basic communications systems class 6. today’s class topics wide area networks circuit switching...

Basic Communications

Systems

Class 6

Today’s Class Topics Wide Area Networks

Circuit Switching Packet Switching

Routing WAN Services

The Internet Services

Chapter 10

Introduction to Wide Area Networks

Data Communications andComputer Networks: A Business User’s Approach

Data Communications and Computer Networks Chapter 10

IntroductionA local area network covers a room, a building or a campus.

A metropolitan area network covers a city or a region of a city.

A wide area network (WAN) covers multiple cities, states, and even countries.

WANs used to be characterized with slow, noisy lines. Today WANs are very high speed with very low error rates.

WANs often follow a mesh topology.


Wide Area Network BasicsA station is a device that interfaces a user to a network.

A node is a device that allows one or more stations to access the physical network and is a transfer point for passing information through a network.

A node is often a computer, a router, or a telephone switch.

The subnet of a network is the underlying connection of nodes and telecommunication links.


Types of Network SubnetsCircuit switched subnet - a subnet in which a dedicated circuit is established between sender and receiver and all data passes over this circuit.

Bandwidth is reserved throughout the call on a circuit-switched subnet, typically using Synchronous Time Division Multiplexing (TDM)

The telephone system is a common example.

The connection is dedicated until one party or another terminates the connection.


Types of Network SubnetsPacket switched subnet - a subnet in which all data messages are transmitted using fixed-sized packages, called packets.

More efficient use of a telecommunications line since packets from multiple sources can share the medium.

One form of packet switched subnet is the datagram. With a datagram, each packet is on its own and may follow its own path.

Virtual circuit packet switched subnets create a logical path through the subnet and all packets from one connection follow this path. However, bandwidth is not pre-reserved (Statistical Time Division Multiplexing)


Types of Network SubnetsBroadcast subnet - a subnet typically found in local area networks but occasionally found in wide area networks.

A workstation transmits its data and all other workstations “connected” to the network hear the data. Only the workstation(s) with the proper address will accept the data.


Connection-oriented versus ConnectionlessThe subnet is the underlying physical component of a network. What about the software or application that uses the network?

A network application can be either connection-oriented or connectionless.


Connection-oriented versus ConnectionlessA connection-oriented application requires both sender and receiver to create a connection before any data is transferred.

Applications such as large file transfers and sensitive transactions such as banking and business are typically connection-oriented.

A connectionless application does not create a connection first but simply sends the data. Electronic mail is a common example.


Connection-oriented versus ConnectionlessA connection-oriented application can operate over both a circuit switched subnet or a packet switched subnet.

A connectionless application can also operate over both a circuit switched subnet or a packet switched subnet but a packet switched subnet may be more efficient.


RoutingEach node in a WAN is a router that accepts an input packet, examines the destination address, and forwards the packet on to a particular telecommunications line.

How does a router decide which line to transmit on?

A router must select the one transmission line that will best provide a path to the destination and in an optimal manner.

Often many possible routes exist between sender and receiver.


RoutingThe subnet with its nodes and telecommunication links is essentially a weighted network graph.

The edges, or telecommunication links, between nodes, have a cost associated with them.

The cost could be a delay cost, a queue size cost, a limiting speed, or simply a dollar amount for using that link.


RoutingThe routing method, or algorithm, chosen to move packets through a network should be:

• Optimal, so the least cost can be found

• Fair, so all packets are treated equally

• Robust, in case link or node failures occur and the network has to reroute traffic.


Flooding RoutingWhen a packet arrives at a node, the node sends a copy of the packet out every link except the link the packet arrived on.

Traffic grows very quickly when every node floods the packet.

To limit uncontrolled growth, each packet has a hop count. Every time a packet hops, its hop count is incremented. When a packet’s hop count equals a global hop limit, the packet is discarded.


Centralized RoutingOne routing table is kept at a “central” node.

Whenever a node needs a routing decision, the central node is consulted.

To survive central node failure, the routing table should be kept at a backup location.

