What resources are used when using speaker call (*80) to a group of HFA telephones?


If a TDM telephone is initiating the paging a DSP channel is used for every hunt group member, this will drop to 1 DSP channel if one of the members answers the page. As OpenScape Business X systems only have 8 DSP channels in default it may be wise to add an OCCB1 (40 DSP channels) or an OCCB3 (120 DSP channels) module to increase the number of DSP channels available if this feature will be widely used between HFA and TDM telephones.


NOTE: It is not possible to increase the number of DSP channels on OpenScape Business X1.


The paging effectively initiates a separate call to each telephone so bandwidth will be a limiting factor if the telephones are connected over a typical ADSL link.


Payload switching (where the voice payload is routed directly between the HFA endpoints) can only occur between two HFA telephones (e.g. one HFA telephone pages another HFA telephone), once more than two HFA telephones are involved (e.g. one HFA telephone pages multiple HFA telephones in a group) the system has to route the payload as an RTP proxy.


As an example, a typical ADSL link has an upload speed of 512 kbps. G.711 A-law uses approximately 80 kbps including the overhead so only 6 calls would fit down the link. If the group contains more than 6 members, the speech quality will get progressively worse with the number of members paged above 6, until no speech will be audible. If the codec is changed to G.729 which uses approximately 32 kbps with overhead it would be possible to fit 16 calls down a typical ADSL link before degradation occurs. Obviously these values assume that no other traffic is occupying the ADSL link at the time.

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