A basic service set (BSS) is the basic building block of an 802.11 WLAN and comprises a group of associated STAs. STAs can communicate with each other when they are located in a conceptual area which is called the basic service area (BSA). The BSA is determined by the transmission feature of the wireless media. An STA can communicate with other STAs in the same BSS since they are in the BSA.

: The basic service area is the coverage area of the BSS.
Equivalent to a wireless unit. Communication between the
member sites within the coverage area can be maintained. Because of the frequent changes in the surrounding environment, the size and shape of the BSA is not always fixed

An extended service set is a set of multiple interconnected BSSs with the same SSID. It is a virtual BSS of a large scale.

A service set identifier is the unique identifier of the BSS. Using SSID, one wireless LAN can be divided into several sub-networks that require independent authentication.
Users can access the corresponding sub-networks only after they pass the authentication. This prevents unauthorized users from accessing the network.
For example, When we search for a wireless network on a laptop, the network name is SSID. SSID consists of up to 32 characters, and case sensitive,configured in all AP and STA radio frequency card.
One AP can support several SSIDs

The basic service set identifier is the MAC address of an AP. It identifies the BSSs managed by the AP. As for one AP, each BSSID maps to a specified SSID. If multiple APs manage the same BSS, the BSS has only one SSID but different BSSIDs for each AP. If one AP manages multiple BSSs, different BSSIDs are assigned to map these SSIDs

For example, each company has some regular visitors who have their own wireless terminals (such as laptops and mobile phones). These terminals need to access the Internet.
An ESS is established for the AP to allow the visitors to access the Internet. Currently, APs can create several ESSs simultaneously. For example, some APs developed by Huawei can support 16 virtual APs per radio. That is, each AP radio can support 16 ESSs.

In IBSS,STAs can directly communicate with each other within an IBSS since the distance between two STAs is within the limited range. An IBSS must consist of at east two STAs. In general, an IBSS is established temporarily for a small number of STAs for specific purposes. For example, an IBSS is established to organize a conference in the meeting room. When the conference begins, the STAs form an IBSS to transmit data. When the conference ends, the IBSS is dismissed immediately

An IBSS is of a small scale, established for specific purposes and lasts for a short period. Therefore, it is also called Ad-hoc BSS or Ad-hoc network

Note: Ad-hoc is originated from Latin, which means special or for special situation. Ad-hoc network is also called P2P network because STAs on this network communicate directly with each other.

infrastructure BSS. If there is an AP on the network, the BSS forms an infrastructure network. An AP manages all the communications within the infrastructure network, including the communications among all the mobile nodes in the BSA.

The wireless network of Ad-hoc typology consists of several wireless STAs. One STA can directly communicate with another STA or several other STAs through the Ad-hoc typology. This network cannot be connected to a wired network, and it works independently. No AP is configured on the network. Each user ensures its own security.

The STAs on the network compete for public channels. When a lot of STAs coexist on the network, the channel competition may congest the network. Therefore, such topology is applicable to small-sized WLAN networks.

On a point-to-point network, each node must "see" other nodes; otherwise, they consider that network connection is interrupted. Therefore, the Ad-hoc network is applicable only when there are a few users, for example, 4 to 8 users

When several APs are connected to cover larger areas, the APs should communicate with each other in order to monitor the mobile STAs. A distribution system is the logical component of an 802.11 WLAN, and is responsible for transmitting frames to the
destination. The distribution system is the backbone network for APs to transmit frames.
For products that have achieved success in the market, most of them use Ethernet as the backbone network.

The wireless AP works in half-duplex modes. It receives, buffers, and forwards data between STAs and the wired network. Wireless communication is implemented by the AP

An AP covers dozens of users and the radius of coverage area can reach a hundred meters. An AP can connect a wireless network to a wired network.

APs are connected to the 802.3 Ethernet network. All the hosts in wireless networks communicate through the APs.

The infrastructure network consists of multiple APs and DSs. The network is also called an ESS. Each AP in the ESS is an independent BSS. All APs share an ESSID.

l A mobile terminal can roam between the wireless networks with the same ESSID. The wireless networks with different ESSIDs form a logical subnet.

The channels between APs cannot overlap. The overlapping signal coverage areas range from 10% to 15%.

WDS can transmit data in a wired network through a wireless network to another wired or wireless network. This function is also called wireless networking bridge because data is transmitted over virtual wireless links.

The wireless networking bridge function usually works in point-to-point mode. However, WDS supports the point-to-multipoint mode and can connect wired systems or wireless network adapters. Therefore, at least two APs of the same function exist in the WDS. The maximum number of APs is determined by the vendor's network structure. WDS connects APs using wireless links and does not affect the coverage capabilities of APs

Companies except for the Telecommunications Department cannot lay out cables for wired network connection in public places. However, the WDS system can flexibly establish private networks through the 2.4 GHz or 5.8 GHz ISM open frequency bands according to the customers' requirements.

