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13. Wireless Networking
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13. Wireless Networking
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* Introduction to Wireless Networking Technologies:
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-> Wireless networking -> A way of networking without wires;
-> IEEE 802.11 standards - list the specifications for wireless communication devices must operate;
-> These set of specification - 802.11 family - Wifi - Wireless fidelity;
-> Wireless networking devices communicate with each other through radiowaves;
-> Different 802.11 standards generally operate using the same basic protocol but might operate at a different frequency bands;
-> Frequency band - A certain section of the radio spectrum that is been agreed upon to be used for certain communications;
- North America - FM radio transmissions -> 88MHz - 108 MHz; ( FM broadcast band);
- Wifi networks operate on different frequency bands - 2.4 GHz - 5 GHz;
Common 802.11 specifications - 802.11a, 802.11b, 802.11g, 802.11n and 802.11ac;
802.11 = physical and data link layers;
802.11 frame has a number of fields -
Octets:
2 2 6 6 6 2 6 0 - 7951 4
| Frame | Duration/ | Address | Address | Address | Sequence | Address | Data | FCS |
| Control | ID | 1 | 2 | 3 | Control | 4 | Payload | |
1. Frame Control - has number of sub-fields that are used to describe how the frame itself needs to be processed. 802.11 version;
2. Duration - specifies how long the total frame is. So the receiver knows how long to expect to the listen to the transmission to last;
3. Address fields (4) -
- Wireless access point - A device that bridges the wireless and wired portions of a network;
- A single wireless network may have a lot of access points to cover a large area;
- Devices on a wireless network will associate with an access point - the one they are physically closest to / signal strength / interference;
a. Source mac address;
b. intended destination on network;
c. receiving address - MAC address of the access point that should receive the frame;
d. treansmitting address - MAC address of what ahs tranmitted the frame;
4. Sequence control - sequence number to keep track of the frames ordering;
5. Data payload - Has all the data of the protocols up the stack;
6. FCS - Frame Check Sequence field - contains a checksum used for cyclical redundancy check (like ethernet);
---------------------------------------------------------------------------------------------------------------------------------------- Wireless Network Configuration :
-----------------------------------
1. Ad-hoc networks -> Nodes speak directly to each other;
- simplest;
- Every device on the network and within range can communicate with every other device;
- Exchange data - photos, messages;
- disaster situation;
2. Wireless LANs (WLANS) - one or more access points act as a bridge between a wireless and a wired network;
- Wired network acts as a normal LAN - contains outbound internet link;
- Wireless devices communicate with access points - forward traffic to the Gateway router - they data transfer occurs;
3. Mesh netwroks - Hybrid of the two;
- A lot devices communicate with each other wirelessly - mostly wireless access points;
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Wireless Channels
------------------
-> Channel - Individual smaller sections of the overall frequency band used by a wireless network;
-> Address - collision domain (Any one network segment where one compute can interrupt another - overlap);
-> Collision domain in wired networks is reduced by switches (They remember which computers live on which physical interfaces);
-> The channels business and neighborhood business overlap as little as possible;
----------------------------------------------------------------------------------------------------------------------------------------
Wireless Security
-----------------
- WEP - Wired Equivalent Privacy - An encryption technology that provides a very low level of privacy;
- More the bits in the key - longer to decrypt it;
- WEP - uses only 40 bits for its encryption keys;
- WEP was replaced with WPA or Wi-Fi Protected Access - 128-bit key;
- Today, WPA - 2 algorithm - 256-bit key;
- MAC filtering - You can configure the access points to only allow for connections from a specific set of MAC addresses belonging to deviced you trust.
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Cellular Networking
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- Mobile networking.
- similar to the 802.11 specifications; and there are lot of different cellular specifications;
- Like wifi, cellular networking operates over radio waves -over specific frequency bands reserved for cellular transmissions;
- Theses frequencies can travel longer distances (KM / miles);
- It is built around a ceoncept of cells - each cell is assigned a particular frequency band for use; neighbouring cells are setup to use bands that don't overlap;
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