Transcript IAP 01 – Introduction to Internet Architecture

Lecture 01 - Roadmap
• Introduction
• Course Objectives, Outline and Grading Policies
• What is the Internet?
– Nuts and Bolts View
– Service Oriented View
• Network Edge
• Network Core
– Circuit Switched Networks
– Packet Switched Networks
• Datagram
• Virtual Circuits
• Network Access and Physical Media
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Course Objectives
 To understand the design philosophy of the Internet and its
basic architectural components.
 To provide in-depth knowledge of major Internet
technologies.
 To understand the components of Internet service provider
and its role in Internet architecture.
 To strengthen the concepts of TCP/IP Protocol Suite.
 To provide comprehensive knowledge and implementation
of routing protocols.
 To realize the need of Quality of Service based
communication and to understand various QoS
techniques.
 To introduce the basic concepts of real time
communications.
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What is the Internet?
• A Nuts and Bolts Description
–
–
–
–
–
–
End systems
Communication Links, Bandwidth
Routers, Packet
ISPs
Protocols, TCP/IP
Internet Standards, RFCs
• A service Description
– Distributed Applications
– Connection Oriented Reliable Service
– Connectionless Unreliable Service
• What is a protocol?
3
Describing the Internet
• Two ways to describe the Internet
– Nuts and Bolts View
• The basic hardware and software components
– Service Oriented View
• The networking infrastructure that provides
services to distributed applications
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Nuts and Bolts View of the Internet
• Hosts or End Systems
– Computing Devices such as PCs, PDAs (Personal
Digital Assistants), TVs, servers, mobile computers,
automobiles, etc. connected to the Internet are called
hosts or end systems.
IT-5302-3 Internet Architecture and Protocols, PUCIT, University of the Punjab, Pakistan
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Nuts and Bolts View of the Internet…
• Communication links
– End systems are connected together by communication
links.
– Communication links are made up of different types of
media, including twisted pair, coaxial cable, fiber optics, and
radio spectrum.
• Bandwidth
– Different links can transmit data at different rates.
– The link transmission rate is often called the bandwidth (i.e,
the width of the band) of the link which is measured in bits
per second (bps).
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Nuts and Bolts View of the Internet…
• Routers
– End systems are not directly connected to each other
via a single communication link.
– They are indirectly connected to each through
intermediate switching devices known as routers.
– A router receives chunk of information from one of its
incoming communication link and forwards it to one of
its outgoing communication link.
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Nuts and Bolts View of the Internet…
• Packets
– The chunk of information is called packet.
• Route or Path
– The path that the packet takes from the sending end system,
through a series of communication links and routers, to the
receiving end system is known as a route or path.
• Packet switching
– The Internet uses a technique known as packet switching
that allows multiple communicating end systems to share a
path, or parts of path at the same time.
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Nuts and Bolts View of the Internet…
• Internet Service Providers (ISPs)
– End systems access the Internet through the Internet
Service Providers (ISPs).
– The different ISPs provide a variety of different types of
network access to the end systems, including 56Kbps
dial up modem access, cable modem or DSL, high
speed LAN access, and wireless access.
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Nuts and Bolts View of the Internet…
• Protocols
– End systems, routers, and other pieces of the Internet,
run protocols that control the sending and receiving of
information within the Internet.
– TCP (Transmission Control Protocol) and IP (Internet
protocol) are two of the most important protocols in
the Internet.
– The Internet’s principal protocols are collectively
known as TCP/IP Protocol Suite.
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Nuts and Bolts View of the Internet…
• Intranets
– There are many private networks, such as many
corporate and government networks, whose hosts
cannot exchange messages with hosts outside of the
private network (unless the messages pass through socalled firewalls, which restrict the flow of messages to
and from the network).
– These private networks are often referred to as
intranets, as they use the same types of hosts, routers,
links, and protocols as the public Internet.
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Nuts and Bolts View of the Internet…
• Internet Standards
– At the technical and development level, the Internet is made
possible through creation, testing, and implementation of
Internet Standards.
– These standards are developed by Internet Engineering Task
Force (IETF).
• RFCs
– The IETF standards documents are called RFCs (Request for
comments).
