Category Archives: WIRELESS NETWORK

Hub And Bridges

In general, a hub is the central part of a wheel where the spokes come together. The term is familiar to frequent fliers who travel through airport “hubs” to make connecting flights from one point to another. In data communications, a hub is a place of convergence where data arrives from one or more directions and is forwarded out in one or more other directions. A hub usually includes a switch of some kind. (And a product that is called a “switch” could usually be considered a hub as well.) The distinction seems to be that the hub is the place where data comes together and the switch is what determines how and where data

is forwarded from the place where data comes together. Regarded in its switching aspects, a hub can also include a router.

1) In describing network topologies, a hub topology consists of a backbone (main circuit) to which a number of outgoing lines can be attached (“dropped”), each providing one or more connection port for device to attach to. For Internet users not connected to a local area network, this is the general topology used by your access provider. Other common network topologies are the bus network and the ring network. (Either of these could possibly feed into a hub network, using a bridge.)

2) As a network product, a hub may include a group of modem cards for dial-in users, a gateway card for connections to a local area network (for example, an Ethernet or a token ring), and a connection to a line (the main line in this example).

BRIDGES

A bridge is used to connect two networks together. Just like a bridge connects two roads, this bridge can join two different networks to extend the network. Say you have two home networks, one in the basement and one upstairs. You can put a bridge in the middle of the house, and then transfer files between networks while still having two seperate networks. The only disadvantage to doing is, is that the collision domain becomes larger (more chance of packets colliding) since the network is much larger.

REPEATERS

A repeater is like a router, but is used to re-strengthen a signal over a long distance. There are analog repeaters, which can only amplify the signal and there are digital repeaters that can restore a signal to near original quality. Some hubs can act as repeaters aswell. Repeaters cannot route internet like a router can though, they are strictly used to regenerate a signal. A repeater should be used when cat5e cabling is over 300feet (100metres) in length. A wireless repeater can be placed between the router and the computer, when length is an issue and the signal is degraded.

linksys bridge

Switch

In a telecommunications network, a switch is a device that channels incoming data from any of multiple input ports to the specific output port that will take the data toward its intended destination. In the traditional circuit-switched telephone network, one or more switches are used to set up a dedicated though temporary connection or circuit for an exchange between two or more parties. On an Ethernet local area network (LAN), a switch determines from the physical device (Media Access Control or MAC) address in each incoming message frame which output port to forward it to and out of. In a wide area packet-switched network such as the Internet, a switch determines from the IP address in each packet which output port to use for the next part of its trip to the intended destination. In the Open Systems Interconnection (OSI) communications model, a switch performs the Layer 2 or Data-link layer function. That is, it simply looks at each packet or data unit and determines from a physical address (the “MAC address”) which device a data unit is intended for and switches it out toward that device. However, in wide area networks such as the Internet, the destination address requires a look-up in a routing table by a device known as a router. Some newer switches also perform routing functions (Layer 3 or the Network layer functions in OSI) and are sometimes called IP switches. On larger networks, the trip from one switch point to another in the network is called a hop. The time a switch takes to figure out where to forward a data unit is called its latency. The price paid for having the flexibility that switches provide in a network is this latency. Switches are found at the backbone and gateway levels of a network where one network connects with another and at the subnetwork level where data is being forwarded close to its destination or origin. The former are often known as core switches and the latter as desktop switches. In the simplest networks, a switch is not required for messages that are sent and received within the network. For example, a local area network may be organized in a token ring or bus arrangement in which each possible destination inspects each message and reads any message with its address. Circuit-Switching version Packet-Switching A network’s paths can be used exclusively for a certain duration by two or more parties and then switched for use to another set of parties. This type of “switching” is known as circuit-switching and is really a dedicated and continuously connected path for its duration. Today, an ordinary voice phone call generally uses circuit-switching. Most data today is sent, using digital signals, over networks that use packet-switching. Using packet-switching, all network users can share the same paths at the same time and the particular route a data unit travels can be varied as conditions change. In packet-switching, a message is divided into packets, which are units of a certain number of bytes. The network addresses of the sender and of the destination are added to the packet. Each network point looks at the packet to see where to send it next. Packets in the same message may travel different routes and may not arrive in the same order that they were sent. At the destination, the packets in a message are collected and reassembled into the original message.

switch

Network Address Translation (NAT)

NAT (Network Address Translation or Network Address Translator) is the translation of an Internet Protocol address (IP address) used within one network to a different IP address known within another network. One network is designated the inside network and the other is the outside. Typically, a company maps its local inside network addresses to one or more global outside IP addresses and unmaps the global IP addresses on incoming packets back into local IP addresses. This helps ensure security since each outgoing or incoming request must go through a translation process that also offers the opportunity to qualify or authenticate the request or match it to a previous request. NAT also conserves on the number of global IP addresses that a company needs and it lets the company use a single IP addressin its communication with the world.

