L21. What is user mobility and how is it implemented in WLAN vs cellular networks?

Question 1

What is user mobility?

Answer 1

User mobility refers to the ability of a user to maintain seamless network connectivity while moving from one location to another.

Question 2

Why is user mobility important?

Answer 2

User mobility is important in modern networking as it ensures continuous access to network services without interruption.

Question 3

How is user mobility implemented in WLAN?

Answer 3

In WLANs, user mobility is managed primarily through a process called handoff or roaming.

Question 4

What is a handoff?

Answer 4

When a user moves out of the range of one Access Point (AP) and into the range of another, the device must switch its connection from the first AP to the second. This process is known as a handoff.

Question 5

How does the handoff process work in a WLAN?

Answer 5

1. Scanning: The device scans for available APs by sending probe requests and receiving probe responses.
2. Authentication: The device authenticates with the new AP, which may involve security protocols like WPA2.
3. Re-association: The device sends a re-association request to the new AP, which responds with a re-association response, completing the handoff.

Question 6

What is seamless roaming?

Answer 6

Seamless roaming is when the handoff process is optimized to be quick enough that users do not notice any interruption. Technologies like Fast BSS Transition (802.11r) and pre-authentication help minimize the delay.

Question 7

How is user mobility in cellular networks different from user mobility in WLANs?

Answer 7

Cellular networks, such as those used in mobile phones, implement user mobility on a much larger scale and with more sophisticated mechanisms. Handoffs are more complex due to the broader coverage and higher speed of user movement.

Question 8

What is the difference between hard and soft handoff?

Answer 8

Hard Handoff was used in older networks (2G and early 3G), where the connection to the current cell was broken before a new connection is established.
Soft Handoff is used in newer technologies (CDMA, LTE), where the device simultaneously connects to multiple cells during the transition to avoid any drop in connection.

Question 9

What are the types of handoffs used in cellular networks?

Answer 9

1. Intra-cell Handoff: Occurs within the same cell but between different frequencies or channels.
2. Inter-cell Handoff: Occurs between different cells, managed by the cellular network’s base stations and the core network.
3. Inter-system Handoff: Involves transitioning between different types of networks (e.g., moving from a 4G to a 5G network).

Question 10

What are the differences between WLAN and cellular mobility?

Answer 10

1. Scale and Speed: Cellular networks handle higher speeds and larger areas compared to WLANs, necessitating more complex handoff mechanisms.
2. Infrastructure: Cellular networks have a more centralized infrastructure with dedicated mobility management entities, whereas WLANs often rely on decentralized APs with optional centralized controllers.
3. Technology: Cellular networks use a combination of hard and soft handoffs and are designed to maintain connections over large geographic areas and at high speeds. WLANs primarily focus on localized mobility within buildings or campuses.