gone down.Event LINKUPDescription The port link specified by the PORT parameter has just come up.Parameters The following command parameter(s) must be specified in the CREATE/SETTRIGGER commands:Parameter DescriptionPORT=port The port on which the event will activate the trigger.Script Parameters The trigger passes the following parameter(s) to the script:Argument Description%1The port number of the port which has just come up.Software Version2.9.1C613-03126-00REV A。

浙江省浙南名校2023-2024学年高二下学期4月期中英语试题

浙江省浙南名校2023-2024学年高二下学期4月期中英语试题

浙江省浙南名校2023-2024学年高二下学期4月期中英语试题学校:___________姓名：___________班级：___________考号：___________一、阅读理解Formerly known as Virtual Field Trips, PacSci’s Digital Discovery Workshops bring unique science experiences to you on your own schedule. With a focus on real world applications and spotlighting STEM careers, they bring classroom content to life and support Next Generation Science Standards (NGSS). Beyond your live class, each program includes a teacher toolkit packed with additional resources such as reading lists, hands-on activity guides, and STEM videos to extend the learning experience.WHO ARE THESE FORDigital Discovery Workshops are designed for Pre K-12 graders joining from classrooms, library programs, or other community groups. Most programs have a max of 50 students to encourage a high level of interactivity for 1-2 classes per program.HOW THEY WORKPacSci educators send you a private Zoom link, or join a virtual platform of your choice. Meet your educator for a short tech check, then start your 40-minute live program.COSTS & BOOKING1-9 participants: $20 per person10-49 participants: $30 per person50+ participants: $40 per personQualified low-income schools will receive a 70% discount. Programs should be booked at least 2 weeks in advance.WHAT YOU WILL NEED● One computer with a screen and speaker● Internet connection● Access to your selected virtual platform, such as Zoom, Teams, or Google Meet● A webcam and microphone● An adult must be present to help facilitateClick on the link below and check out our Program Requirements and Pre-Program Checklist for more details.1．Who will most probably sign up for the program?A．A Pacsci educator. B．A field trip guide.C．A 9th grader. D．A community librarian.2．How much will 10 students in a qualified low-income school pay?A．$90. B．$180 C．$210. D．$300.3．What is necessary for participants?A．A mobile phone. B．Connected Internet.C．Selected teams. D．A peer friend.Our ship sailed on the sea into the Earth’s night. Here, there was no visible light from the Sun or the Earth Engines. But as we looked up, we children saw the starry sky for the first time in our lives. How breathtakingly beautiful it was!Ms Xing put an arm around us while pointing at the sky with her other hand. “Look, children! That is Proxima Centauri (比邻星), our new home!” With these words, tears ran slowly down her face. Before long, we were all in tears—even the captain and crew. We all looked in the direction that Ms Xing was pointing. There was only one point of light among the twinkling stars that shined constantly: Proxima Centauri—the only source of hope and comfort for a hundred future generations. “Whatever risks we might take, we will finally make it there!” said the captain, in an assured voice.On our way back from the sea, we saw the first sign that Earth had begun its journey. In the night sky, a huge comet had appeared. It was the Moon, abandoned by humankind. Lunar Engines had been installed to the Moon to force it out of its orbit so that a disastrous crash could be avoided as the Earth sped up and moved away. As it progressed, the gravitational tide of the Moon caused the ocean to swell, creating gigantic waves. We quickly got off the ship to our destination in the Southern Hemisphere. The next few days were the countdown to our departure.Finally came the big day! As Earth Engines was set at a full power, we got immediately blinded by the bright light from it. This acceleration created massive tsunamis hundreds of meters high that crashed onto the coasts of every continent. Burning hot hurricanes roared through the boiling waves, screaming with wild fury and pulling up almost every tree on Earth.Our Earth, with its blue tail cutting through the darkness of space, had set out on its long journey, and with it went all of humankind.4．Why did we all cry when looking up into the sky?A．Because we had to abandon the Earth.B．Because we were fascinated by the stars.C．Because we saw our new settlement.D．Because we felt lonely in the universe.5．What was the function of the Lunar Engines?A．To protect the Earth from a deadly impact.B．To make sure the Moon runs in its orbit.C．To keep the moon at the same speed as the Earth.D．To shelter humans from the tide of the Moon.6．Which of the following words can best describe the journey?A．Smooth and steady. B．Endless and hopeless.C．Exciting and entertaining. D．Ambitious and adventurous.7．Where is the text probably taken from?A．A personal diary. B．A science fiction.C．A travel magazine. D．An academic article.In the summer of 2021, the Pacific Northwest experienced a severe heatwave that caused widespread panic and destruction. Temperatures reached record levels, including 114℉in Portland.A heatwave, born over the Pacific, drifted inland and grew in intensity, creating a heat dome. Ice was the first victim, and as snowpacks melted, glaciers released fast flowing muddy water that flooded towns. Salmon, sensing the water temperature change, began migrating early. But then they struggled to breathe as the rivers warmed. Vegetation was next—unable to escape the heat, it struggled to hold water. Bighorn sheep moved to higher ground, doves panted like dogs, baby eagles jumped to their deaths in an attempt to fly to escape overheating with their siblings.In 72 hours, the official number of human deaths was 1,000—but the actual number is likely higher, especially among the elderly, poor, and medically vulnerable. The town of Lytton, British Columbia was burned down when temperatures there hit 121℉. Over a billion sea creatures met their deaths over the three days.Such a heatwave in the Pacific Northwest had been thought to be as likely as snow in theSahara. But then it happened. Right now, scientists can’t predict where or when such heat will appear next, but they do know that occurrences such as this are a direct result of human activities. As fossil-fuel burning increases levels of heat-trapping gases like carbon dioxide, the planet warms. Heat is the prime mover of climate chaos, melting ice, . drying soil, , and even reviving ancient bacteria from thawed permafrost (永冻土解冻).Humans might be able to engineer their way out of anything—cities like Los Angeles and Paris are already working to deflect (使偏斜) sunlight and have more shade trees. But there are limits to adaptation for Earth’s population o f nearly 8 billion. Parts of the Middle East and South Asia are already too hot for humans in summer.8．How is the impact of the heatwave presented in Paragraph 2?A．By telling a story. B．By listing examples.C．By giving a definition. D．By making comparisons.9．