DU SOL B.Com 3rd Year E-Commerce Notes Chapter 10 Internet Protocols
Write a short note on Layers and Networking.
A network can consist of two computers connected together on a desk or it can consist of many Local Area Networks (LANs) connected together to form a Wide Area Network (WAN) across a continent. The key is that two or more computers are connected together by a medium and are sharing resources.
These resources can be tiles, printers, hard drives, or CPU numbercrunching power. Data Communications is the transfer of data or information between a source and a receiver. The source transmits: the data and the receiver receives it.
The actual generation of the information is not part of data communications nor is the resulting action of the information at the receiver. Data Communication is interested in the transfer of data, the method of transfer and the preservation of the data during the transfer process.
In Local Area Networks, we are interested in “connectivity”: connecting computers together to share resources. Even though the computers can have different disk operating systems, languages, cabling and locations, they still can communicate to one another and share resources. The International standard organization ISO in 1984 developed a reference model known as OS1 model (The Open System Interconnection OSI reference model) composed of seven layers for standardization, each specifying particular network functions and it is now considered the primary architectural model for intercomputer communications.
The OSI model divides the tasks involved with moving information between networked computers into seven smaller, more manageable task groups. A task or group of tasks is then assigned to each of the seven OSI layers.
Each layer is reasonably self-contained so that the tasks assigned to each layer can be implemented independently. This enables the solutions offered by one layer to be updated without adversely affecting the other layers. .
Basic Components of a Network:
The transmitter of data. Examples are
The communications stream through which the data is being transmitted. Examples are –
- Fiber optics
- Radio Frequencies (RF)
- Infrared Wireless
The receiver of the data transmitted. Examples are –
Data flow is the flow of data between two points. The direction of the data flow can be described as –
Data flows is only one direction on the data communication line (medium) Examples are radio and television broadcasts. They go from the TV station to your, home television.
Data flows in both direction but only direction at a time on the data communication line. For example, a conversation on walkie-talkies is a half-duplex data flow. Each person takes turns talking.
Data flows in both direction simultaneously. Modems are configured to flow data in both directions. Bi-directional both directions simultaneously.
What do you understand by OSI Layering and TCP Layering?
The International Standards Organization (ISO) Open Systems
Interconnect (OSI) is a standard set of rules describing the transfer of data between each layer in a network operating system.
Each layer has a specific function. For example, the physical layer deals with the electrical and cable specifications. The OSI Model clearly defines the interfaces between each layer.
This allows different network operating systems and protocols to work together by having each manufacturer adhere to the standard interfaces. The application of the ISO OSI model has allowed the modem multi protocol networks that exist today.
There are seven layers in the OSI model –
- Layer 7-Application (Top Layer)
- Layer 6-Presentation
- Layer 5-Session
- Layer 4- Transport
- Layer 3-Network
- Layer 2-Data link
- Layer I-Physical (Bottom Layer)
The OSI model provides the basic rules that allow multi protocol networks to operate. Understanding the OSI model is instrumental in understanding how the many different protocols fit into the networking jigsaw puzzle.
The Open System Interconnection (OSI) reference model describes how information from a software application in one computer moves through a network medium to a software application in another computer.
A task or group of tasks is then assigned to each of the seven OSI layers. Each layer is reasonably self-contained so that the tasks assigned to each layer can be implemented independently. This enables the solutions offered by one layer to be updated without adversely affecting the other layers.
Characteristics of the OSI Layers:
The seven layers of the OSI reference model can be divided into two categories: upper layers and lower layers.
The upper layers of the OSI model deal with application issues and generally are implemented only in software. The highest layer, the application layer, is closest to the end user. Both users and application layer processes interact with software applications that contain a communications component. The term upper layer is sometimes used to refer to any layer above another layer in the OSI model.
The lower layers of the OSI model handle data transport issues. The physical layer and the data link layer are implemented in hardware and software. The lowest layer, the physical layer, is closest to the physical network medium (the network cabling, for example) and is responsible for actually placing information on the medium.
The following illustrates the division between the upper and lower OSI layers.
- Data Link Physical
Information being transferred from a software application in one computer system to a software application in another must pass through the OSI Layers. For example, if a software application in System A has information to transmit to a software application in System B, the application program in System A will pass its information to the application layer (Layer 7) of System A.
