I am attempting to put a mind map of WLAN issues. I will look forward at expanding each one of the classifications in the revisions of this blog.
This post covers the important 802.11 Frames which can help in performing the analysis and troubleshoot any issues related to WLAN networks. I have referenced Wireshark filters for the ease of each frame.
Beacon (1000, Subtype : 8) (wlan.fc.type_subtype == 0x08)
- Used to announce the Basic Service Set (BSS) for the Client (STAs).
- Transmitted by AP every 100 time units. 1 TU = 1024 microseconds. Default is 102.4 m/s
- To reduce any potential overhead, TU values might need adjustment in some cases where multiple SSIDs exist on AP radio.
Probe Request and Probe Response (0100, 0101 Subtype : 4 & 5) (wlan.fc.type_subtype == 0x4 or wlan.fc.type_subtype ==0x5)
- Used for active scanning
- STAs send the probe request, AP sends the probe response.
- Amount of probing may be able to be reduced by adjusting the roaming aggressiveness on the client.
- Probe request are sent to broadcast address (DA – ff:ff:ff:ff:ff:ff:ff)
- Directed probe request are when STA sending probe request may specify the SSID they are looking, like in example below.
- The SSID value can also be set to 0, SSID field is present, but empty. This is called Wildcard SSID or null probe request, e.g. below
- Probe requests are always sent on the lowest supported data rates. In above examples they are sent at 1 Mb/s.
- Probe response contain the requested information elements that may have been requested by the probing station. .e.g. below
Authentication & Deauthentication Frames (1011, subtype :11, 12) (wlan.fc.type_subtype == 0xb, wlan.fc.type_subtype==0xc)
- Used to authenticate to an AP to prepare association or roaming
- Used to remove the AID (Authentication ID) and deauthenticate with an AP.
- Frame body consists of
- Authentication Algorithm Number – 0 for Open System and 1 for Shared Key
- Authentication Transaction Sequence Number – Indicate current status of progress
- Status Code – 0 for Success,1 for Unspecified failures
- Challenge Text Used in Shared Key Authentication frame 2 & 3
Association and Disassociation Frames (0000, subtype =0)(0001 subtype =1) wlan.fc.type_subtype==0 or wlan.fc.type_subtype==10
- Simple 4-frame exchange (authentication request, ACK, authentication response & ACK) used to enter the authenticated and associated state with the AP.
- After Association STA may either use the network (open system authentication) or begin the 802.1x/EAP authentication process if used.
- The Disassociation frame is used to change from authenticated/associated state to “authenticated not associated state”. They contain a reason for disassociation. In case of below frame the reason code is unspecified reason.
Reassociation Request and Response Frames – (0010, subtype : 2) (0011, subtype : 3) (wlan.fc.type_subtype == 0x2 or wlan.fc.type_subtype ==0x3)
- These frames are used to roam to another AP within the ESS (extended service set) or to reconnect after brief disconnection.
- The reassociation response frame will also include an AID for the STA and the status code indicating the reassociation success or failure.
RTS / CTS – (1011, Subtype : 11), (1100, Subtype : 12) (wlan.fc.type_subtype == 0x2 or wlan.fc.type_subtype ==0x3)
- RTS and CTS frames are used to clear the medium for transmission of larger frames.
- The Duration Field in RTS/CTS is very important.
- SIFS (Short Interframe Space) – Amount of time in m/s required for a wireless interface to process a received frame and to respond with resoonse frame.
- RTS duration = SIFS(3) + CTS + Data + ACK(1)
- CTS duration = SIFS(2) + Data + ACK(1)
- CTS-to-self > is another method of performing NAV (Network Allocation Vector) distribution that use only CTS frames. It is used strictly as a protection mechanism for mixed mode environment.
Acknowledgement Frames (ACK)(1011, Subtype : 13) (wlan.fc.type_subtype == 0x1d)
- These frames are sent right after data/management frames to inform(ack) the transmitter.
- With ACK frame, the transmitter assumes the frame was lost due to the corruption from interface or some other issue, and so retransmits the frame.
- ACK frame includes Frame Control, Duration, RA and FCS subfields
- Duration Field value is set to : Duration Value of previous frame + ACK(1) + SIFS(1)
Null Data & PS-Poll Frames (0100 Subtype : 4) (wlan.fc.type_subtype == 0x24) or (wlan.fc.type_subtype == 0x1a)
- Null Data Frames are used to notify an AP that the STA is awake and able to receive the frames.
