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| {{short description|Device for interconnecting Ethernet devices}} | |||
| ] | |||
| An '''Ethernet hub''', '''active hub''', '''network hub''', '''repeater hub''' or '''hub''' is a device for connecting multiple ] or ] ] devices together and making them act as a single ]. A hub works at the ] (layer 1) of the ].<ref name=networkingtext/> The device is a form of ]. Repeater hubs also participate in collision detection, forwarding a ] to all ports if it detects a ]. | |||
| ] Ethernet hub with selectable ] port]] | |||
| Some hubs may also come with a ] and/or ] (AUI) connector to allow connection to legacy ] or ] network segments. The availability of low-priced ]es has largely rendered hubs obsolete but they are still seen in older installations and more specialized applications. | |||
| ] connector and eight 10BASE-T ports]] | |||
| An '''Ethernet hub''', '''active hub''', '''network hub''', '''repeater hub''', '''multiport repeater''', or simply '''hub'''{{efn|]es are sometimes called switching hubs.}} is a ] device for connecting multiple ] devices together and making them act as a single ]. It has multiple ] (I/O) ports, in which a ] introduced at the input of any ] appears at the output of every port except the original incoming.<ref>IEEE 802.3-2012 Clause 9.1</ref> A hub works at the ].<ref name=networkingtext /> A repeater hub also participates in collision detection, forwarding a ] to all ports if it detects a ]. In addition to standard ] ("]") ports, some hubs may also come with a ] or an ] (AUI) connector to allow connection to legacy ] or ] network segments. | |||
| ==Technical information== | |||
| A network hub is an unsophisticated device in comparison with, for example, a ]. A hub does not manage any of the traffic that comes through it: any packet entering any port is rebroadcast on all other ports.<ref name="networking">{{cite book | last = Hallberg | first = Bruce | title = Networking: A Beginner's Guide, Fifth Edition | publisher = McGraw Hill | year = 2010 | location = | pages = 68–69}}</ref> Consequently, packet collisions are more frequent in networks connected using hubs than in networks connected using more sophisticated devices.<ref name="networkingtext">{{cite book | last = Dean | first = Tamara | title = Network+ Guide to Networks | publisher = Delmar | year = 2010 | location = | pages = 256–257}}</ref> | |||
| Hubs are now largely obsolete, having been replaced by ]es except in very old installations or ]. As of 2011, connecting network segments by repeaters or hubs is deprecated by IEEE 802.3.<ref>IEEE 802.3 ''9. Repeater unit for 10 Mb/s baseband networks''</ref><ref>IEEE 802.3 ''27. Repeater unit for 100 Mb/s baseband networks''</ref><ref>IEEE 802.3 ''41. Repeater unit for 1000 Mb/s baseband networks''</ref> | |||
| 100 Mbit/s hubs and repeaters come in two different speed grades: Class I delay the signal for a maximum of 140 bit times (enabling translation between 100Base-TX, 100Base-FX and 100Base-T4) and Class II ones delay the signal for a maximum of 92 bit times (enabling installation of two hubs in a single collision domain).<ref> Intel. Retrieved 2011-03-16.</ref> | |||
| == Physical layer function == | |||
| The need for hosts to be able to detect collisions limits the number of hubs and the total size of a network built using hubs (a network built using ] does not have these limitations). For 10 Mbit/s networks built using repeater hubs, the ] must be followed: up to 5 segments (4 hubs) are allowed between any two end stations.<ref name=networking/> For 10BASE-T networks, up to six segments and five repeaters are allowed between any two hosts.{{cn|date=October 2011}} For 100 Mbit/s networks, the limit is reduced to 3 segments (2 hubs) between any two end stations, and even that is only allowed if the hubs are of Class II. Some hubs have manufacturer specific stack ports allowing them to be combined in a way that allows more hubs than simple chaining through Ethernet cables, but even so, a large ] network is likely to require switches to avoid the chaining limits of hubs.<ref name=networkingtext/> | |||
| A layer 1 network device such as a hub transfers data but does not manage any of the traffic coming through it. Any packet entering a ] is repeated to the output of every other port except for the port of entry. Specifically, each bit or symbol is repeated as it flows in. A repeater hub can therefore only receive and forward at a single speed. ]s internally consist of two hubs with a bridge between them. Since every packet is repeated on every other port, packet ] affect the entire network, limiting its overall capacity. | |||
