Difference between Hub and Switch

Difference between Hub and Switch 

Network devices, or networking hardware, are physical devices that are required for communication and interaction between hardware on a TCP/IP network.

Here is the common network device list:

·        Hub

·        Switch

·        Router

·        Bridge

·        Gateway

·        Modem

·        Repeater

·        Access Point

In 2006 The Network Hub is invented at Vancouver, British Columbia, Canada. A hub is a device that connects multiple Ethernet devices on one network and makes them act together as a single network. A hub does not gather information and input in one port results as an output in all ports on the network. A switch is a networking device that performs the same job as the hub but are considered as a more intelligent hub as it gathers information about the data packets it receives and forwards it to only the network that it was intended for. A Hub is a layer-1 device and operates only in the physical network of the OSI Model.

Hubs and switches are devices that are used in data networking on the internet. These devices are used in order to connect two or more networking ports in order to transfer data along the connection. Though the primary job of hubs and switches are the same, to forward data to different networks, they work in different ways.

A hub, also known as Ethernet hub, active hub, network hub, repeater hub or multiport repeater, is a device that connects multiple Ethernet devices on one network and makes them act together as a single network. A hub has multiple input/output (I/O) ports, in which an input in one port results in it being an output in all the other ports, except the port where it was input. In layman’s terms, a hub connects many networks into one, where a data packet that is sent by one networks, is copied and pasted to all network ports, making it so that every port can see that data packet. A hub works on the physical layer or layer 1 of the Open Systems Interconnection (OSI) model. It also works as a data collision detector, sending a jamming signal to all ports if it detects collisions at one port.

It is a simple device that does not examine the data it receives or sends, while just duplicating the data and making it visible for all. The receiving port that has to decide if the data packet is actually intended for it by checking the address on the packet, before passing it on further. Since hubs only have one collision domain, constant collisions occur. Unnecessary traffic is sent to all devices on the network. Originally hubs were popular due to the high price of switches, but switches are not so expensive these days. Hubs are slowly becoming obsolete in many practices, but are still used in special circumstances.

A switch is a networking device that performs the same job as the hub; it connects network segments or devices making them act as a single network. Switches are commonly referred to as a multi-port network bridge that process and routes data on a data link layer or layer of the OSI model. Switches can also process data at the network layer (layer 3) or higher layers and are known as multilayer switches.

Switches are considered as a more intelligent hub as it gathers information about the data packets it receives and forwards it to only the network that it was intended for. When a switch receives a data packet, it examines the data address, the sender and the receiver and stores the memory, after which it then sends the data to the device that the data is meant for.

Most modern Ethernet Local Area Networks (LANs) operate on switches. Small offices and residential devices commonly use single layer switch, while bigger applications require multilayer switches. The switches use a bridge or a router in order to split a larger collision domain to smaller collision domains, resulting in lesser collisions.  Each port has an individual collision domain, allowing computers to maintain dedicated bandwidth.

	Hub	Switch
Definition	A hub is a connection point for different segments of a LAN. It contains multiple ports and when it receives a packet of information at one port, it copies this packet to all segments of the LAN so that it can be viewed by all ports.	A switch is multi-port networking device that connects network devices together. A switch operates at the data link layer (layer 2) of the OSI model. A switch filters and then forwards data packets between networks.
Layer	Physical Layer (Layer 1)	Data Link Layer (Layer 2)
Spanning-Tree	No Spanning-Tree	It allows many Spanning-Trees to take place.
Type of Transmission	Broadcast	Broadcast, Uni-cast & Multicast.
Table	No MAC table. Hubs cannot learn MAC address.	Stores MAC address and maintains address.
Used in	LAN (Local Area Networks)	LAN (Local Area Networks)
No of Ports	4	24-48 depending on type of switch.
Collision	Occurs	No collision occurs
Collision Domain	One collision domain	Every port has its own collision domain.
Transmission Mode	Half duplex	Full duplex

Types of Hub

There are three types of the hub that are given below:

1.  Passive Hub

2.  Active Hub

3.  Intelligent Hub

Passive Hub: The passive hubs are the connection point for wires that helps to make the physical network. It is capable of determining the bugs and faulty hardware. Simply, it accepts the packet over a port and circulates it to all ports. It includes connectors (10base-2 port and RJ-45) that can be applied as a standard in your network. This connector is connected to all local area network (LAN) devices. Additionally, the advanced passive hubs have AUI ports, which are connected as the transceiver according to the network design.

