SIP Load Balancing
- Kelli Higdon
The IMG 2020 can be used in conjunction with a third party Load Balancer to distribute SIP traffic evenly between multiple IMG 2020's. Using the Virtual IP Address feature, the IMG 2020 can be configured as a SIP Server using both Real and Virtual IP addresses. The deployment of multiple IMG 2020's sharing Virtual IP addresses creates in effect a set of redundant SIP signaling paths.
Load Balancer Overview
Load Balancers automatically detect when a server is unavailable using “heartbeats” through either ICMP Ping or . Load balancing takes place between a set of IMG 2020's reachable through such heartbeats. Load Balancing provides increased VoIP network availability and reduces the number of re-transmitted SIP INVITE's by routing traffic through “healthy” signaling paths. This activity is commonly described using one of the following terms:
Server Load Balancing (SLB)
Describe Switchback Routing (DSR)
Direct Server Response (DSR)
Through the use of the SIP Virtual IP address feature, the Load Balancer and SIP Server nodes (IMG 2020's) contain the same IP address but the Load Balancer is the only node allowed to respond to ARPs. This prevents any External Network Elements from obtaining the MAC address of the SIP Servers which forces all external inbound traffic to/through the Load Balancer and then to the SIP Servers. The IP address set allows SIP calls to be terminated concurrently on any of the IP addresses, real or virtual.
The Load Balancer is configured with the MAC address of its SIP Servers. When it receives a SIP message the Load Balancer determines which SIP Server to send the message to. The Load Balancer then exchanges the Destination MAC address in the frame with the desired SIP Server’s MAC address. The frame is then placed on the Ethernet and arrives at the desired SIP Server.
Load Balancers are not SIP-specific, but rather they are SIP-aware which allows them to route subsequent transactions for an existing call to the correct gateway/IMG 2020.
A SIP proxy can be used to load balance SIP traffic. However, the proxy would use the actual IP address of the IMG 2020 and not the MAC address. Therefore, a Virtual IP Address would not be used.
Diagram - SIP-Based Load Balancing
Load balancers can create pools of IMG 2020 gateways, all sharing the same Virtual IP addresses. Accounting for capacity and the balancing algorithm are configured on the Load Balancer, not the IMG 2020. The diagram below shows the relationship between these network endpoints.
Configuring SIP-Based Load Balancing
The Load Balancer’s routing tables must be configured with the MAC addresses of each of the SIP Servers (IMG 2020's) corresponding to the virtual IP address.
Configure Interface with Gratuitous ARPs set to Disable
The SIP Load Balancing feature utilizes SIP Virtual IP's to implement SIP Based Load Balancing. Therefore, the SIP Signaling stack must be configure for a Single IP. The Multiple SIP IP functionality cannot be configured. The configuration of the IP Network object, IP Address object are described in the first section below.
Right click on the physical node and select New Network. The IP Network object is a parent or container object and no configuration is required here. Refer to the IP Network Interface topic for more information on this object.
Right click on the IP Network object just created and select New IP Address. Select Services from the drop down menu of the Source Endpoint field.
In the Logical Interface field, select one of the interfaces from the drop down menu. This will be the interface that the SIP messaging will use to stream the messaging through to communicate with the SIP stack.
Enter an IP address in the IP Address field. This will be the IP address selected for the SIP stack. Enter the Default Gateway IP address as well.
In the Gratuitous ARP and ARP Responses field select Disable from the drop down menu. For more information on configuring the remaining fields in the IP Address object, refer to IP Address topic.
Create SIP Stack
Right click on the physical node object and select New Signaling. The Signaling object is a parent or container object and no configuration is needed here. Refer to the Signaling topic for more information on this object.
Right click on the Signaling object and select New SIP. Verify that the IP Operation Mode field is set to Single IP. Refer to the IMG 1010 - SIP Signaling Object topic for information on configuring each of the remaining fields in this object.
An IP Address that has ARP disabled cannot be a SIP IP Address so the SIP IP Address object is not configured in this situation.
Configure SIP Virtual Address
Right click on the SIP Signaling object again and select New SIP Virtual Address. In the SIP Virtual Address object that appears is a field labeled IP Address. In this field, select the IP address of the interface configured in the IP Address object that has the Gratuitous ARP and ARP Responses field set to Disabled. Refer to the SIP Signaling - Virtual Address topic for information on configuring the remaining fields.
Repeat steps above for each IMG 2020 that requires a virtual SIP address for the load balancing feature.
CDRs
If the Virtual IP is used to initiate a call, the primary IP address is used in the CDR containing the local IP.