Wireless Router

Introduction

A wireless router is a network device that performs the functions of a router but also includes the functions of a wireless access point. It can function in a wired LAN, a wireless only LAN, or a mixed wired/wireless network. Most current wireless routers have the following characteristics:

• -LAN ports, which function in the same manner as the ports of a network switch
• -A WAN port, to connect to a wider area network. The routing functions are filtered using this port. If it is not used, many functions of the router will be bypassed.
• -Wireless antennae. These allow connections from other wireless devices (NICs (network interface cards), wireless repeaters, wireless access points, and wireless bridges, for example).

The wireless functions operate as a separate nested "mini-LAN" within the router. The devices that connect wirelessly use the wireless router as their hub, and the wireless router presents that "mini-LAN" as a single device to the rest of the LAN.

Wireless routers, access points, and bridges are available that utilize each of the commonly used wireless frequencies (used in the Wireless-B, Wireless-A (and -G), and Wireless-N standards). The frequency bands for these wireless standards can be used license-free in most countries.

Wireless routers can work with devices in a point-to-point mode, but more commonly functions in a point to multipoint mode.

Wireless devices used that communicate with the wireless router must be set to the same service set identifier (SSID) and radio channel.

Netbooting Wirelessly

Unless you have a wireless card with a PXE-ROM chip built into it, it is not easy to directly netboot over a wireless connection. BIOS-based PXE algorithms usually only search for a wired NIC card to be used in a PXE netboot.

Some users have cleverly connected a Wireless Bridge (i.e. a wireless router or wireless access point set to the "bridge" mode) to the wired NIC card in their PC. The PC then netboots through the wired Ethernet NIC as usual, but the data is then transmitted from the NIC to the Wireless AP/Router connected to it and then wirelessly "across the bridge" to the central Wireless Router.

This solution works pretty well, but of course you must have two Wireless Access Points/Routers (one on each side of the "bridge"). Still, this is sometimes easier than running extra Ethernet cables throughout your home.

Wirless Networks

Wireless network

Wireless network refers to any type of computer network that is wireless, and is commonly associated with a telecommunications network whose interconnections between nodes is implemented without the use of wires, such as a computer network (a type of communications network).[1] Wireless telecommunications networks are generally implemented with some type of remote information transmission system that uses electromagnetic waves, such as radio waves, for the carrier and this implementation usually takes place at the physical level or "layer" of the network.

Types

Wireless Local Area Network (WLAN) is similar to other wireless devices and uses radio instead of wires to transmit data back and forth between computers on the same network.

• Wi-Fi: Wi-Fi is a commonly used wireless network in computer systems which enable connection to the internet or other machines that have Wi-Fi functionalities. Wi-Fi networks broadcast radio waves that can be picked up by Wi-Fi receivers that are attached to different computers or mobile phones.
• Fixed wireless data : Fixed wireless data is a type of wireless data network that can be used to connect two or more buildings together in order to extend or share the network bandwidth without physically wiring the buildings together.

Wireless MAN

Wireless Metropolitan area networks are type of wireless network that connects several Wireless LANs.

The IEEE 802-2001 standard describes a MAN as being:

A MAN is optimized for a larger geographical area than a LAN, ranging from several blocks of buildings to entire cities. MANs can also depend on communications channels of moderate-to-high data rates. A MAN might be owned and operated by a single organization, but it usually will be used by many individuals and organizations. MANs might also be owned and operated as public utilities. They will often provide means for internetworking of local networks. Metropolitan area networks can span up to 50km, devices used are modem and wire/cable

Implementation

Some technologies used for this purpose are ATM, FDDI, and SMDS. These older technologies are in the process of being displaced by Ethernet-based MANs (e.g. Metro Ethernet) in most areas. MAN links between LANs have been built without cables using either microwave, radio, or infra-red laser links. Most companies rent or lease circuits from common carriers due to the fact that laying long stretches of cable can be expensive.

