Lecture 4 -_internet_infrastructure_2_updated_2011

BITS 2513 – Internet Technology

Lecture 4: Internet Infrastructure (contd)

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Topics Domain Names on the Internet Servers that Help with Communication Bandwidth Technologies

Internet Infrastructure

Domain Names on the Internet

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Domain Names on the Internet Domain names are assigned because IP address

numbers are difficult to remember and because companies might want to change their IP addresses without also changing the Internet name by which the outside world knows them.

The last segment, or suffix, of a domain name is called the top-level domain and tells you something about the function of the host.

The first word in a domain name is used to identify a subcategory within the domain and is called a canonical name, or CNAME.

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DNS Name Space

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Assigning and Tracking Domain Names and IP Addresses The organization responsible for overseeing this

operation is the IANA (Internet Assigned Numbers Authority).

Beginning in the spring of 1999, the responsibility for assigning and tracking domain names and IP addresses was transitioned from IANA to a nonprofit, private sector organization regulated by the U.S. Department of Commerce called ICANN (Internet Corporation for Assigned Names and Numbers).

A company that can register these names and numbers must be approved by ICANN and is called a registrar.

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Domain Name Resolution Domain names and IP addresses do not have to

be permanently related. Two name resolution services that track

relationships between domain names and IP addresses: DNS (Domain Name System, also called Domain Name Service) and Microsoft WINS (Windows Internet Naming Service).

DNS is the more popular of the two because it works on all platforms.

At the heart of DNS is a distributed database, which initially must be created manually.

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How DNS Works DNS has three logical components:

Computers searching for the IP address for a domain name, called resolvers

Servers that contain the information relating domain names to IP addresses, called name servers

The databases of information needed to resolve domain names and IP addresses, called namespaces

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How DNS Works (Continued) The process of discovering an IP address for a

given domain name is called address resolution.

It is also possible to find the domain name for a given IP address; this process is called reverse resolution, or reverse mapping.

Name servers are organized from the top down.

Network Solutions maintains servers called root servers that act as the highest level of authority when locating domain name information.

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How DNS Works (Continued) A network that supports DNS has two or

more name servers, called the primary name server and secondary name server.

The secondary server gets its information from the primary server, and is sometimes called the slave name server.

An authoritative name server is the server that has the most current information about a domain name.

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Address Resolution

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How DNS Works (Continued) The group of networks for which the name

server is responsible collectively is called the name server’s zone.

A zone also can have a caching-only server that does not keep authoritative information, but only caches information as it is used in case it is needed again within a short period of time.

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DNS Resolver & Local Cache

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DNS Records Each name server holds a piece of the

namespace, which is the database

containing information needed to resolve

domain names and IP addresses.

A name server keeps the entries for each

domain name that it knows about in a

resource record, or DNS record.

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DNS Record Types Here are some of the common resource record

types in the DNS database:

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Host Table Before 1983, when DNS began evolving

into an Internet standard, one huge file called the hosts table contained the name and IP address of every named host on the Internet. Host tables can still be used to give a node a

nickname, enhance performance on your local network, or on an isolated internal network.

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Host Table (Continued) To view the hosts table on your computer,

traverse to c:\windows\system32\drivers\etc or c:\winnt\system32\drivers\etc and view the hosts file in Notepad.

Internet Infrastructure

Servers that help with Communication

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Directory Server A directory server stores information

about people, hosts, and other resources on the network in directories and provides this information to computers on the network.

The information in a directory is read more often than it is written.

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X.500 and LDAP To allow directory servers to communicate

with each other and distribute the directory database over multiple networks, the ISO created a Directory Access Protocol (DAP) called X.500.

To streamline the process, the University of Michigan invented in 1993 a lighter version called the Lightweight Directory Access Protocol (LDAP) that can run over TCP/IP.

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How Directories Work Directories follow an upside-down tree

structure with the root at the top and branches underneath the root in a hierarchical structure.