The central node should be designed to support a high amount of traffic consisting of routing requests.


Least Cost Routing AlgorithmDijkstra’s least cost algorithm can be applied to determine the least cost path between any pair of nodes.


Distributed RoutingEach node maintains its own routing table.

No central site holds a global table.

Somehow each node has to share information with other nodes so that the individual routing tables can be created.

Possible problem with individual routing tables holding inaccurate information.


Isolated RoutingEach node uses only local information to create its own routing table.

Advantage - routing information does not have to be passed around the network.

Disadvantage - a node’s individual routing information could be inaccurate, or out of date.


Adaptive Routing versus Static RoutingWith adaptive routing, routing tables can change to reflect changes in the network

Static routing does not allow the routing tables to change.

Static routing is simpler but does not adapt to network congestion or failures.


Network CongestionWhen a network or a part of a network becomes so saturated with data packets that packet transfer is noticeably impeded, network congestion occurs.

Preventive measure include providing backup nodes and links and preallocation of resources.

To handle network congestion, you can perform buffer preallocation, choke packets, or permit systems.

Public Carrier Data Services

How does a customer make use of a public data network? Customer gets Digital Access Lines to

C.O. Customer chooses end-to-end data

service: Leased Data Line Dial-up Data Service Packet Data Network

Access Lines

Central Office

Digital Access LineDSU/CSU

Customer needs access device into network Modem: for analog access line DSU/CSU: for digital access line

Line cost depends on bandwidth (data transfer rate).

Types of Access Lines

Single-Pair Copper Wire Telephone line w/ modem – up to

33.6 Kbps ADSL – up to 1.544 Mbps

2 Pairs Copper Wire 56 Kbps Digital Line – 56 Kbps T1 Digital Line - 1.544 Mbps

Types of Access Lines

Coaxial Cable Cable Modem – up to 40 Mbps DS3 Access – ~45 Mbps

Fiber Optics SONET OC-3 – 155 Mbps SONET OC-12 – 622 Mbps

End-to-End Data Services

Transports data across carrier network

Three types of service: Leased Data Line Dial-up Data Service Packet Data Network

Leased Data Lines

Carrier provides dedicated point-to-point data circuit Fixed digital bandwidth (bit rate) Customer pays fixed price per month

based on Distance Bit rate

Leased Line Examples: Leased 56K Circuit

Bandwidth: 56 Kbps Cost (Chicago - NY): Around $800/month

Leased T1 Circuit Bandwidth: 1.536 Mbps Cost (Chicago - NY): Around

$5000/month

Dial-up Data Services Also known as Circuit-Switched Data Data connection is only made when

customer “dials out” to another device Customer pays

Fixed price per month for access line Per-minute usage charges while service is

in-use

Dial-Up Data Examples: POTS

Bandwidth: 33.6 Kbps (w/ modem) Line Cost: ~ $15/mo. Usage: DDD

Switched 56K Service Bandwidth: 56 Kbps Line Cost: ~ $60/mo. Usage: DDD

ISDN Basic Rate Interface Bandwidth: 144 Kbps Line Cost: ~ $40/mo. Usage: DDD

Packet Data Services

Also known as Packet-Switched Data Customer gets access line to connect

them to closest packet switch Carrier routes each data packet to

destination based on “destination address” in packet header

Customer pays Access line charges monthly packet service fee (typically fixed

price)

Packet Data Examples:

X.25 Service Frame Relay Service Internet Service

End-to-End Bandwidth varies depending on Access line speed (leased or dial-up) How congested the network is

Advantages Leased Data Services:

Ease of Use and Security Performance (guaranteed bandwidth and

minimal delay) Dial-Up Data Services:

Flexibility (can call any destination) Packet Data Services:

Flexibility (No pre-reserved bandwidth – data routed on packet-by-packet basis)

Cost (usually least expensive option)

Packet Data Services

R outer

R outer

R outer

Carrier Network

R outer

ChicagoRouter

LAN Hub

Client

New YorkRouter

LAN Hub

Server

CustomerNetwork

CustomerNetwork

AccessLine

AccessLine

Chapter 11

The Internet

Data Communications andComputer Networks: A Business User’s Approach


IntroductionToday’s present Internet is a vast collection of thousands of networks and their attached devices.

