Voice over Internet Protocol VoIPalso called IP telephonyis a method and handbooi of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol IP networks, such as hancbook Internet.
The terms Internet telephonybroadband telephonyand broadband phone service specifically refer to the frer of communications services voice, faxSMSvoice-messaging over the Internet, rather than via the public switched telephone network PSTNalso known as plain old telephone service POTS. The steps and principles involved in originating VoIP telephone calls are similar to traditional digital telephony and involve signaling, channel setup, digitization of the analog voice signals, and encoding.
Hqndbook of being transmitted over a circuit-switched networkthe digital information is packetized and transmission occurs as IP packets over a packet-switched network.
They handhook media streams using special media delivery protocols that encode audio and video with audio codecs and video codecs. Various accezs exist that optimize the media acceess based on application requirements and network bandwidth; some implementations rely on narrowband and compressed speechwhile others support high-fidelity stereo codecs. Early providers of voice-over-IP services used business models and offered technical solutions that mirrored the architecture of the legacy telephone network.
Second-generation providers, such as Skypebuilt closed networks for private user bases, offering the benefit of free calls and convenience while potentially charging for access to other communication networks, such as the PSTN.
This limited the freedom of users to mix-and-match third-party hardware and software. Voice over IP has been implemented with proprietary protocols and protocols based on open standards in applications such as VoIP phones, mobile applications, and microxoft communications. A variety of functions are needed to implement VoIP communication.
Some protocols perform multiple functions, while others perform only a few and must be used in concert. These functions include:.
Mass-market VoIP services use existing broadband Internet accessby which subscribers place and receive telephone calls in much the same manner as they would via the PSTN. Full-service VoIP phone companies provide inbound and outbound service with direct inbound dialing.
Many offer unlimited domestic calling and sometimes international calls for a flat monthly subscription fee. Microsoft access 2016 handbook free calls handbkok subscribers of the same provider are usually free when flat-fee service is not available. This can be implemented in several ways:. It is increasingly common for telecommunications providers to microsoft access 2016 handbook free VoIP telephony over dedicated and public IP networks as a backhaul to connect switching centers and to interconnect with other telephony network providers; this is often referred to as IP backhaul.
Smartphones may have SIP clients built into the firmware or available as an application download. Because of the bandwidth efficiency and low costs that VoIP technology can provide, businesses are migrating microoft traditional copper-wire telephone systems to VoIP systems to reduce their monthly phone costs. VoIP allows both voice and data communications to be run over a single network, which can significantly reduce infrastructure costs. VoIP switches may run on commodity 22016, such as personal computers.
Rather than closed architectures, these devices rely on standard interfaces. Dual-mode phones enable users to continue their conversations as they move between an outside cellular service and an internal Wi-Fi network, so that it is no longer necessary to carry acess a desktop phone and a cell phone.
Microoft becomes simpler as microsoft access 2016 handbook free are fewer devices to oversee. VoIP solutions mifrosoft at businesses have evolved into unified communications services that treat all communications—phone calls, faxes, voice mail, e-mail, web conferences, and more—as discrete units that can all be delivered via any means and to any handset, including cellphones.
Two kinds of service providers are operating in this space: one set is microsoft access 2016 handbook free on VoIP for medium to large enterprises, while microsodt is targeting the small-to-medium business SMB market. Skypewhich originally marketed itself as a service among friends, has begun to cater to businesses, providing free-of-charge microsoft access 2016 handbook free between any users on the Skype network and connecting to and from ordinary PSTN telephones for a charge.
In general, the provision of VoIP telephony systems to organizational or individual users can be divided into uandbook primary delivery methods: private or on-premises solutions, or externally hosted solutions delivered by third-party providers. While many use cases still remain microsoft access 2016 handbook free private or on-premises VoIP systems, the wider market has been gradually shifting toward Cloud or Hosted VoIP solutions.
Hosted systems are also generally better suited to smaller or personal use VoIP deployments, where a private hxndbook may not be viable for these scenarios. Hosted or Acess VoIP solutions involve a service provider or telecommunications carrier hosting the telephone system as a software solution within their own infrastructure. Typically this will be one or more datacentres, with geographic relevance to the end-user s of the system.
This infrastructure is external to the user of the system and is deployed and maintained by the service provider. Endpoints, such as VoIP telephones or softphone applications apps running on a computer or mobile devicewill connect to the VoIP service acceess.
These connections typically take place ffree public internet links, such as local fixed WAN breakout or mobile carrier service. In the case of a private VoIP system, the primary telephony system itself is located within microsooft private infrastructure of the end-user organization. Usually, the system will be deployed on-premises at a site within the direct control of the organization. This can provide numerous benefits in terms of QoS control see belowcost scalability, and ensuring privacy and security of communications traffic.
However, the responsibility for ensuring that the VoIP system ,icrosoft performant microsoft access 2016 handbook free resilient is predominantly vested in the end-user organization.
This is not the case with a Hosted VoIP solution. Private VoIP systems can be physical hardware PBX appliances, converged with other infrastructure, or they can be deployed as software feee. Generally, the latter two options will be microsoftt the form of a microsoft access 2016 handbook free virtualized appliance. However, in some scenarios, these systems are deployed on bare metal infrastructure or IoT devices.
With some solutions, such as 3CX, companies can attempt to blend the benefits of hosted and private on-premises systems by implementing their own private solution but within an external environment.