The application layer then passes the information to the presentation layer (Layer 6), which relays the data to the session layer (Layer 5), and so on down to te physical layer (Layer 1). At the physical layer, the information is placed on the physical network medium and is sent across the medium to System B. The physical layer of System B removes the information from the physical medium, and then its physical layer passes the information up to the data link layer (Layer 2), which passes it to the network layer (Layer 3), and so on, unit it reaches the application layer (Layer 7) of System B.
Finally, the application layer of System B passes the information to the recipient application program to complete the communication process.
Interaction between OSI Model Layers:
A given layer in the OSI model generally communicates with three other OSI layers: the layer directly above it, the layer directly below it and its peer layer in other networked computer systems. The data link layer in. System A, for example communicates with the network layer of System A, the physical layer of System A, and the data link layer in System B.
- Data Link
- Data Link
OSI Layer Services:
One OSI layer communicates with another layer to make use of the services provided by the second layer. The services provided by adjacent layers help a given OSI layer communicate with its peer layer in other computer systems. Three basic elements are involved in layer services: the service user, the service provider and the service access point (SAP).
The physical layer defines the electrical, mechanical, procedural and functional specifications for activating, maintaining and deactivating the physical link between communicating network systems.
Physical layer specifications define characteristics such as voltage levels, timing of voltage changes, physical data rates, maximum transmission distances and physical connectors. Physical layer implementations can be categorized as 1 either LAN or WAN specifications. Figure illustrates some common LAN and WAN specification. Figure illustrates some common LAN and WAN physical layer implementations.
Data Link Layer:
The data link layer provides reliable transit of data across a physical network link. Different data link layer specifications define different -network and protocol characteristics, including physical addressing, network topology, error notification, sequencing of frames and flow control.
Physical addressing (as opposed to network addressing) defines how devices are addressed at the data link layer. Network topology consists of the data link layer specifications that often define how devices are to be physically connected, such as in a bus or a ring topology.
Error notification alerts upper layer protocols that a transmission error has occurred and the sequencing of data frames reorders frames that are transmitted out of sequence. Finally, flow control moderates the transmission of data so that the receiving device is not overwhelmed with more traffic than it can handle at one time.
The Institute of Electrical and Electronics Engineers (IEEE) has subdivided the data link layer into two sub layers: Logical Link Control (LLC) and Media Access Control (MAC). Figure illustrates the IEEE sub layers of the data link layer.
The Data Link Layer contains Two Sublayers:
The Logical Link Control (LLC) sublayer of the data link layer manages communications between devices over a single link of a network. LLC is defined in the IEEE 802.2 specification and support both connectionless and connection-oriented services used by higher-layer protocols. IEEE 802.2 defines a number of fields in data link layer frames I that enable multiple higher-layer protocols to share a single physical data link The Media Access Control (MAC) sublayer of the data link layer manages protocol access to the physical network medium. The IEEE MAC specification defines MAC addresses, which enable multiple devices to uniquely identify one another at the data link layer.
The network layer defines the network address, which differs from the MAC address. Some network, layer implementations, such as the Internet Protocol (IP), define network addresses in a way that route selection can be determined systematically by comparing the source network address with the destination network address and applying the subnet mask. Because this layer defines the logical network, layout, routers can use this layer to determine how to forward packets.
Because of this, much of the design and configuration work for internet works happens at Layer 3, the network layer. Flow control manages data transmission between – devices so that the transmitting device does not send more data than the receiving device can process. Multiplexing enables data from several applications to be transmitted onto a single physical link, Virtual circuits are established, maintained and terminated by the transport layer.
Error checking involves creating various mechanisms for detecting transmission errors, while error recovery involves acting, such as requesting that data be retransmitted, to resolve any errors that occur. The transport protocols used on the Internet are TCP and UDP.
The session layer established, manages and terminates communication sessions. Communication sessions consist of service requests and service responses that occur between applications located in different network device. These requests and responses are coordinated by protocols implemented at the session layer. Some examples of session-layer implementations include Zone Information Protocol (ZIP), the Apple Talk protocol that coordinates the name binding process; and Session Control Protocol (SCP), the DECnet Phase IV session layer protocol.
The presentation layer provides a variety of coding and conversion functions that are applied to application layer data. These functions ensure that information sent from the application layer of one system would be readable by the application layer of one their system. Some examples of presentation layer coding and conversion schemes include common data representation formats, conversion of character representation formats, common data compression schemes and common data encryption schemes.