What does the underlined word “vulnerable” in Paragraph 3 mean?A．Protected. B．Disturbed. C．Healthy. D．Weak.10．What can we learn from the last two paragraphs?A．People considered the heatwave in the Pacific Northwest as common.B．Such heat will certainly appear again as a result of human activities.C．Los Angeles and Paris have already helped themselves out of heatwaves.D．The earth’s adaptability to heatwaves has limits with such a large population. 11．Which of the following can be the best title for the text?A．Temperatures Reaching Record High B．Human Activities Causing a HeatwaveC．A Heatwave Hitting the Pacific Northwest D．Panic and Destruction Caused by a HeatwaveIf you find yourself embracing the thrilling chaos of completing tasks at the last minute, congratulations—You are not alone! According to a survey, 20% of U.S. adults procrastinate (拖延) at home, at work, in relationships, and more. Another survey found that 88% of people procrastinate at least one hour a day.Sounds alarming? As it tu rns out, if you’re feeling stressed, you may be more likely to procrastinate. Essentially, our brains are structured to approach tasks we find enjoyable and avoidthose we are afraid of. Our limbic brain (边缘大脑), the emotional part of our brain, is screaming, “Let’s do anything but that stressful thing!” while our prefrontal cortex (前额叶皮层) is the CEO of our brain, setting the goals, making a plan, and ensuring we stay on track. CEO vs. Drama Queen Brain — who will win? Actually, there do exist chances when our limbic brain overrides that prefrontal cortex message.Then there’s the burst of energy we often get when we’re up against a deadline, which leads to a reward pathway within our brains and sets the foundation for procrastination as a habit. When you race to the end and get to the goal finally, your previous stress is gone and you almost get in that pattern of “See, I work better under pressure!”So, how to beat procrastination? Well, you need to retrain your brain to cope with the stress. One trick is to take periodic breaks (reward) to refocus your attention on the task. Ever heard of the Promodoro Technique? It’s about working for 25 minutes and resting for 5. During those breaks, forget about brain-burning activities — try relaxing techniques such as meditation or yoga instead. Another trick is to “eat the frog” first thing in the morning, or tackle the most difficult and stressful task of the day, as was once said by Mark Twain.12．Why are the two surveys mentioned in the first paragraph?A．To warn the readers. B．To introduce a concept.C．To present a phenomenon. D．To make a comparison.13．Which of the following statements will the author most probably agree with?A．We are born to prefer what we like and avoid what we fear.B．The limbic brain is under the control of the prefrontal cortex.C．We are more likely to burst when getting close to the deadline.D．Failing to complete a task can lead to habitual procrastination.14．What does the author suggest readers do to stop procrastination?A．Force the brain to focus. B．Take a break regularly.C．Solve a tricky math problem. D．Eat something refreshing first.15．What is the tone of this text?A．Humorous. B．Ironic. C．Serious. D．Unclear.Choosing artwork can feel like an exhausting task if you have no idea where to start andyou can end up staring at a blank wall waiting for that enlightening moment. From traditional landscapes to family photos, the options are endless. 16Look for inspiration in interiors magazines, as well as online, and visit independent stores to figure out what styles appeal to you. There are no set rules when it comes to artwork preferences. 17 Then, make space for it on your walls.Depending on your budget, there are different places you can begin your search for artwork.18 The Affordable Art Fair, for example, features work by a wide range of artists, with pieces that won’t cost the earth. If you prefer prints (which are often more affordable in comparison), take a look at high street shops. Alternatively, many online ones are offering printable designs that you download and print yourself at home.19 Typographic prints will inject the space with a sense of fun and a cool, contemporary feel. Black and white photography, on the other hand, can stimulate a more depressing atmosphere. The colours used in the piece will also be something to consider—greens and blues have comforting properties so are mild for a bedroom. Bolder and brighter tones, on the contrary, suit dynamic areas better.Once you’ve chosen your artwork, it’s time to think about how best to showcase it around your home. Gallery walls are a popular way if you want to create a central point. 20 By the way, you can add vases and potted plants to create another dimension.A．So, how to choose artwork for your home?B．Don’t be afraid of mixing together different styles.C．Picture ledges, or small shelves, are also an ideal choice.D．Trust your feeling if something makes you stop, smile or think.E．Art fairs are a great place to dive in, even if just for inspiration.F．Apart from the style of your chosen artwork, the size of it also needs to be considered. G．The type of artwork you choose can set the tone of a room and greatly impact the mood.二、完形填空My son had just got his driving license. On the way home, I pulled the car over and 21 seats with him, making him drive home. “No, I’m not ready,” he took a deep breath, and 22my father’s words, “Don’t apologize for knowing your 23 .” For a brief moment, time froze.I 24 my family riding the highest roller coaster then at an amusement park one summer. I was secretly terrified of 25 . Not wanting to be the only one to stay behind, I 26 to myself, you can do this, you can do this, trying to 27 my nerves.It was time to step into the waiting area. My body was 28 with fear. At that moment I knew: I just couldn’t do it and finally 29 my fear. Too 30 to face my family, I simply called to Dad that I was leaving.Soon they showed up. No one looked very thrilled about what they had just experienced. I began to feel 31 relieved when I looked up and 32 Dad’s inquiring eyes. “I was just too chicken. Sorry.” I murmured.“Don’t ever apologize for knowing your limits. Don’t eve r let anyone 33 you do something you’re not comfortable with.” This was the exact 34 of what I expected him to say.Instantly, I understood how my son felt. Knowing the limits isn’t a(n) 35 of weakness, but a sign of strength.21．A．shared B．found C．switched D．reserved 22．A．informed B．echoed C．reminded D．grasped 23．A．errors B．weaknesses C．highlights D．limits 24．A．recalled B．anticipated C．imagined D．caught 25．A．budget B．heights C．failure D．conflicts 26．A．repeated B．yelled C．turned D．waved 27．A．set B．lose C．affect D．calm 28．A．blank B．solid C．rigid D．flexible 29．A．face up to B．give in to C．come up with D．reach out for 30．A．relaxed B．delighted C．surprised D．embarrassed 31．A．somehow B．enough C．little D．somewhat 32．A．met B．locked C．avoided D．resisted 33．A．witness B．make C．suggest D．observe 34．A．opposite B．remark C．explanation D．objection35．A．outcome B．display C．indication D．admission三、语法填空阅读下面短文，在空白处填入1个适当的单词或括号内单词的正确形式。

