1. Computer Networks
N Amanquah, PhD

2. What is a Network?
A connection between two nodes for the purpose of electronic data exchange
Same medium, independent hosts -- Tanenbaum

3. Usage Communication Information Access/dissemination
Entertainment & games
E-commerce
Education
Social networking
Resource sharing
Illicit- eg hacking, snooping, gambling etc

4. Types of networks By Size and Scale Media type Topology
PAN, LAN, WAN, MAN, the internet
Media type
copper, fibre, wireless
Topology
Star, bus, ring, mesh

5. A basic network Wireless: BT, IrAD, Wifi etc
serial, parallel, twisted pair
coax
Media: 3 types: copper, fibre, wireless

6. Media
Copper
UTP
Coax
Fibre
Wireless
**Connectors

7. Not so basic
topologies

8. Topologies

9. Ultimate network The internet
*pix – cabinet, satellite, dish, microwave links, etc

10. Network nodes 3 or more nodes: Integrate networks Transmission lines
Hub, Switch
Integrate networks
Routers, bridges, repeaters, gateways
Transmission lines

11. From here to Google & back
From here to B1 & back
From here to Google & back

12. Components of network Transmission lines Circuits & Switching elements
Transmission mechanisms
Store and Forward (excludes satellites)
Circuits & Switching elements
Packet switched vs circuit switched
Subnets
routers

13. Count down to transmission
….….Between two very different hosts
7. Need a program –an application
Eg FTP, , Telnet, http(web)
6. syntax and semantics, presentation
Unix, Mac, Windows are different
Big/little endian
ASCII and EBCDIC, Unicode
EBCDIC supports 2 languages. English, and another.
UTF= unicod transformation format. UTF-8 has same code values as ASCII
Big endian: the high order byte is stores in the lower address ie LSB first is little endian, MSB first is big endian
IBM: Extended binary coded decimal interchange code

14. Count down …II
5. May want to log the session for future review, or to resume the session.
4 End-to-end connection management
Connection setup
Must be able to stream,
distinguish traffic sessions
Guarantee QoS,
Fragmentation,
Error free end to end in-order delivery
Also broadcasting, non guaranteed

15. 3. Route to the destination (next hop),
addressing
Control/avoid congestion,
communication with other networks (heterogeneity)
Datagram segmentation

16. Count down ..III 2a. Further segmentation and reassembly
Error detection
Need to be able to able to detect errors that may occur on the imperfect transmission line
Flow control
Avoid swamping a slow receiver
Framing
Determine where one frame/chunk of data starts and ends (be able to distinguish 000 from a transmission line gone dead)

17. Count down …IV 2b Medium access control 1. Electronic Transmission
With more than two hosts, need some arbitration for transmission.
1. Electronic Transmission
Convert the data (in 01010) to electrical format and transmit
Modulation etc : electrical, mechanical, timing

18. Reference Model Have enough layers with distinct functionality
Well defined functionality
Minimize information flow across layers

19. Internet Model

20. Network Architecture “Set of layers and protocols” Services Protocols
Operations a layer should perform
Protocols
rules/agreements on format of packets
Protocol Stack
Set of protocols used by one system

21. Layers Communication takes place between peer layers
Virtual comms: eg bt layer 3 and layer 3
Actual comms: down/up the stack
An interface is between two layers
Layers perform clearly defined task
Are replaceable
Each layer provides a service to the one above
Abstracts layers below

22. Design issues Broadcast networks Point to Point network (unicasting)
single communication channel shared by all
May use broadcast address  every to host
Multicasting to subset
Point to Point network (unicasting)

23. Design issues Duplexing: Simplex Half duplex Full duplex One way only
(broadcasting is simplex!)
Half duplex
one way at a time
Full duplex
simultaneously

24. Design issues Error control: *Packet sequencing *Flow control
Error correcting codes
Acknowledgements
*Packet sequencing
*Flow control
Multiplexing & de-multiplexing
Same connection for multiple communications

25. Connection oriented service
Establish connection, transmit, tear down connection.
Sequencing is usually preserved.
Connectionless
Each packet carries destination information and is routed independently.

26. Reliability & QoS Acknowledgement Negotiation for QoS parameters
overhead & delay, vs reliability
Negotiation for QoS parameters
**Un/Reliable datagram service

27. Wireless networks Infrastructure Infrastructure-less APs Peer to peer,
Ad hoc

28. Network standards IEEE 802.3 – Ethernet IEEE 802.4 –token bus
IEEE –token ring -IBM
IEEE –wireless LAN
IEEE –wireless PAN
IEEE wirleess WAN

29. Example networks The Internet is a network of networks
ARPANET- Advanced Research Projects Agency Network (DoD)
Precursor to Internet. A resilient network to survive a knock out of network hosts
NSFNET – university research

30. Example Networks Connection oriented X.25 Frame relay, ATM
For interconnecting LANS
in-order delivery, no flow control
ATM
Used by telcos
Move data eg IP over virtual high speed
53byte cell, with 5 byte header.
Inorder delivery
Small overhead. NO error control

31. Example networks Ethernet Wifi Developed from ALOHANET
Uses coax, or UTP
Wifi

32. Readings
Andrew Tanenbaum
Sections 1.0 to 1.9