Accessing the Internet Many people begin their CCENT and CCNA Routing and Switching study never having heard of leased lines, but many of us have heard of two other WAN technologies wont to gain access to the Internet: digital subscriber line (DSL) and cable. These two WAN technologies don’t replace leased lines altogether cases, but they are doing play an important role within the specific case of making a WAN connection between a home or office and therefore the Internet. This last major section of the chapter begins by introducing the basic networking concepts behind the web , followed by some specifics of how DSL and cable provide a way to send data to/from the internet.
The Internet as a large WAN
The Internet is an amazing cultural phenomenon. Most of us use it a day. We post messages on social media sites, we search for information using a program like Google, and that we send emails. We use apps on our phones to tug down information, like weather reports, maps, and movie reviews. We use the internet to purchase physical products and to buy and download digital products like music and videos. the web has created completely new things to do and changed the old ways of living life compared to a generation ago. However, if you instead focus on the networking technology that makes the internet, the internet is just one huge TCP/IP network. In fact, the name “Internet” comes from the core network layer protocol: Internet Protocol. the internet includes many LANs, and since the internet spans the world , it of course needs WAN links to connect different sites. As a network of networks, the internet is really owned by countless companies and other people . the web includes most every enterprise TCP/IP network and a huge number of home-based networks, also as a huge number of individuals from their phones and other wireless devices, as shown in Figure 3-12. the center of the web , called the internet core, exists as LANs and WANs owned and operated by Internet service providers (ISP). (Figure 3-12 shows the internet core as a cloud, because network diagrams show a cloud when hiding the details of a part of the network.) ISPs cooperate to make a mesh of links between each other within the Internet core, so that regardless of through which ISP a specific company or person connects, some path exists to each device.
Figure 3-13 shows a slightly different version of Figure 3-12, in this case showing the concept of the Internet core: ISP networks that connect to both their customers as well as each other, so that IP packets can flow from every customer of every ISP to every other customer of every other ISP.
Internet Access (WAN) Links
The Internet also happens to use a huge number of WAN links. All of these lines connecting an enterprise or home to at least one of the ISPs in Figure 3-13 represent some quite WAN link that uses a cable, while the phones create their WAN link using wireless technology. These links usually go by the name Internet access link.
Historically, businesses tend to use one set of WAN technologies as Internet access links, while home-based consumers use others. Businesses often use leased lines, connecting a router at the business to a router at the ISP. the top of Figure 3-14 shows just such an example..
Consumers often use technologies like DSL and cable for Internet access links. These technologies use cabling that’s already installed in most homes, making these services somewhat inexpensive for home users. DSL uses the analog phone lines that are already installed in homes, while cable Internet uses the cable TV (CATV) cable.
All three of the internet access technologies in Figure 3-14 happen to use a pair of routers: one at the customer side of the WAN link and one at the ISP side. The routers will still think about network layer logic, of sending IP packets to their destination by forwarding the packets to subsequent router. However, the physical and link layer details on the WAN link differ as compared to leased lines. the next few pages examine both DSL and cable Internet to show some of those differences.
Also Read : Overview of Network Layer Functions
Digital subscriber line
Digital subscriber line (DSL) creates a relatively short (miles long, not tens of miles) highspeed link WAN between a telco customer and an ISP. To do so, it uses an equivalent single-pair telephone line used for a typical home phone line. DSL, as a technology, does not attempt to replace leased lines, which run between any two sites, for potentially very long distances. DSL instead just provides a brief physical link from a home to the telco’s network, allowing access to the web. First, to urge a thought about the cabling, believe typical home telephone service within the us , before adding DSL service. Each home has one phone line that runs from a close-by telco CO to the house . As shown on the left side of Figure 3-15, the telephone wiring splits out and terminates at several wall plates, often with RJ-11 ports that are a slightly skinnier cousin of the RJ-45 connector.
Next, think about the telephone line and therefore the equipment at the CO. Sometime within the past, the telco installed all the telephone lines from its local CO to every neighborhood, apartment, and so on. At the CO, each line connects to a port on a telco switch. This switch supports the ability to set up voice calls, take them down, and forward the voice through the worldwide voice network, called the general public switched telephone network, or PSTN. to add DSL service at the house in Figure 3-15, two changes need to be made. First, you would like to add DSL-capable devices at the house . Second, the telco has got to add DSL equipment at the CO. Together, the DSL equipment at all sides of the local telephone line can send data while still supporting the same voice traffic. The left side of Figure 3-16 shows the changes. a new DSL modem now connects to a spare phone outlet. The DSL modem follows the DSL physical and data link layer standards to send data to/from the telco. the house now has a small LAN, implemented with a consumer-grade router, which frequently includes an Ethernet switch and possibly a wireless LAN access point. (Note that the telephones may now also need a short extra cable with a filter in it, installed at the wall jack, to filter the sounds of the higher electrical frequencies used for DSL.)
The home-based router on the left must be ready to send data to/from the internet. to make that happen, the telco CO uses a product called a DSL access multiplexer (DSLAM). The DSLAM splits out the data over to the router on the lower right, which completes the connection to the internet. The DSLAM also splits out the voice signals over to the voice turn on the upper right. DSL gives telcos a useful high-speed Internet service to offer their customers. Telcos have had other offerings that happen to use the same telephone line for data, but these options ran much slower than DSL. DSL supports asymmetric speeds, meaning that the transmission speed from the ISP toward the house (downstream) is far faster than the transmissions toward the ISP (upstream). Asymmetric speeds work better for consumer Internet access from the house , because clicking an internet page sends only a couple of hundred bytes upstream into the web , but can trigger many megabytes of data to be delivered downstream to the house .
Cable Internet creates an internet access service which, when viewed generally rather than specifically, has many similarities to DSL. Like DSL, cable Internet takes full advantage of existing cabling, using the existing cable TV (CATV) cable to send data. Like DSL, cable Internet uses asymmetric speeds, sending data faster downstream than upstream, which works better than symmetric speeds for many consumer locations. And like DSL, cable Internet doesn’t attempt to replace long leased lines between any two sites, instead focusing on the short WAN links from a customer to an ISP. Cable Internet also uses the same basic in-home cabling concepts as does DSL. Figure 3-17
shows a figure based on the earlier DSL Figure 3-16, but with the DSL details replaced with cable Internet details. the telephone line has been replaced with coaxial cable from the CATV company, and therefore the DSL modem has been replaced by a cable modem. Otherwise, the details within the home follow an equivalent overall plan.
On the CATV company side of the cable Internet service, the CATV company has got to split out the data and video, as shown on the right side of the figure. Data flows to the lower right, through a router, while video comes in from video dishes for distribution out to the TVs in people’s homes.
Cable Internet service and DSL directly compete for consumer and small-business Internet access. Generally speaking, while both offer high speeds, cable Internet typically runs at faster speeds than DSL, with DSL providers keeping their prices a little lower to compete. Both support asymmetric speeds, and both provide an “always on” service, therein you’ll communicate with the internet without the need to first take some action to start out the internet connection.
Questions related to this topic
- What kind of media should the company request from its ISP for connecting the corporate WAN to the Internet?
- Is an ISP a WAN?
- How does WAN connect to the Internet?
- What is a DSL connection on the Internet?
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