Module 2 - Design the Network Structure

Section 3 - Provision Hardware and Media for the WAN

Section Objectives

• Recognize scalability constraints and issues for standard WAN technologies.

• Recognize scalability constraints and performance budgets for major Cisco products.

• Recommend Cisco products and WAN technologies that will meet the customer's requirements for performance, capacity, and scalability in an enterprise network.

Time Required to Complete This Section

Completing This Section

1. Study the reading assignment.
2. Click on any links that you see in the reading assignment and review the information that appears.
3. Review any tables and job aids that appear in the reading assignment.
4. Review the case studies at the end of this section.
5. Complete the questions ineach case study.
6. Review the answers provided by our internetworking experts.

Resources Required to Complete This Section

• Access to the World Wide Web and Cisco's Web site
• A downloaded, printed copy of this section
• Paper and pencil
• Microsoft Excel
• Topology drawings you created in Section 1 of Module 2
• Access to the Cisco Reseller Product Selection Tool (located in the /tools directory on this CD)
• "Small and Medium Business Solution Guide" included with this course

Reading Assignment

WAN Design Considerations

To provide reliable services for end-user applications in a cost-effective and efficient manner, you should select the right type of WAN technology. The following table maps some common WAN technologies to typical applications.
 

Selecting a WAN Technology 

Technology	Applications
Analog Modem	Telecommuters and mobile users who access the network fewer than two hours per day.  Backup for another type of link.
Leased Line	Point-to-point networks and hub-and-spoke topologies.  Backup for another type of link.
ISDN	Cost-effective remote access to corporate networks for telecommuters and remote offices.  Support for voice and video.  Backup for another type of link.
Frame Relay	Cost-effective, high-speed, low-latency mesh or hub-and-spoke topology between remote sites.  Both private and carrier-provided networks.
X.25	Reliable WAN circuit or backbone.  Support for legacy applications.
ATM	Support for accelerating bandwidth requirements.  Support for multiple quality of service (QoS) classes for differing application requirements for delay and loss.

Extending into the WAN

Frame Relay is revolutionizing the data networking infrastructure of corporations and small business. The statistical nature of the service means that nationwide networks supporting reasonable speeds can be cost effective.

The area of greatest growth in today's WANs is dial up. With 28.8-kbps modems and the availability of ISDN, PC users have become mobile. They have remote access to both the Internet and corporate LANs. Some carriers and many Internet service providers are building dial up infrastructures for Internet and telecommuting applications.

Provisioning Cisco Hardware for Small- to Medium-Sized Networks

• Cisco Reseller Product Selection Tool, included on this CD or with the course on Cisco's Web site

• "Small and Medium Business Solution Guide," included with this course

• Price list (To obtain a copy of the current Cisco price list, log in to the Reseller's Web site using your reseller account.)

Provisioning Interface Description Blocks on Cisco Routers

The current IDB limit is 300. Each physical interface on the router, whether it is configured or not, and whether it is active or shut down, uses up one IDB.

Each configured channel on a channelized interface (such as the MIP) uses one IDB. For example, if a MIP T1 port has 24 configured channels, the interface uses a total of 24 IDBs.

Each configured subinterface also uses one IDB. For example, if an FSIP port configured for Frame Relay has 10 configured subinterfaces, the interface uses up a total of 11 IDBs (one for the physical interface and one each for the subinterfaces).

Only the subinterfaces use IDBs, not Frame Relay permanent virtual circuits (PVCs). For example, if a Frame Relay interface has ten PVCs, but does not use any subinterfaces, it uses only a single IDB. If a Frame Relay interface has two subinterfaces each terminating five PVCs (for a total of ten PVCs at the interface), it uses three IDBs.

Switching Modes of Routers in a Small- to Medium-Sized Network Design

Process Switching

With this type of switching, an incoming packet is associated with a destination network or subnet in the routing table located in main memory. Process switching is a scheduled process that is performed by the system processor. Process switching is slow compared to other switching modes because it is delayed by latency of scheduling and latency within the process itself. An inbound access list is an example of process switching.

Normally each packet must individually be examined and compared to an access list. Compression or encryption of packets is also an example of process switching. Anything that requires router processor cycles is process switched. Process switching slows down the network and increases the CPU utilization values.