| A network hub is an unsophisticated device in comparison with a ]. As a ''multiport ]'' it works by repeating transmissions received from one of its ports to all other ports. It is aware of ] packets, that is it can detect their start (]), an idle line (]) and sense a collision which it also propagates by sending a ]. A hub cannot further examine or manage any of the traffic that comes through it.<ref name="networking">{{cite book | last = Hallberg | first = Bruce | title = Networking: A Beginner's Guide, Fifth Edition | publisher = McGraw Hill | year = 2010 | pages = 68–69}}</ref> A hub has no memory to store data and can handle only one transmission at a time. Therefore, hubs can only run in ] mode. Due to a larger ], packet collisions are more likely in networks connected using hubs than in networks connected using more sophisticated devices.<ref name="networkingtext">{{cite book | last = Dean | first = Tamara | title = Network+ Guide to Networks | publisher = Delmar | year = 2010 | pages = 256–257}}</ref> | |||
| Most hubs detect typical problems, such as excessive collisions and jabbering on individual ports, and ''partition'' the port, disconnecting it from the shared medium.<ref name=networking/> Thus, hub-based Ethernet is generally more robust than coaxial cable-based Ethernet (''e.g.,'' 10BASE2), where a misbehaving device can adversely affect the entire ].<ref name=networking/> Even if not partitioned automatically, a hub simplifies troubleshooting because hubs remove the need to troubleshoot faults on a long cable with multiple taps; status lights on the hub can indicate the possible problem source or, as a last resort, devices can be disconnected from a hub one at a time much more easily than from a coaxial cable. | |||
| == Connecting multiple hubs == | |||
| Hubs are classified as Layer 1 (physical layer) devices in the OSI model. <ref name=networkingtext/> At the physical layer, hubs support little in the way of sophisticated networking. Hubs do not read any of the data passing through them and are not aware of their source or destination.<ref name=networkingtext/> A hub simply receives incoming ]s, regenerates the electrical signal, and broadcasts these packets out to all other devices on the network.<ref name=networkingtext/> | |||
| The need for hosts to be able to detect collisions limits the number of hubs and the total size of a network built using hubs (a network built using switches does not have these limitations). For 10 Mbit/s networks built using repeater hubs, the ] must be followed: up to five segments (four hubs) are allowed between any two end stations.<ref name=networking /> For 10BASE-T networks, up to five segments with four repeaters are allowed between any two hosts.<ref>{{cite book |url=http://www.ethermanage.com/ethernet/ch13-ora/ch13.html |title=Ethernet: The Definitive Guide |author=Charles Spurgeon |chapter=Chapter 13: Multi-Segment Configuration Guidelines |isbn=978-1-56592-660-8 |date=2000-02-16 |access-date=2012-01-08 |quote=The transmission path permitted between any two DTEs may consist of up to five segments, four repeater sets (including optional AUIs), two MAUs, and two AUIs.}}</ref> For 100 Mbit/s networks, the limit is reduced to three segments between any two end stations, and even that is only allowed if the hubs are of Class II. Some hubs have manufacturer-specific stack ports allowing them to be combined in a way that allows more hubs than simple chaining through Ethernet cables, but even so, a large ] network is likely to require switches to avoid the chaining limits of hubs.<ref name=networkingtext /> | |||
| == Additional functions == | |||
| To pass data through the repeater in a usable fashion from one segment to the next, the packets and the Logical Link Control (LLC) protocols must be the same on each segment. This means that a repeater will not enable communication, for example, between an 802.3 segment (Ethernet) and an 802.5 segment (Token Ring). That is, they cannot translate an Ethernet packet into a Token Ring packet. In other words, repeaters do not translate anything.<ref name=networkingtext/> | |||
