Chapter 7 : The Internet: Addressing & Services. Business Data Communications, 7e. Objectives. Internet History & Growth of the Internet Internet Architecture and its key components: ISPs POPs NAPs Internet Domain and Domain Names Operation of Domain Name System (SNS)
Chapter 7 : The Internet: Addressing & Services Business Data Communications, 7e
Objectives • Internet History & Growth of the Internet • Internet Architecture and its key components: • ISPs • POPs • NAPs • Internet Domain and Domain Names • Operation of Domain Name System (SNS) • Internet Addressing and issues involved
Internet History • A large, wide-area network (WAN) created in the 1960s by the U.S. Department of Defense Advanced Research Projects Agency (ARPA) • Renamed DARPA in the 1970s) for the free exchange of information between universities and research organizations, although the military also used this network for communications. • In the 1980s, MILNET, a separate network, was spun off from ARPANET for use by the military. • ARPANET was the network from which the Internet evolved.
Internet History • The Internet evolved from the ARPANET, which was developed in 1969 by the Advanced Research Projects Agency ARPA Network of the US Department of Defense. It was the first operational packet-switching network. • Initially, began operational in only four nodes: UCLA, UCSB, Utah, and SRI
Internet History • 1969-Internet evolves from ARPANET which was developed by ARPA (Advanced Research Projects Agency of US DOF) • It was the first Packet Switching Network. • ARPANET began its operation in 4 locations (4 nodes: UCLA, UCSB, UTAH, SRI) • Today there are 100s of millions hosts • billion users, nearly 200 participating countries. • Number of connections grow exponentially.
Switching Methods • Traditional or primary methods of electronic communication: • Circuit Switching: • Requires a dedicated communication path for duration of transmission; wastes bandwidth, but minimizes delays, Passive network after setting up the call (specially for voice communication) • Message Switching: • Entire path is not dedicated, but long delays result from intermediate storage and repetition of message. Length of the delay depends on the length of the message, channel’s data rate and number of hops. The transmission channels are only used when they are needed (specially for Telegraph & Telex) • New method of electronic Communication used in ARPANet: • Packet Switching: • Specialized case of message switching, with very little delay
FirstTransmission SecondTransmission ThirdTransmission Circuit Switching holds all channels FourthTransmission Message switching holds one channel at a time Circuit Switching vs Message Switching Message Switching: Entire path is not dedicated, but long delays result from intermediate storage and repetition of message. Channels used when needed, not wasted. Circuit Switching: Requires a dedicated communication path for duration of transmission; wastes bandwidth, but minimizes delays, after the call set up network remains passive. Switches were electromechanical and this was advantageous.
Packet Switching • a special case of message switching • The maximum size of transmitted data is called the packet • messages larger than the Max packet size is broken into a number of packets • Packets passing from switch to switch are stored in RAM -buffering data- (rather than slower peripherals such as discs, magnetic drums, used in message switching) -This makes speed conversion possible too. • Advantages of Packet switching: Shorter Delay • Delay of 1st packet = (Transmission time of the first packet) X (Number of hops on the path) • In using High Speed channels across USA = A few hundred millisec • Unlike the Circuit Switching there is no need to have transmission rates of receiving device the same as sending device • Adaptive routing: packets were routed through faster routes, could avoid congested or failed parts of the network.
example • ARPANET used 50-kbs links, for a path with 5 or less hops and a packet length of less than 1000Byte. Transmission Time = 1000x8/50,000 = 0.16sec • The channels are used as efficiently as for message switching.
ARPANET early applications(1st two important ones) • Early applications developed for the ARPANET offered new functionality. • The 1st two important applications are: • TELNET & FTP-developed for the ARPANET • Telnet provided a common denominator terminal for remote computer types to help the situation where each computer system supports a different terminal • FTP allowed an open architecture for transparent transfer of files from one computer to another
National Science Foundation and the Internet • In the 1980s, NSFNet extended packet-switched networking to non-ARPA organization; eventually replaced ARPANet • In 1990 the ARPANET was shut down • NSF Instituted “Acceptable Use Policies” to control the use of Network (e.g. not for profit or personal business) • 1991 General Atomics operated CERFnet, PSINet & UUNET Technologies provide commercial TCP/IP services. • Needed NSF backbone to communicate between their networks, this brought them under Acceptable Use Policy • CIX (Commercial Internet eXchange) was developed to provide commercial internetworking, and avoid NSF Use policy. By 1996 CIX had 147 member network • LINX (London Internet Exchange) formed in 1994 had 24 member networks by 1996
The World Wide Web • CERN Acronym for Conseil Européen pour la Recherche Nucléaire (the European Laboratory for Particle Physics). CERN, a physics research center located in Geneva, Switzerland, is where the original development of the World Wide Web took place by Tim Berners-Lee in 1989 as a method (Distributed Hypermedia Technology) to facilitate communication among members of the scientific community via the Internet.
