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Technology Focus: Network and Communications Technology Major Network Categories Major Network Types The Global Internet Internal Corporate Networks The Worldwide Telephone System 2 Major Network Categories Telecommunications Spans Two Concerns Voice and Video Communication vs Data Communication At least one party is a computer The two are converging Telecommunications Voice and Video Data Communication 3 Network A network is a system of hardware, software and transmission components that collectively allow two application programs on two different stations connected to the network to communicate well. 4 Elements of a Network Server Station Client Station Mobile Client Station Stations are computers and other devices such as cellphones and PDAs Server Station 5 Elements of a Network Frame Server Station Client Station Mobile Client Station Stations communicate by sending messages called Frames Server Station 6 Elements of a Network Switch Switch Switch Switch Frames may pass through multiple switches 7 Elements of a Network Access Link Access Link Access Link Access links connect stations to the first switch Access Link 8 Elements of a Network Trunk Link Trunk Link Trunk Link Trunk links connect switches Trunk Link Trunk Link Higher capacity than access links Often optical fiber 9 Client/Server Architecture Server Client PC Service Network Clients Receive Services Servers Provide Services 10 Clients and Servers Network Applications - File sharing, Network printing, Email, etc. Clients – Access the server to perform an application Servers – Host one or more applications; Store application files; Respond to client requests Most common desktop operating systems – Windows 95/98/XP (desktop) Common network operating systems: Microsoft Windows Server, Novell Network, UNIX, LINUX A server is not a type of computer. Any computer can be changed from a workstation to a server. It is dependent on the operating system and application programs loaded onto the computer. Since servers need to support simultaneous access from multiple clients and be operational 24x7, they tend to have greater power, storage capacity, and stability. Hence, computer companies label computers “servers”. 11 Packets and Frames Messages in Single Networks are Called Frames Messages traveling across multiple networks (in Internets) are Called Packets 12 Packet vs. Circuit Switching Circuit switching: dedicated path between two nodes. Entire circuit must be available during the transmission. (Example: local telephone network.) Relatively inefficient for data transmission. (Why?) Message switching: store-and-forward process. (Postal mail analogy) Packet switching: also store-and forward, this time messages divided into packets of uniform length: Improved line utilization over message switching. Key differences between circuit switching and packet switching: sharing of links, storing and forwarding, graceful degradation 13 Packet Switching 1. Message Broken into Smaller packets Original Message Packet Switch Computer X A Packet B C Switching Decision E Computer Y F D 2. Packets Routed individually 14 Packet Switching Packet Switching Reduces Trunk Line Costs Packets from several conversations are multiplexed on trunk lines Trunk Link Packet from A to B Packet from C to D 15 Packet Switching Packet Trailer Data Field Header Other Header Field Address Field Message Structure 16 Quality of Service It is not enough that networks work They must work well Quality of Service (QoS) defines quantitative measures of service quality Speed and Delay (Latency) Reliability Security (not a QoS measure but crucial) Service Level Agreements (SLAs) Guarantees for various service parameters Network provider pays performance penalties if guarantees are not met 17 Quality of Service (QoS) Data Transmission Rate Bits per second (bps) Multiples of 1,000 (not 1,024): kbps, Mbps, Gbps, Tbps Congestion and Latency Congestion because traffic chronically or momentarily exceeds capacity Latency (delay measured in milliseconds) Especially bad for some services such as voice communication or highly interactive applications Reliability Availability Percentage of time the network is available to users for transmission and reception Want 24 x 7 x 365 availability Telephone network: Five 9s (99.999%) Error Rate % Lost or damaged messages or bits 18 Geographic Scope Local Area Network (LAN) Limited geographical distance: home, office, building, campus, industrial part Customer premises operation User firm chooses technology User firm needs to manage on ongoing basis Low cost per bit transmitted Companies can afford high speed 100 Mbps to the desktop is typical 19 Geographic Scope Wide Area Network (WAN) WAN To link sites Long distances Requires the use of carriers to provide service Limited and complex choices but carrier manages High cost per bit transmitted Companies cannot afford high transmission rates Charges are distance dependent Typically transmit 1.544 Mbps or less Large organizations, like GMU, have bigger access links (Up to 45 Mbps) Carriers have very large trunk links (155 Mbps – 10 Gbps) 20 Internet An internet is a group of networks linked together with routers in a way that allows an application program on any station on any network in the internet to be able to communicate with an application program on another station on any other network. Network 1 Network 2 21 An Internet Multiple Networks Connected by Routers Path of a Packet is its Route Network 3 Routers Packet Network 2 Network 1 Route 22 An Internet Single Networks Have Switches Switches Connect Station-to-Router or Router-to-Router Network X Switches Network Y Network Z Routers Switches 23 Frames and Packets Within