The GSMA reported in August there are now 4 million new HSPA (High Speed Packet Access) subscribers a month.  The total number of HSPA users has passed the 50 million mark globally from 11 million a year ago.  Mobile Broadband is definitely taking off, as discussed in this previous weblog article.

When I was in the UK in July, I was chatting with a UK Operator’s sales person as I installed a pay-as-you-go mobile broadband card in my laptop in their store.  I was asking about the types of customers using the service, how long they’d been sold-out of the ZTE modems, and what returns they see.  An interesting comment was the only returns are when the 3G service does not work at the customer’s home, it shows there’s a strong fixed to mobile substitution taking place for broadband.

But will mobile broadband provide the same experience as DSL broadband?  Taking a typical 3G roll-out architecture of 3 E1s from a cellsite, which given the recent upgrades in HSDPA to 14.4 Mbit/s means the capacity problem isn’t over the air, its on the backhaul, as I’ve discussed in this previous weblog article.  Given the ATM cell tax, and other framing overheads, the maximum capacity available for the customers’ broadband data is about 4.6 Mbit/s.

Now looking at the figure from a simple MB (megabyte) per month perspective, that gives 1.5 TB (terabytes) available over the month.  Given an urban macro-cell covers between 1200 to 2000 connected customers, assuming 1500 customers means an average 1GB limit.  Which at first glance would appear to provide adequate capacity even if 100% of the customer base were using mobile broadband.

However, the term I used in the title was customer experience.  The key experience is the many customers watching YouTube or BBC iplayer.  The video you see in the BBC iplayer today is encoded using the On2 VP6 codec at a bitrate of 500Kbps, though they’ve recently announced encoding using H.264 at 800 kbit/s.  YouTube is a little more sedate 300 kbit/s.

So this means that one cell-site can only support 9 simultaneous On2 VP6 BBC iplayer streams, or 5 simultaneous H.264 streams, or 15 streams of the more sedate YouTube streams.  And that’s ignoring all the other browsing traffic (which increasingly includes annoying streaming video adverts rather than easy to ignore banner adverts) and P2P (peer to peer) traffic.  Remember when Tiscali launched in the UK and struggled through inadequate backhaul, even today Tiscali still struggles with customer service.

A critical issue is what are the chances of within a cell-site 10 customers (0.66% penetration) watching a streaming video at the same time during that critical 6PM-11PM period?  Unfortunately the statistics coming from the DSL ISPs (Internet Service Providers) appear to show that chance as significant today.

Some ISPs use GE (Gigabit Ethernet) from their DSLAMs into their metro/core networks today.  Compare this to the 3E1s in the example above, which is 0.45% of the capacity of a GE.  To maintain the same experience mobile operators are going to require lots of capacity deep in their network fast, and become more sophisticated than the DSL ISPs in managing the traffic over their ‘longer access networks.’  Especially in managing the highly visible streaming video traffic which customers will likely use as a yard-stick to compare ISPs performance in the near future.