Transcript INE1020 Lecture Notes
Lecture 1: Internet Architecture
Architecture of the Internet Network Internetwork Router Protocol Accessing the Internet Residential access Dedicated access Institutional access Communicating over the Internet Protocol layering (covers only BASIC idea) Internet Addressing INE1020: Introduction to Internet Engineering 1: Introduction 1
1. What’s the Internet
The Internet is a collection of networks connected by interconnecting devices.
The connecting devices are specialized computing devices, e.g. routers forward data from one network to another.
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1.1 Computer network
An interconnected collection of computers
Client-Server Model
File Servers Computer Network Application Servers INE1020: Introduction to Internet Engineering Workstations (Local Processing) 1: Introduction 3
1.1 Classifications of Networks
Based on size: System/Storage area networks (SAN) • within the same room Local area networks (LAN) • in a close proximity Metropolitan area networks (MAN) • span a city Wide area networks (WAN) • connecting computers situated anywhere • Connects many networks together INE1020: Introduction to Internet Engineering 1: Introduction 4
1.2 internetwork
A collection of networks INE1020: Introduction to Internet Engineering 1: Introduction 5
1.2 Internetwork: Another example
Figure 15.3(text book) An example of internet with six networks and three computers attached.
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1.2 The Internet Topology
See http://www.cybergeography.org/atlas/topology.html for more Internet topologies.
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1.2 The Illusion Of A Giant Network
Any computer can send data to any other computer providing they have IP software installed.
The Internet operates like a virtual network.
INE1020: Introduction to Internet Engineering Fig. 15.1 (text book) 1: Introduction 8
1.2 The Reality Of Internal Structure
The Internet contains a complex physical structure users never see Interconnecting networks with routers Fig. 15.2 (text book) INE1020: Introduction to Internet Engineering 1: Introduction 9
1.2 Internet: a service view
communication
infrastructure:
enables distributed applications: WWW, email, games, e commerce, database., cyberspace INE1020: Introduction to Internet Engineering 1: Introduction 10
1.2 Internet: “nuts & bolts” view
millions of connected computing devices:
hosts, end-systems
pc’s workstations, servers PDA’s
communication links
fiber, copper, radio, satellite
routers:
(chunks of data) across networks forward packets router server local ISP workstation mobile company network regional ISP INE1020: Introduction to Internet Engineering 1: Introduction 11
1.2 Internet: “nuts & bolts” view
protocols: control sending, receiving of msgs e.g., TCP, IP, HTTP, FTP Internet: “network of networks” public Internet versus private intranet
collection(s) of SAN, LAN, MAN, WAN
router server local ISP workstation mobile regional ISP INE1020: Introduction to Internet Engineering company network 1: Introduction 12
1.2 Connecting a Computer to a Remote Network
Cables connecting a computer to a LAN are usually short, but may be extended.
Fig 13.1 (text book) INE1020: Introduction to Internet Engineering Modems used to send data across wire, telephone system & optical fibres Fiber optic cable can provide connections across long distances.
Requiring optical modems Using light instead of electricity to carry data 1: Introduction 13
1.3 Incompatible Network Technologies
Not all networks are compatible.
Networks: Vary in speed Vary in electrical voltages Differ in addressing scheme Each technology designed to meet speed, dist, cost constraints.
It is impractical to make computers in an enterprise use the same network technology.
Allow groups to select a network technology based on need INE1020: Introduction to Internet Engineering 1: Introduction 14
1.3 Routers
Special-purpose computers are used to interconnect networks Using standard hardware (CPU, memory, and network interfaces) Running special-purpose software Forwarding packets from one network to another Determining where to send packets Transforms packets as necessary to meet standards for each network Fig. 13.2 (text book) INE1020: Introduction to Internet Engineering 1: Introduction 15
1.3 Routers
Interconnecting LAN to LAN Interconnecting LAN to WAN Fig 13.3 (text book) INE1020: Introduction to Internet Engineering 1: Introduction 16
1.4 Network Protocol
A common language computers use to exchange messages.