The Internet began as the Arpanet during the 1960s.

One high-speed backbone connected several university, government, and research sites.

The backbone was capable of supporting 56 Kbps transmission speeds and eventually became financed by the National Science Foundation (NSF).

What is the Internet?

The Internet is a collection of networks (Autonomous Systems) using the Internet Protocol (IP).

Each Autonomous System (AS), typically owned by an Internet Service Provider (ISP), consists of a collection of IP routers that may be regional, national or international in scope.

Access to Internet

Access lines to ISP routers can be: Dial-up modem over telephone network Dial-up digital line (i.e. 56Kbps switched or

ISDN) Leased access line from customer site to ISP

router (56 Kbps, T1, T3) Example: DePaul has 2 leased T1s to our ISP,

QualNet.

See http://www.thelist.com for list of ISPs and pricing information

ISP Interconnection

ISPs can interconnect their networks via; Public Peering Points called Network

Access Points (NAPs) or Metropolitan Area Exchanges (MAEs)

Ameritech runs a Chicago NAP (http://nap.aads.net/main.html)

Private Peering arrangements (direct communications circuits between ISP networks).

http://nap.aads.net/main.html

Who runs the Internet?• No one: Decentralized, distributed, chaotic growth

• Standards: Internation Standards Organization (ISO), Internet Engineering Task Force (IETF), W3C, etc.

• Names,Numbers: Internet Corporation for Assigned Names and Numbers (ICANN)

• Operational coordination: IEPG (Internet Engineering Planning Group)

• Network: ISPs (Internet Service Providers), NAPs, MAEs

• Cabling: Telephone companies

• Content: millions of companies, universities & individuals

Who Makes Money?

End Users and Businesses pay ISPs to provide IP routing services.

Regional ISPs pay National ISPs to get inter-ISP routing (peering) at NAPs

ISPs pay telecommunications carriers for leased data circuits to interconnect their IP routers


Internet ServicesThe Internet provides many types of services, including several very common ones:

• File transfer protocol (FTP)

• Remote login (Telnet)

• Internet telephony

• Electronic mail


Internet ServicesThe Internet provides many types of services, including several very common ones:

• Listservs

• Usenet

• Streaming audio and video

• The World Wide Web

Clients and Servers

Internet application protocols are Client / Server protocols

Example: to use Web services I need an HTTP client (Netscape or

Internet Explorer) on my PC. I communicate with an HTTP server (a

web server) We exchange data packets containing

HTTP protocol requests and responses

Clients and Servers

Internet applications use Client / Server communications

Example: to use E-mail services I need an SMTP client (such as Eudora

mail or MS Outlook) on my PC. I communicate with an SMTP server

(such as MS Exchange Server) We exchange data packets containing

SMTP protocol requests and responses

Server Port Numbers

What if a single machine is running multiple services?

Port numbers to identify different services on the same machine Example: HTTP protocol = port 80 Example: SMTP protocol = port 25

Port number is carried in the TCP or UDP header of a packet

Who picks the Port Numbers?

Internet port numbers are standardized and stored on your computer.

For example, on Windows NT, they are in file:

C:\winnt\system32\drivers\etc\services

Web Page Request Packet

Web ServerBrowser

GETDEFAULT.HTM

HTTP/1.0

EthernetTrailer

EthernetHeader

IP

Header HeaderTCP

Dest. Port = 80 Dest. Addr = 140.192.81.6

140.192.81.6

The Web

The World Wide Web is a collection of computers on the Internet that use HTTP protocol to transfer files (web pages) Hypertext Markup Language (HTML) to

represent Formatting information for display Clickable Hyperlinks to go to other pages

Web browsers access HTML and other files from servers using HTTP

Web Servers store files and make them available to browsers

Web Sites

To publish a Web Site, a user must Find a Web server, that is

Connected to the Internet at all times (not dial-up access)

Running web server software Has disk space that can be used for storing files.