Directory servers sometimes use a protocol called LDAP (Lightweight Directory Access Protocol) to access directories.

LDAP was designed to run over TCP and can be used on the Internet or on an intranet.

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How Directories Work (Continued)

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How Directories Work (Continued) LDAP is a “lighter” version of DAP (Directory

Access Protocol); LDAP has less code than DAP.

Another important directory standard is X.500, which specifies how global directories can be structured.

X.500 directories are designed to provide a listing of people within an organization so that anyone with Internet access can look someone up by country, organization, organizational level, or name.

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Advantages of X.500 & LDAP

Synchronization The directory on one server can synchronize

with the directory on another server. Replication

Part or all of the directory database on one server can copy itself onto another server.

Scalability There is no limit to the size to which the

directory can grow.

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Using Directories Directories and

directory servers can serve various functions on networks and on the Internet.

Directories on the Web are similar to search engines in the way they operate and provide information.

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Cache Servers Microsoft Internet Explorer supports browser

caching, which allows the user to indicate

how much hard drive space should be

allocated to Web caching.

The same concept implies to a Server. A

cache server improves performance by

caching data so that the number of requests

to the Internet is reduced.

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Cache Servers (Continued) Cache servers save Web pages and other

files that users have requested so that when a page is requested again, it can be retrieved without accessing the Internet.

Cache servers are placed between users and the Internet.

A cache server can run on a system such as a proxy server or a router, or it can be set up as a dedicated computer system.

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Mirrored Servers A mirrored server carries the same data

and services as another server. These servers are exact replicas of the main servers that they mirror and are updated often to ensure that they contain the same data.

Mirrored servers have two main purposes: They reduce download time for users by

handling some of the traffic for a frequently accessed Web site (provides redundancy).

They serve as backups for the main server in case it goes down (provides fault-tolerance).

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Using a Mirrored Server to Handle Site Traffic Web sites that get a lot of traffic often

need more than one server.

If the traffic comes from different parts of the world, it might be necessary to have servers in different locations to provide the best service for international customers.

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Using a Mirrored Server as a Backup Server A mirrored server acts as a very effective

backup system. If the main server goes down, it is faster

and easier to switch operation to a mirrored server than it is to restore information from disks and tapes.

When a mirrored server is used as a backup for a server, it constantly copies short segments of files from the main server as they are updated.

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Print Servers Print servers make printers available for

shared use across a network or even across the Internet.

Each print server can have several printers attached to it, and you can have more than one print server on a network, depending on the size of the network and the needs and locations of the users on it.

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LPD Servers LPD (Line Printer Daemon) server is

print server software that initially was developed on UNIX servers to handle print jobs, but is now supported by Windows Server 2003, Windows 2000 Professional, and Windows NT Server.

A client communicating with an LPD server can use two protocols, LPR and LPQ, which are part of the TCP/IP protocol suite.

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LPD Servers (Continued) The client uses the LPR (Line Printer

Remote) protocol to send print jobs over a TCP/IP network to the server.

Clients that use LPR are sometimes referred to as LPR clients.

A second protocol, LPQ (Line Printer Queue), is required for users to be able to check on the status of print jobs they have sent.

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IPP Another useful and more recently developed printing

protocol is IPP (Internet Printing Protocol). IPP, which also enables printing across LANs and the

Internet, is generally more versatile than LPD and its associated services, and is more easily compatible with various operating systems.

The greatest benefit of IPP is being able to find a printer by using the printer’s IP address or URL.

With IPP, you can find any Internet-connected printer, print to it, and check the status of your print job.

Internet Infrastructure

Bandwidth Technologies

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Bandwidth Technologies Much attention is given to the amount of

data that can travel over a given communication system in a given amount of time.

This measure of data capacity is called bandwidth, also called data throughput or line speed.

The greater the bandwidth, the faster the communication.

