Chapter 1: Cisco SONA and the Cisco Enterprise Architecture (Part03)

Using the Design Methodology Under PPDIOO

The design methodology under PPDIOO consists of three basic steps:

Step 1	Identify customer requirements. In this step, key decision makers identify the initial requirements. Based on these requirements, a high-level conceptual architecture is proposed. This step is typically done during the PPDIOO prepare phase.
Step 2	Characterize the existing network and sites. The plan phase involves characterizing sites, assessing any existing networks, and performing a gap analysis to determine whether the existing system infrastructure, sites, and operational environment can support the proposed system. Characterization of the existing network and sites includes a site and network audit and network analysis. During the network audit, the existing network is thoroughly checked for integrity and quality. During the network analysis, network behavior (traffic, congestion, and so on) is analyzed. This is typically done within the PPDIOO plan phase.
Step 3	Design the network topology and solutions. In this step, you develop the detailed design. Decisions about network infrastructure, intelligent network services, and network solutions (VoIP, content networking, and so on) are made. You may also build a pilot or prototype network to verify the design. You also write a detailed design document.

Identifying Customer Requirements

This section reviews the process for gathering customer requirements for the enterprise network design discussed in the Designing for Cisco Internetwork Solutions (DESGN) course (see Figure 1-6).

Figure 1-6: Identifying Customer Requirements

The design requirements gathering process includes discussions with the staff of the organization to determine and gather the necessary data and documentation.

The data-gathering steps are as follows:

Step 1	Identify network applications and network services. Define which applications have timing constraints in the traffic flows.
Step 2	Define the organizational goals.
Step 3	Define the organizational constraints.
Step 4	Define the technical goals.
Step 5	Define the technical constraints.

The process of identifying required information is not unidirectional. You might return to a step and make additional inquiries about issues as they arise during the design process.

When you complete the data-gathering process, you are ready to interpret and analyze the data and develop a design proposal.

Characterizing the Existing Network and Sites

The first step in characterizing an existing network is to gather as much information about the network as possible. Existing documentation and organizational input, site and network audits, and traffic analysis can provide the key information that you need.

Information gathering typically follows these steps:

Step 1	Gather existing documentation about the network, and query the organization to discover additional information. Organization input, a network audit, and traffic analysis provide the key information you need. (Note that existing documentation may be inaccurate.)
Step 2	Perform a network audit that adds detail to the description of the network. If possible, use traffic-analysis information to augment organizational input when you are describing the applications and protocols used in the network.
Step 3	Based on your network characterization, write a summary report that describes the health of the network. With this information, you can propose hardware and software upgrades to support the network requirements and the organizational requirements.

Note

Although this is a good idea in principle, a network audit is often too costly in terms of time and effort. Some organizations may implement expedited versions of a network audit to target specific areas.

Designing the Topology and Network Solutions

After you gather organizational requirements, and document and audit the existing network, you are ready to design a network solution, plan the implementation, and (optionally) build a network prototype.

Designing an enterprise network is a complex project. Top-down design facilitates the process by dividing it into smaller, more manageable steps. Top-down design clarifies the design goals and initiates the design from the perspective of the required applications and network solutions.

In assessing the scope of a network design, you must determine whether the design is for a new network or is a modification of the entire network, a single segment or module, a set of LANs, a WAN, or a remote-access network. The design scope may address a single function or all of the OSI model layers.

Structured top-down design practices focus on dividing the design task into related, less-complex components or modules:

• Identify the applications that will be needed to support the customer’s requirements.

• Identify the logical connectivity requirements of the applications, with a focus on the necessary network solutions and the supporting network services. Examples of infrastructure services include voice, content networking, and storage networking, availability, management, security, QoS, and IP multicast.

• Split the network functionally to develop the network infrastructure and hierarchy requirements. In this course, the Cisco Enterprise Architecture provides a consistent infrastructure.

• Design each structured element separately in relation to other elements. Network infrastructure and infrastructure services design are tightly connected, because both are bound to the same logical, physical, and layered models.

When the design is completed in the PPDIOO process, the next step is to develop the implementation and migration plan in as much detail as possible. The more detailed the implementation plan documentation, the less knowledgeable the network engineer needs to be to implement the design.

After a design is complete, it often is appropriate to verify the design. You can test the design in an existing or live network (pilot), or in an isolated test network (prototype) that will not affect the existing network.

Example: Dividing the Network into Areas

Use these guidelines to create an enterprise network:

• Divide the network into areas where the enterprise campus module includes all devices and connections within the main campus. Ensure the enterprise edge modules cover all communications with remote locations from the perspective of the enterprise campus. Finally, make certain that the remote modules include the remote branches, teleworkers, and the remote data center.

• Define clear boundaries between the enterprise campus, the enterprise edge, and the remote modules.

Note

Depending on the network, an enterprise can have multiple campus locations. A location might be a remote branch from the perspective of a central campus location, but can locally use the Enterprise Campus Architecture.

Figure 1-7 shows an example of one step in designing an enterprise network. The network is divided into an enterprise campus area, an enterprise edge area, and some remote areas.

Figure 1-7: Example: Dividing the Network into Areas

Summary

This chapter covered the following topics:

• The Hierarchical Network Model enables a modular approach to the design and construction of a deterministic scalable network. The hierarchical network structure is composed of the access, distribution, and core layers.

• Cisco SONA is the enterprise framework for building intelligence into the network:

  • Layer 1 is the network infrastructure layer.

  • Layer 2 is the interactive services layer (infrastructure services).

  • Layer 3 is the application layer (business applications).

• The Cisco Enterprise Architecture consists of modules representing focused views of SONA that target each place in the network. Each module has a distinct network infrastructure and services, and network applications that extend between the modules.

• Infrastructure services add intelligence to the network by supporting application awareness.

• The PPDIOO approach reflects the lifecycle phases of a standard network.

• The design methodology under PPDIOO includes the following:

  • Identifying customer requirements

  • Characterizing the existing network and sites

  • Designing the network topology and solutions

References

For more information, refer to these resources:

• Cisco Systems, Inc. “Lifecycle Services Portfolio,” at http://www.cisco.com/en/US/products/ps6890/serv_category_home.html

• Cisco Systems, Inc. “Service-Oriented Network Architecture Introduction,” at http://www.cisco.com/en/US/netsol/ns629/networking_solutions_market_segment_solutions_home.html

• Cisco Systems, Inc. Enterprise Architectures documentation, at http://www.cisco.com/en/US/netsol/ns517/networking_solutions_market_segment_solutions_home.html

• Cisco Systems, Inc., “Lifecycle Services Strategy Introduction,” at http://www.cisco.com/en/US/products/ps6890/serv_category_home.html

• Oppenheimer, P. Top-Down Network Design, Second Edition. Cisco Press; 2004.

• “Internetworking Design Basics” chapter of Cisco Internetwork Design Guide, at http://www.cisco.com/univercd/cc/td/doc/cisintwk/idg4/nd2002.htm