1.2 Key Characteristics of Scalable Internetworks
1.2.1 List of scalable internetwork characteristics 
In this semester, you will learn about Cisco IOSŪ features and technologies that will enable you to support the following key scalable internetwork characteristics:

Reliable and available --- This includes being dependable and available 24 hours a day, 7 days a week (24 x 7). In addition, failures need to be isolated and recovery must be invisible to the end user.

Responsive --- This includes managing the QoS needs for the different protocols being used without affecting a response at the desktop. For example, the internetwork must be able to respond to latency issues common for Systems Network Architecture (SNA) traffic, but still allow for the routing of desktop traffic, such as Internetwork Packet Exchange (IPX), without compromising QoS requirements.

Efficient --- Large internetworks must optimize the use of resources, especially bandwidth. Reducing the amount of overhead traffic, such as unnecessary broadcasts, service location, and routing updates, results in an increase in data throughput without increasing the cost of hardware or the need for additional WAN services.

Adaptable --- This includes being able to accommodate disparate networks and interconnect independent network clusters (or islands), as well as to integrate legacy technologies, such as those running SNA.

Accessible but secure --- This includes the capability to enable connections into the internetwork using dedicated, dialup, and switched services while maintaining network integrity.

Each of these characteristics is discussed in more detail in the following sections.