Thursday, April 10, 2008

Backhaul is Backing Things Up

If you primarily use a cell phone rather than a landline and make your Internet connection using cellular broadband or WiFi hotspots, you might start thinking the whole word is wireless. It is, between you and the nearest transmitting tower or access point. But then what happens? The connection between the wired and wireless worlds is called backhaul. You may never have heard of it or thought about it, but it could soon be limiting the bandwidth of your wireless connections. Backhaul is getting all backed up.

Backed up? What is this, a plumbing problem? In a way, it is. In the electronic world where wires and fiber optic strands represent pipes, backhaul isn't much of an issue. That's especially true for business telecom services. For instance, a T1 line is symmetrical and full duplex. It's actually a four wire system. One twisted pair is designated as the upload or transmit path. The other is the download or receive path. Each pair is running at a synchronous 1.5 Mbps. The twain, as they say, never meet. You can use the transmit and receive circuits independently. For instance, radio stations use T1 lines to send program audio from studio to transmitter. The signal pair coming back from the transmitter to the studio can be off-air audio, remote pickup signals, or a satellite network feed.

You may have T1 wirelines in your business. Popular uses are for dedicated Internet access and PBX telephone service. But go out to a cell tower and somewhere with the base station equipment you'll notice a little square gray box labeled "T1". That's the T1 line that connect the cellular tower back to the telephone switching office. That's how they do it and that's the part of the circuit called "backhaul." It hauls the traffic from the cell tower to the switching office. But, of course, it also hauls the phone calls and Internet data from the switching office to the cell tower.

Now that you know how it's done, here's the problem. Cell site and T1 lines are well matched. T1 lines can transport or "trunk" multiple telephone conversations and/or internet bandwidth. With few concurrent calls to a particular tower and dial-up speed data transmissions, one T1 line might be all that is needed to serve a tower site. But engineering advancements have greatly increased cellular broadband speeds to 1 Mbps and even 3 Mbps. Suddenly, that T1 line with plenty of bandwidth margin has hit its limit. Without some additional resources, users are limited in the service levels available from the site.

One easy and popular answer is more T1's. If you can run one T1 line, there's probably enough copper in the ground or overhead to support several. T1 lines can be bonded into contiguous data pipes of 3, 4.5, 6 or more Mbps. This solution also works for WISPs or Wireless Internet Service Providers with growing subscriberships. They can start off with 1 or 2 T1 lines and add more as more users come online and revenues increase.

So, that's it? Just add more T1 lines as you need them? To a point, that's it. But what happens when wireless bandwidth needs are 30 Mbps or even 70 Mbps? This is what WiMAX requires. Seventy Mbps would take nearly 50 T1 lines if you could even find a way to bond that many together. The costs are multiplied by the number of lines, so this would also get expensive. The logical approach is to move up to DS3 service over fiber optic lines. DS3 gives you 45 Mbps and two of them is 90 Mbps. SONET fiber optic services go up to a Gbps if you ever need that much.

There's only one little rub. No fiber in the boonies. Cell sites or new WiMAX towers in metropolitan areas can be connected to existing fiber optic rings. But what about up on the hill in the middle of nowhere? There's no fiber optic cable to those sites and the cost of providing them can be a major capital expense. This is where the backup on backhaul can rear its ugly head.

Solutions? New modulation techniques make Ethernet at 10 Mbps and even Fast Ethernet at 100 Mbps practical over copper pair without incurring big construction costs. Still, there are distance limits to these techniques even with repeaters. Point to point microwave transmissions may come back in vogue, especially given the transmitting height advantage of tower locations. Or it may be as simple as WiMAX backhauling WiMAX. After all, this is a wide area transmission scheme. By reserving half the bandwidth for backhaul and the other half for subscribers, a completely wireless system can be constructed.

Are you in need of serious bandwidth to support your business activities? We can help you with T1, DS3, SONET, Ethernet, and Satellite connections, with competitive pricing from a suite of 30 carriers.

Click to check pricing and features or get support from a Telarus product specialist.

Follow Telexplainer on Twitter