The World Wide Web • 1989: Concept proposed by Tim Berners-Lee at CERN on distributed hypermedia technology • 1991 prototype WWW developed at CERN using NeXT computer as platform. • End of 1991: CERN released a line –oriented browser or reader to a limited population. • 1993: First graphical browser (Mosaic) developed by Mark Andreasson at NCSA Centre at University of Illinois • Client-server system with browsers as clients, and a variety of media types stored on servers • Uses HTTP (hyper text transfer protocol) for retrieving files
Internet Architecture • Central Office (CO) • Customer Premises Equipment (CPE) • Internet Service Provider (ISP): Point of Presence (POP) entry point to ISP • Network Service Provider (NSP)-ISP connects to a regional ISP via (Internet exchange) IX point, which connect to NSP • Network Access Point (NAP)-Initially only NY, WA, CHI, San Francisco Individual hosts and LANs are connected to an IPC through a POP. The starting point for connection is CPE. Portion of Internet
Connecting to the Internet • End users get connectivity from an ISP (Internet Service Provider) • Home users use dial-up, ADSL (Asymmetric Digital Subscriber Line), cable modems, satellite • Businesses use dedicated circuits connected to LANs • ISPs use “wholesalers” called network service providers (NSP) and high speed (T-3 or higher) connections.
Internet Architecture: Internet Terminology • Central Office ( CO): The place where telephone companies terminate customer lines and locate switching equipment to interconnect those lines with other networks. • Customer Premises Equipment ( CPE): Telecommunications equipment that is located on the customer’s premises ( physical location) rather than on the provider’s premises or in between. Telephone handsets, modems, cable TV set- top boxes, and digital sub-scriber line routers are examples. Historically, this term referred to equipment placed at the customer’s end of the telephone line and usually owned by the telephone company. Today, almost any end- user equipment can be called customer premises equipment, and it can be owned by the customer or by the provider. • Internet Service Provider ( ISP): A company that provides other companies or individuals with access to, or presence on, the Internet. An ISP has the equipment and the telecommunication line access required to have a POP on the Internet for the geographic area served. The larger ISPs have their own high- speed leased lines so that they are less dependent on the telecommunication providers and can provide better service to their customers. • Internet Exchange Point ( IXP): One of a number of major Internet interconnection points that serve to tie all the ISPs together. The IXPs provide major switching facilities that serve the public in general. Companies apply to use the IXP facilities. Much Internet traffic is handled without involving IXPs, using peering arrangements and interconnections within geographic regions. • Network Service Provider ( NSP): A company that provides backbone services to an ISP. Typically, an ISP connects Internet exchange point ( IXP) to a regional ISP that in turn connects to an NSP backbone. • Point of Presence ( POP): A site that has a collection of telecommunications equipment, usually refers to ISP or telephone company sites. An ISP POP is the edge of the ISP’s network; connections from users are accepted and authenticated here. An Internet access provider may operate several POPs distributed throughout its area of operation to increase the chance that their subscribers will be able to reach one with a local telephone call. The largest national ISPs have POPs all over the country.
Internet Architecture: Internet Organization (compromising three tiers) Tier 2 networks are regional ISP networks, often provided by telecoms carriers. Typically, Tier 2 networks pay a fee to a Tier 1 network to access portions of the Internet that the Tier 2 network cannot reach directly or via peer networking arrangements. Tier 1 networks as is forming a top-level network on the Internert and Internet backbone, with each Tier 1 network having access to an entire Internet routing table so that it knows how to direct traffic to any Internet network. There is a rough equivalence between the concepts of Tier 1 network and NSP, although there is no official definition of either term. Tier 3 networks provide only a local presence and provide services to residential and business customers in a locality. Tier 3 networks always pay fees to obtain access to the larger back-bones via Tier 2 networks.
Internet Domains: Internet Names and Addressing • Data communications through the Internet is in the form of packets. • Each packet includes a numeric destination address. • The numeric address is 32-bit binary numbers (IP address) which provides a unique way of identifying devices attached to the Internet. • The address is interpreted as having two components: • a network number, which identifies a network on the Internet, • A host address, which identifies a unique host on that network.
