CWAP 403 – Start >

I will be summarising each chapter on the Certitrek Publishing – Official Study Guide for CWAP 403 Exam.

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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.

OSI Layers

(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
802.11ay	2020	60 GHz	8000	MU-MIMO	EDMG
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
802.11g	2003	2.4 GHz	20	N/A	ERP
802.11a	1999	5 GHz	22	N/A	OFDM
802.11b	1999	2.4 GHz	20	N/A	HR-DSSS
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.

Troubleshooting Methods

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