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HubA common connection point for devices in a network. Hubs are commonly usedto connect segments of a LAN. A hub contains multiple ports. When apacket arrives at one port, it is copied to the other ports so that all segments ofthe LAN can see all packets.

Apassive hub serves simply as a conduit for the data, enabling it to go from onedevice (or segment) to another. So-called intelligent hubs include additional

features that enables an administrator to monitor the traffic passing through thehub and to configure each port in the hub. Intelligent hubs are alsocalled manageable hubs.

A third type of hub, called a switching hub, actually reads the destination addressof each packet and then forwards the packet to the correct port.


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Technical information

A network hub is an unsophisticated device in comparison with, for example, a switch. A hub

does not examine or manage any of the traffic that comes through it: any packet entering any port

is rebroadcast on all other ports. Effectively, it is barely aware of frames or packets and mostly

operates on raw bits. Consequently, packet collisions are more frequent in networks connected

using hubs than in networks connected using more sophisticated devices.

100 Mbit/s hubs and repeaters come in two different speed grades: Class I delay the signal for a

maximum of 140 bit times.

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. For 10 Mbit/s networks built using repeater hubs, the 5-4-3 rule must be

followed: up to 5 segments (4 hubs) are allowed between any two end stations. For 10BASE-T

networks, up to five segments and four repeaters are allowed between any two hosts.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 fast Ethernet network is likely to require switches to

avoid the chaining limits of hubs.

Most hubs detect typical problems, such as excessive collisions and jabbering on individual ports,

and partitionthe 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.

Hubs are classified as physical layer devices in the OSI model. 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 addressing. A hub simply receives

incoming Ethernet frames, regenerates the electrical signal on the bit (more precisely the symbol)

level, and broadcasts these symbols out to all other devices on the network.

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.


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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 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.

Uses

Historically, the main reason for purchasing hubs rather than switches 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:

For inserting a protocol analyzer into a network connection, a hub is analternative to a network tap or port mirroring.

When a switch is accessible for end users to make connections, for example,in a conference room, an inexperienced or careless user (or saboteur) canbring 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 onthe hub, but not the rest of the network. This hazard can also be avoided byusing switches that can detect and deal with loops, for example byimplementing the spanning tree protocol.

A hub with a 10BASE2 port can be used to connect devices that only support10BASE2 to a modern network. The same goes for linking in an old 10BASE5network segment using an AUI port on a hub. Individual devices that were

intended for thicknet can also be linked to modern Ethernet by using an AUI-

10BASE-T transceiver.


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SwitchA network switch or switching hub is a computer networking device that connects network

segments or network devices. The term commonly refers to a multi-port network bridge that

processes and routes data at the data link layer (layer 2) of the OSI model. Switches that

additionally process data at the network layer (layer 3) and above are often referred to as layer-3

switchesor multilayer switches.


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Function

A switch is a telecommunication device which receives a message from any device connected to

it and then transmits the message only to that device for which the message was meant. This

makes the switch a more intelligent device than a hub (which receives a message and then

transmits it to all the other devices on its network.) The network switch plays an integral part in

most modern Ethernet local area networks (LANs). Mid-to-large sized LANs contain a number of

linked managed switches. Small office/home office(SOHO) applications typically use a single

switch, or an all-purpose converged device such as a residential gateway to access small

office/home broadband services such as DSLor cable internet. In most of these cases, the end-

user device contains a router and components that interface to the particular physical broadband

technology. User devices may also include a telephone interface for VoIP.

Role of switches in networks

Switches may operate at one or more layers of the OSI model, including data link and network. A

device that operates simultaneously at more than one of these layers is known as a multilayer

switch.

In switches intended for commercial use, built-in or modular interfaces make it possible to

connect different types of networks, including Ethernet, Fibre Channel, ATM, ITU-

TG.hnand 802.11. This connectivity can be at any of the layers mentioned. While layer-2

functionality is adequate for bandwidth-shifting within one technology, interconnecting

technologies such as Ethernet and token ring is easier at layer 3.

Devices that interconnect at layer 3 are traditionally called routers, so layer-3 switches can also

be regarded as (relatively primitive) routers.

In some service provider and other environments where there is a need for a great deal of

analysis of network performance and security, switches may be connected between WAN routers

as places for analytic modules. Some vendors provide firewall, network intrusion detection, andperformance analysis modules that can plug into switch ports. Some of these functions may be on

combined modules.[

Layer 1 hubs versus higher-layer switches

A network hub, or repeater, is a simple network device. Hubs do not manage any of the traffic that

comes through them. Any packet entering a port is broadcast out or "repeated" on every other


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port, except for the port of entry. Since every packet is repeated on every other port,

packet collisions affect the entire network, limiting its capacity.

