Information Technology Reference
In-Depth Information
1000BaseCX
Another copper standard has existed since the early inception of Gigabit Ethernet,
1000BaseCX. As the “X” implies, this is simply a nonfiber-based implementation of
the Fibre Channel technology.
This standard is intended to make use of the less expensive direct-copper con-
nection methods, rather than the pricier fiber-optic methods. The CX mode uses a
type of cable known as twinax (see more detail on coaxial and twin-axial shielded
cables in Chapter 5). As shown in Table 12.3, the distance limitations are extreme.
However, this is not seen as a problem, because the CX connection was envisioned
to be used only in the telecommunications closet, and 25 m would be a relatively
long distance to connect in that environment. In reality, CX implementations are
rare, as development of less expensive gigabit optics has greatly increased the cost
associated with a fiber link.
TABLE 12.3
Gigabit Ethernet Copper Link Parameters
IEEE 802.3z
Number
fiber mode
Cable type
of pairs
Range, m
1000BaseCX
Twinax or quad
N/A
25
1000BaseT
Category 5, 5e, 6, or above
4
100
ATM Gigabit Standards
Several methods are available for operating ATM in the local area environment,
whether direct to workstations and servers, or as a backbone technology that might
run between floors or buildings on a campus. As you know, ATM is a signaling pro-
tocol that is independent of data rate and media. As a result, much of the informa-
tion that is available for ATM covers wide-area implementations, such as those for
ATM over T1 or DS3. The ATM-155 UNI and ATM-622 UNI interfaces are capa-
ble of operating both in the local and wide area, and a LAN can certainly be imple-
mented in native ATM networking technology.
Unfortunately, in the LAN, most of the equipment connections are Ethernet-
oriented. Operating a virtual LAN connection, such as Ethernet or Token-Ring, over
an ATM network requires a number of additional protocols that adds a tremendous
complexity to a local network. This technology is called LAN emulation (LANE).
In addition, 155 Mbps and 622 Mbps optical interfaces are fairly expensive, both
for the hub and the workstation.
For these reasons, the market has been much more open to the Gigabit
Ethernet implementations than to the comparable ATM speeds.