– RFCs started out as general request for comments (hence
the name) to resolve architecture problems of the Internet.
– They define protocols such as TCP, IP, HTTP, SMTP.
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Some Pieces of the Internet
router
server
local ISP
workstation
mobile
regional ISP
company
network
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Service Oriented View of the Internet
• Distributed Applications
• Communication Services
– Connection oriented reliable service
– Connectionless unreliable service
• Distributed Applications
– The Internet allows distributed applications running
on its end systems to exchange data with each other.
– These applications include remote login, electronic
mail, web surfing, instant messaging, audio and video
streaming, Internet telephony, distributed games,
peer-to-peer (P2P) file sharing, and much more.
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Service Oriented View of the
Internet…
• Internet Provides
applications:
two
services
to
its
distributed
– Connection Oriented Reliable Service
• It guarantees that data transmitted from a sender
to a receiver will eventually be delivered to the
receiver in order and in its entirety.
– Connectionless Unreliable Service
• It does not make any guarantees about eventual
delivery.
– Note: Distributed applications makes use of one or the other
(but not both) of these two services.
• Thus, Internet is an infrastructure in which new
applications are being constantly invented and deployed.
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What is a Protocol?
• A Human Analogy
– “Assalam u Alaikum”
– “What’s the time?”
• In human protocols specific messages are sent,
and specific actions are taken in response to
messages received, or other events.
• Network protocols
– All activity in the Internet that involves two or more
communicating remote entities is governed by a
protocol.
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What is a protocol?
A human protocol and a computer network protocol
Hi
TCP connection
req
Hi
TCP connection
response
Got the
time?
2:00
<file>
time
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What is a Protocol?…
• A Protocol is a set of rules and regulations that governs
the exchange of information between two or more entities.
• It takes two (or more) communicating entities running the
same protocol in order to accomplish a task.
• All communication activity in Internet governed by
protocols.
• A protocol defines the format, order of messages
exchanged between two or more communicating entities,
as well as the actions taken on the transmission and/or
receipt of a message or other event.
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Net Surfing
• Some Good Hyperlinks:
–
–
–
–
–
–
–
–
http://www.ietf.org
http://www.iab.org
http://www.w3.org
http://www.ieee.org
http://www.acm.org
http://www.acm.org/sigcomm
http://www.computer.org
http://www.comsoc.org
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A closer look at network structure
• Network Edge:
– applications and hosts
• Network Core:
– routers
– network of networks
• Access networks, physical media:
– Residential, company and mobile access
– Twisted Pair, Coaxial, Fiber Optics, Radio Channels
– communication links
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Network Edge
•
•
•
end systems (hosts):
– run application programs
– e.g. Web, email
– at “edge of network”
client/server model
– client
host
requests,
receives
service
from
always-on server
– e.g. Web browser/server;
email client/server
peer-peer model:
– minimal (or no) use of
dedicated servers
– e.g. Gnutella, KaZaA
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Network Edge
• End Systems, Clients and Servers
– In Computer Networking, computers connected to the
Internet are referred to as End Systems, as they sit at the
edge of the Internet.
– End Systems = Hosts
– Hosts are subdivided into two categories: Client and Servers
• Client/Server Applications
– A client program is a program running on one end system
that requests and receives a service from a server program
running on another end system.
– Client/Server Internet applications are, by definition,
distributed applications.
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Network Edge
• Peer to Peer Applications
– In peer to peer application, the program running in a
peer (user’s machine) acts as a client when it requests
a file from another peer; and the program acts as a
server when it sends a file to another peer.
– Examples are peer-to-peer file sharing applications
like Napster, KaZaA etc.
