Computer Networking
Text books
B.A. Forouzan, Data Communications and
Networking, 4th Edition, McGraw Hill, 2007
Peterson and Davie ,Computer Networks: A
Systems Approach (3rd edition), by
Kurose and Ross, Computer Networking: A
Top-Down Approach Featuring the Internet
(3rd edition)
William Stalling, Data and Computer
Communications, 6th Edition, Prentice-Hall.
1997
A.S Tanenbaum, Computer Networks, 4th.
Edition, Prentice Hall
http://pkukmweb.ukm.my/~kbj/CN2008-PKP/
2
Definitions of Computer Networking
"Chain of interconnected computers"
• Oxford Dictionary
"A number of computers connected together for
the purposes of communication of processing"
• Knott, Waites and Callaghan, Computer Studies
"1. A series of interconnected points
2. The interconnection of a number of points by
communications facilities"
• Sippl & Sippl, Computer Dictionary.
"two or more interconnected computers able to
facilitate exchange of information".
• Personal.
“However, an effective network is one which
meets requirements and is used".
3
• Personal.
Simplest Computer Networking
Two computers are connected in a simplest computer networking
system.
A network will have:
-Sender and receiver
- something to share (data)
- “physically” connected (transmission medium)
- communication protocol
4
Figure 1.2 Data flow (simplex, half-duplex, and full-duplex)
5
1-2 NETWORKS
A network is a set of devices (often referred to as nodes)
connected by communication links. A node can be a
computer, printer, or any other device capable of sending
and/or receiving data generated by other nodes on the
network.
6
Figure 1.3 Types of connections: point-to-point and multipoint
7
Figure 1.4 Categories of topology
8
Figure 1.5 A fully connected mesh topology (five devices)
9
Figure 1.6 A star topology connecting four stations
10
Figure 1.7 A bus topology connecting three stations
11
Figure 1.8 A ring topology connecting six stations
12
Figure 1.9 A hybrid topology: a star backbone with three bus networks
13
Figure 1.10 An isolated LAN connecting 12 computers to a hub in a closet
14
Figure 1.11 WANs: a switched WAN and a point-to-point WAN
15
Figure 1.12 A heterogeneous network made of four WANs and two LANs
16
Protocols and Network
Architecture
17
1-4 PROTOCOLS AND STANDARDS
In this section, we define two widely used terms: protocols
and standards. First, we define protocol, which is
synonymous with rule. Then we discuss standards, which
are agreed-upon rules.
Protocols and standards can easily become very complex.
In order to reduce this complexity, the standard is divided
to several layers. Each layer will have its own protocol.
We can use the concept of layers in our daily life. As an
example, let us consider two researchers who speaks only
his own language discussing about a common subject and
communicate through fax machine.
18
C01. 16
Protocol Architecture
Language Translation Example
Dr Wong
Discussing DIS research
Prof Stuber
Interested in DIS
in China
Expert in DIS
Speaks only Chinese
Speaks only German
Chinese Doc
German Doc
Mrs.. Wang
Exchanging Documents
Herr Muller
Chinese - English
in English
German - English
Translator
Ms. Wu
Translator
Fax messages
Expert on FAX
19 Data Communications and Distributed Processing
INFS 612:
Frau. Meier
Expert on FAX
J.M. Hanratty
Protocols and Network Architecture
20
Protocols and Network Architecture
21
- cont
Layered and Network Architecture
22
- cont
THE OSI MODEL
Established in 1947, the International Standards
Organization (ISO) is a multinational body dedicated
to worldwide agreement on international standards. An
ISO standard that covers all aspects of network
communications is the Open Systems Interconnection
(OSI) model. It was first introduced in the late 1970s.
23
Figure 2.2 Seven layers of the OSI model
24
Figure 2.3 The interaction between layers in the OSI model
25
Figure 2.4 An exchange using the OSI model
26
Simulation
http://www.humboldt.edu/~aeb3/tele
com/Encapsulation.html
27
LAYERS IN THE OSI MODEL
In this section we briefly describe the functions of each
layer in the OSI model.
Topics discussed in this section:
Physical Layer
Data Link Layer
Network Layer
Transport Layer
Session Layer
Presentation Layer
Application Layer
28
Physical Layer
The physical layer is responsible for movements
of raw individual bits from one hop (node) to the
next over a communication channel (physical
medium); deals with the mechanical, electrical,
functional, and procedural characteristics to
access the physical medium
Sample Issues:
how to encode a 0 vs. 1?
what voltage should be used?
how long does a bit need to be signaled?
what does the cable, plug, antenna, etc. look like?
Examples:
29
modems
“knock once for yes, twice for no”
Figure 2.5 Physical layer
30
Data Link Layer
The data link layer is responsible for moving
frames from one hop (node) to the next.