Fast Switching

With this type of switching, an incoming packet matches an entry in the fast-switching cache located in main memory. Fast switching is done via asynchronous interrupts, which are handled in real time. Fast switching allows higher throughput by switching a packet using a cache created by previous packets. Fast switching is much faster than process switching because it runs at interrupt level. Also, a route cache is usually much shorter than a routing table, so the searching takes less time.

Silicon Switching

With this type of switching, an incoming packet matches an entry in the silicon-switching cache located in the silicon switching engine (SSE) of the Silicon Switch Processor (SSP) module. This module is available only on Cisco 7000 series routers. Silicon switching provides very fast, dedicated packet switching by allowing the SSE to switch packets independently without needing to interrupt the CPU.

Optimum Switching

Optimum switching is available on the RSP only. Even though optimum switching does not have a dedicated switching engine such as the SSE, it is nonetheless almost twice as fast as RSP fast switching and almost as fast as silicon switching because of major enhancements in the cache data structure and caching algorithm, the use of certain interface processors to perform packet classification, and the speed and power of the RSP module.

NetFlow Switching

NetFlow switching identifies traffic flows between internetwork hosts and then, on a connection-oriented basis, switches packets in these flows at the same time that it applies relevant services, such as security, QoS, and traffic accounting.

Choosing a Router Platform

In the past, much emphasis has been put on the packets-per-second (pps) forwarding rate of routers. Today, less emphasis is placed on pps because routers can process packets so quickly, especially with the newer switching technologies, such as optimum and distributed switching.

Additional Required Reading Assignment

To gain an understanding of the significance of pps measurements, the methods for calculating pps capabilities, and the performance of Cisco routers, read the Router Performance Design and Implementation Guide written by Merike Kaeo from the Enterprise Technical Marketing group at Cisco. This clear and concise guide provides accurate and crucial information on router performance and includes the latest pps statistics for Cisco router platforms.
 

Provisioning WAN Networks

• The T1/T3 format is used primarily in North America and parts of Asia.

• The E1/E3 format is used in most of the rest of the world.

• The J1 format is used primarily in Japan.

Provisioning Frame Relay Networks

     1. Choose a committed information rate (CIR) based on realistic, anticipated traffic rates.

• Determine how much interactive, file transfer, and broadcast traffic the link must support.
 
• Use Cisco IOS Release 11.2 Frame Relay traffic-shaping features for predictability.
 
• If you opt for an inexpensive zero CIR, try to get a service level agreement from your provider.

•  Add up the CIRs used at each access site.
 
• If an access site has a zero CIR, use half of the link speed as a rough estimate.

• Determine the required number of interfaces and the number of data-link connection identifiers (DLCIs) each interface should handle.
 
• If there are multiple protocols, decrease the number of DLCIs per interface.
 
• If the applications use many broadcasts, consider static routes and SAP filtering.

•  Consider processing and memory requirements and interface density.

Traffic Shaping over Frame Relay (Cisco IOS Release 11.2 Feature)

• CIR
• forward/backward explicit congestion notification (FECN/BECN)
• Discard Eligibility (DE) bit

The Frame Relay Traffic Shaping feature provides the following capabilities to improve scalability and performance on a Frame Relay network:

Rate Enforcement on a per-Virtual-Circuit (VC) Basis

You can configure a peak rate to limit outbound traffic to either the CIR or some other defined value such as the excess information rate (EIR). Use rate enforcement to:
 
• Limit the rate at which data is sent to the VC at the central site.
 
• Improve performance in conjunction with the existing DLCI prioritization feature.
 
• Allow other criteria, such as the CIR, to control the router's transmission speed.
 
• Preallocate bandwidth to each VC, creating a virtual time-division multiplexing network.

Generalized BECN Support on a per-VC Basis

The router can monitor BECNs and throttle traffic based on BECN marked packet feedback from the Frame Relay network. The traffic is dynamically throttled based on information contained in BECN-tagged packets received from the network.

With BECN-based throttling, packets are held in the router's buffers to reduce the data flow from the router into the Frame Relay network. The throttling is done on a per-VC basis, and the transmission rate is adjusted based on the number of BECN-tagged packets received.

Priority/Custom/Weighted Fair Queuing (PQ/CQ/WFQ) Support at the VC Level

This feature allows for fine granularity in the prioritization and queuing of traffic, providing more control over the traffic flow on an individual VC. These features improve the scalability and performance of a Frame Relay network by increasing the density of VCs and improving response time. The Frame Relay Traffic Shaping feature applies to Frame Relay PVCs and SVCs.

