Voice Over IP

Configuring an MGCP Trunk Gateway Router(config)#ccm-manager mgcp Router(config)#mgcp 4000 Router(config)#mgcp call-agent 209.165.202.129 4000 Router(config)#controller t1 1/0 Router(config-controller)#framing esf Router(config-controller)#clock source internal Router(config-controller)#ds0-group 1 timeslots 1-24 type none service mgcp Router(config-controller)#exit Router(config)#controller t1 ... [full story]

Configuring an MGCP Residential Gateway Router(config)#ccm-manager mgcp Router(config)#mgcp Router(config)#mgcp call-agent 172.20.5.20 Router(config)#voice-port 1/0/0 Router(config-voiceport)#voice-port 1/0/1 Router(config-voiceport)#exit Router(config)#dial-peer voice 1 pots Router(config-dial-peer)#application MGCPAPP Router(config-dial-peer)#port 1/0/0 Router(config-dial-peer)#exit Router(config)#dial-peer voice 2 pots ... [full story]

Configuring MGCP Example 6-12 highlights the commands required to configure an MGCP residential gateway [full story]

MGCP Gateways Gateways are clustering points for endpoints. These gateways handle the translation of audio between the SCN and the packet network. Although gateways are implemented in real systems, from a modeling point of view, gateways are logical components. In this context, ... [full story]

MGCP Call Agents A call agent, or Media Gateway Controller (MGC), represents the central controller in an MGCP environment, as depicted in Figure 6-36. Figure 6-36. MGCP Call Agent A call agent exercises control over the operation of a gateway and its ... [full story]

Basic MGCP Concepts The following are MGCP's basic concepts: Calls and connections Allow end-to-end calls to be established by connecting two or more endpoints Events and signals Allow a call agent to provide instructions for the gateway Packages and digit maps Allow a gateway ... [full story]

MGCP Sessions End-to-end calls are established by connecting two or more endpoints, as illustrated in Figure 6-37. To establish a call, the call agent instructs the gateway associated with each endpoint to make a connection with a specific endpoint or an ... [full story]

MGCP Control Commands A call agent uses control commands or messages to direct its gateways and their operational behavior. Gateways use the following control commands in responding to requests from a call agent and notifying the call agent of events and ... [full story]

MGCP Call Flows Figure 6-38 illustrates a dialog between a call agent and two gateways. Figure 6-38. MGCP Call Flows Although the gateways in this example are both residential gateways, the following principles of operation are the same for other gateway types: 1. ... [full story]

Robust MGCP Design In the MGCP environment, the call agent controls all call setup processing on the IP and the telephony sides of a gateway. Because a gateway is associated with only one call agent at a time, if that call ... [full story]

MGCP Switchover and Switchback MGCP switchover permits the use of redundant MGCP call agents. This feature requires two or more Cisco Unified CallManager servers to operate as MGCP call agents. One Cisco Unified CallManager server becomes the primary server and functions ... [full story]

MGCP Gateway Fallback MGCP gateway fallback is a feature that improves the reliability of MGCP branch networks. A WAN link connects the MGCP gateway at the remote site to the Cisco Unified CallManager at the central sites (that is, the MGCP call ... [full story]

Cisco's Implementation of MGCP Cisco provides support for MGCP gateways and the call agent in the following ways: Gateways Cisco implements MGCP trunk gateway and residential gateway support in the following devices: - Cisco voice-enabled routers (first available in Cisco IOS Release 12.1) - ... [full story]

Strengths of H.323, SIP, and MGCP Because there are several different telecommunication environments, more than one choice for signaling and call control is necessary. This section describes some of the strengths of the call control models discussed in this chapter. H.323 H.323, which ... [full story]

Ground-Start Signaling Ground-start signaling, illustrated in Figure 2-11, is a modification of loop-start signaling that corrects for the probability of glare. It solves the problem by providing current detection at both ends. Figure 2-11. Ground-Start Signaling Although loop-start signaling works when you ... [full story]

Echo Is Always Present The magnitude or loudness of the echo is high. The delay time between when you speak and when you hear your voice reflected is significant. The listener hears the speaker twice. The two components of echo are loudness and ... [full story]

