SigC5561 Frequently Asked Questions

Q1. Is there a standard configuration of the card?

A1. The SigC5561 card is configurable in that from 2 to 12 DSPs can be installed. The Texas Inst DSP devices are each expensive, so obviously there is no "one size fits all". This is more understandable considering that TI has worked out all licensing arrangements in advance with codec providers (G.729, EVRC, etc), so there is only the one-time chip cost, and no "per channel royalty" during use.

Configurability of the card is why pricing is listed in per-channel terms, rather than per card.

Q2. What is the minimum configuration of the card?

A2. Two (2) Texas Instruments DSPs (TNET devices). To list some examples, 2 TNETs provides 192 G.729 channels, 144 G.723 channels, 96 EVRC channels.

Q3. What echo cancellation (ec) options are available?

A3. From 32 to 128 msec, in 32 msec increments, may be enabled/disabled on per-channel basis. At 64 msec or less, enabling ec has no effect on listed channel capacities. At higher ec values, channel capacity is typically reduced. This occurs on per-DSP basis. For example, at 128 msec ec per channel for each channel, 2-DSP card G.729 capacity is reduced to 96 channels from 192. As another example, if less than half channels required 128 msec ec, then overall G.729 capacity for a 2-TNET card would be 144 channels.

Q4. What Packet Loss Concealment (PLC) options are available?

A4. Both Telogy proprietary PLC and G.711.1 (Appendix I) PLC are available per channel for TDM side.

Q5. What are some significant differences between Texas Instruments and Mindspeed DSPs?

A5. TI DSPs run much cooler and do not require per-chip heatsinks. Since DSP-based boards for VoIP applications typically employ a "DSP farm" (i.e. many DSPs) this has far-reaching effects on card density -- how small the card can be, how many cards can be placed in one server and in what proximity to other cards, and of course cost of the card.

Also TI DSPs are somewhat thinner and smaller, and do not require an external SDRAM device. This again impacts overall card density.

A third difference worth mentioning is that TI DSPs provide carrier grade certified echo cancellation. Texas Instruments specifically purchased a high-performance echo canceller algorithm from a company called Ditech Networks for this purpose. Mindspeed has not (yet) been able to match this level of ec performance.