Internet Phone Basics


Internet phone systems use a collection of communication standards called protocols and codecs to carry out their mission of transporting your voice over the maze of cables and hardware that makes up the Internet. Some of these protocols control how your voice is broken up into pieces called packets; some conserve Internet bandwidth by compressing your communications; and some are responsible for making sure that your communication takes priority over less time-sensitive communications.

Manufacturers of Internet phone devices incorporate these protocols into their designs to create easy-to-use phones and telephone adapters for consumers and businesses. No knowledge of the inner workings of these protocols is actually required to use Internet telephone services, but basic knowledge can help you troubleshoot tricky error codes or configure certain settings for better performance.

Internet protocols

The Internet uses a suite of protocols to transport data from one point to another. These communication rules govern how computers (or phones) format data for transmission. In this section, I discuss protocols you may encounter while using Internet phones.

Common Internet protocols you may encounter during Internet phone configuration are

  • TCP/IP (Transmission Control Protocol/Internet Protocol). Most Internet communications use a suite of protocols collectively known as TCP/IP. TCP and IP combine to provide the infrastructure for voice data transmission.

    TCP/IP uses numeric addresses to route data between computers or devices connected to the Internet. Internet routers locate these addresses and plot the best route to use to deliver data to its destination. You may have seen these addresses when connecting your computer to the Internet.

  • UDP (User Datagram Protocol). A faster cousin of TCP, this protocol is often used for applications, such as voice transmission, in which speed is more important than reliability.

  • DHCP (Dynamic Host Configuration Protocol). This protocol controls Internet address assignment for many computers and devices that connect to the Internet. Devices that do not get their address from DHCP must have the address configured manually.

  • DNS (Domain Naming System). This term denotes both a protocol and a service by which hard-to-remember Internet addresses are translated into simpler addresses, like www.firethephoneco.com.

Many more Internet protocols are involved with Internet phone communications, but most work quietly behind the scenes to ensure priority routing for voice traffic or to maintain the Internet infrastructure by ensuring that traffic is rerouted around downed equipment.

VoIP protocols and codecs

VoIP uses a combination of methods for the conversion of voice to data that can be transmitted over the Internet. These methods can be broadly grouped into two groups: Protocols handle tasks such as voice session control and data transmission, and codecs manage the conversion and compression of voice into digital data.

VoIP Session Protocols

The primary use of protocols in VoIP is to establish and maintain a communication channel between two points. Protocols that perform this task are referred to as session protocols.

Other Internet Terms You Might Encounter

  • Host. Any device having an address on an IP network such as the Internet.

  • IP address. A unique series of numbers that defines a host's address on the Internet. Many current IP addresses use a series of four three-digit numbers separated by decimal points.

  • Packet. A unit of data. Packets are created by splitting data into manageable pieces for transmission over a network.

  • Ping. An Internet troubleshooting utility that can be used to test the ability of the network to transmit data to its intended destination.

  • Route. The path a communication takes across the Internet.

  • Router. A device that directs Internet traffic toward its destination. Routers maintain address lists called routing tables that help them determine the best path to send data along. Another name for a router is a gateway.

  • Server. An Internet host that provides a service or information, such as the computer or computers that host a Web site.

  • URL (Uniform Resource Locator). An Internet address form that incorporates both the host address and the type of service the host is serving. In http://www.firethephoneco.com, for example, the http:// portion denotes a host serving the HTTP protocol (a Web server), and www.firethephoneco.com denotes the host's DNS address. Other URLs may begin with ftp:// (File Transfer Protocol) or sip:// (a host supporting direct voice communication).


The two most familiar VoIP session protocols are

  • SIP (Session Initiation Protocol). Most VoIP providers use this protocol to control VoIP session management. SIP establishes VoIP communication and controls most of the features of VoIP services. It includes everything required to manage features of VoIP that emulate the functions of a standard telephone, such as dial tone, ring tone, busy signal, and caller ID.

  • H.323. A suite of telecommunication protocols that defines signaling and control in a manner similar to that of the SIP protocol. More mature than SIP, this standard is being replaced in many applications by the lighter, faster SIP.

VoIP Transport Protocols

Most VoIP communication is carried by the Realtime Transport Protocol (RTP). After a communication is initiated by the VoIP session protocol, RTP acts as the carrier channel for voice data.

RTP was ratified as a standard in 1996 and has been used in VoIP and streaming audio/video services since then. It is designed to work with UDP (User Datagram Protocol) for maximum speed and efficiency.

Other VoIP Session Protocols

  • IAX (Inter-Asterisk eXchange). A protocol used by Asterisk, a private branch exchange (PBX) system that has Internet connection capabilities.

  • Megaco/MGCP (Media Gateway Control Protocol). A protocol that manages the conversion of voice data between networks or systems that have different protocols or codecs.

  • MiNet. A proprietary protocol used by Mitel to manage its voice network products.

  • SCCP (Skinny Client Control Protocol). A proprietary protocol used by Cisco to manage VoIP sessions between Cisco equipment and compatible phones. SCCP is used mostly in business VoIP installations and probably will not be featured in a consumer VoIP environment.


VoIP Codecs

A codec (short for compressor-decompressor) manages the conversion of voice to digital bits and bytes. It is these algorithms that allow the dulcet tones of your voice to be faithfully reproduced at the other end of your Internet phone call. Codecs differ in the bandwidth they use; those that require less bandwidth typically reproduce less of the full range of voice tones. Some codecs reproduce tones well enough to be equivalent in quality to a good landline call; others are closer in quality to a cellular phone call.

