Sangoma vs. Digium

When Halo Kwadrat first began to work in the open source telephony space, it was natural to use the hardware that was available that time from Digium ( in fact we were one of the first European resellers of Digium) We knew about Sangoma from their long association with the open source community. In early 2004 we heard about the new AFT range of cards that they were producing, and we encouraged them to seriously consider the telephony market in addition to their more traditional data transmission. We hoped that Sangoma products would have fewer problems than the Digium cards we were using.

For Sangoma there were no half measures: If Asterisk was worth the investment, then they were determined to do it right. There was lots of consultation with the community that went into the design concepts. Initially their new product range was limited compared to Digium's, but their products had a unifying design philosophy that contributes to quality, reliability and scalability.

In 2004 Sangoma released their first series of PCI digital cards with Asterisk support. The new A101, A102 released in May and the A104 cards released in December of that year had the following design features right from the start:

Split design: Sangoma split the card telephony interface from the PC interface by using a common PCI main board for all designs. Their long experience in PC hardware had taught them that complex standards like PCI are continually being extended, and that motherboard designers will explore new corners of the design envelope in order to gain an advantage in performance. The unique split design ensured that any PCI interface issue would be solved once only for the entire range of existing cards, and for all cards to come.

Obviously the split design is more expensive to manufacture, but it pays for itself every day in terms of reduced support and reduced RMA handling by distributors and resellers like ourselves, and reduced engineering time on new product development at Sangoma. It is a win-win situation in which Sangoma, distributors and customers all benefit. Other card manufacturers often use different PCI technologies for different cards, which has been the source of many problems related to compatibility, interrupt sharing and performance. If you use Sangoma cards, these are just non-issues.

2U Form factor: Even from the earliest days, Sangoma had its eyes on scalability. The 2U form factor (also a result of the split design) is the lowest practical profile. It allows you to build large, complex telephony projects with half the rack space of a full size machine. Digium released their first low profile card, the TE122 single port T1/E1 card in Q3, 2007 almost four years after Sangoma.

Hardware HDLC: Handling the HDLC framing in hardware on the card relieves the PC of framing, bit-stuffing and CRC loads. Sangoma digital cards have always supported hardware HDLC.

Digium first introduced hardware HDLC support in Q1, 2006, about 1 1/4 years after Sangoma.

Combined 5v and 3.3v PCI support: All Sangoma PCI cards support both PCI and PCIx slots at 5v and 3.3v, and have done so from their first cards released in 2004. Digium's T1/E1 lineup mostly still requires completely different cards for use in 5v and 3.3v busses. Only the TE122 of their digital portfolio supports both.

Software selectable T1/E1: At the time that Sangoma released its original range of T1/E1 cards, Digium still required separate cards for T1, and E1. Since then they have progressed to the extent that now T1/E1 is available on a common board, jumper selectable. Jumper selection is not always easy, for instance on the single port TE122 it requires removal and reinstallation of the echo cancellation module.

Sangoma cards have always supported software selectable T1/E1 (jumper free) from the beginning.

Compliant PCI support: From the outset Sangoma made use of commercial PCI cores and rigorous testing to ensure that their PCI implementation met all requirements. Sangoma cards worked in all machines, almost without exception, and any exception has generated a crash emergency program at their headquarters to fix the PCI problem. Sangoma cards shared interrupts as PCI devices are supposed to do.

This compatibility was hugely assisted by the fact that PCI issues only had to be investigated and resolved once.

Digium cards were notoriously fussy about the motherboards they were installed in. Sharing interrupts was totally forbidden, not a trivial problem on a bus where IRQs are seldom user selectable. There is anecdotal evidence that depending on which card you are using, even in their new range of PCI cards some of these issues are not entirely laid to rest.

Overrun detection: The TDM voice path under Asterisk has very little debugging capability. Packets can be lost at the card level, the driver level and the application level but the symptoms are all the same: voice dropouts and ruined faxes.

Sangoma provides an indication of card buffer overruns which we have found extremely valuable in debugging drop-out issues. Sangoma cards load as Linux devices, so simply running ifconfig will tell you if there are problems at the DMA or interrupt levels. If there are no overruns and dropout exists then packets are being lost in Asterisk/zaptel. If overruns exist at all, Sangoma will treat that as a very serious problem and will take great pains to resolve the issues on your motherboard.

Other cards have to rely on crude tools like zttest that simply take a snapshot of how many IRQs occur in a given time period. It seems to be acceptable to be out by one or two in 8000. How about 3 or 4? And how accurate is the timer?

Dual port T1/E1: Sangoma's A102 dual port T1/E1 card filled a needed gap between single port and quad port T1/E1 cards.

Digium was eventually forced to introduce a competing product in Q3, 2005 about 9 months after the introduction of the A102.

