FIT3165 / FIT4165 COMPUTER NETWORKS
WEEK 1 – PART 2 – INTRODUCTION TO COMPUTER NETWORKS
Faculty of Information Technology © 2022 Monash University
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1.1 Overview of the Internet
1.2 Network Models & Protocol Layering
Circuit & Packet switching
1.3 Internet History
1.4 Standards and Administration
OVERVIEW OF THE INTERNET
1.1.1 Networks
A network is the interconnection of a set of devices capable of communication.
A device can be a host such as a large computer, desktop, laptop, workstation, cellular phone, or security system.
A device in this definition can also be a connecting device such as a router, a switch, a modem that changes the form of data, and so on.
Types of Communication Networks
■ Traditional
■ Traditional local area network (LAN)
■ Traditional wide area network (WAN)
■ Higher-speed
■ High-speed local area network (LAN)
■ Metropolitan area network (MAN)
■ High-speed wide area network (WAN)
■ Point-to-Point WANs
■ Switched WANs
Characteristics of LANs
■ Like WAN, LAN interconnects a variety of devices and provides a means for information exchange among them
■ Traditional LANs
■ Provide data rates of 1 to 20 Mbps
■ High-speed LANS
■ Provide data rates of 100 Mbps to 10 Gbps
Figure 1.1: An Isolated LAN in the past and today
Characteristics of WANs
■ Covers large geographical areas
■ Circuits provided by a common carrier
■ Consists of interconnected switching nodes
■ Traditional WANs provide modest capacity
■ 64000 bps
■ Business subscribers using T-1 service – 1.544 Mbps
■ Higher-speed WANs use optical fiber and transmission technique known
as asynchronous transfer mode (ATM)
■ 10’s and 100’s of Gbps common
Figure 1.2: A Point-to-Point WAN
Figure 1.3: A Switched WAN
Differences between LANs and WANs
■ Scope of a LAN is smaller
■ LAN interconnects devices within a single building or cluster of
■ LAN usually owned by organization that owns the attached devices
■ For WANs, most of network assets are not owned by same organization
■ Internal data rate of LAN is much greater
Figure 1.4: An internetwork made of two LANs and one WAN
Figure 1.5: A heterogeneous network made of WANs and LANs
The Need for MANs
■ Traditional point-to-point and switched network techniques used in WANs are inadequate for growing needs of organizations
■ Need for high capacity and low costs over large area
■ MAN provides:
■ Service to customers in metropolitan areas
■ Required capacity
■ Lower cost and greater efficiency than equivalent service from telephone company
1.1.2 Switching
An internet is a switched network in which a switch connects at least two links together.
A switch needs to forward data from a link to another link when required.
❑ Circuit-Switched Network
❑ Packet-Switched Network
Figure 1.6: A circuit-switched network
Figure 1.7: A packet-switched network
Switching Terms and Techniques
TERMS Switching Nodes:
Intermediate switching device that moves data
Not concerned with content of data
End devices that wish to communicate
Each station is connected to a switching node
Communications Network:
A collection of switching nodes
TECHNIQUES Circuit switching
Dedicated communications path between stations
e.g. public telephone network
Packet switching
Message is broken into a series of packets
Each node determines next leg of transmission for each packet
Circuit Switching
▪ Circuit establishment
– An end to end circuit is established through
switching nodes
– Dedicated path for duration of connection, even when no data is being transmitted ! ?
▪ Information Transfer
– Information transmitted through the network
– Data may be analog voice, digitized voice, or binary data
▪ Circuit disconnect
– Circuit is terminated (‘teardown’)
– Each node de-allocates dedicated resources
CHARACTERISTICS
▪ Can be inefficient
– Channel capacity dedicated for
duration of connection
– Utilization not 100%
– Delay prior to signal transfer for establishment
▪ Once established, network is transparent to the users
▪ Information transmitted at fixed data rate with only propagation delay
Packet Switching
● Data is transmitted in blocks, called packets or datagrams
● Before sending, the message is broken into a series of packets
○ Typical packet length is 1000 octets (bytes)
○ Packets consists of a portion of data plus a packet header
that includes control information
● At each node en route, packet is received, stored briefly and
passed to the next node More features
● No call setup or teardown
● Packets may take different paths
● Packets may arrive in different sequence or be lost in
transit…
● New datagrams admitted even when network is congested!
Stallings – Fig 3.7 Packet switching: Datagram approach
Advantages and disadvantages of Packet Switching
ADVANTAGES
▪ Line efficiency is greater
– Many packets over time can dynamically
share the same node to node link
▪ Packet-switching networks can carry out data-rate conversion
– Two stations with different data rates can exchange information
▪ Unlike circuit-switching networks that block calls when traffic is heavy, packet-switching still accepts packets, but with increased delivery delay
▪ Priorities can be used
DISADVANTAGES
▪ Each packet switching node introduces a delay
▪ Overall packet delay can vary substantially
– This is referred to as jitter
– Caused by differing packet sizes, routes taken and varying delay in the switches
▪ Each packet requires overhead information – Includes destination and sequencing
information
– Reduces communication capacity
▪ More processing required at each node
Packets using circuit switching
● Preplanned route established before packets sent
○ All packets between source and destination follow the same established route
● Routing decision not required by nodes for each packet
● Emulates a circuit in a circuit switching network
but is not a dedicated path
○ Packets still buffered at each node and queued for output over a line
○ Only buffered, no routing..
● Advantages:
○ Packets arrive in original order
○ Packets arrive correctly
○ Packets transmitted more rapidly without routing decisions made at each node
Example 1.1.3
Figure 1.8: The Internet today
The most notable internet is called the Internet and is composed of thousands of interconnected networks. Figure 1.8 shows a conceptual (not geographical) view of the Internet.
