• Service provider edge: Provides a description of connectivity to service providers such as Internet service providers (ISPs), WAN providers, and the public switched telephone network (PSTN).
    • The example in Figure shows a sample network that was deployed following Cisco Enterprise Architecture and the Cisco hierarchical model design. Various modules form an integrated converged network that supports business processes. The campus consists of six modules: Additional modules in the other functional areas represent e-commerce functionality, corporate Internet connections, remote access and VPN connections, and traditional WAN (Frame Relay, ATM, and leased lines with PPP) connections. Web Links SAFE Blueprint
    http://www.cisco.com/en/US/netsol/ns340/ns394/
    ns171/ns128/networking_solutions_package.html
    Content 1.2 Scalable Networks 1.2.1 Scalable Network Design The ECNM breaks the complex problem of network design into smaller, more manageable problems. Each level, or tier in the hierarchy, addresses a different set of problems. This helps the designer optimize network hardware and software to perform specific roles. For example, devices at the lowest tier are optimized to accept traffic into a network and pass that traffic to the higher layers. Layered models are useful because they facilitate modularity. Devices at each layer have similar and well-defined functions. This allows administrators to easily add, replace, and remove individual pieces of the network. This kind of flexibility and adaptability makes a hierarchical network design highly scalable.
    Content 1.2 Scalable Networks 1.2.2 Five Characteristics of a Scalable Network Although every large internetwork has unique features, all scalable networks have essential attributes in common. A scalable network has five key characteristics: The Cisco IOS offers a rich set of features that support network scalability.
    Content 1.2 Scalable Networks 1.2.3 Making the Network Reliable and Available A reliable and available network provides users with 24 hour a day, seven days a week access. In a highly reliable and available network, fault tolerance and redundancy make outages and failures invisible to the end user. However, the high-end devices and telecommunication links that ensure this kind of performance come with a high price tag. Network designers constantly have to balance the needs of users with the resources at hand. When choosing between high performance and low cost at the core layer, the network administrator should choose the best available routers and dedicated WAN links. The core must be designed to be the most reliable and available layer. If a core router fails or if a core link becomes unstable, routing for the entire internetwork might be adversely affected. Core routers maintain reliability and availability by rerouting traffic in the event of a failure. Robust networks can adapt to failures quickly and effectively. To build robust networks, the Cisco IOS offers several features that enhance reliability and availability, including:
    Content 1.2 Scalable Networks 1.2.4 Making the Network Responsive End users notice network responsiveness as they use the network to perform routine tasks. Users expect network resources to respond quickly, as if network applications were running from a local hard drive. Networks must be configured to meet the needs of all applications, especially time delay-sensitive applications, such as voice and video. If the router schedules these packets for transmission on a first-come, first-served basis, users could experience an unacceptable lack of responsiveness. For example, an end user sending delay-sensitive voice traffic may be forced to wait too long while the router empties its buffer of queued packets. Cisco IOS addresses priority and responsiveness issues through queuing. Queuing, sometimes referred to as congestion management, refers to the process that the router uses to schedule packets for transmission during periods of congestion. Congestion management features operate to control congestion once it occurs. By using the queuing feature, a congested router may be configured to reorder packets so that mission-critical and delay-sensitive traffic is processed first. These higher priority packets are sent first even if other lower priority packets arrive ahead of them. Some of the Cisco IOS software congestion management (queuing) features include the following: Each queuing algorithm is designed to solve a specific network traffic problem and has a particular effect on network performance. Web Links Quality of Service Overview
    http://www.cisco.com/en/US/products/ps6350/produ