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The VX system uses a few key concepts which represent the fundamental building blocks of a call routing system. Understanding these key concepts and how they work together is critical to effectively building a VX call routing configuration for a specific environment. If you are new to the VX system, be sure to review this section before proceeding with the configuration of a VX system.

VX Call Routing Structure Elements

The VX system uses several fundamental building blocks to build a call routing system such as ports, trunk groups and call routes. The relationship of these building blocks as used in a call flow is shown in the diagram below:

VX Call Routing Structure Elements

VX Call Routing Structure Example

The following diagram shows an example VX call routing structure connecting a private branch extension (PBX) phone on the left to an IP-based (VoIP) phone device connected to a Microsoft Office Communication Server (OCS) on the right.

Example VX Call Routing Structure

VX Terminology

The VX system uses some key terms to describe its call handling and routing systems. Some of these terms vary from general telecommunications usage, so be sure to review these terms to properly understand their use in the context of VX.


Chassis - The logical representation of the physical box enclosing the VX system, which contains physical Slots for communication interface cards and can contain a virtual slot to represent communication interfaces running over internet protocol (IP).


Slot - A physical Time-Division Multiplexing (TDM) communication interface card installed in the VX chassis, such as interfaces for T1, E1 or Analog FXS (Foreign eXchange Station). VX systems also allow the creation of a virtual slot, which represents a generic container for call connections run over IP networks, such as SIP, H.323 and BSP. On VX systems, the virtual slot is always designated as Slot 15. Slots contain one or more Ports.


Port - In the VX system, a Port refers to a cable connection into a physical port on an communication interface card or a logical grouping of virtual connections in the case of a virtual slot. In the VX system, a Port represents a group of similar Channels. Ports are mapped to Trunk Groups.


Channel - In the VX system, a channel refers to a set of electronic signals or IP message packets which complete one half of a single phone call. Channels are classified as either ingress (inbound) or egress (outbound) relative to the system that is routing the call. In order to route a call, the routing system must have both an ingress and egress channel available in order to receive and then transmit the call. The number of channels available on a routing system limits the total number of calls that can be simultaneously routed through that system. Channels are mapped to Trunk Groups.

  • Physical Channel - In the VX system, a physical channel refers to a timeslot within a physical TDM communications line such as T1, E1 or Analog FXS. The number of physical channels available on a TDM line varies depending on the protocol being used and/or the service provider agreement. However, there is always a fixed upper limit to the total number of physical channels than can be run on a TDM line.
  • Virtual Channel - In the VX system, a virtual channel refers to the logical representation of a channel transmitted over an IP network. There is no fixed upper limit to the number of virtual channels that can be run over an IP network.


Trunk Group - In the VX system, a trunk group is a logical representation of a call source or a call destination used in a Call Route. In the VX system, Ports and Channels (both physical and virtual) are mapped to Trunk Groups so they can be represented in a Call Route. In the simplest case, a Trunk Group represents an entire physical communications connection – such as a DS1 line – and all its Channels. In more complex cases, Trunk Groups represent a subset of Channels on a Port, or represent more than one Port. VX administrators determine the mapping of Ports and Channels to Trunk Groups based on call routing requirements.


Call Route - In the VX system, a Call Route is the decision logic that directs calls from an inbound trunk group source to an outbound trunk group destination. Call Routing in VX is defined in Call Route Table containing one or more Call Route Entries. A trunk group is assigned a Call Route Table in its configuration and then any inbound calls on that trunk group are processed using the assigned Call Route Table.


Call - In the VX system, a Call is a set of signals for a telephone call contained by an ingress (inbound) Channel and a corresponding egress (outbound) Channel. Within VX, a call is tracked by a unique Call Serial Number (CSN) that is created and assigned once the two channels are paired. A Call Serial Number can be used to trace a call in the VX debug log from setup to termination.


Channel Profile - In the VX system, a Channel Profile allows users to modify the settings of a communication protocol used by the VX system such as ISDN, SIP, CAS or BSP in order to fit their environment. The Channel Profile are applied to Ports. A Channel Profiles applied to Port must match the Port's Port Type.


Codec - A device or computer program that encodes and decodes a digital data stream or signal. In the VX system, codecs are used to encode and decode voice call signals and fax transmissions so they can be routed through IP networks.


Media Class - In the VX system, a Media Class is a set of Codecs options that can applied to Channels, Trunk Groups and Call Routes. Once a call has been received by a VX system, it is encoded according to the Media Class settings for the applicable inbound Channel, Trunk Group, Call Route, outbound Trunk Group and the requirements of the receiving phone device. When setting the Media Class for Channels, Trunk Groups and Call Routes, at least one of the codecs in the chosen Media Class must be supported by the device receiving the call (such as a desk phone, desktop computer or other telephony system).

VX Any to Any Concept

The "any to any" concept is derived from VX's unique ability to convert any supported ingress call protocol to any supported egress call protocol.

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Analog FXS

CAS

ISDN

SS7

SIP

H.323

BSP

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CAS

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ISDN

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SS7

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SIP

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H.323

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BSP

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