- It is simply a data frame with no date in the Frame Body field.
- PS-Poll on the other hand are used to notify the AP that the client STA is awake and available for buffered frames.
- STA indicate the power save mode using the Power Management bit the Frame Control field. When a STA is in PM mode = 1 it alternates between awake and sleep states.
- AP may send buffered data frames to the client in two ways.
- If the data belongs to legacy power-save queue, transmission follows the legacy power save.
- If the data belongs to WMM Power Save queue, data frames are downloaded according to a trigger-and-delivery mechanism.
Useful Links for this Post :
Main Objective: To successfully transfer every bit of information(data) from one device to another.
802.11 MAC HEADER
Let us now go through the basics of the frame header and the components. I have captured a simple beacon (management) frame using Wireshark.
I will briefly explain each of the fields. Notice the number in the bracket refers to the bytes. For memory 1 Byte = 8 bits. 🙂
Frame Control > 16 bits | 2 Bytes – contains 11 subfields as displayed in the above examples. Considering the amount of valuable information contained in 802.11 Frame Control sub-fields is mind-boggling
Protocol Version (2 bits): For now, always set to 0 by default. Changes in the version are expected in the future.
Type: Management (0,0), Data(1,0), Control(0,1), Extension Frame(1,1)*only available with 802.11D
Sub Type (4 bits): There are different kinds of management, control and data frames. Therefore the 4-bit Subtype field is required to differentiate. The above examples have Beacon & ACK subtypes.
To DS – if set to “1” – Frame going from STA > Distribution System (DS)
From DS – if set to “1” – Frame going from DS > STA
To DS = 0, From DS = 0 > Management or Control frames where it does not go to DS, Can be STA to STA communication in an ADHOC/IBSS setup.
To DS =0, From DS = 1 > Downstream traffic from AP to the STA.
To DS =1, From DS = 0 > Upstream traffic from STA to AP
To DS =1, From DS = 1 > Data frame using 4 MAC header format, usually occurs in WDS or Mesh Network.
More Fragments – If set to “1” it is usually preceded by another fragment of current MSDU or MMPDU to follow.
Retry – 0 or 1. 1 is for retransmissions. Lot of 1’s may indicate a network with a lot of retry rate due to some issue. The issues can impact the performance by increased application/network latency thereby degrading user experience.
Power Management – if set to “1”, STA is using power save mode.
More Data: if set to “1” it indicates that the AP or STA is holding more frames for the STA to which the current frame is targeted.
Protected Frame – if set to “1” it indicates payload is encrypted.
Order – If set to “1” in any non-QoS data frame when a higher layer has requested that the data be sent using strictly ordered CoS, which tells the receiving STA to process the frames in order.
Duration/ID > 2 Bytes | 16 bits – May be used for 2 purposes, it may contain the duration of the frame. Secondly, it may contain association identifier (AID) of the STA that transmitted the frame.
Address 1,2,3 and 4: Each address contains 6bytes/48 bits of data.
SA > Source Address
DA > Destination Address
TA > Transmitting Address
RA > Receiving Address
Sequence Control Field (2 Bytes/16 bits): Divided into 4-bit fragment number and a 12-bit sequence number. Used when MSDUs are fragmented. 802.11-2016 allows for fragmentation of frames.
QoS Control Field: (2 Bytes/16 bits): Only used in MAC header of QoS frames. Sometimes referred to as WMM (Wi-Fi Multimedia) which provides traffic prioritization.
HT Control Field (4 bytes/32 bits): Parameters related to HT & VHT operations. Only used in Management + QoS control frames.
Frame Body: Contains the actual MSDU payload to be transmitted.
FCS: (Frame check sequence field 4Bytes/32 Bits) – Final field on the frame header. Also known as Trailer as the word says. Used to detect errors in communication.
I will be summarising each chapter on the Certitrek Publishing – Official Study Guide for CWAP 403 Exam.
I’ve learned plenty of concepts from the first chapter – 802.11 – The Protocol. This is one of the chapters which you have to read and learn. One may not learn the contents of this chapter directly while working or experience this in his/her day today. Following the posts should give you a fair idea of what the chapter entails and get close to fulfilling the exam requirements. You still have to go through the book multiple times and revise the concepts discussed in the CWNA exam to fully grasp the knowledge required for this exam.