Common data representation formats or the use of standard image, sound and video formats, enable the interchange of application data between different types of computer systems. Conversion schemes are used to exchange information with systems by using different text and data representations, such as EBCDIC and ASCII.
Standard data compression schemes enable data that is compressed at the source device to be properly decompressed at the destination. Standard data encryption schemes enable data encrypted at the source device to be properly deciphered at the destination. Presentation layer implementations are not typically associated with a particular protocol stack. Some well-known standards for video include QuickTime and Motion Picture Experts Group (MPEG).
QuickTime is an Apple Computer specification for video and audio and MPEG is a standard for video compression and coding. Among the well-known graphic image formats are Graphics Interchange Format (GIF), Joint Photographic Experts Group (JPEG) and Tagged Image File Format (TIFF). GIF is a standard for compressing and coding graphic images. JPEG is another compression and coding standard for graphic images and TIFF is a standard coding format for graphic images.
The application layer is the OSI layer closest to the end user, which means that both the OSI application layer and the user interact directly with the software application. This layer interacts with software applications that implement a communicating component. Such application programs fall outside the scope of the OSI model.
Application layer functions typically, include identifying communication partners, determining resource availability and synchronizing communication. When identifying communication panniers, the application layer determines the identity and availability of communication partners for an application with data to transmit.
When determining resource availability, the application layer must decide whether sufficient network resources for the requested communication exist. In synchronizing communication, all communication between applications requires cooperation that is managed by the application layer. Some examples of application layer implementations include Telnet, File Transfer Protocol (FTP), and Simple Mail Transfer Protocol (SMTP).
What do you understand by TCP, UDP, IP, SLIP and PPP Protocols?
The OSI model provides a conceptual framework for communication between computers, but the model itself is not a method of communication. Actual communication is made possible by using communication protocols. In the context of data networking, a protocol is a formal set of rules and conventions that governs how computers exchange information over a network medium.
A protocol implements the functions of one or more of the OSI layers. A wide variety of communication protocols exist. Some of these protocols include LAN protocols, WAN protocols. Network protocols and routing protocols. LAN protocols operate at the physical and data link layers of the OSI model and define communication over the various LAN media. WAY protocols operate at the lowest three layers of the OSI model and define communication over the various wide-area media.
Routing protocols are network layer protocols that are responsible for exchanging information between routers so that the routers can select the proper path for network traffic. Finally, network protocols are the various upper- layer protocols that exist in a given protocol suite. Many protocols rely on others for operation.
For example, many routing protocols use network protocols to exchange information between routers. This concept of building upon the layers already in existence is the foundation of the OSI model.
Transmission Control Protocol (TCP):
The TCP provides reliable transmission of data in an IP environment. TCP corresponds to the transport layer (Layer 4) of the OSI reference model. Among the services TCP provides are stream data transfer, reliability, efficient flow control, full duplex operation and multiplexing. With stream data transfer, TCP delivers an unstructured stream of bytes identified by sequence numbers.
This service benefits applications because they do not have to chop data into blocks before handing it off to TCP. Instead, TCP groups bytes into segments and passes them to IP for delivery. TCP offers reliability by providing connection-oriented, end-to-end reliable packet delivery through an internetwork. It does this by sequencing bytes with a forwarding acknowledgment number that indicates to the destination the next byte the source expects to receive. Bytes not acknowledged within a specified time period are retransmitted.
The reliability mechanism of TCP allows devices to deal with lost, delayed, duplicate or misread packets. A time-out mechanism allows devices to detect lost packets and request retransmission. TCP offers efficient flow control which means that, when sending acknowledgments back to the source, the receiving TCP process indicates the highest sequence number it can receive without overflowing its internal buffers.
Full-duplex operation means that TCP processes can both send and receive at the same time. Finally, TCP’s multiplexing means that numerous simultaneous upper-layer conversations can be multiplexed over a single connection.
TCP Connection Establishment:
To use reliable transport services, TCP hosts must establish a connection-oriented session with one another. Connection establishment is performed by using a “three-way handshake” mechanism.
A three-way handshake synchronizes both ends of a connection by allowing both sides to agree upon initial sequence numbers. This mechanism also guarantees that both sides are ready to transmit data and know that the other side is ready to transmit as well.
