Topics discussed in this section: 1-1 DATA COMMUNICATIONS The term telecommunication means communication at a distance. The word data refers to information presented in whatever form is agreed upon by the parties creating and using the data. Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable. Topics discussed in this section: Components Data Representation Data Flow 1.#

Figure 1.1 Five components of data communication 1.#

Data Representation TEXT – unicode (32 bits to represent character)- ASCII NUMBERS IMAGES-composed of a matrix of pixel AUDIO- recording or broadcasting of sound or music. VIDEO- recording or broadcasting of a picture or movie 1.#

Figure 1.2 Data flow (simplex, half-duplex, and full-duplex) 1.#

Topics discussed in this section: 1-2 NETWORKS A network is a set of devices (often referred to as nodes) connected by communication links. A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the network. Topics discussed in this section: Distributed Processing Network Criteria Physical Structures Network Models Categories of Networks Interconnection of Networks: Internetwork 1.#

Set of nodes connected via physical links NETWORKS Set of nodes connected via physical links 1) Distributing Processing 2) Sharing Data and centralization 3) Security and robustness 1.#

Network Criteria 1) Performance : Transmission and response times - throughput and delay. 2) Reliability: How often the networks fail 3) Security: Privacy and integrity of communication Data; recovery from breaches and data loss. 1.#

Physical Structures: Types of connections: 1) Point to Point: (P to P) Dedicated link to be utilized only by end devices. 2) Multipoint (Multidrop): Many end devices share the link capacity. 1.#

Figure 1.3 Types of connections: point-to-point and multipoint 1.#

Physical Topology 1.#

Figure 1.4 Categories of topology 1.#

Physical Topology A) Mesh: Each device has dedicated point-to-point link to other devices. Fully connected mesh will have n( n-1)/ 2 F.D. links Where n = number of nodes Advantages: Fast communication, Robust and Privacy (Security) Disadvantages: Cabling Space and cost 1.#

Figure 1.5 A fully connected mesh topology (five devices) 1.#

Physical Topology (cont..) B) Star: Devices are connected Point to Point to a central “Hub” (Controller Exchanger) Advantages: Less cabling and H/W ports, two hops only. Disadvantage: Not robust 1.#

Figure 1.6 A star topology connecting four stations 1.#

Figure 1.7 A bus topology connecting three stations 1.#

Advantage: Less Cabling C) Bus: Multipoint link as “backbone” for a network where devices have drop line to tap into the bus Advantage: Less Cabling Disadvantages: Topology dependent, limit number of nodes on the bus due to signal power loss with distance, not so robust 1.#

Figure 1.8 A ring topology connecting six stations 1.#

Advantages : easy installation, better fault isolation and robustness. C) Ring: Each device connects Point to Point with only two other devices in a left and right neighbors arrangement via a repeater. Advantages : easy installation, better fault isolation and robustness. Disadvantages: N/2 hops communication 1.#

Figure 1.9 A hybrid topology: a star backbone with three bus networks 1.#

D) Hybrid: • Pizza “star” inside a “ ring” Pros: Better robustness, still low cost, Delay is 1 hop (until the star is not with a ring cut, max 2. • Star of busses 1.#

Categories of Networks: Local Area Networks (LAN): Few Kilometers Connects devices (PCs, printers, servers.) within the same room, building, company, and campus. Topologies most used are bus, ring and star. 1.#

Figure 1.10 An isolated LAN connecting 12 computers to a hub in a closet 1.#

Categories of Networks(cont..) Wide Area Networks (WAN): span a large geographical area about 100’s – 1000’s of Km 1) Switched: End users connected via a cloud of switches (subnet). 2) Point-to Point: Line leased from telephone company/ TV connecting users to the ISP for Internet access. 1.#

alternative technologies used include: circuit switching packet switching frame relay Asynchronous Transfer Mode (ATM) 1.#

Circuit Switching uses a dedicated communications path established for duration of conversation comprising a sequence of physical links with a dedicated logical channel eg. telephone network 1.#

