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December 22, 2010

Recent Increase in Use of VoIP T1 Systems



A sudden increase in the implementation of mixed vendor VoIP/IP Telephony systems has been witnessed from the past few years.

On one side, where the call center may be powered by Avaya, the regular telephony operation is supported by Cisco (News - Alert) products. Connecting any two VoIP islands from two different vendors presents significant interoperability issues.

VoIP peering is where two VoIP/IPT islands interconnect/interoperate without using either the PSTN or T1 and PRI trunks with legacy signaling. As the trunk signaling protocol, SIP is the most likely candidate. Not just SIP compatibility but also multiple levels of interoperability/normalization will be required.

From the same vendor, the SIP trunking is available between call managers. Even if SIP is used, it cannot it cannot be guaranteed that this solution will interoperate with other vendor’s IPT systems.

Some of the value and benefits of VoIP peering between two IPT islands from different vendors include:

--Accurate caller ID end-to-end

--A common set Universal Resource Identifiers for the calls

--Global call monitoring, CDR and reports, accounting and operator services

--End-to-end call quality monitoring

--Consistent end-to-end QoS

--Eliminating PSTN connections within the enterprise

--Superior bandwidth efficiency over IP trunks vs. T1 and PRI trunks

--Call security within the enterprise

--Full feature support for the user

--Centralized voice mail, IVR and other functions across the trunk

For the interconnection of two different IPT vendor platforms, all of these goals may not be possible. One of the limitations may the VARs who have to learn about the two vendor’s SIP operations before the task is accomplished. To ensure it still works properly, when new IPT software is released, then the interoperability must be reevaluated by the VAR.

In to support signaling among IP devices for multiple media, the SIP standard, RFC 3261, is designed. It has become the vendor choice for VoIP and IP Telephony signaling for IP phones and SIP trunking to the PSTN. These vendor variations are not interoperable.

The most likely candidates as interoperability/normalization challenges are:

Voice signaling protocols variations, telephony feature variations for example one vendor has 2 ways to transfer a call while the other vendor has 5 ways to transfer a call. What do you do about the 3 non-matching features, voice codec compression differences, transparent feature/function support, support of Unified Communications (News - Alert) features such as presence and multimedia, service delivery for DTMF, multiple codecs, fax, modems etc, trunking security, common trunk management, call management end-to-end, voice quality reporting, firewall limitations. trunk bandwidth management and Call Admission Control, trunk call capacity and uniform enterprise wide dial plan.

The most likely solution for interconnecting different IPT vendors is a Session Border Controller. A Session Border Controller is a device/appliance used in VoIP networks to convert the signaling and the media streams used in setting up, conducting, and tearing down telephone calls.

For the internal network, the SBC acts as a server. It also acts as a client to the external network. The SBC has been used for VoIP peering connections to the PSTN and between VoIP carriers. The SBC also provides:

--Security between the two VoIP islands

--Voice codec conversion

--Converting Fax from the T.38 to T.30 standard and reverse

--SIP INFO/NOTIFY signaling and DTMF conversion to RFC 2833

--SIP to SIP-TLS over TCP or UDP (News - Alert)

Another possibility is the Cisco Unified Border Element, which can be deployed between two IPT networks to resolve the interoperability issues. The Avaya (News - Alert) Session Manager is a possible second solution.

In technology related news, Trisys has released Replay RTP, a 100 percent software solution for recording conversations on most IP-based telephone systems.


Deepika Mala is a contributing editor for TMCnet. To read more of her articles, please visit her columnist page.

Edited by Juliana Kenny


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