Overview IS 8040 Data Communications Dr. Hoganson Course Overview Sending signals over a wire –Data: bits – binary (0/1) –How to transmit the digital data: Digital Signaling Analog Signaling – modulating waves –FSK- Frequency Shift Keying –ASK – Amplitude Shift Keying –PSK – Phase Shift Keying Encoding Compressing Error Checking and Recovery

Overview IS 8040 Data Communications Dr. Hoganson Controlling Access to a Shared Medium Contention-based –Competition for a shared media (Ethernet0 Take turns –Token Passing Centralized Control Example: Ethernet – shared bus, contention CSMA/CD –CS – Carrier Sense, each station listens for idle before sending –MA – Multiple Access – multiple stations share media –CD – Collision Detection – two or more stations detect an idle media, and attempt to send – collision, neither message gets through. Random Back-Off

Overview IS 8040 Data Communications Dr. Hoganson Internetworking How to interconnect multiple networks –TCP/IP –Routers –Bridges –Gateways The Internet

Overview IS 8040 Data Communications Dr. Hoganson Management Issues Network Planning Security –Firewalls –Proxy servers Control of data Remote management of devices

Overview IS 8040 Data Communications Dr. Hoganson Work Distribution Architectures Network of PCs and Servers How to allocate the work between machines –Centralized on Server, Host, or Mainframe –Distributed across multiple clients and/or multiple servers What work to distribute 1.Data Storage work (access to drives) 2.Data Access Logic (database processing) 3.Application Logic (manipulating the data) 4.Presentation Logic (GUI)

Overview IS 8040 Data Communications Dr. Hoganson Centralized Computing Paradigm Most of the work occurs on the Server/Host/Mainframe Only the GUI runs on the PC/client The old centralized mainframe approach Advantages –All data in one place –Easy for security/redundancy/backup –Easy to maintain data integrity –Reliable systems Disadvantages –Does not scale as well – as you add users, server may need to be upgraded. –Users depend on the IS shop/mainframe programmers –Backlog of user requests

Overview IS 8040 Data Communications Dr. Hoganson Distributed Paradigm Distribute work and data across multiple machines Advantages: –Scales well, each user comes with another client machine –User Empowerment – users can generate their own data and manipulate data without having to go through IS shop –With spreadsheet and database tools, each user becomes their own IS shop and programmer Disadvantages –Data is distributed – more work to consolidate data –Data integrity – no central control ensures quality of data –Backups – users rarely backup their data –Dependent upon reliability of the network Poor compared to mainframes, but improving –More expensive than centralized – more support personnel –More Complex

Overview IS 8040 Data Communications Dr. Hoganson True Cost of Computing Includes –Machines –Software –Support personnel Network support PC techs Network management Server/Database management –Cost of network equipment, cable installation, etc. –Cost of downtime/unavailability PCs on a network were “supposed” to kill off the mainframes, because they are cheaper per processing cycle. But true cost of computing analysis indicated otherwise – mainframes are alive and well (some are now called Enterprise Servers.

Overview IS 8040 Data Communications Dr. Hoganson Hybrid Client/Server Centralized servers(s) with client machines –Work is distributed to clients while some remains on server –Data is centralized on server, download to users for short-term processing Advantages: –Scales well – each user comes with a client workstation Additional servers can be added –Data integrity is protected on servers –Each user can do their own processing – User Empowerment –More reliable Disadvantages –Complex system to manage