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[[mgw_pooling]]
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== MGW Pooling
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{program-name} is able to use a pool of media gateway (MGW) instances.
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The aim of MGW pooling is to evenly distribute the RTP voice stream load across
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multiple MGW instances. This can help to scale out over multiple VMs or physical
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machines. Until osmo-mgw includes multithreading support, it may also be used to
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scale-out to multiple cores on a single host.
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The load distribution is managed in such a way that when a new call is placed,
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the pool will automatically assign the call to the MGW with the lowest load.
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MGW pooling is recommended for larger RAN or CN installations. For small networks
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and lab installations the classic method with one MGW per BSC offers sufficient
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performance.
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=== MGW pool VTY configuration
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In {program-name} the MGW is controlled via an MGCP-Client. The VTY commands to
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configure the MGCP-Client are part of the several 'mgw' nodes, one per
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MGCP-Client to set up.
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To setup an MGW pool, the user must first install multiple OsmoMGW instances, so
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that they won’t interfere with each other. This can be done using different
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local host IP addresses or different ports. When OsmoMGW is installed from
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packages, the systemd configuration may also require adjustment.
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By default, MGCP-Client will use whatever source IP address is resolved by the
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kernel routing subsystem, and will also ask the kernel to pick a free UDP port.
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Example configuration with two MGCP-Client instances in a pool:
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----
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mgw 0
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description media-gw-0 <2>
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remote-ip 127.0.0.1
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remote-port 2432
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local-ip 127.0.0.1
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local-port 2431
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endpoint-domain mgw0 <1>
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mgw 1
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description media-gw-1 <2>
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remote-ip 127.0.0.1
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remote-port 2430
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local-ip 127.0.0.1
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local-port 2429
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endpoint-domain mgw1 <1>
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----
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<1> When working with multiple MGW / MGCP-Client instances, the domain name for
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each MGW should be different. Otherwise it won't be possible to distinguish the
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endpoint names in the log. It should also be noted that the domain name must
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match the configuration of the related OsmoMGW instance.
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<2> It is also possible to assign a descriptive name to each MGW instance. The
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MGCP client specific log lines will then use this name as logging context. If
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no description is set, the domain name will be used.
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=== MGW pool management
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The MNGW pool is fully runtime-manageable. The only limitation
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is that an MGCP-Client can not be restarted or removed as long as it is serving
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calls (see also: <<mgw_pooling_blocking>>).
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==== MGW pool status
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The VTY implements a 'show mgw-pool' command that lists the currently configured
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MGW pool members, their status and call utilization. The following snippet shows
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an output example run on OsmoBSC, but it should be also available on other
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applications supporting the MGW pooling VTY featues:
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----
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OsmoBSC> show mgw-pool
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% MGW-Pool:
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% MGW 0:media-gw-0
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% mgcp-client: connected
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% service: unblocked
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% ongoing calls: 1
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% MGW 1:media-gw-1
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% mgcp-client: connected
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% service: unblocked
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% ongoing calls: 0
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----
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==== Adding an MGW / MGCP-Client to the MGW pool
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To add a new MGCP-Client to the pool, the 'mgw' node is used. Like with the
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'bts' or the 'msc' node a reference number is used that usually starts at 0.
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However it is still possible to assign any number from 0-255. The enumeration
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also may contain gaps. The following snippet shows an output example run on
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OsmoBSC, but it should be also available on other applications supporting the
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MGW pooling VTY featues:
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----
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OsmoBSC> enable
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OsmoBSC# configure terminal
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OsmoBSC(config)# network
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OsmoBSC(config-net)# mgw 2
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OsmoBSC(config-mgw)# ?
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local-ip local bind to connect to MGW from
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local-port local port to connect to MGW from
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remote-ip remote IP address to reach the MGW at
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remote-port remote port to reach the MGW at
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endpoint-domain Set the domain name to send in MGCP messages, e.g. the part 'foo' in 'rtpbridge/*@foo'.
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reset-endpoint Add an endpoint name that should be reset (DLCX) on connect to the reset-endpoint list,e.g. 'rtpbridge/*'
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----
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The newly added MGW will immediately appear in the mgw-pool list but it won't
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be used until its configuration finished by reconnecting it.