Preferably, get good software to help in creating graphics and HTML pages.

Cost: Many ISPs provide disk space and web page

building tools to their clients for a small fee.

URLs

Universal Resource Locator (URL) is the format used to specify a particular resource on the Web.

<protocol>://<host>/<directory>/<file>

protocol HTTP:, TELNET:, FTP:, etc.

host Either DNS name or IP address of device on the

Internet

URLs

Example:

HTTP://www.depaul.edu/test.html

Means: “Connect to server named

‘www.depaul.edu’ using HTTP protocol

(port 80), and retrieve a file named

‘test.html’.”

URLs

Example:

Telnet://brewsternt.depaul.edu

Means: “Connect to server named

‘brewsternt.depaul.edu’ using

Telnet protocol (port 21.”

URLs

Example:

http://140.192.33.5:8080

Means: “Connect to server with IP

address 140.192.33.5 using HTTP

protocol to port 8080 and retrieve the

default file (default.htm or index.html)”


File Transfer Protocol (FTP)Used to transfer files across the Internet.

User can upload or download a file.

The URL for an FTP site begins with ftp://…

The three most common ways to access an FTP site is:

1. Through a browser

2. Using a canned FTP program

3. Issuing FTP commands at a text-based command prompt.


Remote Login (Telnet)Allows a user to remotely login to a distant computer site.

User usually needs a login and password to remote computer site.

User saves money on long distance telephone charges.


Internet TelephonyThe transfer of voice signals using a packet switched network and the IP protocol.

Also known as packet voice, voice over packet, voice over the Internet, and voice over Internet Protocol (VoIP).

VoIP can be internal to a company or can be external using the Internet.

VoIP consumes many resources and may not always work well, but can be cost effective in certain situations.


Internet Telephony (VoIP)Three basic ways to make a telephone call using VoIP:

1. PC to PC using sound cards and headsets (or speakers and microphone)

2. PC to telephone (need a gateway to convert IP addresses to telephone numbers)

3. Telephone to telephone (need gateways)


Internet Telephony (VoIP)Three functions necessary to support voice over IP:

1. Voice must be digitized (PCM, 64 Kbps, fairly standard)

2. 64 Kbps voice must be compressed (many standards here - ITU-T G.729A, used by AT&T, Lucent, others; G.723.1, used by Microsoft and Intel)

3. Once the voice is compressed, the data must be transmitted. Many different ways to do this.


Internet Telephony (VoIP)How can we transport compressed voice?

Streaming audio, such as Real Time Streaming Protocol (RTSP) and Microsoft’s Active Streaming Format (ASF)

Resource Reservation Protocol (RSVP) - carries a specific QoS through the network, reserving bandwidth at every node. Operates at the transport layer.

Internet Stream Protocol version 2 (ST2) - an experimental resource reservation protocol that operates at same layer as IP


Electronic MailE-mail programs can create, send, receive, and store e-mails, as well as reply to, forward, and attach non-text files.

Multipurpose Internet Mail Extension (MIME) is used to send e-mail attachments.

Simple Mail Transfer Protocol (SMTP) is used to transmit e-mail messages.

Post Office Protocol version 3 (POP3) and Internet Message Access Protocol (IMAP) are used to hold and later retrieve e-mail messages.


ListservsA popular software program used to create and manage Internet mailing lists.

When an individual sends an e-mail to a listserv, the listserv sends a copy of the message to all listserv members.

Listservs can be useful business tools for individuals trying to follow a particular area of study.


UsenetA voluntary set of rules for passing messages and maintaining newsgroups.

A newsgroup is the Internet equivalent of an electronic bulletin board system.

Thousands of Usenet groups exist on virtually any topic.


