Reasons for Local Area Networks

• Shared Resources
• Connectivity
• Data and Software Security
• Data and Software Backup
• Access to Network Applications

Components of the Physical Layer (OSI Layer 1) of a LAN:

• The Medium that carries the LAN signal
• Twisted Pair
• Coaxial Cable
• Fiber-Optic Cable
• Wireless
• The Network Interfaces to the LAN

Shared Resources

• Printers
• Attached to the File Server
• Attached as a LAN Node
• Disks
• Large Disk on Server; Smaller Disks on Nodes
• CD-ROMs
• Including Multi-disc Players
• Files
• Entire Files through File Locking
• Items within Files through Record Locking
• Elimination of Sneakernet
• Software
• Single User Licenses with Metering Software
• Network Licenses with License Servers
• Site Licenses
• Beware of Software & Information Industry Association (formerly Software Publisher’s Association)

• Between Nodes on the LAN
• Allows access to Resources on Individual Nodes
• To Members of Workgroups
• For Collaborative Efforts
• To Other Interconnected LANs
• Allows access to Remote Resources
• Between Dissimilar Computers
• Allows PC’s and Macs to be Interconnected
• Allows Workstations, Mainframes, etc., to be interconnected

• Access to LAN is Password Protected
• Access can be Limited to Selected Individuals for Selected Applications
• Software can be Hidden (to prevent theft)
• Software Upgrades Done to Server
• Boot PROM’s eliminate local files on public-site (i.e., in educational settings) computers

• All Files on the Server are typically Backed Up Daily
• Files on Individual Nodes can be Backed Up

• Databases
• Can be Written to via Record Locking
• Local or Remote-mounted Databases
• Groupware
• Glorified Electronic Mail
• Scheduling
• Interconnected Applications
• Lotus Notes
• Novell GroupWise
• Specialized Servers
• FAX Servers
• Terminal (Communication) Servers
• Database Servers
• Print Servers

• Electronic Mail
• MHS - Message-Handling System (LAN standard)
• ITU-TSS X.400 (International standard)
• SMTP - Simple Mail Transfer Protocol (the one really used)
• POP - Post Office Protocol
• Eudora
• IMAP - Internet Message Access Protocol
• Netscape
• Internet Explorer
• Electronic Communications Privacy Act (18 USC 2701-2711)
• Lehigh’s Warning Banner:

• Multimedia
• Audio
• Images
• Video
• CD-ROM/DVD

• Network Browsers
• Netscape
• Internet Explorer

Need Becomes Self-Evident

• Productivity Suffers Waiting for Resources
• Communications Need to Be Enhanced
• Access to Information Resources Required

• Develop Strategic Information Plan
• Develop Information Inventory
• Anticipate Future Needs
• Plan an Upgrade Path

The Medium that carries the LAN signal

• Twisted Pair 
• Unshielded (mostly Ethernet)
• Shielded (via metallic sheath) (mostly Token Ring)
• RJ 45 Connectors
• Maximum Point-to-Point Link: 100 Meters (328 Feet)
• 10BaseT - 10 Mbits per second, Baseband, Twisted Pair
• 100BaseT - 100 Mbits per second, Baseband, Twisted Pair
• Twist cancels out electrical interference

• Underwriters’ Laboratories (UL) Performance Levels:
• Category 1
• Untwisted
• Strictly for Voice Transmission
• Category 2
• Untwisted or Low-quality Twisted
• Suitable for RS-232 (Serial) Communications
• Unsuitable for 10BaseT
• Category 3
• Wiring used in most commercial buildings
• Suitable for 10BaseT or 4Mbit/sec Token Ring
• Twists/Foot: 3-5
• Category 4
• Suitable for 10BaseT or 4Mbit/sec Token Ring
• Twists/Foot: 5-8
• Category 5
• Suitable for 10BaseT
• Suitable for 100BaseT or 16Mbit/sec Token Ring
• Twists/Foot: 8-10

• Coaxial Cable

• ThickNet
• Maximum Segment: 500 Meters (1,640 Feet)
• Vampire Tap connections
• Taps must be spaced in multiples of 2.5 meters
• 10Base5 - 10 Mbits per second, Baseband, 500 m.

