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5.2 | |
Cabling the WANs | |
| 5.2.2 | |
WAN serial connections |
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For long distance communication, WANs use
serial transmission. This is a process by which bits of data are sent
over a single channel. This process provides more reliable long
distance communication and the use of a specific electromagnetic or
optical frequency range.
Frequencies are measured in terms of
cycles per second and expressed in Hertz (Hz). Signals transmitted
over voice grade telephone lines use 4 kilohertz (kHz). The size of
the frequency range is referred to as bandwidth. In networking,
bandwidth is a measure of the bits per second that are transmitted.
For a Cisco router, physical
connectivity at the customer site is provided by one of two types of
serial connections. The first type of serial connections is a 60-pin
connector. The second is a more compact ‘smart serial’ connector. The
provider connector will vary depending on the type of service
equipment. If the connection is made directly to a service provider, or a device that provides signal clocking such as a channel/data service unit (CSU/DSU), the router will be a data terminal equipment (DTE) and use a DTE serial cable. Typically this is the case. However, there are occasions where the local router is required to provide the clocking rate and therefore will use a data communications equipment (DCE) cable. In the curriculum router labs one of the connected routers will need to provide the clocking function. Therefore, the connection will consist of a DCE and a DTE cable.
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