What is Extended Service Set?
A key idea in the IEEE 802.11 (Wi-Fi) wireless networking standard, the Extended Service Set (ESS) was created expressly to increase wireless coverage and promote mobility.
The ESS’s features, construction, and operation are explained in detail below:
Definition and Structure
An ESS is described as a service set that typically has two or more Basic Service Sets (BSSs) interconnected with each other.
- Core Components: Several Basic Service Sets (BSSs) make up the ESS. A single Access Point (AP) and the stations (client devices) that are linked to it make up a BSS, which is the fundamental building block of an IEEE 802.11 LAN.
- Interconnection via DS: A shared Distribution System (DS) connects the APs in charge of various BSSs. All of the APs in the ESS are connected by the DS, which acts as the wired or wireless backbone (like a LAN or WAN).
- Purpose: The ESS’s primary objective is to establish a wide, uninterrupted, and seamless wireless network coverage area. A full building or a sizable area (known as the Extended Service Area, or ESA) may be covered by this network. Any size and level of complexity of a wireless network can be created using the ESS design.
You can also read Wireless Principles: 802.11 Standards & WLAN Basics for CCNA
Key Identifiers
To control the expanded network and preserve a single user experience, the ESS employs two major identifiers:
- SSID (Service Set Identifier): A single common network identifier (SSID) is used to identify the entire ESS. When users join to the Wi-Fi network, they see this label, which is readable by humans. The same SSID is used by all participating BSSs. The entire ESS appears to the client device (station) as a single logical network.
- BSSID (Basic Service Set Identifier): Each BSS (or AP) in the ESS has its own BSSID, even though the SSID is shared. The AP’s wireless MAC address is usually used to generate the machine-readable BSSID. Despite sharing the same SSID, the client can differentiate one AP from another because of its own BSSID.
Functionality and Roaming
The ESS’s main purpose is to facilitate mobility over a large area.
- Roaming: The capacity of a wireless client to travel transparently between BSS/AP service areas within the same ESS without losing connectivity is known as roaming, and it is supported by ESS. A common term for this is “jumping from one AP to another.”
- Seamless Experience: Regardless of which BSS the station is linked to, the Logical Link Control (LLC) layer sees the network in the same way. The many APs work together to guarantee that, from the client’s perspective, the service is reliable and smooth.
- Hiding Mobility: The Distribution System (DS) is essential because it conceals from everything and other stations outside the ESS the mobility of every station inside the ESS.
- Design Requirements for Roaming: The Basic Service Areas (BSAs) of each AP must overlap by at least 15% for roaming to be smooth. To avoid interference, each AP should run its BSS on a separate, non-overlapping channel.
- Reassociation: A station must complete a reassociation process with the new AP when it roams between them.
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Advantages and Disadvantages of ESS
Advantages of ESS
- Greater Coverage: Long-range wireless communication and increased coverage across wide regions are two benefits of an ESS. It can cover a big area, such as a complete office building, campus, or a whole structure. The Extended Service Area (ESA) is the total area that the ESS covers.
- Mobility and Roaming: Because ESS facilitates mobility, users can travel between locations without losing network connectivity. Within the same ESS, clients can roam between BSSs (APs) without experiencing any loss of connectivity. Logical Link Control (LLC) is transparent to this smooth wandering. It instantly “jumps” from one AP to another when a client relocates.
- Scalability: By linking several BSSs, an ESS can be expanded to cover a far greater region. More users can join without encountering network or connectivity issues because the ESS network usually has no restrictions on the number of customers who can use it. Large-scale companies, offices, and organizations typically employ ESS because it offers network coverage over these vast regions.
- Signal Quality: ESS strengthens and increases the signal over the wireless network.
- Hides Mobility: The Distribution System (DS) assists in concealing from objects and other stations outside the ESS the mobility of every station inside the ESS.
- Centralized Management: Configuring and maintaining an ESS is made easier when it is handled centrally.
Disadvantages of ESS
- Complexity: Compared to a BSS, an ESS is more complicated. Since it calls for several APs and maybe a central controller, it is difficult to design, set up, and maintain.
- Higher Cost: Because an ESS requires the deployment of numerous APs and a central controller, it may be more costly to set up and operate than a BSS.
- Higher Latency: Because there is more communication between the central controller and the numerous APs, an ESS may have a higher latency than a BSS.
- Lower Security: An ESS is regarded as less secure than a short-range BSS due to its vast coverage area.
- Roaming Issues (Handoff): While ESS allows mobility, travelling between various APs manufactured by different vendors might present problems. Additionally, the standard does not specify or ensure the handoff process, which involves moving a client’s signal from one AP/BSS to another.
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