Voice over IP

Cisco Labs QoS Testing

Cisco conducted the following tests to show not only VoIP quality, but also how Cisco QoS tools work under load. For the testbed, Cisco used a simple network with two Cisco VoIP gateways and one 56-kbps WAN. It completed two tests Test A consisted of testing with and without QoS enabled while steadily increasing the saturation of the WAN link. Test B consisted of testing with and without QoS enabled while sending traffic across the WAN link in a bursty nature. When no QoS was used, FIFO queuing...

Drawbacks to the PSTN

Although the PSTN is effective and does a good job at what it was built to do (that is, switch voice calls), many business drivers are striving to change it to a new network, whereby voice is an application on top of a data network. This is happening for several reasons Data has overtaken voice as the primary traffic on many networks built for voice. Data is now running on top of networks that were built to carry voice efficiently. Data has different characteristics, however, such as a variable...

Packet Telephony Call Centers

In most call centers today, the largest costs are for the brick and mortar holding the building together. You can drastically cut the actual costs of renting a building, putting a phone at each desk, and purchasing the required infrastructure (call-routing technology, PCs, and so on) by using a Packet Telephony Call Center (PTCC). Each call center is different, but for many call centers, the ability to grow the business as needed (perhaps as discretely as one station at a time) is a great...

Plain Old Telephone Service

Standard telephony service is commonly referred to as plain old telephone service (POTS). This service provides a dial tone to rotary and touch-tone telephones, as well as access to national and international carriers. Standard dialing devices such as 500-type telephones (rotary), 2500-type telephones (touch-tone), facsimiles, and modems are compatible with POTS. POTS evolved internationally to include the 911 emergency number service and operator services. The following additional features and...

Mean Opinion Score

You can test voice quality in two ways subjectively and objectively. Humans perform subjective voice testing, whereas computers which are less likely to be fooled by compression schemes that can trick the human ear perform objective voice testing. Codecs are developed and tuned based on subjective measurements of voice quality. Standard objective quality measurements, such as total harmonic distortion and signal-to-noise ratios, do not correlate well to a human's perception of voice quality,...

Local Loops Trunks and Interswitch Communication

The telephone infrastructure starts with a simple pair of copper wires running to your home. This physical cabling is known as a local loop . The local loop physically connects your home telephone to the central office switch (also known as a Class 5 switch or end office switch ). The communication path between the central office switch and your home is known as the phone line, and it normally runs over the local loop. The communication path between several central office switches is known as a...

Telecommunications Deregulation

So far, you have looked at the technical issues of how the PSTN operates, the basic hierarchy, and why you might need to converge voice and data networks. One important reason for this convergence is more political than technical. Various countries throughout Europe, Asia, and the Americas are opening up their telecommunications markets to competition. In addition, in some cases, they are selling off the existing government-run telephone carriers to a private company (or many companies). In the...

Tandem Encoding

As covered in Chapter 1, all circuit-switched networks today work on the premise of switching calls at the data link layer. The circuit switches are organized in a hierarchical model in which switches higher in the hierarchy are called tandem switches. Tandem switches do not actually terminate any local loops rather, they act as a higher-layer circuit switch. In the hierarchical model, several layers of tandem circuit switches can exist, as shown in Figure 8-6. This enables end-to-end...

Chicago Router Overview

The router configurations for the B.A.N.C. project are as follows (only relevant portions of the configuration files are shown) codec complexity high * This command defines which codecs can be used with the Voice Network Module. High Complexity allows G.711, G.726, G.728, G.729, G.723.1 and Fax-Relay dlsw local-peer peer-id 192.168.101.1 promiscuous description 1-8 Denver, 9-10 Tokyo framing esf linecoding b8zs clock source line dsO-group 1 timeslots 1-8 type e&m-wink-start dsO-group 2...

