LAN/WAN Interconnectivity

Learning Objectives Explain the OSI reference model, which sets standards for LAN and WAN communications 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 Discuss communication between OSI stacks when two computers are linked through a network Apply the OSI model to realistic networking situations Apply the OSI model to realistic networking situations continued…

Learning Objectives Describe the types of networks as represented through LAN topologies Describe the types of networks as represented through LAN topologies Describe major LAN transmission methods, including Ethernet, token ring, and FDDI 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 Explain basic WAN network communications topologies and transmission methods, including telecommunications, cable TV, and satellite technologies

LAN/WAN Interconnectivity Intense competition between three sectors: Intense competition between three sectors: Telecommunications companies Telecommunications companies Cable TV companies Cable TV companies Satellite communications companies Satellite communications companies

OSI Reference Model Foundation that brings continuity to LAN and WAN communications Foundation that brings continuity to LAN and WAN communications Product of two standards organizations: Product of two standards organizations: ISO ISO ANSI ANSI Developed in 1974 Developed in 1974 Set of communication guidelines for hardware and software design 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 network devices contact each other; how devices using different protocols communicate How a network device knows when to transmit and not transmit data How a network device knows when to transmit and not transmit data How physical network network devices are arranged and connected How physical network network devices are arranged and connected continued…

OSI Guidelines Specify… Methods to ensure that network transmissions are received correctly Methods to ensure that network transmissions are received correctly How network devices maintain a consistent rate of data flow How network devices maintain a consistent rate of data flow How electronic data is represented on network media How electronic data is represented on network media

OSI Layers

Bottom layers Bottom layers Support for physical connectivity, frame formation, encoding, and signal transmission Support for physical connectivity, frame formation, encoding, and signal transmission Middle layers Middle layers Establish and maintain a communication session between two network nodes Establish and maintain a communication session between two network nodes Monitor for error conditions Monitor for error conditions Uppermost layers Uppermost layers Application/software support for encrypting data and assuring interpretation/presentation of data Application/software support for encrypting data and assuring interpretation/presentation of data

Physical Layer Functions Provides transfer medium (eg, cable) Provides transfer medium (eg, cable) Translates data into a transmission signal Translates data into a transmission signal Sends signal along the transfer medium Sends signal along the transfer medium Includes physical layout of network Includes physical layout of network Monitors for transmission errors Monitors for transmission errors Determines voltage levels for data signal transmissions and to synchronize transmissions Determines voltage levels for data signal transmissions and to synchronize transmissions Determines signal type (eg, digital or analog) Determines signal type (eg, digital or analog)

Analog Signals

Digital Signals

Data Link Layer Functions Constructs data frames Constructs data frames Creates CRC information; checks for errors Creates CRC information; checks for errors Retransmits data if there is an error Retransmits data if there is an error Initiates communications link; makes sure it is not interrupted (ensures node-to-node physical reliability) Initiates communications link; makes sure it is not interrupted (ensures node-to-node physical reliability) Examines device addresses Examines device addresses Acknowledges receipt of a frame Acknowledges receipt of a frame

Data Link Layer Data link frame contains fields consisting of address and control information Data link frame contains fields consisting of address and control information Two important sublayers Two important sublayers Logical link control (LLC) Logical link control (LLC) Media access control (MAC) Media access control (MAC) Connectionless service versus connection- oriented service Connectionless service versus connection- oriented service

Network Layer Functions Determines network path for routing packets Determines network path for routing packets Helps reduce network congestion Helps reduce network congestion Establishes virtual circuits Establishes virtual circuits Routes packets to other networks, resequencing packet transmissions when needed Routes packets to other networks, resequencing packet transmissions when needed Translates between protocols Translates between protocols

Transport Layer Functions Ensures reliability of packet transmissions Ensures reliability of packet transmissions Ensures data is sent and received in the same order Ensures data is sent and received in the same order Sends acknowledgement when packet is received Sends acknowledgement when packet is received Monitors for packet transmission errors and resends bad packets 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 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 Establishes and maintains communications link Determines which node transmits at any point in time Determines which node transmits at any point in time Disconnects when communication session is over Disconnects when communication session is over Translates node addresses Translates node addresses

Presentation Layer Functions Translates data to a format the receiving node understands (eg, from EBCDIC to ASCII) Translates data to a format the receiving node understands (eg, from EBCDIC to ASCII) Performs data encryption Performs data encryption Performs data compression Performs data compression

Application Layer Functions Enables sharing remote drivers and printers Enables sharing remote drivers and printers Handles messages Handles messages Provides file transfer services Provides file transfer services Provides file management services Provides file management services Provides terminal emulation services Provides terminal emulation services

Communicating Between Stacks OSI model provides standards for: OSI model provides standards for: Communicating on a LAN Communicating on a LAN Communicating between LANs Communicating between LANs Internetworking between LANs and WANs and between WANs and WANs Internetworking between LANs and WANs and between WANs and WANs

Peer Protocols

Primitives

Layered Communications

Applying the OSI Model

Types of Networks Three main topologies Three main topologies Bus Bus Ring Ring Star Star

Bus Topology Built by running cable from one PC or file server to the next Built by running cable from one PC or file server to the next Terminators signal the physical end to the segment Terminators signal the physical end to the segment

Advantages of Bus Topology Works well for small networks Works well for small networks Relatively inexpensive to implement Relatively inexpensive to implement Easy to add to it Easy to add to it

Disadvantages of Bus Topology Management costs can be high Management costs can be high Potential for congestion with network traffic Potential for congestion with network traffic

