MCSE Training Kit: Networking Essentials Plus, Third Edition (IT Professional)
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Connectivity Devices
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.
Connection Services
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 Computing
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.