NAT is included as part of a router and is often part of a corporate firewall. Network administrators create a NAT table that does the global-to-local and local-to-global IP address mapping. NAT can also be used in conjunction with policy routing. NAT can be statically defined or it can be set up to dynamically translate from and to a pool of IP addresses. Cisco’s version of NAT lets an administrator create tables that map:

  • A local IP address to one global IP address statically
  • A local IP address to any of a rotating pool of global IP addresses that a company may have
  • A local IP address plus a particular TCP port to a global IP address or one in a pool of them
  • A global IP address to any of a pool of local IP addresses on a round-robin basis

NAT is described in general terms in RFC 1631. which discusses NAT’s relationship to Classless Interdomain Routing (CIDR) as a way to reduce the IP address depletion problem. NAT reduces the need for a large amount of publicly known IP addresses by creating a separation between publicly known and privately known IP addresses. CIDR aggregates publicly known IP addresses into blocks so that fewer IP addresses are wasted. In the end, both extend the use of IPv4 IP addresses for a few more years before IPv6 is generally supported.

 

VIRTUAL PRIVATE NETWORK(VPN)

Vrtual Private Networking, or VPN, is a technology that lets people access their office’s computer network over the Internet while at home or traveling. Accessing a network in this way is referred to as remote access. (For comparison, another common form of remote access is dialing in to the office network over a telephone line.)

But VPN is useful for more than just remote access. It can also be used to link two separate offices over a distance. This is sometimes called a “persistent VPN tunnel”, or “site-to-site VPN”.

VPN for Remote Access

So why would you want to use VPN for remote access? Let’s say you want users to be able to work from home. Or maybe someone needs to retrieve a file while traveling. Without VPN, in order to make resources on the office network available to users, the network administrator would have to weaken the security of your network by opening holes in your firewall — which isn’t usually a good idea. Or the remote user would have to dial in over a phone line, sometimes incurring long-distance charges.

With VPN, the integrity of your office network remains intact, but you can allow remote users to act as part of the office network. After connecting over VPN, remote users can access files, print to printers, and generally do anything with their computers that they would be able to do in the office.

Still, using VPN is not the same as being in the office. Most office networks are pretty fast. Most Internet connections are not. Even the fastest DSL and cable connections are around one-tenth the speed of your average office LAN. This means that accessing resources on the LAN will be much slower over VPN. It would also depend on the “upstream” or upload speed of your office’s network connection. As opposed to working on files directly over the VPN connection, it is often more time-efficient to to copy them to your computer over the VPN connection. When you are done working with them you would copy them back to the file server.

How It Works

In a small office network, VPN is most frequently implemented through a router. Just about every small office that shares an Internet connection with more than one computer already has a router of some kind, but most of them don’t include VPN. For example, small office/home office (SOHO) routers by Linksys, Netgear, or D-Link are popular choices, offering DHCP, NAT, and basic security features in a single device, but they don’t always include VPN support.

Once the VPN router is in place, individual computers can be set up to connect to it from outside the network. Depending on the router and the computers involved, you might need to install software on the computers that will use VPN. Sometimes computers have the ability to connect built-in. Either way, once the hardware and software has been set up, the remote user can initiate a VPN connection.

How a VPN session is initiated depends on how the computer is connected to the Internet. Usually it works something like this: the user double-clicks on a shortcut and the VPN connection window appears. The user enters a username and password and hits “connect.” If the computer has an always-on connection like DSL or cable, the VPN connection is immediately established. If the computer dials in to an ISP in order to access the Internet, that connection is established first and then the VPN connection is established on top of that. Once users are connected to the office network over VPN, they can access files and other resources.

When users are done working, they simply disconnect the VPN connection.

VPN As a Persistent Tunnel

VPN technology can also be used to link two separate networks over the Internet so they operate as a single network. This is useful for organizations that have two physical sites. Rather than set up VPN connections on every person’s computer, the connection between the two sites can be handled by routers, one at each location. Once configured, the routers maintain a constant tunnel between them that links the two sites. In this scenario, users don’t have to do anything to initiate the VPN session because it is always on.

Security and Encryption

There are mainly two kinds of VPN: Point to Point Tunneling Protocol (PPTP) and Layer 2 Tunneling Protocol (L2TP). Both can link a remote computer to a network, but only L2TP offers strong security. If you must transmit sensitive information, do not use PPTP. Remember that when you set up VPN, you’re offering a way into your office network. To minimize the risk of unauthorized parties poking around your network, choose and enforce a strong password policy.

If you allow home users to connect to the office network via VPN, you have to consider viruses or other security threats that could come from the user’s home. One way to address this risk is by giving home users a computer that is owned and maintained by the organization, so is certified as up-to-date and virus-free.

Implementing VPN

Before you implement VPN, evaluate the benefits to your organization and weigh it against the costs of equipment, installation time, and staff training. Maybe you’re considering VPN because your executive director wants to be able to access files on the server while traveling. Maybe VPN would be a good solution. Or perhaps it would work just as well for your executive director to call the office and ask the receptionist to e-mail the file. Given the plethora of online collaboration tools and web-based technologies available now, VPN may not be the only method to access documents off site. However, VPN remains to be the industry standard that is established, scaleable, and secure. Before deciding on any of these technologies, determine the many risks and rewards first.

Once you have decided to implement VPN, determine whether you need help or not. If someone on your staff understands TCP/ IP networking well and can set up the new router, you might be set. If not, consider finding a trusted consultant to help set it up.

In order to use VPN, your Internet connection should have a static IP address. Most types of Internet connections — dial-up, DSL, and cable — provide you with a numerical address on the Internet that changes from time to time. This is called a dynamic IP address. In order to provide VPN access to remote users it is preferable to have an address that doesn’t change, a static IP. Alternately, you can use a dynamic DNS (DDNS) service that can map a domain name to a dynamic IP. There are free services that can map a fixed domain to an account, which your router can update as it obtains different IP addresses. Consult your router or firewall documentation if DDNS is supported

To obtain a static IP address for your Internet connection, talk to your Internet service provider. It may require an additional monthly fee of a few dollars. If you have a friendly ISP, sometimes you can talk it into just giving you a static IP. Occasionally, an ISP will try to sell you much more expensive DSL service, possibly bundled with equipment, when you ask about a static IP. The company might call it a “business class” of service. If the upgrade is too expensive, test the VPN functionality in a pilot phase if DDNS is supported, only then should you decide to pay for the upgrade if necessary.

 

Wireless Range Extender

wireless range extender increases the distance over which a WLAN signal can spread, overcoming obstacles and enhancing overall network signal quality. Several different forms of wireless range extenders are available. These products are sometimes called “range expanders” or “signal boosters.” The Linksys WRE54G (compare prices) 802.11g Wireless Range Expander is shown above.

A wireless range extender works as a relay or network repeater, picking up and reflecting WiFi signals from a network’s base router or access point. The network performance of devices connected through a range extender will generally be lower than if they were connected directly to the primary base station.

A wireless range extender connects wirelessly to a WiFi router or access point. However, due to the nature of this technology, most wireless range extenders work only with a limited set of other equipment. Check the manufacturer’s specifications carefully for compatiblity information.

Range Extender

Range Extender

 

Wireless Internet Video Camera

Allows video (and sometimes audio) data to be captured and transmitted across a WiFi computer network. Wireless Internet video cameras are available in both 802.11b and 802.11g varieties. The Linksys WVC54G (compare prices) 802.11g wireless camera is shown above.

Wireless Internet video cameras work by serving up data streams to any computer that connects to them. Cameras like the one above contain a built in Web server. Computers connect to the camera using either a standard Web browser or through a special client user interface provided on CD-ROM with the product. With proper security information, video streams from these cameras can also be viewed across the Internet from authorized computers.

Wi-Fi Internet video cameras can be connected to a wireless router using either an Ethernet cable or wirelessly. These products include setup software on a CD-ROM that must be installed on one computer to complete initial Wi-Fi configuration of the device.

Features that distinguish different wireless Internet video cameras from each other include:

  • resolution of the captured video images (for example, 320×240 pixel, 640×480 pixel, and other image sizes)
  • motion sensors, and the ability to send email alerts when new activity is detected and captured
  • ability to timestamp images
  • built-in microphones and/or jacks for external microphones, for audio support
  • types of WiFi security supported, such as WEP or WAP.
wireless internet camera

wireless internet camera


Wireless Print Server

It  allows one or two printers to be conveniently shared across a WiFi network. Wireless print servers for home networks generally are available in both 802.11b and 802.11g varieties.

