Intro to Wan
C H A P T E R
3
Chapter Goals
• • •
Become familiar with WAN terminology. Learn about different types of WAN connections. Become familiar with different types of WAN equipment.
Introduction to WAN Technologies
This chapter introduces the various protocols and technologies used in wide-area network (WAN) environments. Topics summarized here include point-to-point links, circuit switching, packet switching, virtual circuits, dialup services, and WAN devices. Chapters in Part III, “WAN Protocols,” address specific technologies in more detail.
What Is a WAN?
A WAN is a data communications network that covers a relatively broad geographic area and that often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer. Figure 3-1 illustrates the relationship between the common WAN technologies and the OSI model.
Internetworking Technologies Handbook 1-58705-001-3
3-1
Chapter 3 Point-to-Point Links
Introduction to WAN Technologies
Figure 3-1
WAN Technologies Operate at the Lowest Levels of the OSI Model
OSI layers WAN specifications
X.25 PLP Frame Relay
Network layer
HDLC
PPP
MAC sublayer SMDS
LAPB
Point-to-Point Links
A point-to-point link provides a single, pre-established WAN communications path from the customer premises through a carrier network, such as a telephone company, to a remote network. Point-to-point lines are usually leased from a carrier and thus are often called leased lines. For a point-to-point line, the carrier allocates pairs of wire and facility hardware to your line only. These circuits are generally priced based on bandwidth required and distance between the two connected points. Point-to-point links are generally more expensive than shared services such as Frame Relay. Figure 3-2 illustrates a typical
3
Chapter Goals
• • •
Become familiar with WAN terminology. Learn about different types of WAN connections. Become familiar with different types of WAN equipment.
Introduction to WAN Technologies
This chapter introduces the various protocols and technologies used in wide-area network (WAN) environments. Topics summarized here include point-to-point links, circuit switching, packet switching, virtual circuits, dialup services, and WAN devices. Chapters in Part III, “WAN Protocols,” address specific technologies in more detail.
What Is a WAN?
A WAN is a data communications network that covers a relatively broad geographic area and that often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer. Figure 3-1 illustrates the relationship between the common WAN technologies and the OSI model.
Internetworking Technologies Handbook 1-58705-001-3
3-1
Chapter 3 Point-to-Point Links
Introduction to WAN Technologies
Figure 3-1
WAN Technologies Operate at the Lowest Levels of the OSI Model
OSI layers WAN specifications
X.25 PLP Frame Relay
Network layer
HDLC
PPP
MAC sublayer SMDS
LAPB
Point-to-Point Links
A point-to-point link provides a single, pre-established WAN communications path from the customer premises through a carrier network, such as a telephone company, to a remote network. Point-to-point lines are usually leased from a carrier and thus are often called leased lines. For a point-to-point line, the carrier allocates pairs of wire and facility hardware to your line only. These circuits are generally priced based on bandwidth required and distance between the two connected points. Point-to-point links are generally more expensive than shared services such as Frame Relay. Figure 3-2 illustrates a typical