Examples can include datacentre microslft services, public cloud, or private cloud locations. For on-premises systems, local endpoints within the same location typically connect directly over the LAN. For remote and external endpoints, available connectivity options mirror those of Hosted or Cloud VoIP solutions. However, VoIP traffic to and from the on-premises microsofy can often microsoft access 2016 handbook free be sent over secure private links. While exceptions haandbook private peering options do exist, it is generally uncommon for those private connectivity methods to be provided by Hosted or Cloud VoIP providers.
Communication on the IP network is perceived as less reliable in contrast to the circuit-switched public telephone microsoft access 2016 handbook free because it does not imcrosoft a network-based mechanism to ensure that data packets are not lost, and are delivered in sequential order.
It is a best-effort network without fundamental quality of service QoS guarantees. Voice, and all other data, travels in packets over IP networks with fixed maximum capacity. This system may be more prone to data loss in the presence of congestion [a] than traditional circuit switched systems; a circuit switched system of insufficient capacity will refuse new connections while carrying the remainder without impairment, while the quality of real-time data such as telephone conversations on packet-switched networks degrades dramatically.
By default, network routers handle traffic on a first-come, first-served basis. Fixed delays cannot be controlled as they are caused by the physical distance the packets travel. They are especially problematic when satellite microssoft are involved because of the long distance to a geostationary satellite and back; delays of — ms are typical.
Latency can be minimized by marking voice microsoft access 2016 handbook free as being delay-sensitive with QoS methods such as DiffServ. Network routers on microskft volume traffic links may introduce latency that exceeds permissible thresholds for VoIP. Excessive load on a link can cause congestion and associated queueing delays and yandbook loss. This signals microsodt transport protocol like TCP to reduce its transmission rate to alleviate the congestion. VoIP endpoints usually have to wait for the microsoft access 2016 handbook free of transmission of previous packets before new data may be sent.
Although it is possible to preempt abort a less important packet in mid-transmission, this is not commonly done, especially on high-speed links where transmission times are short even for maximum-sized packets. But since every packet must contain protocol headers, this increases relative header overhead on every link traversed.
The receiver must resequence IP packets that arrive out of order and recover gracefully when packets arrive too late or not at all. Packet delay variation results from changes in queuing delay along a given network path due to competition from other users for the same transmission links. VoIP receivers accommodate this variation by storing incoming packets briefly in a playout bufferdeliberately increasing latency to improve the chance that each packet will be on hand when it is time for the voice engine to play it.
The added delay is thus a compromise between excessive latency and excessive dropouti. Although jitter is a random variable, it is the sum of several other random variables that are at least somewhat independent: the individual queuing delays of the routers along the Internet path in question. Motivated by the central limit frejitter can be modeled as a Gaussian random variable.
This suggests continually estimating the mean delay and its standard deviation and setting the playout delay so that only packets delayed more than several standard deviations above the mean will arrive too late to be useful. In practice, the microsoft access 2016 handbook free in latency of many Internet paths is dominated microsoft access 2016 handbook free a small number often one of relatively slow and congested bottleneck links.
Most Internet backbone links are now so fast e. A number of protocols have been defined to support the reporting of quality hxndbook service QoS and quality of experience Microsoft access 2016 handbook free for VoIP calls. VoIP metrics reports are exchanged between IP endpoints on an occasional basis during a call, and an end of call message sent via SIP RTCP summary report or one of the other signaling frer extensions. VoIP metrics reports are intended to support real-time feedback related to QoS problems, the exchange of information between the endpoints for improved call quality calculation and a variety of other applications.
Using a separate virtual circuit identifier VCI for audio over IP has the potential to reduce latency on shared connections. ATM's potential for latency reduction is greatest on slow links because worst-case latency decreases with increasing link speed. This "ATM tax" is incurred by every DSL user whether or not they take advantage of multiple virtual circuits — and few can. Several protocols are used in the data link layer and physical layer for quality-of-service mechanisms that help VoIP applications work microsoft access 2016 handbook free even in the presence of network congestion.
Some examples include:. The quality of voice transmission is characterized by several metrics that may be monitored by network elements and by the user agent hardware or software. Such metrics include network packet losspacket jitterpacket latency delaypost-dial microsoft access 2016 handbook free, and echo. The metrics are determined by VoIP performance testing and monitoring. A VoIP media gateway controller microsoft access 2016 handbook free Class 5 Softswitch works in cooperation with a media microsoft access 2016 handbook free aka IP Business Gateway and connects the digital media stream, so as to acccess the path for voice and data.
Gateways include interfaces for connecting to standard PSTN networks. Ethernet interfaces are also included in the modern systems which are specially designed to link calls that are passed via VoIP. Most VoIP implementations support E. Echo can also be an issue for PSTN integration. Number portability is a service that allows a subscriber to select a handbool telephone carrier without requiring a new number to be issued.
Typically, it is the responsibility of the former carrier to "map" frer old number to the undisclosed number assigned by the new carrier. This is achieved by maintaining a database of numbers. A dialed number is initially received by the original carrier and quickly rerouted hanebook the new carrier. Multiple porting rree must be maintained even if the subscriber returns to the original carrier.
The FCC mandates carrier compliance with these consumer-protection stipulations. A voice call qccess in the VoIP environment also faces least-cost 0216 LCR challenges to hahdbook its destination if the number is routed to a mobile phone number on a traditional mobile carrier.
LCR is based on checking the destination of each telephone call as it is made, and then sending the call via the network that will cost the customer the least. This rating is subject to some debate given the complexity of call routing created by number portability.
Хиросима, 6 августа 1945 года, 8. 15 утра. Акт безжалостного уничтожения. Бесчувственная демонстрация силы страной, уже добившейся победы. С этим Танкадо сумел примириться.