The fundamental purpose of data communications is to ...ziegler/CORC1312/notes/pdf/CORC1312… ·...

Intro-1Copyright © August 2, 2011 by Chaim Ziegler, Ph.D.

Simplified Communications System Block Diagram

Introduction to Networking

The fundamental purpose of data communications is toexchange information between user's computers, terminalsand applications programs.


Interconnection via a Communications Network

Data Communications Networking

! In its simplest form data communications takes placebetween two devices that are directly connected bysome form of point-to-point transmission medium.

! Often it is impractical for two devices to be directlyconnected:

a) The devices are far apart,b) There is a large set of devices to be

interconnected.

! The solution is to connect each device to aCOMMUNICATIONS NETWORK.


WANS - Wide Area Networks

! Generally cover a large geographic area.

! Usually require the crossing of public rights-of-way.

! Often rely, at least in part, on circuits provided by acommon carrier.

! Typically consist of a number of interconnected switchingnodes (see next page).

! A transmission from any one device is routed throughthese internal nodes to the specified destination devicesusing a specified switching method.


A Generic Switched Communications Network

Switched Communications Networks

Communications between stations is accomplished viatransmission and switching.

! Common Switching Methods:- Circuit Switching- Message Switching- Packet Switching- ATM (Asynchronous Transfer Mode) - Cell Relay


Switching Methods

1. Circuit Switching:

! Prior to the start of data transmission, an end-to-end(station-to-station) physical path must beestablished.

! During data transmission, all channels in the path areused simultaneously.

! The entire path remains dedicated to the pair ofcommunicating stations until circuit release.

! Three phased operation:- Circuit Establishment (Allocation of Resources)- Data Transfer (Use of Resources)- Circuit Termination (Deallocation of Resources)

2. Message Switching:

! A MESSAGE represents a logical unit of informationthat one station wishes to send to another station.

! No dedicated path is established prior to datatransfer. Instead, the message will travel over onechannel at a time.

! A message travels (hops) through the network fromnode-to-node, in a store-and-forward fashion, untilit reaches its final destination.


3. Packet Switching:

! Messages are decomposed into smaller units of datacalled PACKETS and then sent outpacket-by-packet.

! Many packets of the same message can be in transitat the same time.

! Reassembly of the original message is required at thedestination.


Virtual Circuit Packet Switching

Packet Switching Alternatives

A. Virtual Circuit Packet Switching:! A LOGICAL CONNECTION (virtual circuit) is

established between communicating stations priorto the transmission of data packets.

! The logical connection establishes the route overwhich all data packets will travel between stations.

! Packet delivery across the virtual circuit will be insequential order.

! Connection-Oriented Operation:- Connection Establishment Phase- Data Transfer Phase- Connection Termination Phase


Datagram Packet Switching

B. Datagram Packet Switching:

! Each data packet is treated independently from oneanother.

! Each packet finds its own route through the network.

! Packets may arrive at the destination out ofsequential order.

! Connectionless Operation:- Data Transfer Phase


ATM - Asynchronous Transfer Mode Networks

! ATM Networks are sometimes referred to as cell relay orcell switching networks.

! ATM is a culmination of developments in circuit switchingand packet switching.

! ATM uses small, fixed-length packets called cells.

! As with frame relay, ATM provides little internal overheadfor error control.

! Small, fixed-length cells provide for reduced processingoverhead as compared to frame relay.

! User data rates reaching Gbps can be provided.

! ATM is so efficient that it can offer a constant-data-ratechannel (useful for real-time audio and videoapplications) even though it is packet switched.

! Today, most of the Internet backbone consists of ATMnetworks.


Broadcast Communications Networks

A transmission from one station can be received by all otherstation within the network.

Sample Networks:

! Satellite Networks

! Radio Networks

! Local Area Networks (LANs)


Satellite Network Topology Radio Network Topology

Bus Topology Ring Topology

Sample Broadcast Network Topologies

! Common Access Methods:- Contention (e.g., CSMA/CD, etc.)- Reservation- Token Passing


Local Area Networks - LANs

! The scope of a LAN is typically small (a room, singlebuilding, or small cluster of buildings).

! Usually owned by the one organization.

! Provides relatively high user data rates (as compared tomost WANs).

! LAN Configurations:- Broadcast LANs- Switched LANs- Wireless LANs


Local Area Network Topologies


Shared Media vs. Switched LAN Architectures


The Internet - Key Elements

! The Internet is a globally interconnected set of networks.

! Hosts:End systems that are sources and destinations of data.

! Networks:WANs or LANs used to transmit the data between hosts.

