Session Border Controller
Before I start explaining what is a Session Border Controller, let me first explain the architecture of a typical VoIP network, which will help you visualize and understand the purpose and functionality of SBC easily.
In a typical company, each employee has an extension on his/her desk connected to an IP PBX or phone system. The phone system may be connected to the outside world using a combination of analog or digital telco lines and VoIP. If a person dials a local extension, the IP PBX diverts the call internally to that extension. If the number dialed is on the public telephone network or PSTN, then that call is routed to the PSTN network. Since long-distance calls can be expensive, it is usually cost advantageous to route the call to a VoIP service provider instead of the local telco line to reduce the phone bill of the company significantly. Therefore, a device known as a Session Border Control or SBC is deployed on the border of company’s private network and VoIP service provider’s public network.
While sitting on the border of public and private network, the Session Border Control or SBC can perform the following functions:
- The SBC can protect the private network and other devices from malicious attacks such as a Denial-of-Service attack (DoS) or Distributed DoS, Toll Fraud via rogue media streams. It can also provide Malformed packet protection and perform encryption of signaling and media for privacy and security.
- The SBC can allow different parts of the network to communicate through the use of a variety of techniques such as NAT traversal, SIP message and header manipulation, IPv4 to IPv6 interworking, VPN connectivity, Protocol translations between SIP, SIP-I, H.323.
- The Session Border Control can provide QoS benefits to a network including functions like traffic policing, resource allocation, call admission control, etc.
- Session Border Controllers also often provide support for regulatory requirements such as emergency calls prioritization and lawful interception.
- Some newer SBCs also have built-in digital signal processors (DSPs), through which they can have greater control over media/voice and can provide services such as DTMF Relay and Interworking, Media Transcoding, Tones and Announcements, Data and Fax Interworking, etc.
- Finally, since all outside communication occurs through the Session Border Control, it is a natural point to gather statistics and usage based information on these sessions.
The most robust and reliable Session Border Controllers are the Patton Smartnode Session Border Routers including the SN5200 and SN5400 product series. These products combine Session Border Controller and Router into one customer premise device.
Patton Smartnode 5200 Session Border Router:
The SmartNode 5200 connects the Enterprise’s LAN to an Internet telephony service provider (ITSP), creating a single conduit for multimedia components including voice, video and data.
The SN5200 includes SIP-aware NAT and access controlled lists (ACLs) for maintaining secure communications when SIP traffic crosses the Enterprise edge.
SN5200 provides advanced features like NAT/ NAPT in addition to ACLs and PBR for security and QoS that keep malicious traffic from affecting bandwidth requirements of PBR-marked essential traffic. Downstream QoS ensures important voice and fax calls don’t get bogged down by such resource hungry lower priority TCP traffic as FTP downloads.
Patton Smartnode 5400 Session Border Router with Transcoding:
The SmartNode 5400 series adds Media Transcoding features to the Session Border Router.
The SN5400 enables transcoding for up to 64 sessions. Most VoIP traffic within Enterprise LANs is uncompressed whereas traffic on the WAN is often compressed to save bandwidth. SN5400 transcoding between any VoIP codecs enables this optimal utilization of transport network at both sides of the Enterprise border.
Below is given a typical deployment of Patton SmartNode 5400 Session Border Router.
So if all this is done by a Session Border Controller or an SBC, you might be wondering what is the job of a VoIP Gateway. A VoIP Gateway is simply a translation device, which converts analog and digital telco lines to VoIP and vice versa. For example, if you have traditional telco phone lines and you want to use them with a VoIP phone system, you will need a VoIP Gateway.
The main functions of a VoIP Gateway include voice and fax compression or decompression, control signaling, call routing, and packetizing. High-end VoIP gateways also have additional features such as interfaces to external controllers like Gatekeepers or Softswitches, network management systems, and billing systems.
Some popular VoIP gateways are mentioned below:
Patton Smartnode 4110 Series Analog VoIP Gateway:
The business-class SmartNode 4110 VoIP Media Gateway supports up to eight transparent phone calls and leverages VoIP for carrier and corporate access. Connecting to any analog phone, fax, or PBX, the SN4110 is an effective and flexible solution for toll-bypass, remote/branch office voice connectivity, and enhanced carrier services.
Patton’s SmartNode 4110 delivers the legacy phone interfaces, service transparency, and flexible PSTN integration for true converged packet voice.
AudioCodes MediaPack 118 Analog VoIP Gateway:
The MediaPacks are well-suited for commercial VoIP deployment.
Field-proven voice and fax technology and feature-rich design makes the MediaPacks an excellent solution for various emerging VoIP applications. The MediaPacks are used in VoIP-based PBX or IP-PBX architecture as a mediation gateway and remote analog extension.
It is also used for optimizing voice transmission over satellite links, payphone networks, centralized IVR and Quality Monitoring applications.
Mediatrix 3531 Single T1 Digital VoIP Gateway:
Designed specifically for enterprise applications, the Mediatrix 3500 Series gateways make use of existing broadband access equipment to connect to any standards-based VoIP network.
The Mediatrix 3500 Series gateways meet the requirements of enterprises that want to connect their ISDN equipment, such as PBXs, through a T1 PRI interface to an IP network or as a gateway to the PSTN.
The Mediatrix 3500 Series offers security features such as TLS, SRTP, certificates management, and HTTPS designed to bring enhanced security for the network management, SIP signalling and media transmission aspects.
SmartNode 4940 T1/E1/PRI Enterprise VoIP Media Gateway
Providing a high-density seamless link between the circuit-switched telephone network and voice-over-IP, the SN4960 is ideal for PBX business trunking or corporate VoIP access. Offering up to four software configurable T1/E1/PRI interfaces the SN4960 connects to any switch, PBX and data network with up to 120 simultaneous calls using SIP, T1, E1 or PRI signaling. With its built-in CSU/DSU, any T1/E1 port can be selected as a WAN port for truly integrated voice and data access.
Like every SmartNode, the SN4940 delivers toll-quality voice with all industry standard CODECs including low-bandwidth G.723/G.729. Business class services are supported with T.38 fax, fax bypass and modem bypass features.
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