D-Link DGS-1248T in Switches

There may be a plethora of Gigabit switches to choose from but D-Link's Green Ethernet technology adds an extra dimension to its new smart switches. Whereas the majority of switches don't care two hoots about their power consumption the DGS family has this as a top priority.

The DGS-1248T on review looks good value even without its power awareness as it offers 48 Gigabit ports and four dual-personality SFP ports for long range uplinks over fibre. At its foundation, the DGS-1248T is a fully managed L2 switch supporting standard features such as VLANs, QoS and 802.1x port based authentication.

All Green Ethernet enabled switches have this feature implemented in hardware. It provides two key functions with the first being the ability to dynamically sense cable length and reduce power to the port accordingly. D-Link's thinking here is that most switches only supply full power to each port to ensure they support the maximum segment length.

The switch can also sense when an end device has been powered down and when this happens it'll put the corresponding port in standby mode to reduce consumption further. The 16- and 24-port models also use a fanless design to cut usage even further. The DGS-1248T has three internal fans which are noisy enough to make the smaller models a better bet for a quiet office.

The web interface is a tidy affair offering easy access to the various features. The power saving mode is enabled by default but must be switched off if you want to use the network cable diagnostics tool. This measures the cable length and advises if there are any faults. We tested this with five, ten and twenty metre cable lengths but the switch only ever stated they were all less than fifty metres. This does raise a question about the switch's dynamic detection of cable lengths as if it's this vague how can it accurately control power requirements?

To test D-Link's power claims we compared the DGS-1248T to a standard HP ProCurve Switch 2848 which has an identical port count. Using an inline power meter we called HP up to the chair first and used sixteen test devices comprising servers, workstations and storage appliances. With nothing connected we saw the ProCurve sucking up 69W and with all devices linked this rose to 78W.

Swapping over to the DGS-1248T, we measured this pulling a much lower 30W with no devices connected and with them all plugged in this went up to 39W. In our next test we powered each device off but left them connected and in standby mode. For the DGS-1248T we saw the power draw settle at 33W whilst the ProCurve dropped to 72W.

Clearly, the base power consumption of the DGS-1248T is much lower than the ProCurve but all devices appeared to be drawing just under 0.5W per port on either switch so there's little if anything to be gained here. We also found that D-Link's port standby mode didn't make a significant difference either.

As a high port density L2 Gigabit switch the DGS-1248T hits the spot for value and offers a good range of switching features for the price. Basic power consumption is very low for a 48-port switch but our tests didn't show any significant benefits to be had from D-Link's Green Ethernet technology.

Author: Dave Mitchell