Active Hub: As compared to a passive hub, it includes some additional features. It is able to monitor the data sent to the connected devices. It plays an important role between the connected devices with the help of store technology, where it checks the data to be sent and decides which packet to send first.

It has the ability to fix the damaged packets when packets are sending, and also able to hold the direction of the rest of the packets and distribute them. If a port receives a weak signal, but still it is readable, then the active hub reconstructs the weak signal into a stronger signal before its sending to other ports. It can boost the signal if any connecting device is not working in the network. Therefore, it helps to make the continuity of services in LAN.

Intelligent Hub: It is a little smarter than passive and active hubs. These hubs have some kinds of management software that help to analyze the problem in the network and resolve them. It is beneficial to expend the business in networking; the management can assign users that help to work more quickly and share a common pool efficiently by using intelligent hubs. However, it offers better performance for the local area network. Furthermore, with any physical device, if any problem is detected, it is able to detect this problem easily.

The important applications of a hub are given below:

·        Hub is used to create small home networks.

·        It is used for network monitoring.

·        They are also used in organizations to provide connectivity.

·        It can be used to create a device that is available thought out of the network.

Advantages of Hub

1. It provides support for different types of Network Media.

2.  It can be used by anyone as it is very cheap.

3.  It can easily connect many different media types.

4.  The use of a hub does not impact on the network performance.

5.  Additionally, it can expand the total distance of the network.

Disadvantages of Hub

1. It has no ability to choose the best path of the network.

2.  It does not include mechanisms such as collision detection.

3.  It does not operate in full-duplex mode and cannot be divided into the Segment.

4.  It cannot reduce the network traffic as it has no mechanism.

5.  It is not able to filter the information as it transmits packets to all the connected segments.

6.  Furthermore, it is not capable of connecting various network architectures like a ring, token, and ethernet, and more.

Factors to Consider When Purchasing a PTZ IP Camera

Factors to Consider When Purchasing a PTZ IP Camera

PTZ IP cameras are commonly used for surveillance in large home compounds and public areas such as commercial car parks, stadiums and conference halls. PTZ stands for Pan Tilt Zoom, and that means you can use the IP software for cameras through the internet or your network to manipulate what the IP camera displays.

Different IP camera brands sport different kinds of zooms, and lower end cameras will simply feature the digital zoom. Proper optical zoom is the recommendable zoom type and this, together with the price, will always be specified in the product description.

Basically, a PTZ IP camera lets the user view real time images of the protected areas over the internet. You can simply monitor your office, home, building, yard or anywhere from miles away using a PC or a high end smartphone, tablet or PDA. Some network cameras even feature built-in Web server functions such that the IP camera doesn’t necessarily need to be connected to a computer.

DESIGN

IP PTZ cameras are traditionally spherical in shape, and this is mainly because they are meant to be completely mobile. Either the network camera itself (the sensor and camera mechanism) has been designed to take the shape of a sphere, and held so that it can pivot accordingly, or the camera is structured more traditionally and cased in a spherical protective bubble where it can tilt, pan and zoom and take images from within the shield.

NIGHT VISION

IP cameras with night vision capabilities come with built-in LED lighting to enable object visibility in dark settings, or at night. For outdoor surveillance, specifically in places without artificial lighting, night vision cameras may come in handy.

PTZ vs PT

Some IP cameras can only pan and tilt but not zoom. The two functions will usually be enough if the area you want to cover is small, like, say, your living room. However, if you want to cover a large area such as a shopping mall, an IP camera with the zoom function will be more effective.

HOW DO THEY WORK ?

