Fulbond Digital System Ltd.

 

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Discussion Subject

 

Subject: About 11 Mb Wireless LAN　    

Description: Basic FAQ

 

Question and Answer

Question: What is Building-to-building connectivity?

 

Answer: Where regulations permit, you can establish high-speed, license-free connections between separate Local Area Networks (LANs). Connections that can be set up quickly, and are very cost-effective with wired alternatives, saving you the expenditure of a leased line.

All you need are two Access Points. Using the directional antennas, typically attached to facing windows, you can create line-of-sight connections.

 

Question: What is "Roaming”? And how does it work?

Answer: Roaming is the ability of an untethered portable computer user to communicate continuously while moving freely throughout an area greater than that covered by a single access point.

Before using the roaming function, the workstation must make sure that it is the same channel number with the Access Point of dedicated coverage area.

To achieve true seamless connectivity, the wireless LAN must incorporate a number of different functions. Each node and access point, for example, must always acknowledge receipt of each message. Each node must maintain contact with the wireless network even when not actually transmitting data.

Achieving these functions simultaneously requires a dynamic RF networking technology that links access points and nodes. In such a system, the user’s end node undertakes a search for the best possible access to the system. First, it evaluates such factors as signal strength and quality, as well as the message load currently being carried by each access point and the distance of each access point the wired backbone. Based on that information the node next selects the right access point and registers its address.

Communications between end node and host computer can then be transmitted up and down the backbone. As the user moves on, the end node’s RF transmitter regularly checks the system to determine whether it is in touch with the original access point or whether it should seek a new one. When a node no longer receives acknowledgment from its original access point, it undertakes a new search. Upon finding a new access point, it then reregisters, and the communication process continues.

Question: What is DSSS? What is FSSS? And what are their differences?

Answer: Frequency-hopping spread-spectrum (FHSS) uses a narrowband carrier that changes frequency in a pattern that is known to both transmitter and receiver. Properly synchronized, the net effect is to maintain a single logical channel. To an unintended receiver, FHSS appears to be short-duration impulse noise.
Direct-sequence spread-spectrum (DSSS) generates a redundant bit pattern for each bit to be transmitted. This bit pattern is called a chip (or chipping code). The longer the chip, the greater the probability that the original data can be recovered. Even if one or more bits in the chip are damaged during transmission, statistical techniques embedded in the radio can recover the original data without the need for retransmission. To an unintended receiver, DSSS appears as low-power wideband noise and is rejected (ignored) by most narrowband receivers.
Most wireless LAN vendors have been adopting DSSS technology after considering the trade off between cost and performance, and so does Fulbond.

Question: What is Spread Spectrum?

Answer: Spread Spectrum technology is a wideband radio frequency technique developed by the military for use in reliable, secure, mission-critical communications systems. And Spread-Spectrum is designed to trade off bandwidth efficiency for reliability, integrity, and security. In other words, more bandwidth is consumed than in the case of narrowband transmission, but the trade off produces a signal that is, in effect, louder and thus easier to detect, provided that the receiver knows the parameters of the spread-spectrum signal being broadcast. If a receiver is not tuned to the right frequency, a spread-spectrum signal looks like background noise. There are two main alternatives, Direct Sequence Spread Spectrum (DSSS) and Frequency Hopping Spread Spectrum (FHSS)

Question: What is ISM band?

Answer: The FCC and their counterparts outside of the U.S. have set aside bandwidth for unlicensed use in the so-called ISM (Industrial, Scientific and Medical) band. Spectrum in the vicinity of 2.4 GHz, in particular, is being made available worldwide. This presents a truly revolutionary opportunity to place convenient high speed wireless capabilities in the hands of users around the globe.

Question: What is IEEE 802.11 standard? How about the approach of Airbond to IEEE 802.11?

Answer: The IEEE 802.11 Wireless LAN standards subcommittee, which is formulating a standard for the industry. The objective is to enable wireless LAN hardware from different manufacturers to interoperate.

Airbond is designed to meet the specifications of the IEEE 802.11 wireless LAN standard draft 5. The IEEE 802.11 will be ratified in June of this year. To ensure investment protection and future interoperability with other standard compliant wireless LAN products. Fulbond will provide new operating software for users to upgrade to the final version of the standard (when ratified).

Question: What is Ad hoc?

Answer: An Ad hoc wireless LAN is a group of computers, each with an Airbond adapter, connected as an independent wireless LAN. Ad hoc wireless LAN is applicable at a departmental scale for a branch or SOHO operation.

Question: What is "Infrastructure"?