The O&M troubleshooting is difficult on wired networks. Fault locating and recovery can be quickly implemented in the WDS because you only need to maintain bridging devices

It can be constructed without laying out cables or digging grooves. The deployment and capability extension can be implemented rapidly.

The WDS network can be deployed quickly, which provides assurance in temporary, emergency, or anti-disaster situations.

For indoor WDS deployment, you can select the P2P or P2MP networking modes flexibly according to the service requirements and architecture designs. In indoor scenarios where network cabling is difficult or the coverage area is far away from the switch, WDS networking is an effective solution. However, the WDS application in indoor scenarios is subjected to restrictions caused by building obstacles.

Outdoor WDS deployment: select the networking modes flexibly according to the service requirements and architecture designs. When there are obstacles between two LANs or the transmission distance is too far, you can connect the two LANs using APs as repeaters.

Basic Concepts
WirelessMeshNetwork WMN is a communication network that consists of multiple wirelessly connected APs in a mesh topology and connects to a wired network through a portal node or 2 portal nodes

Mesh point (MP): is a Mesh-capable node that uses IEEE 802.11 MAC and physical layer protocols for wireless communication on a WMN. This node supports automatic topology discovery, automatic route discovery, and data packet forwarding. MPs can provide both Mesh service and user access service.

Mesh access point (MAP): is an AP that supports the AP function and provides access to STA

Mesh point portal (MPP): connects to a WMN or another type of network and communicates with an MP or MAP on a WMN. This node provides the Portal function and enables Mesh nodes to communicate with external networks.

Fast deployment: Mesh nodes can be easily installed to construct a WMN in a short time, much shorter than the construction period of a traditional WLAN.

Dynamic coverage area expansion: As more mesh nodes are deployed on a WMN, the WMN coverage area can be rapidly expanded.

Robustness: A WMN is a peer network that will not be affected by the failure of a single node. If a node fails, packets are forwarded to the destination node along the backup path

Flexible networking: An AP can join or leave a WMN easily, allowing for flexible networking

Various application scenarios: Besides traditional WLAN scenarios such as enterprise networks, office networks, and campus networks, a WMN also applies to scenarios such as large-scale warehouses, docks, MANs, metro lines, and emergency communications.

Cost-effectiveness: Only MPPs need to connect to a wired network, which minimizes the dependency of a WMN on wired devices and saves costs in wired device purchasing and cable deployment

In an outdoor WMN, two MPs can interconnect over dozens of kilometers by using different antennas. Mesh technology can implement data transmission across office buildings or areas. It overcomes the limitations of wired networks such as difficult deployment, high deployment costs, and low flexibility. Therefore, outdoor WMN networking applies to campuses, plantations, mountain areas, and high buildings.

Outdoor obstacles include trees and high buildings. The radian of the earth must be considered for long-distance transmission. Select and install antennas based on site requirements

802.11 physical layer standard defines the frequency, modulation method, and highest rate.

802.11 MAC layer standard defines the features of WLAN at the MAC layer, such as QoS, security, and roaming.

IEEE 802.11e standard allows WLAN MAC protocols to support multimedia traffic transmission and QoS on all radio interfaces.

IEEE 802.11i uses user and device authentication of IEEE 802.1x. It is an amendment to MAC layer standard. IEEE 802.1i defines strict encryption and authentication mechanism to improve WLAN security.

DFS DFS ensures that channels containing radar are avoided by an Access Point (AP) and energy is spread across the band to reduce interference to satellites

TPC ensures that the average power is less than the regulatory maximum to reduce interference to satellites.

The IEEE 802.11h standard provides an additional 11 channels to the 802.11a standard’s 12 non-overlapping channels for a total of 23 non-overlapping channels

IEEE 802.11r, fast BSS transition (FT), reduces the delay to transit clients between APs. IEEE 802.11h is designed to manage spectrum.

IEEE 802.11s is an IEEE 802.11 amendment for mesh networking, defining how wireless devices can interconnect to create a WLAN mesh network, which may be used for static topologies and ad-hoc networks.

PLCP combines the MAC frames with radio waves. PLCP adds a header to frames. Usually, a frame contains a preamble to synchronize data receiving. However, the preambles vary according to modulation method. Therefore, PLCP adds its own preamble to the frames to be transmitted. Then PMD transmits the frames from PLCP to the air.