PTZ IP cameras are typically controlled using remote systems. Users can do an initial configuration to have the camera moving and rotating in a certain predetermined pattern, or do it manually using a keyboard or mouse controlled interface. The angle of the lens can also be manually controlled, and this facilitates automatic position adjustment of the camera.

BENEFITS OF PTZ IP CAMERAS

·         User does not need to be close to the camera to operate it.

·         Requires little maintenance after it has been installed (except for regular cleaning of course).

·         Has 360-degree mobility. This way, it can detect and track objects as they move in the covered area as long as the target object is within lens range.

Factors to Consider When Purchasing a PTZ IP Camera

INDOOR OR OUTDOOR USE ?

If you’re looking for a PTZ IP camera for outdoor surveillance, you need one with night vision, weatherproof enclosure, miniature architecture for “outsider” visibility reasons, and vandal-proof capability for fortification in high crime areas.

YOUR DESIRED CAMERA FORM FACTOR

Each form factor has its own benefits, and the brand you opt for should cover all your surveillance requirements. Would you prefer a dome-shaped or an inconspicuous mini-dome camera? A wireless option or just an ordinary corded PTZ IP camera? You know your place and specifications best.

LEVEL OF DETAIL

When weighing different camera alternatives, you need to be sure of the detail level you want to see in your images. For wide area surveillance, you need a higher resolution, of course, as this will allow you to view even the furthest of images in relatively great detail.

Another factor that affects a camera’s resolution is its field of view (FOV). This is the viewable expanse of a given scene taken by the camera, and is sometimes referred as the angle of coverage or angle of view. A small FOV generally leads to the target object appearing smaller than it would in a fairly larger FOV.

The type of lens featured in the camera will also have an impact on resolution and field of view alike. A lens with low focal length number will bring about a wide field of view but less magnification while a higher focal length number will provide more magnification.

PTZ IP cameras, just like ordinary cameras, come with different resolution capabilities, and if you choose a high-resolution one, you also need to choose a high resolution megapixel lens so that the resolution required to produce a clear and detailed image can be maintained. If you combine a high resolution camera sensor with a less powerful lens, then your images will not be as detailed and crisp as you may desire.

POWER

PTZ cameras have multiple motors built-in which draw a considerable amount of power compared to a regular surveillance camera. Power can be supplied locally at the camera location or a cable can be pulled from a power source to the camera. The size of the wire dictates the maximum distance the cable can extend from the camera to the power source. See the chart below.

·        12 Gauge Wire – Maximum Distance 320 Feet

·        14 Gauge Wire – Maximum Distance 225 Feet

·        16 Gauge Wire – Maximum Distance 150 Feet

·        18 Gauge Wire – Maximum Distance 100 Feet

Each PTZ camera is shipped with its own power supply. Some cameras operate on 12v DC and some on 24v AC. Make sure you note the type of power the camera uses and that the power supply matches the camera. 

360 degrees of protection with the dome security camera

360 degrees of protection with the dome security camera

Pan/Tilt/Zoom cameras or PTZ cameras or 360degree cameras remain critical parts of many surveillance systems, especially in large security operations. Because of this it is important to understand and consider the key elements in selecting and using PTZ cameras.

In this guide we cover the basics of PTZ cameras and their selection, including:

• Pan/tilt/zoom basic terms
• Zoom ratios explained
• Using angle of view instead of zoom rating
• E-flip examined
• Available PTZ resolutions and their advantages/disadvantages
• Form factor selection (speeddomes, mini PTZs, positioners)
• Integrated IR PTZs
• PTZ lens issues
• Actual versus effective PPF
• Presets and tours
• Common applications

Pan/Tilt/Zoom Camera Basics

PTZs combine a camera with a motorized mechanism which allows it to move in multiple directions. These movements are referred to as:

• Pan: Left/right horizontal movement
• Tilt: Up/down vertical movement
• Zoom: Near and far 

This example demonstrates each of these movements:

Note that the extent to which cameras may be moved varies. Some models may be limited to 340° panning, some may tilt above horizontal, and zoom levels may vary from only slight magnification to extremely long distance. These specs depend on the type of PTZ (detailed below) and individual manufacturer/model.