This is necessary so that packets are not transmitted or retransmitted during session establishment or after session termination. Each host randomly chooses a sequence number used to track bytes within the stream it is sending and receiving. Then, the three-way handshake proceeds in the following manner: The first host (Host A) initiates a connection by sending a packet with the initial sequence number (X) and SYN bit set to indicate a connection request.
The second host (Host B) receives the SYN, records the sequence number X, and replies by acknowledging the SYN (with an ACK = X + 1). Host B includes its own initial sequence number (SEQ = V). An ACK = 20 means the host has received bytes 0 through 19 and expects byte 20 next. This technique is called forward acknowledgment. Host A then acknowledges all bytes Host B sent with a forward acknowledgment indicating the next byte Host A expects to receive (ACK = Y + Data transfer then can begin.
Positive Acknowledgment and Retransmission (PAR):
A simple transport protocol might implement a reliability-and-flow-control technique where the source sends one packet, starts a timer and waits for an acknowledgment before sending a new packet. If the acknowledgment is not received before the timer expires, the source retransmits the packet. Such a technique is called positive acknowledgment and retransmission (PAR). By assigning each packet a sequence number, PAR enables hosts to track lost or duplicates packets caused by network delays that result in premature retransmission.
The sequence numbers are sent back in the acknowledgments so that the acknowledgments can be tracked. PAR is an inefficient use of bandwidth, however, because a host must wait for an acknowledgment before sending a new packet and only one packet can be sent at a time.
TCP Sliding Window:
A TCP sliding window provides more efficient use of network bandwidth than PAR because it enables hosts to send multiple bytes or packets before waiting for an acknowledgment. In TCP, the receiver specifies the current window size in every packet. Because TCP provides a byte-stream connection, window sizes are expressed in bytes.
This means that a window is the number of data bytes that the sender is allowed to send before waiting for an acknowledgment. Initial window sizes are indicated at connection setup. But might vary throughout the data transfer to provide flow control.
A window size of zero, for instance, means, “Send no data.” In a TCP sliding-window operation, for example, the sender might have a sequence of bytes to send (numbered I to 10) to a receiver who has a window size of five.
The sender then would place a window around the first five bytes and transmit them together. It would then wait for an acknowledgment. The receiver would respond with an ACK – 6, indicating that it has received bytes l to 5 and is expecting byte 6 next. In the same packet, the receiver would indicate that its window size is 5.
The sender then would move the sliding window five bytes to the right and transmit bytes 6 to 10. The receiver would respond with an ACK=11, indicating that it is expecting sequenced byte 11 next. In this packet, the receiver might indicate that its window size is 0 (because, for example, its internal buffers are full). At this point, the sender cannot send any more bytes until the receiver sends another packet with a window size greater than 0.
TCP Packet Field Description:
The following description summarize the TCP packet fields
- Source Port and Destination Port – Identifies points at which upper- layer source and destination processes receive TCP services.
- Sequence Number – Usually specifies the number assigned to the first byte of data in the current message. In the connection- establishment phase, this field also can be used to identify an initial sequence number to be used in an upcommg transmission.
- Acknowledgment Number-Contains the sequence number of the next byte of data the sender of the packet expects to receive.
- Data Office:-Indicates the number of 32-bit words in the TCP header.
- Reserved-Remains reserved for future use.
- Flags – Carries a variety of control information, including the SYN and ACK bits used for connection establishment and the FIN bit used for connection termination.
- Window-Specifies the size of the sender’s receive window (that is, the buffer space available for incoming data).
- Checksum-Indicates whether the header was damaged in transit.
- Urgent Pointer – Points to the first urgent data byte in the packet.
- Options-Specifies various TCP options
- Data-Contains upper-layer information.
User Datagram Protocol (UDP):
The User Datagram Protocol (UDP) is a connectionless transport-layer protocol (Layer 4) that belongs to the Internet protocol family. UDP is basically an interface between IP and upper-layer processes. UDP protocol ports distinguish multiple applications running on a single device from one another.
Unlike the TCP, UDP adds no reliability, flow-control or error-recovery functions to IP. Because of UDP’s simplicity, UDP headers contain fewer bytes and consume less network overhead than TCP.
UDP is useful in situations where the reliability mechanisms of TCP are not necessary, such as in cases where a higher-layer protocol might provide error and flow control.
UDP is the transport protocol for several well-known application-layer protocols, including Network File System (NFS), Simple Network Management Protocol (SNMP), Domain Name System (DNS) and Trivial File Transfer Protocol (TFTP).
The UDP packet format contains four fields. These include source and destination ports, length and checksum fields.
A UDP packet consists of four fields
Source and destination ports contain the 16-bit UDP protocol port numbers used to demultiplex datagrams for receiving application-layer processes. A length field specifies the length of the UDP header and data. Checksum provides an (optional) integrity check on the UDP header and data.
Internet Protocol (IP):
The Internet Protocol (IP) is a network-layer (Layer 3) protocol that contains addressing information and some control information that enables packets to be routed. IP is documented in RFC 791 and is the primary network-layer protocol in the Internet protocol suite. Along with the Transmission Control Protocol (TCP), IP represents the heart of the Internet protocols.
IP has two primary responsibilities: providing connectionless, best-effort delivery of datagrams through an internetwork and providing fragmentation and reassembly of datagrams to support data links with different maximum- transmission unit (MTU) sizes.
An IP packet contains several types of information
- Version-Indicates the version of IP currently used.
- IP Header Length (IHL)-Indicates the datagram header length in 32- bit words.
- Type-of-Service-Specifies how an upper-layer protocol would like a current
- Total Length – Specifies the length, in bytes of the entire IP packet, including the data and header.
- Identification – Contains an integer that identifies the current datagram. This field is used to help piece together datagram fragments.
- Flags – Const of 3-bit field of which the two low-order (least- significant) bits control fragmentation. The low-order bit specifies whether the packet can be fragmented. The middle bit specifies whether the packet is the last fragment in a series of fragmented packets. The third or high-order bit is not used.
- Fragment Offset – Indicates the position of the fragment’s data relative to the beginning of the data in the original datagram, which allows the destination IP process to properly reconstruct the original datagram.
- Time-to-Live – Maintains a counter that gradual ly decrements down to zero, at which point the datagram is discarded.This keeps packets from looping endlessly.
- Protocol – Indicates which upper-layer protocol receives incoming packets after IP processing is complete.
- Header Checksum – Helps ensure IP header integrity.
- Source Address – Specifies the sending node.
- Destination Address – Specifies the receiving node.
- Options-Allows IP to support various options, such as security.
- Data-Contains upper-layer information.
One of the most practical and economical connections to the Internet is to -dial in to an Internet Access Provider (l AP) using either the Serial-Line Internet Protocol (SLIP) or the Point-to-Point Protocol (PPP). If you plan to use one of these methods, you’ll probably want to install a Web browser so you can access the full range of graphical and multimedia presentation available on the World Wide Web. However, to take advantage of these features, you must also install and configure the Remote Access Service (RAS) for Windows NT Workstation/ Server 3.5.
The Internet protocols are the world’s most popular open-system (nonproprietary) protocol suite because they can be used to communicate across any set of interconnected networks and are equally well suited for LAN and W AN communication. The Internet protocols consist of a suite pf communication protocols of which the two best known are the Transmission Control Protocol (TCP) and the Internet Protocol (IP).
The Internet protocol suite not only includes lower-layer protocols (such as TCP and IP), but it also specifies common applications such as electronic mail, terminal emulation and file transfer. Internet protocols were first developed in the mid-1970s, when the Defense Advanced Research Projects Agency (DARPA) became interested in establishing a packet-switched network that would facilitate communication between dissimilar computer systems at research institutions.
With the goal of heterogeneous connectivity in mind, DARPA funded research by Stanford University and Bolt, Beranek and Newman (BDN). The result of this development effort was the Internet protocol suite, completed in the late 1970s. TCP/IP later was included with Berkeley Software Distribution (BSD) UNIX and has since become the foundation on which the Internet and the World Wide Web (WWW) are based.
The Internet protocol suite includes many application-layer protocols that represent a wide variety of applications, including the following –
- File Transfer Protocol (FTP) – Moves files between devices
- Simple Network-Management Protocol (SNMP)-Primarily reports anomalous network conditions and sets network threshold values
- Telnet-Serves as a terminal1 emulation protocol
- X Windows-Serves as a distributed windowing and graphics system used for communication between X terminals and UNIX workstations
- Network File System (NFS), External Data Representation (XDR) and Remote procedure Call (RPC) – Work together to enable transparent access to remote network resources.
- Simple Mail Transfer Protocol (SMTP) – Provides electronic mail services
- Domain Name System (DNS) – Translates the names of network nodes into network addresses.
What are the Emerging scenario in ISP and internetwork?
