LAN/WAN Interconnectivity
This learning resource provides an in-depth overview of LAN (Local Area Network) and WAN (Wide Area Network) interconnectivity through the OSI (Open Systems Interconnection) reference model. It outlines the key functions of each OSI layer, discusses various LAN topologies (bus, ring, star), and examines major LAN transmission methods, including Ethernet and token ring. The document further explores WAN communications methods, including telecommunications and satellite technologies, alongside the necessary principles for effective networking and device intercommunication.
LAN/WAN Interconnectivity
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Presentation Transcript
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)