Streaming Audio and VideoThe continuous download of a compressed audio or video file, which can be heard or viewed on the user’s workstation.

Real-time Protocol (RTP) and Real Time Streaming Protocol (RTSP) support streaming audio and video.

Streaming audio and video consume a large amount of network resources.


World Wide WebThe World Wide Web (WWW) is a immense collection of web pages and other resources that can be downloaded across the Internet and displayed on a workstation via a web browser.

The most popular service on the Internet.

Basic web pages are created with the HyperText Markup Language (HTML).

HTML

Hypertext Markup Language allows a text file to be augmented with tags that specify Formatting information (font size, bold,

italics, table formats, etc) Locations to include image files (using

GIF, JPEG or other graphics formats) Hyperlinks (highlighted text and an

associated URL to go to if clicked) Associated executable applets (written

in Java, Javascript, ??)


World Wide WebWhile HTML is the language to display a web page, HyperText Transport Protocol (HTTP) is the protocol to transfer a web page.

Many extensions to HTML have been created. Dynamic HTML is a very popular extension to HTML.

Common examples of dynamic HTML include mouse-over techniques, live positioning of elements (layers), data binding, and cascading style sheets.


World Wide WebExtensible Markup Language (XML) is a description for how to create a document - both the definition of the document and the contents of the document.

The syntax of XML is fairly similar to HTML.

You can define your own tags, such as <CUSTOMER> which have their own, unique properties.


e-CommerceThe buying and selling of goods and services via the Internet.

Many agree that e-commerce consists of four major areas:

1. e-retailing

2. Electronic Data Interchange (EDI)

3. Micro-marketing

4. Electronic security


Cookies and State InformationA cookie is data created by a web server that is stored on the hard drive of a user’s workstation.

This state information is used to track a user’s activity and to predict future needs.

Information on previous viewing habits stored in a cookie can also be used by other web sites to provide customized content.

Many consider cookies to be an invasion of privacy.


Intranets and ExtranetsAn intranet is a TCP/IP network inside a company that allow employees to access the company’s information resources through an Internet-like interface.

When an intranet is extended outside the corporate walls to include suppliers, customers, or other external agents, the intranet becomes an extranet.


Internet ProtocolsTo support the Internet and all its services, many protocols are necessary.

Some of the protocols that we will look at:

• Internet Protocol (IP)

• Transmission Control Protocol (TCP)

• Address Resolution Protocol (ARP)

• Domain Name System (DNS)


Internet ProtocolsRecall that the Internet with all its protocols follows the Internet model.

An application, such as e-mail, resides at the highest layer.

A transport protocol, such as TCP, resides at the transport layer.

The Internet Protocol (IP) resides at the Internet or network layer.

A particular media and its framing resides at the interface layer.


The Internet Protocol (IP)IP prepares a packet for transmission across the Internet.

The IP header is encapsulated onto a transport data packet.

The IP packet is then passed to the next layer where further network information is encapsulated onto it.


The Internet Protocol (IP)Using IP, a subnet router:

Makes routing decision based on the destination address.

May have to fragment the datagram into smaller datagrams (very rare) using Fragment Offset.

May determine that the current datagram has been hopping around the network too long and delete it (Time to Live).

To perform these functions, an IP header is encapsulated onto each transport layer packet.


The Transmission Control Protocol (TCP)The TCP layer creates a connection between sender and receiver using port numbers.

The port number identifies a particular application on a particular device (IP address).

TCP can multiplex multiple connections (using port numbers) over a single IP line.


The Transmission Control Protocol (TCP)The TCP layer can ensure that the receiver is not overrun with data (end-to-end flow control) using the Window field.

TCP can perform end-to-end error correction (Checksum).

TCP allows for the sending of high priority data (Urgent Pointer).


Internet Control Message Protocol (ICMP)ICMP, which is used by routers and nodes, performs the error reporting for the Internet Protocol.

ICMP reports errors such as invalid IP address, invalid port address, and the packet has hopped too many times.


