# Summarize Wireless Standards ## IEEE 802.11 Wireless Standards ----------------------- - Wi-Fi modulation and carrier methods - Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) - Ack undamaged frames - Request to Send/Clear to send - Original data rate was just 1 Mbps ## IEEE 802.11a and 5 GHz Channel and Bandwidth ------ - every wireless device operates on a specific radio frequency range within an overall frequency band - 2.4 GHz - Better propagation (thru solid surfaces), but fewer channels and greater interference risk - 5 GHz - lower range, but less congested - IEEE 802.11a (54 Mbps) - Orthogonal Frequency Division Multiplexing (OFDM) - 5 GHz frequency - 23 x non-overlapping 20 Mhz channels - Dynamic frequency selection (DFS) and regulatory impacts ## IEEE 802.11b/g and 2.4 GHz Channel Bandwidth ------ - IEEE 802.11b (11 Mbps) - Direct Sequence Spread Spectrum (DSSS), along with Complementary Code Keying (CCK) signal encoding - 14x5 MHz channels - Wi-Fi still needs 20 MHz channel bandwidth - Channels require careful configuration to avoid overlap - 2.4 Ghz - IEEE 802.11g (54 Mbps) - OFDM (Orthogonal Frequency Division Multiplexing) - 802.11b compatibility mode ## IEEE 802.11n, MIMO, and Channel Bonding - Single User Multiple Input Multiple Output (SU-MIMO) - AxB:C transmit and receive antennas plus maximum simultaneous streams - Spatial multiplexing and spatial diversity - Can use 5 GHz or 2.4 GHz bands with channel bonding - High Throughput (HT)/Greenfield - 288.8 Mbps for a single channel and 600 Mbps for bonded channels - HT mixed mode for compatibility with other standards - Wi-Fi 4 ## WiFi 5 & 6 (802.11AC) ---------------------------------- #### Wi-FI 5 (802.11AC) - 5 GHZ only - 80 or 160 MHz channel bonding - up to 8 spatial points #### Wi-Fi 6 (802.11AX) - High Efficiency (HE) - 2.4 GHz or 5 GHz (plus new 6 GHz mode) - Enhancements to support IoT devices - OFDM with multiple access points (OFDMA) - not so much throughput, but reduced latency ## Multi-user MIMO -------------------------------------- In basic 802.11 operation modes, bandwidth is shared between all stations because of the CSMA/CA contention protocol. An AP can communicate with only one station at a time; multiple station requests go into a queue. Wi-Fi 5 and Wi-Fi 6 products address this problem using beamforming or Multiuser MIMO (MU-MIMO). Downlink MU-MIMO (DL MU-MIMO) allows the AP to use its multiple antennas to process a spatial stream of signals in one direction separately to other streams. This means that groups of stations on a different alignment can connect simultaneously and also obtain more bandwidth. For example, if four stations are positioned north, south, east, and west of a 4x4:4 AP, the AP should be able to allow each of them to connect at close to the maximum speed. If another station is added to the north, those two northern stations will share the available bandwidth along that beam path. Both stations and AP must support MU-MIMO. Where Wi-Fi 5 supports up to four stations communicating in parallel over 5 GHz only, Wi-Fi 6 can support up to eight in 2.4 GHz, 5 GHz, and 6 GHz bands, giving it better performance in congested areas. With DL MU-MIMO, only the AP can initiate beamforming, so it is only available on the downlink from AP to station (not station to AP). Wi-Fi 6 supports uplink MU-MIMO (UL MU-MIMO), allowing stations to initiate beamforming with the access point. ## 2g and 3g Cellular Technologies ---------------------- - GSM - Global system for mobile Communication - based phones use Time division multiple access (TDMA) - Code division multiple access (CDMA) - uses a code to key the modulation of their signal ## 4G and 5G Cellular Technologies # Install Wireless Networks ## Infrastructure and Wireless Access Points Wireless Network Devices are referred to as stations (STA) - mostly deployed in an infrastructure topology - each station is configured to connect though a base station or access point (AP), thus forming a logical star toplogy - The AP mediates communications between client devices and can also provide a bridge to a cabled network segment - according to 802.11 docs this is referred to as an infrastructure Basic Service Set (BSS) - The MAC address of the AP is used as the Basic Service Set Identifier (BSSID) - more then 1 BSS can be grouped together into an Extended Service Set (ESS) ## Wireless Site Design - Clients join a WLAN through the network same or Service Set identifier (SSID) #### SSID Broadcast and Beacon Frame A WLAN is typically configured to advertise its presence by broadcasting the SSID. This allows a user