Information Technology Reference
In-Depth Information
1 TX_D1+
2 TX_D1-
3 RX_D2+
4 BI_D3+
5 BI_D3-
6 RX_D2-
7 BI_D4+
8 BI_D4-
1 TX_D1+
2 TX_D1-
3 RX_D2+
4 BI_D3+
5 BI_D3-
6 RX_D2-
7 BI_D4+
8 BI_D4-
RJ-45
RJ-45
where BI represents the bi-directional transmission signals, TX the transmit signals and RX
the receive signals. These cable connections are difficult to set-up and most connections use
a straight through connection (as given in Table 26.3). Ports which have the cross-over
connection internal in the port are marked with an “X”.
26.16 Notes from the author
Until recently, it seemed unlikely that Ethernet would survive as a provider of network back-
bones and for campus networks, and its domain would stay, in the short-term, with connec-
tions to local computers. The world seemed distended for the global domination of ATM, the
true integrator of real-time and non real-time data. This was due to Ethernet's lack of sup-
port for real-time traffic and that it does not cope well with traffic rates that approach the
maximum bandwidth of a segment (as the number of collisions increases with the amount of
traffic on a segment). ATM seemed to be the logical choice as it analyses the type of data
being transmitted and reserves a route for the given quality of service. It looked as if ATM
would migrate down from large-scale networks to the connection of computers, telephones,
and all types analogue/digital communications equipment. But, remember, not always the
best technological solution wins the battle for the market - a specialist is normally always
trumped by a good all-rounder.
Ethernet also does not provide for quality of service and requires other higher-level pro-
tocols, such as IEEE 802.1p. These disadvantages are often outweighed by its simplicity, its
upgradeability, its reliability and its compatibility. One way to overcome the contention
problem is to provide a large enough bandwidth so that the network is not swamped by
sources which burst data onto the network. For this, the gigabit Ethernet standard is likely to
be the best solution for most networks.
