Networked Information Systems

1. Networked Information Systems 4. Network Hardware and Software

2. Network Hardware • The main bits of network hardware are: • Network interface card (NIC) • Wireless Access Point, (WAP) • Server (e.g. file, application, proxy, DHCP servers) • Switch and hub • Router • Modems

3. Hardware - NIC • The Network interface card (NIC) allows a stand-alone computer to connect to a network. These can be cabled, or wireless (radio) cards. • WAP connects wireless communication devices to a wired or wireless network • NICs are rated by speed: 10, 100, or ‘Gigabit’ 1000Mbps. • For a NIC to work at its maximum speed, all the other network devices between it and the server must have the same – or greater – bandwidth (data-carrying capacity).

4. Hardware – Hubs, Switches Hubs and switches are connection points where cables can join up or be split. Typically, a single incoming cable is split into multiple outgoing cables.

5. Hardware – Hubs, Switches Hubs and switches are the same except.. Hubs pass along all network traffic they receive. Switches (“switching hubs”) are clever enough to only pass on relevant network traffic. Switches greatly reduce network congestion, various sizes, 24, 48 port

6. Hardware – Routers • Security device that guards the connection between a LAN and the outside world (another LAN or a WAN.) A junction between 2 networks • Can be programmed to only allow authorised incoming and outgoing traffic. E.g. it can block certain external sites or forbid MP3 music files to enter. Like an enthusiastic bouncer at the door of a club. • Routers can protect one part of a network from another part of the same network, e.g. school admin LAN and curriculum LAN.

7. Hardware – Modems • Short for modulator-demodulator. A modem is a device to transmit data over telephone or cable lines. • Computer information is stored digitally whereas information transmitted over telephone lines is transmitted in the form of analog waves. A modem converts between these two forms. • Maximum 56k • Very slow

8. Hardware – Modems, DSL & ADSL • DSL uses existing copper phone lines; ADSL one type • Asymmetric digital subscriber line (ADSL); asymmetric b/c more bandwidth is reserved for receiving data than sending, download speeds from 256 kbps to 8 mbps; upload speeds, 16 to 640 kbps • Faster data transfer rates, up to 1500kbps, broadband • Simultaneously talk on phone, send fax • Always on • Cost effective; no dropped connections, faster downloads, no busy signals • Major problem is distance from station, 5 km max. • Security issues, need firewall software

9. Hardware – Modems - ISDN • A standard for sending voice, video, & data over digital telephone lines • Supports data transfer rates in multiples of 64kbps • Relatively expensive

10. Servers Robust central computers at the heart of a network. File servers are the most common server type. There are also application servers, proxy servers, CD servers, DHCP servers, login servers etc which offer specialised services.

11. File Servers • File servers run the Network operating system (NOS) which offers “community services” such as: • authenticating users during login • controlling users’ access to resources based on their rights • managing print queues • doing backups • running centralised software such as virus scanners • running services like DHCP to give out IP addresses to workstations • controlling internet services

12. File Servers Servers don’t really have anything special in terms of hardware. Expensive because of their high-quality components, and “scalability” (expandability). • Memory – servers need lots of RAM. Application servers require huge amounts of RAM to run programs for remote users. • Storage –very large and fast hard disks – often RAID (discussed soon)

13. File Servers vs Desktops 1 • Processing power –not so important in a file server, but application servers benefit greatly from having multiple CPUs. • Backup – most servers have inbuilt high-capacity tape backup drives to protect against data loss. Tape drives usually use QIC (Quarter Inch Cartridge) DAT (Digital audio tapes) tapes. Servers are the muscle men in the computer world

14. File Servers vs Desktops 2 Connectivity – servers often have two or more fast network cards to increase their data-throughput. Robustness - servers run all day for years, and need rugged high-quality components Scalability – servers are designed to be expandable as network demand grows. Scalability is the ability to increase the size and power of equipment and networks as required. Many servers let you add up to 8 hard disks, two power supplies, two NICs, two CPUs, large amounts of RAM etc. Designing and engineering this expandability is expensive.

15. File Servers - RAID Redundant Array of Independent [or Inexpensive] Disks) arrays for reliability and/or speed. RAID uses a group of hard disks that work as a single disk under a RAID controller. Flavours of RAID: RAID0 to RAID5 offer increasing reliability and/or speed (at ever-increasing cost). Includes mirroring (for reliability), error correction, and striping (for speed). RAID disks are usually "Hot Swap". 3-disk raid array

16. Application Servers Application servers run applications for users. They do the processing for the workstations. Thin client: dumb terminals attach to an application server – very little bandwidth needed. The user’s terminal simply sends the user’s keyboard and mouse actions to the server, which does the processing, and sends back screen images.

17. Application Servers • Pros • cheap, expendable, old, low powered workstations • Software is installed and configured centrally once, rather than on hundreds of machines. • All data is stored centrally and securely on the server – no chance of data loss if remote workstations are stolen or destroyed. • Cons • cost and complexity of the powerful servers that are required to run program for many simultaneous users • not good with high-bandwidth multimedia

18. Network segments A network segment is a self-contained section of a network bounded by a bridge, router, or switch. Using segments reduces network congestion and groups nodes together.