Media Proxy Support

Effective media proxying of VOIP call media streams is an important aspect of any robust VOIP telephony system. The LanScape Centrex Proxy Server® has been designed to work seamlessly with LanScape's VOIP Media Proxy Server® software. When you combine the capabilities of the LanScape Centrex Proxy Server® with LanScape's VOIP Media Proxy Server®, you have the ability to deploy your own VOIP telephony network (domain) that will overcome all of the issues that are caused by firewalls and NAT routers. In addition to solving NAT related issues, proxying your media give you the ability to control a single point of entry of media streams in and out of your organization. This simplifies network management and increases network security.

LanScape media proxy support is fully scalable. Take for example the case where you deploy a single Centrex Proxy Server® and a single VOIP Media Proxy Server® for your domain. Lets assume the SIP proxy can handle 10,000 calls per minute and the media proxy can handle 3000 concurrent media sessions. In this configuration, you will be able to add users to your VOIP domain until you hit the upper limit of your single media proxy. What do you do to increase your concurrent call handling capability?

The simple answer is: "Add another VOIP Media Proxy Server® to your domain".

The Centrex Proxy Server® can communicate with one or more VOIP Media Proxy Servers. If you need additional media handling capability, deploy and configure another VOIP Media Proxy Server® on another host machine. Configure the media proxy so that it can communicate with your Centrex Proxy Server® and you are done. The Centrex Proxy Server® will use both VOIP Media Proxy Servers and load share media sessions between the two.

The maximum number of VOIP Media Proxy Servers that can be used by a Centrex Proxy Server® is only limited by the version of Centrex Proxy Server® you have purchased. In the enterprise versions of the Centrex Proxy Server® and the VOIP Media Proxy Server®, there are no imposed limits.

Another interesting point to make is that if your VOIP deployment uses more than one Centrex Proxy Server® and load shares between them, you can take your "farm" of VOIP Media Proxy Servers and configure then such that any one of your multiple Centrex Proxy Servers can have access to them.



The following dialog is used to configure media proxy settings:
 

Enable media proxy support:

This setting must be enabled to allow one or more LanScape VOIP Media Proxy Servers to communicate with the Centrex Proxy Server®. Once you enable this setting, other options in the dialog will become enabled so that you can change their settings.



Media proxy control port:

This value specifies the UDP port that is used to receive command response data from the media proxies. You can set this port value to whatever is appropriate for your installation. Note that the Centrex Proxy Server® uses symmetrical signaling on this UDP port. Symmetrical signaling is just a fancy way of saying the Centrex Proxy Server® sends and receives protocol packets using the same configured UDP port.



Media proxy command response timeout:

When the Centrex Proxy Server® communicates with a media proxy, it sends commands to the media proxy. This value specifies the amount of time that the Centrex Proxy Server® will wait for a response from the media proxy. If a response is not received from a media proxy in the specified amount of time, the Centrex Proxy Server® assumed a network error has occurred and attempts to continue with call normal processing.



Maximum allowed media proxy errors:

If the Centrex Proxy Server® does not receive a command response from a media proxy, it keeps track of this as a network error. If the Centrex Proxy Server® continually experiences network errors while attempting to use a media proxy it will stop using the media proxy if the number of network errors exceed this set value. If this condition occurs, all is not lost. Communications between the Centrex Proxy Server® and the VOIP Media Proxy Server® is bidirectional. As soon as the media proxy "back communicates" with the Centrex Proxy Server®, the Centrex Proxy Server® will again start using the media proxy.



Proxy all call media regardless of source or destination.

If this option is selected, all call media will be assigned to an available media proxy. This setting should only be used as a last resort and if you are experiencing call audio problems. The reasons why VOIP phone call audio problems occur are many. You can enable this capability while you diagnose the real problem.



Proxy the media of calls going to other domains:

For most (if not all) installations, you should enable this setting. Because you cannot make an assumption regarding media proxying capabilities of another SIP VOIP domain, you must assume that the other domain cannot proxy media properly. Enabling this setting will make sure media is handled properly when you make calls to users that reside in other VOIP domains.



Proxy the media of calls coming from other domains:

This setting is very similar to the setting immediately described above. Because you cannot make assumptions about media handling capabilities of another domain, you must assume that the other domain cannot proxy media properly. Enabling this setting will make sure media is handled properly when you receive calls from users of other VOIP domains. This setting should be enabled for most (if not all) installations.



Orphaned call history timeout:

Internally, the Centrex Proxy Server® maintains small amounts of call history data as calls are processed. When a call is terminated, the internal call history is deleted. If for some reason a call is started but aborts unexpectedly, the call history data needs to eventually be deleted. This time value specifies when such call history is deleted. To allow the Centrex Proxy Server® to perform accurate call "accounting", make sure you set this to the maximum call duration you want to support. The default value is 86400 seconds which is the same as 24 hours. If you have users that will be making VOIP phone calls that last longer than 24 hours, then you should increase this value.



Call history garbage collection interval:

Another time value used internally by the proxy. Allows for various memory saving operation to take place. Leave set to the default unless instructed by LanScape support personnel.





Media Proxy Authentication:

The Centrex Proxy Server® uses a challenge MD5 authentication mechanism when communicating with slave media proxy servers. Using this technique dramatically increases communications security between Centrex Proxy Servers and VOIP Media Proxy Servers. This authentication mechanism cannot be disabled. When you configure the Centrex Proxy Server® with the appropriate authentication information, you must also configure each media proxy with the same authentication information. This authentication information is only used to authenticate transactions between the Centrex Proxy Server® and the media proxies and is not related to any other authentication settings the Centrex Proxy Server® uses.



User Name:

Specify any secure user name. Any text string is acceptable.



Password:

Specify the authentication password.  Any text string is acceptable.



Realm:

Allows you to specify a name for the realm.  Any text string is acceptable.





Special Note - The media deadlock problem:

Deploying SIP proxies along with media proxy support solves problematic issues that are introduced by network address translation (NAT). However, all SIP proxy and media proxy solutions are not created equal. When deploying session and media proxies, most users eventually identify the "media proxy deadlock problem" when making inter-domain calls (calls from one media proxied domain to another media proxied domain). This "catch 22" dilemma results when a user in one domain calls a user in another domain. Both domains attempt to proxy the call media. This is problematic due to the fact that no call media (voice) will flow between the call endpoints. This behavior is generally due to poorly implemented or lacking capabilities in the SIP and media proxies.

The LanScape Centrex Proxy Server® and VOIP Media Proxy Server® software do not experience this media deadlock issue. They have been developed with added intelligence such that media deadlocks will not occur for inter-domain calling, even if one of the domains does not use LanScape VOIP server software.