Represents a Continuously Varying Signal by a Continuously Varying Signal, a Digital Transmission Can Be Broken Down Into Discrete Messages
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1 www.onlineeducation.bharatsevaksamaj.net www.bssskillmission.in ADVANCED NETWORK MANAGEMENT Topic Objective: At the end of this topic student would be able to: Understand RAD Data Communications Explain Analogy of Telephone Network Highlight Telecommunication Network Elaborate Distributed Computing Environment Evaluate TCP / IP-Based Networks Analyze Communications Protocols Examine Communication Architectures Define Importance of Topology Describe Information Technology Managers Identify Network Provisioning Learn about the Future of Network Management Definition/Overview: Digital communications refers to the transmission of a sequence of digital messages (a bit stream) or a digitized analog signal. This is in contrast to analog communications. While analog communicationsWWW.BSSVE.IN represents a continuously varying signal by a continuously varying signal, a digital transmission can be broken down into discrete messages. The messages are either represented by a sequence of pulses by means of a line code, or by a limited set of analogue wave forms, using a digital modulation method. Transmitting data in discrete messages allows for greater signal processing capability. The ability to process a communications signal means that errors caused by random processes can be detected and corrected. Digital signals can also be sampled instead of continuously monitored. The multiplexing of multiple digital signals is much simpler to the multiplexing of analog signals. Because of all these advantages, and because recent advances in wideband communication channels and solid-state electronics have allowed scientists to fully realize these advantages, digital communications has grown quickly. Digital communications is quickly edging out www.bsscommunitycollege.in www.bssnewgeneration.in www.bsslifeskillscollege.in 2 www.onlineeducation.bharatsevaksamaj.net www.bssskillmission.in analog communication because of the vast demand to transmit computer data and the ability of digital communications to do so. Key Points: 1. RAD Data Communications RAD Data Communications (also known as "RAD") is a privately held corporation, based in Tel Aviv, Israel, which designs and manufactures specialized networking equipment. It was founded in 1981 by Zohar Zisapel and his brother, Yehuda. RAD's research, development and engineering includes TDM, Ethernet, MPLS, IP, ATM, Frame Relay, E1/T1, E3/T3, xDSL, SDH/SONET, pseudowire circuit emulation and service emulation, clock synchronization, voice compression, wireless, mobile and satellite connectivity, fiber optics, SFPs (small form-factor pluggable) and ASICs (application- specific integrated circuit), and integrated network management. In 1998, RAD invented TDMoIP (TDM over IP) technology. The company's installed base exceeds 10,000,000 units and includes more than 150 telecommunications carriers and operators. RAD products are sold by distributors in 164 countries. RAD Data Communications is a member of the RAD Group of companies. 2. Analogy of Telephone Network Network effects become significant after a certain subscription percentage has been achieved, calledWWW.BSSVE.IN critical mass. At the critical mass point, the value obtained from the good or service is greater than or equal to the price paid for the good or service. As the value of the good is determined by the user base, this implies that after a certain number of people have subscribed to the service or purchased the good, additional people will subscribe to the service or purchase the good due to the positive utility:price ratio. A key business concern must then be how to attract users prior to reaching critical mass. One way is to rely on extrinsic motivation, such as a payment, a fee waiver, or a request for friends to sign up. A more natural strategy is to build a system that has enough value without network effects, at least to early adopters. Then, as the number of users increases, the system becomes even more valuable and is able to attract a wider user base. Joshua Schachter has explained that he built Del.icio.us along these lines - he built an online system where he could keep bookmarks for himself, such that even if no other user www.bsscommunitycollege.in www.bssnewgeneration.in www.bsslifeskillscollege.in 3 www.onlineeducation.bharatsevaksamaj.net www.bssskillmission.in joined, it would still be valuable to him. It was relatively easy to build up a user base from zero because early adopters found enough value in the system outside of the network aspects. The same could be said for many other successful websites which derive value from network effects, e.g. Flickr, MySpace. Beyond critical mass, the increasing number