The idea
You already know how a LAN carries Ethernet frames between neighbouring machines. A student at home still needs to reach a server in another country, and no organisation owns every cable in between. A wide area network is how that reach is built, and the rest of this module is about the last stretch that physically touches the user.
Lecture 9 states the goal plainly: carry Ethernet/IP traffic from and to end users. Its list of topics for the day covers WAN overview, dial-up (legacy), xDSL, SDH/SONET (legacy), ATM (legacy), FTTx, cable networks and MPLS.
| LAN | WAN | |
|---|---|---|
| Interconnects | Hosts (computer, laptop, cellular phone, workstation) | Connecting devices (switches, routers, modems) |
| Ownership | Usually privately owned | Normally run by communication companies and leased by the organisation that uses it |
| Span | A single office, building or campus | A large geographic area: a town, a state, a country, or the world |
How it works
Point-to-point and switched WANs
A point-to-point WAN connects two communication devices through a transmission medium, either cable or air.
A switched WAN is a network with more than two ends. The lecture says it is used in the backbone of global communication.
How it works
Internetwork
When LANs and WANs are connected to one another, the result is an internetwork. The lecture’s figures show Ethernet/IP running on top of xDSL and HFC, or directly over fibre, and notes that regardless of direct or indirect delivery, the traffic is carried using FTTx architectures. Those are covered in FTTx.
How it works
Accessing the Internet
To reach the Internet, a user needs a physical connection to an Internet Service Provider (ISP). It is normally a point-to-point WAN, called the last mile or the access network. The lecture lists these possibilities:
- hybrid optical fibre
- copper networks
- cable networks
- wireless networks
The next topics take the copper case (DSL), the cable case (Cable and HFC) and the fibre case (FTTx). The lecture’s last topic, MPLS, is described as a WAN at the network layer for FTTx backbone networks, with IP routers connected to OLTs, DSLAMs or cable heads. The slide gives no more detail than that.
In the exam
- LAN versus WAN is a two-column answer: what is interconnected, who owns it, how far it spans.
- Point-to-point versus switched is about the number of ends: two, or more than two.
- The last mile is a point-to-point WAN to the ISP. Know the four media options.
- Dial-up, SDH/SONET and ATM appear in the lecture only as legacy items in the topic list.
Check yourself
- A LAN interconnects hosts, is usually private and covers one site. A WAN interconnects connecting devices, is run by carriers and covers large areas.
- WAN types: point-to-point (two ends) and switched (more than two, backbone).
- LANs and WANs joined together form an internetwork.
- The user reaches the ISP over a point-to-point WAN, the access network, built from fibre, copper, cable or wireless.