Extending the LAN with Wireless Solutions

The following section is a summary of the major points you should be aware of in this chapter.

WLANs provide network connectivity almost anywhere
WLANs can typically be implemented at much less cost than traditional wired LANs
The wired infrastructure is based on the IEEE 802.3 standards
A wireless network uses radio waves to transmit data and connect devices
WLANs are defined in the IEEE 802.11 standards
The advantages of WLANs over wired LANs include the following:
1. Monetary Cost
2. Flexibility
3. Load Distribution
4. Redundancy

The 802.11 components are:
1. Client or Station (STA)
2. Access Point (AP)
3. Independent Basic Service Set (IBSS)
4. Basic Service Set (BSS)
5. Extended Service Set (ESS)
6. Distribution System (DS)
The wireless client or station (STA) is an appliance that interfaces with the wireless medium
The STA operates as an end user device
The wireless AP functions as a bridge between the STAs and the existing network backbone
An IBSS is a wireless network, consisting of at least two STAs and no DS
The WLAN infrastructure architecture is based on a cellular architecture
The WLAN architecture divides the system into cells, referred to as a Basic Service Set (BSS)
The BSS is controlled by a Base Station, or more commonly, an Access Point
Access Points may be interconnected using the switched network, creating an ESS
The DS allows for the interconnection of the APs of multiple cells (BSSs)
Three types of Distribution System are:
1. Integrated
2. Wired
3. Wireless

The IEEE 802 standards define two separate layers for the Data Link layer of the OSI Model
These two layers are the LLC and MAC sublayers
The IEEE 802.11 standards cover the operation of the MAC sublayer and the Physical layer
The 802.11 frame consists of a 32-byte MAC header, a variable length, and an FCS
The fields contained in the MAC header are:
1. The Frame Control Field (2 bytes in length)
2. The Duration / ID Field (2 bytes in length)
3. The Sequence Control Field (2 bytes in length)
4. The Four Address Fields (6 bytes each)
5. The Quality of Service Field (2 bytes in length)

On wired Ethernet LANs, CSMA/CD is used to detect collisions
The 802.11 standards seek to avoid, rather than to detect, collisions and thus use CSMA/CA
Collision avoidance works well when the medium is not heavily loaded
Collision avoidance requires STAs to sense the medium before sending any traffic

There are two types of coordination functions used to ensure collision free access:
1. The Distributed Coordination Function (DCF)
2. The Point Coordination Function (PCF)
The DCF is a MAC sublayer technique that employs CSMA/CA to avoid collisions
The DCF also uses an exponential random backoff algorithm to avoid collisions
The DCF is used in IEEE 802.11 networks to manage access to the Radio Frequency medium
The DCF is composed of the following two main components:
1. Interframe spaces
2. Random backoff
The IFS allow 802.11 to control which traffic gets first access to the channel
In DCF, there are two types of interframe spaces that are used. These are:
1. Short Interframe Space (SIFS)
2. DCF Interframe Space (DIFS)
The SIFS is used to separate transmissions belonging to a single dialog
The DIFS is used by a station that is ready to start a new transmission
The PCF is used by the AP to coordinate communication within the wireless network

The 802.11 standard uses three main types of frames:
1. Control Frames
2. Management Frames
3. Data Frames
The IEEE 802.11 standard uses control frames to control access to the medium
The most common control frames are:
1. Ready (Request) To Send (RTS)
2. Clear To Send (CTS)
3. Acknowledgement (ACK)
802.11 management frames enable stations to establish and maintain communications
There are several management frame subtypes, which are:
1. Association request frame
2. Association response frame
3. Disassociation frame
4. Reassociation request frame
5. Reassociation response frame
6. Probe request frame
7. Probe response frame
8. Beacon frame
9. Authentication frame
10. Deauthentication frame
Data frames are sent by any STA and contain higher layer protocol information or data

At the PHY layer, IEEE 802.11 defines a series of encoding and transmission schemes
The most common of which are the FHSS, DSSS, and OFDM
Although IR also exists at this layer, very little development of this standard has occurred
The 802.11 standards are:
1. IEEE 802.11 (original)
2. IEEE 802.11b
3. IEEE 802.11a
4. IEEE 802.11g
5. IEEE 802.11n

The Cisco Unified Wireless Network is composed of 5 interconnected elements, which are:
1. Client Devices
2. Access Points and Wireless Bridges
3. Network Unification
4. Network Management
5. Mobility Services
Client devices are secure devices that work right out of the box
Client device examples include Cisco Secure Services Client and Cisco Aironet client devices
Cisco Aironet APs provide network access for both indoor and outdoor environments
A Wireless Bridge can connect another Wireless Bridge
A Wireless Bridge can also transparently bridge two networks and connect wireless clients
Network unification integrates the CUWN into all major switching and routing platforms
Network management is used to manage the WLAN in a manner similar to the wired LAN
Mobility services provide support for unified cellular and voice over WLAN services

The Cisco Wireless LAN solution of WLCs and their associated LAPs
WLCs are responsible for system wide wireless LAN functions, such as:
1. Integrated Intrusion Prevention System (IPS)
2. Zero-Touch Deployment of Lightweight Access Points (LAPs)
3. Real-time Radio Frequency (RF) management
4. Wireless LAN Redundancy
5. Dynamic Channel Assignment for each LAP
6. Dynamic Client Load Balancing across LAPs
7. Dynamic LAP Transmit Power Optimization
8. Wireless LAN Security Management
WLCs communicate with Controller-based APs over any Layer 2 or Layer 3 infrastructure
WLCs communicate with LAPs using LWAPP or CAPWAP
LWAPP is an IETF draft protocol
CAPWAP, which is based on LWAPP, is a standard, interoperable protocol
The Cisco WLAN supports three types of roaming:
1. Intra-controller Roaming
2. Inter-controller Roaming
3. Inter-Subnet Roaming
In order to support roaming, Mobility Groups must be configured
A Mobility Group is a group of WLCs in a network with the same Mobility Group name
Lightweight Access Points (LAPs) can operate in several modes. These modes are:
1. Local Mode
2. Monitor Mode
3. REAP Mode
4. Rogue Detector Mode
5. Sniffer Mode

Extending the LAN with Wireless Solutions – Chapter Summary