Kevin Evans has put a post on his blog on HSDPA backhaul over ADSL. At first, it seems like a pretty good idea he says but has some second thoughts:
Kevin says Internet Service Providers (ISP) would probably be less than happy to connect HSDPA ADSL links to their backbone. I agree! Cells where HSDPA is used heavily will pretty much use most of the bandwidth of an ADSL link for a considerable time per day. Consequently, such links would substantially increase the load of the ISPs ADSL backbone.
He then goes on to say that the alternative for mobile operators is to do their own ADSL backhauling. He thinks this is also not a good idea due to having to build an overlay network for backhauling next to the E-1s currently used for real time voice traffic. But why is it such a bad idea for operators to put their own 'mini' DSLAMs in central offices and have a little fiber there for backhauling? There is cost whatever you do, E-1, microwave, etc. so why not ADSL?
Some operators might have already decided to do this (speculation on my part). O2 Germany for example has said that they want to become an integrated fixed- and mobile telecommunication company, providing both high speed fixed line Internet access via DSL and high speed mobile Internet access via HSDPA. If they decide to build their own ADSL network, they can use it for both purposes.
As an alternative, Kevin suggests to use Ethernet for carrying both real time voice traffic and non real time background and streaming traffic generated by web browsing, podcast downloads, etc. But what about the distance you can cover with commercial Ethernet equipment today over phone cables?
When I first read about HSDPA over ADSL backhaul it immediately made sense to me due to the fact that ADSL has become a cheap technology to bridge larger distances than what is possible with other technologies. Have new long distance Ethernet technologies caught up in the meantime?
Whatever operators decide, I hope they decide quickly as HSDPA over 2 MBit/s E-1s is not going to make people happy.
Good comments Martin.
Re: the self-build approach, I think it could make sense. Certainly the business case is good since dry copper is very cheap. Several MNO's are experimenting - SFR is a good example.
There are 2 problems though:
1. Most MNO's don't have DSL engineering/operations expertise so they'd have to get some
2. DSL for HSDPA backhaul *only* will be an operational headache. MNO's already have TDM and ATM networks and those are proving to be expensivfe and difficult to operate. So adding a 3rd one will compound the problem.
using DSL to backhaul all traffic (2G, 3G Rel 99 and HSDPA) is a good idea if you can get the copper and the distances are OK and if you know how to do it.
Mobile operators with fixed line businesses will certainly explore this option.
Re: your questions on ethernet. Ethernet is usually delivered to the site over fiber so distance limitations are not that big a deal. It is possible to deliver ethernet over copper but you run into distance issues as you say. But ethernet over copper will be in urban areas primarily (short distances) and will be aggregated at a nearby metro fiber headend.
Posted by: Kevin Evans | July 12, 2006 at 04:43 PM