关于一台电脑安装多个(虚拟)网卡问题

关于一台电脑安装多个(虚拟)网卡问题

一台电脑安装多个(虚拟)网卡问题1、 VMware是什么？从某种意义上说，一台物理计算可以做什么，VMware Workstation 的虚拟机就可以做什么。

从理论上讲，VMware 可以做的事情只受到硬件和想象力的限制。

它支持的客户操作系统涵盖绝大多数主流操作系统，包括 Microsoft 全系列的操作系统以及大多数版本的 Linux。

由于虚拟机运行时使用同一个虚拟 BIOS 以及一系列统一的虚拟硬件，在一定程度上实现了虚拟机的硬件无关性，并且客户操作系统中的所有内容在主机上以文件形式存在，所以又具有可携带性和可迁移性。

最值得关注的是 VMware 强大的网络功能，你可以在一台计算机上建立一个局域网，这个网络的行为与真实的网络完全一致，而且你不用担心虚拟网卡和虚拟交换机会损坏，这样你就可以抛开真实网络中各种琐碎的硬件冲突的可能性，潜下心来通过虚拟网络研究物理网络的核心逻辑。

VMWare支持如下Guest OS：MS-DOS、Win3.1、Win9x/Me、WinNT、Win2000、WinXP、、Linux、FreeBSD、NetWare6、Solaris x86。

