Microsoft Lync Server 2010 communications software and Microsoft Office Communications Server 2007 R2 interoperate with the NET (Network Equipment Technologies) Session Border Controller (SBC) when used for SIP Trunking to Internet telephony service providers (ITSPs). This article describes the supported topologies for using Lync Server 2010 or Office Communications Server 2007 R2 with NET’s SBC. 

Author: Marcel de Kruif

Publication date: June 2011

Product version: Microsoft Lync Server 2010 and Office Communications Server 2007 R2

Introduction

Microsoft Lync Server 2010 and Microsoft Office Communications Server 2007 R2 introduced several new enhancements, including support for SIP Trunking. Lync Server 2010 and Office Communications Server 2007 R2 interoperate with NET’s (Network Equipment Technologies) Session Border Controller (SBC). NET and Microsoft work in close partnership to ensure that the NET products continue to be qualified under the Unified Communications Open Interoperability Program (UCOIP) and support use of certified service providers to connect enterprise networks with SIP Trunking services. NET joined Microsoft in the Unified Communications Interoperability Forum (UCIF), http://www.ucif.org, as a contributing member.

An SBC is not required to be deployed for Lync Server or Communications Server 2007 R2. However, some Internet telephony service providers (ITSPs) may require an organization to deploy an SBC as managed customer premises equipment (CPE) for the following reasons:

  • Support for existing Telco equipment during migration to Lync Server 2010 or Office Communications Server 2007 R2
  • Signaling and media interworking (transcoding): The service provider may support certain codecs such as G.729 that are not supported by internal enterprise telephony networks. A carrier managed CPE can handle the media and signaling differences between the networks.
  • Quality of Service (QoS) assurance: Using a carrier managed SBC, the service provider can ensure that the enterprise networks properly interoperate with the carrier network and in the process ensure that a certain Qualify of Service is guaranteed.

This article describes the supported and unsupported topologies for using NET’s SBC in Microsoft Lync Server 2010 and Office Communications Server 2007 R2 SIP Trunk deployments. The preferred deployment model includes an SBC at the core of service provider networks. Another supported deployment is to have an SBC on the customer network when it is owned and managed by the Telco, service provider, or ITSP.

Supported Topologies

The following topologies are supported by Microsoft for interoperating SIP Trunking service providers with Office Communications Server 2007 R2.

  • Mediation Server connected directly to the service provider’s SIP Trunk network infrastructure
  • Mediation Server connected to a NET’s SBC that is managed or owned by the ITSP deployed in the customer’s network perimeter

Figures 1 and 2 illustrate the Microsoft and NET supported deployment options and work when used with ITSPs qualified through the UCOIP program. The topology in figure 4 is unsupported.

Mediation Server connected directly to the ITSP network. Organizations can connect Mediation Server with a qualified ITSP by using Direct SIP. An SBC is not required at the customer premises for this topology. IP virtual private network (VPN) is used for helping to securely connect the enterprise Lync Server or Office Communications Server network with the public switched telephone network (PSTN) over a SIP Trunking service provider network. A VPN or a private network is used for connecting the Microsoft UC and the PSTN networks, which helps to guarantee voice data security and QoS. Additional security with Transport Layer Security (TLS) for SIP signaling and Secure Real Time Transport Protocol (SRTP) for media are not required. In this topology, an SBC is deployed in the ITSP network for terminating SIP Trunk from the ITSP side.

Figure 1. Mediation Server connected directly to qualified service providers by using Direct SIP

If an IP-public branch exchange (PBX) exists in the network, the IP-PBX is connected directly to the Mediation Server through Direct SIP. This configuration requires that Direct SIP connectivity is supported by the IP-PBX. The list of IP-PBXs that supports Direct SIP is available on the UCOIP page.

NET’s SBC deployed in customer’s network perimeter. Figure 2 illustrates the NET’s SBC (VX1200/VX1800, UX2000, or Tenor series) connected to the Mediation Server and legacy telephony equipment. In this topology, SIP Trunk connectivity for the Lync Server 2010 or Office Communications Server is provided through the SBC that is owned or managed by the ITSP. Additionally, an SBC is also deployed in the ITSP network to terminate SIP trunk from the ITSP side. The NET’s SBC allows the customer to migrate to Lync Server 2010 or Office Communications Server 2007 R2 from their existing voice network.

Another option is to connect NET SBC to the IP-PBX and connect the IP-PBX to the Mediation Server through Direct SIP. In this topology, SIP Trunk to Lync Server 2010 or Office Communications Server 2007 R2 is provided though the existing IP-PBX environment. The IP-PBX has an existing SIP Trunk to the ITSP.

Figure 2. Mediation Server connected through a NET’s SBC that is owned or managed by ITSP

In figure 3, the NET’s SBC is used to deploy SIP Trunks from multiple service providers for load balancing or for failover reasons between ITSPs when necessary.

  

Figure 3. High-Availability (HA), resiliency, and least cost routing among different SIP Trunking service providers

Unsupported Topologies

As illustrated in figure 4, an Edge Server uses enhanced security and therefore an SBC is not required between Edge Servers and external Microsoft Lync 2010 or Microsoft Office Communicator clients, or between any two Lync clients or Communicator clients. Edge Servers help provide protection against unauthorized access by using various security measures. The communications are encrypted and authenticated.

 

Figure 4. SBC connected to an Edge Server (not supported)

Summary

Microsoft and NET have collaborated to support direct connectivity deployment models between Lync Server 2010 Mediation Server, Office Communications Server 2007 R2 Mediation Server, and NET SBC.

An SBC is not required in the enterprise network when Lync Server 2010 or Office Communications Server 2007 R2 is connected to a qualified service provider. However, when an organization wants to connect an existing Time Division Multiplexing (TDM) or an unqualified IP-PBX in the network, needs a gateway to connect different networks with different codecs, or if the carrier wants to ensure a consistent Quality of Service, a carrier managed NET SBC can be deployed in the network.

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Keywords: Session Border Controller, SBC, SIP Trunking, Lync Server, Office Communications Server