Specifying exact format and meaning of each message specify actions taken during sending and receiving of data INE1020: Introduction to Internet Engineering 1: Introduction 17
1.4 Network Protocol
a human protocol and a computer network protocol: Hi Hi Got the time?
2:00 TCP connection req.
TCP connection reply.
Get http://gaia.cs.umass.edu/index.htm
1.4 Network Protocol
human protocols: “what’s the time?” “I have a question” introductions … specific messages
sent
… specific actions taken when messages received, or other events network protocols: machines rather than humans all communication activity in Internet governed by network protocols
protocols define format, order of messages sent and received among network entities, and actions taken on message transmission, receipt
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1.4 Internet Protocol (IP)
IP defines computer communication details.
Specifying how packets are formed Specifying how routers forward each packet Computers connecting to the Internet must follow the IP rules.
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1.4 IP Software On Every Machine
Computer hardware does not understand IP.
Connecting a computer to the Internet does not mean it can use the Internet Computers need IP software before using the Internet.
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2. Accessing the Internet
User’s computers or hosts connect to the Internet through an access network . Residential access: • dial-up access vs. dedicated access.
• dial-up access advantages: least expensive.
• dedicated access advantages: higher speed of delivery and remains connected at all times.
– instantaneous access access network – continuous availability Institutional access • dedicated access.
The Internet access network INE1020: Introduction to Internet Engineering 1: Introduction 22
2.1. Access Network:
Residential access Residential access is normally through an ISP (Internet Service Provider) Most ISPs offer dial-up access based system.
through a telephone Requires a modem and software that uses the modem.
Speed: up to 56Kbps.
Fig. 14.1
(text book) INE1020: Introduction to Internet Engineering 1: Introduction 23
2.2. Access Network: dedicated access
Three newer technologies used by ISPs to offer inexpensive dedicated access : Cable modems • use cable television wiring (most homes already have cable TV wiring).
• Cable modems send data over coax cable but transmission does not interfere with TV signals – cable system is designed to carry many more signals than are currently available, cable modem use the unused bandwidth • advantages: – deliver data faster than a dial-up connection.
– provide continuous connectivity.
– use existing wiring system.
• chief disadvantage: – customers share the wiring (share bandwidth) - data transmission may slow down if many customer send data at the same time; but even at the slowest speed it still operate faster than dial-up modem INE1020: Introduction to Internet Engineering 1: Introduction 24
2.2. Access Network : dedicated access
DSL (Digital Subscriber Line) technology • use conventional telephone wiring • unlike dial-up modem (which encode data with sound), DSL does not use the telephone system. Instead DSL transfer data by using the underlying telephone wires to send electrical signals • does not affect normal telephone service • e.g. ADSL: asymmetric digital subscriber line.
– 6.144 Mbps downstream (data flowing to user), 576Kbps upstream (data flowing from user).
• advantages – use existing wiring – provide continuous connectivity.
– does not share bandwidth with other subscribers (unlike cable modem) INE1020: Introduction to Internet Engineering 1: Introduction 25
2.2. Access Network : dedicated access
Wireless access similar to cellular phones • use radio transmissions • a transmitter runs all the time to to provide continuous access • chief advantage is the ability to reach remote areas.
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2.3. Access Network: Institutional access
Institutional access is mainly through company/university local area network (LAN).
E.g. using Ethernet: • shared cable connects user computers • speeds: 10 Mbs, 100Mbps, Gigabit Ethernet Router INE1020: Introduction to Internet Engineering 1: Introduction 27
3. Communicating over the Internet
To communicate over the Internet, the computers must: use a common language exchange of messages.
have a way to address or a protocol one another.
to govern the Protocol: specifies exact format, order of messages sent and received among network entities, and actions taken on message transmission and receipt.
Addressing: defines where to deliver the messages. INE1020: Introduction to Internet Engineering 1: Introduction 28
3.1 Protocol Layering
Internet has a large collections of protocols organized in a layering model. Application : enables the user, whether human or software, to access the network.