不支持的Guest OS：BeOS、IBM OS/2 and OS/2 Warp、Minix、QNX、SCO Unix、UnixWare。

2.Vm安装这个和WINDOWS的其他软件一样，用默认的安装方法就可以。

3．VM的配置1）选择菜单理的FILE>>NEW>>Virtual Machine创建一个新的虚拟机.2)选择下一步.Typical,典型设置3)下一步是选择你要设置的虚拟机操作系统,这个我选的是LINUX.根据个人的需要可以选择你要的操作系统.我不清楚选择其他操作系统是否对虚拟机有影响,但是我选OTHERS装的LINUX也是正常使用的.4)填写你的虚拟机安装的位置和你使用的名字,名字么,选个形象好记的就行,位置要注意,因为VM是装在WINDOWS操作系统下的,所以如果你选择的硬盘空间不够,那就无法安装.5)network connection网络连接,第一个是和现有的网络相连,第二个使用NAT,第三个是选择独立的主机,并和主机相连,第四个是不使用网络连接.我选择的是第一个,后面再讲网络的具体设置.6)磁盘空间这里有两个选项,第一个是手动设置磁盘大小,第二个是使用磁盘的剩余空间.安装2000最少要在系统上预留4G的空间,因为划分的空间不可修改,所以你一定要规划好你的硬盘大小,不然以后只能重新安装了.LINUX我设置的是5个GB.,最小也要给3个G因为,LINUX安装了编译器和系统服务最少就要这么多的空间了.建议划分5G以上.7)设置完成.二.安装完后在系统中左侧出现了你设置的系统名字我这里是REDHAT LINUX,但是必须要安装了系统之后才能使用.选择你的系统名称.右侧出现的是你系统的配置.COMMAND栏目有3项,第一个是启动虚拟机.START有个绿色的三角的.第二个是编辑虚拟主机设置第三个是COPY你已经安装好的系统.这个功能我没有用过,应该是连系统带软件都可以复制过去的.三.编辑主机的设置.虚拟主机的设置有内存大小,磁盘位置,网卡,USB设备,声卡,CPU等项目,在你希望修改的项目上双击就可以进出现配置对话框.首先的是内存,VM默认的是使用你当前可用内存的一半.你可以根据你系统的实际情况调整你的虚拟机使用的内存.第二个是硬盘,这个一般不用改,除非你有两块物理硬盘.第三个是CDROM.双击进入设置对话框.Divice status设备状态:一个是连接,另一个在开机时连接.默认选择的2,这里所谓的开机连接是你启动虚拟机时进行连接.底下有连接选项.第一个是使用物理设备.Use Physical divice.也就是使用你的物理光驱.点开下拉菜单你可以进行选择.值得注意的一点.是你使用DEMON TOOLS所创建的虚拟光驱盘符也会出现在这里,也就是说你可以使用虚拟光驱的文件进行安装.和光驱没有什么不同.另一个选择项是使用ISO文件(use ISO,如果你没有装虚拟光驱,用ISO文件也是可以的.比如我就是将从网上下载的Redhat linux安装镜相.映射为光盘进行安装的.第四个是network.的设置.网络的设置是VM的强项,你机器要是有网卡的话,并且你希望和你安装VM的机器通讯.那你要注意以下的内容,网络如果和现有网络相连(我使用的是这个,用来和你的主机通讯)而且它不仅可以和现有主机通讯还可以和你现有网络通讯.*_^很强八.下面我把VM的帮助理的内容翻译下.? Connected — Check or uncheck this option while the virtual machine is running to connect or disconnect the virtual network adapter.连接=选择此项当虚拟机启动时自动连接到你的虚拟网卡.Connect at power on当启动时连接,当虚拟机启动时自动连接你的网卡,如果你不选择此项目,则网卡会在系统启动后不启动,其实说白点就是系统启动后,你的虚拟网卡没有激活,需要你手动激活.Under Network connection, you can choose:在网络连接中你可以选择:1. Bridged=网桥.这个和物理网桥的功能类似.2. Bridged — If the host computer is on an Ethernet network, bridged networking is often the easiest way to give your virtual machine access to that network. With bridged networking, the virtual machine appears as an additional computer on the same physical Ethernet network as the host. A virtual machine with bridged networking may transparently use any of the services available on the network to which it is bridged,including file servers, printers, gateways and so on. Likewise, any physical host or other virtual machine configured with bridged networking can use resources of that virtual machine.3. 