1. Choose VLAN from the Configuration Menu to open the VLAN Configuration page.
2. In the Wireless column on the right side of the page, select the VLAN to use for the wireless traffic.
3. Click Modify to save the modified VLAN settings.
12
Survivability
This chapter describes how to manage survivability on the EdgeMarc appliance. It contains the following sections:
! Overview
! SIP Server Redundancy
! SIP Server Availability
! MGCP Survivability Configuration
! Survivability in Transparent Mode
! Survivability Voice Mail
Overview
Survivability is a collection of features that enables the system to extend the availability of VoIP services. These features include support for redundant SIP soft switches and local call control in the event of WAN link failure, softswitch failure or during periods of network congestion that result in loss of connectivity to a remote softswitch.
Dynamic WAN links (for example, DHCP and PPPoE) can renegotiate their public IP address at any time, interrupting VoIP services. All system services must be restarted when the WAN connection is restarted, because the WAN IP address may have changed. Because survivability must communicate with the Softswitch/IP PBX, survivability will be restarted when a WAN link renegotiation occurs, interrupting any local calls that are in progress. For this reason, survivability is not recommended for systems that use dynamic WAN links.
Survivability allows users connected to an EdgeMarc appliance to make and receive calls when the softswitch or the link to the softswitch is down. Survivability encompasses the following capabilities:
! Detection of when the softswitch is unreachable (Availability)
! Switching to a redundant softswitch (Redundancy)
! Making and receiving station to station calls while the softswitch is unreachable (Survivability)
! Making and receiving PSTN calls while the softswitch is unreachable.
To switch to survivability mode, the EdgeMarc appliance must be able to detect when the softswitch is unreachable. The softswitch may be unreachable for reasons such as the following:
! The softswitch is down.
! A router on the path to the softswitch is malfunctioning.
! The network is physically disconnected.
The most reliable way to ensure that the softswitch is reachable and available is to make a request at the application layer. If the request receives a response, the softswitch is reachable at the IP layer and also up and servicing requests.
The survivability process works as follows:
1. SIP requests sent to the softswitch, and their responses, are monitored to check for softswitch availability. If requests are sent to the softswitch but no responses are received in a configured time interval, the softswitch is considered
unreachable and a backup server (if available) is selected as the current server.
The default time interval is configured so that failover occurs before the phone has finished resending its request. This enables the call to be connected with only a slight delay.
2. A configuration option also allows the active softswitch to be monitored with keepalive messages. The messages are sent at a configurable intervals with time allowed for a response to be received. If too many messages are unanswered, the softswitch is considered unreachable.
3. When a softswitch is marked as unreachable, the EdgeMarc appliance uses a different keepalive mechanism to determine when it becomes available again.
The EdgeMarc appliance sends keepalive messages to failed servers using a backoff algorithm that progressively increases the interval, until a maximum is reached. By default, the maximum interval is longer than the one used when no other backup server is available.
4. An upstream EdgeMarc appliance or EdgeProtect device can send a specially marked keepalive response to inform the downstream EdgeMarc appliance about loss of connectivity to the softswitch. This causes an immediate fallback to the backup server or survivability mode in the downstream EdgeMarc appliance without a time delay.
5. The EdgeMarc appliance can choose the active softswitch from a list of multiple redundant softswitches based on priority and availability. It can obtain the list of redundant softswitches dynamically by doing a DNS SRV lookup on the SIP Server domain name or from a list entered in the appliance user interface. When multiple IP addresses are configured, the highest priority one is used. If this server becomes unreachable, the next reachable server in the order of priority is used. If a previously unreachable server becomes available and it has a higher priority than the currently used server, the higher priority server is used again.
6. If no softswitch is available, the EdgeMarc appliance enters survivability mode and handles call signaling itself. Because the EdgeMarc appliance forwards all messages between the phones and the softswitch, it knows the address of all phones and can direct calls to the phones itself.
7. A SIP PSTN gateway can be installed on the LAN side of the EdgeMarc appliance and used for inbound and outbound calling during survivability.
Survivability
can be configured to send any incoming calls to the EdgeMarc appliance, and the EdgeMarc appliance can be configured to use the gateway as the default destination for calls not directed to another local phone.
8. When connectivity to the softswitch is restored, the EdgeMarc appliance automatically returns control of all subsequent call requests to the softswitch.
Calls in progress that were established while the EdgeMarc appliance was in fallback mode are not disrupted.