Answer: An integrated wireless and wired LAN is called an Infrastructure configuration. Infrastructure is applicable to enterprise scale for wireless access to central database, or wireless application for mobile workers.

Question: What is ESS ID?

Answer: An Infrastructure configuration could also support roaming capability for mobile workers. More than one BSS can be configured as an Extended Service Set (ESS) User within an ESS could foam freely between BSSs while served as a continuous connection to the network Airbond stations and Access Points within an ESS must be configured with the same ESS ID and the same radio channel.

Question: What is BSS ID?

Answer: A specific Ad hoc LAN is called a Basic Service Set (BSS). Computers in a BSS must be configured with the same BSS ID.

Question: What is the mode that Fulbond PC Card supports for indoor use?

Answer: Fulbond PC Card supports for two modes:
1.Infrastructure: Wireless clients use Access Points to construct wireless local network and communicate with wired clients and wireless clients.
2.Ad-hoc: Wireless client work with each other wireless clients and construct wireless local network without Access Point.

Question: What is the mode that Fulbond Access Point supports for indoor and outdoor use?

Answer: Fulbond Access Point supports for four modes:
1.Access point: AP only works as a bridge to communicate between Ethernet LAN and Wireless Client.
2. Access Point and repeater function enabled: AP works as a bridge to communicate between Ethernet LAN and Wireless Client. AP also can use radio to communicate with other AP if repeater function is enabled.
3. Inter-building (Point to Point): Two Access Points can use radio to communicate.
4. Multi-point to Multi-point: Several Access Points can use radio to communicate with each other.

 

Question: What is Fragmentation Mechanism and what is the benefit for the customers?

 

Answer: Fragmentation mechanism is used for improving the efficiency when high traffic flows along in the wireless network. If customers always let your 11M products transmit large files in wireless network, they can set the Fragmentation Threshold and the mechanism will split the packet that packet size exceeds the value customers set.

 

Question: What is RTS Mechanism?

 

Answer: RTS mechanism is used for avoiding the “Hidden Node Problem”. A “Hidden Node Problem” is that the collision may happen in wireless network when two wireless nodes can’t see each other and send the packets concurrently. RTS implements a mechanism to reduce collision of hidden nodes, but some throughput drop is expected.

 

Question: What is multi-path fading?

Answer: When you speak in a large building you experience more echoes then when you speak in a small room. The RF signal suffers from the same phenomenon. The echoes are actually multiple reflections of the original radio signal that can be detected by the receiver. An environment that has severe echoes is said to have a “delay spread”.

Question: What is multi-channel roaming (MCR) and what is the benefit for the customer?

Answer: In the existing wireless system, roaming is supported, but only if all cells are on the same frequency channel. With the new product, roaming between cells with different frequency channels is also possible. The roaming client station automatically switches to the frequency channel of the Access Point, which gives best link quality. The advantage is that you can now exploit the capacity of 3 independent channels, and segment your network, instead of sharing one frequency channel with multiple cells. This allows more users to use the wireless network, without jeopardizing response time or throughput.

Question: What security is provided with the XI-Series products?

Answer: The XI-Series products use the highly secure Direct Sequence Spread Spectrum technology. On top of that, logical codes are used to prevent messages of one network to be interpreted by another network. On the access point, the access of the mobile stations can be regulated: in the access control feature the user can list exactly those mobile stations that are allowed to connect to the infrastructure network. As an option, IEEE defined an encryption based privacy mechanism (RC4), to provide protection against eavesdropping. This Wired Equivalent Privacy (WEP) will be provided as an option at a later date.

Question: What are its operation frequency/operation channels?

Answer: 2.412~2.462 GHz (N.America)/11 channels;
2.412~2.472 GHz (Japan TELEC)/13 channels;
2.412~2.472 GHz, 2.497GHz (Japan ARIB)/14 channels;
2.412~2.472 (Europe ETSI)/13 channels;
2.457~2.462 GHz(Spain)/2 channels;
2.457~2.472 GHz (France)/4 channels.

Question: What protocol does XI-series products support?

Answer: It supports CSMA/CA+ACK (per IEEE802.11b Spec.)

Question: What modulation does XI-series products use?

Answer: Direct Sequence Spread Spectrum (CCK, DQPSK, DBPSK). CCK, which is based on Direct Sequence Spread Spectrum Technology (DSSS), works with complex code words of 8 chips long and will provide speeds of 11 and 5.5 Mbit/s, using the same bandwidth as the 2 Mbit/s DSSS 802.11 standard.

 

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