• ThinNet

• RG-58 Cable
• Maximum Segment:

185 Meters (607 Feet)
• Up to 800 Meters w/Repeater
• BNC (Bayonet Nut Couple) Connectors
• 30 or fewer connections per segment
• Connection spacing of no less than 0.5 meters (1.64ft)
• 10Base2 - 10 Mbits per second, Baseband, 200 m.

• Fiber-Optic Cable
• Maximum Point-to-Point Link: 2,000 Meters (6,560 Feet)
• Can routinely carry data rates up to 565 Mbits per second
• Immune to electrical interference

• Wireless
• Radio Signals (RF)
• Low transmission speed
• Immune to most barriers (e.g., walls!)
• Infrared Signals (IR)
• High frequency
• Easily disrupted

• Medium Attachment Unit (MAU) - IEEE 802.3 term
• Transceiver - Ethernet term
• The device which connects the LAN cable to the workstation
• Medium dependent
• 10Base5 - Part of Vampire Tap
• Attachment Unit Interface (AUI) - connection between MAU and workstation; DB-15 connector
• 10Base2 - Part of Network Interface Card
• 10BaseT - Part of Network Interface Card
• External device - 10BaseT to AUI
• Functions:
• Transmission of traffic to the LAN media
• Reception of traffic from the LAN media
• Detection of collisions
• Monitors LAN media to prevent transmission
• Jabber detection from defective nodes
• Hubs - central signal distributors
• Multiport Repeater (lowest level)
• Can be expandable
• Bridge Cards to connect similar LANs
• Router Cards to connect dissimilar LANs
• Network management (e.g., Packets per Port)
• SNMP - Simple Network Management Protocol
• Individual port control and security
• Multistation Access Unit (MSAU)
• Hub in a token ring network

• Switch-based Hubs
• Each connection at full LAN speed
• Limited only by speed of backplane
• ATM (Asynchronous Transfer Mode) Hubs
• Connections established as needed
• Predictable cell (53 byte packets) delivery period
• High speeds to 155 Mbits per second
• Ideal for multimedia
• Network Interface Cards
• Bus type: ISA, PCI
• Connector types
• Ethernet Combo cards
• 10BaseT only cards
• Token Ring cards

Models of Network Architectures

• Proprietary - different vendors, different architectures
• IBM - SNA/SDLC - Systems Network Architecture/Synchronous Data Line Control
• Digital Equipment Corporation - DECnet
• Open Systems - architecture adheres to published standards with defined interfaces
• ISO/OSI - Open Systems Interconnection Reference Model
• TCP/IP - Transmission Control Protocol/Internet Protocol
• Protocol - standard - a formal set of rules setting the format and control of data exchange

• Seven Layer Network Architecture
• Connectivity is provided in layers 1-3 (communications subnet)
• Interoperability is provided in layers 5-7 (host process)
• Regardless of equipment vendor
• Transport Layer 4 acts as a buffer between connectivity and interoperability
• Peer protocols used between corresponding layers on communicating systems
• Each layer communicates or passes data to adjacent layers

• Application Layer - provides end-user services - user applications interact with this layer and with each other through this layer

• Presentation Layer - establishes a common syntax in which data is exchanged between the two hosts

• Session Layer - establishes and terminates process-to-process communication sessions
• synchronizes flow of data
• can have multiple session connections
• Transport Layer - lets processes at each end transmit and receive data reliably (i.e., end-to-end transparency)
• Segments long messages into smaller packets prior to transmission and assures the reassembly of those packets at the receiving end
• Sequentially handles multiple sessions
• Allows each protocol to use its own Service Access Point (also referred to as a Port or Socket)
• Network Layer - establishes a path (route) for the data packets along the communication subnet from the source node to the destination node
• Data Link Layer - maintains a reliable communication link between adjacent nodes

• Logical Link Control
• Passes outbound application data to Media Access Control (i.e., places data on the LAN)
• Sends the received data to the correct protocol stack; each protocol has a Service Access Point (a Port or Socket)
• Provides standard software interface to higher level protocols
• Insulates higher layers from any network tasks or problems

• Media Access Control

• Physical Layer - handles the electrical and mechanical interface and transmission of signals from one system to another