Okay, before I talk about the serial encapsulation connections used on Cisco routers (HDLC, PPP, and Frame Relay), I’m going to discuss cable modems and DSL (including ADSL and PPPoE) as solutions for connections to wide area networks because I think it will really help you understand the practical differences between DSL and cable modem networking.
DSL and cable Internet services truly do have a lot in common, but they still have some basic, essential differences that are important for you to understand:
Speed Most would say that cable is faster than DSL Internet, but cable doesn’t always win the race in real-world use.
Security DSL and cable are based on different network security models, and until recently, cable has been the reputed loser in this contest. But now, it’s pretty much a toss-up, and both offer adequate security that meets the needs of most users. And when I say adequate, I mean that there are still some very real security issues relating to both alternatives, no matter what your ISP says!
Popularity Cable Internet is definitely “best in show” in the U.S., but DSL is beginning to catch up.
Customer Satisfaction Here, the reverse is true—in the U.S., DSL is top dog. But still, do you know anyone that’s really totally satisfied with their ISP?
Figure 1 shows how a connection can terminate from modems to either a PC directly or a router. Typically, your router would run DHCP on that interface, as well as PPPoE. Both DSL and cable high-speed Internet services are available to millions of residential and business consumers worldwide, but in some areas, only one (sometimes neither) service is available.
Figure 1 : Broadband access using cable or DSL
Always-on Voice, Video, and Data Services
Surprisingly, some of the differences between DSL and cable modem have nothing to do with the actual technologies—it comes down to the individual ISP. All other things being equal, issues like cost, reliability, and quality of customer support for both installation and maintenance issues vary significantly from one provider to the next.
Cable Cable is a great cost-effective connection for a small office or home office, or SOHO—yes, there is an acronym for everything! And even in larger organizations, cable (or DSL for that matter) can be great to have as a backup link.
Here are a few cable network terms:
Headend This is where all cable signals are received, processed, and formatted. The signals are then transmitted over the distribution network from the headend.
Distribution network These are relatively small service areas that usually range in size from 100 to 2,000 customers. They’re typically composed of a mixed, fiber-coaxial, or HFC architecture, with optical fiber substituting for the distribution network’s trunk portion. The fiber forms both the connection from the headend and an optical node that changes light to radio frequency (RF) signals that are then distributed through a coaxial cable throughout the specific area being serviced.
DOCSIS (data over cable service interface specification) All cable modems and like devices have to measure up to this standard.
Figure 2 shows where you would find the various types of networks and how the terms I just listed would be used in a network diagram.
Figure 2: Cable network and terms
The problem is that ISPs often use a fiber-optic network that extends from the cable operator’s master headend, sometimes even to regional headends, out to a neighborhood’s hubsite that then arrives at a fiber-optic node, which serves anywhere from 25 to 2,000 or more homes. (Don’t get me wrong, all links have problems—I’m not picking on cable—really!)
And here’s another issue: If you have cable, open your PC’s command prompt, and type ipconfig check out your subnet mask. It’s probably a /20 or /21 class B address. Oh my. You already know that’s either 4,094 or 2,046 hosts per cable network connection. Not good!
When we say “cable,” we really mean using coax (coaxial) cable for transmission. And CATV, or community antenna television, is now used as a means to offer cost-effective broadcasting to subscribers. Cable is able to provide voice and data, plus analog and digital video, without requiring you to pony up your whole paycheck.
Your average cable connection gives you a maximum download speed of 2Mbps. And remember—you have to share that bandwidth with all the other subscribers. As if that weren’t enough, there are other things like overloaded web servers and plain old Net congestion that factor in as well. But your email-checking neighbors really aren’t making that much of a difference. So who or what is? Well, if you’re an online gamer, you would likely notice a bit more lag during peak periods (which could be a matter of virtual life and death!). And if somebody in your neighborhood is uploading a large amount of data—like, well, an entire collection of pirated Star Wars movies—that could definitely max out the entire connection and bring everyone’s browser to a crawl.
