Wireless Communications and Mobile Internet Midterm Exam, Study notes of Computer Networks

Download Wireless Communications and Mobile Internet Midterm Exam and more Study notes Computer Networks in PDF only on Docsity! 『 Wireless Communications and Mobile Internet Midterm Exam 』 姓名：李杰锋 学号：5140309376 Overview of Wireless Networks (Chapter 1) 1. 1(1831)法拉第电磁感应实验 2(1837)莫尔斯电报 3(1873)Maxwell 电磁场理论 4(1876)电话 5(1894) 特斯拉短波无线通信实验 6(1895)马可尼无线电 7(1906)范信 AM 8(1927)跨洋电视广播 9(1946)公共 移动电话系统 10(1958)通信卫星 11(1981)NMT 12(1988)GSM 13(1997)无线局域网 2. Mobile IP 、 cellular network 、 Wi-Fi 、 mobile management Radio Propagation (Chapter 2) 1. Wired ： transmit by line ， big bandwidth ， low interference，stable environment；Wireless：transmit by air，less bandwidth，higher interference，unstable environment 2. Licensed：devices operate within the portion of the radio spectrum designated by the FCC to be reserved for organizations that have been granted licenses；Unlicensed：Unlicensed wireless devices on the smart grid operate in one of the bands set aside by the FCC for industrial, scientific or medical (ISM) applications. 3. Reflection & Transmission: Electromagnetic waves reflect the surface of the medium when the scale is greater than the wavelength, otherwise spread to the surrounding; Diffraction: Electromagnetic waves in the transmission through the media edge, will turn the spread; Scattering: On the surface of the rough medium, the electromagnetic waves will be reflected in all directions, called scattering. 4. Indoor: many reflection, less diffraction and scattering; Outdoor: Reflected by air and ground, scattered at the edge of building. 5. Longer Distance，higher Pass Loss；Transmission Power multiply pass Loss and antenna gain = receive power；higer the mobile station and base station is，less interference and higher the SNR is. 6. Free Space：10lg Pr=10lg P0 -20lgd；Two-ray： 10lgPr=10lgP0-20α lg 𝑑𝑑 7. Shadowing Fading means the SNR changed with the location in long term. 8. Lp = 𝐿𝐿0 + 10𝛼𝛼 lg𝐷𝐷 + 𝑋𝑋 9. Macro: Lp(𝑃𝑃) =𝐴𝐴 + 𝐵𝐵 lg 𝑑𝑑 10. multipath/small-scale fading: After the signal is propagated through different paths, there is a phase difference when superimposed. Doppler shift: The transmitter or receiver is moving, causing the receiver to see the frequency of change. 11. Rayleigh distribution is used for the envelope distribution of multipath fading received signals. Lace distribution is used to describe the envelope attenuation of the received signal. 12. f ′ = 𝑓𝑓 𝑐𝑐±𝑣𝑣1 𝑐𝑐±𝑣𝑣2 13. The signal strength can be calculated by the Rayleigh distribution and the probability distribution function of the Rice distribution. 14. Pz(𝑍𝑍) = 2𝑚𝑚𝑚𝑚𝑧𝑧2𝑚𝑚−1 Γ(𝑚𝑚)𝑃𝑃𝑟𝑟𝑚𝑚 𝑒𝑒− 𝑚𝑚𝑧𝑧2 𝑃𝑃𝑟𝑟 Cellular System (Chapter 3 and 4) 1. 3G on the basis of 2G, using CDMA technology, the current development into three kinds of standards, CDMA2000, WCDMA, TD-SCDMA 2. Higher transmitting power, cell radius is bigger and system capacity is larger. 3. C=MJN 4. Base station: shared mobile communication station; Uplink: link from the ground station to the satellite; Downlink: from the satellite down to one or more ground stations; Cell: radio can cover the work area; mobile switching center: is between the telephone and data systems to provide call conversion services and Call control place. 5. VLR is a database, is stored in the area of the customer's incoming, outgoing calls required to retrieve the information and the user contracted business and additional business information. HLR is responsible for moving the user-managed database. 6. Handoff management: responsible for the identification of new base stations and in the new base station to support data and control signal channel allocation. Location management: home network agent management. 7. Can simultaneously transmit voice and data information, the rate increases, in a few hundred kb/s or more. 8. In 3G, the use of the concept of soft capacity, each new call generation will increase the interference level of all other existing calls, thus affecting the overall system capacity and call quality. So it is important to control the access network call in the appropriate way. Third-generation and future mobile communication systems are required to support multimedia services such as low-speed voice, high-speed data and video, so call admission control becomes more complex. 9. SGSN routing update is the most complex routing update. The MS switches from one SGSN area to another, and then re-connects to the new area. 10. CDMA2000、WCDMA、TD-SCDMA 11. Can simultaneously transmit voice and data information, global roaming, to achieve high-speed data transmission, to achieve broadband multimedia services. 12. Transmission rate：200kb/s or higher；bandwidth is bigger；frequency is higher. 13. broadband Internet access, audio and video entertainment, video calls, mobile TV. 14. Normalization mechanism in wireless network. Future Technologies (Chapter 5) 1. Mobile cloud computing, mobile web pages, mobile Internet initiative Mobility Management (Chapter 6) 1. Monitor the signal strength changes, once exceeded the threshold, to switch. Then identify the new base station, establish a connection. 2. Intra-switch：From a cellular system to a cellular system controlled by the same MTSO. Inter-switch： From a cellular system to another cellular system that is controlled by a different MTSO. 3. MCHO: The mobile station monitors the signal strength and selects the best way. MCHO: Network monitoring signal strength and turn on the switch. MAHO: Mobile station monitor signal strength, network switch. 4. Hard：At any one time a call uses only one channel, but it will be ping-ponging. Soft：Can reduce the probability of signal connection to the target cell, but requires the phone to have complex hardware conditions. 5. Monitor the signal strength changes, once exceeded the threshold, to switch. 