SIP Trunking for the Contact Center
SIP Trunking is a real-time IP communications service delivered by an Internet Telephony Service Provider (ITSP) that allows enterprises with contact centers to route inbound and outbound voice and fax traffic over a broadband data service using the Session Initiation Protocol (SIP), Real-Time Transport Protocol (RTP), and Fax over IP (FoIP) protocol known as T.38. As an access alternative to the traditional Public Switched Telephone Network (PSTN), SIP trunking extends VoIP and FoIP connectivity beyond the enterprise network edge.
A SIP trunk is primarily implemented as a set of concurrent call sessions routed over the IP backbone of an Internet Service Provider (ISP) by an ITSP. The ISP and ITSP may be one and the same, or an ITSP may leverage third-party ISP IP backbones and enterprise broadband connections to deliver the SIP trunking service. Because SIP trunking enables an enterprise to use the same IP connection for voice, fax, and data communications, it can yield significant cost savings compared to TDM trunking. SIP trunking also offers more provisioning flexibility than TDM trunking.
An Enterprise Session Border Controller Addresses SIP Trunking Deployment Issues
When deploying a SIP trunking service in an enterprise environment, several important issues should be considered: secure firewall traversal, SIP interoperability and security, VoIP service demarcation, legacy PBX integration, and Fax over IP (FoIP) support. A Dialogic® BorderNet™ 500 Gateway can help deliver SIP trunking services smoothly and efficiently by delivering enterprise session border control functions.
The drawing on this page shows the placement of a BorderNet 500 Gateway in an enterprise network.
Dialogic® BorderNet™ 500 Gateway in the Enterprise Network
Secure Firewall Traversal
Typical data network firewall implementations aim to allow public internet data traffic to securely traverse the enterprise network edge. They normally do not support the SIP protocol and consider inbound telephone calls using the SIP protocol that seek a particular IP endpoint or address within the enterprise network domain as unexpected external requests. In fact, data firewalls are specifically designed to protect against such external requests, which are seen as an attack and a danger to the internal network.
BorderNet 500 Gateways work seamlessly with existing firewalls on the customer premise to allow authenticated SIP traffic through the enterprise firewall at the network edge. While traditional firewalls normally block SIP traffic — including mission-critical applications such as VoIP — BorderNet 500 Gateways resolve this issue by working with existing security solutions to permit authenticated traffic from SIP trunks to flow freely into an enterprise.
SIP Interoperability
SIP protocol implementations from various service providers and customer premise equipment vendors usually have subtle differences, and SIP components and extensions supported by one vendor may not be supported by another.
BorderNet 500 Gateways can resolve SIP interoperability issues in a number of ways. First, BorderNet 500 Gateways have been tested for interoperability with IP-PBXs from leading vendors such as Alcatel, Avaya, Cisco, Mitel, NEC, Nortel, and Siemens. In addition, their Session Border Control (SBC) function has been tested with service providers such as AT&T, Level 3, Broadvox, and many others.
BorderNet 500 Gateways are also equipped with a SIP interoperability toolkit that allows the customization of SIP protocol messages through header manipulation, advanced routing capabilities, and a Back-to-Back User Agent (B2BUA), which can be used to rapidly enable connectivity between new services and premise endpoints.
SIP Security
Data network firewall implementations typically protect the enterprise from IP data threats originating on the public internet. They are not designed to secure the corporate network from threats that use the SIP communications protocol.
To supplement firewall security and protect the enterprise from SIP communications threats, BorderNet 500 Gateways include a wide variety of SIP security features, such as B2BUA network elements, deep packet inspection, NAT traversal, SRTP, TLS, and HTTPS. These features can provide a secure border for the premise network edge, nullifying threats from denial of service, theft of service, SPAM, and SPIT attacks, and addressing additional SIP security concerns.
VoIP Service Demarcation
When the PSTN is in use, a demarcation point (an actual physical location) exists on the enterprise premise at which the service provider terminates its trunking service. On one side, the enterprise owns and maintains services and equipment while on the other, the service provider takes that responsibility.
Since no clear physical demarcation point normally exists when SIP trunking is used, BorderNet 500 Gateways can supply a logical service termination point along with detailed call quality statistics for managing service quality.
Legacy PBX Integration
While many enterprise PBX systems are now based on the SIP protocol, a substantial number of non-SIP-based hybrid PBXs, IP-PBXs, and TDM PBXs are still in use. Many of these legacy PBX systems either cannot handle the SIP protocol, or a very expensive upgrade may be required to enable SIP trunking service.
BorderNet 500 Gateways are available with SIP-to-TDM gateway subsystems capable of converting SIP trunks into T1/E1, PRI, CAS, or ISDN BRI trunk groups to create an interface with legacy PBX systems. The TDM interfaces can also be used for connectivity to the PSTN, either for failover or for general call routing.
Fax over IP Support
Fax is often overlooked when a SIP trunk deployment is planned, and the traditional fax transmission protocol (T.30) has proven unreliable when sent over packet networks. Although T.30 fax pass-through techniques improve reliability, better results can be achieved by using the FoIP T.38 protocol across an IP network, including an Internet Telephony Service Provider (ITSP) network.
BorderNet 500 Gateways support both standard T.30 fax and T.38 FoIP gateway capabilities, and can handle up to 120 channels of simultaneous fax traffic. The gateways also support high V.34 transmission rates (33.6 kbps) for both T.30 and T.38 protocols, which significantly reduces the time needed to send a fax with the older and considerably slower V.17 (14.4 kbps) fax transmission technique.