Cable modem access may or may not be faster or easier to install than DSL, and your mileage will vary, depending on where you live plus a variety of other factors. But it’s usually more available and a tad less pricey, making it a winner by a nose. But no worries, if cable access isn’t available in your neighborhood, DSL is okay—anything is better than dial-up!
DSL and cable Internet services truly do have a lot in common, but they still have some basic, essential differences that are important for you to understand:
Speed Most would say that cable is faster than DSL Internet, but cable doesn’t always win the race in real-world use.
Security DSL and cable are based on different network security models, and until recently, cable has been the reputed loser in this contest. But now, it’s pretty much a toss-up, and both offer adequate security that meets the needs of most users. And when I say adequate, I mean that there are still some very real security issues relating to both alternatives, no matter what your ISP says!
Popularity Cable Internet is definitely “best in show” in the U.S., but DSL is beginning to catch up.
Customer Satisfaction Here, the reverse is true—in the U.S., DSL is top dog. But still, do you know anyone that’s really totally satisfied with their ISP?
Figure 1 shows how a connection can terminate from modems to either a PC directly or a router. Typically, your router would run DHCP on that interface, as well as PPPoE. Both DSL and cable high-speed Internet services are available to millions of residential and business consumers worldwide, but in some areas, only one (sometimes neither) service is available.
Figure 1 : Broadband access using cable or DSL
Surprisingly, some of the differences between DSL and cable modem have nothing to do with the actual technologies—it comes down to the individual ISP. All other things being equal, issues like cost, reliability, and quality of customer support for both installation and maintenance issues vary significantly from one provider to the next.
Cable Cable is a great cost-effective connection for a small office or home office, or SOHO—yes, there is an acronym for everything! And even in larger organizations, cable (or DSL for that matter) can be great to have as a backup link.
Here are a few cable network terms:
Headend This is where all cable signals are received, processed, and formatted. The signals are then transmitted over the distribution network from the headend.
Distribution network These are relatively small service areas that usually range in size from 100 to 2,000 customers. They’re typically composed of a mixed, fiber-coaxial, or HFC architecture, with optical fiber substituting for the distribution network’s trunk portion. The fiber forms both the connection from the headend and an optical node that changes light to radio frequency (RF) signals that are then distributed through a coaxial cable throughout the specific area being serviced.
DOCSIS (data over cable service interface specification) All cable modems and like devices have to measure up to this standard.
Figure 2 shows where you would find the various types of networks and how the terms I just listed would be used in a network diagram.
Figure 2: Cable network and terms
The problem is that ISPs often use a fiber-optic network that extends from the cable operator’s master headend, sometimes even to regional headends, out to a neighborhood’s hubsite that then arrives at a fiber-optic node, which serves anywhere from 25 to 2,000 or more homes. (Don’t get me wrong, all links have problems—I’m not picking on cable—really!)
And here’s another issue: If you have cable, open your PC’s command prompt, and type ipconfig check out your subnet mask. It’s probably a /20 or /21 class B address. Oh my. You already know that’s either 4,094 or 2,046 hosts per cable network connection. Not good!
When we say “cable,” we really mean using coax (coaxial) cable for transmission. And CATV, or community antenna television, is now used as a means to offer cost-effective broadcasting to subscribers. Cable is able to provide voice and data, plus analog and digital video, without requiring you to pony up your whole paycheck.
Your average cable connection gives you a maximum download speed of 2Mbps. And remember—you have to share that bandwidth with all the other subscribers. As if that weren’t enough, there are other things like overloaded web servers and plain old Net congestion that factor in as well. But your email-checking neighbors really aren’t making that much of a difference. So who or what is? Well, if you’re an online gamer, you would likely notice a bit more lag during peak periods (which could be a matter of virtual life and death!). And if somebody in your neighborhood is uploading a large amount of data—like, well, an entire collection of pirated Star Wars movies—that could definitely max out the entire connection and bring everyone’s browser to a crawl.
Cable modem access may or may not be faster or easier to install than DSL, and your mileage will vary, depending on where you live plus a variety of other factors. But it’s usually more available and a tad less pricey, making it a winner by a nose. But no worries, if cable access isn’t available in your neighborhood, DSL is okay—anything is better than dial-up!
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