More about network technologies and devices

Hubs, switches and bridges

Hubs are essentially used as connection boxes to allow several pieces of equipment to share a single Ethernet connection. Usually 5-24 devices can be connected to one hub. If more devices are used, another hub can be added. To speed up the network, you can use switched hubs, that allow several data packets to be transmitted simultaneously.

Gateways and Routers

Gateways or Routers are essentially packet forwarders that operate at layer 3 (i.e, the IP layer). Forwarding decisions are made based on IP addresses and IP routing tables. A gateway makes it possible to connect two networks of different technologies into one network. For example, an Ethernet network can be connected with a Token-Ring network.

NAT routers

All devices connecting directly to the Internet must have a unique public IP address. Public IP addresses are sold by Internet Service Providers (ISPs). A device called a Network Address Translator (NAT) makes it possible to connect a LAN with private addresses to the Internet by translating internal private addresses into public addresses.

DHCP servers

It takes time to administer the IP addresses for large numbers of devices on a network. To reduce this administration time and keep the number of IP addresses to a minimum, a DHCP server can be used. This type of server automatically issues network devices with IP addresses when they connect to the network.

DNS Domain Name Servers

In larger networks a Domain Name Server (DNS) is included. This is literally a ‘name’ server. It associates and remembers given names to corresponding IP addresses. For example, a network camera monitoring a door is more easily remembered and accessed by the word ‘door’ than it is by its IP address, such as 192.36.253.80.

Firewall

A firewall is designed to prevent unauthorized access to or from a private network. Firewalls can be implemented in both hardware and software, or a combination of both. Firewalls are frequently used to prevent unauthorized Internet users from accessing private networks connected to the Internet, especially intranets. All messages entering or leaving the intranet pass through the firewall, which examines each message and blocks those that do not meet the specified security criteria. For example, using firewalls, one can make sure that video terminals are able to access the cameras while communication from other computers with the cameras will be blocked.

DDNS and dynamic IP addresses

Dynamic DNS is a method of keeping a domain name linked to a changing IP address as not all computers use static IP addresses. Typically, when a user connects to the Internet, the user's ISP assigns an unused IP address from a pool of IP addresses, and this address is used only for the duration of that specific connection. This method of dynamically assigning addresses extends the usable pool of available IP addresses. A dynamic DNS service provider uses a special program that runs on the user's computer, contacting the DNS service each time the IP address provided by the ISP changes and subsequently updating the DNS database to reflect the change in IP address. In this way, even though a domain name's IP address will change often, other users do not have to know the changed IP address in order to connect with the other computer.

In a network video application, a camera watching an entrance door is more easily remembered as "door.camera.axis.com" for instance. But when using DHCP, the camera’s IP address may change over time. So a static mapping between “door.camera.axis.com” into the camera’s IP address "192.36.253.80" may not be valid after a while. DDNS provides the solution: every time the camera changes IP address, it will contact the DNS server and update the mapping.

SNMP

SNMP (Simple Network Management Protocol) is a set of protocols for managing complex networks – and for remotely controlling and managing network-attached devices.

IPSec

"IP Security" (IPSec) consists of a set of protocols to support secure exchange of packets at the IP layer. IPsec has been deployed widely to implement Virtual Private Networks (VPNs).

UPnP

Universal Plug and Play (UPnP) is a networking architecture that provides compatibility among networking equipment, software and peripherals of the 400+ vendors that are part of the Universal Plug and Play Forum. UPnP works with wired or wireless networks and can be supported on any operating system. Simply, it allow devices to connect seamlessly and to simplify the implementation of networks in the home and corporate environments.

UPnP is a common way for instance to discover network cameras. When you connect a camera for the first time, it may get an address from the DHCP server which you have no idea of what this address is. With UPnP you can search for camera devices and see them pop up.

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