Specifications

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The other useful tweak affects the maximum chunk of data that can be transmitted; this is called the
maximum transmission unit (MTU). In an Ethernet network the maximum packet size is 1500 bytes.
Normally this setting is fine. However PPPoE encapsulation adds 8 bytes to each packet. This reduces the
maximum packet size to 1492 bytes. If the source attempts to send larger packet it will either be rejected or
fragmented into two parts, with attendant degradation in performance.
A good way to optimize your setting is to go the DSLR Tools page and run the tweak test. Once you know
the optimum settings download the DrTCP utility to make the changes.
4.6 Acceptable Use Policy
ISPs have a written policy that sets limits on how the service may be used. For example, reselling the
service is forbidden. Verify your ISP does not specifically prohibit operating a LAN. Even though the ISP
does not prohibit using a LAN it is unreasonable to expect technical help from them in setting it up. Some
services place monthly quotas on maximum download or upload. Make sure you fit in any restrictions.
Most ISP’s reserve the right to revise the policy at any time making for a pretty one-sided contract.
4.7 Privacy Policy
Examine the privacy policy to determine how your information will be treated. It is reasonable for the ISP
to collect and use information for diagnostic purposes and to improve service. However, some ISPs sell
customer information to 3
rd
parties. Your ISP knows every web page you access, every file you download
or upload and every mail, USENET and IM message that flows over their network. All that information is
potentially marketable depending on the privacy policy.
4.8 Service Level Agreement
Business class DSL includes a service level agreement (SLA). This defines minimum speed, maximum
latency, and time to repair if something goes wrong, etc. These guarantees are one of the reasons business
class service is more expensive then consumer. The upside is a guaranteed minimum level of service rather
then a best effort promise that make it hard to determine if the provider is delivering the service or not.
Data communication is the lifeblood of most business. One needs to carefully consider the impact of
communication failure.
4.9 Thoughts about DSL
Successfully delivering DSL service has turned out to be more difficult then expected. The decline in stock
market valuation makes it much harder to obtain financing. This has caused severe problems for many
companies. In our case our first and second choice for DSL supplier no longer exist. It is unlikely Verizon
will go under but it means almost no competition exists in the local DSL market. As a result we had to
scale back our DSL wish list.
DSL as delivered:
Symmetric speed at least 500kbp/s (1500/384)
No prohibition against using a LAN (OK)
Reasonable price (Half the price of Vitts SDSL service)
Single static IP address (Dynamic address via PPPoE))
Service Level Agreement (Not offered – best effort only)
True always on service (No – PPPoE emulates dialup)
No content filtering (Port 80 and SMTP filters, new prohibition on any kind of server)
Does not require special software (Install only. PPPoE is not proprietary)
Good technical support (Nonexistent)