Networking

Add network ports and more with 3Com's Network Jack

If you need more ports in an office without additional network cable or hubs cluttering up the place, 3Com's Network Jack is for you. It's actually a four-port switch disguised as a network jack.


Your CIO tells you that, due to space limitations, a few people will be sharing offices, and some of them will need network printers. Unfortunately, your network cabling was installed a while back by an outside contractor, and only one drop was run to each office. The core switch is already almost at capacity, with no budget to upgrade it. Power outlets are scarce, and you don’t want to clutter up people’s offices with hubs and switches to get the job done. Oh—and the CIO wants it done by Tuesday, and today is Friday. What do you do? You look to 3Com and its Network Jack product.

Ho hum, a network jack—but wait…
It’s hard to get excited about a network jack, unless you’re talking about 3Com’s relatively new and innovative version of this typically mundane office accoutrement. The new 3Com Network Jack is more than a simple network jack. It’s actually a four-port switch in network jack form.

The form factor for this four-port switch is quite impressive. It’s a single-gang cover plate measuring 2.81" x 1.75". The jack contains four 10/100 network jacks and two cutouts that can provide either phone outlets or additional RJ-45 connections back to your network.

Flexible, like a tightrope walker
The flexible options make the 3Com Network Jack ideal for almost any situation. With as few as three Category 5 (Cat 5) cables running into an office, a single 3Com network jack can support four network devices and two telephones, or up to six network devices if you don’t need voice in the same jack. Two of the six network devices would be directly cabled back to the core, while four of them would use a single RJ-45 connection, thanks to the network jack’s four-port switch.

What does it look like?
As I stated, this small four-port switch fits comfortably inside a wall receptacle. It looks like any other jack plate, but it sticks out about a half-inch from the wall, and it has a small power connection in the lower right-hand corner.

On the back of the unit is a female RJ-45 jack, just like you’d expect to find as an uplink on a regular switch. Of course, this means that you’ll need to have an RJ-45 jack crimped into the cable at the wall rather than an existing jack—or you can push the female RJ-45 connector back into the wall and use a short patch cable to connect to the 3Com Network Jack. To reduce the number of areas where you can have network problems, I don’t recommend this path: I highly recommend crimping a new RJ-45 end on the cable instead.

On the left-hand side of the switch are two cutouts where you can place specific connectors that the 3Com Network Jack supports, including RJ-11 voice connectors and RJ-45 network connectors.

A switch, you say?
Since the unit is a small, four-port switch, it stands to reason that it would have specific operating parameters, which are as follows:
  • Four 10/100 Ethernet ports
  • Supports 802.3af (power-over-Ethernet) to provide power to the unit rather than having to use a power adapter
  • Store-and-forward switching method
  • Supports both full- and half-duplex and auto negotiates to determine the best method

This is not a managed switch, though. If you want to be able to manage the traffic that comes from it, you’ll need to do it at your core switch.

Consider the power decisions
Because this unit is in reality a four-port switch with a rather unique form factor, it needs to be powered in some way, and 3Com gives you a couple of different options. The first and easiest way to power the unit is to use the adapter (purchased separately) and the power jack on the front of the unit. This is effective, although it’s not particularly attractive, and it also requires a power outlet within reach of the Network Jack.

A more elegant solution involves making use of power-over-Ethernet, IEEE 802.3af. In fact, 3Com supplies two possible solutions that use this method. The first one powers a single network jack, while the second one can power up to 24 jacks. For both solutions, you install the power equipment in the wiring closet and run the connections to the 3Com Network Jacks and then, in turn, to the network gear. These units are what 3Com calls “power-over-Ethernet midspan solutions,” since they are placed between the network gear and the wall jack. The company has a number of RJ-45 jacks that accommodate the various connections, as well an AC connection to the wall. In fact, the 24-port version of the power distribution unit looks very much like a hub or switch with up to 48 ports—up to 24 to go to your network equipment or patch panel, and up to 24 more to go out to power network jacks.

The 3Com Network Jack also supports pre-802.3af equipment by making changes to the DIP switch settings inside the jack itself. 3Com even sells a pre-802.3af power solution that was originally used to power its NBX (voice over Ethernet) switch, but which can also be used for other purposes. The default setting of the DIP switches on the jack allows for either a directly connected AC power supply or for IEEE 802.3-af compatible power solutions.

For any of the IEEE 802.3af or prestandards power-over-Ethernet solutions, the wires that are not used in the Cat 5 or 5e cable are instead used to transfer power to compatible devices, providing a very clean cabling and power plant that is also very easy to maintain. Pins 1, 2, 3, and 6 maintain data communications, while pins 4, 5, 7, and 8 transmit power. Of course, this means that, if you install your own cabling, you should be careful to make sure that all cable pairs are properly terminated, rather than just the four that you use for network communications.

You don’t have to worry about plugging devices that don’t require power into the network jack by mistake because the technology detects whether or not it’s needed.

What else can it do?
When I mentioned earlier that this jack solution was flexible, I wasn’t kidding. Between the various jack configurations and power solutions, there’s a lot you can do with this unique device. But there’s still more.

When you use the 3Com Network Jack and power it with one of the two 802.3af-compatible power solutions, that power is also pushed through to port 1 of the included four-port switch. This means that you can power an additional compatible device, such as a 3Com NBX telephone or a 3Com 800D wireless access point. No messy power cords to worry about for either of these devices, or even for the jack itself! Personally, I think solutions like this are elegant and easy to maintain. Once the 802.3af standard is finally ratified and becomes more common, I’m sure that there will be other devices that can take advantage of this capability as well.

Show me the money
The 3Com Network Jack has the potential to save you a significant amount of money. Most cable runs cost between $150 and $250, and sometimes more, depending on the length and complexity of the run. If you’re installing a network from scratch, pulling multiple cables is easy and much less expensive, but if you simply need additional ports in an existing network, you could save anywhere between $300 and $600, taking into consideration the cost of running additional cables.

Jack-of-all-trades
As far as I know, no one else has released a device with the features and flexibility of the 3Com Network Jack. This device can help almost any solution, and it integrates well with the rest of the network. I especially like the power-over-Ethernet solution, which gives the product many uses without the need for a bunch of AC power adapters at the wall jack.

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