当前各种接入网技术（Access Network technologies）
1. Dial-Up
Back in the 1990s, almost all residential users accessed the Internet over ordinary analog telephone lines using a dial-up modem.
The term "dial-up" is employed because the user's software actually dials an ISP's phone number and makes a traditional phone connection with the ISP. As shown in following picture.
Dial-Up Internet access
2. DSL
Today the two most prevalent types of broadband residential access are digital subscriber line(DSL) and cable.
DSL Internet Access
3. Cable
Many residences in the North America and elsewhere receive hundreds of broadcast television channels over coaxial cable networks.
Cable Internet access makes use the cable television company's existing cable television infrastructure. A residence obtains cable Internet access from the same company that provides it cable television. as the following Figure.
A hybrid fiber-coaxial access network
4. Fiber-To-The-Home(FTTH)
Fiber optics can offer significantly higher transmission rates than twisted-pair copper wire or coaxial cable.
Some local telcos(in many different countries), having recently laid optical fiber from their COs to homes, now
provide high-speed Internet access as well as traditional phone and television services over the optical fibers.
The following figure shows FTTH using the PON distribution architecture. Each home has an optical network terminator(ONT),
which is connected by dedicated optical fiber to a neighborhood splitter, the splitter combines a number of homes ont o a single,
shared optical fiber, whichi connects to an optical line terminator(OLT) in the telco's CO. The OLT, providing conversion between
optical and electrical signals, connects to the Internet via a telco router.
In the home, users connect a home router(typically a wireless routor) to the ONT and access the Internet via this home router.
In the PON architecture, all packets sent from OLT to the splitter are replicated at the splitter(similar to a cable head end).
5. Ethernet
On corporate and university campuses, a local area network(LAN) is typically used to connect an end system to the edge router.Although, there are
many types of LAN technologies, Ethernet is by far the most prevalent access technology in corporate and university networks.
as the follow figure shown.
Ethernet users use twisted-paire copper wire to connect to an Ethernet switch.
7. WIFI
Increasingly, people access the Internet wirelessly, either through a laptop computer of from a mobile handheld device.
Today, there are two common types of wireless Internet access, In a wireless LAN, wireless users transmit/receive packets to/from
an access point that in turn is connected to the wired Internet. A wireless LAN user must typically be within a few tens of meters of the access point.
In wide-area wireless access networks, packets are transmitted to a base station over the same wireless infrastructure used for cellular telephony.
Wireless LAN access base on IEEE 802.11 technology, that is WIFI, is now just about everywhere - universities, business offices, cafes,airports,homes,
and even in airports.
8.Wide-Area wireless Access
When you access the Internet through wireless LAN technology, you typically need to be within a few tens of meters of access point
.This is feaible for home access, coffee shop access, and more generally, access within and around a building.
Telecommunications companies have made enormous investments in so-called third generation(3G) wireless, which provides packet-switched
wide-area wireless Internet access at speeds in excess of 1Mbps. Today millions of users are using these networks to read and send
email, surf the web adn download music while on the run.
9. WiMAX
There is a potential "killer" technology waiting to dethrone these standards, WiMAX, also known as IEEE802.16, is a long-distance cousin
of the 802.11 WiFi protocol discussed above.
来自“Computer Networking：A top to down approach”