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Network Edge –
Connection Oriented Services
• Connection Oriented Service
– Reliable Data Transfer
• Using acknowledgements and retransmissions
– Flow Control
• sender won’t overwhelm receiver
– Congestion Control
• senders “slow down sending rate” when network
congested
– TCP
• Applications using TCP are:
– HTTP (Web), FTP (file transfer), Telnet (remote login),
SMTP (email)
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Network Edge –
Connectionless Services
• Connectionless Service
– Unreliable Data Transfer
• no flow control
• no congestion control
– Fast
• connectionless
– UDP
• Applications using UDP are:
– multimedia,
telephony
videoconferencing,
DNS,
Internet
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TCP vs. UDP
• Reliable Protocol
• Connection Oriented
• Performs three ways
handshake
• Provision for error
detection and
retransmission
• Most applications use
TCP for reliable and
guaranteed transmission
•
•
•
•
Unreliable Protocol
Connectionless
Much faster than TCP
No acknowledgement
waits
• No proper sequencing of
data units
• Suitable for applications
where speed matters more
than reliability
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The Network Core
• Mesh
of
Routers
interconnected
• The fundamental question:
how is data transferred
through net?
– circuit switching
• dedicated circuit per
call: telephone net
– packet-switching
• data sent through net
in discrete “chunks”
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Network Core –
Concept of Switched Networks
• Long distance transmission is typically done
over a network of switched nodes
• Nodes not concerned with content of data
• End devices are stations
– Computer, terminal, phone, etc.
• A collection of nodes and connections is a
communications network
• Data routed by being switched from node to
node
• Node to node links usually multiplexed
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Simple Switched Network
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Network Core: Circuit Switching
End-to-end
resources
reserved for “call”
• link bandwidth,
switch
capacity
• dedicated resources: no
sharing
• circuit-like
(guaranteed)
performance
• call setup required
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Network Core – Circuit Switching
• Switched circuits allow data connections that
can be initiated when needed and terminated
when communication is complete
• Circuit switched network - a network in which a
dedicated circuit is established between sender
and receiver and all data passes over this
circuit.
• The telephone system is a common example.
• The connection is dedicated until one party or
another terminates the connection.
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Circuit Switching
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Network Core – Circuit Switching
• Dedicated communication path between two
stations
• Three phases (Establish, Transfer, Disconnect)
• Inefficient (for data traffic)
– Channel capacity dedicated for duration of connection
– Much of the time a data connection is idle
– If no data, capacity wasted
• Set up (connection) takes time
– Once connected, transfer is transparent
– Circuit switching designed for voice
– Constant Data rate
• Both ends must operate at the same rate
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Network Core - Circuit Switching
• Multiplexing in Circuit Switched Networks
– Multiplexing is a technique, in which a single
transmission medium is being shared among multiple
users.
• Types of Multiplexing
– Frequency Division Multiplexing FDM
– Time Division Multiplexing TDM
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Circuit Switching: FDM and TDM
Example: 4 users
FDM
Frequency
time
TDM
Frequency
time
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Synchronous TDM
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Synchronous TDM with empty time slots
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Statistical TDM or Asynchronous TDM
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Network Core: Packet Switching
• Packet switched network
– A network in which data is transmitted in the form of
packets
– Multiple users share network resources
– No dedicated bandwidth is allocated
–
–
–
–
–
No resources are reserved, resources used as needed
Each packet uses full link bandwidth
Good for bursty traffic, simpler, no call setup
Packets queued and transmitted as fast as possible
Packets are accepted even when network is busy,
which causes the delivery to slow down
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Packet Switching: Statistical Multiplexing
10 Mb/s
Ethernet
A
B
C
statistical multiplexing
1.5 Mb/s
queue of packets
waiting for output
link
D
E
Sequence of A & B packets does not have fixed pattern 
statistical multiplexing.
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Network Core: Packet Switching
• The goal of packet switching is to move
packets through routers from source to
destination
• Packets sent one at a time to the network
• Two approaches are used:
– Datagram Approach
– Virtual Circuits Approach
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Packet Switching - Datagram
• Datagram Approach:
– Each packet is treated independently
– No reference to packets that have gone before
– Each node chooses next node on path using
destination address
– Packets with same destination address may not follow
same route
– Packets may arrive out of sequence, may be lost
– It is up to receiver to re-order packets and recover
from lost packets
– No Call setup
– For an exchange of a few packets, datagram quicker
– Analogy: driving, asking directions
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Packet Switching - Datagram
• The Internet is a Datagram network
• Datagram network is not either connectionoriented or connectionless.
• Internet provides both connection-oriented
(TCP) and connectionless services (UDP) to
applications.