Ring Topology Continuous path for data with no logical beginning or ending point, and thus no terminators 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 Easier to manage; easier to locate a defective node or cable problem Well-suited for transmitting signals over long distances on a LAN Well-suited for transmitting signals over long distances on a LAN Handles high-volume network traffic Handles high-volume network traffic Enables reliable communication Enables reliable communication

Disadvantages of Ring Topology Expensive Expensive Requires more cable and network equipment at the start Requires more cable and network equipment at the start Not used as widely as bus topology Not used as widely as bus topology Fewer equipment options Fewer equipment options Fewer options for expansion to high-speed communication Fewer options for expansion to high-speed communication

Star Topology Oldest and most common network design Oldest and most common network design Multiple nodes attached to a central hub Multiple nodes attached to a central hub

Advantages of Star Topology Good option for modern networks Good option for modern networks Low startup costs Low startup costs Easy to manage Easy to manage Offers opportunities for expansion Offers opportunities for expansion Most popular topology in use; wide variety of equipment available Most popular topology in use; wide variety of equipment available

Disadvantages of Star Topology Hub is a single point of failure Hub is a single point of failure Requires more cable than the bus Requires more cable than the bus

Bus Networks in a Physical Star Layout No exposed terminators No exposed terminators Capability for connecting multiple hubs to expand network in many directions Capability for connecting multiple hubs to expand network in many directions Expansion opportunities for implementing high-speed networking Expansion opportunities for implementing high-speed networking Popular design; wide range of equipment available Popular design; wide range of equipment available

LAN Transmission Methods Ethernet Ethernet IEEE specifications IEEE specifications Broadest options for expansion and high- speed networking Broadest options for expansion and high- speed networking Token ring Token ring IEEE specifications IEEE specifications FDDI (Fiber Distributed Data Interface) FDDI (Fiber Distributed Data Interface) High-speed variation of token ring High-speed variation of token ring

Ethernet Uses CSMA/CD access method for data transmission on a network Uses CSMA/CD access method for data transmission on a network Typically implemented in a bus or bus-star topology Typically implemented in a bus or bus-star topology Carrier sense Carrier sense Collision Collision

Ethernet Communications

Ethernet II

Ethernet Standards

Token Ring Developed by IBM in the 1970s; remains a primary LAN technology Developed by IBM in the 1970s; remains a primary LAN technology Employs physical star topology with logic of ring topology 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 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 Frame

Token Ring Terms Multistation access unit (MAU) Multistation access unit (MAU) Beaconing Beaconing Broadcast storms Broadcast storms

FDDI Fiber-optic data transport method capable of a 100-Mbps transfer rate using a dual ring topology Fiber-optic data transport method capable of a 100-Mbps transfer rate using a dual ring topology Synchronous versus asynchronous communications Synchronous versus asynchronous communications Nodes monitor network for error conditions Nodes monitor network for error conditions Long periods of no activity Long periods of no activity Long periods where the token is not present Long periods where the token is not present Class A and Class B nodes Class A and Class B nodes

WAN Network Communications Typical providers of WAN network services Typical providers of WAN network services Telecommunications companies Telecommunications companies Cable TV companies Cable TV companies Satellite providers Satellite providers Newer sources of WAN connectivity Newer sources of WAN connectivity Cable television networks Cable television networks Satellite TV companies Satellite TV companies Wireless WANs Wireless WANs Wide use of star topology Wide use of star topology

Telecommunications WANs Earliest source of WAN connectivity Earliest source of WAN connectivity Regional telephone companies, also called: Regional telephone companies, also called: Telcos Telcos Regional bell operating companies (RBOCs) Regional bell operating companies (RBOCs) Long-distance telecommunications companies Long-distance telecommunications companies Plain old telephone service (POTS) or public switched telephone network (PSTN) Plain old telephone service (POTS) or public switched telephone network (PSTN)

General Topology Linking LATA and IXC Lines

Connecting LANs through a T-Carrier Line

T-Carrier Services and Data Rates

Cable TV WANs Also called cablecos or multiple system operators (MSOs) Also called cablecos or multiple system operators (MSOs) Use a distributed architecture that consists of several star-shaped centralized locations Use a distributed architecture that consists of several star-shaped centralized locations Headend is the main focal point in the star Headend is the main focal point in the star

Wireless WANs Use radio, microware, and satellite communications Use radio, microware, and satellite communications Packet radio communications Packet radio communications

Topology of a Radio Wave WAN Joining Two LANs

WAN Transmission Methods Use different switching techniques to create data paths (channels) for transmitting data Use different switching techniques to create data paths (channels) for transmitting data Switching Switching Enables multiple nodes to simultaneously transmit and receive data, or Enables multiple nodes to simultaneously transmit and receive data, or Enables data to be transmitted over different routes to achieve maximum efficiency in terms of speed and cost Enables data to be transmitted over different routes to achieve maximum efficiency in terms of speed and cost

Switching Techniques Time division multiple access (TDMA) Divides channels into distinct time slots Frequency division multiple access (FDMA) Divides channels into frequencies Statistical multiple access Dynamically allocates bandwidth based on application need Circuit switching Uses a dedicated physical circuit Message switching Uses store-and-forward method of data transmission Packet switching Combines circuit and message switching

Chapter Summary Open Systems Interconnection (OSI) model Open Systems Interconnection (OSI) model Basic network topologies Basic network topologies Key LAN transmission methods Key LAN transmission methods WAN communications options WAN communications options WAN transmission methods WAN transmission methods