A SAF forwarder, which is a Cisco IOS router configured for
SAF, notifies the local
Cisco Unified Communications Manager cluster when remote call-control
entities advertise their hosted DNs patterns. In addition, the SAF forwarder
receives publishing requests from the local
Cisco Unified Communications Manager cluster for each configured and
registered trunk that is configured in the CCD Advertising Service window; the
publishing request contains the Hosted DN patterns for the
Cisco Unified Communications Manager, the PSTN failover configuration, the
listening port for the trunk, and, for SIP trunks, the SIP route header field,
which contains a URI for the trunk.
The following table describes the SAF deployment models that
Cisco Unified Communications Manager supports.
Table 2 SAF Deployment Models
All nodes in the cluster can connect to all SAF forwarders.
The clusterwide deployment model can support primary and
backup SAF forwarders.
Particular nodes in the cluster are assigned to the SAF
forwarders, and those nodes prioritize these SAF forwarders over other
configured SAF forwarders in the network; this means that the particular nodes
always contact the assigned SAF forwarders first over other configured SAF
The node-specific deployment model can support primary and
backup SAF forwarders.
This deployment model is recommended for cluster over WAN
deployments where each node in the cluster is separated geographically and you
route local traffic through local nodes; for COW deployments, you can configure
multiple sets of primary and backup SAF forwarders to support different
You can assign up to two SAF forwarders to a particular node.
You can configure a single SAF forwarder, which provides no
failover support, or you configure a primary and backup SAF forwarder to
provide failover support. With primary and backup SAF forwarders, the
Cisco Unified Communications Manager advertises to and subscribes to the
backup SAF forwarder when the primary SAF forwarder is unavailable.
The SAF forwarder contains the IPv4 address and port that
Cisco Unified Communications Manager uses to communicate with the SAF
network. At start-up time, the SAF client control, which is a nonconfigurable,
inherent component of
Cisco Unified Communications Manager, marks the first SAF forwarder that
Cisco Unified Communications Manager as the primary SAF forwarder. Be aware
that the primary SAF forwarder subscribes to the hosted DN services; the backup
does not perform this task. The backup SAF forwarder immediately gets promoted
to the primary SAF forwarder if/when the primary SAF forwarder becomes
unavailable for any reason.
The SAF client control component in
Cisco Unified Communications Manager maintains the connection to the SAF
forwarder by sending keepalive messages to the SAF forwarder at regular
intervals. The SAF client control component experiences keepalive response
timeouts with network errors, TCP connection failures, or SAF forwarder
failures. When the primary SAF forwarder becomes unreachable, the backup SAF
forwarder automatically becomes the primary SAF forwarder, and the SAF client
Cisco Unified Communications Manager tries to establish a connection with
the failed SAF forwarder. When the connection is successfully established, the
SAF forwarder gets designated again as the backup SAF forwarder. Under these
circumstances, the SAF client control component uses the newly (currently)
promoted primary SAF forwarder and notifies the CCD advertising and requesting
services that the current primary SAF forwarder is being used. The CCD services
send all publishing and subscription requests to the current primary SAF
forwarder, and the current primary SAF forwarder sends notifications for all
the Hosted DNs service advertisements that it receives to the SAF client
control component, which forwards the advertisements to the CCD requesting
service. The CCD requesting service compares the notifications that it received
from the backup SAF forwarder with its cached information and updates, deletes
or adds new information, as appropriate. The SAF client control component
attempts to reconnect to the failed SAF forwarder at regular intervals. When
the connection attempt is successful, the SAF client control component
registers again with the previously failed SAF forwarder and redesignates the
other SAF forwarder as the backup.
Cisco Unified Communications Manager always advertises to and subscribes to
the primary SAF forwarder, even when you have more than 2 SAF forwarders
configured in the database. If the primary SAF forwarder gets deleted from the
database, then the backup SAF forwarder automatically becomes the primary SAF
Cisco Unified Communications Manager promotes another configured SAF
forwarder to the backup SAF forwarder.
For clusterwide deployments, you cannot designate the primary and
backup SAF forwarders. The
Cisco Unified Communications Manager database sends an ordered list of SAF
forwarders to the
Cisco Unified Communications Manager.
If one or both of the SAF forwarders do not work,
Cisco Unified Communications Manager does not attempt to connect to a third
SAF forwarder, even if a third SAF forwarder is configured. If the connection
is lost for the primary and backup SAF forwarder, the
Cisco Unified Communications Manager does not connect to the third SAF
forwarder, even if a third SAF forwarder is configured.
If the CCD advertising or requesting service loses
connection with SAF network, the SAF forwarder informs all other call control
discovery services about the service interruption. The client continually
attempts to register to the SAF forwarder. After the CCD service reconnects
with the SAF network, the SAF forwarder immediately informs all CCD services
about the service restoration.
When the SAF forwarder detects a TCP connection failure with
other SAF forwarders or one of its external clients, such as
Cisco Unified Communications Manager or
Cisco Unified Communications Manager Express,
Cisco Unified Communications Manager marks learned patterns as unreachable
after it receives a network withdrawal notification from the SAF forwarder. All
subsequent calls to these learned patterns get routed over the PSTN by using
the PSTN failover configuration for the unreachable learned patterns. The timer
for the CCD PSTN Failover Duration feature parameter starts as soon as the
network withdrawal notification is received. If
Cisco Unified Communications Manager receives another network withdrawal
notification when the timer is going,
Cisco Unified Communications Manager restarts the timer.
Cisco Unified Communications Manager uses digest authentication (SHA1) to
communicate with the SAF forwarder. You configure a SAF Forwarder security
profile, which includes the username and password in requests that
Cisco Unified Communications Manager sends to the SAF forwarder; the
requests must include the MESSAGE INTEGRITY attribute to include the username
When a connection loss occurs between the SAF forwarder and
Cisco Unified Communications Manager, for example, a cable for the server
or router gets unplugged, the registration status may look correct, even when
it is not. In this case, patterns may appear to be reachable until the SAF
keepalive timer (on the SAF forwarder) or the TCP timer expires. After the
timer for the TCP timer expires, the patterns are marked as unreachable.