Snom 4S manual Architecture, NAT Filter and SIP

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2Architecture

2.1The NAT Filter and SIP

In the SIP architecture, the SBC acts as the first proxy that is contacted by user agents. There are two ways to make sure that the rel- evant traffic gets routed trough the filter:

User agents can be set up to use the filter as outbound proxy. When using this method, all SIP traffic will flow through the SBC, whether it is destined to the operator or not. That means that service for calls outside of the operator’s domain may also be serviced by the SBC. However, by redirecting all outgoing traffic of the SBC to a proxy the operator can make sure that the authentication, authorization and accounting (AAA) requirements for requiring the service are fulfilled. Alternatively, you can use the application server interface to do the job on the SBC itself.

User agents resolve the SBC though the RFC3263 DNS resolving process. That means that only the traffic that is destined to the operator’s domain will use the service of the NAT Filter. However, users might be annoyed if they place a call to a domain that does not properly support NAT services. In this case, the SBC can also redirect the traffic to another proxy.

We recommend using the first alternative and to only choose the second alternative if it is too difficult to provision user agents with the outbound proxy or when there are concerns about providing service for foreign operators.

Usually, the SBC acts as stateless proxy. This means, that it just forwards the packets by default and that it does not change the content of the attachments or the headers themselves. The SBC will not interfere with applications (instant messaging, presence, weather report, etc).

There are three exceptions to this rule:

The first exception is a REGISTER request. When a user agent tries

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Contents Snom 4S NAT Filter Admin Manual Snom 4S NAT Filter Version Table of Contents Snmp Overview Applications FeaturesSnom technology AG Overview NAT Filter and SIP ArchitectureNAT Signalling SIP How does NAT work?Symmetrical RTP Classification of User Agents Media RTPRole of the NAT Filter Probing Media PathsNAT Optimizing the Media Path for SymmetricalRegistering SBC BehaviourRTP Relay Snom technology AG NAT Scaling and RedundancyDetecting the right NAT Filter Requirements on User Agents Non NAT-Aware User AgentsSTUN/ICE-Aware User Agents Defining the Maximum Session Time Architecture Windows InstallationInstallation Snom technology AG Installation Snom technology AG Linux Rpm -ihv snomnatf-2.10.*.rpm Installation Port Binding LoggingStandard Port Random Port Logging System SettingsGeneral Outound Proxy Preparing RecoveryPort Budgets Media PortsMedia Relay Controlling RoutingMultiple 2xx Handling Challenging Trusted AddressesMaximum Packet Size Silence Suppression Connection Oriented MediaRemoving Headers Codec Control Web Server IntegrationClir Addresses Register Timeouts Timeout SettingsCall Timeouts Security Settings Snom technology AG Outbound Proxy List Server Log System InformationTrace Call History Current Ports Memory Statistics Currently Handled UAConfiguration Web Server Integration Interface to the Web Server AuthenticationSnom technology AG Web Server Integration Registration Call Initiation Snom technology AG Call Termination Snom technology AG Web Server Integration Setup of the Tools Setup of the SBCOID Available OIDSnom technology AG Snmp Checklist for Installation Checklist for Installation Reader‘s Feedback Snom technology AG All rights reserved