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----
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% MGW-Pool:
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% MGW 0:media-gw-0
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% mgcp-client: connected
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% service: unblocked
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% ongoing calls: 2
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% MGW 1:media-gw-1
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% mgcp-client: connected
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% service: unblocked
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% ongoing calls: 3
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% MGW 2:mgw <1>
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% mgcp-client: disconnected
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% service: unblocked
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% ongoing calls: 0
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----
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<1> In this example a description is not set yet, so the domain name ("mgw")
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is displayed.
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==== Reconnecting an MGW / MGCP-Client
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It may become necessary to reconnect an MGCP-Client. This is the case when the
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VTY configuration was changed at runtime. In order to make the changes effective
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the MGW configuration must be reloaded by reconnecting the MGW connection. Also
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newly created MGW instances require a reconnect once their configuration is
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done.
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To reconnect an MGCP-Client use the 'reconnect' VTY command:
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----
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OsmoBSC# mgw 2 reconnect
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----
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The mgcp-client status should immediately change to 'connected'. The MGW is now
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ready to be used for new calls.
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----
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OsmoBSC# show mgw-pool
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% MGW-Pool:
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% MGW 0:media-gw-0
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% mgcp-client: connected
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% service: unblocked
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% ongoing calls: 2
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% MGW 1:media-gw-1
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% mgcp-client: connected
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% service: unblocked
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% ongoing calls: 3
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% MGW 2:mgw
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% mgcp-client: connected
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% service: unblocked
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% ongoing calls: 0
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----
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It should be noted that MGCP a protocol is used via UDP, the connect only
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happens locally to forward the UDP datagrams properly. Also (unless a reset
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endpoint is configured like in the example config above) there will be no
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immediate interaction with the MGW. However, the log should at least confirm
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the the connect worked and the MGCP client has been created successfully.
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----
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Mon Aug 2 17:15:00 2021 DLMGCP mgcp_client.c:788 MGCP client: using endpoint domain '@mgw'
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Mon Aug 2 17:15:00 2021 DLMGCP mgcp_client.c:908 MGCP GW connection: r=127.0.0.1:2427<->l=127.0.0.1:2727
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----
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It is strongly advised to check the activity on the related MGW and to follow
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the log in order to see that the communication between {program-name} and the MGW is
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working correctly.
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[[mgw_pooling_blocking]]
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==== Blocking an MGW / MGCP-Client
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If it becomes apparent that an MGCP-Client must be restarted or removed from
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the config (maintenance) the operator can put that MGCP-Client into a blocked
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mode. A blocked MGCP-Client will still serve the ongoing calls but it will not
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be picked for the assignment of new calls.
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To block an MGCP-Client use the 'block' VTY command:
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----
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OsmoBSC# mgw 2 block
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OsmoBSC# show mgw-pool
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% MGW-Pool:
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% MGW 0:media-gw-0
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% mgcp-client: connected
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% service: unblocked
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% ongoing calls: 11
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% MGW 1:media-gw-1
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% mgcp-client: connected
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% service: unblocked
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% ongoing calls: 12
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% MGW 2:mgw
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% mgcp-client: connected
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% service: blocked
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% ongoing calls: 10
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----
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When the number of ongoing calls has tapered off, the MGW / MGCP-Client can be
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restarted or removed if necessary.
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----
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OsmoBSC# show mgw-pool
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% MGW-Pool:
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% MGW 0:media-gw-0
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% mgcp-client: connected
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% service: unblocked
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% ongoing calls: 15
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% MGW 1:media-gw-1
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% mgcp-client: connected
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% service: unblocked
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% ongoing calls: 14
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% MGW 2:mgw
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% mgcp-client: connected
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% service: blocked
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% ongoing calls: 0
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----
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If the blockade should be reverted, the 'unblock' VTY command can be used in
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the same way to remove the blockade. (Reconnecting will not remove the
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blockade.)
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==== Removing an MGW / MGCP-Client
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An MGCP-Client is removed from the pool using the 'no mgw' command from the
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configure terminal. The MGCP-Client instance will automatically be terminated
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and the related resources are freed. The only requirement is that there are no
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ongoing calls on the selected instance.
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----
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OsmoBSC# configure terminal
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OsmoBSC(config)# network
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OsmoBSC(config-net)# no mgw 2
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----
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