Cisco AS5850 Series Universal Gateways

TDM Switching in the Cisco AS5850 Series Gateways

Q. What is time division multiplexing (TDM) switching?
A. TDM switching is the ability of the Cisco AS5000 Series Gateways to switch information directly between two DS0 circuits (DS01 and DS02) without change as shown in figure.

[TDM Switching]

Q. What are the key benefits of TDM switching?
A. 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. How does TDM switching fit into Cisco ASAP?
A. Cisco ASAP replaces the multiple overlay networks currently needed to deploy multiple services, with one unified network.

TDM switching enables service providers to migrate to Cisco ASAP by allowing them to cap investment in the legacy technology, and continue the use of legacy services, a key component of managed migration to new services as shown below in figure.

[Overlay to Cisco ASAP Network]

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. Please note that 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. Does TDM switching require any DSP resource?

A. It depends on the type of the calls (incoming and outgoing call legs, and the location of the time slot interchange circuit in the gateway.

• TDM switching between SS7-PRI, SS7-SS7 and PRI-PRI calls
  For universal gateway platforms (Cisco AS5350, AS5400, and AS5850), no digital signal processor (DSP) is used. The T1/E1/DS3 cards, used in the universal  gateway contain the time slot interchange circuit.
  
  The Cisco AS5800 requires a voice DSP card or a modem DSP card for TDM switching. The time slot interchange circuit is available only in the DSP card, andis not available in the T1, E1, and DS3 card used in the Cisco AS5800 platform.
  
  Cisco AS5800 when used with a Double Density Modem Module (DMM) card doesnot use a DSP. The DMM card is used only for the time slot interchange circuit.
  

• Cisco AS5800 when used with a voice feature card (VFC) card uses the DSP during call setup. After call setup is complete, the DSP resource is released.
  A modem DSP will be used if both modem and voice DSPs are present in the  platform.
  

• The Cisco AS5300 requires a voice DSP card for TDM switching. The time slot interchange circuit is available only in the voice DSP card and is not available in the T1/E1 card used in the Cisco AS5300 platform. The DSP is used only during the call setup and teardown. The DSP resource is not used once the call setup is completed.
  

• TDM switching between SS7-CAS and PRI-CAS calls
  

When a Channel Associated Signaling (CAS) call is involved in TDM switching,   DSP resource is used to setup or release the call. DSP resource stays in the call path once the call is established to monitor the in-band signaling, so that the call  can drop normally.

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?

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 and benefits of TDM switching are:

• Cap investments in legacy technology—TDM switching can be used to protect the investments already made in the legacy technology and equipment while enabling the new investments in the technology for new services. The legacy systems can continue to be transparently used using the PRI/CAS trunk interfaces.

• Resell PRI generated from intermachine trunks (IMT)—PRI interface can be generated from the IMT (SS7) interface, which can then be sold to customers for new revenue. Cisco universal gateways are ideally suited for customers requiring PRI grooming in conjunction with dial, voice over IP (VoIP) or fax services.

• Lower interconnect costs with SS7—IMT trunks are 40-70 percent cheaper than PRI. Customers can migrate to SS7, directly connected to the Cisco gateway and continue receiving benefits from their legacy systems.

• Managed migration to new services—Migration to new IP-based services which provide a new revenue source can be easily accomplished by gradually cutting over the customers to new services, starting with the new customers first, followed by the existing customers. Refer to figure below.

[Managed Migration to New Services]

• Support for call redirection—SS7 calls can be redirected back to the SS7 network based on dialed number. This feature may be used for LNP service in Europe, provided ISUP-ISUP transparency is not required.

• TDM switching without a DSP—TDM switching uses no DSPs and therefore lowers cost of grooming service. This enables service providers to pay as they grow for new services.

• Use of external test equipment—TDM switching can be used to connect to test tone-generating devices needed to meet the service providers provisioning or homologation requirement. Connecting to external test equipment using TDM switching can provide type 105 test tones in the Cisco AS5000 Series Gateways.

Q. Which gateways support TDM switching?

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

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 dial peer in the gateway.

Q. Is TDM switching between SS7-SS7 call transparent?

A. No, not all the information elements from the incoming ISUP message is passed to the outgoing ISUP message. ISUP to ISUP transparent TDM switching will be available by the end of 2001.

Q. How much does the transparent TDM switching between SS7-SS7 feature cost?

A. This feature is offered at no additional charge.

Q. When is this feature going to be available?

A. TDM switching feature is available now in Cisco AS5350 and Cisco AS5400 Universal Gateways, Cisco AS5800 Access Server and Cisco AS5300 Voice Gateway. TDM switching in the Cisco AS5850 Universal Gateway will be available in the second half of 2001.