6. straight-line model: The behavior is linear. Fluid- flow model: Used to describe the level in the reservoir during a randomly determined period of time. 7. Sorry I don’t know. 8. Intra-switch: When the mobile signal in the given hive becomes very weak, the MTSO discovers that the other cells in the system can transmit the signal, and the MTSO uses the intra-switch; Inter-switch: MTSO can not find other replaceable cells in the system to transmit signals, so use inter-switch. 9. I can’t figure out the handoff rate. 10. The smaller area of the cell is, the handoff frequency is higher. 11. The two-tier structure is a client that runs on the presentation layer or interface of the software architecture and stores the data layer or data structure on the server. 12. Ocation update: When the mobile device is restarted or shut down, the mobile network asks for the reporting location and interrupts the time to send the location information. Service delivery: The mobile network is looking for a viable channel for the called person. If successful, the caller will send a feedback signal to terminate the delivery. 13. Mobile IP (Chapter 7) 1. Once the user's location changes, a new address is required, but most of the network data is transmitted over TCP. Changing the IP address will create a new connection accordingly, resulting in application interruption and loss of data. 2. MN: The location is often changed, that is, nodes that are often switched from one link to another host. HA: A node on the mobile node's home link, which is used to keep the location information of the mobile node. FA: A router on the local link where the mobile node is located. COA: An IP address associated with the node when the mobile node switches to the foreign link. CN: A communication object for a mobile node. 3. MH -> FA. FA tunnels packets to HA by encapsulation. HA forwards the packet to the receiver. 4. 5. The mobile node sends a registration request to the prospective foreign agent to begin the registration process. The foreign agent processes the registration request and then relays it to the home agent. The home agent sends a registration reply to the foreign agent to grant or deny the request. The foreign agent processes the registration reply and then relays it to the mobile node to inform it of the disposition of its request. 6. The limited lifetime allows the mobile node to register with its home agent using the registration request message so that its home agent can create or modify the mobility binding of the mobile node. 7. The only change to the Mobility Agent Advertisement Extension is the additional 'T' bit. A foreign agent that sets the 'T' bit MUST support the two delivery. 8. If the 'T' bit is set, the mobile node asks its home agent to accept a reverse tunnel from the care-of address. Mobile nodes using a foreign agent care- of address ask the foreign agent to reverse-tunnel its packets. 9. If the external or home agent that does not support the reverse tunnel receives a request with the "T" bit set, the registration request fails. 10. IP in IP encapsulation: In IP in IP technology, the entire IP packet is directly encapsulated as a new IP packet payload. Minimum package: In the smallest encapsulation technology, the new IP header is inserted between the original IP header and the original IP payload, the smallest encapsulation by removing the IP. General routing encapsulation: The generic routing encapsulation defines a protocol that encapsulates any of the other network layer protocols on any network layer protocol. 11. Every tube has a beginning and an end. The big tube, your SSH connection, started with your SSH client and ends up at the SSH server you connected to. All the smaller tubes have the same endpoints. 12. Because reverse tunneling may be the only way to go in certain situations. IEEE 802.11 WLAN (Chapter 8) 1. PCF: a MAC technique used in WLANs. It resides in a point coordinator also known as Access Point (AP), to coordinate the communication within the network. The AP waits for PIFS duration rather than DIFS duration to grasp the channel. PIFS is less than DIFS duration and hence the point coordinator always has the priority to access the channel. 2. 3. IEEE 802.11e-2005 or 802.11e is an approved amendment to the IEEE 802.11 standard that defines a set of quality of service (QoS) enhancements for wireless LAN applications through modifications to the Media Access Control (MAC) layer. With EDCA, high-priority traffic has a higher chance of being sent than low-priority traffic: a station with high priority traffic waits a little less before it sends its packet, on average, than a station with low priority traffic. Within the HCF, there are two methods of channel access, similar to those defined in the legacy 802.11 MAC. 4. An Ad-hoc network allows each device to communicate directly with each other. An Infrastructure mode network requires the use of an Access Point. 5. Ad-hoc networks are only able to communicate with other Ad-hoc devices. Infrastructure mode: increased levels of security, potentially faster data transmission speeds and integration with a wired network. 6. Responsible for reliable link-to-link data transfer. Including Channel access, Addressing, Frame Validation, Error Detection and Security Mechanisms. 7. MAC: access mechanism, fragmentation, encryption PLCP: carrier sensing assessment, forming packets for PHYs. PMD: modulation and coding. 8. Infrared is used in devices for short-range communication. Radio wireless networks is used in longer range. Advantages: Simple Circuit, Low Power Consumption, Higher Security, Simple Shielding and Portable. Disadvantages: Works ONLY on Line-of-Sight (LOS) Mode, Short Range, Blocked by common materials: people, walls, etc. Low bandwidth, Speed is comparatively slow. 9. 802.11: 83.5Mhz; 802.11a: 300MHz; 802.11b: 83.5MHz; 802.11g: 83.5MHz. 10. After one node has finished sending, many other nodes can compete for the right to send. The first objective of the prioritization phase is to make sure that no node with a lower priority gains access to the medium while packets with higher priority are waiting at other nodes. 11. DCF: Distributed Coordination Function. PCF: Point coordination function. HCF: the hybrid coordination function.