E-Flip

Many PTZs include a feature called "E-flip" which automatically rotates the camera 180° when the operator is following a subject directly beneath it. This is a more intuitive control method than models which do not include E-flip, as the user must manually rotate the camera to follow the subject as they pass below.

This example shows the camera flipping as it is tilted down to 0° and beyond, while only the down tilt control is pressed.

Zoom Ratio

Manufacturers most often advertise PTZs using their optical zoom ratio, e.g., 18x, 26x, 36x, etc. This ratio is formed simply by dividing the camera's maximum focal length by its minimum, such as:

Use View Angle Instead

However, using only zoom ratio as an indicator of PTZ zoom performance misses some key details. Since lenses have differing wide/telephoto focal lengths, two cameras with the same ratio may have very different fields of view.

For example, looking at the specs of two 18x zoom cameras, we can see that one has a telephoto angle of view ~30% narrower (and thus higher PPF) than the other due to varying lens specs. But the reverse is also true, with the camera on the right having a wider possible angle of view, which may be more useful in some applications.

Users must beware of these issues when selecting PTZs and choose based on their required areas of interest. 

Ignore Digital Zoom

Some PTZ models include digital zoom in addition to optical, even in some cases  multiplying the two to create a deceptive "total zoom" figure, such as this camera:

However, digital zoom is a "fake" zoom, not providing additional details, only enlarging pixels captured and these specs should effectively be ignored in favor of angle of view as discussed above.

Resolutions Available

PTZs are now available in varying HD resolutions, as well as standard definition. Historically, zoom lenses for megapixel cameras were not available, though in the past few years, 1080p PTZs with 36x zoom have become readily available.

Note that HD is not necessarily preferable in PTZ applications, due to flaws in long focal length megapixel lenses, detailed later in this report.

PTZ Form Factors

There are three typical types of PTZ camera in use today, with different strengths and weaknesses, overviewed in this chart and detailed below:

Speeddome

The most common type of PTZ in use is the speeddome, which packages the camera/lens and pan/tilt mechanism in a dome form factor, typically 8-10" in diameter.

Speeddomes have several advantages:

• Pre-packaged: Due to their construction, speeddomes typically require less work to mount than positioning systems (below), and may be mounted in a variety of locations. Wall, pendant, recessed ceiling, and other mounts are all readily available.
• Integrated IR available: Several manufacturers now offer speeddomes with integrated IR (detailed further below), which greatly improves their usefulness in low light, as speeddomes historically have used relatively high F-Stop lenses, poor in dark scenes.
• Fast PTZ speeds: Speeddomes are the fastest movable cameras available. Speeds over 300º per second are not uncommon, and over 400º per second is not unheard of. This allows tracking of faster-moving subjects, and shorter movement times when switching between presets, often a fraction of a second.
• Pan/tilt range: Speeddomes typically feature full 360º pan range, without stops, and 180º tilt range with e-flip, to allow trailing of subjects as they move beneath the camera. Many cameras have extended tilt beyond 90º, with some offering up to 15º of up-tilt, above the horizon. Up-tilt previously required a pan/tilt positioner.
• Less wind loading: Compared to pan/tilt positioning systems, reviewed below, speeddomes do not have as many issues in strong winds, which may cause vibration in pan/tilt cameras.

Mini PTZ

Mini PTZ domes are a relatively recent development, with several manufacturers now offering models. These smaller PTZs have two key advantages:

• Low cost: Mini PTZs are must less expensive than full size speeddomes, often ~$300 USD or less, compared to $800-2000 for a speeddome.
• Small size: These models are much smaller than typical speeddomes, close to the size of a typical fixed dome camera (5-6" diameter) and much smaller in height.

