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Transcript
TDC 461 Basic Communications Systems Local Area Networks 29 May, 2001 Agenda • Local Area Networks – Components • Local Area Network Technologies – Topologies – Ethernet – Transmission Media – Token Ring – Network Interface Cards (NICs) – Network Operating System software • Client vs Server functions • Peer-to-Peer vs. Serverbased • LAN Interconnection – LAN Switches – Routers What is a LAN? • Key Elements: – – – – – LAN Components • Workstations (PCs, etc.) – • Interconnecting Cable – • Network Operating System (NOS) Software The Network Interface Card (NIC) and Networking Software (NS) m us t be com patible with each other and with the com puter or device into which they are ins talled. Networking Software (NS) Network Interf ace Card (NIC) NIC NS NS NS Network Hub or Wiring Center NIC Media NIC NIC NS NIC NS NIC NS NIC Shared Application Serv er GOLDMAN: LAN FIG. 01-05 Shared Laser Printer LAN Topologies • How are Workstations connected together? – – – Bus Topology Bus Topology Example: 10Base5 Ethernet Attachment Unit Interface (AUI Cable) Terminating Resister Medium Attachment Unit (MAU) Thick Coaxial Cable Ring Topology Dual Ring Example: Fiber Distributed Data Interface (FDDI) Dual-Attached Workstations in Normal Operation Dual-attached counter rotating rings Self healed after Link Failure Self-healing FDDI dual- link failure attached adapters GOLDMAN: LAN Star Topology Star Topology Example: 10BaseT Ethernet Twisted Pair 10Base-T Hub LAN Cable • LAN Cable can be of several types: – – – Twisted Pair • Unshielded Twisted Pair (UTP) – Similar to telephone cable, but • Usually 4-pair cable is used • UTP Category ratings – Category 3 - 10 Mbps up to 100 meters – Category 4 - 16 Mbps up to 100 meters – Category 5 - 100 Mbps up to 100 meters • Shielded Twisted Pair (STP) – Coaxial Cable • LAN coaxial cable is similar to Cable TV cable (and can be identical) – Construction • • • – Advantages • – Disadvantages • Coaxial Cable Solid metal inner core Plastic insulator - Foil shield Braided shield/outer Plastic or vinyl jacket usually white conductor GOLDMAN: LAN FIG. 08-17 Fiber Optic Cable • Transmits data using light rather than electricity – Structure • • – Advantages • • – Disadvantages • diameters Fiber Optic Cable Glass core Glass cladding 50 microns 62 microns 100 microns Multimode 125 microns 125 microns 140 microns 2-8 microns Singlemode Plastic or vinyl jacket Note: A micron is a millionth of a meter GOLDMAN: LAN FIG. 08-18 LAN Hardware • Cabling and NIC card specs dictated by standards document for the particular LAN Access Method: – – – – – Ethernet Token Ring ARCNet Fiber Distributed Data Interface (FDDI) etc. NIC Card Sales - 1Q 1998 (percentage of 10.9 millions units sold) Fast Ethernet 46% Source: In-Stat Other FDDI 2% 1% Ethernet 41% Token Ring 10% Network Operating Systems • Popular NOSes: – – – • NOS determines workstation role: – – Installed LAN Servers 2Q 1998 NetWare 36% NT Server 17% UNIX 42% Other 5% Source: Dataquest New Servers Deployed Jan-June 1998 NT Server 39% NetWare 34% UNIX 23% Other 4% Source: Network World File Servers • A File Server • Shared files accessed via – – • • Network Drives Client File Server (PC w/ NOS software) (PC w/ Server software) Drive F: C:\USERS\GREG Security • Login (Log on) • Network Manager controls access rights for each user to each resource. Client File Server (PC w/ NOS software) (PC w/ Server software) Drive F: C:\USERS\GREG File Servers • • Client File Server (PC w/ NOS software) (PC w/ Server software) Request Response Example: Get File Open File File Opened Read Data Data Close File File Closed Client File Server NOS Types • Peer-to-Peer NOS – – • Dedicated Server NOS – – – Peer-to-Peer All workstations are loaded with the same Peer-to-Peer network operating sy stem Each workstation conf igured as serv ice requester (client), serv ice prov ider (serv er), or both. Client/Server Client workstations are loaded with specialized client sof tware. Serv er computers are loaded with specialized serv er sof tware designed to be compatible with client sof tware. Printer Serv er GOLDMAN: LAN FIG. 10-01 to other LANs File Serv er with gateway to other networks. LAN Standards • IEEE 802 Committee Standards – 802.3 - Ethernet – 802.5 - Token Ring LAN Standards • IEEE 802 Standards include – Physical (Layer 1) • Cable Types • Maximum length restrictions • Data rate and bit encodings – Medium Access Control (Layer 2) • Access control protocol (determines which device can transmit