to connect to a named network. If SSID broadcast is suppressed, the user must configure the connection to the network manually. A beacon is a special management frame broadcast by the AP to advertise the WLAN. The beacon frame contains the SSID (unless broadcast is disabled), supported data rates and signaling, plus encryption/authentication requirements. The interval at which the beacon is broadcast (measured in milliseconds) can be modified. The default is usually 100 ms. Increasing the interval reduces the overhead of broadcasting the frame but delays joining the network and can hamper roaming between APs. #### Speed and Distance Requirements - devices supporting the Wi-Fi standard should have an indoor range of at least 30m (100 ft) - 2.4 GHz radios support better ranges then 5 GHz ones - 802.11n and later standards improve range - outdoor range will always be better then indoor range (double or triple) - stations determine appropriate data rated based on the quality of the signal using a mechanism called Dynamic Rate Switching/Selection (DRS) - basically each stations automatically finds the rate to send data at with DRS - Radio waves can pass thru walls, but may be interference from - fluorescent lighting, microwave ovens, cordless phones, power motors, heavy machinery ## Site Surveys and Heat Maps - Site survey is performed first - examine blueprints or floor plan - understand the layout and identify features that might produce radio frequency interference (RFI) - backed up by visually inspecting for things not shown in blueprints - such ass thick metal shelves surrounding a room that needs WLAN access - each AP needs a network port and power jack - next create a new plan on which WLAN cells and associated APs and booster cells will be marked - APs need to be close enough to prevent dead zones, but far enough apart that one AP does not interfere with another ## Wireless Roaming and Bridging Clients can roam within an extended service area (ESA). An ESA is created by installing APs with the same SSID and security configuration connected by a wired network, or Distribution System (DS). The access points are configured with different channels so that where BSAs overlap, there is no interference. When the client detects that it is no longer receiving a good signal, it checks for another signal with the same SSID on other channels or on a different frequency band, and if there is a stronger signal, it disassociates from the current AP. The station can then reassociate with the new AP. ## Wireless LAN Controllers An enterprise network might require the use of tens or hundreds of access points. If APs are individually managed, this can lead to configuration errors on specific APs and can make it difficult to gain an overall view of the wireless deployment, including which clients are connected to which APs and which clients or APs are producing the most traffic. - centralized way of managing APs Capable of supporting 1500 APs An AP whose firmware contains enough processing logic to be able to function autonomously and handle clients without the use of a wireless controller is known as a **fat AP** (SOHO ROUTER), while one that requires a wireless controller in order to function is known as a **thin AP**. Cisco wireless controller usually communicate with the APs by using the Lightweight Access Point Protocol (LWAPP). LWAPP allows an AP configured to work in lightweight mode to download an appropriate SSID, standards mode, channel, and security configuration. Alternatives to LWAPP include the derivative Control And Provisioning of Wireless Access Points (CAPWAP) protocol or a proprietary protocol. ## Ad Hoc and Mesh Topologies Most corporate and many SOHO networks are configured in infrastructure mode, there are also wireless topologies that allow stations to establish peer-to-peer links. #### Ad Hoc Topology - the wireless adapter allows connections to and from other devices - 802.11 -> Independent Service Set (IBSS) - Does not require an access point - all stations within the Ad Hoc network must be within range of each other - suitable for small work group of devices, or connectivity to a single device like a share printer. Not scalable to large network implementations #### Mesh Topology - 802.11s -> Wireless Mesh Network (WMN) - various proprietary mesh protocol and products - Nodes in a WMN are capable of discovering one another and peering forming a Mesh basic Service Set (MBSS) # Troubleshoot Wireless Networks ## Wireless Performance Assessment - Issues are mainly signal strength, interference, or configuration issues - speed and data