| Most hubs detect typical problems, such as excessive collisions and jabbering on individual ports, and ''partition'' the port, disconnecting it from the shared medium. Thus, hub-based ] is generally more robust than coaxial cable-based Ethernet (e.g. 10BASE2), where a misbehaving device can adversely affect the entire ].<ref name=networking /> Even if not partitioned automatically, a hub simplifies troubleshooting because hubs remove the need to troubleshoot faults on a long cable with multiple taps; status lights on the hub can indicate the possible problem source or, as a last resort, devices can be disconnected from a hub one at a time much more easily than from a coaxial cable.{{Citation needed|date=October 2015}} | |||
| To pass data through the repeater in a usable fashion from one segment to the next, the framing and data rate must be the same on each segment. This means that a repeater cannot connect an 802.3 segment (Ethernet) and an 802.5 segment (Token Ring) or a 10 Mbit/s segment to 100 Mbit/s Ethernet.{{Citation needed|date=October 2015}} | |||
| =={{visible anchor|Dual speed hubs}}==<!--other articles or redirects link here. please preserve this anchor if the section is renamed --> | |||
| In the early days of fast Ethernet, Ethernet switches were relatively expensive devices. Hubs suffered from the problem that if there were any ] devices connected then the whole network needed to run at 10 Mbit/s. Therefore a compromise between a hub and a switch was developed, known as a '''dual-speed hub'''. These devices consisted of an internal two-port switch, dividing the 10 Mbit/s and 100 Mbit/s segments. The device would typically consist of more than two physical ports. When a network device becomes active on any of the physical ports, the device attaches it to either the 10 Mbit/s segment or the 100 Mbit/s segment, as appropriate. This prevented the need for an all-or-nothing migration fast Ethernet networks. These devices are considered hubs because the traffic between devices connected at the same speed is not switched. | |||
| == Dual-speed hub == | |||
| ==Uses== | |||
| In the early days of Fast Ethernet, Ethernet switches were relatively expensive devices. Hubs suffered from the problem that if there were any ] devices connected then the whole network needed to run at 10 Mbit/s. Therefore, a compromise between a hub and a switch was developed, known as a '''dual-speed hub'''. These devices make use of an internal two-port switch, ] the 10 Mbit/s and 100 Mbit/s segments. When a network device becomes active on any of the physical ports, the device attaches it to either the 10 Mbit/s segment or the 100 Mbit/s segment, as appropriate. This obviated the need for an all-or-nothing migration to Fast Ethernet networks. These devices are considered hubs because the traffic between devices connected at the same speed is not switched.{{Citation needed|date=October 2015}} | |||
| Historically, the main reason for purchasing hubs rather than ] was their price. This motivator has largely been eliminated by reductions in the price of switches, but hubs can still be useful in special circumstances: | |||
| == Fast Ethernet== | |||
| * For inserting a ] into a network connection, a hub is an alternative to a ] or ].<ref>{{cite web |url=http://www.netresec.com/?page=Blog&month=2011-03&post=Sniffing-Tutorial-part-1---Intercepting-Network-Traffic |title=Sniffing Tutorial part 1 - Intercepting Network Traffic |publisher=NETRESEC Network Security Blog |date=2011-03-11 |accessdate=2011-03-13}}</ref> | |||
| 100 Mbit/s hubs and repeaters come in two different classes: Class I delay the signal for a maximum of 140 bit times. This delay allows for translation/recoding between 100BASE-TX, 100BASE-FX and 100BASE-T4. Class II hubs delay the signal for a maximum of 92 bit times. This shorter delay allows the installation of two hubs in a single collision domain.<ref> Intel. Retrieved 2011-03-16.</ref> | |||
| * When a switch is accessible for end users to make connections, for example, in a conference room, an inexperienced or careless user (or ]) can bring down the network by connecting two ports together, causing a loop. This can be prevented by using a hub, where a loop will break other users on the hub, but not the rest of the network. This hazard can also be avoided by using switches that can detect and deal with loops, for example by implementing the ]. | |||