1.1.4 Accessing the Internet
■ Today’s Internet is an internetwork that allows any user to become part of it.
■ The user, however, needs to be physically connected to an ISP.
■ The physical connection is normally done through a point-to-point WAN.
■ In this section, we briefly describe how this can happen, technical details will be discussed in the later sections of the lecture series.
❑ Using Telephone Networks ▪ Dial-up Service
❑ Using Cable Networks
❑ Using Wireless Networks
❑ Direct Connection
NETWORK MODELS AND PROTOCOL LAYERING
Example 1.2.1 Why do we need a layered architecture
Figure 1.9: A single-layer protocol
Figure 1.10: A three-layer protocol
Figure 1.11: Logical connection between peer layers
1.2.2 TCP/IP Protocol Suite
• TCP/IP is a protocol suite used in the Internet today
• It is a hierarchical protocol made up of interactive modules.
• Each of which provides a specific functionality.
• The term hierarchical means that each upper level protocol is supported by the services provided by one or more lower level protocols.
• The original TCP/IP protocol suite was defined as four software layers built upon the hardware.
• Today, however, TCP/IP is thought of as a five-layer model.
1.2.2 TCP/IP Protocol Suite (continued)
Layered Architecture
Layered in the Suite
Description of Each Layer
❖ Application Layer
❖ Transport Layer
❖ Network Layer
❖ Data-link Layer
❖ Physical Layer
❑ Encapsulation and Decapsulation
❖ Encapsulation at the Source Host
❖ Decapsulation and Encapsulation at Router
❖ Decapsulation at the Destination Host
❑ Addressing
❑ Multiplexing and Demultiplexing
Figure 1.12: Layers in the TCP/IP protocol suite
Figure 1.13: Communication through an internet
Figure 1.14: Logical connections between layers in TCP/IP
Logical connections
Figure 1.15: Identical objects in the TCP/IP protocol suite
Identical objects (messages)
Identical objects (segment or user datagram)
Identical objects (datagram)
Identical objects (datagram)
Identical objects (frame) Identical objects (frame)
Identical objects (bits)
Identical objects (bits)
Figure 1.16: Encapsulation / Decapsulation
Figure 1.17: Addressing in the TCP/IP protocol suite
Figure 1.18: Multiplexing and demultiplexing
1.2.3 The OSI Model
• OSI model established in 1947
• 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.
❑ OSI versus TCP/IP
❑ Lack of OSI Model’s Success
Figure 1.19: The OSI model
Figure 1.20: TCP/IP and OSI model
HISTORY OF INTERNET
There were some communication networks, such as telegraph and telephone networks, before 1960.
These networks were suitable for constant-rate communication at that time, which means that after a connection was made between two users, the encoded message (telegraphy) or voice (telephony) could be exchanged.
Birth of Packet-Switched Networks ❑ ARPANET
1.3.1 Early History
1.3.2 Birth of the Internet
In 1972, and , both of whom were part of the core ARPANET group, collaborated on what they called the Inter-netting Project.
They wanted to link dissimilar networks so that a host on one network could communicate with a host on another.
There were many problems to overcome:
☞ diverse packet sizes,
☞ diverse interfaces,
☞ diverse transmission rates, as well as
☞ differing reliability requirements.
1.3.3 Internet Today
• Today, we witness a rapid growth both in the infrastructure and new applications.
The Internet today is a set of pier networks that provide services to the whole world.
What has made the Internet so popular is the invention of new applications.
❑ Multimedia
❑ Peer-to-Peer Applications
World Wide Web
1.4.1 Internet Standards
• An Internet standard is a thoroughly tested specification.
• It is useful to and adhered to by those who work with the Internet.
• It is a formalized regulation that must be followed.
• There is a strict procedure by which a specification attains Internet standard status.
• A specification that begins as a Internet draft.
Maturity Levels
❖ Proposed Standard
❖ Draft Standard
❖ Internet Standard
❖ Historic
❖ Experimental
❖ Informational
❑ Requirement Levels
❖ Required
❖ Recommended
❖ Elective
❖ Limited Use
❖ Not Recommended
1.4.1 Internet Standards (Continued)
Figure 1.21: Maturity levels of an RFC
1.4.2 Internet Administration
• The Internet, with its roots primarily in the research domain, has evolved and gained a broader user base with significant commercial activity.
• Various groups that coordinate Internet issues have guided this growth and development.
1.4.2 Internet Administration (continued)
❑ IANA and ICANN
❑ Network Information Center (NIC)
Figure 1.22: Internet administration
References
■ Computer Networks A Top-Down Approach by Behrouz A. Forouzan & by Hill 1st edition 2012
■ Open Systems InterconnectionOpen Systems Interconnection Reference Model (OSI) – http://en.wikipedia.org/wiki/OSI_model
■ ., An introduction to cable modems, Cable Modem Technology, Asia/Pacific Open Systems Review, , August 1996, 60-63, 4pp.
■ ., Digital subscriber line technologies – The technical issues, Asia/Pacific Open Systems Review, , September 1996, 50-51, 2pp.
■ ., Networking – A perspective,Networking – A perspective, PPP Protocol, Asia/Pacific Open Systems Review, , November 1996, 24-28, 5pp.
● So far we have discussed
○ Overview of internet
○ Network models and protocol layering
○ History of internet
○ Standards and Administration of Internet
● Next week
○ TCP/IP Protocol Stack – Application layer
Reminder : TUTORIALS start next week
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