User Datagram Protocol (UDP)A transport layer protocol used in place of TCP.

Where TCP supports a connection-oriented application, UDP is used with connectionless applications.

UDP also encapsulates a header onto an application packet but the header is much simpler than TCP.


Address Resolution Protocol (ARP)When an IP packet has traversed the Internet and encounters the destination LAN, how does the packet find the destination workstation?

Even though the destination workstation may have an IP address, a LAN does not use IP addresses to deliver frames. A LAN uses the MAC layer address.

ARP translates an IP address into a MAC layer address so a frame can be delivered to the proper workstation.

Address Resolution Protocol (ARP)

The ARP Protocol allows any machine to determine the 6-byte LAN address of any other machine on the same subnet if it knows the IP address of that machine Each PC keeps an ARP Table that stores IP

address and LAN address of devices on local subnet

ARP Table entries are kept up-to-date automatically by sending ARP Broadcast messages when necessary to determine addresses

Two Addresses??

In an IP LAN environment, every PC

will have two addresses: 4-byte IP address

6-byte LAN (Ethernet) address

Two Addresses??

Why?? LAN address can only deliver data

to destination on the same LAN

(that is, the same IP subnet)

IP address is used to deliver data to

any destination, regardless of

destination network.

Two Addresses??

The 6-byte destination address in the

Ethernet header is used to deliver the

data to the next device: If the packet is not on the final LAN, then

Ethernet destination address identifies the

address of the next router

If the packet is on the final LAN, then

Ethernet destination address identifies the

address of the destination host (server).

IP Routing Example

NFS F ile Serv ices

SoftwareTCP/IP

NetworkingSoftware

NICDriver SW

N IC C ard

C lien t

Create O PEN F ILERequest in NFS form at

Add E thernet Infow ith Router M AC Address

NFS F ile Serv ices

SoftwareTCP/IP

NetworkingSoftware

N ICD river SW

N IC C ard

Execute O PENFILE O peration

S erver

R outingS oftware

N ICD rive r S W

N IC C ard

N ICD rive r S W

N IC C ard R ecognize M AC Addr.R em ove Token R ing In fo

C heck TC P/IP In fo .R em ove TC P/IP H eaders

R ecognize M AC Addr.R em ove E thernet In fo

Look up IP D est.N etw ork in

R outing TableAdd TCP/IP Headers

w ith Server IP Address

Translate Server IP Address toServer

M AC Address

Add Token R ing Infow ith Server M AC Address

E thernetT ra ile r

E thernetH eader

TC P /IPH eaders

N FSR equest

TokenR ing

T ra ile r

TokenR ing

H eader

TC P /IPH eaders

N FSR equest

IP Router

Token Ring LANIP Netw ork 140.86

Ethernet LANIP Netw ork 140.192

IP Address 140.192.55.10 IP Address 140.86.22.5

MAC#17

MAC#22

S rc: 140.192.55.10D est: 140.86.22.5

S rc: 140.192.55.10D est: 140.86.22.5

S rc: 15D est: 17

S rc: 22D est: 23


Tunneling ProtocolsThe Internet is not normally a secure system.

If a person wants to use the Internet to access a corporate computer system, how can a secure connection be created?

One possible technique is by creating a virtual private network (VPN).

A VPN creates a secure connection through the Internet by using a tunneling protocol.


BOOTPEvery workstation attached to the Internet needs:

• Its IP address

• Its subnet mask

• The IP address of a router

• The IP address of a name server


BOOTPThin client workstations do not have a disk drive, and its ROM does not contain the previous four pieces of information.

How do we tell the machine this information? BOOTP.


BOOTPThere are two types of BOOTP operations:

REQUEST – A workstation asks a server for the information (source IP address = all 0s, destination IP address = all 1s).

REPLY – The server returns the information to the workstation.


Dynamic Host Configuration Protocol (DHCP)BOOTP is not dynamic (when a client requests its IP address, it is retrieved from a static table).

DHCP is a dynamic extension of BOOTP.