如果你的真实主机在一个以太网络内,桥网通常是最容易的办法,给你的虚拟主机访问以太网.当桥网络,虚拟主机成为了附加在物理以太网的一台主机.,一个使用桥网络的虚拟主机可以使用物理网络的任何服务,同样也可以提供任何服务,比如文件服务器,打印机,网关等.(翻译的很烂,但就是这个意思)就是说你的虚拟机器可以变成一台真正的服务器?,建议使用此配置.4. NAT (Network Address Translation) — If you want to connect to the Internet or other TCP/IP network using the host computers dial-up networking connection and you are not able to give your virtual machine an IP address on the external network, this is often the easiest way to give the virtual machine access to that network. The virtual machine does not have its own IP address on the external network. Instead, a separate private network is set up on the host computer. The virtual machine obtains an address on that network from the VMware virtual DHCP server5. NAT(网络地址传输)-如果你希望连接到互联网或者其他的TCP/IP网络,使用物理主机的拨号网络并且你不能给你的虚拟主机在现有网络一个IP地址,这是最容易的办法.一个私有网络地址可以设置在你的物理主机上,而虚拟机则可以从VMware的虚拟DHCP服务器上获得一个IP地址.(这个主要用于拨号连接,我不清楚这里所说的虚拟DHCP是什么东西.但是我个人认为可能指的是以前的猫拨号的情况.现在应该不需要的.或者可以使用主机的NAT解决ADSL拨号的问题,)6. Host-only — When you use this type of network connection, the virtual machine is connected to the host operating system on a virtual privatenetwork, which normally is not visible outside the host. Multiple virtual machines configured with host-only networking on the same host are on the same network.7. 只是主机=当你使用这种网络连接,虚拟主机被连接到物理主机操作系统上,一个虚拟私有网络.在此主机之外,外网是不可见的.只有在这个主机上配置多个虚拟主机才可以访问此网络.(这个话翻译的不通,我觉得是这样,就是你设置成这种模式,只有你本机和你的虚拟机可以访问这个网络,你的物理网络的设备是访问不到你的虚拟机器的),8. Custom —自定义咯,你自己要怎么设置随你.:)不多说了.我是这样作的.首先把网卡设置为桥的形式,然后到EDIT菜单的Virtual network setting理把Autobridging 选择上,让系统自动去连接网桥上的虚拟网卡.然后把DHCP理设置的两个虚拟网卡,删除把主机虚拟网卡,删除把HOSTMAPPING 设置为bridge to an automatically chose adapter,也就是让桥去自动选择网卡.设置完后选择应用.VM的设置就完成了.第五个是设置USB控制器,这里VM是和你的主机共用的USB接口.也就是你USB 接口上的东西,VM理的系统是都可以用的,当然你要把自动连接选择项加上,不然你在VM理识别不到.下一个是AUDIO,你要是想在虚拟机发声音,就把这个设置上巴.一般默认就可以了.虚拟机自己会识别的,当然你所安装的系统也要识别你的声卡.最后的是你的CPU,你可以设置1个或者2个.当然这只会是你一向情愿.骗下你虚拟机的系统识别罢了.性能上是不可能有任何提升的.以上为VM的设备设置，设置完后,你可以把光驱或者ISO映象加载到你的光驱理,然后选择绿箭头启动你的虚拟机了.虚拟机理还有它的BIOS你可以F2进去看看?设置下.然后就可以开始你的系统安装了, 那就和VM没多大关系, 最后说两点,一个是要注意你的虚拟机要设置和你主机在同一个网络段理否则是无法访问的.第二个是笑三少所说的文件传输的问题,他说的可以直接把文件拖进虚拟机的窗口就可以拷贝文件了,可能2003是可以这样,毕竟都是微软出的操作系统.但是我在linux下测试的是不行的,因为LINUX的文件系统是EX3的.于是我想了个办法是在windows底下装个UltraISO,虚拟机要使用什么文件我都做成ISO文件,然后挂到虚拟机的光驱上,然后在linux底下MOUNT上去用.一点也不麻附：[DHCP]协议： /Class/DHCP/0532918532679135.html 注：文章为拷贝，方法大致一样。