Custom queuing with the per-VC queuing and rate enforcement capabilities enable Frame Relay VCs to be configured to carry multiple traffic types (such as IP, SNA, and IPX), with bandwidth guaranteed for each traffic type.

Frame Relay Planning Spreadsheet

To provision Frame Relay networks, including the Frame Relay CIR, use the the Frame Relay Design Tool (Microsoft Excel) spreadsheet. Click here to install the tool.

Case Studies

In this section, you will provision hardware for the WAN.

Read each case study and complete the questions that follow. Keep in mind that there are potentially several correct answers to each question.

When you complete each question, you can refer to the solutions provided by our internetworking experts. The case studies and solutions will help prepare you for the Sylvan exam following the course.

In this section, you will review the following case studies:

1. CareTaker Publications, a publishing company
2. PH Network Services Corporation, a health care company
3. Pretty Paper Ltd., a European wall covering company
4. Jones, Jones, & Jones, an international law firm

Case Study: CareTaker Publications

Refer to the topology drawing you created for CareTaker Publications in Section 1. In this section, you will provision WAN hardware and media for CareTaker Publications.

The parent company HI has advised Mr. Smith that the CareTaker headquarter's router will soon need additional functionality, but it will not make firm recommendations on the media, protocols, or type of interface until next year.

Exercise

• Start the Cisco Reseller Product Selection Tool (refer to the instructions at the beginning of Module 2 - Section 2.) You will see the initial Cisco Reseller Product Selection Tool window.

 
• Click on "Access Routers/Servers." The Router Product Selection Tool window appears.

 
• Click on the product features you want to select in each category, based on the case study requirements. A short list of potential products appears.

 
• Once you have the short list of products, use the "Small and Medium Business Solutions Guide" that came with this course to select the right product that meets this customer's needs.

 
• Answer the following questions.



 

     4. Can you recommend any third-party products for the load-sharing CSU (multiplexer) and the
         Open Connect gateway products?

Case Study: PH Network Services Corporation

Refer to the topology drawing you created for PH Network in Section 1. In this section, you will provision WAN hardware and media for PH Network.

Exercise

• Start the Cisco Reseller Product Selection Tool (refer to the instructions at the beginning of Module 2 - Section 2.) You will see the initial Cisco Reseller Product Selection Tool window.

 
• Click on "Access Routers/Servers." The Router Product Selection Tool window appears.

 
• Click on the product features you want to select in each category, based on the case study requirements. A short list of potential products appears.

 
• Once you have the short list of products, use the "Small and Medium Business Solutions Guide" that came with this course to select the right product that meets this customer's needs.

 
• Answer the following questions.



 

Case Study: Pretty Paper Ltd.

Refer to the topology drawing you created for Pretty Paper in Section 1. In this section, you will provision WAN hardware and media for Pretty Paper.

Exercise

• Start the Cisco Reseller Product Selection Tool (refer to the instructions at the beginning of Module 2 - Section 2.) You will see the initial Cisco Reseller Product Selection Tool window.

 
• Click on "Access Routers/Servers." The Router Product Selection Tool window appears.

 
• Click on the product features you want to select in each category, based on the case study requirements. A sort list of potential products appears.

 
• Once you have the short list of products, use the "Small and Medium Business Solutions Guide" that came with this course to select the right product that meets this customer's needs.

 
• Answer the following questions.

Now that you have completed the exercise, click here to view the solutions provided by our internetworking design experts.

Case Study: Jones, Jones, & Jones

Refer to the topology drawing you created for Mr. Jones in Section 1. In this section, you will provision WAN hardware and media for Mr. Jones.

Exercise

• Start the Cisco Reseller Product Selection Tool (refer to the instructions at the beginning of Module 2 - Section 2.) You will see the initial Cisco Reseller Product Selection Tool window.

 
• Click on "Access Routers/Servers." The Router Product Selection Tool window appears.

 
• Click on the product features you want to select in each category, based on the case study requirements. A short list of potential products appears.

 
• Once you have the short list of products, use the "Small and Medium Business Solutions Guide" that came with this course to select the right product that meets this customer's needs.

 
• Answer the following questions.



 

Now that you have completed the exercise, click here to view the solutions provided by our internetworking design experts.

If you have finished this section, click here to advance to Module 2, Section 4.