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Network Structures

Network Structures. Refer: Burgess Ch 3. Resource Sharing Hardware Data storage & retrieval Software Processing power Internet Access. Efficient Cooperation Security Centralized Common backup Also a Risk! Costs Costly to install but savings later. Why Network ??.

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Network Structures

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  1. Network Structures Refer: Burgess Ch 3

  2. Resource Sharing Hardware Data storage & retrieval Software Processing power Internet Access Efficient Cooperation Security Centralized Common backup Also a Risk! Costs Costly to install but savings later Why Network ?? Networks appear when several computers in organization. Why?

  3. Networks contain…. • Hosts that run Clients and Services • Media and equipment that connect Hosts • Protocols that govern connections • Users (Vendors or Customers !?!) • Networks allow cooperationCooperation leads to Communities of Users

  4. Clients and Servers • The Hosts and their services need an Identity • Identities are usually names • However protocols use numeric addresses • Addresses can be associated with names using resolver services and directories • This is an Infrastructure service • SysAdmins maintain these too….

  5. Host Identities & Name Services A host has many different names used in various contexts: • HostID – NIC or CPU serial# • Install Name - /etc/hostname.* • Application Names – eg Oracle database name • Local name list - /etc/hosts • Network Information Service – “yellow pages” • Transport level addresses – TCP/UDP port# + IP# • Physical level addresses – NIC address • DNS names – IP names & info • WINS names – IP, NetBIOS & WfW names

  6. Establishing Network Identity • Identity = Address = Name • Some addresses are fixed (eg HostID, NIC#) • Some must be initialised (eg during startup) • Internet Addresses must be Globally Unique therefore can’t use NIC# (IPv6 excepted?) • Static Allocation • continuous identity (RARP,BOOTP,DNS) • Dynamic Allocation • transient identity (BOOTP,DHCP)

  7. Naming Services • Used to convert Address to Name or vice-versa • A Performance and Security nexus • DNS or bind used world-wide • NIS or NIS+ used in Unix • WINS used in Windows • Authentication (Kerberos,Radius) • Directory (X500,ldap,NDS,ActiveServer)

  8. Network Operating Systems • Peer-to-Peer .vs. Server-Workstation • Unix – most general, open and variant • Windows NT/2000/XP – Workgroups or Domains • Novell - NDS • Macintosh – now like Unix (System X)

  9. NOS Functions • I/O optimisation – Various forms of Cache • Fault Tolerance • Directory – Manage server resources • User Sessions – Directory, history & preferences • Multi-Processing - Concurrency • Print Spooling • Backup

  10. Network Sharing models Based on Synchronous Request/Reply protocols (RPC) • Drive mapping • File System Mount • Resource Share & Subscribe • Terminal session – CLI or shell based • GUI interface – X11,Windows • Web-based

  11. Network Hardware • Ethernet, Fast Ethernet, Gigabit Ethernet • Token Ring • Wireless (IEEE 802.11b) • Fibre Distributed Data interface (FDDI) • ATM • Fibre Channel • High Performance Parallel Interface (HIPPI)

  12. Ethernet Hardware • Network Interface Cards (NIC) • Connector, RAM, DMA, I/O port, IRQ • Workstations – PCs or “Thin Clients” • Cables & Connectors

  13. Network Connections-- Repeaters, Bridges and Routers • An Ethernet is a single collision domain ie a single shared medium (segment) • Bus topology (physical or logical) • Media Access Control (MAC) “contest” based • CSMA/CD • Ethernet Frame format • Ethernet, EthernetII and SNAP • Ethernet cable characteristics: Min.Frame size, Signal propagation speed, Max.Segment length = Collision window size

  14. Network Design with Ethernet • Uses repeaters, hubs, bridges, switches • Repeaters copy incoming bit-stream to all outputs • Bridges filter (MAC address) – isolate local traffic • Both extend range (4 repeats max.) or adapt different media and connectors • Router also, but uses network (IP) address • Switch forwards packet only to target address • Switching Hubs create virtual private cables

  15. Network Segments • In a single network, devices share a media access protocol (eg CSMA/CD in ethernet) • A packet being transmitted usually occupies the medium exclusively over the entire cable • To reduce the traffic density in large networks, they need to be divided into separate media areas or segments • Segments can then be joined using bridges, switches or routers which forward appropriately • What about Broadcasts? Switches usually forward them but Routers usually don’t

  16. Topology Subnets Network addresses Default routes Netmask What’s connected Host Functions Locate key services Network Analysis Checklist

  17. (end)

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