(APSTNDP) – For the purpose of our CWAP exam we will be concentrating our efforts on layer 1-4 only. More so we have to aim at learning layers 1 and 2 as IEEE 802.11 is focussed around them.
IEEE 802.3(Ethernet) & 802.11 (WLAN) operate primarily at Layers 1 & 2 of the OSI model. The Internet Engineering Task Force (IETF) operates at Layer 3 & 4.
Layer 4 is typically TCP/UDP. TCP is a connection-oriented protocol that uses a 3-way handshake, whereas UDP is a connectionless protocol typically used in time-sensitive applications where occasionally dropping packets is better than waiting.
Layer 3 is typically IP with the exception of WAN related protocols like HDLC, ATM, Frame Relay, etc.
Layer 2 (Data Link layer) – This is subdivided into MAC(lower) + LLC (upper). Frames are organized and meaningful collection of bits that are prepended and appended to upper-layer data within the network communications. When Network layer 3 sends data to the Data-Link layer (2), the data is handed off to the LLC and becomes known as MSDU (MAC Service Data Unit). The MSDU consists of data payload that contains the IP packet + some LLC data. When LLC sends the MAC service data unit info to the MAC sublayer, the MAC header information gets added in a MAC Protocol Data Unit (MPDU).
Layer 1 (PHY) – Physical Medium can be RF, Light Waves, Fibre cables. Capabilities include encoding, modulation, demodulation, timing & signals. This layer is subdivided into PLCP (Physical Layer Convergence protocol – Upper) & PMD (Physical Medium Dependent). The PLCP sublayer prepares the frame for transmission by taking the frame from the MAC sublayer and creating the PLCP Protocol Data Unit (PPDU).
802.11 Physical Layers
|Protocol||Year (adopted)||Frequency||Channel Width (MHz)||MIMO||PHY|
|802.11az||Late 2021||60 GHz|
|802.11ax||Late 2019||2.4 or 5GHz||20,40,80, 160||MU-MIMO||HEW|
|802.11ac wave2||2015||5 GHz||20,40,80, 160||MU-MIMO||VHT|
|802.11ac wave1||2014||5 GHz||20,40,80||SU-MIMO||VHT|
|802.11n||2009||2.4 or 5 GHz||20,40||SU-MIMO||HT|
|802.11 Prime||1997||2.4 GHz||22||N/A||DSSS|
Modulation is the process of imposing bits on a transmission medium. I have detailed the keying methods useful in understanding the basics of Modulation here. Also, refer to mcsindex.com for numbers related to Modulation and Coding. We will be exploring in detail about this in the forthcoming chapters which entail about PHY Layers and Technologies.
The industry troubleshooting methods e.g. from Cisco, Microsoft or CompTIA are not tested on the CWAP exam. The CWAP exam objectives list the following troubleshooting actions.
- Define the Problem
- Identify the Scale of the Problem
- Identity Probable Causes
- Capture and Analyze the Data (Most of the CWAP concentrated here)
- Observe the Problem
- Choose appropriate Remedial Steps.
- Document the Problem and Resolution.
Special Thanks to Rasika as I’ve learned a lot from his blogs.
Summary of the 802.11 Mac Header
Network Layer – IP header is added.
Data Link Layer – MAC header is added.
Physical Layer – PHY header is added.
Data is eventually transmitted as individual bits at the Physical layer.
BIT > 0/1, Octet > Byte of data.
Data Link Layer – LLC (802 based networks), MAC
MAC Service Data Unit > When network layer sends data to the Data Link layer, the data is handed off to the LLC and becomes MSDU
MSDU = IP Packet + Some LLC Data.
Only 802.11 Data Frames carry MSDU – Ratification 802.11n-2009, introduced A-MSDU
MSDU = 2304 Octets, A-MSDU = up to 7935 Octets.
MAC Protocol Data Unit > When the LLC sublayer sends MSDU to the MAC sublayer, the MAC header info is added to identify it.
MPDU = MAC Header + Frame Body(MSDU) + FCS (Trailer)
A-MPDU > transmissions are created by transmitting multiple MPDUs as one PHY frame as opposed to A-MSDU transmissions, which are created by passing MSDUs down the PHY layer as single MPDU.
