ICND2 200-105

ICND2 200-105

Enabling the Internet Connection

The Internet is a special case of a wide-area network. In describing Internet connectivity, we will explain popular options for Internet access, such as DSL and cable-based technologies.

Packet Switching

Several options exist for Internet connectivity. Knowing that the Internet speaks the IP language and we know that packets need to traverse a global network, then packet switched technologies are an option. Packet switching is an umbrella term that refers to packets as the unit of information being carried or transported across a shared network. It is shared in the sense that it will be shared across multiple customers using the service provider network. Some packet switching networks like frame relay will try to simulate virtual connections between locations. Some others will simply transmit packets in a connectionless manner with no dedicated path between source and destination.

Packet Switching

One option for Internet connectivity is the digital subscriber line service, or DSL. It is an always-on technology that allows service providers to offer high-speed Internet services reusing the same copper facilities that they have and have traditionally offered to provide telephone services. It is high-speed and that is one of the advantages. You see commonly, speeds that go beyond the limits of a T-1 line, and current offerings are around the 8 Mb/s or can reach the 8 Mb/s line.

The second advantage is that you can share that line to transmit voice and Internet traffic. The way it works is this modem can connect your telephone lines in your telephone devices, and at same time, connect your Ethernet router with your local area network. The modem will use different frequency ranges for voice and data, up to 4 kHz for voice traffic and then it actually spreads the data frequencies in two, allowing you to define different speeds for uploads and downloads, upstream and downstream traffic, resulting in things like ADSL or asymmetric DSL, suitable for residential Internet access, with more bandwidth for downstream traffic than upstream traffic.

Again, the way it works is using frequency multiplexing. On the other end of the line you'll have to DSLAN, which aggregates multiple subscribers and is also able to terminate the DSL, a physical layer, and connect multiple subscribers to the rest of the network. This is the same device that, using the alternative devices, split voice back into the voice network and then data to either another DSL destination, or actually the Internet. So, that is how it works. Typically at the point behind the DSLAN, you will see other services like DHCP, AAA for authentication services. Subscribers can get an IP address and also authenticate, provide credentials to demonstrate that they are valid subscribers. This is a very common and popular Internet access option.

DSL Service Types Overview

The advent and popularity of DSL as an Internet connectivity option resulted in multiple flavors, types, and standards for DSL technology. Some categories include asymmetric versus symmetric DSL taking advantage of the inherent frequency multiplexing capabilities of DSL; smart endpoints can provide a different bandwidth for download or downstream traffic than bandwidth for upload or upstream traffic. That is what is known as asymmetric DSL. Typically, downstream traffic is higher than upstream traffic, because it is suitable for residential internet access.

The other category is symmetric DSL, which provides the same capacity of bandwidth in both directions. Other flavors of DSL include HDSL, IDSL, SDSL, or VDSL, and there are several differences in terms of bandwidth capabilities, distance limitations between the customer and the service provider, and other criteria.

Those differences between the different flavors of DSL may represent disadvantages in selecting this technology. Availability is subject to the ability of the service provider to reuse their existing copper facilities for DSL. Distance limitations may prevent certain customers from obtaining the service. The advantages are clear, higher speeds and broadband access as compared to older technologies, especially in the residential market, and most importantly the capability to simultaneously transmit voice and data using the same channel and again, taking advantage of existing telephone company facilities.

Cable-Based WANs

Cable-based WANs are an increasingly popular option for Internet connectivity, especially in the residential market. After all, cable companies have been laying out fiber and facilities to reach customers for broadcast analog video initially and then digital services, including data services. Today’s cable company offerings include not only Internet access but also on-demand video and voice services that compete with the telephone service providers. They represent an important option in Internet connectivity.

The Global Internet

In today’s world, it is almost redundant to give the Internet a definition or to present the Internet as a concept. It is almost an inherent part of our lives in terms of not only communications, but also entertainment and business. The network has drawn into the largest network on earth, providing access to information and communication for businesses and home users.

Its reachability has made it an option for wide area network connectivity in terms of private networking through the use of virtual private networks. It is also the option of choice for mobile users, teleworkers, and remote locations. Soon enough, we will see not only cell phones and PDAs connected to the Internet, but our coffee makers and refrigerators will soon have an IP address.

Getting an Interface Address from a DHCP Server

In terms of specific connectivity options, your router may be connected to the Internet with a manually configured IP address or it could be used as a DHCP client. The ISP would provide the IP address dynamically via DHCP. This is sometimes due to the fact that we are running out of IPV4 Internet addresses and so reusing the same address toward multiple customers is an important feature of the Internet service provider network. This is typically seen in smaller locations with only one connection to the Internet.