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FAQs on Voice Gateways using TDM Switching


This document answers  frequently asked questions about the Voice Gateways using TDM Switching mode

Q. What is time division multiplexing (TDM) switching?
TDM switching is the ability of the Voice Gateways to switch information directly between two DS0 circuits (DS01 and DS02) without change, permanently dedicated for the Voice Conversation

Q. What are the key benefits of TDM switching?
Some of the key benefits of TDM switching are:

·       TDM switching can positively impact investment, cost and the revenues of the service providers.

·       TDM switching enables service providers to cap their investments in the legacy technology and provide a way to use the legacy services and the new services simultaneously.

·       The service providers can reduce their recurring Primary Rate Interface (PRI) costs by moving to Signaling System 7 (SS7) and generate new revenues from reselling PRI generated from the SS7/Inter Machine Trunks (IMT) trunks.

·       TDM switching is an integral part of Cisco Any Service, Any Port (ASAP) architecture, which the service providers can exploit to their advantage.

Q. Where the TDM Switching Feature available in Cisco Equipments?

A. TDM switching feature is available in Cisco AS5350 and Cisco AS5400 Universal Gateways, Cisco AS5800 Access Server and Cisco AS5300 Voice Gateway.

Q. Which Cisco gateways support TDM switching?

A. The Cisco AS5300, AS5350, AS5400, AS5800 and AS5850 support TDM switching.

Q. Which Voice Circuits are Supported in the Cisco Voice Gateways ?


T1 – Uses TDM to transmit digital data over 24 voice channels

E1 - Uses TDM to transmit digital data over 30 voice channels


Q. What is mean by DS0 in Voice GW ?

A. DS0 is a Logical Voice Port in the E1/T1 and ds0-group command creates the logical ports in the voice gateways in the slot/port. 1 DS0 is 64 Kbps.

E1 has 30 DS0 & T1 has 24 DS0

Q. How does the platform decide that a call needs to be TDM switched?

A. The dialed numbers for TDM switching is specified through the configuration of POTS dial peer in the gateway.

Q. How many DS0 channels does it take to provide TDM switching to a call?

A. A TDM switched call consists of an incoming call leg and an outgoing call leg. Each leg of the call takes one DS0 channel. Therefore TDM switched call uses two channels.

Q. Can the two DS0 channels used for TDM switching come from two different T1 or E1 interfaces?

A. Yes. The two DS0 channels used for TDM switching can come from any two T1 or E1 interfaces in the platform.

Q. Can E1 and T1 co-exists on Voice Gateways ?

A. T1 and E1 interfaces cannot co-exist simultaneously in the Cisco AS5000 Series Gateways.

Q. How many TDM switched calls can a Cisco AS5000 Series platform support?

A. The number of TDM switched calls that a Cisco AS5000 Series platform can support depends on the DS0 capacity of the platform. Since it takes two DS0 channels to TDM switch a call, the maximum number of TDM switched calls in the platform is equal to half the number of DS0 channels available in the platform.

Q. Which type of calls (SS7, PRI, CAS) can be TDM switched?

A. The Cisco AS5000 Series Gateways allow TDM switching of calls between SS7, PRI and CAS trunks.

Q. What are some of the applications of TDM switching using Voice Gateway?

A. TDM switching can be used in various situations to reduce cost, increase revenue and provide services that would not be possible otherwise. Some of the major applications includes

  • Telcom Mobile & landline Service providers for transiting local and long distance voice calls thru TDM & GSM technology
  • Prepaid calling card service
  • Hosted IP telephony
  • Unified communications in call centre solutions

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Last update:
‎10-07-2010 11:56 PM
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