Echo Suppression [View full size image] Echo suppression has shortcomings in addressing certain echo conflict situations. Echo cancellation, a schematic of which is shown in Figure 2-23, is a more sophisticated method of eliminating echo. [full story]

Echo Cancellation Rather than breaking or attenuating the return path (as in echo suppression), echo cancellation uses a special circuit to build a mathematical model of the transmitted speech pattern and subtracts it from the return path. Note Echo cancellation applies the ... [full story]

Analog-to-Digital and Digital-to-Analog Voice Encoding This section covers the fundamentals of digitally encoding voice, specifically, the basics of voice digitization and the various compression schemes that are used to transport voice while using less bandwidth. Digitizing speech was a project first undertaken ... [full story]

Analog-to-Digital Signal Conversion Step Procedure Description 1 Sample the analog signal regularly. The sampling rate must be at least twice the highest frequency, to accurately represent the original signal. 2 Quantize the sample. Quantization consists of a scale made up of 8 major divisions or chords. Each chord is ... [full story]

Sampling and the Nyquist Theorem One of the major issues with sampling is determining how often to take those samples (that is, "snapshots") of the analog wave. You do not want to take too few samples per second because when the ... [full story]

Quantization Quantization involves dividing the range of amplitude values that are present in an analog signal sample into a set of discrete steps that are closest in value to the original analog signal, as illustrated in Figure 2-28. Each step is ... [full story]

Voice Compression Standards To conserve valuable WAN bandwidth, you can compress the quantized voice waveforms. Two categories of waveform encoding include: Waveform algorithms (coders) Waveform algorithms have the following functions and characteristics: - Sample analog signals at 8000 times per second - Use predictive ... [full story]

CODECs and Compression Standards CODEC Compression Technique Bit Rate (kbps) G.711 PCM 64 G.726 ADPCM 16,24,32 G.728 LDCELP 16 G.729 CS-ACELP 8 G.729A CS-ACELP 8 A common type of waveform encoding is pulse code modulation (PCM). Standard PCM is known as ITU standard G.711, which requires 64,000 bits per second of bandwidth to transport the voice payload (that ... [full story]

Pulse Code Modulation Figure 2-30 shows that PCM requires 1 polarity bit, 3 segment bits, and 4 step bits, which equals 8 bits per sample. The Nyquist Theorem requires 8000 samples per second; therefore, you can figure the required bandwidth ... [full story]

Two-Wire to Four-Wire Conversion and Echo [View full size image] Telephone networks can experience two types of echo: Acoustic echo Acoustic echo frequently occurs with speakerphones, when the received voice on the speaker excites the microphone and travels back to the speaker. Electrical ... [full story]

E&M Delay-Start Signaling Delay-start signaling, as depicted in Figure 2-19, is the original start protocol for E&M. Figure 2-19. Trunk Supervisory Signaling: Delay-Start [View full size image] Delay-start is used when all of the equipment is mechanical and requires time to process requests. ... [full story]

E&M Immediate-Start Signaling Immediate-start signaling occurs occasionally if a PBX vendor implements wink-start, shown in Figure 2-18, but does not conform to the standards. Figure 2-18. Trunk Supervisory Signaling: Immediate-Start [View full size image] The following scenario summarizes the sequence of events for ... [full story]

E&M Signaling E&M signaling supports tie-line type facilities or signals between voice switches. Instead of superimposing both voice and signaling on the same wire, E&M uses separate paths, or leads, for each. To call a remote office, your PBX must route a ... [full story]

PBX to Intermediate Device Signaling Type Lead On Hook Off Hook I M Ground Battery(-48 VDC) II M Open Battery(-48 VDC) III M Ground Battery(-48 VDC) IV M Open Ground V M Open Ground [full story]

Intermediate Device to PBX Signaling Type Lead On Hook Off Hook I E Open Ground II E Open Ground III E Open Ground IV E Open Ground V E Open Ground Four-wire E&M Type I signaling, shown in Figure 2-12, is actually a six-wire E&M signaling interface common in North America. One wire is the E-lead; the second wire is the M-lead, and the ... [full story]

E&M Type I [View full size image] With the Type I interface, the Cisco voice equipment (tie-line equipment) generates the E signal to the PBX by grounding the E-lead. The PBX detects the E signal by sensing the increase in current through ... [full story]