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Introduction to Cisco Network Design

Chapter Description

This chapter from Cisco Press provides an overview of the technologies available today to design networks. Discussions are divided into designing campus networks, designing WANs, utilizing remote connection design, providing integrated solutions, and determining networking requirements.

Utilizing Remote Connection Design

Remote connections link single users (mobile users and/or telecommuters) and branch offices to a local campus or the Internet. Typically, a remote site is a small site that has few users and therefore needs a smaller-size WAN connection. The remote requirements of a network, however, usually involve a large number of remote single users or sites, which causes the aggregate WAN charge to be exaggerated.

Because there are so many remote single users or sites, the aggregate WAN bandwidth cost is proportionally more important in remote connections than in WAN connections. Given that the three-year cost of a network is nonequipment expenses, the WAN media rental charge from a service provider is the largest cost component of a remote network. Unlike WAN connections, smaller sites or single users seldom need to connect 24 hours a day.

Consequently, network designers typically choose between dialup and dedicated WAN options for remote connections. Remote connections generally run at speeds of 128 kbps or lower. A network designer might also employ bridges in a remote site for their ease of implementation, simple topology, and low traffic requirements.

Trends in Remote Connections

Today, there is a large selection of remote WAN media that includes the following:

  • Analog modem
  • Asymmetric Digital Subscriber Line
  • Leased line
  • Frame Relay
  • X.25
  • ISDN

Remote connections also optimize for the appropriate WAN option to provide cost-effective bandwidth, minimize dialup tariff costs, and maximize effective service to users.

Trends in LAN/WAN Integration

Today, 90% of computing power resides on desktops, and that power is growing exponentially. Distributed applications are increasingly bandwidth-hungry, and the emergence of the Internet is driving many LAN architectures to the limit. Voice communications have increased significantly, with more reliance on centralized voice-mail systems for verbal communications. The network is the critical tool for information flow. Networks are being pressured to cost less, yet support the emerging applications and higher number of users with increased performance.

To date, local- and wide-area communications have remained logically separate. In the LAN, bandwidth is free, and connectivity is limited only by hardware and implementation costs. The LAN has carried data only. In the WAN, bandwidth has been the overriding cost, and such delay-sensitive traffic as voice has remained separate from data. New applications and the economics of supporting them, however, are forcing these conventions to change.

The Internet is the first source of multimedia to the desktop and immediately breaks the rules. Such Internet applications as voice and real-time video require better, more predictable LAN and WAN performance. These multimedia applications are fast becoming an essential part of the business productivity toolkit. As companies begin to consider implementing new intranet-based, bandwidth- intensive multimedia applications over IP —video training, videoconferencing, and voice, for example—the impact of these applications on the existing networking infrastructure is a serious concern. If a company has relied on its corporate network for business-critical SNA traffic, for example, and it wants to bring a new video training application online, the network must be able to provide guaranteed QoS that delivers the multimedia traffic but does not allow it to interfere with the business-critical traffic. ATM has emerged as one of the technologies for integrating LANs and WANs. The QoS features of ATM can support any traffic type in separate or mixed streams (either delay-sensitive traffic or non-delay-sensitive traffic), as shown in Figure 1-4.

ATM can also scale from low to high speeds. It has been adopted by all the industry's equipment vendors, from LAN to private branch exchange (PBX).

Figure 1-4 ATM Support of Various Traffic Types

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