| In recent years, Internet is fast growing, and permeate through each field of life gradually, The new technology of the network is emerging constantly too .VoIP (Voice over Internet Protocal) is one of them . VoIP is a kind of digital telephone technology, understand from literal meaning that exactly transmits the pronunciation signal by IP network. Its integrated pronunciation compresses / decompresses, data storing and exchanging and treatment technology of multiple information that the route is distributed,etc., Because it can utilize the resources of the existing network to offer cheap even free pronunciation service, widely used in recent years, VoIP greatest advantage widely adopt the environment of Internet and interconnection of global IP, offer more, better services than traditional business. It is a hot issue of Internet application at present too. Become the powerful rival of traditional PSTN.Compared with ordinary telephone, the advantage of IP telephone is very obvious, because IP telephone combines the traditional telecommunication telephone network in the data network, save huge PSTN long-distance. But the speech for building campus network of the high-speed data network, VoIP advantage is self-evident.Natural VoIP has his shortcomings too, while continuing time, conversing to prolong with the rapid increase of user's quantity, IP telephone, conversation quality will all be influenced. And then IP network opens the network, obviously insufficient on security in the network business and managerial ability, hacker often attack etc. in the business have, All these will lead to the fact IP telephone service quality obviously drop. On network management, traditional IP network was not defined and designed and directed against the management maintenance system of the public environment, When the network breaks down, trouble clearing more traditional telephone network is difficult.This text has introduced VoIP development both at home and abroad at first, and compare, Then introduced VoIP some questions in signal transmission. Utilize Sniffer take to bandwidth that pronunciation make situation act as analysis assess. And then this text make registration and call news of SIP of system and go on deep analysis to VoIP letter because of the mistake producing in operation. Because the address of IPv4 is scarce, NAT is extensive in technical application, but some problems that SIP passes through NAT and exists, This text provides a easy to operate solution. Will coexist with riper PSTN system for some time as VoIP that is employed newly, so PSTN and VoIP enterprise layer important part of VoIP too, The technology in this text is interconnected with VoIP to PSTN is discussed. VoIP is a kind of real-time application, so let the existing network offer the sufficient bandwidth for VoIP data, the ones that so as to ensure it can be continuous provide service and becom. Then QoS becomes first-selection which meets requirement described above. This text analysis most suitable for some QoS technology that the pronunciation is transmitted at present. Finally, direct against some hot problems in VoWLAN, For example: Delay, roam, insert the security, has analyzed and put forward the solution. To university's own characteristic and advantage, propose the feasible scheme, dispose the simulation of campus network VoIP, make certain effect.VolP (Voice-over-IP), adopts the swapper of dividing into groups to realize a kind of pronunciation communication of transmitting business of speech through the data network.At present, domestic most universities have already built more complete campus network well. The bandwidth is very abundant within these networks, In exporting, except that and the connection of CERNET is exported, have export abundant in bandwidth that joins with the backbone network of the operator more too. Time of students' conversation is increasing at full speed, in order to fully utilize the resources of campus network, Save school work communication expenses of system, financial burden to lighten student, VoIP has already become the first-selected scheme of pronunciation communication of the school.The bandwidth of voice is taken up:Step1:Confirm the compiled code algorithm and bale cycle. We adopt the compiled code algorithm of G.711 [1 ] PCM [2 ], The bandwidth 64Kbit/s taken, bales cycle 20ms, i.e. each sample of encapsulating two pronunciations and sampling.Step2: Confirm various chain relevant information. There are no security feature such as tunnel.Step3: Calculate package. G.711 compiled code algorithm, the bandwidth 64Kbit/s taken, bale cycle 20ms. 64000 0 (bit/s). 