of subscribers generally cannot continue indefinitely. After a certain point, most networks become either congested or saturated, stopping future uptake. Congestion occurs due to overuse. The applicable analogy is that of a telephone network. While the number of users is below the congestion point, each additional user adds additional value to every other customer. However, at some point the addition of an extra user exceeds the capacity of the existing system. After this point, each additional user decreases the value obtained by every other user. In practical terms, each additional user increases the total system load, leading to busy signals, the inability to get a dial tone, and poor customer support. The next critical point is where the value obtained again equals the price paid. The network will cease to grow at this point, and the system must be enlarged. The congestion point may be larger than the market size. New Peer-to-peer technological models may always defy congestion. Peer-to-Peer systems, or "P2P," are networks designed to distribute load among their user pool. This theoretically allows true P2P networks to scale indefinitely. The P2P based telephony service Skype benefits greatly from this effect. But market saturation will still occur. Network effects are commonly mistaken for economies of scale, which result from business size rather than interoperability (see also natural monopoly). To help clarify the distinction, people speak of demandWWW.BSSVE.IN side vs. supply side economies of scale. Classical economies of scale are on the production side, while network effects arise on the demand side. Network effects are also mistaken for economies of scope. The network effect has a lot of similarities with the description of phenomenon in reinforcing positive feedback loops description of system dynamics. System dynamics could be used as a modeling method to describe such phenomenon such as word of mouth and Bass model of marketing. 3. Telecommunication Network A telecommunications network is a network of telecommunications links and nodes arranged so that messages may be passed from one part of the network to another over multiple links and through various nodes. Telecommunications network links (including their endpoints or "nodes") may in turn be built out of hierarchical transmission systems. www.bsscommunitycollege.in www.bssnewgeneration.in www.bsslifeskillscollege.in 4 www.onlineeducation.bharatsevaksamaj.net www.bssskillmission.in 4. Distributed Computing Environment The Distributed Computing Environment (DCE) is a software system developed in the early 1990s by a consortium that included Apollo Computer (later part of Hewlett- Packard), IBM, Digital Equipment Corporation, and others. The DCE supplies a framework and toolkit for developing client/server applications. The framework includes a remote procedure call (RPC) mechanism known as DCE/RPC, a naming (directory) service, a time service, an authentication service and a distributed file system (DFS) known as DCE/DFS. The largest unit of management in DCE is a cell. The highest privileges within a cell are assigned to a role called cell administrator, normally assigned to the "user" cell_admin. Note that this need not be a real OS-level user. The cell_admin has all privileges over all DCE resources within the cell. Privileges can be awarded to or removed from the following categories: user_obj, group_obj, other_obj, any_other for any given DCE resource. The first three correspond to the owner, group member, and any other DCE principal respectively. The last group contains any non-DCE principal. Multiple cells can be configured to communicate and share resources with each other. All principals from external cells are treated as "foreign" users and privileges can be awarded or removed accordingly. In addition to this, specific users or groups can be assigned privileges on any DCE resource, something which is not possible with the traditional UNIX file system, which lacks ACLs. Major components of DCE within every cell are: The Security Server that is responsible for authentication. The Cell DirectoryWWW.BSSVE.IN Server (CDS) that is the repository of resources and ACLs. The Distributed Time Server that provides an accurate clock for proper functioning of the entire cell. Modern DCE implementations such as IBM's are fully capable of interoperating with Kerberos as the security server, LDAP for the CDS and the Network Time Protocol implementations for the time server. While it is possible to implement a distributed file system using the DCE underpinnings by adding filenames to the CDS and defining the appropriate ACLs on them, this is not user-friendly. DCE/DFS is a DCE based application which provides a distributed filesystem on DCE. DCE/DFS can support replicas of a fileset (the DCE/DFS equivalent of a filesystem) on multiple