OFDM Orthogona Frequency Frequency Division Multiplexing

TheroughPut 54 Mbit/s
Uses orthogonal frequency division multiplexing OFDM
Data raet 6 9 12 18 24 36 48 and 54 Mbit/s
Works at 5 Ghz unlicensed national information strcuture U-NII band
23 nonOverlapping channels

54 Mbit/s Uses OFDM
Data raet 6 9 12 18 24 36 48 and 54 Mbit/s and rates supporteed by 802.11b
Workd ar 2.4 Ghz ISM band
13 Channels

3 non Overlapping Channels

workd on 5 Ghz frequency band
is forward compatible with 802.1 specification. it improves the PHY frame structure and channel management when diffrent bandwidths are used
in terms of security 802.11ac compiles with the 802.11i security standard
802.11ac helps implement seamless roaming for enterprises and households

higher Throuput > wave 2 supports a max of 3.47 Gbit/s
Less Interference > the 5 Ghz frequency band is the mainstream band
High access capacity . provides higher throughput and multiUser MIMO (MU-MIMO) objectively improves the user access capability

Fat APs have WAN and LAN interfaces and suppport Dynamic Host Configs Protocol DHCP servers, domain name servser DNS and MAC Address Clone as well as VPN access and firewall function

For many years, the conventional access point was a standalone WLAN portal device where all three planes(Management Plane, Control Plane, Data Plane) of operation existed and operated on the edge of the network architecture. These APs are often referred to as fat APs, or standalone APs. However, the most common industry term for the traditional access point is autonomous AP

All configuration settings exist in the autonomous access point itself, and therefore, the management plane resides individually in each autonomous AP. All encryption and decryption mechanisms and MAC layer mechanisms also operate within the autonomous AP

A typical fat AP is a wireless router. Unlike traditional APs, wireless routers have WAN and LAN interfaces and support Dynamic Host Configuration Protocol (DHCP) servers, domain name server (DNS), and MAC address clone, as well as VPN access and firewall functions

The next progression in the development of WLAN integration is the centralized WLAN architecture. This model uses a central WLAN controller that resides in the core of the network. In the centralized WLAN architecture, autonomous APs have been replaced with controller-based access points, also known as lightweight APs or Fit APs (thin APs).

To build operational WLAN and to realize quick deployment of WLAN, centralized management of network devices, and fine-grained user management. Enterprises and carriers prefer the fit AP + AC networking to the fat AP networking because the fit AP + AC networking realizes fast WLAN deployment, centralized network device, and refined user management, helping build a maintainable, manageable WLANs

An AC and a fit AP run the CAPWAP protocol to communicate with each other

Background
since traditional WLAN architecture cannot satisfy the demands of large-scale networking. IETF established Control and Provisioning of Wireless Acccess Points (CAPWAP) team to create large-scale WLAN solutions that connect ACs and APs

LWAPP Light Weight Access Point Protocol- RFC5413
LWAPP has a complete protocol architecture and defines detailed packet structure and multiple control control messages. However, the effectiveness of the newly created security mechanism is yet to be proven

SLAPP Secure Light Access Point Protocol-RFC5413
The highlight of SLAPP is the DTLS technology, which is highly applauded in the industry

CTP and WiCoP can satisfy the demands of centralized WLAN architecture. However, they have drawbacks, especially in terms of security

CAPWAP Overview
used for interconnection between AP and AC. it enables an AP to manage connected APs in a centralized manner
provides Following functions

automatic AC discovery and operation and maintenance of the AP & AC state machine
AP mangement and service configuration delivery
STA data forwarding over a CAPWAP tunnel

Service data of APs is forwarded locally and the AC only manages the APs. That is, AP management packets are encapsulated in CAPWAP tunnels and terminated on the AC; whereas AP service flows are directly forwarded to switching devices without being encapsulated.

Service data of APs is encapsulated and forwarded to the AC over the CAPWAP tunnel. The AC manages the APs and forwards service data of APs to the upper layer network. Both the AP's management flows and data lows are encapsulated in the CAPWAP tunnel and sent to the AC.

CAPWAWP Packet Format
CAPWAP is an application-layer protocol using UDP ports.
CAPWAP transmits two types of packets

Data packets: encapsulate wireless frames
Control packets: management packets exchanged between APs and ACs.

CAPWAP data and control packets are transmitted on different UDP ports:

Control packets are transmitted on UDP port of 5246.
Data packets are transmitted on UDP port of 5247.

If an AC IP address list is configured on an AP, the AP starts the static discovery process after being powered on and associates with a specified AC
If no AC IP address list is configured, the AP starts the dynamic AC discovery process. In this process, the AP obtains it own IP address and DNS server address through DHCP, obtains an AC IP address list from the DHCP server or DNS server, and broadcasts discovery packets to discover an AC and associates with the AC.

1. After an AP starts, it obtains an IP address, DNS server address, and domain nam through the DHCP server
   
   

3. If the AP does not receive a response after 30s, it starts Layer 3 discovery. The AP obtains the IP address of an AC using Option 43 or the domain name of an AC using Option 15 from the DHCP server, and then sends a discovery request to the IP address or domain name

4. After receiving the discovery request, the AC checks whether the AP has the right to access the AC. If the AP is authorized, the AC replies with a discovery response

2. The AP broadcasts a request packet at Layer 2 to attempt to associate with an AC.