SIP User's Manual 456 Document #: LTRT-12801
MP-500 MSBG
9.2 SBC Application
This section provides a detailed description of the device's SBC application. This section
includes the following subsections:
îš„ Overview of the SBC application (refer to ''Overview'' on page 456)
îš„ SIP networking definition
s (refer to ''SIP Network Definitions'' on page 458)
îš„ SIP dialog initiation pro
cess (refer to ''SIP Dialog Initiation Process'' on page 460)
îš„ User regi
stration and the device's database (refer to ''User Registration and Internal
Database'' on page 466)
îš„ Media ha
ndling (refer to ''SBC Media Handling'' on page 468)
îš„ Config
uration example of SBC (refer to ''SBC Configuration Example'' on page 468)
9.2.1 Overview
The SBC application provides the following main features:
îš„ NAT traversal (refer to ''NAT Traversal'' on page 456)
îš„ VoIP firewall and security for both
signaling and media (refer to ''VoIP Firewall'' on
page 457)
îš„ Topolo
gy hiding (refer to ''Topology Hiding'' on page 457)
îš„ Survivability (refer to ''Su
rvivability'' on page 458)
îš„ Routin
g (refer to ''SIP Network Definitions'' on page 458 and ''SIP Dialo
g Initiation
Process'' on page 460):
• IP-to-IP routing translations of SIP, UDP, TCP, TLS (when extensive transcoding
is not required)
• Load balancing and redundancy of SIP servers
• Routing according to Request-URI\Specific IP address\Proxy\FQDN
• Alternative routing
• Routing between different Layer-3 networks (e.g., LAN and WAN)
îš„ Load balancing\redundancy of SIP servers
îš„ Internet Telephony Service Providers (ITSP) accounts
îš„ SIP URI user and host name manipulations (refer to ''SIP Dialog Initiation Process'' on
page 460)
9.2.1.1 NAT Traversal
The device supports NAT traversal, allowing for example, communication with ITSPs with
globally unique IP addresses, for LAN-to-WAN VoIP signaling (and bearer), using two
independent legs. In addition, it also enables communication for "far-end" users located
behind a NAT on the WAN. The device supports this by performing the following:
îš„ Continually registering far-end users in its dynamic database
îš„ Maintaining remote NAT binding state, by frequent registrations, thereby, off-loading
far-end registrations from the LAN IP PBX
îš„ Uses Symmetric RTP (RFC 4961) to overcome bearer NAT traversal
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