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 cooperation Cooperation 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 b) 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 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 Network Connections -- Repeaters, Bridges and Routers

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 Network Analysis Checklist 1.Topology 2.Subnets 3.Network addresses 4.Default routes 5.Netmask 6.What’s connected 7.Host Functions 8.Locate key services

(end)