| The 18Mbit is only the top speed that the DSLAM can do when talking to the modem.
Bottle necks can occur in several places:
DSLAM port.
Not sure what PCCW is using for this but for other customers (not in HK) we sell them a card and per 1.5Mbit port they will wire 3 customers who will get 512Mbit. So they oversell the port.
DSLAM to server heads.
The DSLAM operate at short range from the customer site as the connection is copper based. When they get the data, they will use one of the several ATM networks PCCW uses for different ADSL services. The ATM network will transport the data through it is 172.x.x.x network to where ever the ISP is (not only Netvigator is on this ATM network).
Each of the ISPs server heads which connect to this ATM network is normally on the 172.22.254.x regardless of where they are in physically in HK. For netvigator sometimes your traffic will go to Wan Chai Telecom house, or Quarry bay.
Using an ISP that uses PCCW ADSL has the advantage that they will bitch scream and moan if the DSLAM, ATM is slow and is not delivering what is agreed. They have far more know how and control to demand PCCW to deliver the bandwidth agreed. It also seems that the DSLAM ports do better and not as oversold as PCCWs. An example of this is Netfront 1.5M/512Kbit is can peak at 1.7/850Kbit
I find that PCCW delivers about 1/3 of the bandwidth that you signup for.
ISPs distribution network:
after going through the ISP server heads (typically a Cisco 7206VXR, we sell lots of these) it will hit the ISP distribution network, which will guide the traffic to the core and will then route it to the appropriate international pipe or HKIX. If some router crashes or some fiber or GigEthernet line goes does before you are able to hit the international pipes you will get reroute to other circuits which may not have enough capacity. This happens oftens to Netvigator going to HKIX (intra HK).
The core: Core routers can choke when overwhelmed with excessive traffic, virus, DDOS attacks etc can crash them...
International pipe:
I think nearly all ISPs in HK are overselling their international bandwidth where say they have requirements of 2Gbit from the customers but only have a 1Gbit. So then you will have to fight and get a percentage of the capacity of what your link, atm network etc is able to deliver to your PC.
As you can see odds are stacked against you getting the 18Mbit.  | 