! Routers:Devices that interconnect two or more networks and

route data packets to their destinations.! Each packet traverses through a series of routers and

networks as it travels from its source to its destination.


Internet Architecture - Simplified View


Internet Terminology

! Central Office (CO):The place where telephone companies terminatecustomer lines and locate switching equipment tointerconnect those lines with other networks.

! Customer Premise Equipment (CPE):Telecommunications equipment that is located on thecustomer’s premises.

! Internet Service Provider (ISP):A company that provides other companies or individualswith access to, or presence on, the Internet. ISPs canbe regional or backbone.

! Network Access Point (NAP):In the Unites States, a NAP is one of several majorInternet interconnection points that serve to tie all theISPs together.

! Network Service Provider (NSP):A company that provides backbone service to ISPs.

! Point of Presence (POP):A site that has a collection of telecommunicationsequipment. Usually refers to ISP or telephone companysites. An ISP POP is the access point where users areaccepted and authenticated.

.


Typical Networking Configuration


Intranets

! Implementation of Internet technologies within acorporate organization, rather than for externalconnection to the global Internet

! Rapid prototyping and deployment of new services

! Scales effectively

! Virtually no user or developer training required- Services and user interfaces familiar from Internet

! All platforms with complete interoperability

! Open architecture- Lots of add-on applications available

! Range of distributed computing architectures - Few central servers or many distributed servers

! Support of "legacy" information sources - Databases, word processing documents, groupware

! Range of media types (audio, video, interactiveapplications)

! Inexpensive to start


Connectionless Internetworking - The IP Approach

The Internet Protocol (IP) is a DoD standard. It providesa connectionless data delivery service by routing databetween end stations across an internet.

A connectionless internet facility is flexible in that itrequires very little of its constituent networks.


IP Address Structure

! IP addresses are communicated as four bytes usingdotted decimal notation. e.g.,

00001010 00000000 00000000 00000000 = 10.0.0.0 (ClassA netid=10 (ARPANET))

10000000 00000011 00000010 00000011 = 128.3.2.3(Class B netid=128.3 hostid=2.3)

11000000 00000000 00000001 11111111 = 192.0.1.255(Class C netid=192.0.1 all hosts broadcast)

(BC - IP Address: 146.245.XXX.YYY)


Internet Routing Example


Transport Protocols

! Transmission Control Protocol (TCP)Connection-Oriented

! User Datagram Protocol (UDP)Connectionless

! TCP Services:- Provides reliable communications across reliable and

unreliable networks and internets.- Designed specifically and exclusively to work with IP.

! UDP Services:- Provides a transport-level, unreliable, datagram

service.- Delivery and duplicate detection are not guaranteed.


;/ Client-Server Model for Applications

! Client-Server Model defines a paradigm forcommunications between two programs called the clientand the server.

! Server:Any application that provides a service to a networkuser.

- File Server- Print Server- Communications Server- Telephony Server- Fax Server- Web Server

! Client:Any program that makes a request to the server.(e.g., a browser)


TCP/IP Application Layer Schematic


TCP/IP Application Protocols


TCP/IP Adress Composition

Directory Services - Address Resolution Service

! Within real system environments users (people and APs)are known by symbolic names.

! Directory Services are used to find the addresses of anamed destination user.

! Addresses can consist of:- Network Point-of-Attachment (physical address)- IP address- TCP/UDP port number


TCP/IP Domain Name System (DNS)! The total directory system in a TCP/IP suite is known as the

Domain Name System (DNS).! It uses a hierarchical structure for naming entities.! The Internet uses a partition of Domains at the highest level of

its hierarchy:- COM commercial organizations- EDU educational institutions- GOV government institutions- MIL military groups- NET (Internet) network support centers- ORG nonprofit organizations- BIZ private businesses- PRO medical, legal, and accounting professions- INFO unrestricted use- country code (e.g., .us, .ca, .uk, .il)- etc.


Name-to-Address Resolution Protocols and Sequence

The Domain Name Server! Associated with each institution network is a host that runs

an AP known as the Domain Name Server.! Associated with the DNS server is a Directory

Information Base (DIB) which contains all the directoryrelated information for that institution.

! Each host has a client process known as the NameResolver which communicates the DNS server.


Uniform Resource Locators (URL)

! A Uniform Resource Locator (URL) is a compactrepresentation of the location and access method for aresource available via the Internet.

! General form of a URL:<scheme>:<scheme-specific-part>

! URL Schemes:

http://www.brooklyn.cuny.edu/index.htmlhttp://acc6.its.brooklyn.cuny.edu/~cc312/ftp://myhost.sci.brooklyn.cuny.edu/ziegler/myfile.txtmailto:[email protected]

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