VoIP(Voice over Internet Protocol : VoIP(Voice over Internet Protocol By
Kothanda Raman G Agenda : Agenda Why VoIP?
What is VoIP?
PSTN vs. Internet.
How VoIP works?
Basic techniques in VoIP.
Protocols used in VoIP.
Challenges/limitations. Introduction : Introduction Traditional method used for transmitting voice is PSTN.
Now more and more communication is done in digital format and transported via data network i.e., internet.
As data traffic is much faster than the telephone traffic, we prefer to send voice over data networks(VoIP). Why VoIP? : Why VoIP? To make and receive calls with / without a computer
Can surf the net while making calls
Can make and receive call to / from PSTN
Digital features not commonly available on PSTN lines such as :
conference and so on are available in VoIP. What is VoIP? : What is VoIP? Voice over Internet Protocol (VoIP) is a technology that enables one to make and receive phone calls through the Internet instead of using the traditional analog PSTN (Public Switched Telephone Network) lines.
VoIP is packetisation and transport of classic public switched telephone system audio over an IP network.
It allows 2-way voice transmission over broadband connection.
It is also called IP telephony, internet telephony, voice over broadband, broadband telephony. PSTN vs. INTERNET : PSTN vs. INTERNET PSTN
Voice network use circuit switching.
Dedicated path between calling and called party.
Bandwidth reserved in advance.
Cost is based on distance and time. INTERNET
Data network use packet switching.
No dedicated path between sender and receiver.
It acquires and releases bandwidth, as it needed.
Cost is not based on distance and time. How does VoIP work? : How does VoIP work? VoIP converts the voice signal from your telephone into a
digital signal , typically reduced in data rate using speech
compression techniques encapsulated in a data packet that
travels over the Internet. : The users voice (or fax) is converted into a digital signal, compressed, and broken down into a series of packets.
The packets are then transported over private or public IP networks and reassembled and decoded on the receiving side.
At the receiving end, the re-assembled packets arrive as a normal sounding voice call.
Packet switching is very efficient. It lets the network route the packets along the least congested and cheapest lines. It also frees up the two computers communicating with each other so that they can accept information from other computers, as well. PACKET SWITCHING What’s Inside the PSTN? : What’s Inside the PSTN? End Office Switch Enterprise Network Subscribers Subscribers Enterprise Network Public Switched Telephone Network What’s Inside an IP Network? : What’s Inside an IP Network? Enterprise Network Enterprise Network Subscribers Subscribers Public Internet or Private WAN Firewall Firewall Routers Routers Routers In most cases, IP Routing Logic is still managed by a Service Provider’s Network
– Not yours VoIP Connections : VoIP Connections ATA (Analog Telephone Adapters)
Connects a standard phone to a computer or an Internet connection for use with VoIP.
The ATA is an analog-to-digital converter.
connect directly to a router and have all the hardware and software necessary right onboard to handle the IP call.
There are several companies offering free or very low-cost software that you can use for this type of VoIP.
All you need is the software, a microphone, speakers, a sound card and an Internet connection How does it work? : How does it work? VoIP is not a protocol. VoIP is a collection of protocols and devices that allow for the encoding, transport and routing of audio calls over IP networks.
Native VoIP Native VoIP
Native VoIP PSTN
PSTN VoIP PSTN What are VoIP Media Gateways? : Fax
VoIP<-> PSTN IP
RTP PSTN PBX Ethernet
ATM IP Voice Applications/
VoIP <-> PSTN Fax
Suppression IP Network VoIP Media Gateways provide the bridge between Phone Systems and VoIP What are VoIP Media Gateways? Bridging Public and Private Networks : PSTN IP Network Ethernet Ethernet User Side
Trunks Enterprise Network Private Extensions FXS
Lines Network Side
Lines Trunking VoIP Gateway Analog VoIP Gateway Bridging Public and Private Networks Basic techniques in VoIP : Basic techniques in VoIP Audio codec's.
Data transport (RTP, RTCP)
RTP (Real-Time Transport Protocol)
RTCP (Real-Time Control Protocol)
Signaling (SIP, H.323). AUDIO CODECS : AUDIO CODECS Here analog signal is converted into digital data.
PCM is used to convert analog voice to digital signal.
Three popular audio codec's
G.723.1(5.3kpbs or 6.3kpbs).
Since voice contains lot of data, it is compressed by Vocoders without compromising the quality and reliability of voice signal. Data Transport (RTP, RTCP) : Data Transport (RTP, RTCP) RTP
RTP stands for Real-Time Transport Protocol.
Application layer protocol for transmitting real time audio, video etc.
The data transfer protocol, deals with the transfer of real-time multimedia data.
Information provided by this protocol include timestamps (for synchronization), sequence numbers (for packet loss detection) and the payload format which indicates the encoded format of the data. Cont… : Cont… RTCP
RTCP stands for Real-Time Control Protocol.
The RTCP is used to specify Quality of Service (QOS) feedback and synchronization between the media streams.
Responsible for periodical transmission of control packets to all participants in the session.
Supports for multi-point communication. Addressing : Addressing Here phone no. is converted into IP address.
Simple format addressing:
<user | phone no.>@<domain | hostname | IP address>
If you make a call using a phone with an adaptor, you’ll be able to dial just as you always have.
If there is no adapter we have to use the IP address of the particular phone. Signaling : Signaling Signaling in VoIP is needed for:
Agreeing on port numbers for RTP/RTCP sessions.
Agreeing on coding/decoding procedures.
Types of signaling protocols:
SIP (Session Initiation Protocol). H.323 : H.323 Recommended by ITU-T.
It is designed to act above transport layer and mainly used for transmission of voice, data and video conferencing over packet networks. SIP Developed by IETF.
It is text based application-layer control protocol for creating, modifying and terminating sessions.
Sessions include Internet Multimedia conferences or Internet Telephone calls. How VoIP works? : How VoIP works? Advantages : Advantages Cheaper call rates.
Better voice quality using wideband codec's.
Adding new features and application over time is easy.
Integration of voice, data, fax and video is possible.
VoIP lets you have many features without paying extra fees
Forwarding Challenges/Limitations : Challenges/Limitations Some VoIP services don’t work during power outages
VoIP is susceptible to worms, viruses and hacking.
Because VoIP uses an Internet connection, it's susceptible to all the hiccups normally associated with home broadband services. All of these factors affect call quality:
Jitter (time variation of a periodic signal or variable delay in communication)
Phone conversations can become distorted, garbled or lost because of transmission errors. Qos- in VoIP : Qos- in VoIP Quality of Service is essential for the success of VoIP.
The human ear is extremely sensitive to even minor changes in an audio signal.
Loss of quality occurs when the voice packets are transferred over the inherently unreliable packet-based networks. Qos- in VoIP : Some methods to enhance the QoS achieved in VoIP are:
Classification of Service: Using the TOS bits in the IP header to set a priority for the voice packet.
Tagging the packets with labels and using the labels to decide the route. Voice packets can be routed over less congested networks.
Reserving resources to meet requirements for bandwidth, delay, jitter, etc. along a particular path through a series of routers.
Thus using above techniques the challenges/limitations of VoIP can be overcomed. Qos- in VoIP Thank you : Thank you