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Bandwidth Technologies Used to Connect to an ISP A local area network has much less need for data

throughput than does a national backbone. Lying between these two extremes on the spectrum are

many types of systems that require varying degrees of bandwidth.

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Regular Telephone Lines Regular telephone lines, the most common

way to connect to an ISP, require an internal or external modem.

When data packets travel over telephone lines, the Data Link layer protocol used is PPP or SLIP.

PPP (Point-to-Point Protocol) most often is used to transmit TCP/IP packets from a computer connected to an ISP or intranet access point by telephone line.

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Cable Modem Cable modem communication uses cable

lines that already exist in millions of households in the United States.

Just as with cable TV, cable modems are always connected.

A cable modem is an example of broadband media.

Broadband refers to any type of networking media that carries more than one type of transmission.

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PPPoE (Point-to-Point Protocol over Ethernet) PPPoE (Point-to-Point Protocol over

Ethernet) is a protocol that adapts PPP to work with Ethernet.

PPPoE describes how the computer is to interact with the converter box or modem when the two are connected by an Ethernet cable connected to an Ethernet network card in the computer.

PPPoE gives the user the security and authentication that is offered with PPP.

PPPoE also sets standards for networks to connect to the Internet via DSL modems and other high-speed access services.

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DSL In the race to produce a fast data

transmission technology that is affordable for home use and that offers a direct connection rather than a dial-up connection, the telephone industry has developed several similar technologies that collectively are called DSL (Digital Subscriber Line).

The most popular version of DSL is ADSL (Asymmetric Digital Subscriber Line), which is 50 times faster than ISDN and is direct connect.

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Satellite Connections to the Internet People who live in remote areas and want

high-speed Internet connections often are limited in their choices.

DSL and cable modems might not work where they live, but satellite access is available from almost anywhere.

Technology is even being developed to use satellites to offer Internet access on commercial airlines.

New technology allows data to be transmitted both ways over the satellite so that telephone line connections are not needed.

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Wireless Connections Wireless is an important technology for

mobile devices and for Internet access in remote locations where other methods are not an option.

For Internet access, two popular applications of wireless are fixed-point wireless, sometimes called Wireless Local Loop (WLL), and mobile wireless.

With fixed-point wireless, an antenna sits on your house or office building and communicates with a base station antenna.

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Wireless Application Protocol The high demand for wireless access to the

Internet, including Web pages and e-mail, led to the creation of the WAP (Wireless Application Protocol).

One goal of WAP is to bridge the gap between the needs of traditional Internet access devices and wireless Internet access devices.

WAP is a communication standard designed for mobile Internet access.

One feature of WAP is WML (Wireless Markup Language).

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Uses of Wireless Devices One popular service that is being provided

to customers with wireless Internet devices is instant notification, or alerts.

Assignment 1 In Group of 2 (minimum) or 3 (maximum). Due date: 17th October 2011 23:59 Submission: ULearn Question 1: T Lines and E Lines was the first successful

system that supported digitized voice transmission. Describe and elaborate what you understand on T and E Lines in terms of the technology, usage and applications in the industry. Give examples.

Question 2: X.25 and Frame Relay are used for long distance communications that use Packet Switching Technology. Using a diagram, differentiate between Packet Switching Technology and Circuit Switching Technology.

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ATM ATM (Asynchronous Transfer Mode) is a very

fast network technology that can be used with LANs, as well as WANs.

It uses fixed-length packets, called cells, to transmit data, voice, video, and frame relay traffic.

ATMs also use virtual circuits, meaning that the two endpoints are stationary, but the paths between these two endpoints can change.

They can use either PVCs or SVCs. SVCs (switched virtual circuits) are logical,

point-to-point connections that depend on the ATM to decide the best path to send the data.

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Mesh Topology A mesh topology provides multiple point-

to-point links between routers in a wide area network, giving more than one choice on how data can travel from router to router.

In a mesh topology, a router searches out multiple paths and determines the best path to take.