020 8 (bit / byte) (s) =160 bytesStep4: Calculate the whole frame size. IP head 20 bytes, UDP head 12 bytes, RTP head 8 bytes, Frame head 14 bytes of Ethernet. So, whole frame size =160 20 12 8 14=214Byte.Step5: Calculate the package speed. Wrap up the speed =Bale the reciprocal of cycle. Package speed in this example =1/0.020 =50pps.Step6: Calculate all bandwidth. Every VoIP calls out the bandwidthAt present, VoIP system have H.323 and two of SIP intact and independent letter make standard, design this use SIP letter make standard.NAT that this case should be solved passes through the problem, It is mainly that proxy server uses one or more common network IP addresses to do ports mapping, To offer ability of connecting Internet of a privately inside address to Internet.The pronunciation gateway to be used in this case is a sharp victory SVG6116.SVG6116 has four communication modules:"VoIP Client","VoIP Trunk","FXS"and"FXO". Pass the cooperation of these four communication modules, The gateway of thevoice can conbine VoIP system, ordinary telephone terminal and PSTN is systematic together, achieve the goal of interflowing . The ones that adopt more popular DiffServ model at present and wrap up to IP data on the edge of network are classified, follow SIP, RTP agreement to type, and set PRI 5(voice PRI of IP). Use LLQ to make the data of high PRI wrapped up and had priority on the line through throwing away the data of low PRI to wrap up more than the busy position.Wireless LAN (WLAN) employ wireless communication make computer apparatus getting interconnected. Form and can communicate and realize the network system of resource-sharing each other. Wireless LAN essential characteristic loud advantage to no longer use the communication cable most too most, thus make construction and movement of the network more flexible. But the conflict that the medium of the sharing type determines to adopt CSMA/CA prevents the way from solving the conflict problem. And way this might bring than wired high delay.Through the little honeycomb, can cover the whole garden, use one to move in the garden freely, through roaming between different AP, users can maintain network link. Users can also distribute the flow between different AP, and then increase each user's throughput. Utilize these eclipsed AP to realize WLAN backbone.Because the access that open AP can be very easy, the disabled user can get resources free, And the encryption based on WEP is easy to be analysed and explained, there are unfavourable factors a lot. Then we have adopted the encryption scheme of WPA.WPA is equivalent to that RC4 used for WEP has encrypted the scheme and added a safe shell in fact, can offer the login between users and the networks, carrying on the automatic and safe key exchanges and offers the protection to that the pronunciation (and the data) charter. Through replacing RC4 as encrypting the engine by encrypting the standard (AES) [13 ] advancedly, WPA2 has strengthened the security of WPA. Moreover, exchange the mechanism through adopting the similar automatic key, WPA2 can protect user's infrastructure investment on WPA.As 802.11i norm of RSN a part of framework, have offered to two kinds of different authentication mechanisms, i.e.: Share the mode of key (PSK) and authentication mode based on 802.1x in advance. Because there is more quantity of user of the school, propose using the enterprise layer scheme, use WPA-EAP authentication scheme based on RAIDIUS server of 802.1x. Benefit management like this and the security is relatively high.Dispose and design in campus network VoIP simulation:Will register the server, will put to and employ serving the module with apparatus such as the acting server, the gateway of the pronunciation, benefit centralized management of type, network imprison VoIP network and PSTN PBX of network exchanger interconnected through pronunciation, The wireless module realizes the access of VoIP mobile devices on the basis of the existing wireless network infrastructure, The way to adopt DHCP distributes privately owned IP in order to solve the tense problem of address of IPv4. Office park and dormitory area can pass soft SIP phone software on installing IPhone private plane or computer, Realize it with the computer in VoIP network, IP private plane, the simulation telephones of different types moved in IP telephone and PSTN carry on the communication.Each unit has built one's own network with the development of network, The traditional network application concept is to inquire in the network information sends mails, and convey the file, online official working,etc.. Will become one of the widest a application on the basis of existing network after VoIP.Have no network to phone to be already to utilize realized in Dalian Polytechnic University and JinZhou area.This project can be popularized to the free mode. Through upgrading to the server of grade of telecommunication, can offer " 0 " telephone expenses pronunciation of high quality service for the teachers and students of the whole school, Replace existing fat AP with thin AP wireless mode of controller, can offer high usability in the campus and high dependability wireless to roam conversing. |
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