Understanding Network Structures for Efficient Data Sharing

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

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