DQDB, Distributed Queue Dual Bus, is the Metropolitan Area Network standard for data communication. It is specified in the IEEE 802.6 standard. Using DQDB, networks can be up to 30 miles (50km) long and operate at speeds of 34 to 155 Mbit/s.

Several notable networks started as MANs, such as the Internet peering points MAE-West, MAE-East, and the Sohonet media network

Mobile devices networks

• Global System for Mobile Communications (GSM): The GSM network is divided into three major systems which are :the switching system, the base station system, and the operation and support system (Global System for Mobile Communication (GSM)). The cell phone connects to the base system station which then connects to the operation and support station; it then connects to the switching station where the call is transferred where it needs to go (Global System for Mobile Communication (GSM)). This is used for cellular phones, is the most common standard and is used for a majority of cellular providers.[3]
• Personal Communications Service (PCS): PCS is a radio band that can be used by mobile phones in North America. Sprint happened to be the first service to set up a PCS.
• D-AMPS: D-AMPS, which stands for Digital Advanced Mobile Phone Service, is an upgraded version of AMPS but it is being phased out due to advancement in technology. The newer GSM networks are replacing the older system.

Wireless networks have had a significant impact on the world as far back as World War II. Through the use of wireless networks, information could be sent overseas or behind enemy lines easily, effieciently and more reliably. Since then wireless networks have continued to develop and its uses have significantly grown. Cellular phones are part of huge wireless network systems. People use these phones daily to communicate with one another. Sending information over seas is possible through wireless network systems using satellites and other signals to communicate across the world. Emergency services such as the police department utilize wireless networks to communicate important information quickly. People and businesses use wireless networks to send and share data quickly whether it be in a small office building or across the world.^[4]

Another important use for wireless networks is as an inexpensive and rapid way to be connected to the Internet in countries and regions where the telecom infrastructure is poor or there is a lack of resources, like most developing countries.

Compatibility issues also arise when dealing with wireless networks. Different components not made by the same company may not work together, or might require extra work to fix compatibility issues. Wireless networks are typically slower than those that are directly connected through an Ethernet cable.

A wireless network is more vulnerable because anyone can try to break into a network broadcasting a signal. Many networks offer WEP -Wired Equivalent Privacy- security systems which have been found to be vulnerable to intrusion. Though WEP does block some intruders, the security problems have caused some businesses to stick with wired networks until security can be improved. Another type of security for wireless networks is WPA - Wi-Fi Protected Access. WPA provides more security to wireless networks than a WEP security set up. The use of firewalls will help with security breaches which can help to fix security problems in some wireless networks that are more vulnerable.

Network bridge

Network bridge

A network bridge connects multiple network segments at the data link layer (layer 2) of the OSI model, and the term layer 2 switch is often used interchangeably with bridge. Bridges are similar to repeaters or network hubs, devices that connect network segments at the physical layer, however a bridge works by using bridging where traffic from one network is managed rather than simply rebroadcast to adjacent network segments. In Ethernet networks, the term "bridge" formally means a device that behaves according to the IEEE 802.1D standard—this is most often referred to as a network switch in marketing literature.
Since bridging takes place at the data link layer of the OSI model, a bridge processes the information from each frame of data it receives. In an Ethernet frame, this provides the MAC address of the frame's source and destination. Bridges use two methods to resolve the network segment that a MAC address belongs to.
Transparent bridging – This method uses a forwarding database to send frames across network segments. The forwarding database is initially empty and entries in the database are built as the bridge receives frames. If an address entry is not found in the forwarding database, the frame is rebroadcast to all ports of the bridge, forwarding the frame to all segments except the source address. By means of these broadcast frames, the destination network will respond and a route will be created. Along with recording the network segment to which a particular frame is to be sent, bridges may also record a bandwidth metric to avoid looping when multiple paths are available. Devices that have this transparent bridging functionality are also known as adaptive bridges.
Source route bridging – With source route bridging two frame types are used in order to find the route to the destination network segment. Single-Route (SR) frames comprise most of the network traffic and have set destinations, while All-Route(AR) frames are used to find routes. Bridges send AR frames by broadcasting on all network branches; each step of the followed route is registered by the bridge performing it. Each frame has a maximum hop count, which is determined to be greater than the diameter of the network graph, and is decremented by each bridge. Frames are dropped when this hop count reaches zero, to avoid indefinite looping of AR frames. The first AR frame which reaches its destination is considered to have followed the best route, and the route can be used for subsequent SR frames; the other AR frames are discarded. This method of locating a destination network can allow for indirect load balancing among multiple bridges connecting two networks. The more a bridge is loaded, the less likely it is to take part in the route finding process for a new destination as it will be slow to forward packets. A new AR packet will find a different route over a less busy path if one exists. This method is very different from transparent bridge usage, where redundant bridges will be inactivated; however, more overhead is introduced to find routes, and space is wasted to store them in frames. A switch with a faster backplane can be just as good for performance, if not for fault tolerance.
Advantages of network bridges

