Topic Last Modified: 2011-01-26
If you plan to use Enterprise Voice with SIP trunking, you must deploy a Mediation Server and ensure that other infrastructure and components meet the support requirements appropriate to your deployment model. For details about determining whether to implement SIP trunking, see Why Use SIP Trunking? in the Planning documentation.
You can use the Microsoft Unified Communications Open Interoperability Program for enterprise telephony infrastructure to find qualified PSTN gateways, IP-PBXs, and SIP trunking services, including qualified IP telephony service providers. For details, see the Microsoft Unified Communications Open Interoperability Program website athttp://go.microsoft.com/fwlink/?LinkId=187781.
Mediation Server Support
To implement SIP trunking, you must route the connection through a Mediation Server, which proxies communications sessions between Lync Server 2010 clients and the service provider. The Mediation Server decodes the media traffic from clients and servers and re-encodes it before sending it to the service provider. The re-encoding is needed because SIP trunks do not support some codecs used like Real Time Audio (RTA) or Interactive Connectivity Establishment (ICE) protocol negotiation for firewall traversal.
Each Mediation Server can have two network adapters, which provide an internal and an external network interface. The external interface is commonly called the gateway interface because traditionally it has been used to connect to a PSTN gateway or an IP-PBX. To implement a SIP trunk, you connect the external interface to a Session Border Controller (SBC) at a service provider.
Centralized vs. Distributed SIP Trunking
Centralized SIP trunking routes all VoIP traffic, including branch site traffic, through your data center. The centralized deployment model is simple, cost-effective, and generally the preferred approach for implementing SIP trunks with Lync Server 2010.
Depending on usage patterns within your enterprise, you may not want to route all users through the centralized SIP trunk. To analyze your needs, answer the following questions:
- How big is each site? How many users?
- Which Direct Inward Dialing (DID) numbers at each site get the
most phone calls?
Distributed SIP trunking is a deployment model in which you implement a local SIP trunk at one or more branch sites. VoIP traffic is then routed from the branch site directly to their service provider, without going through your data center.
Distributed SIP trunking is required only in the following cases:
- The branch site requires survivable phone connectivity (for
example, if the WAN goes down). If the branch does need redundancy
and failover, the service provider will charge more and the
configuration will take longer. This should be analyzed for each
branch site. Some of your branches may require redundancy and
failover, while others do not.
- The branch site and data center are in different
countries/regions. For compatibility and legal reasons, you need at
least one SIP trunk per country/region.
The decision about whether to deploy centralized or distributed SIP trunking requires a cost-benefit analysis. In some cases, it may be advantageous to opt for the distributed deployment model even if it is not required. In a completely centralized deployment, all branch site traffic is routed over WAN links. Instead of paying for the bandwidth required for WAN linking, you may want to use distributed SIP trunking.
|For details about why and how you might use distributed SIP trunking, see Branch Site SIP Trunking in the Planning documentation.|
Supported SIP Trunking Connection Types
Lync Server 2010 supports the following connection types for SIP trunking:
- Multiprotocol Label Switching (MPLS) is a private network that
directs and carries data from one network node to the next. The
bandwidth in an MPLS network is shared with other subscribers, and
each data packet is assigned a label to distinguish one
subscriber’s data from another’s. This connection type does not
require VPN. A potential drawback is that excessive IP traffic can
interfere with VoIP operation unless VoIP traffic is given
- A private connection with no other traffic is typically the
most reliable and secure connection type (for example, a leased
fiber-optic connection or T1 line). This connection type provides
the highest call-carrying capacity, but is typically the most
expensive. VPN is not required. Private connections are appropriate
for organizations with high call volumes or stringent security and
- The public Internet is the least expensive connection type, but
also the least reliable with the lowest call-carrying capacity.
Note: Internet connection is the only Lync Server 2010 SIP trunking connection type that requires VPN.
Selecting a Connection Type
The most appropriate SIP trunking connection type for your enterprise depends on your needs and your budget.
- For mid-size or larger enterprise, generally an MPLS network
provides the most value. It can provide the necessary bandwidth at
a cheaper rate than a specialized private network.
- Large enterprises may require a private fiber-optic or T1
- For a small enterprise or branch site with low call volume, SIP
trunking through the Internet may be the best choice, however this
connection type is not recommended for mid-size or larger
The service provider proxy must support the following codecs:
- G.711 a-law (used primarily outside North America)
- G.711 µ-law (used in North America)