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Applicability

SBC Edge version 3.0 or later.

Summary

This article describes the SG Signaling/Media Source IP and NAT Traversal configuration

When an INVITE is sent from the SBC to a SIP destination:

  1. The call route specifies the egress SG.
  2. If the SG Signaling/Media Source IP is set to Auto, the egress Ethernet is selected by the best match in the IP Routing Table.
  3. If the SG Signaling/Media Source is set to a specific Ethernet/IP interface, the INVITE is forwarded out that specified port; however, the IP Route Table must have an IP Route to the destination network.  Even when a specific port is selected, the IP Routing engine must still be able to route the packet towards the destination IP network.

 

The Signaling/Media IP Source configuration overrides the IP Routing Table for selecting a particular egress Ethernet interface. Regardless, the IP Route Table must contain the appropriate routing entries for the SBC to send the packet towards the destination IP network.

SG Signaling/Media Source IP Configuration

Signaling/Media Source IP Set to Auto

This is what happens when Signaling/Media Source IP is set to Auto.

Figure : Signaling/Media Source IP - Auto

 

In a call from the phone to SIP Server 10.3.1.253:

  • The call route specifies the  Network 1 SG  Destination Signaling Group.
  • The  Network 1 SG  Signaling Group specifies that calls be sent to the destination server configured in the  Network 1 SIP Servers Table.
  • The  Network 1 SIP Server Table  specifies the SIP Server IP 10.3.1.253 .
  • With the Network SG 1's Signaling/Media Source IP configured to Auto, the IP Route Table is consulted and the Ethernet 1 IP (Next Hop) is selected because 10.3.1.0/24 is the best matching route.
  • The INVITE is sent out Ethernet 1 to the SIP Server.

Calls with Signaling/Media set to a specific Ethernet/IP interface

Figure : Calls With Signaling/Media Set to Specific Ethernet/IP Interface

 

 

In a call from the phone to SIP Server 50.2.2.201:

  • The call route specifies the  Network 2 SG  Destination Signaling Group.
  • The  Network 2 SG  Signaling Group specifies that calls be sent to the destination server configured in the  Network 2 SIP Servers Table.
  • The  Network 2 SIP Server Table  specifies the SIP Server IP 50.2.2.201.
  • With the Network SG 2's Signaling/Media Source IP configured to  Ethernet 2 IP (50.2.2.1) , the INVITE confined to egress on Ethernet Port 2.
  • IP Routing Table is consulted to ensure there is an IP route to the 50.2.2.0/24 network.  
  • The INVITE is sent out Ethernet 2 to the SIP Server.

 

In a call from the phone to SIP Server 50.3.3.153:

  • The call route specifies the  Network 2 SG  Destination Signaling Group.
  • The  Network 2 SG  Signaling Group specifies that calls be sent to the destination server configured in the  Network 2 SIP Servers Table.
  • The  Network 2 SIP Server Table  specifies the SIP Server IP 50.3.3.153.
  • With the Network SG 2's Signaling/Media Source IP configured to  Ethernet 2 IP (50.2.2.1) , the INVITE confined to egress on Ethernet Port 2.
  • IP Routing Table is consulted to ensure there is an IP route to the 50.3.3.0/24 network.  
  • The INVITE is not sent as there is no IP Route to the 50.3.3.0/24 network .

Calls to a SIP Server Not On the Specified Signaling/Media Interface

What happens when the SIP Server is on a different interface than the one set in the SG Signaling/Media configuration:

Figure : Calls to SIP Server - Not on Specified Signaling/Media Interface

In a call from the phone to SIP Server 10.3.1.253:

  • The call route specifies the  Network 2 SG  Destination Signaling Group.
  • The  Network 2 SG  Signaling Group specifies that calls be sent to the destination server configured in the  Network 2 SIP Servers Table.
  • The  Network 2 SIP Server Table  specifies the SIP Server IP 10.3.1.253 .
  • With the Network SG 2's Signaling/Media Source IP configured to  Ethernet 2 IP (50.2.2.1) , the INVITE confined to egress on Ethernet Port 2.
  • IP Routing Table is consulted to ensure there is an IP route to the 10.3.1.0/24 network.   The IP Route table specifies the 10.3.1.253 SIP Server is on Ethernet/IP port 1.
  • The INVITE is not transmitted because the Signaling/Media IP is configured for Ethernet 2 IP (50.2.2.1) while the destination SIP Server is on Ethernet/IP port 1.

Setting a NAT Public IP Address

What happens when NAT Public IP is configured.

Figure : Setting NAT Public IP Address

 

In a call from the phone to SIP Server 50.2.2.201:

  • The call route specifies the  Network 2 SG  Destination Signaling Group.
  • The  Network 2 SG  Signaling Group specifies that calls be sent to the destination server configured in the  Network 2 SIP Servers Table.
  • The  Network 2 SIP Server Table  specifies the SIP Server IP 50.2.2.201.
  • With the Network SG 2's Signaling/Media Source IP configured to  Auto , the IP Routing Table is consulted to ensure there is an IP route to the 50.2.2.0/24 network.  
  • The INVITE is sent out Ethernet 3 to the SIP Server with the Source IP address of SBC's Ethernet/IP port 3.
  • The SIP and SDP IP addresses are set to 50.4.4.155 because NAT Public IP is configured in the egress Signaling Group.