| * A hub with a 10BASE2 port can be used to connect devices that only support 10BASE2 to a modern network. The same goes for linking in an old 10BASE5 network segment using an AUI port on a hub (individual devices that were intended for thicknet can be linked to modern Ethernet by using an AUI-10BASE-T ]). | |||
| == Gigabit Ethernet == | |||
| ==See also== | |||
| Repeater hubs are defined in the standards for ]<ref>IEEE 802.3 Clause 41</ref> but commercial products have failed to appear<ref>{{cite book| url=https://books.google.com/books?id=k9BE4eKK2CIC&dq=gigabit+ethernet+hub&pg=PT720 |title=Network Maintenance and Troubleshooting Guide |author=Neil Allen |date=18 October 2009 |publisher=]|isbn=9780321647627 }}</ref> due to the industry's transition to switching. | |||
| * ] | |||
| == |
== Uses == | ||
| Historically, the main reason for purchasing hubs rather than switches was their price. By the early 2000s, there was little price difference between a hub and a low-end switch.<ref>{{cite web |title=Switches and Hubs |author=Matthew Glidden |work= About This Particular Macintosh blog |date= October 2001 |access-date= June 9, 2011 |url=http://www.atpm.com/7.10/networking-1.shtml }}</ref> Hubs can still be useful in special circumstances: | |||
| {{reflist}} | |||
| * For inserting a ] into a network connection, a hub is an alternative to a ] or ].<ref>{{cite web |url=http://www.netresec.com/?page=Blog&month=2011-03&post=Sniffing-Tutorial-part-1---Intercepting-Network-Traffic |title=Sniffing Tutorial part 1 - Intercepting Network Traffic |publisher=NETRESEC Network Security Blog |date=2011-03-11 |access-date=2011-03-13}}</ref> | |||
| * A hub with both 10BASE-T ports and a 10BASE2 port can be used to connect a 10BASE2 segment to a modern ] network. | |||
| * A hub with both 10BASE-T ports and an AUI port can be used to connect a 10BASE5 segment to a modern network. | |||
| * As hubs have lower latency and jitter compared to switches – as long as there are no collisions – they may be better suited for ], e.g. ].<ref>{{Citation |author= Ethernet Powerlink Standardization Group |url= https://www.ethernet-powerlink.org/fileadmin/user_upload/Dokumente/Technical_documents/EPSG_DS_301_V-1-4-0.pdf |access-date= 2019-05-06 |page= 35 |year= 2018 |title= Ethernet POWERLINK Communication Profile Specification. Version 1.4.0}}</ref> | |||
| One of the first Ethernet hubs, the HP Starlan for ], the first Ethernet-over-twisted-pair standard, was announced in 1986.<ref>{{cite magazine |magazine=] |url=https://books.google.com/books?id=Dx4EAAAAMBAJ&dq=hp+starlan&pg=PA6 |page=6 |date=1986-11-06 |title=HP adopts Starlan plan}}</ref> Its successor, the Starlan 10, was announced in 1987.<ref>{{cite magazine |magazine=] |url=https://books.google.com/books?id=M8uwmICKZwMC&dq=H-P+Starlan+10&pg=PP6 |title=HP's 10Mbit/sec. LAN needs no special wiring |date=1987-08-31}}</ref> By 1994, the industry had started to shift to switching.<ref>{{cite magazine |magazine=] |url=https://books.google.com/books?id=hhAEAAAAMBAJ&dq=switch+vs+hub&pg=PA34 |title=Switching strategy will be key as internet markets collide |date=1994-02-21}}</ref> | |||
| ==External links== | |||
| * | |||
| == See also == | |||
| {{Commons category|Ethernet hubs}} | |||
| * ] | |||
| * ] | |||
| == Notes == | |||
| {{Notelist}} | |||
| == References == | |||
| {{Reflist}} | |||
| == External links == | |||
| * {{cite web |url=https://gitlab.com/wireshark/wireshark/-/wikis/HubReference |title=Hub Reference |website=GitLab |access-date=2021-12-01}} | |||
| {{Authority control}} | |||
| {{DEFAULTSORT:Ethernet Hub}} | {{DEFAULTSORT:Ethernet Hub}} | ||
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Latest revision as of 19:38, 4 September 2024
Device for interconnecting Ethernet devices
An Ethernet hub, active hub, network hub, repeater hub, multiport repeater, or simply hub is a network hardware device for connecting multiple Ethernet devices together and making them act as a single network segment. It has multiple input/output (I/O) ports, in which a signal introduced at the input of any port appears at the output of every port except the original incoming. A hub works at the physical layer. A repeater hub also participates in collision detection, forwarding a jam signal to all ports if it detects a collision. In addition to standard 8P8C ("RJ45") ports, some hubs may also come with a BNC or an Attachment Unit Interface (AUI) connector to allow connection to legacy 10BASE2 or 10BASE5 network segments.