However, there are disadvantages to mini PTZs as well:

• Limited zoom: Mini PTZs are typically limited to low optical zoom ratios such as 3x, though some may be found up to ~10x. Compared to other PTZs, often 30x or more, this is very low.
• Limited positioning range: Mini PTZs typically do not include full 360° panning, nor e-flip found in speeddomes.
• Slow pan/tilt speed: Panning speed of a mini PTZ is typically very low, 30-90 degrees per second, a fraction of speeddome panning speed.

Pan/Tilt Positioners

Pan/tilt positioners are the oldest type of movable camera system, available prior to integrated PTZ speeddomes. These systems historically consisted of separate componentes which were manually integrated: the positioner itself, a separate camera, and zoom lens. 

However, some manufacturers now offer pre-packaged IP positioning systems, such as the Axis Q86/Q87 and Pelco Esprit.

The key advantage to pan/tilt positioners is flexibility. Users may choose from multiple cameras and zoom lenses, instead of being limited to available speeddome options. This is useful when extremely long-range zoom lenses are required, as lenses over 100x zoom are available.

Positioners were previously the only option when infrared illuminators were desired in a PTZ camera. However, speeddomes with integrated IR have now largely caught up, offering long range infrared.

There are two key drawbacks to positioners:

• PTZ speed: Positioners often have low pan/tilt speeds, due to the weight and balance of cameras mounted on them. Increasing speeds could lead to increased vibration and "bounce" as cameras started and stopped moving, making tracking more difficult.
• Wind loading: Due to their increased profile, positioning systems in exposed areas may suffer from vibration due to wind, which is reduced or not present when using speeddomes.

Integrated IR Speeddomes

One recent advance in PTZ speeddomes is the addition of integrated IR, previously mainly found in positioners only. Many manufacturers now offer integrated IR speeddomes, such as Bosch, Dahua, Hikvision, and Samsung.

Integrated IR speeddomes have outperformed non-IR models in our tests at all ranges, with illumination at 450' and beyond. For example, the comparison below shows a 1080p IR PTZ versus a non-IR model at ~485' distance, with the subject clearly displayed in the IR model. The non-IR PTZ displays only noise, no usable image.

PTZ Lens Issues

When planning PTZ camera use, users should be aware that PTZ and other long focal length lenses do not resolve images the same as shorter focal length lenses, resulting in a reduction in practical details delivered. Because of this, when calculating needed PPF using PTZ cameras, users should expect a ~50% or higher reduction in delivered details.

For example, the image below shows a subject at ~420' using a 1080p camera, in an 87 PPF scene. However, details delivered are similar to ~35-40 PPF, less than half of actual.

Note that SD PTZs do not suffer typically suffer from these effects. For example, the VGA PTZ below displays a better image than the 1080p model at the same range, despite its much lower actual PPF.

PTZ Presets and Tours

In order to make PTZ operation easier, these cameras include the option to define predetermined positions, called "presets", which may be used to quickly move the camera to a specific position. For example, the clip below shows several presets covering a parking lot, quickly called in succession using a VMS.

In addition to presets, PTZs include tours (also called patterns) which move the camera automatically on a preset time schedule (typically every 3-10 seconds). Tours in current cameras most often call presets in a specific order (called a preset tour).

However, in the past, tours were typically defined by recording an operator manually moving the camera. This style of tour has generally fallen out of favor, though, as it becomes more difficult to spot small objects in motion as the camera is moving, and the constant PTZ movement precludes the use of camera-side video motion detection, which may be used in preset tours.

Most Common PTZ Applications

For the most part, PTZ usage is dropping in favor of fixed megapixel cameras, but there are still applications in which they are frequently used.

• Live monitoring operations: In systems with surveillance operators, PTZs are still often used, as they allow the user to more closely inspect and follow subjects than is possible with fixed cameras. Live monitoring is most often used in larger, higher security systerms, such as airports, critical infrastructure, city surveillance, etc., though many large retailers also employ PTZs and operators.
• Large areas: In very large areas, PTZs on preset patterns are still sometimes used instead of fixed megapixel cameras due to the higher details they may deliver at long range. For example, the image below compares 4K and 5MP cameras against HD and SD PTZs, with even the lowest resolution PTZ delivering details of the subject at this range: