1.19 WAN Concepts

       A WAN is used to connect two or more local area networks (LANs). A
LAN is a privately owned comm...
(T1), 45 Mbps (T3), and
                           560.160 Mbps (T5)
ISDN                       64 Kbps – 128 Kpbs        ...
heavy. Frame relay requires less equipment and less lines than other
methods thereby making it a good option for multi-sit...
problem in this shared environment as anyone with the correct
      knowledge and experience can view unencrypted informat...
Other duties of the router:
  • It ensures that information doesn’t go where it’s not needed. This is
     crucial for kee...
shared their information over the Internet. Today, however, the Internet is
now accessible by millions of businesses and p...
firewall settings. Network administrators can program the firewall to block
certain types of traffic such as Instant Messe...
server uses its own IP address to request the page from the Internet.
When the page is returned, the proxy server forwards...
The wireless option makes sense for many school districts. There are
many factors involved in bringing the Internet and ne...
Wireless LANs and wireless WANs are not secure. The basic problem
is that information is being transmitted through the air...
southern sky is possible. Download speeds are about 8 times
            faster than dial-up modem service, with upload spe...
Dial-up services can allow teachers and other staff an opportunity to
access network resources from remote locations. In e...
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WAN Concepts

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WAN Concepts

  1. 1. 1.19 WAN Concepts A WAN is used to connect two or more local area networks (LANs). A LAN is a privately owned communications system that is designed to allow users to access and share resources (computers, printers, servers) with other users. The best known example of a WAN is the Internet itself. LANs that are interconnected by a WAN may be located in the same geographical area, such as a campus setting, or in separate geographic areas, such as different cities or regions. To provide access between different schools and to the Internet, a school district will install a district WAN. This WAN will connect all schools to each other, as well as, to the Internet via an ISP. The actual connection between the different points is handled by a provider, such as the telephone company. What type of WAN technology is used may be determined by budgetary funds and/or the options available through the ISP. When determining the cost of WAN technology, you must determine both recurring and non-recurring costs. Recurring costs include fees paid to the ISP either monthly and/or yearly, maintenance fees for equipment, management fees (if any), etc. . Non-recurring costs include the cost of equipment, installation, and set-up fees. Non-recurring costs are usually paid only once at the beginning of the service. Data travels over a WAN in two different directions, from the ISP to the building, and from the building to the ISP. The first is called the downlink because the data is being sent down (download) from the ISP, and the second is called uplink because the data is being sent up (upload) to the ISP. Different technologies offer different rates for this transmission depending on whether both directions are transmitted at the same rate. Different Technology and Transmission Speeds Technology Speeds Maximum Distance POTS – Plain Old 9.6 Kbps – 52.6 Kbps Unlimited Telephone Lines (Analog) Leased Line (digital) from 56.6 kbps & up Unlimited for example: 1.544 Mbps
  2. 2. (T1), 45 Mbps (T3), and 560.160 Mbps (T5) ISDN 64 Kbps – 128 Kpbs Unlimited Wireless 2 Mbps 25 miles Cable TV 4 Mbps Satellite 56 Kbps – 115 Kbps Unlimited Fiber 10 Mbps – 1 Gbps 1000 meters POTS (Dial-up Service): This technology relies on standard phone lines to connect to the Internet. Using current analog technology, this service runs at speeds up to 52.6 Kbps in each direction. It is a cheap and easy way to get a machine connected to the Internet quickly. It has low start-up costs and low monthly rates. The only additional equipment required on each machine that requires connectivity is a modem. LEASED LINE: Leased lines are often used for WAN connections. These lines go point-to-point with a fixed rate of speed. With a leased line, the district buys a permanent connection from the phone company either to another school or to an ISP. The district sets up a router and a CSU/DSU (Channel Service Unit/Digital Service Unit) at each school that will be connected, the leased line connects to the CSU/DSU. This establishes a network connection between the two ends of the leased line. Leased line speeds range from 56 Kbps through 560 Mbps (T5) and beyond. Typically universities and schools use a T1 line, with a speed of 1.544 Mbps, to connect the WAN. T3 lines are usually used as major arteries for connections for universities, ISPs, and large corporations. Leased lines support almost any distance. Installation costs can be high, and monthly fees are distance sensitive. Along with connecting each building, a connection needs to run to an ISP. However, leased lines used in conjunction with wireless technology may offer a more economical approach to creating a WAN. FRAME RELAY SERVICE: These are point-to-point lines that pass through a central cloud. Numerous schools could connect into one cloud. Speeds range from those mentioned above with guaranteed based speed rates and “burst” rates for periodic faster speed when the network usage is
  3. 3. heavy. Frame relay requires less equipment and less lines than other methods thereby making it a good option for multi-site networks. ISDN: Integrated Services Digital Network (ISDN) is a technology (type of phone line) that offers connections at either 64 Kbps or 128 Kbps in each direction. The basic service called Basic Rate Interface (BRI), contains two 64 Kbps data lines called B-channels, and a 16 Kbps control line called a D-channel. ISDN lines are usually metered, meaning that you pay for connect time, unlike a leased line where you pay for connection time 24/7. The use of ISDN on a WAN is very similar to that of a leased line except that a Network Terminator, Type 1 (NT-1) is used to connect to the phone line rather than a CSU/DSU. Many routers can now be purchased with ISDN connection capability. ISDN can transmit data, voice, and video at the same time on one line. This allows for multiple devices (computers, faxes, telephones) to share one line. WIRELESS: Another approach to providing network services is wireless communications to connect multiple buildings. Wireless offers high speed and minimal or no recurring costs. Start up costs for wireless technologies will be higher than for leased lines, but over the lifetime of the network, wireless will prove more cost effective. Wireless technologies require expensive towers to clear natural and man-made obstructions around the schools because all wireless communications require a clear line of sight between transmitting and receiving equipment. CABLE TV: Cable TV is another alternative to consider. Cable TV allows a district to provide WAN connectivity using the cable TV wiring. While cable TV can offer high speeds at low costs, there are several limitations that must be considered: • Television broadcasting is a one directional process. Information is not sent back to the central office when broadcasting television. New cable equipment that allows two-way communication is now available to address this issue, and many cable companies are installing upgrades to the cable TV equipment to help eliminate this problem. • Many buildings share a cable TV signal. This leads to the problem of shared capacity and security. This results in each building getting only a small part of the total bandwidth. Security can also be a
  4. 4. problem in this shared environment as anyone with the correct knowledge and experience can view unencrypted information placed on the network. In terms of cost, the cable company will charge a monthly fee for each building that connects. SATELLITE: For districts located in remote areas, where other technologies are either not available or extremely expensive, satellite connection may be the option of choice. With this technology, the district buys a satellite dish and the necessary hardware needed to connect the dish to the network. A building may have a downlink of up to 115 Kbps. While the rates for this type of connection may be much higher than other options previously discussed, this may be the best option in rural areas. FIBER: The ideal solution for a district is to connect all of its buildings with fiber-optic cables. Fiber speeds exceed 1 Gbps, allowing districts to connect WANs at high speeds immediately and to upgrade to even faster speeds in the future. Fiber can be very expensive running between $2/foot to $2.50/foot. Installation can also be expensive requiring the acquisition of land “right of way” rights. ROUTERS AND BRIDGES Routers and bridges are also covered in Sections 1.17 Ethernet Concepts. Information from these two sections is referenced here. This article will highlight a few areas of interest to these two devices as related to WAN concepts. The router connects a LAN to another LAN, a WAN or can be used to partition a larger WAN into smaller segments to increase performance. Routers operate at the network layers of the OSI model. Routers offer some level of security between the different networks. Routers determine how information gets to various destinations and translate the various protocols between various networks. Routers can also acts as barriers (security) between the local network and the WAN by filtering through various ports and protocols.
  5. 5. Other duties of the router: • It ensures that information doesn’t go where it’s not needed. This is crucial for keeping large volumes of data from clogging the connections of non-intended recipients. • Since every device on the network has its own individual and unique address, it makes sure that information makes it to the intended destination(s). A routing table is maintained internally by a router about specific routes data may take. The router has the ability to “self-learn” from these tables therefore increasing efficiency. Routing is the process of finding appropriate paths for data packets across networks as it moves throughout a LAN or WAN. The router reads the information contained in each packet or frame, uses complex network addressing procedures to determine the appropriate network destination, transmits the data to the appropriate destination. Packets destinations other than the LAN will travel out onto the WAN and continue its path through other routers until its destination is reached. Bridges are more simplistic devices than routers which have more capacity to direct traffic. Used to connect two separate LANS over a private communications link, they read the destination address of each packet and allow only necessary traffic to pass through. Traffic not allowed to pass through is forwarded to the correct segment. Hence, they can be thought of as drop or forward machines. Bridges do not analyze and/or re- route packets to the WAN destination—just “bridge” the data to the correct WAN segment. Bridges are protocol dependent while routers are not. FIREWALLS Computer networks are generally designed to do one thing: allow any computer connected to the network to freely exchange information with any other computer also connected to the same network. Internet Protocol (IP) was designed to be an open protocol that allows any IP device to freely connect to any other. In the early days of the Internet it was common for users to leave his/her files open to sharing. At this time most Internet users were professors, students, and researchers who collaborated and
  6. 6. shared their information over the Internet. Today, however, the Internet is now accessible by millions of businesses and personal users from all over the world. Security is now a major issue. In the real world, a firewall is a hardened, fire-resistant wall designed to keep a fire contained within a building. In the Internet world, a firewall is a special type of router designed to keep intruders out of a private network. A firewall disrupts free communication between trusted and non- trusted networks, attempting to manage the information flow and restrict dangerous free access. A true firewall is a computer that you connect between the Internet and your LAN which intercepts every connection and packet coming in to your LAN from the Internet. It is the TCP/IP equivalent of a “guard shack” at the physical entrance to your company. All traffic must pass through it, and the guard on duty requires proper credentials to allow anyone to pass into the facility. Consequently, a firewall works closely with a router program examining each network packet to determine whether to forward it toward its destination. Just as a guard at the entrance to your physical building limits the freedom of movements of those who should be in the building, a firewall will create some compromises on the ability of those in your building who “sit behind a firewall” to access systems outside on the Internet. But in many cases, the security is worth the tradeoff in usability, just as it is in those cases where guards and security procedures are used in physical buildings. The firewall connects a private LAN to the public Internet. Because the firewall connects between the LAN and the outside world, the firewall has no effect on normal LAN traffic. Computers on the LAN can communicate with one another with no restrictions. Most hardware-based firewalls also include a third interface called the DMZ connection (named after the demilitarized zones that divide Korea). The DMZ is used to connect Web servers, email servers, and other devices that must be freely available on the Internet. Clients on the protected LAN can access Internet resources such as Web and email servers, as long as that access is allowed by the current
  7. 7. firewall settings. Network administrators can program the firewall to block certain types of traffic such as Instant Messenger, peer file sharing, and network game programs. Client computers on the Internet can access public Web and email servers connected the firewall’s DMZ port. As traffic arrives from the Internet, the firewall inspects each packet and allows traffic into the firewall only if it was requested by a client computer on the protected LAN. Uninvited traffic coming from the Internet is ignored. There are several firewall screening methods. A simple one is to screen requests to make sure they come from acceptable domain name and IP address. A firewall implementing a packet filter looks at one packet at a time, and considers it in isolation in order to make a forwarding decision. A filtering firewall functions at the Network Layer of the OSI model. What data enters or leaves the network is determined by the rules established by the firewall software. Filtering occurs based on the type of packet, the source address, the destination address, and the port information. Packets are allowed to arrive (in) or leave (out) based on each filter rule that the network administrator creates. Each filter rule created applies only to packets that move in the direction which was specified in the rule. Therefore, there are separate rules for packets received in and packets sent out. Another type of firewall is a proxy server. A proxy server is a server that acts as an intermediary between a user and the Internet so that the network can ensure security, administrative control, and caching service. Proxy servers are usually associated with or are part of a gateway server that separates the network from the outside. Proxy servers provide these three features: 1. firewall protection and filtering 2. connection sharing 3. caching The proxy server receives requests for an Internet service (Web page) from a user. If the request is allowed based on filtering rules, the proxy server looks in its local cache (if it’s a cache server) of previously downloaded pages. If it finds the page, it returns it to the user without going to the Internet. If the page is not in the server’s cache, the proxy
  8. 8. server uses its own IP address to request the page from the Internet. When the page is returned, the proxy server forwards it on to the user. Firewall technology also serves a useful function on school networks. Firewalls allow outgoing request for Web pages (HTTP) to pass through to the public Internet, but it generally prevents messages (other than replies to those specific requests) from traveling in the opposite direction. The filtering capability of proxies allows network administrators to explicitly disallow access to any “unacceptable” domains. The functions of proxy and firewall can be in separate server programs or combined in a single package. However, network administrators often configure and deploy firewall hardware separately from proxy server hardware. WIRELESS The term wireless is used to describe telecommunications in which electromagnetic waves rather than wires carry a signal over a communication path. Today’s society has many resources available through wireless technology: cellular phone and pagers, Global Positioning Systems (GPS), remote control garage door openers, satellite television, and wireless networks. A wireless network is one where a mobile user can connect to a LAN through a wireless (radio) connection. The standard, IEEE 802.11 (Wi-Fi) specifies the technologies for wireless LANS. For a few years, 802.11b reigned supreme, gathering momentum as prices plummeted. Wi-Fi operates at 2 to 11 Mbps at distances from 50 to 150 feet indoors to well over 1,000 feet line-of-sight outdoors. It works on Windows, Macintosh, and various Linux/Unix/BSD flavors, sending TCP/IP and other packet data as an extension to plain old Ethernet networking. Recently, new specifications have been added to the Wi-Fi mix. These specifications include 802.11a and 802.11g from the IEEE, and the commercially supported HomeRF and Bluetooth protocols. HomeRF, Bluetooth, and 802.11g all share the 2.4-GHz band frequency with 802.11b. The standard that you choose to employ for your wireless needs will determine the type of radio card that is chosen for user devices and access points.
  9. 9. The wireless option makes sense for many school districts. There are many factors involved in bringing the Internet and networks to schools. Wireless LANs/WANs offer productivity, convenience, and cost advantages: • Provide users with access to real-time information anytime, anywhere to increase productivity, efficiency, achievement, etc. Due to factors such as class size, course offerings, etc. teachers who use technology in their teaching may be forced to move their classrooms. Wireless connectivity would allow teachers to move their entire “collection” of computers with them without worrying about connection availability. • Wireless installation requirements are minimal and relatively easy to install—no cables to pull through walls and ceilings. Setup is generally simple. • Provides installation flexibility because wireless WAN technology can go where wire cannot venture. Numerous additions and renovations chop up building access and wiring layout making wireless an option for these hard to reach areas. • While the investment required for wired LANs hardware will initially be higher than the cost of wired LAN hardware, overall wireless LAN and WAN installation expenses and significantly lower. The long-term cost benefits of wireless LANs are greatest in environments requiring frequent moves and changes. • Wireless WAN configuration is applied in a variety of ways to meet the needs of specific applications and installations. These configurations are easily changed and range from peer-to-peer networks to large wireless LANs which include thousands of users. • The performance of wireless networks has increased greatly in the last 5 years or so. Currently wireless networks can operate at speeds up to 10 Mbps which is faster than some T-1 lines. As great as these advantages seem, there are several challenges that must be addressed. There are some issues: • low speed and interference problems with existing IEEE Standard 802.11b applications. • Limited range of both 802.11a and 802.11b standard options • Incompatibility between the above two standards. • Security of data transmission
