the world is going to wireless …. wireless networking ccnp switch hossein shamloo

The world is going to wireless …

Wireless NetworkingCCNP Switch

Hossein Shamloo

IEEE 802.11

In IEEE 802.11 terminology, any group of wireless devices is known as a service set. The devices must share a common service set identifier (SSID), which is a text string included in every frame sent. If the SSIDs match across the sender and receiver, the two devices can communicate.

IEEE 802.11Network Types

IEEE 802.11 Network Types

A) IBSS (Independent basic service set)

The 802.11 standards allow two or more wireless clients to communicate directly witheach other, with no other means of network connectivity


B) BSS (basic service set)

An 802.11 BSS centralizes access and control over a group of wireless devices by placingan access point (AP) as the hub of the service set.

Any wireless client attempting to usethe wireless network must first arrange a membership with the AP



Requirement for membership :

■ A matching SSID ■ A compatible wireless data rate ■ Authentication credentials



Membership with the AP is called an association

The client must send an association requestmessage, and the AP grants or denies the request by sending an association replymessage



Keep in mind that regardless of the association status, any PC is capable of listeningto or receiving the frames that are sent over a wireless medium. Frames are freely availableover the air to anyone who is within range to receive them



An AP manages its wireless network, advertises its own existence so that clients can associate, and controls the communication process

For example, recall that every data frame sent successfully (without a collision) over a wireless medium must be acknowledged. The AP is responsible for sending the acknowledgment frames back to the sending stations


An AP can also uplink into an Ethernet network because it has both wireless and wired capabilities.


B) ESS (extended service set)



If APs are placed at different geographic locations, they can all be interconnectedby a switched infrastructure



In an ESS, a wireless client can associate with one AP while it is physically located near that AP. If the client later moves to a different location, it can associate with a different nearby AP. The 802.11 standards also define a method to allow the client to roam or to be passed from one AP to another as its location changes

Access Point Operation


An AP’s primary function is to bridge wireless data from the air to a normal wired network

An AP can also act as a bridge to form a single wireless link from one LAN to another over a long distance. In that case, an AP is needed on each end of the wireless link. AP-to-AP or line-of-sight links are commonly used for connectivity between buildings or betweencities

Point to Point


APs act as the central point of access


Any client attempting to use the WLAN must first establish an association with an AP

The AP can allow open access so that any client can associate, or it cantighten control by requiring authentication credentials or other criteria before allowing associations

The AP can control many aspects of its WLAN by requiring conditions to be met before clients can associate. For example, the AP can require that clients support specific data rates, specific security measures, and specific credentials during client association and …


You can think of an AP as a translational bridge, where frames from two dissimilar media are translated and then bridged at Layer 2


For example : the AP is in charge of mapping a VLAN to an SSID.

Access Point OperationFor example : the AP is in charge of mapping a VLAN to an SSID.

Wireless LAN Cells

An AP can provide WLAN connectivity to only the clients within its range

The signal range is roughly defined by the AP’s antenna pattern. In an open-air setting, this might be a circular shape surrounding an omnidirectional antenna. At least the pattern will appear as a circle on a floor plan

Wireless LAN Cells

An AP’s coverage area is called a cell

Clients within that cell can associate with the AP and use the wireless LAN

This concept is shown in Figure. One client is located outside the cell because it is beyond the AP’s signal range

Wireless LAN Cells

keep in mind that the pattern is three-dimensional, also affecting floors above and below, in a multilevel building

Wireless LAN Cells

The AP’s location must be carefully planned so that its range matches up with the coverage area that is needed

Wireless LAN Cells

Good Bad

Wireless LAN Cells

The best approach to designing an AP’s location and range or coverage area is to perform a site survey

Wireless LAN Cells

The best approach to designing an AP’s location and range or coverage area is to perform a site survey

A test AP is placed in a desirable spot while a test client moves about, taking live measurements of the signal strength and quality. The idea is to plot the AP’s range using the actual environment into which it will be placed, with the actual obstacles that might interfere with the client’s operation.

Wireless LAN Coverage Area

Suppose that a typical indoor AP cell has a radius of 100 feet covering several rooms or part of a hallway. Clients can move around within that cell area and use the WLAN from any location. However, that one cell is rather limiting because clients might need to operate in other surrounding rooms or on other floors without losing their connectivity.


To expand the overall WLAN coverage area, other cells can be placed in surrounding areas simply by distributing other APs throughout the area


The idea is to place the APs so that their cells cover every area where a client is likely to be located. In fact, their cell areas should overlap each other by a small percentage, as shown in Figure

Wireless Roaming

When a client associates with one AP, it can freely move about. As the client moves from one AP’s cell into another, the client’s association is also passed

from one AP to another.

Wireless Roaming

Moving from one AP to another is called roaming

Wireless Roaming

When a client moves from one AP to another, its association must be established with the new AP. As well, any data that the client was sending just prior to the roaming condition is also relayed from the old AP to the new AP. In this way, any client connects to the WLAN through only one AP at a time. This also minimizes the chance that any data being sent or received while roaming is lost

Wireless RoamingIf the client maintains its same IP address as it roams between APs, it undergoes Layer 2 roaming.

If the client roams between APs located in different IP subnets, it undergoesLayer 3 roaming

WLAN ArchitectureTraditional WLAN Architecture

Traditional WLAN architecture centers around the wireless access point. Each AP serves as the central hub of its own BSS, where clients located with the AP cell gain an association. The traffic to and from each client has to pass through the AP to reach any other part of the network.


Notice that even though an AP is centrally positioned to support its clients, it is quite isolated and self-sufficient. Each AP must be configured individually, although many APsmight be configured with identical network policies. Each AP also operates independently.

the AP handles its own use of radio frequency (RF) channels, clients associate withthe AP directly, the AP enforces any security policies unassisted, and so on


Cisco calls this an autonomous mode AP


Because each AP is autonomous, managing security over the wireless network can be difficult. Each autonomous AP handles its own security policies, with no central point of entry between the wireless and wired networks. That means no convenient place exists for monitoring traffic for things like intrusion detection and prevention, quality of service, bandwidth policing, and so on


In the figure, SSID A and SSID B are offered on two APs. The two SSIDs correspond to VLAN A and VLAN B, respectively. The APs must be connected to a common switched network that extends VLANs A and B at Layer 2. This is done by carrying VLANs A and B over an 802.1Q trunk link to each AP. Because SSIDs and their VLANs must be extended at Layer 2, you should consider how they are extended throughout the switched network. In Figure 15-7, SSID A and VLAN A have been shaded everywhere they appear. Naturally, they form a contiguous path that appears on both APs so that wireless clients can use SSID A in either location or while roaming between the two


This concept becomes important when you think about extending SSIDs to many APs over a larger

network

WLAN ArchitectureCisco Unified Wireless Network Architecture

Cisco has collected a complete set of functions that are integral to wireless LANs and called them the Cisco Unified Wireless Network

This new architecture offers the following capabilities, which are centralized so that they affect wireless LAN devices located anywhere in the network:

■ WLAN security ■ WLAN deployment ■ WLAN management ■ WLAN control

WLAN ArchitectureCisco UWNA Vs Legacy Model


In the Cisco unified wireless network, a lightweight access point (LAP) performs only the real-time 802.11 operation.


The management functions are all performed on a wireless LAN controller (WLC)

the world is going to wireless …. wireless networking ccnp switch hossein shamloo

Documents

wireless slide

ap slide

ethernet network

wireless medium

wireless clients

group of wireless devices

ap grants

ibss independent basic