CHAPTER III
Wireless LAN and WAN Technology
WIRLESS LAN
WIRLESS LAN
Productivity is no longer restricted to a fixed work location.
It enables people to be connect at any time and place.
Users now expect to be able to roam wirelessly.
Roaming enables a wireless device to maintain Internet access without
losing a connection.
Benefits of Wireless
Increased flexibility
Increased productivity
Reduced costs
Ability to grow and adapt to changing requirements
Cont.…
Wireless Technologies
Wireless personal-area network (WPAN) – Operates in the range of a few
feet (Bluetooth).
Wireless LAN (WLAN) – Operates in the range of a few hundred feet.
Wireless wide-area network (WWAN) – Operates in the range of miles.
Bluetooth – An IEEE 802.15 WPAN standard; uses a device-pairing
process to communicate over distances up to 100m.
Wi-Fi (wireless fidelity) – An IEEE 802.11 WLAN standard; provides
network access to the users.
Cellular broadband – Consists of various corporate, national, and
international organizations using service provider cellular access to provide
mobile broadband network connectivity.
Satellite Broadband – Provides network access to remote sites through the
use of a directional satellite dish.
Cont.…
802.11 Standards
Comparing WLANs to LANs
Wireless NICs
Wireless deployment requires:
– End devices with wireless NICs
– Infrastructure device, such as a wireless router or
wireless AP
Wireless Router
A home user typically interconnects wireless devices using a small,
integrated wireless router.
These serve as: access point, Ethernet switch, Router
Small Wireless Deployment Solutions
Cont.
Wireless Antennas
• Omnidirectional Wi-Fi Antennas – Factory Wi-Fi gear often uses
basic dipole antennas, also referred to as “rubber duck” design, similar
to those used on walkie-talkie radios. Omnidirectional antennas
provide 360-degree coverage.
• Directional Wi-Fi Antennas – Directional antennas focus the radio
signal in a given direction, which enhances the signal to and from the
AP in the direction the antenna is pointing.
• Yagi antennas – Type of directional radio antenna that can be used for
long-distance Wi-Fi networking.
Wi-Fi Association Parameters
SSID – Unique identifier that wireless clients use to distinguish between
multiple wireless networks in the same vicinity.
Password – Required from the wireless client to authenticate to the AP.
Sometimes called the security key.
Network mode/standard – Refers to the 802.11a/b/g/n/ac/ad WLAN standards.
APs and wireless routers can operate in a mixed mode; i.e., it can simultaneously
use multiple standards.
Security mode – Refers to the security parameter settings, such as wired
equivalent privacy (WEP), wireless protected access (WPA), or WPA2.
Channel settings – Refers to the frequency bands used to transmit wireless data.
Discovering APs
Passive mode
AP advertises its service by sending broadcast message containing the SSID,
supported standards, and security settings.
The message’s primary purpose is to allow wireless clients to learn which
networks and APs are available in a given area.
Active mode
Wireless clients must know the name of the SSID.
Wireless client initiates the process by broadcasting its request frame on
multiple channels.
The request includes the SSID name and standards supported of a AP.
Authentication
Open authentication – A NULL authentication where the wireless client says
“authenticate me” and the AP responds with “yes.” Used where security is not
concerned.
Shared key authentication – Technique is based on a key that is pre-shared
between the client and the AP.
WAN
Why we Choose a WAN?
Operates beyond the geographic scope of a LAN
Used to interconnect the enterprise LAN to remote LANs in branch site.
Owned by a service provider
Organization must pay a fee to use the provider’s services to connect sites
Are WANs Necessary?
Businesses require communication among geographically separated sites.
Regional or branch offices must be able to communicate and share data.
Organizations must share information with other customer organizations.
Computer users must send and receive data across increasingly larger
distances.
Customer communicate over the Internet with banks, stores, and a
variety of providers of goods and services.
Students do research by accessing library indexes and publications
located in other parts of the country and in other parts of the world.
WANs - Data Link Encapsulation
The data link layer protocols define how data is
encapsulated for transmission to remote sites, and the
mechanisms for transferring the resulting frames.
A variety of different technologies are used, such as, Frame
Relay or Asynchronous Transfer Mode (ATM).
These protocols use the same basic framing mechanism,
high-level data link control (HDLC), an ISO standard, or
one of its sub-sets.
Circuit Switched
When a subscriber makes a telephone call, the dialed number is used to set
switches in the exchanges along the route of the call so that there is a
continuous circuit from the originating caller to that of the called party.
The internal path taken by the circuit between exchanges is shared by a
number of conversations.
Time division multiplexing (TDM) is used to give each conversation a share
of the connection in turn.
Packet Switching
Packet-switched describes the type of network in which relatively
small units of data called packets are routed through a network
based on the destination address contained within each packet.
Packet Switching allows the same data path to be shared among
many users in the network.
Most traffic over the Internet uses packet switching and the Internet
is basically a connectionless network.
Frame Relay
Frame Relay differs from other in several aspects.
Most importantly, it is a much simpler protocol that works at the data
link layer rather than the network layer.
Frame Relay implements no error or flow control.
The simplified handling of frames leads to reduced latency, and
measures taken to avoid frame build-up at intermediate switches help
reduce jitter.
Frame Relay provides permanent shared medium bandwidth
connectivity that carries both voice and data traffic.
Asynchronous Transfer Mode (ATM)
ATM has data rates beyond 155 Mbps.
It is a technology that is capable of transferring voice, video, and data
through private and public networks.
ATM cells are always a fixed length of 53 bytes.
Small, fixed-length cells are well suited for carrying voice and video
traffic because this traffic is intolerant of delay.
Video and voice traffic do not have to wait for a larger data packet to
be transmitted.
A typical ATM line needs almost 20% greater bandwidth than Frame
Relay to carry the same volume of network layer data
Digital Subscriber Line(DSL) Technology
DSL technology is a broadband technology that uses existing twisted-pair
telephone lines to transport high-bandwidth data to service subscribers.
It allows the local loop line to be used for normal telephone voice
connection and an always-on connection for instant network connectivity.
The two basic types of DSL technologies are asymmetric (ADSL) and
symmetric (SDSL).
All forms of DSL service are categorized as ADSL or SDSL and there are
several varieties of each type.
Asymmetric service provides higher download or downstream bandwidth to
the user than upload bandwidth.
Symmetric service provides the same capacity in both directions.
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