LAN WAN Difference
Carrier Ethernet E-Line and
E-LAN are blurring the distinction between local and wide area
By: John Shepler
There has always been something of a technical
"digital divide" between Local Area Networks or LANs,
and Wide Area Networks or WANs. The difference in standards reflects
the difference in heritage. LANs came from the computer industry
and WANs came from the telephone industry. But today those standards
are beginning to merge.
Heritage of LANs
Local Area Networks were developed to link computers within a
building or corporate campus. Hence the name local. Various protocols
have been used over the last sixty or so years, but the overwhelming
favorite has become Ethernet. Ethernet is a packet based protocol
that runs on both copper and fiber optic cable. Unshielded twisted
pair copper is the cabling of choice. Nearly every piece of computing
gear from PCs through routers support Ethernet connections. Basic
Ethernet speed is 10 Mbps, but Fast Ethernet at 100 Mbps is more
common, with Gigabit Ethernet or GigE as the emerging standard.
Ten GigE or 10 Gbps Ethernet is being deployed in larger organizations
to keep up with the demand for user bandwidth.
Heritage of WANs
On the other side of the fence, Wide Area Networking has typically
been the purview of the telephone companies. WANs extend your
network across town or interstate to international distances.
The Bell System had a virtual lock on all landlines until deregulation.
They developed the standards for voice and data lines. Voice
grade lines will support low bandwidth modems, but digital carriers
are needed for higher speeds. The low end is dominated by T1
lines running at 1.5 Mbps with an upgrade path to T3 lines at
45 Mbps. The T-carriers, as they are called, use TDM or time
division multiplexing technology developed to carry phone calls
rather than the information packets used by Ethernet. Protocol
conversion is needed to go from one standard to another.
At the high end, telco based WANs are based
on SONET or Synchronous Optical NETwork standards. The basic
service is OC3 running at 155 Mbps, with OC12 at 622 Mbps and
OC48 at 2.5 Gbps reasonably available. Network backbones might
use OC192 at 10 Gbps for metro and long haul traffic. SONET is
also TDM based and originally designed for voice trunking. But
the bandwidths of the available SONET circuits are suitable for
carrying equivalent Ethernet data. For instance, OC3 will support
Fast Ethernet, OC48 will carry GigE and OC192 can handle 10GigE.
IP as a Universal Networking Standard
Various forces are at work to promote Ethernet and its WAN equivalent
IP Networking as a universal standard. Most visible is the Internet,
which is based on TCP/IP standards. Heavy business need for point
to point and mesh networking between physically diverse locations
is a driving factor for efficient WAN networking. The ongoing
corporate switch from TDM based telephone systems to VoIP telephony
is also driving this desire for a single protocol end to end.
In response, IP WANs and Carrier Ethernet
are emerging as alternatives to the traditional telecommunication
links. The MEF or Metro Ethernet Forum is the standards body
defining Carrier Ethernet services. E-Line is a point to point
Ethernet service. It is available in two flavors, EPL or Ethernet
Private Line and EVPL or Ethernet Virtual Private Line. The virtual
service allowsmore than one Ethernet service at the same User
Network Interface. ELAN is multipoint to multipoint virtual Ethernet
As IP packet networks proliferate, the
line between LAN and WAN will blur and then disappear. Your far-flung
business locations across the country or even around the world
will be interconnected on business networks that appear to be
one large company LAN.
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