Voice codecs in common use are

  • G.711. The most common codec for VoIP communication, G.711 uses 64 Kbps to transmit high-quality voice and fax communications. Two versions of this codec exist: m-law (pronounced "m-law"), used in the United States and Japan, and a-law, which is used in the rest of the world.

    The version of G.711 that you use becomes important because each region uses this protocol in its native version to compress voice on standard phone lines. Having the correct version ensures that the voice stream can be transmitted directly to the standard phone system without conversion.

    Wait! How Do I Keep all These Acronyms Straight?

    Relax! Take a deep breath.

    Better?

    Okay.

    For now, forget about the Internet protocol acronyms. You'll see them again when you need them. I'll make sense of them at the appropriate time.

    Of the VoIP session protocols, just remember SIP. Almost all providers now support the SIP standard. The H.323 standard is used mostly in commercial installations; the others are even more obscure.

    Most VoIP providers support more than one codec, G.711 being the most popular. Chances are that you will select your provider based on other factors, so I will discuss how to manage codecs at the appropriate time.

    So just relax, and enjoy a quick tour of VoIP hardware.


  • G.723.1. This codec uses 5.3 Kbps to 6.3 Kbps of bandwidth (the lowest of the codecs I will examine in this book), making it useful for very-low-bandwidth VoIP applications such as VoIP over dial-up Internet. The voice reproduction quality is below that of G.711, and the codec is not suitable for fax transmission.

  • G.726. Another low-bandwidth codec, G.726 can use as little as 16 Kbps or as much as 40 Kbps. At the lower settings, it may enable VoIP over dial-up Internet links. Quality is still less than that of G.711, however; therefore, this codec is not suitable for fax communication.

  • G.729. A very-low-bandwidth codec in common use, G.729 uses as little as 6 Kbps to 8 Kbps to transmit voice data. Quality is less than that of G.711, but this codec remains a good choice for bandwidth-limited connections.

Internet phone devices

Consumers have an array of devices to consider as they evaluate VoIP services and options. Most VoIP providers specify a list of preconfigured devices for their services, but some, such as BroadVoice, allow clients to use any device compatible with their systems. For this reason, it may be important to understand the capabilities of various devices and to be able to analyze their compatibility with your chosen service. Most providers will also supply a list of compatible devices you can choose, many of them already configured for their services. Often, you can get the preconfigured device free or choose among a selection of device upgrades for a small fee. VoIP starter kits are also available at most retail computer stores; usually, these kits are free after rebates.

VoIP device manufacturers list the specifications of their devices on the packaging, and these specs usually appear on their Web sites as well (Figure 1.1). When evaluating a VoIP device, check to be sure that the device in question supports the same VoIP session protocol and codecs used by your service provider.

Figure 1.1. Product specifications for a Linksys telephone adapter


SIP Phones

Many VoIP providers support one or more SIP telephone handset models. These devices look and feel like standard telephones but contain VoIP circuitry instead. Some can access the VoIP service directly through your Internet connection and are portable enough to travel with you when you want to take your home number on a trip.

SIP phones come in three configurations:

  • USB handsets connect directly to your computer, using its brains for network connectivity and signal processing (Figure 1.2). These devices are relatively inexpensive and work with many VoIP services. Most USB handsets are used with softphones software telephone applications that use a computer to process voice codecs and VoIP protocols.

    Figure 1.2. VoIPVoice CyberPhone K Skype USB handset


  • SIP phone sets contain all the necessary circuitry for VoIP communication (Figure 1.3). These are desktop phones that look at home in an office environment. Manufacturers such as Cisco have many models to choose among.

    Figure 1.3. Cisco desktop VoIP phone


  • Wireless handsets use wireless networks in homes or offices to transmit data to and from the telephone handset (Figure 1.4). These devices look like common wireless handsets but contain all the circuitry for wireless VoIP.

    Figure 1.4. Cisco 7920 wireless VoIP handset


Softphones

Many free and low-cost VoIP services use computer softphones (Figure 1.5). A softphone uses the computer's hardware to perform codec processing and protocol signaling, which dramatically lowers the cost of hardware for the user of these services. The softphone software may be created by the provider itself, as is the case with the Skype service, or the provider may use a custom-branded version of a softphone from a software supplier like XTen.

Figure 1.5. Vonage's SoftPhone is a custom-branded XTen softphone.


Telephone Adapters

Telephone adapters allow you to use a standard telephone to make VoIP calls (Figure 1.6). These devices convert the analog telephone signals to digital VoIP signals, using the selected VoIP session protocol and voice codec, and transmit these over your Internet connection to the VoIP provider's system.

Figure 1.6. Linksys PAP2 telephone adapter


Most telephone adapters, also called TAs or PAs, are supplied with starter kits for each VoIP provider, but they can also be obtained without presets for those who intend to use them for direct SIP-to-SIP communications or with a "bring your own device" provider like BroadVoice.

Voice/Data Routers or Gateways

Many manufacturers of VoIP products also manufacture integrated appliances that contain the TA circuitry along with Internet gateway functionality (Figure 1.7). These devices can provide Internet connectivity to a home or small office, as well as VoIP capabilities. Many incorporate Internet firewalls and wireless networking features. They are a great way to reduce clutter on your desktop yet still have access to many communications services.

Figure 1.7. Linksys WRT54GP2 VoIP router/gateway




Fire the Phone Company. A Handy Guide to Voice over IP
Fire the Phone Company: A Handy Guide to Voice Over IP
ISBN: 0321384865
EAN: 2147483647
Year: 2004
Pages: 94
Authors: David Field

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