Transport : responsible for reliable source-to-destination (end-to-end) delivery of the entire message.
Network : responsible for routing a packet (also called datagram) from source-to-dest (possibly) across multiple (different) networks. Data link (also called network interface) network.
: specify how to organize data into frames and how to deliver a frame over a Physical : coordinates the functions required to transmit a bit stream over a physical medium.
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3.1 Protocol Layering
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3.1 Protocol Layering
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3.1 Protocol Layering
TCP/IP Protocol Suite.
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3.1 Protocol Layering
Two key protocols are: • IP (Internet Protocol) – Oversee end-to-end delivery of individual packets – Does not recognize relationships among packets – Treats each packet independently, as if they belong to different message • TCP (Transport Control Protocol) – Ensure whole message arrive intact and in order – (eg, check if packets are missing or arrive out of order) INE1020: Introduction to Internet Engineering 1: Introduction 33
3.1 Router Overrun with Datagrams
Router becomes overrun with datagrams Eg, routers 1 & 2 each receives 5000 datagrams both routers send all datagrams they received (5000+5000) across network d to router 3 but router 3 can only handle 5000 datagrams Analogy: traffic jam Eg, cars from roads a and b attempt to merge into road d, causing traffic congestion INE1020: Introduction to Internet Engineering 1: Introduction 34
3.1 Transmission Control Protocol
When a router is overrun with datagrams, some of them will be discarded.
As a result some datagrams will be lost TCP checks for lost datagrams When hardware in a router or network system fails, other routers start sending datagrams through new (alternative) paths.
As a result, some datagrams arrive in a different order than they were sent TCP checks for out-of-order datagrams Network hardware failure sometimes result in duplication of datagrams TCP checks for duplication of datagrams INE1020: Introduction to Internet Engineering 1: Introduction 35
3.1 Recovering Lost Datagrams: TCP Retransmission
TCP includes an identification of each datagram.
Ignores duplicate copies Receiver uses identification (sequence numbers) to put out-of-order datagram back in order Recovers lost datagrams Uses timers Sends an acknowledgement back to the source - this guarantees that all data arrives If timer expires before an acknowledgement arrives, TCP assumes the datagram is lost and retransmit the datagram INE1020: Introduction to Internet Engineering 1: Introduction 36
3.2 Internet Addresses
Every Computer Is Assigned A Unique Address Each computer attached to the Internet must be assigned a unique address.
IP Addresses Are Not Random Computers on the same network have the same prefix (Netid).
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3.2. Internet Addressing
IP or Internet address is a 32-bit (4 byte) address that uniquely defines every computing devices on the Internet.
Decimal notation to make it easier to read.
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3.2 Classes of IP addresses
Designers chose a compromise - multiple address formats that allow both large and small prefixes Each format is called an address class Class of an address is identified by first four bits INE1020: Introduction to Internet Engineering 1: Introduction 39
3.2 Dotted decimal notation
Class A, B and C all break between prefix and suffix on byte boundary Dotted decimal notation is a convention for representing 32-bit internet addresses in decimal Convert each byte of address into decimal; display separated by periods (``dots'') INE1020: Introduction to Internet Engineering 1: Introduction 40
3.2 IP Address classes at a glance
Class A, B and C are primary classes Used for ordinary host addressing Class D is used for multicast, a limited form of broadcast Class E is reserved INE1020: Introduction to Internet Engineering 1: Introduction 41
3.2. Internet Addressing: An Example
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Further Reading
Chapters 13, 14, 15, & 16 of the textbook.
Note: This lecture is designed with the objective of providing an introduction to the architecture of the Internet and communicating over the internet .
Details of these topics are beyond the scope of this course and will NOT be taught or discussed. Students who wish to invest more time on studying more details for these topics are referred to: Forouzan Chapter 2 .
Doug Comer, Computer Networks & Internets with Internet Applications, chapter 17, 18, 20 & 24 Details of protocol layering will be covered in IEG3310 INE1020: Introduction to Internet Engineering 1: Introduction 43