Physical Layer comprises of PLCP & PMD – PLCP prepares the frame for transmission by taking the frame MAC sublayer and creating the PLCP Protocol Data Unit.
PPDU = PLCP + Frame from Mac Layer.
PLCP Service Data Unit > Pretty much like MPDU at PHY layer.
PLCP = PPDU + PSDU
I managed to get my CWNA certification today, this was my 2nd attempt. The first attempt was a failure a few months ago.
Failed Attempt: 53%
Passed Attempt: 82%
Below are a few tips which I would like to share so that you get most for this certification.
It would be quite beneficial if you already work for a Network/Wireless service provider or Manage wireless network for a company. Being in such a position certainly pays and gives room for joining the pieces of this puzzle.
This course will require some monetary investment. I managed to get some certification videos. Though the videos are for old CWNA course but majority of the conceptual stuff does not change for new revision. Here is the link > https://www.udemy.com/certified-wireless-network-administrator-cwna/
There are no video training courses available on CBT nuggets or INE as of today. I did check with CBT Nuggets via twitter but they do not have any official dates for the.
So back to the actual course curriculum. It would be highly beneficial to check the course outline and objectives – https://www.cwnp.com/uploads/cwna-107-objectives-2017.pdf You can check the differences from CWNA 106 so that you can prepare better https://www.cwnp.com/uploads/cwna-107-what-changed-2017.pdf
If would be good a good buy to get the new sybex CWNA official study guide > https://www.wiley.com/WileyCDA/WileyTitle/productCd-1119425786,miniSiteCd-SYBEX.html
This one is quite a thick book with over 1000 pages. I guess this book will be used throughout your career in wireless as a reference guide and a starting point for everything wireless. Some great work by the 2 David(s) Westcott & Coleman. When you buy the book you also get online flash cards + practice test questions valid for 1 year which you can use for further strengthen your knowledge.
Would be great and worth downloading the common terms used in the exam/book for the CWNA – https://www.cwnp.com/wp-content/uploads/pdf/cwnp_exam_terms.pdf
I read almost 1-2 chapters per week. The book might give you a feeling of information overload every once in a while. Another resource which I used during the preparation were some podcasts listed below.
- CleartoSend – https://www.cleartosend.net/
- WLAN Professional – https://www.wlanpros.com/
- Packet Pushers – https://packetpushers.net/
- WiFi for Beginners – https://wififorbeginners.com/category/podcast/
Twitterati (Twitterverse/Twitter users) – Would highly recommend you to join and follow the wireless enthusiasts. Thankful to the wireless online community! Many of them have a vast industry experience and certifications which go a long way in helping and coaching someone who is new to the wireless domain.
Slack Groups to recommended –
All the best with your CWNA Study and the Exam! Please buy the exam voucher directly form CWNP website (https://www.cwnp.com/cwna107v/) rather than going directly via PearsonVue. I saved $50USD by doing so.
I am on to the next Adventure of CWAP and will try and blog more often about the learnings from the course study.
Wireless has somehow made it to the human needs pyramid and has become mission-critical for most of the business around the world. Proper RF and QoS design is the only way to ensure real-time apps have acceptable QoE (Quality of Experience).
The wireless environments are
802.11e was introduced to bring QoS to Wi-Fi
• EDCA was introduced by IEEE 802.11e in
• WMM is now a mandatory part of modern Wi-Fi
• 802.11a/b/g are based on DCF (no QoS) • 802.11n/ac are based on EDCA (QoS is supported)
NOTE: The post describes about QoS in general and can be applied to any networking realm.
Latency, Jitter, and Loss
The quality of a network transmission is a result of three things:
Latency is how long it takes for a packet to be received by the endpoint after it is sent from the source. Latency is also referred to as delay. Asymmetrical tunneling after a Layer 3 roaming event between controllers can introduce delay. Again, symmetrical mobility tunneling is the recommended configuration.
Delay can be broken into two parts:
■ Fixed delay: The time it takes to encode and decode the packets and the time it takes for the packet to traverse the network.
■ Variable delay: Caused by network conditions. If the network is highly utilized at certain times of the day, the variable delay would be higher at those times than others.
Jitter is the value that results from the difference in end-to-end latency between packets. If a packet takes 50 ms to traverse the network and the next packet takes 100 ms, you have a jitter value of 50 ms.
