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What is an SBC?

To understand the role of a Session Border Controller, let us break the term down to its basic elements:


A session is defined as a single connection between a pair of signaling devices that passes through the SBC system.  Each session is comprised of two call legs: one call leg on a trusted interface and the other on an untrusted interface. Each session in the SBC is identified by a Global Call ID, which is a globally unique identifier assigned by the SBC software.

A call leg is defined as a single connection between the SBC and another device. So a session between two devices includes a call leg between device A and the SBC, and a call leg between the SBC and device B.

A call may require a single session or it may require multiple sessions resulting from call forking, conference call, call transfer, call recording or other mechanisms. For example, a call between two registered users through a feature server consumes two sessions: one session from User A to the Feature Server and one session from the Feature Server to User B.

The total number of concurrent sessions supported on the SBC platform may be limited by different factors, including:

  • Available Bandwidth – For calls with pass-through media, the SBC computes the media bandwidth required for each call leg, and determines if there is sufficient bandwidth available to host the call. Calls exceeding the bandwidth limit of the interface are rejected.
  • Call Rate – If the incoming call rate exceeds the rated capacity of the platform, calls are discarded to protect the system from overload. The number of concurrent sessions required is directly related to the Call Rate and the Call Hold Time (CHT). High call rates with a low average CHT value will result in fewer sessions than the same call rate with a high average CHT value.
  • System Limits – Each platform includes upper limits on the number of sessions supported. For example, the SBC 5200 supports a maximum of 64,000 sessions, while the SBC 5100 supports a maximum of 10,000 sessions.
  • License Limits – The SBC is licensed for the maximum number of sessions desired. However, the license limit may be less than what the Bandwidth, Call Rate or System limits support. Any call that exceeds the licensed limit of the SBC platform are rejected.

Example #1: Call with one Session

A customer has purchased a 5,000 package of licenses, calls are coming in and egressing the SBC with no call forking – so each ingress and egress is one session. The maximum number of active calls is 5,000.

Figure : Call with one session

Example #2: Call with two Sessions

A customer has purchase a 5,000 package of licenses. Calls are coming in and getting transferred back through the SBC. Each call consists of two sessions, so the maximum number of simultaneous active calls is 2,500. 

Figure : Call with two sessions


For multiple transfers, each new GCID and SIP REFER is considered a session.



Typically, these sessions will traverse one or more IP networks, whether on an enterprise network or multiple service provider networks. The SBC sits at the border of each network in order to control the amount and type of sessions, as well as the type of data that can be used during these sessions. In this sense the SBC is part firewall, protecting the network from malicious IP traffic, and part traffic cop, policing how much traffic can enter the network in order to prevent overloads.


The SBC is a controller, which means it controls not only whether traffic can enter the network, but where it should be sent (referred to as session routing) and what type of modifications should be made to the traffic (example, transforming a SIP message header into an H.323 message header or downgrading an HD voice call to a compatible voice codec).

Sonus SBC Portfolio Components

The Sonus SBC Portfolio is comprised of the following Sonus Session Border Controller products:

Sonus SBC Edge

  • SBC 1000/2000

Sonus SBC Core

  • SBC 5000 series
  • SBC 5400
  • SBC 7000
  • SBC Software Edition (SWe)
  • SBC SWe Cloud


The focus of this documentation space is on the SBC Core platforms. To view SBC 1000/2000 product documentation, navigate to

The SBC Core addresses the next-generation needs of SIP communications by delivering embedded media transcoding, robust security and advanced call routing in a high-performance, small form-factor device enabling service providers and enterprises to quickly and securely enhance their network by implementing services like SIP trunking, secure Unified Communications and Voice over IP (VoIP).

The SBC Core provides a reliable, scalable platform for IP interconnect to deliver security, session control, bandwidth management, advanced media services and integrated billing/reporting tools in an SBC appliance. This versatile series of SBCs can be deployed as peering SBCs, access SBCs or enterprise-SBCs (e-SBCs). The SBC product family is tested for interoperability and performance against a variety of third party products and call flow configurations in the customer networks.

The SBC Core can be further expanded to:

  • SBC 5000 Series
    • SBC 5100/5110 Platforms
      Targets small to medium session count deployments (250 to 10,000). These capacities make this product particularly well suited for medium enterprises and small to medium service providers.
    • SBC 5200/5210 Platforms
      Targets medium to large session count deployments (500 to 64,000). These capacities make this product particularly well suited for large enterprises and medium to large service providers.
  • SBC 5400
    Targets medium to large session count deployments (700 to 75,000). These capacities make this product particularly well suited for large enterprises and medium to large service providers.
  • SBC 7000 Series
    Targets large session count deployments (up to 150,000 sessions). These capacities make this product particularly well suited for large service providers. Example deployment scenarios include:
    • Service Provider Access – High subscriber and simultaneous call scale coupled with high availability and redundancy.
    • Service Provider Peering – High simultaneous call scale coupled with high availability and redundancy.
    • Enterprise and Service Provider Video – Supports large WAN interface bandwidth.
    • Wireless – Supports a large number of subscribers and calls where high availability is essential.

  • SBC Software Edition (SBC SWe)
    Targets small to large session count deployments (25 to unlimited). These capacities make this product particularly well suited for small to large enterprises and service providers. SBC SWe application resides on a private or public virtualized cloud,or on a dedicated server.

Table : SBC Platform Comparison

(tick) = supportedMedium Enterprises / Small to Medium Service ProvidersLarge Enterprises / Medium to Large Service Providers Scalable SBC






SBC 5400

SBC 7000

SBC SWe / SWe on Cloud

Maximum number of
non-transcoded sessions
 10,000 64,00075,000150,000(Refer to SBC SWe Performance Metrics)
Call handling capacity250 - 10,000 sessions 450 - 64,000 sessions700 - 75,000 sessionsup to 150,000 sessions25-unlimited
Full SBC Feature Set(tick)(tick)(tick)(tick)(Refer to  SBC Core Key Features)
User Interface Embedded EMA or external EMS   Embedded EMA or external EMSEmbedded EMA or external EMS Embedded EMA or external EMS  Embedded EMA or external EMS
DSP Expansion Module Types
  • 5100: SPS100 / SPS100DB (FRU)
  • 5110: DSP20 / DSP25 (CRU)
  • 5200: SPS100 / SPS100DB (FRU)
  • 5210: DSP20 / DSP25 (CRU)
DSP20 / DSP25 (CRU)



The following table lists the number of ports and storage capacities of the various SBC Core platforms.

Table : Ports and Storage Capacities

TypeSBC 5100 SBC 5110SBC 5200SBC 5210SBC 5400SBC 7000SBC SWe
Number of Management ports2222421
Number of High Availability (HA) ports2222221
Number of Media ports22441x10Gb or 4x1Gb42
Flash Drive capacity80 GB 128 GB256 GB256 GBMin. 480 GBMin. 800 GB(See Hardware and Software Requirements)
RAM capacity12 GB24 GB24 GB24 GB32 GB128 GB(See Hardware and Software Requirements)

SBC Core Architecture

This following pages detail the SBC Core and SBC Software Edition architectures: