Introduction to WLAN Radio Transmission WLAN Topologies Access Points Bridges 802.11 IEEE & NIC Wireless Network
1- What does a WLAN stand for? A WLAN is a wireless local area network, which is the linking of two or more computers without using wires. WLAN utilizes spread-spectrum or OFDM (802.11a) modulation technology based on radio waves to enable communication between devices in a limited area. This gives users the mobility to move around within a broad coverage area and still be connected to the network.
A WLAN, just like a LAN, requires a physical medium through which transmission signals pass. Instead of using twisted-pair or fiber-optic cable, WLANs use infrared light (IR) or radio frequencies (RFs). The use of RF is far more popular for its longer range, higher bandwidth, and wider coverage.
2- Why do we need WLAN and what are its benefits? Wireless LAN is becoming more and more popular because of its convenience, High-speed connectivity, cost efficiency, and ease of integration with other networks and network components. Some of the WLAN benefits are: • Convenience: The wireless nature of such networks allows users to access network resources from nearly any convenient location within their primary networking environment. • Mobility • Reliability • Expandability • Cost Saving • Installation advantages
3- What is the Networking medium for the WLAN? Wireless connectivity uses the atmosphere as a Network medium. Wireless signals are electromagnetic waves that can travel through space. So no physical media are necessary for transmitting and receiving signals.
The ability of Radio waves to travel in great distances and be spread in covered spaces makes wireless a versatile way to build a network.
4- WLAN Components and Topologies: The various components of a Wireless LAN which should fully comply with the IEEE 802.11 standards and deliver up to 54-Mbps performance are: • Wireless Client Receiver: it is needed to connect a computing device (e.g. desktop, laptop, PDA…) to the wired networked via an access point. It includes PCMCIA, LM, PCI card….
Access points (APs): they are needed only in the Infrastructure Mode of WLANs. They provide the wireless client with a point of access into a network. They are like Ethernet switches in a wired network and operate in half-duplex mode (e.g. They either receive or transmit at any given time).
Bridges: they are used to connect two or more networks. There are currently 3 series of Cisco Bridges: The 350 Wireless Bridge (BR350), Cisco 350 Series Workgroup Bridge (WGB350), and Cisco Aironet 1400.
WLAN Antennas: adding an antenna does not increase the power of transmission but it focuses the signal in a particular direction to increase reception.
The WLAN supports four Network Topologies: • Peer-to-peer (Ad hoc) Topology • Hybrid Topology • Infrastructure Topology • Point-to-point Topology (A detailed coverage of components and topologies will be provided later in the presentation).
1- 802.11 standards: • 802.11 is the generic name of a family of standards for wireless networking. The numbering system for 802.11 comes from the IEEE (a nonprofit professional organization), who uses “802” for many networking standards like Ethernet (802.3) • 802.11 standards define rules for communication on WLAN. Popular 802.11 standards include 802.11a, 802.11b, 802.1g. • 802.11 was the original standard in this family, ratified in 1997. 802.11 defined WLANs that operate at 1-2 Mbps. This standard is obsolete today. • Each extension to the original 802.11 appends a unique letter to the name. Some important standards organizations are:
2- 802.11 Logical Architecture The IEEE 802.11 architecture has 5 components: • BSS: The basic service set (BSS) is the basic building block of an IEEE 802.11 LAN. It covers a single RF area, or cell, as indicated by the circle.
IBSS (Independent Basic Service Set): In this mode of operation, IEEE 802.11 stations communicate directly. it is also called a peer-to-peer network
DS (Distribution System): This mode is about connecting two WLAN stations physically. • ESS (Extended service set): It is defined as two or more BSSs connected by a common DS.
Roaming:it gives the wireless client the ability to move from one cell to another without losing the connection to the network.
Radio is the wireless transmission of signals, by modulation of electromagnetic waves with frequencies below those of visible light. • Radio transmissions travel in the air without requiring a medium of transport.
