DSL and Cable broadband are doing well in Asia. A closer look at both technologies. by Dr Seamus Phan

Interestingly, terrestrial broadband seems to be doing exceptionally well in Asia-Pacific, surpassing the US and Europe. According to US-based RHK, Asia-Pacific had over 7.5 million DSL (Digital Subscriber Line) subscribers at the end of 2001, which is 44 percent of the world's DSL connections.

Innovation continues in Asia, with the likes of Global Telecom in the Philippines about to launch the first publicly-deployed wireless LAN service coupled with DSL Internet access. Globe Telecom plans to launch the "Blink" service with hot spots in populated areas, including airports, coffee shops, hotels, and schools, using the 802.11b WLAN technology connected to standard copper DSL lines.

Already, the Oakwood Premier Ayala Center is equipped with this trial service, making the building the first service hotel in the Philippines to offer broadband Internet service in all of its rooms.

DSL is usually served by service providers in the ADSL (asymmetric DSL) variety, which means that your download speed is far more than your upload speed. This is a marketing and practical strategy since most consumers and small business users do not require consistently high-volume uploads, but usually require bursty high-volume downloads. By mechanically limiting the uplink speed, the upstream service provider can better plan their existing infrastructure resources without running into frequent congestion.

There is another form of DSL known as SDSL (symmetric digital subscriber line), which means that your download and upload speeds are identical. For example, Pacific Internet in Singapore offers the Unlimited SDSL service providing 512 Kbps upload and download speeds for a fixed fee. This service is targeted at growing businesses with a need for always-on, unlimited bandwidth that runs almost like a fractional T1 line.

In practice, other than infrequent scheduled downtime, the SDSL performs just like a dedicated leased circuit, with less hassle or administrative headaches associated with more traditional technologies such as ISDN, and costs far less than a dedicated leased circuit.

DSL services frequently require just a simple DSL CPE (customer premise equipment), which looks like a small box with three ports (one for power, usually DC, one for the DSL line, and another for RJ45). The RJ45 port is connected to your network through a switch, hub or router, and the service provider usually provides a single IP for your organization. Should you require the running of mail, DNS or Web servers behind the DSL connection, you can request additional fixed IPs from your service provider for additional costs, or run port mapping through your routers.

Cable modem is different from DSL, but offers a reasonably high access speed as well. Cable modem technology uses two radio frequency (RF) carrier signals from the CATV spectrum to provide a low latency broadband service, typically to residential customers. It is a shared access service, which means that if there are only 10 users in a small neighborhood, the aggregate bandwidth will be shared by the 10 users, and users can typically experience a decent speed in accessing the Internet.

However, if there are more than 100 users, the same aggregate bandwidth will be shared by the 100 users, and the experience can be best described as slow.

Security and other caveats
Cable modem technology is promiscuous, since it is a shared medium Ethernet service where all stations sharing the same medium can read and write frames transmitted over the same medium. This raises security concerns, including the possibility of passive monitoring, forgery, and denial of service (DoS) attacks.

For personal and corporate customers running DSL or cable services, it is advisable that a decent firewall protection is erected before the network resources. Some proponents of broadband technology have claimed that users may experience more than 10 hacks per day when using cable modems, and it is wise to leave yourself out of the intruders' hacking list with adequate protection.

Immediately, users of cable and DSL connections should disable port 80 access from the Internet, since this port (http) is the most often used by intruders to create DDoS (distributed DOS) attack platforms. There is no reason for you to enable incoming port 80 access, and in fact, for residential customers using cable and DSL connections, it is also against most usage policies set by service providers to enable incoming port 80 to run http services, or any server service for that matter.

Some service providers may shut down residential connections if they are found to be running Internet servers of any kind.

Line quality
Service providers commissioning DSL connections typically have to ensure that the line quality is up to par with the technical demands of DSL. Before DSL is installed, service providers will test the line to ensure that it can be used, and when installed, is properly provisioned to ensure a minimum standard that customers expect.

It does not end here. DSL connections are notorious for occasional line drops and reduced quality. Service providers often have to check and provision the lines again, sometimes requiring a hard reset of the line. This makes DSL very different from leased circuits which can be typically described as "plug, use and forget", at least until the month-end bill arrives.

Should you experience a drastic drop in performance in your DSL connection, especially if it is a corporate connection, call your service provider's network operations centre (NOC) and ask if there is something wrong with your line. The NOC typically will perform a short test and will inform you if your line is working fine, or if some kind of reset or house call is necessary. This level of diligence is necessary for DSL connections.

As for cable, any degradation of performance is usually attributed to the fact that it is a shared medium, and you typically have no resolution with your service provider. If you really depend on your broadband connection, and should cable not work well for you in your neighborhood, you may speak with DSL service providers instead.

Seamus Phan is research director at KnowledgeLabs News Center (www.knowledgelabs.net), an independent technology news bureau and writes for Network Computing-The Asian Edition. He can be reached at seamus@knowledgelabs.net