rate -> physical, data link layers - throughput -> network layer - goodput -> layer 7 ## Signal Strength - Received Signal Strength Indicator (RSSI) - strength of the signal from the transmitter at the client end - When measuring - dBm will be a negative value (fraction of a milliwatt) with values closer to 0 representing better performance - a value around -65 dBm is good signal - anything over -80 dBm is likely to cause packet loss or be dropped ## Antenna Types - Determines the propagation pattern or shape of the radio waves transmitted - most have a simple omnidirectional vertical rod type - send and receive signals in all directions more or less equally - ideally mounted on the ceiling - propagation is shaped like a donut - radiates more powerfully horizontally then vertically - to extend signal to a particular area you can use a unidirectional antenna - sender and receiver must use directional antennas in this case - includes yagi (a bar with fins), dish/grid (parabolic) - useful for point to point wireless bridge connections - polarization is the orientation of the wave propagating from the antenna ## Antenna Placement - bad placement can cause of make works attenuation and interference problems - use site survey and heat maps to determine optimum AP positions ## Antenna Cable Attenuation - Another source of attenuation is where the antenna is connected at some distance from the point via coax cabling. Signal can be lost over this cable (antenna cable attenuation) ## Effective Isotropic Radiated Power/Power Settings The power at which an AP transmits is configurable - calculated as - sum of transmit power, antenna cable/connector loss, and antenna gain ## Channel Utilization and Overlap Issues Channel overlap refers to interference issues resulting from multiple AP that are all in range of one another and are configured to use similar wavelengths. There are 2 main types of channel interference - **Co-Channel Interference (CCI)** -> This can be more accurately described as contention. When multiple access points use the same channel, opportunities to transmit are reduced. The wireless devices must use CSMA/CA to find opportunities to transmit. CCI can be measured as a percentage referred to as channel utilization. Channel utilization can be measured from the access point or using a Wi-Fi analyzer. As a design goal, a channel should exhibit no more than 50% utilization. - **Adjacent channel interference (ACI)** -> This occurs when access points are configured to use different but overlapping channels, such as 1 and 3 in the 2.4 GHz band. ACI slows down the CSMA/CA process and raises noise levels. ## Overcapacity Issues ## Interference Issues - Mirrors or shiny objects cause signals to reflect, meaning variable delay is intrroduced - refraction -> glass or water can cause radio waves to bend and take a different path to receiver. Can cause data rate to drop - Absorption -> degree to which walls and windows reduce signal strength - EMI -> Interference from powerful radio or electromagnetic sources # Configure and Troubleshoot Wireless Security ## Wi-Fi Encryption Standards the first type was WPA. - very week, do not use at all (WPA1) - WPA2 is more stronger and uses EAS, and blockchaining - preshared pin, group authentication, all stations use the same passphrase or pin - WPA3 - - still group based authentication - still passphrase - little more security ## Enterprise/IEEE 802.1X Authentication ## WIFI configuration security issues - Wrong SSID/bad passphrase - incorrect manual configuration - selecting wrong SSID - Encryption protocol mismatch ## Client Disassociation Issues If clients are disassociated unexpectedly and there is no roaming, interference or diver issue, suspect a malicious attack. - This type of attack exploits the lack of encryption in management frame traffic to send spoofed frames - may inject management frames that spoof the MAC address of a single victim station causing it to be disconnected from the network - may also be trying to disconnect all stations - frames can be spoofed to send either disassociation or de-authentication notifications ## Open Authentication and Captive Portal Issues - the client is not required to authenticate - Used on a public AP or hotspot - in WPA/WPA2 - data sent over the link is unencrypted - open authentication may be combined with a secondary authentication mechanism managed via a browser - after connecting client will be redirected to a captive portal or splash page to authenticate - can enforce terms and agreements or take payment - the redirect may not work - should use HTTPS & TLS