Wide Area Networks (WANs)-

                LAN implementations have physical and geographic limitations.  Wide area networks (WANs) meet a need for networking that requires connectivity over larger distances.

                Most WAN are simply combinations of local area networks and additional communications links between the LANs.  The following terms are used to dercribe the scope or size of a WAN:

·         Metropoliton Area Networks (MANs)-  MANs are WANs is a small geographic area.  Generally, they are localized to single city or region.

·         Campus area networks (CANs)-  CANs  is a common designation for WANs that link regions of a university campus.

For practical implementation, these are no different from a wide area network except for the area they physically cover.  

                Communications over a WAN use one of the following transmission technologies:

·         Analog

·         Digital

·         Packet Switching

Analog and digital technologies commonly are implemented as point-to-point technologies.  In other words, they are configured between two distinct hosts.  Packet switching, on the other hand, links several hosts using a mesh or cloud technology.  Any host participating in t;he cloud can establish a session to another host in the cloud.

Analog WAN Connectivity-

                Analog phone lines can be used to connect networks despite the poor line quality and slower speeds.  The public switched telephone network (PSTN) was primarily designed for voice traffic; it also can be used for data traffic.  Remote users connecting to the home network from the road often use PSTN access.  Although it is possible to purchase a dedicated analog line to connect networks, the cost of a conditioned line generally is prohibitive, and other networking solutions are investigated.

Digital Wide Area Network Connectivity-

                A more common method of linking a WAN is to use digital data service (DDS) lines.  DDS provides a point-to-point synchronous connection.  A company can lease dedicated circuits that provide full-duplex bandwidth by setting up a permanent link from each endpoint of the network.

                Digital lines are preferable to analog lines due to increased speed and lack of transmission errors.  Digital traffic does not require a modern Instead, data is sent from a router on a network to a channel service unit/data service unit (CSU/DSU).

                The following are common digital connectivity methods:

·         T1/E1

·         T3/E3

·         ISDN

·         Switched 56

T1/E1-  T1 service (known as E1 in Europe) is the most widely used digital service at higher data speeds.  T1 can transmit a full duplex signal at a rate of 1.544 Mbps.  It can be used to transmit voice, data, and video signals.

Because of the high cost of a T1 line, many subscribers opt for fractional-T1 service. Instead of using a T1’s full bandwidth, the subscriber uses one or more T1 channels, Each T1 channel is a 64Kbps increment.

T3/E3-  T3 service (known as E3 in Europe) can provide voice and data-grade service at speeds up to 45Mbps.  This is the highest-capacity service available to the consumer today.  As with T1 service, fractional-T3 service is available as an alternative to multiple T1 lines.

Integrated Services Digital Network(ISDN)-  ISDN is an inter LAN connectivity method that can carry data, voice and imaging signals.  Two flavors olf ISDN are available: basic rate and primary rate.
Basic rate ISDN provides two bearer channels (known as B Channels) that communicate at 56Kbps; an 8Kbps link-management channel; and one data channel (known as a D channel) that carry signal and link management data at a r ate of 16Kbps.  A network using both B channels can provide a 128Kbps data stream.

Primary rate ISDN provide the entire bandwidth of a T1 link by provide the entire bandwidth of a T1 link by providing 23B channels and one D Channel.  In Europe, 30B channels are used.  The D channel under primary rate ISDN communicates at 64Kbps and still is used only for signal and link management data.

ISDN is a demand-dial interface, Instead of remaining active at all hours, it demand-dials whenever a connection is required.