Hubs are now largely obsolete, having been replaced by network switches except in very old installations or specialized applications. As of 2011, connecting network segments by repeaters or hubs is deprecated by IEEE 802.3.
Physical layer function
A layer 1 network device such as a hub transfers data but does not manage any of the traffic coming through it. Any packet entering a port is repeated to the output of every other port except for the port of entry. Specifically, each bit or symbol is repeated as it flows in. A repeater hub can therefore only receive and forward at a single speed. Dual-speed hubs internally consist of two hubs with a bridge between them. Since every packet is repeated on every other port, packet collisions affect the entire network, limiting its overall capacity.
A network hub is an unsophisticated device in comparison with a switch. As a multiport repeater it works by repeating transmissions received from one of its ports to all other ports. It is aware of physical layer packets, that is it can detect their start (preamble), an idle line (interpacket gap) and sense a collision which it also propagates by sending a jam signal. A hub cannot further examine or manage any of the traffic that comes through it. A hub has no memory to store data and can handle only one transmission at a time. Therefore, hubs can only run in half duplex mode. Due to a larger collision domain, packet collisions are more likely in networks connected using hubs than in networks connected using more sophisticated devices.
Connecting multiple hubs
The need for hosts to be able to detect collisions limits the number of hubs and the total size of a network built using hubs (a network built using switches does not have these limitations). For 10 Mbit/s networks built using repeater hubs, the 5-4-3 rule must be followed: up to five segments (four hubs) are allowed between any two end stations. For 10BASE-T networks, up to five segments with four repeaters are allowed between any two hosts. For 100 Mbit/s networks, the limit is reduced to three segments between any two end stations, and even that is only allowed if the hubs are of Class II. Some hubs have manufacturer-specific stack ports allowing them to be combined in a way that allows more hubs than simple chaining through Ethernet cables, but even so, a large Fast Ethernet network is likely to require switches to avoid the chaining limits of hubs.
Additional functions
Most hubs detect typical problems, such as excessive collisions and jabbering on individual ports, and partition the port, disconnecting it from the shared medium. Thus, hub-based twisted-pair Ethernet is generally more robust than coaxial cable-based Ethernet (e.g. 10BASE2), where a misbehaving device can adversely affect the entire collision domain. Even if not partitioned automatically, a hub simplifies troubleshooting because hubs remove the need to troubleshoot faults on a long cable with multiple taps; status lights on the hub can indicate the possible problem source or, as a last resort, devices can be disconnected from a hub one at a time much more easily than from a coaxial cable.
To pass data through the repeater in a usable fashion from one segment to the next, the framing and data rate must be the same on each segment. This means that a repeater cannot connect an 802.3 segment (Ethernet) and an 802.5 segment (Token Ring) or a 10 Mbit/s segment to 100 Mbit/s Ethernet.