互联网英语作文80词初二

互联网英语作文80词初二

互联网初二英语作文1The Internet has become an indispensable part of our lives, especially for junior high school students. It offers a wide range of functions that greatly enrich our daily experiences.One of the most fundamental functions is information query. For example, when we need to find learning materials for our studies, we can use search engines like Google or Baidu. Just by typing in relevant keywords, a vast amount of information pops up, which is extremely helpful for our study.The Internet also plays a significant role in social entertainment. We can use social media platforms such as Facebook, Instagram or WeChat to chat with friends, share our daily lives, and even make new friends from all over the world. Through these platforms, we can post pictures, videos and our thoughts, and interact with others instantly.Moreover, online learning has become more and more popular. There are many excellent online learning platforms, like Coursera and Khan Academy. On these platforms, we can choose various courses according to our interests and needs, such as English learning, science knowledge and art appreciation. It provides us with a convenient and flexible way to expand our knowledge and skills. In conclusion, the Internet has brought us great convenience and broadened our horizons in many aspects.2The Internet has become an inescapable part of our lives, especially for junior two students. It has both positive and negative impacts on them.On the positive side, the Internet broadens their horizons. For example, many students can access different cultures and knowledge from all over the world. It is also very convenient for learning. Some students use online courses to improve their English or learn math skills that they are not good at in school. There are various educational resources such as e - books and educational videos which are helpful for their study.However, there are negative influences as well. One of the most serious problems is that some students get addicted to the Internet, especially to online games. Take my classmate Tom for instance. He used to be a good student, but since he got addicted to a popular online game, he has spent a great deal of time on it every day. As a result, his grades have dropped significantly. Besides, on the Internet, there is a large amount of information, and it is difficult for students to distinguish between true and false information, which may mislead them.In conclusion, the Internet is a double -edged sword for junior two students. They should make good use of it and avoid being negatively affected.3The Internet has become an indispensable part of our daily lives. It has brought us great convenience in various aspects.Take online shopping for example. My mother often buys daily necessities on the Internet. Instead of going to the crowded supermarket, she can just sit on the sofa, browse different websites, compare the prices and qualities of various products, and then place an order with a few clicks. It saves a lot of time and energy.Online booking is also very popular. My family once planned a trip. We booked train tickets and hotel rooms through the Internet. We also bought tickets for the scenic spots we wanted to visit online in advance. This not only ensured that we could have a smooth journey, but also allowed us to get some discounts sometimes.In addition, the Internet is also a great tool for learning. We can search for all kinds of knowledge, watch educational videos and even take online courses. It has truly changed the way we live and will continue to play an important role in the future.4The Internet has revolutionized the way people communicate in numerous remarkable ways.In the past, communication was often restricted by geographical distance. However, with the advent of the Internet, this has completely changed. People can now engage in instant communication regardless of where they are. For instance, families with members living in different countries can easily keep in touch. Take a family where the parents are in China and their son is studying in the United States. Through video - call applications on the Internet, they can see each other's faces and share their daily lives as if they were in the same room.Moreover, the Internet allows multiple people to communicate simultaneously. Group chats and online meetings have become common. People can exchange ideas, discuss work or simply chat with friends all at once. It has not only made communication faster but also more inclusive and convenient, bringing people closer together in this globalized world.5The Internet has become an indispensable part of our lives. It has changed the way we communicate, study, work and entertain. Looking into the future, the Internet is bound to develop in some amazing ways.First of all, the speed of the Internet will be much faster. Just like the emergence of 5G technology has greatly enhanced the Internet speed, in the future, there maybe even more advanced technologies that will make data transmission almost instantaneous. This will enable us to download large -scale files, such as high -definition movies and complex software, in the blink of an eye.Secondly, the functions of the Internet will be more diverse. Virtual reality (VR) related functions are likely to become more prevalent. For example, we may be able to have immersive shopping experiences through the Internet. Instead of just looking at pictures of products, we can "walk" into virtual stores, pick up items and examine them closely. Also, in the field of education, students can participate in virtual classrooms more realistically, as if they were sitting in a real classroom thousands of miles away.In conclusion, the future of the Internet is full of infinite possibilities, which will continue to have a profound impact on our lives.。