LAN, WAN, private network, public network, intranet, extranet, circuit switched network, packet switched network, ring network, star network, optical network— network terminology is very broad, but it all has something to do with the various types of network that exist. There are so many network types because there are many ways in which networks can be divided.
In this section, we will divide networks based on geographical coverage and topological forms. We’ll also describe the principles for these two divisions as well as the basic characteristics of all types of networks.
As you progress through this section, please pay attention to the following points:
• Definitions of LAN and WAN and the differences between them • Common LAN and WAN technologies
• The characteristics of networks with different topologies. After completing this section, you should be able to: • Describe the basic concepts of LAN and WAN. • Understand the basic states of LAN and WAN.
• Understand the characteristics of networks with different topologies.
1.3.1
LAN and WAN
Based on geographical coverage, networks can be divided into Local Area Networks (LANs) and Wide Area Networks (WANs). Table1.6 compares these two of networks.
Table 1.6 Comparison between LAN and WAN
Network type
Basic features Technology used
LAN • Coverage is generally within a few kilometers • Mainly used to connect several computer terminals
distributed within close proximity of each other (for example, within a home or office, between several buildings, or across a work campus)
• Does not involve telecom operator communication lines
Some examples are: • Token bus • Token ring
• Fiber distributed data interface (FDDI) • Ethernet • Wireless LAN
(WLAN) WAN • Coverage generally ranges from a few kilometers to
thousands of kilometers
• Mainly used to connect several LANs distributed across great distances (for example, to connect LANs in different cities or countries)
• Involves telecom operator communication lines
Some examples are: • T1/E1, T3/E3 • X.25
• High-level data link control (HDLC) • Point-to-point protocol (PPP) • Integrated services digital network (ISDN) • Frame relay (FR) • Asynchronous transfer mode (ATM) • Synchronous digital hierarchy (SDH) 1.3 Network Types 15
The geographical coverage of LAN and WAN is notfirmly established. When we talk about LAN or WAN, we are referring to the technology used by LAN or WAN.
There are many different types of LAN technology, such as Token bus (IEEE 802.4), Token ring (IEEE 802.5), FDDI, Distributed Queue/Dual Bus (DQDB, IEEE 802.6), isoEthernet (IEEE 802.9a), and 100VG-AnyLAN (IEEE 802.12). Two of the most widely used LAN technologies are Ethernet and WLAN, which have achieved active development and widespread application. Most LAN tech- nologies other than Ethernet and WLAN have disappeared or are being phased out due to market changes and developments. As such, a deep understanding of these outdated technologies is not required (unless you’re particularly interested in the history of network technology). Figure1.9shows the topology of token bus and FDDI networks, which are no longer common but can still be found on some older networks.
WAN’s deployment environment and conditions are more complicated than LAN’s, and improving and upgrading WAN is also more complicated than for LAN. This is partly why older WAN technologies are still in use. However, the general trend is phasing out antiquated WAN technologies such as T1/E1, T3/E3, ISDN, and FR. Optical network technologies, such as SDH and Optical Transport Network (OTN), are increasingly being used in thefield of WAN communication.
Token Computer A Computer B Computer C Computer D Token ring Single-ring structure Token Computer A Computer B Computer C Computer D Token FDDI dual-ring structure
Fig. 1.9 Token bus network and FDDI network topologies
1.3.2
Forms of Network Topology
Apart from geographic coverage of the network, network has its topology. Network topology is a graphical representation of a network structure. Table1.7illustrates some examples of network topology.
Table 1.7 Various types of network topology
Network type Topology map Basic characteristics
Star network All nodes are connected through a central node
• Advantages: New nodes can be easily added to a network. All data to be communicated must pass through the central node, which makes network monitoring easier
• Disadvantages: Failure of the central node will disrupt all network communication
Bus network All nodes are connected along a single bus
(such as a coaxial electrical cable)
• Advantages: Simpler installation and shorter cable lengths than most other network topologies. Failure of a given node will not usually disrupt all network communication • Disadvantages: Failure of the bus will disrupt
all network communication. All nodes connected to the bus can receive information sent out from any given node, lowering security
Ring network All nodes are connected within a single closed
ring
• Advantages: Shorter cable lengths than other network topologies
• Disadvantages: Adding new nodes will disrupt network communication
Tree network Nodes are connected in a kind of layered star
structure
• Advantages: Easy to expand by connecting multiple star networks
• Disadvantages: The higher the layer in which a node fails, the greater the disruption caused to network communication
Fully meshed network
All nodes are interconnected • Advantages: High reliability and
communication efficiency
• Disadvantages: Increased costs because the more nodes connected, the greater the number of physical ports and cables required. Problematic to expand
Partially meshed network
Only strategic nodes are interconnected • Advantages: Costs less than a fully meshed
network
• Disadvantages: Less reliable than a fully meshed network
Some of the network topologies shown in Table1.7are usually combined to meet various practical requirements such as cost, communication efficiency, and reliability. For example, the network shown in Fig.1.10 combines the ring, star, and tree topologies.
1.3.3
Review Questions
1. Into which geographical categories can networks be divided? (Choose all that apply)
a. Local Area Network b. Ethernet
c. Internet
d. Wide Area Network
2. LAN is typically limited to a range of how many kilometers? (Choose one) a. 0.1 km
b. 1 km c. 10 km d. 100 km e. 1000 km
3. Which of the following networks is most reliable? (Choose one) a. Star network
b. Bus network c. Ring network d. Tree network
e. Fully meshed network
Fig. 1.10 Hybrid network topology
4. Which of the following characteristics does not apply to a tree network? (Choose one)
a. Prone to a single point of failure b. Easy to expand
c. The higher the layer in which a node resides, the lower the requirements for reliability.