Yes agree Jaime, thanks for pointing that out : Its listed in the URL I referenced in my earlier post although I should have explained.
Copy pasting for Patrick's benefit
http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/srnd/8x/uc8x/media.html#wp1254577
Media Resource Groups and Lists
Media resource groups (MRGs) and media resource lists (MRGLs) provide a method to control how resources are allocated that could include rights to resources, location of resources, or resource type for specific applications. This section assumes you have an understanding of media resource groups and lists, and it highlights the following design considerations:
•
The system defines a default media resource group that is not visible in the user interface. All resources are members of this default MRG when they are created. When using MRGs to control access to resources, it is necessary to move the resources out of the default MRG by explicitly configuring them in some other MRG. If the desired effect is for resources to be available only as a last resort for all calls, then the resources may remain in the default group. Also, if no control over resources is necessary, they may remain in the default group.
•Consumers of media resources use resources first from any media resource group (MRG) or media resource group list (MRGL) that their configuration specifies. If the required resource is not available, the default MRG is searched for the resource. For simple deployments, the default MRG alone may be used.
•Use media resource groups (MRGs) and media resource group lists (MRGLs) to provide sharing of resources across multiple Unified CMs. If you do not use MRGs and MRGLs, the resources are available to a single Unified CM only.
•MRGLs will use MRGs in the order that they are listed in the configuration. If one MRG does not have the needed resource, the next MRG is searched. If all MRGs are searched and no resource is found, the search terminates.
•Within an MRG, resources are allocated based on their order in their configuration even though Unified CM Administration displays the devices in an MRG in alphabetical order. If you want media resources to be allocated in a specific order, Cisco recommends that you create a separate MRG for each individual resource and use MRGLs to specify the order of allocation.
•When there are multiple devices providing the same type of resource within an MRG, the algorithm for allocating that resource load-balances across all those devices. The load balancing depends on the capacity of each device providing similar resources, so it frequently might not be a round-robin behavior. For example, if an MRG has more than one device providing MTP resources, the system will load-balance across each device for MTP requirements. When a resource has been used, a pointer for that MRG is incremented to the next device. A device may be present in more than one MRG, which will affect the pointers of all groups of which the device is a member.
•An MRG may contain multiple types of resources, and the appropriate resource will be allocated from the group based on the feature needed. MTPs and transcoders are a special case because a transcoder may also be used as an MTP. For example, when both MTPs and transcoders exist in the same MRG and an MTP is required, the allocation is done based on the order in which the resources appear in the MRG. If transcoder devices appear earlier than MTPs in the MRG, transcoder resources will be allocated for the MTP requirement until the transcoder resources are exhausted and then the system will start allocating MTPs. For this reason, it is important to consider the order of resources when creating MRGs and MRGLs.
•MRGs can also be used to group resources of similar types. As explained in the example above, because a transcoder is a more expensive resource, Cisco recommend grouping transcoders and MTPs into separate MRGs and invoking the right resource by assigning MRGs appropriately. Another example involves conference bridges. Conference bridge resources vary in the number of participants they support, and different MRGs could be used to group the conference resources by conference bridge size.
•You can also use MRGs and MRGLs to separate resources based on geographical location, thereby conserving WAN bandwidth whenever possible.
•Ensure that the media resources themselves have configurations that prevent further invocation of other media resources. For example, if an MTP is inserted into a call and the codec configured on that MTP does not match the one needed by Unified CM for the call, then a transcoder may also be invoked. A frequent mistake is to configure an MTP for G.729 or G.729b when Unified CM needs G.729a.
-Terry
Please rate all helpful posts
