1. S4-Chapter 3 WAN Design Requirements

2. WAN Technologies Leased Line –PPP networks –Hub and Spoke Topologies –Backup for other links ISDN –Cost-effective remote access –Support for voice and video –Backup for other links Frame Relay –Cost-effective, high-speed, low-latency topology –Used for private and carrier-provided networks

3. WAN Communication Service –Network provider charges uses for WAN service Circuit Switching –Dedicated bandwidth for specific time interval Packet Switching –Devices share single point to point link to transport packets Characteristics –Low throughput –High delay –High error rates –Rent media

4. WAN Design Requirements Optimize WAN bandwidth Minimize cost Maximize effective service to end users

5. WAN Problems (Overtaxed systems) Increase in network usage Accelerated rate of change (push technologies) Required distinct network quality of service Increased number of connections Increased growth of corporate intranets and extranets Increased use of enterprise servers

6. New WAN Requirements More complex infrastructure Complex application mix Higher level of service 300% traffic increase in next five years Suggested services –Traffic optimization –Multiple paths for redundancy –Dial backup for disaster recovery

7. Bandwidth Issues LAN –Free; connectivity limited only by hardware and implementation costs WAN –Bandwidth is overriding cost –Delay-sensitive traffic has remained separate from data –New technologies require more predictable LAN and WAN performance

8. Design Goals Application availability –applications must be available to network users Total cost of ownership needs to balance organizational goals Three factors to consider –Environmental variables –Performance constraints Reliability, throughput, speeds –Network variables Topology, line capacities, packet traffic

9. Application Availability Response time – time to execute a command to deliver a response Throughput-intensive with low response- time requirements Reliability, e.g. 100% uptime for online business activities

10. Analyze Requirements Business requirements Technical requirements New applications or business operations Performance requirements Availability requirements

11. Factors Influencing Network Dynamics Time-dependent nature of network access Different types of traffic –Some protocols sensitive to dropped packets –Some applications require more bandwidth Random nature of network traffic Need to apply a factor for –Protocol overhead, packet fragmentation, traffic growth, and safety margin

12. Sensitivity Testing Break stable links and observe what happens –Remove active interface –Observe how traffic is rerouted –Observe speed of convergence –Observe lost connectivity –Observe special traffic problems Change the level of traffic to determine effects from media saturation

13. Benefits of Scalable Design Scalability Ease of implementation Ease of troubleshooting Predictability Protocol support Manageability

14. Hierarchical Network Design Core Layer – provides optimal transport between sites; point to point, no hosts T1/T3, SMDS, Frame Relay Distribution Layer – provides policy-based connectivity; network services to multiple LANS – backbone on Fast Ethernet Access Layer – provides workgroup and user access to the network; LAN or group of LANS – Ethernet or Token Ring

15. Core Layer Functions Redundant paths Load Sharing Rapid convergence Efficient use of bandwidth –No access control lists or filtering –WAN that needs redundant paths –Load sharing and rapid convergence

16. Distribution Layer Controls access to services Defines Path Metrics Controls network advertisements Demarcation point between ACCESS and CORE layers –Provides boundary definition –Packet manipulation

17. Distribution Layer Functions Includes Campus backbone Address or area aggregation Departmental or workgroup access to core layer Broadcast/multicast domain definition Virtual LAN routing Media transitions Security

18. Access Layer Provides logical segmentation Groups users with common interests Isolates broadcast traffic Includes: –Shared bandwidth –Switched bandwidth –MAC layer filtering –Micro-segmentation

19. One-Layer Design Implemented when there are only a few remote locations Access to applications if done via local LAN to file server Each site is its own broadcast domain

20. Two-layer Design WAN used to interconnect separate sites Each LAN is its own broadcast domain

21. Server Placement Enterprise Servers – place at higher layer in hierarchy Workgroup Servers – place at access layer where there is largest concentration of users