The wireless connection is the transfer of information over a distance without the use of electrical conductors or wires. It is generally considered to be a branch of Telecommunications.
Radio wave propagation In a vacuum, 2.4 GHz microwaves travel at the speed of light. Once started, these microwaves will continue in the direction they were emitted forever, unless they interact with some form of matter. Since WLANs are usually on earth, within the atmosphere, the microwaves are traveling in air, not in a vacuum. The signal will then face some refraction and reflection caused by obstacles like mountains, buildings…
WLAN categories WLAN products fit into two main categories: • Wireless in-building LANs • Wireless building-to-building bridging
Wireless repeater • In a place where an extended network is needed, we can use a wireless repeater that acts like an access point. • But the throughput for client devices will be low because each repeater must receive and re-transmit each packet.
Roaming As the roaming let the client move between different stations without changing the network, some steps have to be done before changing stations: • The client sends out a request for association and immediately receives a response from all access points within its coverage area. • The client decides which access point to associate. • After an association is established, the client’s MAC address drops into the table of the selected access point. • After the client roams to another access point, its MAC address drops into the tale of the new access point that sends a broadcast message. • The original access point forwards any data it had for the client to the other access point, which responds by sending the same to the client.
Access point coverage As the client roams from one access point to another, when he moves away from one access point, the data rate will decrease without losing the connection.
VLAN VLAN (virtual local area network) is a method of creating independent logical networks within a physical network. Some of the benefits and the reasons a company might have VLAN are: • Security • Increase control over multiple traffic types. • It does not pass traffic to nodes and automatically it reduces broadcasts.
Introduction A wireless access point is a device that connects wireless communication devices together to form a wireless network. The WAP usually connects to a wired network, and can relay data between wireless devices and wired devices. Several WAPs can link together to form a larger network that allows roaming.
Access Point Cabling • Plug the RJ-45 Ethernet cable into the Ethernet port on the back of the access point. • Connect the other end of the Ethernet cable to the 10/100 Ethernet LAN. • Plug the power adapter into a suitable power receptacle. • Plug the power connector into the back of the access point. At start-up, all three LEDs on the access point slowly blink amber, red, and green in sequence. The sequence takes a few minutes to complete. During normal operation, the LEDs blink green. • Follow the configuration steps to assign basic settings to the access point. The access point does not have an on/off switch. Power is applied to the unit when it is plugged in. Do not connect the Ethernet cable when the access point is powered up. Always connect the Ethernet cable before applying power to the access point.
Security Wireless access has special security considerations. Many wired networks base the security on physical access control, trusting all the users on the local network, but if wireless access points are connected to the network, anyone on the street or in the neighboring office could connect. The most common solution is wireless traffic encryption. Modern access points come with built-in encryption.
Introduction A wireless bridge is used for connecting two or more network segments separated physically, operating on the 802.11 standard. Wireless bridges usually work only in pairs or more, and can be used in two types of implementations. They are point to point link (PtP Link), or point to multi point (PtMP Links).
Bridge Cabling The 350 series bridge receives power through the Ethernet cable. The 350 series bridge power options include: • A switch with inline power, such as a Cisco Catalyst 3524-PWR-XL • An inline power patch panel, such as a Cisco Catalyst Inline Power Patch Panel • A Cisco Aironet power injector (shipped with the unit) • The WGB350, on the other hand, can only be powered with the AC power adapter supplied with the unit • The 1400 is powered using a power injector over a coaxial cable.
Always make sure to connect and disconnect the antennas only when the bridge is powered down.
1400 Series Bridge The Cisco Aironet 1400 Series Wireless Bridge is a high-performance 801.11a wireless bridge designed to connect multiple LANs in a metropolitan area.
The 1400 Series Wireless Bridge support the features below: • Support for both point-to-point or point-to-multipoint configurations • Support data rates up to 54 Mbps • Enhanced security mechanisms based on 802.11i standards • Rugged enclosure optimized for harsh outdoor environments with extended operating temperature range • Integrated or optional external antennas for flexibility in deployment.