Chapter Summary

• Modems make it possible to communicate over telephone lines.
• There are two types of modems: synchronous and asynchronous.
• It is important to choose the right cable when connecting hubs; crossover cables will not work in place of standard patch cables.
• Asymmetric digital subscriber line (ADSL) is a technology for increasing the�speed of transmission on telephone lines.
• Repeaters are used to connect two segments of similar or dissimilar media and to regenerate a signal to increase the distance transmitted.
• Repeaters should not be used where network traffic is heavy, segments are using different access methods, or filtering is needed.
• Bridges have all the features of repeaters.
• Bridges are used to connect two segments to expand the length or number of�nodes on the network, to reduce traffic by segmenting the network, or to connect dissimilar networks.
• Routers are used to connect two networks, limit unnecessary traffic, and to separate administrative networks.
• Brouters combine the features of bridges and routers; a brouter can act as a router for one protocol and as a bridge for all the others.
• Gateways perform protocol and data conversion.
• Gateways are limited in several ways: they are task-specific, expensive, and can be slow.

• Two types of telephone lines are available for modem communications: public telephone lines (dial-up lines) and leased lines (dedicated lines).
• Most long-distance carriers use switched circuits to provide what appear to be dedicated lines, also called virtual private networks (VPNs).
• To make a Remote Access Service (RAS) connection, the server on the network must be configured with RAS, and the computer connecting to the network must be configured as a client or with dial-up networking (DUN).
• RAS connections can use any one of three protocols: Serial Line Interface Protocol (SLIP), Point-to-Point Protocol (PPP), or Point-to-Point Tunneling Protocol (PPTP).
• RAS provides four levels of security: auditing, callback, security host, and PPTP filters.
• The Point-to-Point Tunneling Protocol (PPTP) allows a remote client to make a secure connection to a network over the Internet.
• Organizations that need a more secure and faster connection than can be provided by an analog line can convert to DDS (digital data service).
• T1 service is the most widely used kind of digital line.
• Packet-switching networks offer a fast and efficient way to transit data over wide areas.
• Frame relay is an advanced fast-packet variable-length, digital, packet-switching technology.
• Asynchronous Transfer Mode (ATM) is an advanced implementation of packet switching that provides high-speed transmission rates to send fixed-size packets over broadband and baseband LANs and WANs.
• Integrated Services Digital Network (ISDN) is an inter-LAN digital connectivity specification that accommodates voice, data, and imaging.
• Fiber Distributed Data Interface (FDDI) is a specification that describes a high-speed token-passing network that uses fiber-optic media.
• Synchronous Optical Network (SONET) is an emerging technology based on�fiber optics.
• Switched Multimegabit Data Service (SMDS) is a connectionless switching service provided by local exchange carrier services that offers high bandwidth at reduced network costs.

• Remote Access Service (RAS) is used to provide remote access to a network.
• A RAS connection requires that the server on the network be configured with RAS service and the computer connecting to the network be configured as a client or dial-up networking (DUN) computer.
• RAS connections can use any one of three protocols: Serial Line Interface Protocol (SLIP), Point-to-Point Protocol (PPP), or Point-to-Point Tunneling Protocol (PPTP).
• RAS provides four levels of security: auditing, callback, security host, and PPTP filters.
• Use RAS if the bandwidth is less than 128 Kps, you do not require a full-time connection, or you need to keep the system cost down.
• Don't use RAS if you need a higher bandwidth than provided by a synchronous-modem, you need a dedicated full-time connection, or if leased lines are already available.