Wireless print servers offer the following advantages:

  • Allows printers to be conveniently located anywhere within wireless network range, not tied to the location of computers
  • Does not require a computer be always turned on in order to print
  • Does not require a computer to manage all print jobs, that can bog down its performance
  • Allows administrators to change computer names and other settings without having to re-configure the network printing settings.

A wireless print server must be connected to printers by a network cable, normally USB 1.1 or USB 2.0. The print server itself can connect to a wireless router over WiFi, or it can be joined using an Ethernet cable.

Most print server products include setup software on a CD-ROM that must be installed on one computer to complete the initial configuration of the device. As with network adapters, wireless print servers must be configured with the correct network name (SSID) and encryption settings. Additionally, a wireless print server requires client software be installed on each computer needing to use a printer.

The Linksys WPS54G (compare prices) 802.11g USB wireless print server is shown. Print servers are very compact devices that include a built-in wireless antenna and LED lights to indicate status.

print server

print server

Wireless network Adapter

wireless network adapter allows a computing device to join a wireless LAN. Wireless network adapters contain a built-in radio transmitter and receiver. Each adapter supports one or more of the 802.11a, 802.11b, or 802.11g Wi-Fi standards.

Wireless network adapters also exist in several different form factors. Traditional PCI wireless adapters are add-in cards designed for installation inside a desktop computer having a PCI bus. USB wireless adapters connect to the external USB port of a computer. Finally, so-calledPC Card or PCMCIA wireless adapters insert into a narrow open bay on a notebook computer.

One example of a PC Card wireless adapter, the Linksys WPC54G (compare prices) is shown above. Each type of wireless network adapter is small, generally less than 6 inches (0.15 m) long. Each provides equivalent wireless capability according to the Wi-Fi standard it supports.

Some notebook computers are now manufactured with bulit-in wireless networking. Small chips inside the computer provide the equivalent functions of a network adapter. These computers obviously do not require separate installation of a separate wireless network .

Wireless Net. Adapter

Wireless Net. Adapter

Wireless Router

The centerpiece product of many home computer networks is a wireless router. These routers support all home computers configured with wireless network adapters (see below). They also contain a network switch to allow some computers to be connected with Ethernet cables.

Wireless routers allow cable modem and DSL Internet connections to be shared. Additionally, many wireless router products include a built-in firewall that protects the home network from intruders.

Illustrated above is the Linksys WRT54G (compare prices). This is a popular wireless router product based on the 802.11g Wi-Fi network standard. Wireless routers are small box-like devices generally less than 12 inches (0.3 m) in length, with LED lights on the front and with connection ports on the sides or back. Some wireless routers like the WRT54G feature external antennas that protrude from the top of the device; others contain built-in antennas.

Wireless router products differ in the network protocols they support (802.11g, 802.11a, 802.11b or a combination), in the number of wired device connections they support, in the security options they support, and in many other smaller ways. Generally only one wireless router is required to network an entire household.

wireless access point (sometimes called an “AP” or “WAP”) serves to join or “bridge” wireless clients to a wired Ethernet network. Access points centralize all WiFi clients on a local network in so-called “infrastructure” mode. An access point in turn may connect to another access point, or to a wired Ethernet router.

Wireless access points are commonly used in large office buildings to create one wireless local area network (WLAN) that spans a large area. Each access point typically supports up to 255 client computers. By connecting access points to each other, local networks having thousands of access points can be created. Client computers may move or “roam” between each of these access points as needed.

In home networking, wireless access points can be used to extend an existing home network based on a wired broadband router. The access point connects to the broadband router, allowing wireless clients to join the home network without needing to rewire or re-configure the Ethernet connections.

As illustrated by the Linksys WAP54G (compare prices) shown above, wireless access points appear physically similar to wireless routers. Wireless routers actually contain a wireless access point as part of their overall package. Like wireless routers, access points are available with support for 802.11a, 802.11b, 802.11g or combinations.

router

router

Wireless Network

Wireless networks utilize radio waves and/or microwaves to maintain communication channels between computers. Wireless networking is a more modern alternative to wired networking that relies on copper and/or fiber optic cabling between network devices.

A wireless network offers advantages and disadvantages compared to a wired network. Advantages of wireless include mobility and elimination of unsightly cables. Disadvantages of wireless include the potential for radio interference due to weather, other wireless devices, or obstructions like walls.

Wireless is rapidly gaining in popularity for both home and business networking. Wireless technology continues to improve, and the cost of wireless products continues to decrease. Popular wireless local area networking (WLAN) products conform to the 802.11 “Wi-Fi” standards. The gear a person needs to build wireless networks includes network adapters (NICs), access points (APs), and routers.