Internet Domains: Internet Names and Addressing • 32-bit IP addresses have two drawbacks • Routers can’t keep track of every network path • Users can’t remember dotted decimals easily • Domain/Domain names address these problems by providing a name for each network domain (hosts under the control of a given entity) • See Figure for example of a domain name tree
Internet Domains: Internet Names and Addresses-Cntd. • Domain: Refers to a group of hosts that are under administrative control of a single entity (e.g. a company or government agency) • Domains are UNIQUE & organized hierarchically. • A domain may consist of a number of subordinate domains. • Each subordinate level is named by prefixing a subordinate name to the name at the next highest level. • edu is the domain for educational institute • mit.edu is the domain for Massachusetts Institute of Technology • lcs.mit.edu is the domain for the Computer Science lab at MIT
Portion of Internet Domain Tree At the top level there are a small number of domains that encompass the entire Internet
Top-level Internet Domainsare assigned by theInternet Assigned Numbers Authority (IANA)
Internet Domains: Internet Names and Addresses-Cntd. • Internet Corporation for Assigned Names and Numbers (ICANN)- is the organization for which administer the top-level names. • Addresses are assigned hierarchically. • Example1: • mil domain is assigned a large group of addresses • DoD allocates a portion of this address space to various organizations for assigning to hosts. • Example2: • MIT with a domain name of mit.edu has 4 IP addresses: • (18.104.22.168), (22.214.171.124), (126.96.36.199), (188.8.131.52) • The subordinate domain lcs.mit.edu has IP address (184.108.40.206)
Domain Name System (DNS) • DNS is directory lookup service that maps hosts names to their numeric address. • DNS contains 4 elements: • Domain name space • Tree-structured name space to identify resources on the Internet. • DNS database • Each node of name space tree has a set of information (e.g. IP, name server for this domain) that is contained in a Resource Record (RRs). The collection of all RRs is organized into a distributed database. • Name servers • Server programs that hold information about a specific portion of the domain name space tree • Resolvers • Programs that extract information from name servers based on client requests
DNS Database • A hierarchical database containing Resource Records (RRs) which provides name-to-address directory services. DNS includes: • name • IP address • and related information for hosts • Key features of DNS database: • Variable-depth hierarchy for names: • Unlimited levels using the period (.) • Distributed database: • The db resides on DNS servers scattered throughout the Internet • Distribution controlled by the database: • DNS db is divided into thousands of separately managed zones, managed by separate administrators. • Distribution & update of records is controlled by the database software.
DNS Database- Cntd. DNS Operation: • User program request an IP address for a domain • A resolver module in the local host or local ISP queries a local name server in the same domain as the resolver. • The local name server checks its local database or cache or send to other name servers, if necessary going to the root server • if found returns IP address to the requestor. • If not found, queries other available name servers, starting down from the root of the DNS tree or as high up the tree as possible. • When local name server receives a response it saves the name/address mapping in its local cache and keep it for the amount of time specified in the time to live field of the retrieved RR. • The user program is give the IP address or an error message.
DNS Database- Cntd. DNS Server Hierarchy • Each name server configured for a specific local zone • Includes subdomains and associated RRs • Authoritative source for that portion of hierarchy • Root servers are at top of hierarchy • Different root servers for different top level domains • Some redundancy within domain spaces to prevent bottlenecks
DNS Database- Cntd. DNS Name Resolution • Query begins with name resolver located in the user host system • Each resolver is configured to know the IO address of a local DNS name server • If the resolver does not have the requested name in its cache, it sends a DNS query to the local DNS server • returns an address immediately, or • returns an address after querying other servers • Two possible types of queries • Recursive: Query another name server for the desired result and then send the result back to the resolver • Iterative: Return to the resolver the address of the next server; the resolver then sends out a new DNS request
DNS Name Resolution • Name Resolution: Each query begins at a name resolver at the user host system • Recursive • Iterative
Internet Addressing • 32-bit global internet address for source & destination in the IP header • Includes a network identifier and a host identifier • Dotted decimal notation • 11000000 11100100 00010001 00111001 (binary) • 220.127.116.11 (decimal)
Summary • Internet domains • Internet names and addresses • Domain name system • Dynamic host configuration protocol • The structure of the Internet • Business and the Internet • The use of packet switching • Key elements • The World Wide Web • Internet architecture • Chapter 7: The Internet