- Read More From Juanita Ellis
- Voice over IP - Wikipedia
- Chapter 2. Voice over Data: Many Conversations, One Network
- What network changes have you had to make to support convergence?
Cells from the same VC are always sent sequentially. Every Ethernet frame must be completely transmitted before another can begin. If a second VC were established, given high priority and reserved for VoIP, then a low priority data packet could be suspended in mid-transmission and a VoIP packet sent right away on the high priority VC. Then the link would pick up the low priority VC where it left off. Because ATM links are multiplexed on a cell-by-cell basis, a high priority packet would have to wait at most 53 byte times to begin transmission.
There would be no need to reduce the interface MTU and accept the resulting increase in higher layer protocol overhead, and no need to abort a low priority packet and resend it later. ATM's potential for latency reduction is greatest on slow links, because worst-case latency decreases with increasing link speed. A number of protocols that deal with the data link layer and physical layer include quality-of-service mechanisms that can be used to ensure that applications like VoIP work well even in congested scenarios. Some examples include:. The quality of voice transmission is characterized by several metrics that may be monitored by network elements, by the user agent hardware or software.
Such metrics include network packet loss , packet jitter , packet latency delay , post-dial delay, and echo. The metrics are determined by VoIP performance testing and monitoring. A VoIP media gateway controller aka Class 5 Softswitch works in cooperation with a media gateway aka IP Business Gateway and connects the digital media stream, so as to complete creating the path for voice as well as data media.
The Ethernet interfaces are also included in the modern systems, which are specially designed to link calls that are passed via the VoIP. Most VoIP implementations support E. Often VoIP implementations employ methods of translating non-E. Echo can also be an issue for PSTN integration. Typically, it is the responsibility of the former carrier to "map" the 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 to the new carrier. Multiple porting references 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 originating in the VoIP environment also faces challenges to reach its destination if the number is routed to a mobile phone number on a traditional mobile carrier.
Read More From Juanita Ellis
VoIP has been identified in the past as a Least Cost Routing LCR system, which 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. With GSM number portability now in place, LCR providers can no longer rely on using the network root prefix to determine how to route a call.
Instead, they must now determine the actual network of every number before routing the call. In countries without a central database, like the UK, it might be necessary to query the GSM network about which home network a mobile phone number belongs to. As the popularity of VoIP increases in the enterprise markets because of least cost routing options, it needs to provide a certain level of reliability when handling calls.
Voice over IP - Wikipedia
MNP checks are important to assure that this quality of service is met. Handling MNP lookups before routing a call provides some assurance that the voice call will actually work. A telephone connected to a land line has a direct relationship between a telephone number and a physical location, which is maintained by the telephone company and available to emergency responders via the national emergency response service centers in form of emergency subscriber lists. When an emergency call is received by a center the location is automatically determined from its databases and displayed on the operator console.
In IP telephony, no such direct link between location and communications end point exists. Even a provider having hardware infrastructure, such as a DSL provider, may know only the approximate location of the device, based on the IP address allocated to the network router and the known service address. IP communication provides for device mobility.
For example, a residential broadband connection may be used as a link to a virtual private network of a corporate entity, in which case the IP address being used for customer communications may belong to the enterprise, not being the IP address of the residential ISP. On mobile devices, e. In such cases, the Internet telephony service provider ITSP knows only that a particular user's equipment is active.
Chapter 2. Voice over Data: Many Conversations, One Network
Service providers often provide emergency response services by agreement with the user who registers a physical location and agrees that emergency services are provided to that address only if an emergency number is called from the IP device. The VoIP E emergency-calling system associates a physical address with the calling party's telephone number.
All VoIP providers that provide access to the public switched telephone network are required to implement E,  a service for which the subscriber may be charged. The VoIP E system is based on a static table lookup. Unlike in cellular phones, where the location of an E call can be traced using assisted GPS or other methods, the VoIP E information is accurate only if subscribers, who have the legal responsibility, keep their emergency address information current.
Transmission of fax documents was problematic in early VoIP implementations, as most voice digitization and compression codecs are optimized for the representation of the human voice and the proper timing of the modem signals cannot be guaranteed in a packet-based, connection-less network. A standards-based solution for reliably delivering fax-over-IP is the T. The T. The fax machine may be a standard device connected to an analog telephone adapter ATA , or it may be a software application or dedicated network device operating via an Ethernet interface.
UDP provides near real-time characteristics due to the "no recovery rule" when a UDP packet is lost or an error occurs during transmission. Some newer high end fax machines have built-in T. Two successive packets have to be lost to actually lose data integrity. Telephones for traditional residential analog service are usually connected directly to telephone company phone lines which provide direct current to power most basic analog handsets independently of locally available electrical power.
IP Phones and VoIP telephone adapters connect to routers or cable modems which typically depend on the availability of mains electricity or locally generated power. Such battery-backed devices typically are designed for use with analog handsets. Some VoIP service providers implement services to route calls to other telephone services of the subscriber, such a cellular phone, in the event that the customer's network device is inaccessible to terminate the call. The susceptibility of phone service to power failures is a common problem even with traditional analog service in areas where many customers purchase modern telephone units that operate with wireless handsets to a base station, or that have other modern phone features, such as built-in voicemail or phone book features.
The security concerns of VoIP telephone systems are similar to those of other Internet-connected devices. This means that hackers with knowledge of VoIP vulnerabilities can perform denial-of-service attacks, harvest customer data, record conversations, and compromise voicemail messages.
Compromised VoIP user account or session credentials may enable an attacker to incur substantial charges from third-party services, such as long-distance or international calling. The technical details of many VoIP protocols create challenges in routing VoIP traffic through firewalls and network address translators , used to interconnect to transit networks or the Internet. Private session border controllers are often employed to enable VoIP calls to and from protected networks.
What network changes have you had to make to support convergence?
Though many consumer VoIP solutions do not support encryption of the signaling path or the media, securing a VoIP phone is conceptually easier to implement than on traditional telephone circuits. A result of the lack of encryption is that it is relatively easy to eavesdrop on VoIP calls when access to the data network is possible. IPsec is available to secure point-to-point VoIP at the transport level by using opportunistic encryption.
Voice over IP protocols and equipment provide caller ID support that is compatible with the facility provided in the public switched telephone network PSTN. Wireline telephones which are manufactured in, imported to, or intended to be used in the US with Voice over IP service, on or after February 28, , are required to meet the hearing aid compatibility requirements set forth by the Federal Communications Commission.
VoIP has drastically reduced the cost of communication by sharing network infrastructure between data and voice. Secure calls using standardized protocols, such as Secure Real-time Transport Protocol , as most of the facilities of creating a secure telephone connection over traditional phone lines, such as digitizing and digital transmission, are already in place with VoIP.
It is necessary only to encrypt and authenticate the existing data stream. Automated software, such as a virtual PBX , may eliminate the need of personnel to greet and switch incoming calls. Throughout the developing world, particularly in countries where regulation is weak or captured by the dominant operator, restrictions on the use of VoIP are often imposed, including in Panama where VoIP is taxed, Guyana where VoIP is prohibited.
The country has installed firewalls to prevent international calls being made using VoIP. These measures were taken after the popularity of VoIP reduced the income generated by the state owned telecommunication company. VoIP services operating in Canada are required to provide emergency service.