When a DHCP client issues an IP request, the DHCP server looks in its static table. If no entry exists, the server selects an IP address from an available pool.


DHCPThe address assigned by the DHCP server is temporary.

Part of the agreement includes a specific period of time.

If no time period specified, the default if one hour.

DHCP clients may negotiate for a renewal before the time period expires.


Network Address Translation (NAT)NAT lets a router represent an entire local area network to the Internet as a single IP address.

Thus it appears all traffic leaving this LAN appears as originating from a global IP address.

All traffic coming into this LAN uses this global IP address.

This security feature allows a LAN to hide all the workstation IP addresses from the Internet.


NATSince the outside world cannot see into the LAN, you do not need to use registered IP addresses on the inside LAN.

We can use the following blocks of addresses for private use:

•10.0.0.0 – 10.255.255.255

•172.16.0.0 – 172.31.255.255

•192.168.0.0 – 192.168.255.255


NATWhen a user on inside sends a packet to the outside, the NAT interface changes the user’s inside address to the global IP address. This change is stored in a cache.

When the response comes back, the NAT looks in the cache and switches the addresses back.

No cache entry? The packet is dropped. Unless NAT has a service table of fixed IP address mappings. This service table allows packets to originate from the outside.


Locating a Document on the InternetWhen a user, running a web browser, enters a URL, how is the URL translated into an IP address?

The Domain Name System (DNS) is a large, distributed database of URLs and IP addresses.

The first operation performed by DNS is to query a local database for URL/IP address information.

If the local server does not recognize the address, the server at the next level will be queried.

Domain Name System

The Internet utilizes a system of Domain Name System (DNS) servers. These allow a user to refer to a device by

DNS Name (i.e. brewster.cs.depaul.edu) rather than by IP address (i.e. 140.192.32.9)

brew ster.cs.depaul.edu

H o s t s ubdo m a in to p -le ve ldo m a in

do m a in

Domain Name System Top-Level Domains (TLDs):

2-letter top-level domains for each country - .fr for France, .de for Germany, etc.

.edu - Educational Institutions .com - Commercial .gov - Government .mil - Military .org - Organizations .net - Network providers .int - Internet organizations

ICANN The Internet Corporation for

Assigned Names and Numbers (ICANN) has responsibility to: Determine what new Top-Level

Domains will be created (.biz? .jobs?) Determine what groups can register

domain names Determine some policy on copyright

and name ownership issues

Who owns what names? Domain Name registrars can assign

ownership of domain names one level below the TLDs One master database of all domain

name owners is kept Example: DePaul U. owns “depaul.edu” Registrars charge a nominal fee ($15-

$30 per year) for names Networksolutions.com is the best known

registrar

Types of TLDs Uncontrolled TLDs

Anyone can register any name under these TLDs. Examples of uncontrolled TLDs: .com, .net, .org

Controlled TLDs Only certain qualifying groups can register a

name under these TLDs – example: .edu.

National TLDs Most countries have a national registrar that

handles all names for that country’s TLD.

Domain Name System

Top-Level DNS Servers store address of each Domain Server for a particular top-level domain (i.e. “.edu”)

Domain DNS Servers store names and IP addresses for organization (i.e. depaul.edu)

Domain Names are registered with the ICANN and associated with IP address prefixes. Example (depaul.edu <=> 140.192.x.x)

Domain Name System Example: You type “http://www.ibm.com”

Your PC sends DNS request to DePaul DNS server DePaul DNS server sends DNS request packet to

“.com” top-level DNS server Top-level DNS server sends back address for

“ibm.com” Domain DNS Server at IBM Corp. DePaul DNS server sends DNS request packet to

“ibm.com” Domain DNS Server IBM DNS server looks up IP address and sends result

back to DePaul DNS Server. DePaul DNS server sends IP address back to your

PC.


IP AddressesAll devices connected to the Internet have a 32-bit IP address associated with it.

Think of the IP address as a logical address (possibly temporary), while the 48-bit address on every NIC is the physical, or permanent address.