There are specialized applications where a hub can be useful, such as copying traffic to multiple

network sensors. High end switches have a feature which does the same thing called port

mirroring.

By the early 2000s, there was little price difference between a hub and a low-end switch.[

Layer 2

A network bridge, operating at the data link layer, may interconnect a small number of devices in

a home or the office. This is a trivial case of bridging, in which the bridge learns the MAC

address of each connected device.

Single bridges also can provide extremely high performance in specialized applications such

as storage area networks.

Classic bridges may also interconnect using a spanning tree protocol that disables links so that

the resulting local area network is a tree without loops. In contrast to routers, spanning tree

bridges must have topologies with only one active path between two points. The older IEEE

802.1D spanning tree protocol could be quite slow, with forwarding stopping for 30 seconds while

the spanning tree would reconverge. A Rapid Spanning Tree Protocol was introduced as

IEEE 802.1w, but the newest edition of IEEE 802.1D adopts the 802.1w extensions as the base

standard.

The IETF is specifying the TRILL protocol, which is the application of link-state routing technology

to the layer-2 bridging problem. Devices which implement TRILL, called R Bridges, combine the

best features of both routers and bridges.

While layer 2 switchremains more of a marketing term than a technical term,the products that

were introduced as "switches" tended to use microsegmentation andFull duplex to prevent

collisions among devices connected to Ethernet. By using an internal forwarding plane much

faster than any interface, they give the impression of simultaneous paths among multiple devices.

'Non-blocking' devices use a forwarding plane or equivalent method fast enough to allow full

duplex traffic for each port simultaneously.

Once a bridge learns the topology through a spanning tree protocol, it forwards data link layer

frames using a layer 2 forwarding method. There are four forwarding methods a bridge can use,of which the second through fourth method were performance-increasing methods when used on

"switch" products with the same input and output port bandwidths:

1. Store and forward: The switch buffers and verifies each frame before

forwarding it.

2. Cut through: The switch reads only up to the frame's hardware address

before starting to forward it. Cut-through switches have to fall back to


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3. store and forward if the outgoing port is busy at the time the packetarrives. There is no error checking with this method.

4. Fragment free: A method that attempts to retain the benefits of both storeand forward and cut through. Fragment free checks the first 64 bytes of

the frame, whereaddressing information is stored. According to Ethernetspecifications, collisions should be detected during the first 64 bytes of theframe, so frames that are in error because of a collision will not beforwarded. This way the frame will always reach its intended destination.Error checking of the actual data in the packet is left for the end device.

5. Adaptive switching: A method of automatically selecting between the otherthree modes.

While there are specialized applications, such as storage area networks, wherethe input and output interfaces are the same bandwidth, this is not always thecase in general LAN applications. In LANs, a switch used for end user accesstypically concentrates lower bandwidth and uplinks into a higher bandwidth.

Layer 3

Within the confines of the Ethernet physical layer, a layer-3 switch can performsome or all of the functions normally performed by a router. The most commonlayer-3 capability is awareness of IP multicast through IGMP snooping. With this

awareness, a layer-3 switch can increase efficiency by delivering the traffic of amulticast group only to ports where the attached device has signaled that it wantsto listen to that group.

Layer 4

While the exact meaning of the term layer-4 switchis vendor-dependent, italmost always starts with a capability for network address translation, but thenadds some type of load distribution based on TCP sessions.

The device may include a stateful firewall, a VPN concentrator, or be

an IPSec security gateway.

Layer 7

Layer-7 switches may distribute loads based on Uniform ResourceLocatorURL or by some installation-specific technique to recognize application-

level transactions. A layer-7 switch may include a web cache and participate ina content delivery network.


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Wi-Fi

Wi-Fi is a popular technology that allows an electronic device to exchangedata wirelessly(using radio waves) over a computer network, including high-speed Internet connections. The Wi-Fi Alliance defines Wi-Fi as any "wirelesslocal area network (WLAN) products that are based on the Institute of Electrical

and Electronics Engineers' (IEEE) 802.11 standards".[1] However, since mostmodern WLANs are based on these standards, the term "Wi-Fi" is used ingeneral English as a synonym for "WLAN".

The name Wi-FiThe term Wi-Fi, first used commercially in August 1999,

[15]was coined by a brand-consulting firm

called Interbrand Corporation that the Alliance had hired to determine a name that was "a little

catchier than 'IEEE 802.11b Direct Sequence'".[16][17][18]

Belanger also stated that Interbrand

invented Wi-Fias a play on words with Hi-Fi, and also created the Wi-Fi logo.