Dual-speed hub
In the early days of Fast Ethernet, Ethernet switches were relatively expensive devices. Hubs suffered from the problem that if there were any 10BASE-T devices connected then the whole network needed to run at 10 Mbit/s. Therefore, a compromise between a hub and a switch was developed, known as a dual-speed hub. These devices make use of an internal two-port switch, bridging the 10 Mbit/s and 100 Mbit/s segments. When a network device becomes active on any of the physical ports, the device attaches it to either the 10 Mbit/s segment or the 100 Mbit/s segment, as appropriate. This obviated the need for an all-or-nothing migration to Fast Ethernet networks. These devices are considered hubs because the traffic between devices connected at the same speed is not switched.
Fast Ethernet
100 Mbit/s hubs and repeaters come in two different classes: Class I delay the signal for a maximum of 140 bit times. This delay allows for translation/recoding between 100BASE-TX, 100BASE-FX and 100BASE-T4. Class II hubs delay the signal for a maximum of 92 bit times. This shorter delay allows the installation of two hubs in a single collision domain.
Gigabit Ethernet
Repeater hubs are defined in the standards for Gigabit Ethernet but commercial products have failed to appear due to the industry's transition to switching.
Uses
Historically, the main reason for purchasing hubs rather than switches was their price. By the early 2000s, there was little price difference between a hub and a low-end switch. Hubs can still be useful in special circumstances:
- For inserting a protocol analyzer into a network connection, a hub is an alternative to a network tap or port mirroring.
- A hub with both 10BASE-T ports and a 10BASE2 port can be used to connect a 10BASE2 segment to a modern Ethernet-over-twisted-pair network.
- A hub with both 10BASE-T ports and an AUI port can be used to connect a 10BASE5 segment to a modern network.
- As hubs have lower latency and jitter compared to switches – as long as there are no collisions – they may be better suited for real-time networks, e.g. Ethernet Powerlink.
One of the first Ethernet hubs, the HP Starlan for StarLAN, the first Ethernet-over-twisted-pair standard, was announced in 1986. Its successor, the Starlan 10, was announced in 1987. By 1994, the industry had started to shift to switching.
See also
Notes
- Network switches are sometimes called switching hubs.
References
- IEEE 802.3-2012 Clause 9.1
- ^ Dean, Tamara (2010). Network+ Guide to Networks. Delmar. pp. 256–257.
- IEEE 802.3 9. Repeater unit for 10 Mb/s baseband networks
- IEEE 802.3 27. Repeater unit for 100 Mb/s baseband networks
- IEEE 802.3 41. Repeater unit for 1000 Mb/s baseband networks
- ^ Hallberg, Bruce (2010). Networking: A Beginner's Guide, Fifth Edition. McGraw Hill. pp. 68–69.
- Charles Spurgeon (2000-02-16). "Chapter 13: Multi-Segment Configuration Guidelines". Ethernet: The Definitive Guide. ISBN 978-1-56592-660-8. Retrieved 2012-01-08.
The transmission path permitted between any two DTEs may consist of up to five segments, four repeater sets (including optional AUIs), two MAUs, and two AUIs.
- "What is the difference between Class I and Class II hubs?" Intel. Retrieved 2011-03-16.
- IEEE 802.3 Clause 41
- Neil Allen (18 October 2009). Network Maintenance and Troubleshooting Guide. Fluke Networks. ISBN 9780321647627.
- Matthew Glidden (October 2001). "Switches and Hubs". About This Particular Macintosh blog. Retrieved June 9, 2011.
- "Sniffing Tutorial part 1 - Intercepting Network Traffic". NETRESEC Network Security Blog. 2011-03-11. Retrieved 2011-03-13.
- Ethernet Powerlink Standardization Group (2018), Ethernet POWERLINK Communication Profile Specification. Version 1.4.0 (PDF), p. 35, retrieved 2019-05-06
- "HP adopts Starlan plan". Network World. 1986-11-06. p. 6.
- "HP's 10Mbit/sec. LAN needs no special wiring". Computerworld. 1987-08-31.
- "Switching strategy will be key as internet markets collide". Network World. 1994-02-21.
External links
- "Hub Reference". GitLab. Retrieved 2021-12-01.