ShoreTel - Group Paging Feature
Preface
Please take the time to read this feature in its entirety. There are a lot of misconceptions about how the Group Paging feature works on the ShoreTel system. Hopefully after reading this information you will have a better understanding on how it functions.
Feature Overview
- Group Paging allows a user to make an announcement over a group of IP phones.
- The announcement will be a one-way page.
- Group Paging can be used as an alternative to overhead paging systems in some cases.
How it works: (Group Paging is Simultaneous, Not Synchronous)
Group Paging is TAPI, TAPI Wave application running on the main ShoreWare server.
When you dial the group paging extension, the main server answers and begins to “record” the user’s voice and then moments later begins to “play” the user’s voice to each member in the group. Group paging does not run on the ShoreGear voice switches.
Each extension in the paging group will cause a telephone call to be generated from the main server to the extension. Care should be taken in designing paging groups that include members at sites other than the main site.
Do the math
If you have a multi-site deployment, with ten people in the paging group at a remote site, this will generate ten simultaneous phone calls across the network.
Using G.711 voice encoding (64kbps for media plus 18kbps for overhead means 82kbps per call) results in 10 calls x 82kbps / call = 820kbps of WAN bandwidth used for the group page. System administrators must ensure they have sufficient bandwidth or make their remote paging groups relatively small.
From a planning perspective, system administrators should assume G.711 will be used at all times for paging calls across the WAN since there may not be sufficient DSP resources available to transcode the G.711 media stream from the main server down to G.729a. When DSP resources are depleted, G.711 will automatically be used.
Group Paging is Simultaneous, Not Synchronous
Since Group Paging needs to record and playback the user’s voice as well as generate a call for each member in the group, there will be some time delay between each member of the group receiving the page. The amount of latency between telephones in the paging group will vary based on the speed of the server, the size of the group and the number of ShoreGear voice switches sharing the load placing the phone calls.
In general, testing has shown pages are about 150msec between telephones. For instance, if you have ten people in the paging group, there will be 10 x 150 msec = 1.5 second delay from the start of the page at the first telephone to the start of the page at the last telephone in the group.
This latency should not be an issue when users can only hear a single telephone (i.e. one phone in a classroom, one phone in an office); however, in open air environments, this can be perceived be users.
In open air environments, telephones in the paging group should be placed apart to avoid hearing the delay and paging groups should be kept smaller to reduce bandwidth consumption.
Key Items to Note: (Group Paging Should be Limited to 20 Members)
The maximum number allowed in software release 7.5 and below is 20 users per paging group.
Starting in 8.0 and above, the maximum is 100 users per paging group. Both release 7.5 and 8.X allow a paging extension (associated with a site's overhead paging system) to be added to the paging group.
The maximum number allowed in software release 8.0 and above is 100 users per paging group. (40 maximum per ShoreGear switch)
ShoreTel streams the pages simultaneously (it does not use multicast routing). Depending on the CODEC used, this can consume all available WAN bandwidth very quickly.
For example, using the G.711 CODEC between sites consumes roughly 82K (with overhead) of bandwidth per remote user in the paging group. 15 users at a remote site in the paging group would utilize (15 * 82 = 1230 = 1.23M) 1.23M of bandwidth. Use with caution!
If you must have more than 20 parties in the paging group, you need to ensure no more than 40 members of the group are on single ShoreGear voice switch.
If you have a paging group of 100 users, you should spread the members of the group across 3 different ShoreGear voice switches – so each switch would only page about 33 - 34 phones each. Having a single ShoreGear voice switch try to simultaneously establish 100 phone calls will result in some percentage of the calls not completing.
Important – A single ShoreGear voice switch supports a maximum of 40 members that can receive a group page.
Additional details
- The initiating party must have the class of service “Allow Overhead and Group Paging”.
- A tone will be played to all parties when the group page begins.
- When a call is placed to the extension associated with a paging group, every user on the list is paged.
- Pages to on-hook IP phones are automatically announced on the IP phone speaker.
- Pages to off hook IP phones or to analog phones are treated as normal calls.
- Pages to telephones that are not available (i.e. IP phones that are unplugged) will not receive the page.
- Pages to telephones across sites when there is insufficient bandwidth will not receive the page.
- System administrators should ensure enough bandwidth is available for multi-site paging calls and / or keep the size of the remote groups small.
- Call handling does not apply to paging calls. If a telephone is call forwarded, the page will still be presented to the phone.
- Group paging extension are available for internal users only. External callers cannot access paging group extensions.
Final Note about Group Paging:
ShoreTel recommends paging groups be limited to 20 members maximum. Although you can configure up to 100, this will consume significant bandwidth and lead to call blocking across the WAN.
In addition as the paging group grows, there will be some delay in the paged call from the first to the last extension.
In general, the first ten extensions will be synchronous (it will vary based on server and network performance).
Enhanced Paging Application
ShoreTel Professional Services has also developed an Enhanced Paging Application to allow the system to have paging super groups.
In addition to groups of stations, the system will also allow the creation of super groups. Super groups are groups of groups. Creating super groups allows more than 100 stations to be paged. Pages sent to super groups are sent to one group at a time until all members of all contained groups have been notified.
We will save that topic for another factoid.