ISUP Call Control Messages

Table 4-4 identifies the most important ISUP call control signaling messages. All ISUP signaling messages contain the ISUP message type parameter. Table 4-4 identifies the most important ISUP call control signaling messages. All ISUP signaling messages contain the ISUP message type parameter. Table 4-4. ISUP Messages and Message Types The ISUP call control message formats, including signaling parameters, optional and mandatory fields, and field lengths, are listed in Appendix A, ISUP Messages...

BOWIEnet Multiservice Networks

BOWIE.net is a regional Internet service provider (ISP) with 60 points of presence (POPs) throughout the Southeast and along the East Coast of the United States. It has a Cisco-powered network and currently provides residential and business access to the Internet, managed network services, and Web hosting. In early 1999, BOWIE.net began offering 100 minute long-distance VoIP services throughout its 60 POPs. It focused this service primarily to its existing business customers because it had a...

ISDN L2 and L3 Protocols

ISDN user-network interface L2 and L3 specifications also are referred to as Digital Subscriber Signaling System No. 1 (DSS1). L2 provides error-free and secure connections for two endpoints across the ISDN reference configuration. L3 provides the mechanism for call establishment, control, and access to services. The L2 protocol for ISDN is Q.920 921, and the L3 protocol is Q.930 931. Q.932 enables general procedures for accessing and controlling supplementary services. The specifications for...

Call Control Signaling H225

In H.323 networks, call control procedures are based on International Telecommunication Union (ITU) Recommendation H.225, which specifies the use and support of Q.931 signaling messages. A reliable call control channel is created across an IP network on TCP port 1720. This port initiates the Q.931 call control messages between two endpoints for the purpose of connecting, maintaining, and disconnecting calls. The actual call control and keepalive messages move to ephemeral ports after initial...

Voice Coding Standards

The ITU-T standardizes CELP, MP-MLQ PCM, and ADPCM coding schemes in its G-series recommendations. The most popular voice coding standards for telephony and packet voice include G.711 Describes the 64 Kbps PCM voice coding technique outlined earlier G.711-encoded voice is already in the correct format for digital voice delivery in the public phone network or through Private Branch eXchanges (PBXs). G.726 Describes ADPCM coding at 40, 32, 24, and 16 Kbps you also can interchange ADPCM voice...

Basic Call Setup and Teardown Example

This example demonstrates the steps involved in basic call setup and teardown. The example also shows ways you can use the ISUP protocol to connect and disconnect calls in the SS7 network. Figure 4-16 provides the network topology for this example. Figure 4-16. Network for Call Setup and Teardown Figure 4-16. Network for Call Setup and Teardown In this example, the analog subscriber connected to SSP1 places a call to the analog subscriber connected to SSP2. The following steps occur when the...

CCITT No 5 Signaling

The CCITT adopted the CCITT No. 5 signaling system in the 1960s for use in international networks. This signaling system is still used today, usually on long international trunks and, in some cases, over transoceanic and satellite links. This signaling system was designed to operate over analog trunks equipped with Time Assignment Speech Interpolation (TASI). TASI is similar to voice activity detection (VAD), in that it enables unused bandwidth (silences or pauses in speech) to be used for...

Figure 1011 Gatekeeper Routed Call Signaling Same Gatekeeper

EnglpflintO Gatekeeper t Endpoin T EnglpflintO Gatekeeper t Endpoin T inseotlii & in ll ie E nejp irtte Figure 10-11 illustrates call-flows using gatekeeper call routed signaling between two endpoints sharing the gatekeeper. Note that the H.245 procedure is handled directly between the endpoints and is not gatekeeper-routed. The examples in Figures 10-12 and 10-13 detail call setup procedures for dual-gatekeeper implementations. Specifically, Figure 10-12 illustrates call-flows using direct...

Q931 Call Control Messages

The message structure and signaling elements of Q.931 are used in ISDN networks to provide call control capabilities. Q.931 messages are sent from the network to the user and from the user to the network. They are referred to as user-network and network-user messages, as illustrated in Tables 3-11 and 3-12. Some of the most important Q.931 messages are listed in Table 3-11. The message type field in the general format of the Q.931 message is used to determine the type of message being sent....