The Wi-Fi Alliance initially used an advertising slogan for Wi-Fi, "The Standard for Wireless

Fidelity",[16]

but later removed the phrase from their marketing. Despite this, some documents

from the Alliance dated 2003 and 2004 still contain the term Wireless Fidelity.[19][20]

There was no

official statement related to the dropping of the term.

The yin-yang Wi-Fi logo indicates the certification of a product for interoperability.

[19]

Non-Wi-Fi technologies intended for fixed points such as Motorola Canopy are usually described

as fixed wireless. Alternative wireless technologies include mobile phone standards such

as 2G, 3G or 4G.


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Wi-Fi certification

The IEEE does not test equipment for compliance with their standards. The non-profit Wi-Fi

Alliance was formed in 1999 to fill this void to establish and enforce standards for

interoperability and backward compatibility, and to promote wireless local-area-network

technology. As of 2010 the Wi-Fi Alliance consisted of more than 375 companies from around the

world.[21][22]

The Wi-Fi Alliance enforces the use of the Wi-Fi brand to technologies based on

the IEEE 802.11 standards from the Institute of Electrical and Electronics Engineers. This

includes wireless local area network (WLAN) connections, device to device connectivity (such as

Wi-Fi Peer to Peer aka Wi-Fi Direct), Personal area network(PAN), local area network (LAN) and

even some limited wide area network (WAN) connections. Manufacturers with membership in the

Wi-Fi Alliance, whose products pass the certification process, gain the right to mark those

products with the Wi-Fi logo.

Uses

To connect to a Wi-Fi LAN, a computer has to be equipped with a wireless network interface

controller. The combination of computer and interface controller is called a station. All stations

share a single radio frequency communication channel. Transmissions on this channel are

received by all stations within range. The hardware does not signal the user that the transmission

was delivered and is therefore called abest-effort delivery mechanism. A carrier wave is used to

transmit the data in packets, referred to as "Ethernet frames". Each station is constantly tuned in

on the radio frequency communication channel to pick up available transmissions.


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ROUTERA router is a device that forwards data packets between computer networks,creating an overlay internetwork. A router is connected to two or more data linesfrom different networks. When a data packet comes in on one of the lines, therouter reads the address information in the packet to determine its ultimate

destination. Then, using information in its routing table or routing policy, it directsthe packet to the next network on its journey. Routers perform the "traffic

directing" functions on the Internet. A data packet is typically forwarded from onerouter to another through the networks that constitute the internetwork until it getsto its destination node.

Applications

When multiple routers are used in interconnected networks, the routers exchange information

about destination addresses, using a dynamic routing protocol. Each router builds up a table

listing the preferred routes between any two systems on the interconnected networks. A router

has interfaces for different physical types of network connections, (such as copper cables, fiber

optic, or wireless transmission). It also contains firmware for different


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networking protocol standards. Each network interface uses this specialized computer software to

enable data packets to be forwarded from one protocol transmission system to another.

Security

External networks must be carefully considered as part of the overall security

strategy. Separate from the router may be a firewall orVPN handling device, or

the router may include these and other security functions. Many companies

produced security-oriented routers, including Cisco Systems' PIX and ASA5500

series, Juniper's Netscreen, Watchguard's Firebox, Barracuda's variety of mail-

oriented devices, and many others.

WIMAX

WiMAX (Worldwide Interoperability for Microwave Access) isa wireless communications standard designed to provide 30 to 40 megabit-per-second data rates, with the 2011 update providing up to 1 Gbit/s for fixedstations. It is a part of a fourth generation, or4G, of wireless-communicationtechnology. WiMax far surpasses the 30-metre (100-foot) wireless range of aconventional Wi-Filocal area network (LAN), offering a metropolitan areanetwork with a signal radius of about 50 km (30 miles).

Uses

The bandwidth and range of WiMAX make it suitable for the following potentialapplications:

Providing portable mobile broadband connectivity across cities and countries

through a variety of devices.

Providing a wireless alternative to cable and digital subscriber line (DSL) for"last mile" broadband access.


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Providing data, telecommunications (VoIP) and IPTV services (triple play).

Providing a source of Internet connectivity as part of a business continuity

plan. Smart grids and metering

Comparison with Wi-Fi

The following table only shows peak rates which are potentially very misleading.In addition, the comparisons listed are not normalized by physical channel size

(i.e., spectrum used to achieve the listed peak rates); this obfuscates spectralefficiency and net through-put capabilities of the different wireless technologieslisted below.