  10. 10. Wireless LANs and wireless WANs are not secure. The basic problem is that information is being transmitted through the air, making it virtually impossible to secure. While measures have been taken to try to establish levels of security, to date no technology has been developed to guarantee security. Several options are available to help address this problem: • Take advantage of the security features that are offered by your operating system using the security features available through it. • In most situations, wireless serves best as an add-on, not a replacement, for wired networks. • Make use of firewalls to keep the wired and wireless networks separate from one another. • Carefully plan the location of access points to minimize interference. • Limit the number of users per access point. For high-bandwidth tasks, a wired Ethernet network connected with a fiber backbone is still the best option. Save the wireless portion of the network for lower-bandwidth needs. Additional considerations: • HomeRF is wireless network, RF standing for radio frequency. Using a standard called Shared Wireless Access Protocol (SWAP), it allows for up to 127 devices per network. Because it uses a wireless transceiver built into a PCI card inside the computer, no access point is needed. Speed, range and interference can be problems with this form of wireless. • Bluetooth is a relatively new technology created in combination with several large telecommunications/technology companies. Bluetooth offers low cost, untethered connectivity to the Internet and other WANs using a variety of devices (PCs, cell phones, PDAs, etc.). As mentioned earlier, Bluetooth operates at a 2.4 GHz band frequency (very high). • Satellite technology can offers connectivity via a satellite dish mounted in a location where an unobstructed view of the
  11. 11. southern sky is possible. Download speeds are about 8 times faster than dial-up modem service, with upload speeds about equal to or slightly faster than dial-up modems. DIAL-UP SERVICE/MODEMS Telephone lines were designed to transmit human voice, not electronic data from computers. Modem is an acronym for Modulator Demodulator. Modems are devices that convert data from digital computer signals to analog signals that can be transmitted over a phone line. The conversion from digital to analog is called modulation. The conversion from analog to digital is called demodulation. A modem on one end will dial the telephone line. The other side will ring; the modem will “hear” the ring and answer the call. The receiving modem will put tone on the line and the other modem will recognize the tone and recognize it as being another modem. Humans do not make a tone so the modem knows if it had misdialed. The modems listen to these tones and convert the data as appropriate. Modems are available in different speeds and can be installed inside the computer (internal) or connected to the serial port (external). Early modems transmitted data at 2400 Bps (bits per second). Dial-up modems today reach speeds up to 56.6 Kbps. Most modems contain features like error control and data compression to increase the speed and accuracy of the transmission. There are a number of different protocols for converting data to be transmitted over telephone lines. Some are official standards, while others have been developed by private companies. Most modems have built-in support for the more common protocols—at least at slower speeds. Higher transmission speeds protocol standards are less standardized. There are many ways of connecting to the Internet. Most people still connect via Dial-up: the user’s modem calls an ISP server where an ISP’s modem answers and provides them with a signal to make the connection.
  12. 12. Dial-up services can allow teachers and other staff an opportunity to access network resources from remote locations. In effect, the dial-up connection becomes an extension of the network. This service can be expensive as a host computer with an interface, modem, and telephone line, must be dedicated to every remote session. DSL Digital Subscriber Line (DSL) is a high-speed technology that uses copper telephone lines to connect to the Internet. A DSL line can remain connected to the Internet (always on) so you don’t need to dial-up to go online. However, you still need a type of modem and a network card to connect. Typically with DSL, data is downloaded to a computer at rates up to 1.544 Mbps and data can be uploaded at 128 kbps. Since DSL carries both voice and data, you don’t have to install another phone line. Many times existing lines can be used to establish DSL service, however DSL isn’t available in all areas because it is “distance sensitive”. This means that you must reside within a specified distance from the telephone switching office. CABLE MODEMS Cable TV is another option that offers high-speed Internet access. Cable modems offer speeds up to 36 Mbps and can download data in seconds. Working over a TV cable, it doesn’t tie up a telephone line, and like DSL it’s always on so there is no need to connect.

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