Modem (Modulator / Demodulator) is able to modulate digital data in analogue (tone) signals and analogue signals to demodulate in digital signals. The modem connects to the appropriate RJ11 head heads. The modems work at 57.6 Kbps downstream and 33.6 Kbps upstream, which corresponds roughly to sending 2 pages of text per second. The performance of these modems is often provided through standards V.90 or V.92.
ISDN
ISDN (Integrated Services Digital Network) is a telecommunications standard, provided by telecoms. Data and speech are digitized before transmission and then transmitted at the same frequency band as the analogue broadcast so far. The simplest ISDN connection is the ISDN base connection, which includes three separate transmission channels. Two B channels offer respectively 64 KB / s and are actually responsible for data transmission, while the third, Channel D, provides additional services and manages connectivity.
DSL
DSL is the abbreviation of Digital Subscriber Line. With the help of DSL technologies, the digital use of existing copper cable connections of the traditional analog telephone network, which is also called POTS (Plain Old Telephone Servica), has been made possible.
Using modern modulation techniques and increasing the bandwidth used up to the MHz level enables the transmission of a data stream up to 52 Mbit / s.
Sharing of DSL technologies
Special DSL technologies are summarized below the xDSL term and differ from the number of used pair pairs, frequency bands, and types of modulation:
An ADSL feature is the asymmetrical division of the bandwidth available. Private clients receive much more data than they send. For this reason, upstream flows are limited in order to favor a larger stream of downstream data.
Other connectivity options
- Cable television networks (Internet via cable modem).
- Electrical network (Internet from electrical outlets).
- Satellite (Internet via satellite connection)
- Frame Relay
- Asynchronous Transfer Mode (ATM)
The aforementioned connections are provided by the family of WAN protocols, from which we can mention ATM protocol, Frame Relay, ISDN, DSL, and so on.
Wireless networks - WLAN (Wireless LAN)
In wireless networks (WLANs), the transmission of signals is done through radio waves. This brings with it some basic advantages:
Within the coverage of the signal coverage, network access can be made from a preferred location, unconditioned by the cable length, or the location of the network jack.
For networking, no changes to the building should be contemplated (eg spouts, cinnamon, plugging, etc.)
Flexible technology for further expansion.
Public spaces (such as roads, water areas, etc.) are easily overcome.
Problems encountered in wireless networks:
High interference
There is no high security against tapping
Small port density
Compared to the LAN with lower transmission speed
A complex identification process is needed
Today's two topologies for WLAN are:
Ad-Hoc Networks
Infrastructure Networks
Ad-Hoc Networks
In an Ad-Hoc network, two or more network devices communicate directly to each other, as long as they are within the receiving range. The latter will be called the Basic Service Area (BSA). In this case we will talk about a Peer-to-Peer network. Here, all devices are partners of the same rank. This has the effect of reducing the network's extensibility and its security. Ad-Hoc networks are primarily used by private individuals and small network companies. They are simple to configure.
Infrastructure Networks
An infrastructure network is built as a central access node. This node will be called the Access Point (AP) and represents the interface between the network with and without cable. All nodes wishing to participate in network communications must be identified in the AP before they can communicate with other network devices.
Infrastructure networks are used primarily in large networks to serve as interfaces between stationary networks and mobile devices. They are a bit more difficult to configure than Ad-Hoc networks but allow differentiated scaling Of the network.
The protocols defined by IEEE for wireless networking standards are summarized in the standard 802.11 that appears in the following table. They define actions in one and two layers of the OSI (Physical and Data Link), and determine, inter alia Transmission speeds and access procedure.
802.11 b Determines the transmission speed of up to 11 Mbps in the 2.4GHz band
802.11 a Specifies transmission speeds up to 54 Mbps in the 5-Ghz band
802.11 g Determines higher transmission speeds of up to 54 Mbps in the 2.4GHz band
802.11 n Determines higher transmission speeds of up to 300 Mbps in the 2.4 / 5-Ghz band
* Coverage with signal about 100 m.
Security features in wireless networks (WLANs)
Below are some measures that can be taken while configuring an access point or wireless router to help secure that security.
1. Change the device administrator password (do not leave "default password").
2. Change the device name (SSID) and disable the broadcast (broadcast).
3. Enable a WEP / WPA / WPA2 encryption method for access.
4. MAC address filtering is activated.
5. Activate the firewall.
6. IP addresses are assigned manually.
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