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VoP
Tutorial
Voice over Packet
A VoP application allows both voice and signaling information to be
transported over a packet network. This allows providers to take advantage
of the flexibility and efficiency of packet networks. It also reduces
costs for the providers by consolidating voice, data and fax traffic
on one network.
For comparison:
A circuit-switched network is a network in which a physical path
is obtained for and dedicated to a single connection between two
end-points in the network for the duration of the connection.
A packet-switched network is a network in which small units of
data (packets) are routed through a network based on the destination
address contained within each packet. This type of communication
is connectionless, rather than dedicated like the circuit-switched
network. This means that once the data is sent, the connection is
broken until further information is either sent or received. This
allows the communication network to be shared by a larger number
of users.
In VoP systems, a gateway is needed to connect network traffic
between circuit-switched and packet-switched networks for service providers.
Examples of the various gateways include voice over IP gateways, softswitch
media gateways, voice over broadband (cable and DSL) gateways, and IP
Centrex systems. These systems primarily carry voice, but the traffic
can also include data or fax.
Types of VoP
VoIP (Internet
Protocol)
VoIP is a connectionless
protocol that allows traffic (packets) to be routed along paths
with the least congestion. Because VoIP uses
a connectionless, best effort methodology, challenges
exist with voice quality, latency and packet loss, as well as call
control and system management.
VoDSL (Digital
Subscriber Line)
DSL is employed by the phone companies to provide data and communications
services on their existing infrastructure. VoDSL can be delivered
over ATM, frame relay or IP. Because of the ability to offer QoS,
most initial implementations used ATM, but IP networks are increasing
in popularity. There are two basic components in a VoDSL system:
- DSL modem (or Integrated Access Device - IAD) in the consumer's
home to interface between the DSL network service and the
customer's voice/data equipment.
- Voice gateway,
which receives the voice traffic from the data network, depacketizes
it and sends it to a Class-5 switch on the PSTN (Public Switched
Telephone Network). The switch provides dial tone, call routing
and other services for the circuit-switched network.
VoFR (Frame Relay)
This technology is most widely used in corporate networks
due to its flexible bandwidth, maturity and diverse traffic support.
It was originally developed to transport data, though, and therefore
the protocol mechanisms and QoS (Quality of Service) were not defined
for voice traffic. Much work is being done to develop standards that
enable frame relay for voice communication - specifically to suppress
silence, ensure consecutive delivery and decrease delays.
VoATM (Asynchronous
Transfer Mode)
ATM is a high-speed scalable technology that can support voice,
data and video simultaneously. It uses short, fixed-length packets
called cells for transport. Information is divided within the
cells, transported and then re-assembled at their destination.
ATM allows providers to guarantee QoS - for this reason, 80% of
the world's carriers use ATM in the core of their networks. It
is also chosen by large corporations to connect locations over
a WAN.
ATM
uses a technique called out-of-band signaling which enables
it to
establish
call paths for the voice samples using signaling-only circuits
that handle signaling for a large number of calls. This is
a more
efficient system than the in-band signaling used in the
PSTN because in-band signaling requires that some part of the
bandwidth used to carry the voice samples is used for control
information.
Additional
sources of information*
Telogy
Networks' VoP White Paper
Protocols.com
- Voice over FR, IP and ATM
ATM
Forum
Companies
providing VoP solutions
Intel
Brooktrout
Technology
AudioCodes
*The WAVE Report is
not responsible for content on additional sites |
