Throughput vs. Path Loss
NOTE: We don't refer to "range" in these plots, but instead use the more accurate "Path Loss". For an explanation, see the How we Test Wireless article.
Figure 12 was generated using the Compare Benchmarks tool of our Wireless Charts and shows up and downlink performance in 20 and 40 MHz channel modes in the 2.4 GHz band. There is a good throughput boost from 40 MHz mode at stronger signal levels. But the downlink curves in both 20 and 40 MHz modes end a bit earlier than uplink, indicating perhaps a slightly shorter range for downlink.
Figure 12: Throughput vs. Path Loss - 2.4 GHz
Figure 13 shows the curves in the 5 GHz band. Even though you can't directly compare 2.4 and 5 GHz results, it's clear that the DIR-855 follows the pattern set by many other dual-band draft 11n products with curves that end much earlier than the 2.4 GHz plots. This indicates a shorter range, which was confirmed by my walk-around tests.
But other than the shorter range, the 2.4 and 5 GHz throughput performance is very similar.
Figure 13: Throughput vs. Path Loss - 5 GHz
Throughput vs. Path Loss - D-Link Comparison
Since D-Link has three dual-band AP/router options, I thought I'd first compare them. Figure 14 shows 2.4 GHz, 20 MHz downlink plots for the 855, DGL-4500 and DAP-1522. It's surprising to see the 855 have significantly lower throughput than the 4500, especially since both are using the same mini-PCI radio.
But I think the answer lies in the clients used for the tests. The DGL-4500 was tested with the D-Link DWA-652, which is a Cardbus card using a single-band 2.4 GHz 3T3R (3 transmit, 3 receive) radio. The 855 was tested with the Netgear WNDA3100, which is a dual-band USB 2.0 adapter using a 2T2R radio. I suspect that using 3T3R radios on both AP and STA is the reason for the 4500's higher performance.
Figure 14: D-Link dual-band comparison - 2.4GHz, 20 MHz, downlink
What's more interesting, however, is that the Ralink-based DAP-1522 has higher throughput than the 855 at stronger signal levels, even with 2T2R radios on both ends! But the same isn't true for uplink. Figure 15 shows the 855 doing better than the DAP-1522, thoughput the path loss range.
Figure 15: D-Link dual-band comparison - 2.4GHz, 20 MHz, uplink
Switching to 5 GHz, the 4500 is held back by its odd performance at stronger signal levels, which I theorized was due to some incompatibility between the Atheros-based 4500 and the Broadcom-based Linksys WPC600N dual-band card, which I used for the 4500's 5 GHz testing. But once signal levels start falling off, the two have similar performance.
Figure 16: D-Link dual-band comparison - 5 GHz, 20 MHz, downlink
For uplink, the 4500 does better, including staying connected longer. I attribute this to the WPC600N's 3T3R radio.
Figure 17: D-Link dual-band comparison - 5 GHz, 20 MHz, uplink
Use the Wireless Charts to generate other comparisons or dig deeper into these.