• Self configuring
• Primitive bridges are often inexpensive
• Reduce size of collision domain by microsegmentation in non switched networks
• Transparent to protocols above the MAC layer
• Allows the introduction of management - performance information and access control
• LANs interconnected are separate and physical constraints such as number of stations, repeaters and segment length don't apply

Disadvantages of network bridges

• Does not limit the scope of broadcasts
• Does not scale to extremely large networks
• Buffering introduces store and forward delays - on average traffic destined for bridge will be related to the number of stations on the rest of the LAN
• Bridging of different MAC protocols introduces errors
• Because bridges do more than repeaters by viewing MAC addresses, the extra processing makes them slower than repeaters
• Bridges are more expensive than repeaters

Bridging versus routing

Bridging and Routing are both ways of performing data control, but work through different methods. Bridging takes place at OSI Model Layer 2 (Data-Link Layer) while Routing takes place at the OSI Model Layer 3 (Network Layer). This difference means that a bridge directs frames according to hardware assigned MAC addresses while a router makes its decisions according to arbitrarily assigned IP Addresses. As a result of this, bridges are not concerned with and are unable to distinguish networks while routers can.
When designing a network, you can choose to put multiple segments into one bridged network or to divide it into different networks interconnected by routers. If a host is physically moved from one network area to another in a routed network, it has to get a new IP address; if this system is moved within a bridged network, it doesn't have to reconfigure anything.

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Types of Routers

Types of routers

Routers may provide connectivity inside enterprises, between enterprises and the Internet, and inside Internet Service Providers (ISP). The largest routers (for example the Cisco CRS-1 or Juniper T1600) interconnect ISPs, are used inside ISPs, or may be used in very large enterprise networks. An example of an enterprise router would be the Cisco 7600 (pictured above). The smallest routers provide connectivity for small and home offices (for example the Linksys BEFSR41).
Routers intended for ISP and major enterprise connectivity will almost invariably exchange routing information with the Border Gateway Protocol. RFC 4098[3] defines several types of BGP-speaking routers:

Routers for Internet connectivity and internal use

* Provider Edge Router: Placed at the edge of an ISP network, it speaks external BGP (eBGP) to a BGP speaker in another provider or large enterprise Autonomous System (AS).
* Subscriber Edge Router: Located at the edge of the subscriber's network, it speaks eBGP to its provider's AS(s). It belongs to an end user (enterprise) organization.
* Inter-provider Border Router: Interconnecting ISPs, this is a BGP speaking router that maintains BGP sessions with other BGP speaking routers in other providers' ASes.
* Core router: A router that resides within the middle or backbone of the network rather than at its periphery.