An internetwork is a collection of individual networks, connected by intermediate networking devices, that functions as a single large network. Internetworking refers to the industry, products and procedures that meet the challenge of creating and administering internet works. Figure illustrates some different kinds of network technologies that can be interconnected by routers and other networking devices to create an internetwork.
Internet working Challenges:
Implementing a functional internetwork is no simple task. Many challenges must be faced, especially in the areas of connectivity, reliability, network management, and flexibility. Each area is key in establishing an efficient and effective internetwork. The challenge when connecting various systems is to support communication among disparate technologies.
Different sites, for example, may use different types of media operating at varying speeds or may even include different types of systems that need to communicate.
Because companies rely heavily on data communication, internetworks must provide a certain level of reliability. This is an unpredictable world, so many large internetworks include redundancy to allow for communication even when problems occur. Furthermore, network management must provide centralized support and troubleshooting capabilities in an internetwork.
Configuration, security, performance and other issues must be adequately addressed for the internetwork to function smoothly. Security within an internetwork is essential. Many people think of network security from the perspective of protecting the private network from outside attacks. However, it is just as important to – protect the network from internal attacks, especially because most security breaches come from inside.
Networks must also be secured so that the internal network cannot be used as a tool to attack other external sites. Early in the year 2000, many major web sites were the victims of distributed denial of service (DDOS) attacks. These attacks were possible because a great number of private networks currently connected with the Internet were not properly secured. These private networks were used as tools for the attackers. Because nothing in this world is stagnant, internetworks must be flexible-enough to change with new demands.
Objectives of Data Communication Network:
The major criteria that a data communication network much meet are –
Performance is the defined as the rate of transference of error-free data. It is measured by the response time. Response time is the elapsed time between the end of an inquiry and the beginning of a response, for example, requesting a file transfer and starting the file-transfer.
Factors that affect response time are –
(a) Number of Users: The more users are on a network, the slower the network will run
(b) Transmission Speed: The speed that the data will be transmitted at measured in bits per second (bps)
(c) Media Type: The type of physical connection used to connect nodes together
(d) Hardware Type: Slow computers such as XT or fast ones such as Pentiums
(e) Software Program: How well is the network operating system (NOS)
Consistency is the predictability of response time and accuracy of data.
(a) Users prefer to have consistent response times; they develop a feel for normal operating conditions. For example, if the “normal” response time is 3 seconds for printing to a network printer but a response time of over 30 seconds occurs, we know that there is a problem in the system.
(a) Accuracy of data determines if the network is reliable! If a system loses data, then the users will not have confidence in the information and will often not use the system.
Reliability is the measure of how often a network is usable. MTBF (Mean Time Between Failures) is a measure of the average time a component is expected to operate between failures, and is normally provided by the manufacturer.
A network failure can be caused by a problem with the hardware, the data carrying medium or the Network Operating System.
Recovery is the network’s ability to return to a prescribed level of operation after a network failure. This level is where the amount of lost data is nonexistent or at a minimum. Recovery is based on having back-up files.
Security is the protection of hardware, software and data from unauthorized access. Restricted physical access to computers, password protection, limiting user privileges and data encryption are common security methods. Anti-virus monitoring programs to defend against computer viruses are also a security measure.
- Electronic Mail (e-mail or Email) replaces snail mail. E-mail is the forwarding of electronic files to an electronic post office for the recipient to pick up.
- Scheduling Programs allow people across the network to schedule appointments directly by calling up their fellow worker’s schedule and selecting a time
- Videotext is the capability of having a two-way transmission of picture and sound. Games like Doomand Hearts, distance education lectures, etc. use video text.
- Groupware is the latest network application. It allows user groups to share documents, schedules databases, etc. (ex. Lotus Notes).
- Teleconferencing allows people in different regions to “attend” meetings using telephone lines.
- Telecommuting allows employees to perform office work at home by “Remote Access” to the network.
- Automated Banking Machines allow banking transactions to be performed everywhere: at grocery stores, drive-in machines etc.
- Information Service Providers provide connections to the Internet and other information services. Examples are CompuServe, Genie, Prodigy, America online (AOL), etc.
- Electronic Bulletin Boards (BBS – Bulletin Board Services) are dialup connections (using a modem and phone lines) that offer a range of services for a fee.
