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What is a SBC and why not a Firewall

by Toan Nguyen Quang
SBC deployment

A session border controller (SBC) is a dedicated hardware device or software application that governs the manner in which phone calls are initiated, conducted and terminated on a Voice over Internet Protocol (VoIP) network. Phone calls are referred to as sessions.


SBC vs. Firewall



Firewall with ALG

Firewall ALG

Terminates, re-initiates and initiates signaling & SDP

Unable to terminate, initiate, re-initiate signaling & SDP

Two sessions – one on each side of system

Single session dialog across system

Layer 2-7 state aware

Layer 2-4 state aware

Inspects and modifies any application layer header info (SIP, SDP, ect)

Inspects and modifies only application layer addresses (SIP, SDP, etc)

Static & dynamic ACLs

Static ACLs only


Benefits of Session Border Controllers

Session border controllers uniquely provide all controls required for delivering trusted, reliable, and high-quality IP interactive communications:

  • Security: IP private branch exchange (PBX) and UC server denial of service/distributed denial of service (DoS/DDoS) attack protection, SBC self-protection
  • Communications reach maximization: IP PBX and UC protocol interworking, remote network address translation (NAT) traversal
  • Service-level agreement (SLA) assurance: IP PBX and UC server session admission and overload control, data center disaster recovery, remote site survivability, Quality of Experience (QoE)-based routing, SBC high-availability operation
  • Regulatory compliance: session replication for recording Data firewalls with application layer gateways (FW/ALG) are only effective securing data-oriented application infrastructure (PCs, servers).


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