Summary

This chapter introduced the several types of WAN technologies and categorized them into three main types: private, leased, and public. WAN design was introduced, and the steps of the PDIOO methodology were discussed. Finally, a look at the technologies of route selection and switching inside the router were presented.

Several specific WAN technologies were described in this chapter. SDLC was used by IBM mainframes and ported for use by networking vendors in the form of HDLC, which is the default encapsulation on Cisco router serial interfaces. ISDN is an alternative to slow analog lines and is a popular backup connection type for today’s high-speed Frame Relay networks. PPP is implemented on many of today’s networks to provide Data Link layer transport for Network layer protocols. Frame Relay has become a very popular WAN connection type along with the routing hardware. Frame Relay supports many different Network layer protocols and is readily available from local carriers and router manufacturers. There are many design considerations with Frame Relay, including DLCI, LMI, subinterface needs, and meshed network designs. The best solution for most designs is a partial mesh topology with subinterfaces creating full connectivity between all networks. Finally, DSL is increasingly popular as an Internet- connectivity tool and as a technology that can use existing copper originally installed for the PSTN.