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For every user the admin can pre-configure a list of speed dial keys. Selecting the check box next to the entry enables BLF presence functionality. sipXecs uses a centralized phone presence server (called Resource List Server) to offer presence information for the entire systemto phones that support RLS. This approach is much more scalable and versatile vis-a-vis a peer-to-peer approach where every phone would subscribe for presence directly with the other phone. Tests have shown that the peer-to-peer approach causes significant network traffic that can cause a LAN to break down with only several hundred phones connected. The centralized approach implemented by sipXecs, in contrary, scales very well.
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