DSL and Cable Speed - Bottom LineCable modem Internet services on average promise higher levels of bandwidth than DSL Internet services, and this bandwidth roughly translates to raw speed. However, while cable Internet will theoretically run faster than DSL, several technical and business reasons can reduce or even eliminate this advantage.
DSL vs Cable Raw Speed - Advantage CableIn terms of theoretical peak performance, cable modem runs faster than DSL. Cable technology supports approximately 30 Mbps of bandwidth, whereas most forms of DSL cannot reach 10 Mbps.
One type of DSL technology, VDSL, can match cable's performance, also supporting 30 Mbps. However, Internet service providers generally do not offer VDSL, but rather the cheaper and slower ADSL or SDSL services.
DSL vs Cable - Real-World SpeedIn practice, cable's speed advantage over DSL is much less than the theoretical numbers suggest. Why?
- Cable modem services can slow down significantly if many people in your neighborhood access the Internet simultaenously.
- Both cable modem and DSL performance vary from one minute to the next depending on the pattern of use and traffic congestion on the Internet.
- DSL and cable Internet providers often implement so-called "speed caps" that limit the bandwidth of their services.
- Some home networks cannot match the speed of the Internet connection, lowering your performance
DSL and Cable Speed CapsBoth cable and DSL service providers commonly employ bandwidth / speed caps for residential customers. Bandwidth caps place an artificial limit on the maximum speed a customer can achieve by monitoring their individual traffic flow and throttling network packets if necessary. Bandwidth caps can reduce a 30 Mbps service down to 3 Mbps or even lower.
Service providers may have several motivations for imposing speed caps including the following:
1. Providers concerned about the capacity limits of their network may implement a cap so that they can accomodate more customers.
2. Providers may believe that the vast majority of customers do not actually need any more bandwidth than that allowed under the cap.
3. Providers may want to create a fair-and-equal distribution of bandwidth of customers. Without a cap, for example, some DSL subscribers would enjoy much higher bandwidth levels than others in the same neighborhood.
4. Providers may be want to charge higher or lower rates for greater or lesser bandwidth levels.