Value Added Networks are common carriers such as AGT, Bell Canada, etc. (they can be private or public companies) who provide additional leased line connections to their customers. These can be Frame Relay, ATM (Asynchronous Transfer Mode), X.25, etc. The leased line is the Value Added Network.
A wide variety of organizations contribute to internetworking standards by providing forums for discussion, turning informal discussion into formal specifications and proliferating specifications after they are standardized. Most standards organizations create formal standards by using specific processes: organizing ideas, discussing the approach, developing draft standards, voting on all or certain aspects of the standards and then formally releasing the completed standard to the public. Some of the best- known standards organizations that contribute to internet working standards include these:
International Organization for Standardization (ISO) – ISO is an international standards organization responsible for a wide range of standards, including many that are relevant to networking. Its best-known contribution is the development of the OSI reference model and the OSI protocol suite.
- American National Standards Institute (ANSI) – ANSI which is also a member of the ISO, is the coordinating body for voluntary standards groups within the United States. ANSI developed the Fiber Distributed Data Interface (FDDI) and other communications standards.
- Electronic Industries Association (EIA) – EIA specifies electrical transmission standards including those used in networking. The EIA developed the widely used EIAffIA-232 standard (formerly known as RS-232).
- Institute of Electrical and Electronic Engineers (IEEE) – IEEE is a professional organization that defines networking and other standards. The IEEE developed the widely used LAN standards IEEE 802.3 and IEEE 802.5.
- International Telecommunication Union Telecommunication Standardization Sector (ITU-T) – Formerly called the Committee for International Telegraph and Telephone (CCITT), ITU- T is now
an international organization that develops communication standards. The ITU- T developed X.25 and other communications standards.
Internet Activities Board (lAB) – lAB is a group of internetwork researchers who discuss issues pertinent to the Internet and set Internet policies through decisions and task forces. The 1AB designates some Request For Comments (RFC) documents as Internet standards, including Transmission Control Protocol Internet Protocol (TCPIIP) and the Simple Network Management Protocol (SNMP).
Topology refers to the shape of a network or the ‘ network’s layout. How different nodes in a network are connected to each
other and how they communicate are determined by the network’s topology. Topologies are either physical or logical. Below are diagrams of the most common network topologies. Two networks have the same topology if the connection configuration is the same, although the networks may differ in physical interconnections, distances between nodes, transmission rates and/ or signal types.
A network topology in which all nodes, i.e., stations are connected together by a single bus. All devices are connected to a central cable, called the bus or backbone.
Fully connected topology:
A network topology in which there is a direct path (branch) between any two nodes. In a fully connected network with nodes, ’ there are n(n-l)/2 direct paths, i.e., branches.
A combination of any two or more network topologies. Instances can occur where two basic network topologies, when connected together, can still retain the basic network character and therefore not be a hybrid network. For example” a tree network connected to a tree network is still a tree network.
Therefore, a ‘hybrid network accrues only when two basic networks are connected and the resulting network topology fails to meet one ‘ of the basic topology definitions. For example, two star networks connected together exhibit hybrid network topologies. A hybrid topology always accrues w when two different basic network topologies are connected.
A network topology in which there are at least two nodes with two or more paths between them. Devices are connected with many , N redundant interconnections between network nodes. In a true mesh topology every node has a connection to every other node in the network.
A network topology in which every node has exactly two branches to it. All devices are … to one another in the shape of a closed loop, so that each device is …. directly to two other devices,… on either side of it.
A network topology in which peripheral nodes are connected to a central node, which rebroadcasts all transmissions received from any peripheral node to all peripheral nodes on the network, including the originating node. All peripheral nodes may thus communicate with all others by transmitting to and receiving from, the central node only.
The failure of a transmission line, i.e., channel, linking any peripheral node to the central node will result in the isolation of that peripheral node from all others. If the star central node is passive, the originating node must be able to tolerate the reception of an echo of its own transmission, delayed by the two-way transmission time, i.e., to and from the central node, plus any delay generated in the central node. An active star network has an active central node that usually has the means to prevent echo-related problems.
Tree topology. A network topology that, from a purely topology viewpoint, resembles an interconnection of star networks in that individual peripheral nodes are required to transmit to and receive from one other node only, toward a central node and are not required to act as repeaters or regenerators.
The function of the central node may be distributed. As in the conventional star network, individual nodes may thus still be isolated from the network by a single-point failure of a transmission path to the node. A single-point failure of a transmission path within a distributed node will result in partitioning two or more stations from the rest of the network.