What is VoIP?

VoIP: Voice over Internet Protocol

VoIP stands for Voice over Internet Protocol (VoIP), which is a technology that allows traditional telephone calls to be transmitted over data networks instead of a regular telephone network. Voice signals are converted into data packets (IP packets) and transmitted over an IP network (private or public). Data packets are disassembled into smaller chunks of data packets on the transmitting end and reassembled on the receiving end to complete the transmission.

Circuit-Switched vs. Packet Switched

Circuit-Switched: When a call is made between two parties, the connection is maintained for the entire duration of the call. With two end points in both directions connecting, the connection is called a circuit. This is the foundation of the Public Switched Telephone Network (PSTN). The connection is kept open and constant between two end points for the duration of the call and no other users are allowed to re-use the circuit.

Packet-Switched: When a call is made between two parties, the user’s transmitting device chops the call into small data packets. Each data packet has an IP address assigned to it which tells the network where to send each packet. When the receiving end gets the packets, it reassembles them into the original data format which forms the audio portion of the call. The connection between the two parties is only open long enough to send small chucks of data. This makes more efficient use of the network since a dedicated circuit is not built between calling parties.

Packet Switch Network Components

VoIP networks are built on software-based switching platforms that provide the functionality of a traditional telephone switch (PSTN circuit switch) without the costs and inefficiencies of the PSTN.

A soft switch platform encompasses the following functionalities and elements which make up a VoIP soft switch:

• Media Control – audio or voice path through the network.

• Routing Processing – manages moving packets through the network to the correct end points.

• Signaling Control – handles the set up and tear down of calls through the network.

Media control is accomplished through the Media Gateway (MGs) which handles the actual transport of voice and takes care of trans-coding the voice traffic from the PSTN to-and-from packet networks. MGs are primarily hardware devices responsible for converting analog voice signals into packet-voice signals for use on a VoIP network.

Other functions the MGs handle are echo cancellation, jitter control, and applying appropriate voice compression algorithms

Routing processing is performed by the Media Gateway Controller (MGC). The MGC is also known as the “Call Agent” in the VoIP space. The MGC is situated centrally in the network and takes SS7 or SIP signaling information from the signaling gateway to provide routing instruction for calls through the network to the correct end points.

Network signaling is performed on the Signaling Gateway which provides the connection to the SS7 network. The Signaling gateway provides the signaling control information to the Media Gateway Controller or “Call Agent” for call set up and call tear down between end points on the network. This is a software based system with special interfaces to interconnect with the SS7 network/elements with the IP based elements of a VoIP network.

Definitions

SIP Session Initiated Protocol

H.323 A suite of protocols to facilitate multimedia communications

MGCP Media Gateway Control Protocol

RTP Real-Time Transfer (Transport) Protocol

UDP User Datagram Protocol

TCP/IP Transmission Control Protocol / Internet Protocol

Call Flow

• VoIP Enables a telephone call utilizing a computer/data network

• Voice signal is converted to a digital signal passed over a network and converted back to voice on the other end

• Phone to Phone, Computer to Phone, Computer to Computer