Computers, networks and routers use the 32-bit binary address, but a more readable form is the dotted decimal notation.


IP AddressesFor example, the 32-bit binary address

10000000 10011100 00001110 00000111

translates to

128.156.14.7

There are basically four types of IP addresses: Classes A, B, C and D.

A particular class address has a unique network address size and a unique host address size.

Network and Host parts

So – the first fixed part of the IP

address is the Network address

or Network Prefix Determines what network address

is on

Used by routers to determine which

direction to send the packet

Network and Host parts

The rest of the IP address is the

Host address or Host Number Determines which particular device

on the network is addressed

Used by the last router in the path

to deliver the packet to the specific

machine


IP AddressesWhen you examine the first decimal value in the dotted decimal notation:

All Class A addresses are in the range 0 - 127

All Class B addresses are in the range 128 - 191

All Class C addresses are in the range 192 - 223


IP Subnet MaskingSometimes you have a large number of IP address to manage.

By using subnet masking, you can break the host ID portion of the address into a subnet ID and host ID.

For example, the subnet mask 255.255.255.0 applied to a class B address will break the host ID (normally 16 bits) into an 8-bit subnet ID and an 8-bit host ID.

IP Address Subnetting

Subnetting splits the bits of the IP

address into three address fields: IP Network – identifies network prefix

assigned by the ICAAN

IP Subnet – identifies internal subnet

number determined by local network

administrator

IP Host – identifies individual machine

IP Packet Delivery

IP routers deliver data packets as follows: Internet routers only look at IP Network

address to determine destination network

Once inside destination network, local routers

look at IP Subnet address to determine

destination LAN

The last router attached to the destination LAN

looks at IP Host address to determine which

particular destination machine.

Subnet Masks

How do Host machines and routers know which bits are Subnet Bits?

A Subnet Mask is entered into every Host machine and every router to tell them: Out of each 32-bit IP address: How many bits are Network bits? How many bits are Subnet bits? How many bits are Host bits?

Subnet Masks An IP subnet mask is a 32-bit value defined

as follows: Every IP address bit position that should be a

Network bit or a Subnet bit position is marked with a 1 bit

Every IP address bit position that should be a Host bit is marked with a 0 bit

Subnet masks are written in dotted decimal notation, just like IP addresses – but they are not IP addresses.

Subnet Mask Example

Network Host

140 192 30 100

1 0 0 0 1 1 0 0 0 1 1 0 0 1 0 00 0 0 1 1 1 1 01 1 0 0 0 0 0 0

1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 01 1 1 1 1 1 1 11 1 1 1 1 1 1 1

Address:

SubnetMask:

Subnet Mask: 255.255.255.0


The Future of the InternetVarious Internet committees are constantly working on new and improved protocols.

Examples include:

• Internet Printing Protocol

• Internet fax

• Extensions to FTP

• Common Name Resolution Protocol

• WWW Distributed Authoring and Versioning


IPv6The next version of the Internet Protocol.

Main features include:

• Simpler header

• 128-bit IP addresses

• Priority levels and quality of service parameters

• No fragmentation


Internet2A new form of the Internet is being developed by a number of businesses and universities.

Internet2 will support very high speed data streams.

Applications might include:

• Digital library services

• Tele-immersion

• Virtual laboratories


The Internet In Action: A Company Creates a VPNA fictitious company wants to allow 3500 of its workers to work from home.

If all 3500 users used a dial-in service, the telephone costs would be very high.


The Internet In Action: A Company Creates a VPNInstead, the company will require each user to access the Internet via their local Internet service provider.

This local access will help keep telephone costs low.

Then, once on the Internet, the company will provide software to support virtual private networks.

The virtual private networks will create secure connections from the users’ homes into the corporate computer system.

basic communications systems class 6. today’s class topics wide area networks circuit switching...

Documents

computer networks chapter

data passes

data messages

physical network

network application

local area networks

metropolitan area network

wide area network wan