5-4-3 rule
Encyclopedia
The 5-4-3 rule also referred to as the IEEE way (as opposed to the Ethernet way) is a design guideline for Ethernet
computer networks covering the number of repeater
s and segment
s on shared-access Ethernet backbone
s in a tree topology. It means that in a collision domain there should be at most 5 segments tied together with 4 repeaters, with 3 segments containing active senders (i.e. terminals
).
s of the signals.
For the purposes of the rule, a segment is in accordance with the IEEE definition: an electrical connection between networked devices.
In the original 10BASE5
and 10BASE2
Ethernet varieties, a segment would therefore correspond to a single coax cable and any devices tapped into it. On modern twisted-pair Ethernet, a network segment corresponds to the individual connection between end station to network equipment or the connections between different pieces of network equipment.
The rule divides a collision domain into two types of physical segments: populated (user) segments, and unpopulated (link) segments. User segments have users' systems connected to them. Link segments are used to connect the network's repeaters together. The rule mandates that there can only be a maximum of five segments, connected through four repeaters, or concentrators
, and only three of the five segments may contain user connections. This last requirement applies only to 10BASE5 and 10BASE2 Ethernet segments.
This rule is also known as the 5-4-3-2-1 rule with there being two network segments and one collision domain
.
The 5-4-3 rule was created when 10BASE5 and 10BASE2 were the only types of Ethernet network available. The rule only applies to shared-access Ethernet backbones. The rule does not apply to switched Ethernet because each port on a switch constitutes a separate collision domain.
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
computer networks covering the number of repeater
Repeater
A repeater is an electronic device that receives asignal and retransmits it at a higher level and/or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances.-Description:...
s and segment
Network segment
A network segment is a portion of a computer network. The nature and extent of a segment depends on the nature of the network and the device or devices used to interconnect end stations.-Ethernet:...
s on shared-access Ethernet backbone
Backbone network
A backbone network or network backbone is a part of computer network infrastructure that interconnects various pieces of network, providing a path for the exchange of information between different LANs or subnetworks. A backbone can tie together diverse networks in the same building, in different...
s in a tree topology. It means that in a collision domain there should be at most 5 segments tied together with 4 repeaters, with 3 segments containing active senders (i.e. terminals
Terminal (telecommunication)
In the context of telecommunications, a terminal is a device which is capable of communicating over a line. Examples of terminals are telephones, fax machines, and network devices - printers and workstations....
).
Details
The original Ethernet protocol requires that a signal sent out over the collision domain reach every part of the network within a specified length of time. The 5-4-3 rule ensures this. Each segment and repeater that a signal goes through adds a small amount of time to the process, so the rule is designed to minimize transmission timeTransmission time
In telecommunication networks, the transmission time, is the amount of time from the beginning until the end of a message transmission. In the case of a digital message, it is the time from the first bit until the last bit of a message has left the transmitting node...
s of the signals.
For the purposes of the rule, a segment is in accordance with the IEEE definition: an electrical connection between networked devices.
In the original 10BASE5
10BASE5
10BASE5 was the original commercially available variant of Ethernet.For its physical layer it used cable similar to RG-8/U coaxial cable but with extra braided shielding. This is a stiff, diameter cable with an impedance of 50 ohms , a solid center conductor, a foam insulating filler, a shielding...
and 10BASE2
10BASE2
10BASE2 is a variant of Ethernet that uses thin coaxial cable , terminated with BNC connectors...
Ethernet varieties, a segment would therefore correspond to a single coax cable and any devices tapped into it. On modern twisted-pair Ethernet, a network segment corresponds to the individual connection between end station to network equipment or the connections between different pieces of network equipment.
The rule divides a collision domain into two types of physical segments: populated (user) segments, and unpopulated (link) segments. User segments have users' systems connected to them. Link segments are used to connect the network's repeaters together. The rule mandates that there can only be a maximum of five segments, connected through four repeaters, or concentrators
Ethernet hub
An Ethernet hub, active hub, network hub, repeater hub or hub is a device for connecting multiple Ethernet devices together and making them act as a single network segment. A hub works at the physical layer of the OSI model. The device is a form of multiport repeater...
, and only three of the five segments may contain user connections. This last requirement applies only to 10BASE5 and 10BASE2 Ethernet segments.
This rule is also known as the 5-4-3-2-1 rule with there being two network segments and one collision domain
Collision domain
A collision domain is a section of a network where data packets can collide with one another when being sent on a shared medium or through repeaters, in particular, when using early versions of Ethernet. A network collision occurs when more than one device attempts to send a packet on a network...
.
The 5-4-3 rule was created when 10BASE5 and 10BASE2 were the only types of Ethernet network available. The rule only applies to shared-access Ethernet backbones. The rule does not apply to switched Ethernet because each port on a switch constitutes a separate collision domain.