Comparison of Mobile Internet Access methods

Common

NameFamily

Primary Use

RadioTech

Downstream

(Mbit/s)

Upstr

eam(Mbit/

s)

Notes

HSPA+ 3GPPUsed in4G

CDMA/FDDMIMO

214284

672

5.811.522

168

HSPA+ iswidelydeployed.Revision 11of the 3GPPstatesthatHSPA+ is

expected tohave athroughputcapacity of

672 Mbps.

LTE 3GPPGeneral4G

OFDMA/MIMO/SC-FDMA

100 Cat3150 Cat4300 Cat5(in 20 MHz

50Cat3/475 Cat5(in 20

LTE-Advanced updateexpected to


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Common

NameFamily

Primary Use

RadioTech

Downstream

(Mbit/s)

Upstr

eam(Mbit/

s)

Notes

FDD)[31] MHzFDD)[31]

offer peakrates up to 1Gbit/s fixed

speeds and

100 Mb/s tomobile users.

WiMaxrel 1

802.16WirelessMAN

MIMO-SOFDMA

37(10 MHzTDD)

17(10 MHzTDD)

With 2x2MIMO.[32]

WiMaxrel 1.5

802.16-2009

WirelessMAN

MIMO-SOFDMA

83

(20 MHzTDD)141(2x20 MHzFDD)

46

(20 MHzTDD)138(2x20 MHz FDD)

With 2x2

MIMO.Enhanced with20Mhzchannels in802.16-2009[32]

WiMAX

rel 2802.16m

WirelessM

AN

MIMO-

SOFDMA

2x2 MIMO110(20 MHz

TDD)183

(2x20 MHzFDD)4x4 MIMO

219(20 MHz

2x2MIMO70

(20 MHzTDD)

188(2x20 MHz FDD)

4x4MIMO

Also lowmobilityusers canaggregatemultiple

channels forup to DLthroughput1Gbps[32]


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Common

NameFamily

Primary Use

RadioTech

Downstream

(Mbit/s)

Upstr

eam(Mbit/

s)

Notes

TDD)365(2x20 MHz

FDD)

140(20MHzTDD)

376

(2x20 MHz FDD)

Flash-OFDM

Flash-OFDM

MobileInternetmobility upto200 mph(350 km/h)

Flash-OFDM5.310.615.9

1.83.65.4

Mobile range30 km (18miles)extendedrange 55 km(34 miles)

HIPERMAN

HIPERMAN

MobileInternet

OFDM 56.9

Wi-Fi 802.11(11n)

Mobile Internet

OFDM/MIMO

288.8 (using 4x4configuration in

20 MHz bandwidth)or 600 (using 4x4configuration in

40 MHz bandwidth)

Antenna, RF

front

end enhanceme

nts and minor

protocol timer

tweaks have

helped deploy

long

range P2P netw

orks


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Common

NameFamily

Primary Use

RadioTech

Downstream

(Mbit/s)

Upstr

eam(Mbit/

s)

Notes

compromising

on radial

coverage,

throughput

and/or spectra

efficiency

(310 km & 382 k

m)

UMTS-

TDD

UMTS/3GSM

MobileInternet

CDMA/TDD 16

Reportedspeeds

accordingto IPWirelessusing16QAMmodulationsimilarto HSDPA+HSUPA


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WAP(WIRELESS ACCESS POINT)

In computer networking, a wireless access point (WAP) is a device that allowswireless devices to connect to a wired network using Wi-Fi, Bluetooth or related

standards. The WAP usually connects to a router (via a wired network) if it's astandalone device, or is part of router itself.

Common WAP applicationsA typical corporate use involves attaching several WAPs to a wired network and then providing

wireless access to the office LAN. The wireless access points are managed by a WLAN

Controller which handles automatic adjustments to RF power, channels, authentication, and

security. Further, controllers can be combined to form a wireless mobility group to allow inter-

controller roaming. The controllers can be part of a mobility domain to allow clients access

throughout large or regional office locations. This saves the clients time and administrators

overhead because it can automatically re-associate or re-authenticate.


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WAP 2

A re-engineered 2.0 version was released in 2002. It uses a cut-down version of XHTML with

end-to-end HTTP, dropping the gateway and custom protocol suite used to communicate with it.

A WAP gateway can be used in conjunction with WAP 2.0; however, in this scenario, it is used as

a standard proxy server. The WAP gateway's role would then shift from one of translation to

adding additional information to each request. This would be configured by the operator and could

include telephone numbers, location, billing information, and handset information.

Mobile devices process XHTML Mobile Profile (XHTML MP), the markup language defined in

WAP 2.0. It is a subset of XHTML and a superset of XHTML Basic. A version of cascading style

sheets (CSS) called WAP CSS is supported by XHTML MP.

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