Loss is simply the ratio of packets that are successfully received by the endpoint to those that were sent by the transmitter.
Correct Packet Marking
Depending on the traffic flow of a packet, traffic can be classified or tagged. This can be used to prioritise the packet thereby impacting the traffic flow. Efforts should be made to ensure that QoS policies are applied end to end which means from WLAN Controller > Core Switch Ports > Access Switch Ports > AP Ports.
Upstream and Downstream QoS
As discussed above, it is important to understand the terminology and direction of the traffic flow to and from the AP and the controller. You have both upstream and downstream QoS
Radio upstream: Traffic leaving the WLAN clients and travelling to the AP. Enhanced Distributed Channel Access (EDCA) rules provide upstream QoS settings for WLAN clients
Network downstream: Traffic leaving the controller travelling to the AP. QoS can be applied at this point to prioritize and rate-limit LWAPP/CAPWAP traffic to the AP.
WMM is a certification that applies to both clients and APs. The features are taken from the 802.11e draft.
Each of the four WMM queues competes for the wireless bandwidth available on the channel. Four queues namely – Background, Best Effort, Video, Voice. WMM uses Enhanced Distributed Coordination Function (EDCF) for handling the queue traffic. If more than one frame from different access categories collides internally, the frame with the higher priority is sent. The lower-priority frame adjusts its backoff parameters as though it had collided with a frame external to the queuing mechanism.
CWNA Chapter 2 – IEEE 802.11 Standards and Amendments.
“Defined” means the amendment either no longer exists or it was rolled into the existing (or prior versions) 802.11-2007 spec. “Defines” means it is a ratified amendment that will be rolled into 802.11-2011. “Will define” means it is a work in progress and not yet amended.
802.11-1997 (sometimes called 802.11 “prime”) — the original 802.11 specifications included the base functionality along with FHSS and DSSS PHYs.
802.11a — Defined OFDM usage in 5 GHz with data rates up to 54 Mbps.
802.11b —Defined 5.5 and 11 Mbps with HR/DSSS in 2.4 GHz.
802.11c — Defined MAC bridging for 802.11. Was incorporated into 802.1D.
802.11-1999 rolled up 802.11 prime with new enhancements.
802.11d — Defined 802.11 operation in new regulatory domains.
802.11e — Defined QoS
802.11F — Recommended Inter-Access Point Protocol (IAPP) for interoperability of different vendor products. Was not used by anyone and is now withdrawn.
Note: A capital letter designates a recommended practice standalone standard (similar to 802.1X). A lowercase letter designates an amendment to a parent standard. Hence, 802.11F was designed to be a standalone document (and also happened to be a recommended practice), not a part of the full 802.11 standards. This is often a confusing topic in standards naming.
802.11g — Defined ERP PHY, which introduces data rates up to 54 Mbps in 2.4 GHz.
802.11-R2003 rolled up 802.11-1999 and prior amendments, excluding 802.11e.
802.11h — Defined Dynamic Frequency Selection (DFS) for radar detection and avoidance in some 5 GHz bands. Also defined Transmit Power Control (TPC) for managing client transmit power.
802.11i — Defined security enhancements including TKIP, CCMP, and use of 802.1X with WLANs.
802.11j — Defined 4.9 – 5 GHz operation in Japan.
802.11-2007 rolled up 802.11-R2003 with prior amendments.
802.11k — Defines radio resource management processes for RF data collection and sharing.
802.11l — Due to potential confusion between an “l” (letter) and “1” (number), 802.11l was bypassed.
802.11m — Was used as a maintenance amendment that updated inaccuracies, omissions, and ambiguities.
802.11n — Defines High Throughput (HT) PHY with MCS rates up to 600 Mbps in 2.4 GHz and 5 GHz.
802.11o — For similar reasons as 802.11l, 802.11o was bypassed. ‘Is that an “o” (letter) or a “0” (number)? I don’t know, let’s just skip it.’
802.11p — Defines wireless access for the vehicular environment (WAVE).
802.11q — Due to potential confusion with 802.1Q, 802.11q was bypassed.
802.11r — Defines fast BSS transitions (fast secure roaming). Maybe one of these days we’ll use it.
802.11s — Will define 802.11 mesh internetworking.
802.11T — Specified a way to test wireless performance prediction. Remember, capital letters are recommended practices standalone standards. 802.11T was canceled.