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Packet Switching - Datagram
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IT-5302-3 Internet Architecture and Protocols, PUCIT, University of the Punjab, Pakistan
45
Packet Switching – Virtual Circuits
• Virtual Circuit Approach:
– Virtual circuit packet switched network create a
logical path through the subnet
– Call request and call accept packets establish a
virtual connection
– Virtual route remains fixed through the call.
– All packets from one connection follow this path.
– Each packet contains a virtual circuit identifier
instead of destination address to determines the next
hop
– Not a dedicated path
– No routing decisions required for each packet
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Switching Technique –
Virtual Circuit
• Preplanned route established before packets sent
• All packets follow same route
• Similar to circuit in circuit-switching network
– Hence virtual circuit
• Each packet has virtual circuit identifier
– Nodes on route know where to direct packets
– No routing decisions
• Not dedicated path, as in circuit switching
– Packet still buffered at node and queued for output
– Routing decision made on before that virtual circuit
• Network may provide services related to virtual circuit
– Sequencing and error control
• Packets should transit more rapidly
• If node fails, all virtual circuits through node lost
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Virtual Circuits
• Network
can
provide
sequencing
and
error
control
• Packets are forwarded
more quickly
– No routing decisions to
make
• Less reliable
– Loss of a node looses all
circuits
through
that
node
• Less Node Delay
vs.
Datagram
• No call setup phase
– Better if few packets
• More flexible
– Routing can be used to
avoid congested parts of
the network
• More reliable
– If a node fails, packets
may find an alternate
route that bypass that
node
• More Node Delay
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Circuit Switching
• Path
– A dedicated path is
established between two
devices for the duration
of session.
• Reserved Resources
– The link (multiplexed /
not multiplexed) that
makes the path are
dedicated, and cannot be
used
by
other
connections
vs.
Virtual Circuits
• Route
– No dedicated path is
established. Only a route
is defined. Each switch
creates an entry in its
routing table for the
duration of virtual circuit
• Shared Links
– The link that makes a
route can be shard by
other connections
• constant data rates.
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Features of Circuit and Packet
Switching
Feature
Packet Switching
Circuit
Switching
Data sent as packets?
No
Yes
Packets follow same route?
N/A
Yes (VC), No (Datagram)
Resources reserved in network?
Yes
No
Data send can have variable latency No
(response time)
Yes
Connection made?
Yes
VC: Yes, Datagram: No
State info stored at network nodes?
N/A
VC: Yes, Datagram: No
Addressing info needed?
only when call VC: virtual circuit
is set up
number
Datagram: destination
Address
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Network Taxonomy
Telecommunication
networks
Circuit-switched
networks
FDM
TDM
Packet-switched
networks
Networks
with VCs
Datagram
Networks
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Network Access
• Network Access:
– The physical link that connects an end system to its Edge
Router, which is the first router on a path from the end
system to any other distant end system.
• Classification of Network Access:
– Residential Access
• Connecting a home end system to an edge router
• Dial-up modems, DSL, HFC system
– Company Access
• Switched Ethernet LANs
– Mobile Access
• Wireless LAN (802.11b)
• Wide Area Wireless Access Networks (GPRS, 3G, WAP)
• Note: these categories are not hard and fast
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Physical Media
• Twisted Pair Cable
– UTP Cat 5
• Coaxial Cable
– Baseband and Broadband Cable
• Fiber Optics
– Multimode and single mode
• Terrestrial Radio Channels
– Local Area Radio Channels (Wireless LANs)
– Wide Area Radio Channels (WAP, I-mode, 3G)
• Satellite Radio Channels
– Geostationary Satellites (36000 km)
– Low Altitude Satellites
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Internet Addressing Schemes
• IP Addressing Scheme
– Dotted decimal Notation, Use hierarchal Address Space
– IPv4 and IPv6
• MAC addresses
– 48 bits Unique addresses, Use flat Address Space
– IEEE assigned vendor ID (first 24 bits)
– Vendor serial numbers (last 24 bits)
• Why two addressing mechanisms are used?
• Significance of using a MAC address
– Communication over a LAN
• Identifying Destination Network
– Extracting destination network address from destination IP
address.
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