Within an ISP: Internal to the provider's AS, such a router speaks internal BGP (iBGP) to that provider's edge routers, other intra-provider core routers, or the provider's inter-provider border routers.
"Internet backbone:" The Internet does not have a clearly identifiable backbone, as did its predecessors. See default-free zone (DFZ). Nevertheless, it is the major ISPs' routers that make up what many would consider the core. These ISPs operate all four types of the BGP-speaking routers described here. In ISP usage, a "core" router is internal to an ISP, and used to interconnect its edge and border routers. Core routers may also have specialized functions in virtual private networks based on a combination of BGP and Multi-Protocol Label Switching (MPLS)[4].

Small Office Home Office (SOHO) connectivity

Main article: Residential gateway

Residential gateways (often called routers) are frequently used in homes to connect to a broadband service, such as IP over cable or DSL. A home router may allow connectivity to an enterprise via a secure Virtual Private Network.

While functionally similar to routers, residential gateways use network address translation instead of routing. Instead of connecting local computers to the remote network directly, a residential gateway must make local computers appear to be a single computer.

Enterprise Routers

All sizes of routers may be found inside enterprises. While the most powerful routers tend to be found in ISPs, academic and research facilities, as well as large businesses, may need large routers.

A three-layer model is in common use, not all of which need be present in smaller networks [5].

Access

Access routers, including SOHO, are located at customer sites such as branch offices that do not need hierarchical routing of their own. Typically, they are optimized for low cost.

Distribution

Distribution routers aggregate traffic from multiple access routers, either at the same site, or to collect the data streams from multiple sites to a major enterprise location. Distribution routers often are responsible for enforcing quality of service across a WAN, so they may have considerable memory, multiple WAN interfaces, and substantial processing intelligence.

They may also provide connectivity to groups of servers or to external networks. In the latter application, the router's functionality must be carefully considered as part of the overall security architecture. Separate from the router may be a Firewall or VPN concentrator, or the router may include these and other security functions.

When an enterprise is primarily on one campus, there may not be a distinct distribution tier, other than perhaps off-campus access. In such cases, the access routers, connected to LANs, interconnect via core routers.

Core

In enterprises, core router may provide a "collapsed backbone" interconnecting the distribution tier routers from multiple buildings of a campus, or large enterprise locations. They tend to be optimized for high bandwidth.

When an enterprise is widely distributed with no central location(s), the function of core routing may be subsumed by the WAN service to which the enterprise subscribes, and the distribution routers become the highest tier.

Router

Router is a device to connect networks with each other.It blocks broadcasting & allows point to point communication there by reducing traffic on the network & works on the network layer.

A Router is a layer 3 network device that moves data between different network segments and can look into a packet header to determine the best path for the packet to travel. Routers can connect network segments that use different protocols.

They also allow all users in a network to share a single connection to the Internet or a WAN. It is used to improve network performance.Router Components (internal)ROM ROM is used to store the router's bootstrap startup program, operating system software, and power-on diagnostic tests programs. In order to perform ROM upgrades you remove and replace pluggable chips on the motherboard.Flash MemoryIt holds operating system image(s).

Flash memory is erasable, reprogrammable ROM.You can perform Cisco® IOS software upgrades without having to remove and replace chips. Flash content is retained when you switch off or restart the router.RAMRAM is used to store operational information such as routing tables, router's running configuration file. RAM also provides caching and packet buffering capabilities.

Its contents are lost when you switch off or restart the router.NVRAMNVRAM (nonvolatile RAM), is used to store the router's startup configuration file. It does not lose data when power is switched off. So the contents of the startup configuration file are maintained even when you switch off or restart the router.

Network InterfacesThe router's network interfaces are located on the motherboard or on separate interface modules. You configure Ethernet or Token Ring interfaces to allow connection to a LAN. The synchronous serial interfaces are configured to allow connection to WANs. You can also configure ISDN BRI interfaces to allow connection to an ISDN WAN..Router Components (External)A router can be configured over any of its network interfaces. You can supply configuration information to a router using:- TFTP servers : Trivial File Transfer Protocol; A simplified version of FTP that allows files to be transferred from one computer to another over a network