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LAN/WAN Interconnectivity. Learning Objectives. Explain the OSI reference model, which sets standards for LAN and WAN communications Discuss communication between OSI stacks when two computers are linked through a network Apply the OSI model to realistic networking situations. continued….
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Learning Objectives • Explain the OSI reference model, which sets standards for LAN and WAN communications • Discuss communication between OSI stacks when two computers are linked through a network • Apply the OSI model to realistic networking situations continued…
Learning Objectives • Describe the types of networks as represented through LAN topologies • Describe major LAN transmission methods, including Ethernet, token ring, and FDDI • Explain basic WAN network communications topologies and transmission methods, including telecommunications, cable TV, and satellite technologies
LAN/WAN Interconnectivity • Intense competition between three sectors: • Telecommunications companies • Cable TV companies • Satellite communications companies
OSI Reference Model • Foundation that brings continuity to LAN and WAN communications • Product of two standards organizations: • ISO • ANSI • Developed in 1974 • Set of communication guidelines for hardware and software design
OSI Guidelines Specify… • How network devices contact each other; how devices using different protocols communicate • How a network device knows when to transmit and not transmit data • How physical network network devices are arranged and connected continued…
OSI Guidelines Specify… • Methods to ensure that network transmissions are received correctly • How network devices maintain a consistent rate of data flow • How electronic data is represented on network media
Bottom layers Support for physical connectivity, frame formation, encoding, and signal transmission Middle layers Establish and maintain a communication session between two network nodes Monitor for error conditions Uppermost layers Application/software support for encrypting data and assuring interpretation/presentation of data OSI Layers
Physical Layer Functions • Provides transfer medium (eg, cable) • Translates data into a transmission signal • Sends signal along the transfer medium • Includes physical layout of network • Monitors for transmission errors • Determines voltage levels for data signal transmissions and to synchronize transmissions • Determines signal type (eg, digital or analog)
Data Link Layer Functions • Constructs data frames • Creates CRC information; checks for errors • Retransmits data if there is an error • Initiates communications link; makes sure it is not interrupted (ensures node-to-node physical reliability) • Examines device addresses • Acknowledges receipt of a frame
Data Link Layer • Data link frame contains fields consisting of address and control information • Two important sublayers • Logical link control (LLC) • Media access control (MAC) • Connectionless service versus connection-oriented service
Network Layer Functions • Determines network path for routing packets • Helps reduce network congestion • Establishes virtual circuits • Routes packets to other networks, resequencing packet transmissions when needed • Translates between protocols
Transport Layer Functions • Ensures reliability of packet transmissions • Ensures data is sent and received in the same order • Sends acknowledgement when packet is received • Monitors for packet transmission errors and resends bad packets • Breaks large data units into smaller ones and reconstructs them at the receiving end for networks using different protocols
Session Layer Functions • Establishes and maintains communications link • Determines which node transmits at any point in time • Disconnects when communication session is over • Translates node addresses
Presentation Layer Functions • Translates data to a format the receiving node understands (eg, from EBCDIC to ASCII) • Performs data encryption • Performs data compression
Application Layer Functions • Enables sharing remote drivers and printers • Handles e-mail messages • Provides file transfer services • Provides file management services • Provides terminal emulation services
Communicating Between Stacks • OSI model provides standards for: • Communicating on a LAN • Communicating between LANs • Internetworking between LANs and WANs and between WANs and WANs
Types of Networks • Three main topologies • Bus • Ring • Star
Bus Topology • Built by running cable from one PC or file server to the next • Terminators signal the physical end to the segment
Advantages of Bus Topology • Works well for small networks • Relatively inexpensive to implement • Easy to add to it
Disadvantages ofBus Topology • Management costs can be high • Potential for congestion with network traffic
Ring Topology • Continuous path for data with no logical beginning or ending point, and thus no terminators
Advantages of Ring Topology • Easier to manage; easier to locate a defective node or cable problem • Well-suited for transmitting signals over long distances on a LAN • Handles high-volume network traffic • Enables reliable communication
Disadvantages ofRing Topology • Expensive • Requires more cable and network equipment at the start • Not used as widely as bus topology • Fewer equipment options • Fewer options for expansion to high-speed communication
Star Topology • Oldest and most common network design • Multiple nodes attached to a central hub
Advantages of Star Topology • Good option for modern networks • Low startup costs • Easy to manage • Offers opportunities for expansion • Most popular topology in use; wide variety of equipment available
Disadvantages ofStar Topology • Hub is a single point of failure • Requires more cable than the bus
Bus Networks in a Physical Star Layout • No exposed terminators • Capability for connecting multiple hubs to expand network in many directions • Expansion opportunities for implementing high-speed networking • Popular design; wide range of equipment available
LAN Transmission Methods • Ethernet • IEEE 802.3 specifications • Broadest options for expansion and high-speed networking • Token ring • IEEE 802.5 specifications • FDDI (Fiber Distributed Data Interface) • High-speed variation of token ring
Ethernet • Uses CSMA/CD access method for data transmission on a network • Typically implemented in a bus or bus-star topology • Carrier sense • Collision
Token Ring • Developed by IBM in the 1970s; remains a primary LAN technology • Employs physical star topology with logic of ring topology • Each node connects to a central hub, but the frame travels from node to node as though there were no starting or ending point
Token Ring Terms • Multistation access unit (MAU) • Beaconing • Broadcast storms
FDDI • Fiber-optic data transport method capable of a 100-Mbps transfer rate using a dual ring topology • Synchronous versus asynchronous communications • Nodes monitor network for error conditions • Long periods of no activity • Long periods where the token is not present • Class A and Class B nodes
WAN Network Communications • Typical providers of WAN network services • Telecommunications companies • Cable TV companies • Satellite providers • Newer sources of WAN connectivity • Cable television networks • Satellite TV companies • Wireless WANs • Wide use of star topology
Telecommunications WANs • Earliest source of WAN connectivity • Regional telephone companies, also called: • Telcos • Regional bell operating companies (RBOCs) • Long-distance telecommunications companies • Plain old telephone service (POTS) or public switched telephone network (PSTN)