802.11u — Will define internetworking with external networks, such as cellular.
802.11v — Will define enhancements for network management.
802.11w — Defines protected management frames to prevent some security vulnerabilities.
802.11x — 802.11 technologies as a whole are often referred to as 802.11x, so this amendment was bypassed.
802.11y — Defines use of OFDM in 3650-3700 MHz.
802.11z —Defines enhancements to Direct Link Setup, which no one uses.
802.11aa — Will define enhancements to video transport streams.
802.11ab —Was bypassed to avoid confusion with devices using 802.11a and 802.11b PHY technologies, which are often abbreviated as 802.11ab.
802.11ac — Will define Very High Throughput (VHT) with gigabit speeds, building on 802.11n MIMO technology.
802.11ad — Will define short range Very High Throughput (VHT) in the 60 GHz spectrum.
802.11ae — Will define enhancements for QoS management.
802.11af — Will define the usage of Wi-Fi in newly opened TV whitespace frequencies.
802.11ag — Similar to 802.11ab, 802.11ag was skipped to avoid confusion with devices using 802.11a and 802.11g PHY technologies, which are often abbreviated as 802.11ag.
802.11ah — Will define the usage of Wi-Fi in frequencies below 1 GHz. Also used as an expression of Wi-Fi pleasure. 802.11…ah!
802.11ai — Will define FILS (fast initial link setup). Designed to address challenges in high-density environments which a large number of mobile users face.
802.11aj – Will define modifications to the IEEE 802.11ad-2012 amendment’s PHY and MAC layer to provide support to the Chinese Millimeter Wave (CMMW).
802.11ak – Will define amendment to General Link for use in bridged networks.
802.11aq – Will define delivery of network service information prior to the association of stations on 802.11 networks.
802.11ax – Will define HE(High Efficiency). Expected to be next big PHY enhancement to the 802.11 standards. Operate in both 2.4/5GHz.
802.11ay – Will define improvement of an 802.11ad amendment providing faster speeds.
802.11az – TBC
Overview of Wireless Standards, Organisations and Fundamentals.
4 Key organisations involved with wireless networking industry
– FCC and other regulatory domains (ITU-R (ACMA (Australia)) (ARIB(Japan)) – FCC regulates communication from/to/within US. Both licensed and unlicensed communications are typically regulated in the following 5 areas
– Frequency, Bandwidth, Maximum power of the intentional radiator (IR), Maximum equivalent isotropically radiated power (EIRP), Use (indoor and/or outdoor), Spectrum sharing rules.
– IEEE – 802.11 working group is responsible for creating WLAN standard.
– IETF – International community of people whose goal is to make the internet work better.
– Wi-Fi Alliance – Global, non-profit organisation of more than 550 member companies devoted in making the wireless communication better. Its main task is to ensure interoperability of WLAN products by providing certification testing.
ISO – international Organisation for Standardisation.
OSI model – Open Systems Interconnection (APSTNDP)
Application Layer 7- WWW browsers, NFS, SNMP, Telnet, HTTP, FTP
Presentation Layer 6 – Include encryption, ASCII, TIFF, GIF, JPEG, MPEG, etc..
Session Layer 5 – NFS, NetBIOS names, RPC, SQL
Transport Layer 4 – TCP, UDP
Network Layer 3 – Provides switching and routing technologies, creates logical paths, known as virtual circuits.
Data Link Layer 2 -The MAC layer and the Logical link control (LLC) layer. IEEE 802.3, ATM, Frame Relay.
Physical Layer 1 – Cables, Ethernet, Fibre, etc.
The 802.11-2016 standard defines communication mechanism only at the Physical and the MAC sublayer of the Data-Link layer of the OSI model.
Simplex – Device is either capable of transmitting or receiving.
Half-Duplex- Capable of transmitting and receiving but not at the same time. Only 1 device can transmit at a time.
Full- Duplex – Capable of transmitting and receiving at the same time.
Radio Frequency Fundamentals
1. Amplitude – Height, force, or the power of the wave.
2. Wavelength – Distance between similar points on two back to back waves.
Frequency – Describes a behaviour of waves. How fast the wave travels, or more specifically how many waves are generated over a period of time, is known as frequency.
Phase – is a relative term. It is the relationship between 2 waves with the same frequency
Keying Methods – Some more explanation here.
