For original Ethernet, however, having the bus wires in the coax, or the Tx/Rx pair in the TP short-circuited would result into a permanent collision. A loop test requires exactly that: Listening to your own data at the same time you are sending it. Note, however, that Ethernet was originally conceived as a half-duplex technology: A device can either send or receive data but not both at the same time. Moving to more technically involved nature of the issue, a loop test is basically performed by short-circuiting the Transmit and Receive leads in a cable, so that a device sending a test data pattern can hear it back practically in the same time. Telco cabling is much more unpredictable over time, and so it was helpful to have a method for functional testing.
Cisco loopback test ethernet free#
If you think how telco cables are installed and run then you'll immediately see how much more difficult it is for a local telco loop to keep its properties: Running out there, either in free air on poles, or underground, with very variable length, through connection boards that oxidize over time, enduring the heat in summer, cold in winter, air moisture, etc. Of course, it would not hurt if Ethernet had some kind of a loop test, but in most cases, because the entire LAN cabling was relatively small in its size and readily accessible in a building, it was also fairly easy to diagnose if a problem appeared. As long as your cabling was installed according to valid norms and standards, your entire LAN system complied with the Ethernet technical specifications, and so it was guaranteed to work. Whether you were using Ethernet with the thick coax, thin coax, or TP cabling, there were strict rules on the length and the electrical properties of the cabling (think TP cable categories), and Ethernet cables were manufactured to comply with these rules. The transmission properties of the physical wiring for a LAN technology were much more tightly specified, and they were also much easier to maintain, compared to telco lines. When Ethernet was developed, it was a LAN technology only, inteded to be used inside a single building.
Cisco loopback test ethernet code#
In the preceding example, remote payload ANSI bit loopback sends a repeating 16-bit ESF data link code word (of 00010100 11111111) to the remote end requesting that it enter into a network payload loopback.You actually have a very valid and wise question, and a one that's not entirely easy to answer. Router(config-if)# loop remote payload fdl ansi Set the first T1 into remote payload FDL ANSI bit loopback, as follows: In the preceding example, remote line FDL ANSI bit loopback sends a repeating 16-bit ESF data link code word (of 00001110 11111111) to the remote end requesting that it enter into a network line loopback. Router(config-if)# loop remote line fdl ansi
Set the first T1 into remote line FDL ANSI bit loopback, as follows: In the preceding example, remote line inband loopback sends a repeating 5-bit inband pattern (of 00001) to the remote end requesting that it enter into a network line loopback. Router(config-if)# loop remote line inband Set the first T1 into remote line inband loopback, as follows: The syntax of the loopback remote command follows: loopback In the preceding example, network payload loopback loops just the payload data back toward the network at the T1 framer. Router(config-if)# loopback network payload Set the first T1 into network payload loopback as follows: Router# config t In the preceding example, network line loopback loops the data back toward the network (before the T1 framer). Set the first T1 into network line loopback as follows: Router# config t In the preceding example, local loopback loops the router output data back toward the router at the T1 framer and sends an AIS signal out toward the network. Set the first T1 into local loopback as follows:Įnter configuration commands, one per line. Specify the loopback format using the loopback command.Įxamples of specific loopback modes follow: There are three main loopback modes as follows: local, network (both line and payload), and remote (line and payload). Cisco Default Administratitve Distances.
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