User guide

A-20 Cisco 2500 Series Access Server User Guide
Desktop Protocols
Frame Relay WANs should be carefully designed with the above considerations in mind.
(see the publication Internetwork Design Guide).
Dial-on-Demand Routing
Dial-on-demand routing (DDR) enables you to make a standard telephone connection or an
Integrated Services Digital Network (ISDN) connection only when required by the volume
of network traffic. DDR may be less expensive than a leased-line or multipoint solutions.
See the publication Access and Communication Servers Configuration Guide for assistance
in selecting, designing, and configuring dial-on-demand solutions.
Desktop Protocols
Desktop protocols are the network layer protocols that are commonly used by desktop
workstations and are supported by the Cisco 2500 series access server. This section briefly
describes the three most common desktop protocols—IP, IPX, and AppleTalk.
Network designers and administrators should be familiar with which networking functions
are performed by the data link layer (Layer 2) and which are performed by the network
layer (Layer 3) of the OSI reference model. For more information about the OSI reference
model, see the section “LANs and WANs” earlier in this appendix.
IP, IPX, and AppleTalk are all defined as routed (or routable) protocols. The unique
numbering of each network (data link) and the addressing of each data packet based on this
numbering allow efficient packet routing through the internetwork. This is similar to the use
of zip codes to allow efficient routing of mail through the national mail infrastructure.
This section includes the following information:
• The common design goals of each desktop protocol
• How each protocol meets these goals
• Example configurations of IP, IPX, and AppleTalk