1. Amplitude-Shift Keying
2. Frequency-Shift Keying
3. Phase-Shift Keying.
1. Know the 4 Industry Organisations
2. Understand core, distribution and access layer
3. Explain the difference between simplex, half-duplex, and full duplex.
4. Understand Wavelength, Frequency, Amplitude & Phase.
5. Keying Methods.
A couple of days ago I bumped into an opportunity to setup Cisco Mobility Express for one of the clients. Cisco has enabled to accomplish a mobility solution which can hep you deploy wireless LAN networks and be able to manage WLAN with APs on the network acting as the controller. Here’s how Cisco describes it in layman’s terms –
“Mobility Express integrates wireless LAN (WLAN) controller functions into the Cisco Aironet 3800, 2800, 1850, 1830, 1815, 1560 and 1540 Series Access Points. As such, Mobility Express is the latest in a series of Cisco efforts to turn WLAN controllers into a software function that any network component can host. Cisco controller capabilities also can be housed in standalone appliances (Cisco Wireless LAN Controllers, or WLCs), Cisco switches, Cisco routers, a private cloud, and a public cloud.”
I started with first AP to be converted to mobility express. In my case I’ve used a Cisco 3800 indoor AP. You will either need a POE+ capable switch or a POE+ injector. In case you only have POE injector the configuration is still possible but radios will receive insufficient POE to power up and cannot test the solution. You can convert the AP to mobility express but radios won’t receive enough power to start up.
Also remember that – When trying to convert to Mobility Express Image the Access point must not join and existing WLC in your network
Download Mobility Express image from www.cisco.com. You will need a Cisco account and valid entitlement to download this image. Connect Console and Ethernet cables into their correct interface ports, Ethernet will also be used to power through the use of a Power injector. Plug Ethernet cable from network switch into data port of POE power injector unit and apply power to POE injector. Login to AP via console with username and password : Cisco
Check that the AP has been assigned a IP address from the DHCP server on your network. Identify that an IP address has been assigned to the AP. In my case I configured a DHCP on the switch and let the AP receive a newly assigned lease. Setup your TFTP server, (for this I will using Tftpd64) and browse to the folder that contains the Mobility Express image
In the Command line of the LAP enter the following to download and change the configuration to Mobility Express.
AP#ap-type mobility-express tftp://<TFTP Server IP>/<path to tar>/file
The transfer will now start and wait for it to complete. Once completed issue the command “reboot” on the AP to make sure that it starts extracting the file it has downloaded and apply the new mobility express software. Once the software is applied it will go through the CLI setup wizard.
enter “yes” to terminate the auto install
Enter your required configuration items in the config wizard.
Enter all the details with regards to the management interface IP, netmask, default gateway etc. Setup the SSID and provisioning. These settings can also be done at the later stage when you access the GUI. The AP will reboot with the settings.
I managed to add 3 APs in the network and complete the setup.
- 5G is 5th Generation of Wireless Technology.
- 5G is Software defined network.
- 10x faster than 4G, 2hour film – 3G – 26 hours, 4G – 6hours, 5G – around 4 seconds.
- Response times faster – 4G – 0.045 m/s, 5G – 0.01 m/s.
- Foundation for ViR, IoT, Autonomous Driving, Online Gaming is just a start.
- Might only start showing in production up late 2019 or early 2020.
Millimeter Waves – Millimeter waves are broadcast at frequencies between 30 and 300 gigahertz, compared to the bands below 6 GHz that were used for mobile devices in the past. They are called millimeter waves because they vary in length from 1 to 10 mm, compared to the radio waves that serve today’s smartphones, which measure tens of centimeters in length.
Small Waves – Use mini base stations, small stations to relay signals around obstacles.
While traditional cell networks have also come to rely on an increasing number of base stations, achieving 5G performance will require an even greater infrastructure.
Massive Mimo – Support up-to 100 ports, increase capacity of network by factor of 22 or more. Can cause more obstruction, next point helps.
Beamforming –Base station can send directional signals, focussed stream. Beamforming can help massive MIMO arrays, which are base stations arrayed with dozens or hundreds of individual antennas, to make more efficient use of the spectrum around them.
Full Duplex – Basic antenna can either send or receive at one point, but 5G can give room to send and receive at same time. This is similar to one track train but when it arrives/goes through a station/junction there is a room for another train to pass through on the same line.