Packet Switching data sent out of sequence small chunks (packets) of data at a time packets passed from node to node between source and destination used for terminal to computer and computer to computer communications 1.#

Frame Relay packet switching systems have large overheads to compensate for errors modern systems are more reliable errors can be caught in end system Frame Relay provides higher speeds with most error control overhead removed 1.#

Asynchronous Transfer Mode (ATM) evolution of frame relay fixed packet (called cell) length with little overhead for error control anything from 10Mbps to Gbps constant data rate using packet switching technique with multiple virtual circuits 1.#

Figure 1.11 WANs: a switched WAN and a point-to-point WAN 1.#

Figure 1.12 A heterogeneous network made of four WANs and two LANs 1.#

Categories of Networks(cont..) Metropolitan Area Networks: MAN town/city High-speed backbone linking multiple LAN’s, DSL, TV cables. 1.#

Topics discussed in this section: 1-3 THE INTERNET The Internet has revolutionized many aspects of our daily lives. It has affected the way we do business as well as the way we spend our leisure time. The Internet is a communication system that has brought a wealth of information to our fingertips and organized it for our use. Topics discussed in this section: A Brief History The Internet Today (ISPs) 1.#

The Internet Internet evolved from ARPANET first operational packet network applied to tactical radio & satellite nets also had a need for interoperability lead to standardized TCP/IP protocols 1.#

The Internet: Huge number of interconnected Networks (100000’s) private organized, e.g.’ government, schools, research facilities, in many countries Collection of LAN’S, MAN’S and WAN’s. 􀂄 The internet protocol stack is the TCP/IP 􀂄 End users use the internet via Internet Service providers (ISPs) which are of the following hierarchies: 1.#

Figure 1.13 Hierarchical organization of the Internet 1.#

Internet Elements Stallings DCC8e Figure 1.4 illustrates the key elements that comprise the Internet, whose purpose is to interconnect end systems, called hosts; including PCs, workstations, servers, mainframes, and so on. Most hosts that use the Internet are connected to a network, such as a local area network (LAN) or a wide area network (WAN). These networks are in turn connected by routers. 1.#

Internet Architecture The Internet today is made up of thousands of overlapping hierarchical networks, an overview of the common, general characteristics can be made. Stallings DCC8e Figure 1.5 illustrates this. See hosts grouped into LANs, linked to an an Internet service provider (ISP) through a point of presence (POP). The connection is made in a series of steps starting with the customer premises equipment (CPE). ISPs can be classified as regional or backbone, with peering links between. 1.#

Example Configuration Stallings DCC8e Figure 1.6 illustrates some of the typical communications and network elements in use today. In the upper-left-hand portion of the figure, we see an individual residential user connected to an Internet service provider (ISP) through some sort of subscriber connection. The Internet consists of a number of interconnected routers that span the globe. The routers forward packets of data from source to destination through the Internet. The lower portion shows a LAN implemented using a single Ethernet switch. This is a common configuration at a small business or other small organization. 1.#

Topics discussed in this section: 1-4 PROTOCOLS AND STANDARDS In this section, we define two widely used terms: protocols and standards. First, we define protocol, which is synonymous with rule. Then we discuss standards, which are agreed-upon rules. Topics discussed in this section: Protocols Standards Standards Organizations Internet Standards 1.#

What is a protocol? Communications between computers requires very specific unambiguous rules A protocol is a set of rules that governs how two or more communicating parties are to interact Examples Internet Protocol (IP) Transmission Control Protocol (TCP) HyperText Transfer Protocol (HTTP) Simple Mail Transfer Protocol (SMTP) 1.#

Elements: 1) Syntax: PDU format 2) Semantics: The meaning of each PDU’s field 3) Timing: Synchronization of communication when PDU is to be transferred and its data rate. 1.#

What is a standard? • A “ standard is set of guidelines” to users and manufactures to ensure interconnectivity. 1) “Defacto” not approved but widely used (TCP/IP) 2) “Dejure”: approved by recognized body (IEEE 802.X). 1.#

Summary introduced data communications needs communications model defined data communications overview of networks introduce Internet Chapter 1 summary. 1.#