A WLAN (Wireless Local Area Network) is a group of devices linked together by wireless within a relatively small space like a single office building or home. Three WLAN technologies were included in the original 802.11 standard: Infrared, Frequency Hopping Spread Spectrum (FHSS), and Direct Sequence Spread Spectrum (DSSS). 802.11b focused exclusively on DSSS; 802.11a/g/n also used Orthogonal Frequency Division Multiplexing (OFDM).
Wi-Fi is a certification applied to 802.11a/b/g/n products tested by the Wi-Fi Alliance, an industry consortium that promotes interoperability in heterogeneous WLANs. For example, all 802.11g products implement standard OFDM and DSSS, but only Wi-Fi certified products have proven that they correctly support a mandatory subset of features and options.
To create a WLAN, enterprises, small businesses, and home owners can purchase Wi-Fi certified Access Points (APs) and clients (laptops, phones, printers). Clients must be no more than a few hundred feet from the closest AP. Larger buildings can be covered by installing multiple APs that are connected to each other. Most WLANs are deployed indoors, but WLANs can also cover parking lots or courtyards or other local outdoor areas.
Wireless Metropolitan Area Networks (WMANs) use wireless “last mile” technologies to connect subscriber stations (customer premise equipment) to base stations (carrier network infrastructure), providing a wireless alternative to wireline Internet access technologies like DSL, cable, or fiber.
802.16 standards define several WMAN technologies that operate at various frequencies, distances, and speeds to deliver Broadband Wireless Access (BWA). The original 802.16 focused on Fixed BWA, using point to point wireless uplinks to connect subscriber networks to carrier networks and the Internet. More recently, the 802.16e amendment defined Mobile BWA to serve subscriber stations that are not fixed in place, like laptops used in cars and trains.
WiMax is a certification applied to 802.16 products tested by the WiMAX Forum. Carriers build and operate WMANs by purchasing licensed spectrum and then deploying WiMAX base stations throughout a city, region, or other designated coverage area. To use the WMAN, subscribers must purchase wireless services from a carrier. For example, Sprint recently launched a commercial WiMAX service called XOHM in Baltimore. Consumers in and around Baltimore that want to use XOHM must purchase a compatible WiMAX device and pay Sprint for air time.
Here are some key differences between WLANs and WMANs, supported by Wi-Fi and WiMAX products:
- It’s possible to use WMAN technology indoors, but 802.16 protocols are optimized for outdoor operation. It’s possible to use WLAN technology outside, but 802.11 protocols were primarily designed for indoor networks.
- Larger WLANs can be constructed using many densely-spaced Wi-Fi APs, but to blanket miles of territory with wireless, you really want to create a WMAN technology. On the other hand, using WiMAX products for communication between PCs inside the same building would be pricey and impractical–that’s precisely what WLAN technologies were created for.
- Most office and home WLANs are composed of Wi-Fi products operating in unlicensed spectrum — channels freely available for use by anyone. WiMAX products most often operate in spectrum licensed to wireless carriers who use them to deliver commercial BWA services.
The bottom line is that WLANs and WMANs are complementary network architectures, supported by standard technologies that were designed for very different environments and purposes. This is why your next laptop may well include both Wi-Fi and Mobile WiMAX adapters. Use the Wi-Fi adapter to connect to your office or home WLAN free-of-charge, but use the WiMAX adapter when you’re on the go to reach the Internet through a carrier’s WMAN.
Resource from http://searchnetworking.techtarget.com/
----------------------------------------------------------------------------------------------------------------------------------------------------------------------
Next Generation Networks
As we continually churn out more and more data that must be transmitted over our networks, the challenge of handling the onslaught fuels research and development of Next Generation Networks. A Next Generation Network is usually defined as a change in the core network technology to a packet-switched network. Let’s review a little of the background of telecommunications networks and then take a look at some of the key features of Next Generation Networks (NGNs).
Circuit-switched vs. Packet-switched
Telecommunication networks were originally designed for voice traffic. A person calling another person essentially creates a complete circuit from one phone to the other. The switch identifies which path the circuit should take and assigns that circuit to the caller for the duration of the call. This type of switching is generally called a circuit-switched network.
The internet is founded on IP, so it is by nature, packet-switched. Circuit-switched networks and packet-switched networks are inherently different. In a circuit switched network, a connection between two nodes is held for the duration of the call; no other connections are possible, even if there is no traffic on the line. In a packet-switched network, there is no need to make a connection; the packets can be sent as required to other users.
The advantage of the circuit-switched network is a built in quality of service; if the switch cannot take any more traffic, then the call is not completed. Once the call is in progress, the circuit is kept until the caller hangs up. The disadvantage is that it is inefficient when there is not a constant stream of data being transmitted. In contrast, a packet switched network has (traditionally) had best effort delivery of packets, but it does not need to establish a constant connection to the other user(s).
One solution to the problems of packet-switched and circuit-switched networks is to run two different networks; the older circuit-switched type network for voice only, and a newer packet-switched network for all other data. This is fairly costly, as there are basically two separate pieces of infrastructure that need to be maintained. The obvious solution is to run only one network. An NGN is another solution to this problem.
NGN Key Components
As was mentioned above, Next Generation Networks are packet-switched and use IP at the network layer. The centre of the network is the IP multimedia service (IMS). This provides an independent platform through which access services such as 4G can use the network. The principle idea is to have seamless communication; people can be connected anywhere and anytime. A key component of this is the Session Initiation Protocol (SIP). SIP acts as a signalling protocol. It differs from other protocols such as H.323 in that it was designed by the Internet Engineering Task Force (IETF) specifically for IP. SIP is an enabling protocol that allows applications such as IPTV, VoIP and messaging to be easily integrated.
The implementation of LTE or WiMAX works towards adoption of NGNs. The reason for this is simple. LTE and WiMAX were built from the start to use an all IP core network. LTE does not have a native voice service (though several are proposed). The assumption for WiMAX and LTE is simple: voice traffic is data.
The main issue with treating voice traffic as data traffic is being able to distinguish it from other traffic. This is where technologies such as DiffServ (or DS) can be used. DS can assist in separating out traffic that has different Quality of Service requirements. An example may be separating out voice traffic, which requires a low level of packet loss but also a low delay, and web browsing traffic, which can tolerate delay but cannot tolerate data loss.
Next Generation Networks represent a significant departure from the older style of networks. There are other areas that form part of NGN, but this post touches on the critical areas. This includes the use of SIP as a signaling protocol, and some of the advantages of a Next Generation Network.
0 comments:
Post a Comment