These features of the cards released by Sangoma in 2004 set a new standard for usability and reliability, and in many ways were responsible for the growth of Asterisk from a technician's plaything to a system reliable enough to be used in crucial telephony applications. It was several years before Digium was able to clean up its designs and produce cards that came anywhere near Sangoma's overall quality. And by that time, of course, Sangoma had moved on:

Sangoma introduced Telco grade hardware echo cancellation in Q4, 2005. Hardware echo cancellation removed one of the major voice quality barriers to entry for Asterisk, eliminating the hand tuning of each installation that was needed to hopefully reduce echo to acceptable levels. Together with reliable PCI operation, it allowed the mass production of Asterisk PBX solutions, such as those by Switchvox and Fonality.

Digium introduced its first hardware echo canceller in Q1, 2006, but the performance was poor. It was later replaced by the same solution that Sangoma had pioneered.

In Q3, 2006 Sangoma released PCIe (PCI Express) support for their entire range of cards. This was easy for Sangoma, as their split design meant that once they had designed one PCIe base card, it would apply to all digital and analog cards. PCI Express support is crucial in that it is the preferred interface for all high performance servers, the very machines needed to support large Asterisk installations.

Digium introduced its first PCIe card in Q3, 2007, about a year after Sangoma. Support for PCIe continues to trickle in. Currently the B410P BRI card is still not available in PCIe.

The zaptel telephony module originally written by Jim Dixon in 2000 is a magnificent piece of work, but it is showing its age. With its 1ms interrupt timing and context switching on a per channel basis, it is simply not capable of scaling to large systems. In 2005 Sangoma began working with other members of the open source community to produce an alternative PSTN connection gateway based on the woomera protocol. The first implementation was to support SS7, followed by BRI. PRI is rumoured to follow shortly.SS7 is a typical large system protocol, where many hundreds of channels are controlled by a few SS7 links. The very large reductions in computing load made possible by the woomera solution makes systems possible that handle over 500 simultaneous calls per host.

Digium apparently has no plans to move forward from zaptel.

In Q2, 2006 Sangoma introduced the 8 span A108 T1/E1 card. The A108 supports up to 240 channels on a single PCI slot, allowing medium sized systems of about 200 channels to be hosted on single slot 1U servers. For larger systems, a single 2U machine hosting four A108 cards can support 960 calls when using woomera, well in excess of the capacity of a T3.

Because Digium's telephony philosophy is tied to the unscalable zaptel/dahdi system, they cannot support a 240 channel card like the A108 in any useful way. Their largest capacity is 4 spans.

In Q2, 2007 Sangoma announced that their cards now supported clock synchronization between an analog card supporting FAX machines or modems and a digital connection to the PSTN such as T1, E1 or BRI. There is always an issue with FAX over E1, say, because the E1 is synchronized to the Telco's super-accurate cesium clock, while the sampling on an analog card is driven by a $3 crystal oscillator. Inevitably, the analog sampling is at a different rate than the Telco clocking, leading to gradual filling or emptying of transmit and receive buffers. When the buffers over or under run blocks of data are lost, leading to FAX or modem errors. The Sangoma modification allows the Telco clock to be used for analog sampling, avoiding the problem.

In Q2, 2008 Sangoma introduced the first mixed mode card, The B700. The B700 has 4 channels of ISDN BRI (i.e. it can support 8 telephone calls) and in addition it supports 2 channels of FXS/FXO. In Europe BRI is the dominant voice carrier, but ISDN FAX machines have never been widely accepted. The B700 allows analog FAX machines to be connected through an FXS port with the faxes being routed synchronously through BRI ports to the PSTN. This eliminates the need for separate analog lines to support FAX, saving hundreds of Euros per year.

Watch out for more mixed mode cards from Sangoma. We expect that Digium will be forced to introduce similar hardware in the future.

Why is it that Sangoma is the innovation and quality leader in this space? To be fair to Digium, cards are simply neither their focus as a company nor their area of expertise. Their executives will readily admit that center of effort is on the Asterisk infrastructure and its commercialization, such as PBX implementations like Switchvox, appliances, training, support etc. Their company trajectory is not card-based: Cards are simply a cash cow whose revenues can be used to fund other activities.

Sangoma lives and dies by card sales. They are application agnostic, supporting all platforms from Microsoft OCS under Windows, to Yate under Linux. Sangoma wins if the industry succeeds as a whole: They are not tied to a specific application. This is also majorly important to our customers as increasingly they are using multiple OST or even commercial platforms depending on project needs.

The folks at Sangoma cheerfully admit that they do not have a monopoly of ideas. Because their customers tend to be the larger and more professional OST players, they get thoughtful suggestions from the field based on sound business principles. And they listen! There is no Not Invented Here syndrome. In many ways, Sangoma's innovations in software and hardware have resulted from the very close partnership they have with their user base.