a single network, the packet is carried in the data field of that network’s frame, probably across multiple switches Packet Frame 24 Frames and Packets Router removes packet from source network’s frame, sends back out in receiving network’s frame format Same Packet Frame Different Frame Format 25 Frames and Packets Router removes packet from source network’s frame, sends back out in receiving network’s frame format Same Packet 3d Frame Format Different Frame Format 26 Frames and Packets Like passing a shipment (the packet) from a truck (frame) to an airplane (frame) at an airport. Shipper Same Shipment Truck Airport Receiver Airport Truck Airplane 27 The Internet: Universal Addressing Scheme Browser Webserver Software Network Packet Router Packet Route Router Router Packet User PC (Host) IP Address=128.150.50.9 Webserver (Host) IP Address=128.171.17.13 Host name=voyager.cba.hawaii.edu 28 Hosts All computers connected to the Internet are hosts Server hosts (webservers, FTP servers, etc.) Also client PCs at home, at school, and at work Also PDAs and Internet-enabled cellphones The Internet treats all hosts of all sizes as equals Only application software distinguishes between them (browsers for client PCs, webserver applications for server hosts, etc.) 29 Host Addresses and Host Names Host IP Address Official address of host on the Internet Every host must have an IP address, including client PCs and PDAs 32 bits long Often expressed in dotted Decimal Notation for human reading (e.g., 128.171.17.13) Hosts and routers work with 32-bit binary form IP Address: 128.171.17.13 30 Internet Service Providers (ISPs) and Internet Backbone Carriers Webserver User PC Internet Backbone (Multiple Carriers) Router ISP ISP Internet Service Provider Internet Service Provider 31 Wide Area Networks (WANs) Organizations connect their computing resources locally through so-called LAN’s (Local Area Newtorks) LAN’s are typically considered a local IT resource, internally owned and operated So called WAN’s , wide area networks are needed to interconnect geographically distant computing resources (branches of a bank, factories and warehouses, production and R&D facilities etc) of a single organization Businesses WAN connectivity options include: Connecting their corporate servers (and/or LAN’ s) together using leased lines (i.e., building private WANs) Using the existing infrastructure owned by specialized providers: Public switched data networks Using the Internet infrastructure (Virtual Private Network technology) (VPN) 32 Trunk-Line Based Leased Line T1 Trunk Line (1.544 Mbps) Access Line Computer Telephone Switch Trunk Line Telephone Switch Telephone Switch Server T1 Leased Line (1.544 Mbps) End-to-End Circuit with Trunk Line Speed 33 Leased Line Networks Leased Line (Private Line or Dedicated Line) Point-to-point connection Always on (no dialing or other “call setup” procedures) If used extensively, lower cost per minute than dial-up service Must be provisioned (set up) ahead of time (instantaneous provisioning not possible) T1s have historically been very expensive to lease. Lower-cost alternatives include: Fractional T1 Lease a portion of the T1 (in DSO (64 Kbps) or 2-DSO (128 Kbps) increments). Common increments: 64 Kbps (Called a DS-0, not Fractional T1) 128 bps, 256 kbps, 384 kbps, 512 kbps, 768 kbps Essentially, a leased line is a circuit switched service 34 Alternative #1: Leased Line Corporate Data Network Site A Multisite Leased Line Mesh Network Site B OC3 Leased Line T3 Lease Line 56 kbps Leased Line T1 Leased Line Site C T1 Leased Line 56 kbps Leased Line 56 kbps Leased Line Site D Site E 35 Leased Line Trade-Offs Leased Line Network Many leased lines, often span long distances Pricing is distance-sensitive Company must design/install the network, buy the switching equipment (e.g., Routers), order many leased lines, and maintain the network. Pros: Control, Security, Predictable Performance Cons: More expensive, more management and administration responsibilities scalability issues for large number of nodes 36 Alternative #2: Corporate Use of a Public Switched Data Networks Alternative: Use a public Packet-Switched Network Site B Site A POP POP Packet-Switched Network (Based on Frame Relay, SONET, or other WAN technology) Point of Presence POP Site D POP Site C Site E One leased line per site. Typically in form of a “service” (not a ‘leased line’) that includes the physical layer protocol. 37 Public Switched Data Network Trade-Offs Public Packet-Switched Network Owned and operated by the telecommunications Companies (AT&T, Sprint UUNet etc.) Only need one leased line from each site to a POP Short distances to the first available POP (intra-LATA) Pricing is typically not distance sensitive Mostly it is based on requested data rate parameters Business still needs one router per site and some maintenance, but bulk of the design, installation, equipment, and maintenance falls to the Communications Company. Pros: Less expensive, less administration and management Cons: Less control, potential security issues, less performance predictability 38 Alternative #3: Corporate Customer orders Internet VPN services VPN connection The Internet (A collection of networks owned by Communications Companies). Customer connects to its ISP’s POPs. The ISP Sends traffic over its own TCP/IP network or to other TCP/IP networks, as needed. VPN connection LAN(s) Ethernet Switch(es) Customer Premises B VPN connection Customer Premises C 39 What is ordered? The customer orders (1) either: Leased Lines from the telephone company to connect its sites to the ISP POPs; or The physical line connection comes bundled with the ISP’s Internet VPN services (2) VPN services (3) A Service Level Agreement (SLA) 40