A softswitch is a central device in a telephone network which connects calls
from one phone line to another, entirely by means of software running on a
computer system. This work was formerly carried out by hardware, with physical
switchboards to route the calls.
A softswitch is typically used to control connections at the junction point
between circuit and packet networks. A single device containing both the
switching logic and the switching fabric can be used for this purpose; however,
modern technology has led to a preference for decomposing this device into a
Call Agent and a Media Gateway.
The Call Agent takes care of functions like billing, call routing, signalling, call services
and so on and is the 'brains' of the outfit. A Call Agent may control several different
Media Gateways in geographically dispersed areas over a TCP/IP link.
The Media Gateway connects different types of digital media stream together to
create an end-to-end path for the media (voice and data) in the call. It may
have interfaces to connect to traditional PSTN networks like DS1 or DS3 ports
(E1 or STM1 in the case of non-US networks), it may have interfaces to connect
to ATM and IP networks and in the modern system will have Ethernet interfaces to
connect VoIP calls. The call agent will instruct the media gateway to connect
media streams between these interfaces to connect the call - all transparently
to the end-users.
The softswitch generally resides in a building owned by the telephone company
called a central office. The central office will have telephone trunks to carry
calls to other offices owned by the telephone company and to other telephone
companies (aka the Public Switched Telephone Network or PSTN).
Looking towards the end users from the switch, the Media Gateway may be
connected to several access devices. These access devices can range from small
Analog Telephone Adaptors (ATA) which provide just one RJ11 telephone jack to an
Integrated Access Device (IAD) or PBX which may provide several hundred
telephone connections.
Typically the larger access devices will be located in a building owned by the
telephone company near to the customers they serve. Each end user can be
connected to the IAD by a simple pair of copper wires.
The medium sized devices and PBXs will typically be used in a business premises
and the single line devices would probably be found in residential premises.
In more recent times (i.e., the IP Multimedia Subsystem or IMS), the Softswitch
element is represented by the Media Gateway Controller (MGC) element, and the
term "Softswitch" is rarely used in the IMS context.
Feature server as a part of softswitch The feature server, often built into a call
agent/softswitch, is the functional component that provides call-related features.
Capabilities such as call forwarding, call waiting, and last call return, if implemented in
the network, are implemented in the feature server. The feature server works closely
with the call agent, and may call upon the media server to provide these services.
These features do not require the subscriber to explicitly request them but tend to be
triggered within the call handling logic.
Take the last call return feature. While there are at least two common variants
on this feature in the PSTN today, we are describing the one in which the user
picks up the phone, dials *69, and hears, “The number that last called you was
303-555-1212. Press 1 to return this call.”
This is a service of the feature server. When the call agent sees the dial string *69, it
triggers an invocation of the feature server function. The feature server examines its
database, finds the user and the caller identification of the last call, then asks the
media server to play the announcement and collect a digit. When the media server
returns a “1”, the feature server instructs the call agent to establish a call between
the user and the party that last called that user.
Attributes and Credits
The information and facts supplied on this subject
derive from http://en.wikipedia.org/wiki/Main_Page
from one phone line to another, entirely by means of software running on a
computer system. This work was formerly carried out by hardware, with physical
switchboards to route the calls.
A softswitch is typically used to control connections at the junction point
between circuit and packet networks. A single device containing both the
switching logic and the switching fabric can be used for this purpose; however,
modern technology has led to a preference for decomposing this device into a
Call Agent and a Media Gateway.
The Call Agent takes care of functions like billing, call routing, signalling, call services
and so on and is the 'brains' of the outfit. A Call Agent may control several different
Media Gateways in geographically dispersed areas over a TCP/IP link.
The Media Gateway connects different types of digital media stream together to
create an end-to-end path for the media (voice and data) in the call. It may
have interfaces to connect to traditional PSTN networks like DS1 or DS3 ports
(E1 or STM1 in the case of non-US networks), it may have interfaces to connect
to ATM and IP networks and in the modern system will have Ethernet interfaces to
connect VoIP calls. The call agent will instruct the media gateway to connect
media streams between these interfaces to connect the call - all transparently
to the end-users.
The softswitch generally resides in a building owned by the telephone company
called a central office. The central office will have telephone trunks to carry
calls to other offices owned by the telephone company and to other telephone
companies (aka the Public Switched Telephone Network or PSTN).
Looking towards the end users from the switch, the Media Gateway may be
connected to several access devices. These access devices can range from small
Analog Telephone Adaptors (ATA) which provide just one RJ11 telephone jack to an
Integrated Access Device (IAD) or PBX which may provide several hundred
telephone connections.
Typically the larger access devices will be located in a building owned by the
telephone company near to the customers they serve. Each end user can be
connected to the IAD by a simple pair of copper wires.
The medium sized devices and PBXs will typically be used in a business premises
and the single line devices would probably be found in residential premises.
In more recent times (i.e., the IP Multimedia Subsystem or IMS), the Softswitch
element is represented by the Media Gateway Controller (MGC) element, and the
term "Softswitch" is rarely used in the IMS context.
Feature server as a part of softswitch The feature server, often built into a call
agent/softswitch, is the functional component that provides call-related features.
Capabilities such as call forwarding, call waiting, and last call return, if implemented in
the network, are implemented in the feature server. The feature server works closely
with the call agent, and may call upon the media server to provide these services.
These features do not require the subscriber to explicitly request them but tend to be
triggered within the call handling logic.
Take the last call return feature. While there are at least two common variants
on this feature in the PSTN today, we are describing the one in which the user
picks up the phone, dials *69, and hears, “The number that last called you was
303-555-1212. Press 1 to return this call.”
This is a service of the feature server. When the call agent sees the dial string *69, it
triggers an invocation of the feature server function. The feature server examines its
database, finds the user and the caller identification of the last call, then asks the
media server to play the announcement and collect a digit. When the media server
returns a “1”, the feature server instructs the call agent to establish a call between
the user and the party that last called that user.
Attributes and Credits
The information and facts supplied on this subject
derive from http://en.wikipedia.org/wiki/Main_Page
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| Selecting a VoIP Solution Phone System for Home and Business. |
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The VoIp Solution Workbook is a comprehensive guide to terms and definitions that
are commonly used in reference to understanding a VoIP Solution.
are commonly used in reference to understanding a VoIP Solution.
| Softswitch |