when • Frame header/trailer format Ethernet • Physical Standards: – 10Base5 (1985) • 10 Mbps Thick Coaxial Cable (Bus) – 10Base2 (1988) • 10 Mbps Thin Coaxial Cable (Bus) – 10BaseT (1990) • 10 Mbps Twisted Pair (Star) Ethernet • Physical Standards: – 100BaseT (1995) • 100 Mbps Twisted Pair (Star) – 100BaseF (1995) • 100 Mbps Fiber (Star) – 1000BaseX (1998) • 1 Gbps Fiber (Star) Ethernet • IEEE Naming System: – <data rate><signal type><length of longest cable in 100s of meters> – Example: 10Base5 • 10 Mbps data rate • Baseband signal type • Longest cable length = 500 meters Ethernet • IEEE Naming System: – <data rate><signal type><length of longest cable in 100s of meters> – Example: 10Base5 • 10 Mbps data rate • Baseband signal type • Longest cable length = 500 meters 10Base5 Ethernet Attachment Unit Interface (AUI Cable) Terminating Resister Medium Attachment Unit (MAU) Thick Coaxial Cable 10Base2 Ethernet Thin Coaxial Cable 10BaseT Ethernet Twisted Pair 10Base-T Hub 100BaseT Ethernet (Fast Ethernet) • Requires high-quality (Category 5) twisted pair cabling • Requires 100 Mbps NIC cards in PC workstations • Requires 100 Mbps hub 100BaseT Ethernet (Fast Ethernet) Twisted Pair 100Base-T Hub Switched Ethernet • Switched vs. shared • Bandwidth to desktop • Additional hardware – Switches • Switched 10 • Switched 100 Gigabit Ethernet • Requires fiber optic cabling • Requires Gigabit NIC cards in PC workstations • Requires Gigabit Ethernet hub or Gigabit Ethernet switch 1000BaseX Ethernet Fiber 1000BaseX Hub Ethernet MAC Protocol • Medium Access Control (MAC) layer protocol is identical for all Ethernets: – Ethernet Frame format – Carrier Sense Multiple Access with Collision Detection (CSMA/CD) used to determine which workstation can send at any given time. Ethernet Frame Format Preamble Dest. Source Length Address Address Data CRC Ethernet Frame • Header: – Preamble - 8 bytes - alternating 1/0 bits for clock synchronization – Dest. Address - 6 bytes – Source Address - 6 bytes – Length - 2 bytes - Packet length • Trailer: – CRC - 4 bytes - Cyclic Redundancy Check MAC Protocol • • • Carrier Sense Multiple Access with Collision Detection • To transmit data packet: – First, listen to see if any other station is transmitting (Carrier Sense) • – When network is quiet, start transmitting • • Carrier Sense Multiple Access with Collision Detection • Station Backoff – Each station involved in collision: • • • – As number of collisions grows, range of random values (N) increases (“exponential backoff”) Ethernet Enhancements • Switched Ethernet – • Full-duplex Ethernet – Ethernet Switches • Ethernet Switch – – – Switches vs. Routers • How is Switch different than a Router? – Addressing • Switch uses layer 2 MAC addresses • Router uses layer 3 IP address – Speed & security • Switch forwards packets fast (~50-100 nsec). • Router takes more time (~1-50 msec) and provides other security features Switched Ethernet Twisted Pair Ethernet Switch Switches vs. Hubs • How is Switch different than a Hub? – Broadcasting (and Security) • Hub broadcasts every packet to every device • Switch forwards packet out single port – Matching Data Rates • All ports on hub must run at same data rate • Switch ports can run at different rates (can buffer incoming packet at one data rate and re-transmit at another data rate). Full-Duplex Ethernet • Full-Duplex Ethernet allows a workstation to send and receive data simultaneously. • Requirements – Must have a full-duplex NIC card – Must be connected to Ethernet switch Switched Hierarchy • Switches allow network manager to put bandwidth where it is needed. – Some users get 10 Mbps shared (hub) – Some users get 10 Mbps dedicated (switch) – Some users get 100 Mbps shared (hub) – Some users get 100 Mbps dedicated (switch) POWER USERS DeskTop Switch 10Base-T Hub Backbone Switch 100 Mbps Ethernet links File Server File Server Token Ring • Physical Layout: – Dual Ring of Stars • Medium Access Control Protocol – Token Passing Token Ring • Advantages over Ethernet: – – • Disadvantages over Ethernet: – – Twisted Pair RO RI Multistation Access Unit (MAU) Ring In Port Patch Cable (TP, STP, Fiber) Multistation Access Unit (MAU) RO Ring Out Port RI Token Ring Frames 1. Token Frame SD AC ED 2. Data/Control Frame SD AC FC Dest. Source Address Address SD -- Start Delimiter AC -- Access Control FC -- Frame Control Data CRC ED -- End Delimiter FS -- Frame Status ED FS Access Control Byte Access Control Byte P P P T M R R R Priority Bits Reservation Bits Token Monitor Bit Bit Token Ring Operation 1 4 MAU 3 2