Grandstream DP760 (DECT Repeater)

The following pre-release review was conducted in May 2017 as part of Grandstream's Beta Club. The Grandstream DP720 wireless VoIP handset and Grandstream DP750 base station was used to conduct the review.

Introduction

The Grandstream DP760 is a powerful wideband DECT repeater that pairs with Grandstream’s DP750 DECT base station for extended mobility and range. The DP760 claims to add an additional range of 300 meters outdoors and 50 meters indoors to give users the freedom to move around work or home environments.

The DP760 relays up to two concurrent HD calls when it is connected to the LAN via Ethernet or one HD call in daisy chain utilizing the RF interface for transport. The Ethernet connection provides Power over Ethernet (PoE) for convenient installation and a variety of remote management features, including provisioning, status monitoring, and repeater firmware upgrades.

First Impressions

The Grandstream DP760 repeater looks exactly like the DP750 base station. The device has a set of backlit LED status indicators, an Ethernet jack, a micro USB power jack, and a button used for manual pairing. The DP760 supports PoE, but the micro USB jack can also power the device with the supplied adapter or any standard USB 5 Volt DC micro USB adapter. There are mounting slots on the back of the device for wall mounting in various orientations. Overall, the repeater is clean, simple, and unobtrusive.

Features

The Grandstream DP760 supports RF link (daisy chain) mode or pairing with the DP750 over a network for transport. Each method has slightly different supported features. The DP760 supports one HD call in “daisy chain” mode or two HD calls when using Ethernet-based pairing and transport. The device supports G.722, the wideband codec, or G.726, the narrowband codec. The Grandstream DP750 base station itself actually has support for several more codecs (more on this later).

Configuration

The Grandstream DP760, unlike the DP750, appears to be a multi-region device. The DECT radio standard utilizes different frequencies in Europe, Asia, and the United States. The DP760 is capable of operating on any of the required DECT spectrums, whereas the DP750 has region-specific variants.

The DP760 is advertised as supporting "auto pairing," but this is not quite true. Pairing the Grandstream DP760 to the Grandstream DP750 requires a little effort, at least in the United States. Out of the box, the DP760 appears to be set to scan for pairing requests on the European DECT standard frequencies. As a result, it will not auto-pair with a US region DECT base station. Perhaps this will change with the launch device. We'll have to wait and see.

To pair the Grandstream DP760 repeater with a DP750 base station in the United States, you must:

1. Connect the Grandstream DP760 to the same LAN as the DP750 using an Ethernet cable.
2. Enable Repeater Mode and Repeater Management under the DECT General Settings tab on your DP750 base station.

3. Reboot the Grandstream DP750.

4. Go to the Status DECT Repeater Status page of the DP750. You may need to refresh your page or clear your browser cache for this new option to appear. Pair the DP750 with the newly discovered DP760.

Testing

Voice and Sound Quality

Currently, the Grandstream DP750/DP760 cannot display the handsets associated with each device. However, this is apparently a planned feature. You can determine which handset is associated with the device from the handset settings menu. We made sure that the DP720 handset was associated with the repeater for all tests, and our DP760 repeater was connected to a LAN at all times, rather than using the RF link in daisy chain mode.

Voice quality was excellent for all of our test calls. It's worth noting that the DECT interface only specifies two codecs for the RF interface, or the link between the handset and the base or repeater station. The voice codecs are G.722 for wideband and G.726 for narrowband. It's important to note that all calls from a Grandstream DP720 handset start using the G.722 wideband codec per the DECT specification. The calls are then transcoded by the base station to the codec specified in the profile.

This is one of the reasons why only a single call is supported when using RF daisy chain mode. The actual RF bandwidth utilized for the G.722 codec doesn't allow for more calls. While this does sacrifice capacity for the sake of quality, we can say the quality is very good. Grandstream does recommend using G.722 at the SIP profile level to support the highest-quality audio and prevent any transcoding.

Range

Our test of the DP720 DECT phone's range was not in any way a scientific test. We did our best with the circumstances. The building we tested in is all brick, built circa 1881, and roughly 150 feet long and approximately 50 feet wide. The base station was at one end of the building and the repeater was at the opposite end of the building, approximately 150 feet away. Both devices were connected to the LAN via Ethernet.

Within the building coverage, there weren't any dead zones or areas where calls started to break up. We were able to make calls and keep conversations going for approximately 100 yards outside of either end of the building. That's 100 yards away from either the base station, or the repeater, through a brick wall, with a total coverage area of about 250 yards in diameter. This seems reasonably in line with Grandstream's claims of “300 meters outdoors and 50 meters indoors.”

Compatibility Testing

At OnSIP, we put each of the phones we use through a multi-step interoperability test in which we apply ~30 test cases. An example of a test case would be the following:

Test phone calls phone B


B picks up


B puts test phone on hold


B calls phone C


C picks up


B transfers test phone to C

Call must be transferred correctly to C. B must be released correctly after the transfer. When C picks up, audio must work in both ways between test phone and C. When test phone is on hold, there is no audio between it and phone B.

The Grandstream DP760 meets all of our interoperability testing requirements.

Conclusions

The Grandstream DP760 is a simple-to-use, range-extending DECT repeater. It supports HD call quality, though it sacrifices capacity to achieve this. The DP760 does provide some flexibility in deployment, allowing you to use a pure RF link for areas without an Ethernet drop. It would be nice if Grandstream allowed you to select wideband or narrowband transmissions to customize your calling experience. We'll see what the final product brings.

The pairing mechanisms were a little confusing and convoluted, but that's largely because the Grandstream DP760 was advertised as an “auto-pairing” device. In reality, it's not. We believe this is being addressed either in the install guide or in documentation during the beta program. While the capacity of the DP760 is fairly low, so is its price. We would expect it to cost about as much as the Grandstream DP750 base station. The competitive price allows you to build out a DECT system with the coverage you need at a potentially lower cost than a rival DECT system.