It provides the reliable transfer of information
across the physical link; sends blocks of data
(frames) with necessary synchronization,
error control, and flow control
Sample Issues:
how big is a frame?
can I detect an error in sending the frame?
what demarks the end of the frame?
how to control access to a shared channel?
Examples:
Ethernet framing
31
Figure 2.6 Data link layer
32
Figure 2.7 Hop-to-hop delivery
33
The Network Layer
The network layer is responsible for the
delivery of individual packets from the source host to
the destination host.
Sample Issues:
How to route packets that have to travel several hops?
control congestion – when there are too many messages at
any one time
accounting - charge for use of the network
fragment or combine packets depending on rules of link
layer
Examples:
IP
34
Figure 2.8 Network layer
35
Figure 2.9 Source-to-destination delivery
36
The Transport Layer
The transport layer is responsible for the
delivery of a message from one process to
another.
Provides reliable, transparent transfer of data
between end points; provides end-to-end
(host-to-host) error recovery and flow control
Sample Issues:
how to rearrange messages and detect any
duplicates
error detection (corrupt packets) and
retransmission
Examples:
TCP
37
Figure 2.10 Transport layer
38
Figure 2.11 Reliable process-to-process delivery of a message
39
The Session & Presentation Layers
Goal: Provides independence from the application
processes for any differences in data representation
(syntax), and
To establishes, manages, and terminates connections
(sessions) between application processes
The session layer is responsible for dialog
control and synchronization.
The presentation layer is responsible for translation,
compression, and encryption.
Sample Issues:
network representation of bytes, ints, floats, etc.
encryption??
synchronization
Examples:
eXternal Data Representation (XDR)
40
Figure 2.12 Session layer
41
Figure 2.13 Presentation layer
42
Application Layer
The application layer is responsible for
providing services to the user
Sample Issues:
when sending email, what demarks the subject field
how to represent cursor movement in a terminal
Examples:
Simple Mail Transport Protocol (SMTP)
File Transfer Protocol (FTP)
Hyper-Text Transport Protocol (HTTP)
Simple Network Management Protocol (SNMP)
Network File System (NFS)
Network Time Protocol (NTP)
Net News Transport Protocol (NNTP)
X (X Window Protocol)
43
Figure 2.14 Application layer
44
Figure 2.15 Summary of layers
45
TCP/IP PROTOCOL SUITE
The layers in the TCP/IP protocol suite do not exactly
match those in the OSI model. The original TCP/IP
protocol suite was defined as having four layers: host-tonetwork, internet, transport, and application. However,
when TCP/IP is compared to OSI, we can say that the
TCP/IP protocol suite is made of five layers: physical, data
link, network, transport, and application.
Topics discussed in this section:
Physical and Data Link Layers
Network Layer
Transport Layer
Application Layer
46
Figure 2.16 TCP/IP and OSI model
47
Stallings, High-Speed Networks, p. 38
48
Stallings, High-Speed Networks, p. 39.
49
Stallings, High-Speed Networks, p. 40.
50
Stallings, High-Speed Networks, p. 41.
51
2-5 ADDRESSING
Four levels of addresses are used in an internet employing
the TCP/IP protocols: physical, logical, port, and specific.
Topics discussed in this section:
Physical Addresses
Logical Addresses
Port Addresses
Specific Addresses
52
Figure 2.17 Addresses in TCP/IP
53
Figure 2.18 Relationship of layers and addresses in TCP/IP
54
Example 2.1
In the following Figure, a node with physical address 10
sends a frame to a node with physical address 87. The two
nodes are connected by a link (bus topology LAN). As the
figure shows, the computer with physical address 10 is the
sender, and the computer with physical address 87 is the
receiver.
55
Figure 2.19 Physical addresses
56
Example 2.2
Most local-area networks use a 48-bit (6-byte) physical
address written as 12 hexadecimal digits; every byte (2
hexadecimal digits) is separated by a colon, as shown
below:
07:01:02:01:2C:4B
A 6-byte (12 hexadecimal digits) physical address.
57
Example 2.3
In the following Figure, shows a part of an internet with
two routers connecting three LANs. Each device
(computer or router) has a pair of addresses (logical and
physical) for each connection. In this case, each computer
is connected to only one link and therefore has only one
pair of addresses. Each router, however, is connected to
three networks (only two are shown in the figure). So each
router has three pairs of addresses, one for each
connection.
58
Figure 2.20 IP addresses
59
Example 2.4
In the following Figure, shows two computers
communicating via the Internet. The sending computer is
running three processes at this time with port addresses a,
b, and c. The receiving computer is running two processes
at this time with port addresses j and k. Process a in the
sending computer needs to communicate with process j in
the receiving computer. Note that although physical
addresses change from hop to hop, logical and port
addresses remain the same from the source to destination.
60
Figure 2.21 Port addresses
61