1. Computer Network Basics
Lappeenrannan teknillinen yliopisto
TITE
Prof. Esa Kerttula
Computer Network Basics
Päivä 1: luento 4
An overview of computer networking which introduces many key concepts and terminology

2. Operating systems

3. Operating Systems Developed for Portable Devices

4. A closer look at network structure:
network edge: applications and hosts
network core:
routers
network of networks

5. General Architecture of Computer Networks

6. The Network Core mesh of interconnected routers
the fundamental question: how is data transferred through net?
circuit switching: dedicated circuit per call: telephone net
packet-switching: data sent thru net in discrete “chunks”
End-to-end dedicated “circuit…. Like a telephone connection… vs. a point-to-point (e.g. between routers) connection for small chunkc of data.
Can you use a packet switching network for classical “circuit oriented” applications???? Voice over the internet…. Streaming video…. Radio on the internet….

7. Connection of Networks

8. Network Topology a) bus, b) star, c) ring, d) tree structure a) b) c)

9. 12

10. The Internet 8

11. Bandwidth Progression of the Internet
Kbps
Kbps
Mbps (often called T1 Speed)
Mbps (often called T3)
Mbps
Mbps
Mbps
Mbps
2006 … 19

12. Types of Connections Dialup Terminal or SLIP/PPP (up to 56 kbps)
Integrated Services Digital Network (ISDN, up to 128 kbps)
Leased Lines: T1 or T3 33

13. NSFNET Backbone Structure20

14. Flow-control and Congestion Prevention
Flow-control: to protect the receiver against the overload, i.e.: the sender (source) sends more data than the receiver can process
it is mainly necessary in link and transport level
Congestion prevention: to prevent the intermediate nodes against the overload
it is mainly necessary in network level

15. Overload and Congestion
Overload: Too many packets occur in a subnetwork in the same time, which prevent each other and in such a way the throughput decreases
Congestion: the queues in the routers are too long, the buffers are full.
As a consequence some packages are dropped if the buffers of the routers are overloaded
In extreme case: grid-lock, lock-up

16. Deadlock
Deadlock: the most serious situation of the congestion, the routers wait for each other
Direct store and forward deadlock: the buffers of two neighbouring routers are full with the packets to be sent to the other router
Indirect store and forward deadlock: the deadlock occurred not between two neighbouring routers but in a subnetwork, where any of the routers has not free buffer space for accepting packets

17. Internet protocol stack
application: supporting network applications
ftp, smtp, http
transport: host-host data transfer
tcp, udp
network: routing of datagrams from source to destination
ip, routing protocols
link: data transfer between neighboring network elements
ppp, ethernet
physical: bits “on the wire”
application
transport
network
link
physical

18. Layering: logical communication
data
E.g.: transport
take data from app
add addressing, reliability check info to form “datagram”
send datagram to peer
wait for peer to ack receipt
analogy: post office
application
transport
network
link
physical
transport
ack
data
data
transport

19. Layering: physical communication
data
application
transport
network
link
physical
network
link
physical
application
transport
network
link
physical
data
application
transport
network
link
physical
application
transport
network
link
physical

20. Protocol layering and data
Each layer takes data from above
adds header information to create new data unit
passes new data unit to layer below
source
destination
application
transport
network
link
physical
application
transport
network
link
physical M H t n l
message M H t n l
segment
datagram
frame

21. Operation of Protocols

22. Communication among the layers
Connection oriented network service
Reliable transport service
Unreliable transport service
Connectionless network service

23. Network Tools
Repeater: connects network segments logically to one network
Hub: multiport repeater
Bridge: datalink level connection of two networks
Switch: multiport bridge
Router: connects networks that are compatible in transport level
subnetworks are connected to the interfaces of the repeater
Gateway (proxy server): router between two individual network. The “Way Out”

24. Soft and Hard States
State: the data collection, which are necessary for keeping the connection between two protocol entities
Hard state
If the connection is established once, it is never timed out, even if it is not in usage
Even there is not data exchange for a while, the client can trust in it that the state is existing
To cancel the connection one of the participants of the connection must explicitly close it
Soft state
To keep the connection the participants must send occasionally keep-alive messages, since without keep-alive message the state information is timed out after a certain period
The state is called as “soft” since in the ordinary operation the state can change easily
The clients are responsible for the maintenance of the state at the partner, therefore they have to refresh the state information at the communicating partner

25. Roots of the Recent Advantages
Advantages of the computers (prices)
Telecommunication network (fibre and satellite telecommunication)
Evolution of the network software

26. The Next Generation of the Computers
The development rate is prognostised up to 2047
In the USA there is technological development projects up to 2010
New physical phenomena and laws - technological development
Moore-law (duplication in 24 months)
In 2047 the capacity of a storage chip is 100 human brains
The power of one processor will be equals to 500 million Pentium

27. Some Internet Related organizations
Internet Society (ISOC)
Internet Architecture Board (IAB)
Internet Research Task Force (IRTF)
Internet Engineering Steering Group (IESG)
Internet Engineering Task Force (IETF)
WWW Consortium (W3C)

28. Standardization Types: Evaluation of RFC:
patented standard (e.g.: IBM SNA)
public standard (e.g.: ITU, ISO or IEEE standards)
non-official standard (e.g.: RFC)
Evaluation of RFC:
proposed standard (6 month)
draft (6 month maximum, but after 4 months it can became RFC)
standard (RFC) (up to obsolescence)

29. Different Levels of Authority
Public Domain
can copy without any restriction
Freeware
can be used, but copyrighted, the copy or the modification can be limited
Shareware
for evaluation purposes (before buying), only
Mixed:
individuals and non-profit organizations obtain freely
the profit oriented organizations must buy