1

Network Operation

2

Outlines

Network Protocols OSI 7-layer TCP/IP Protocol Suits

3

Part 1

Network Protocols

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How to Create A Network?

A network is a combination of hardware and software that sends data from one location to another. Physical equipments carry signals from one

point to another. Ex: interface card, cable, router, wire, … which all

satisfy their especial protocols or standard. Programs make the services that we expect

from a network possible. Ex: device driver, processes for the protocol suites

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Network Protocols

To provide the services required to perform a task, the Internet has created a set of rules called protocols.• These allow different networks, using different

technologies, to be connected together and carry a message from one point to another.

• Example: TCP, UDP, IP, HTTP, IEEE 802.3, IEEE 802.11, GSM… We will describe them later.

Internet standards IETF: Internet Engineering Task Force RFC: Request for comments

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Communication Protocols

通訊協定（ Communication Protocol ）是用來溝通不同電腦的一種標準架構。

網路通訊協定是網路上各個機器間的社會規範，描述電腦之間對於彼此通訊行為的一種期待。

Example ： A says Hello ！ B says Hi ！ 這種「對於對方合理反應的期待」就是通訊協定。

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Human v.s. Machine Protocols

Hi

Hi

Got thetime?

2:00

TCP connection requestTCP connectionresponse

Get http://www.awl.com/kurose-ross

<file>time

A human protocol A computer network protocol

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Protocols

Protocols define format, order of messages sent and received among network entities, and actions taken on message transmission & receipt.

TCP connection requestTCP connectionresponse

Get http://www.awl.com/kurose-ross

<file>

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Physical Equipments

Connecting devices Hub, switch, bridge Cable, UTP line, fifer Radio, transmitter,

receiver Router

End devices Notebook, personal

computer, smart phone Network interface card

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Connections between Nodes

Node-to-node delivery Point-to-point delivery The link connection between two adjacent hosts

Source-to-destination delivery End-to-end delivery The connection between source and destination

hosts

source destination node node

end end

computer/node/hop/host/component

linkconnection

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Local Area Network

LAN (Local Area Network) is a network where any two devices in this network has a link and can communicate directly.

We use physical addresses on the network interface card (NIC) to distinguish these network interface cards on the devices.

By using a repeater/hub/switch, we can connect several computers such that there exists a link between any two devices of them.

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Network Interface Card (1/2)

Ethernet card, PCMCI card, 802.11 card

Combination of hardware, software, firmware

Sending side: Encapsulates

datagram in frame Adds error checking

bits, flow control, etc.

controller

physicaltransmission

cpu memory

host bus (e.g., PCI)

network adaptercard

host schematic

applicationtransportnetwork

link

linkphysical

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Network Interface Card (2/2)

Receiving side Looks for errors, flow control, etc Extracts datagram, passes to upper layer at

receiving side.

controller controller

sending host receiving host

datagram datagram

datagram

frame

PHY addr. 2

Physical address 2 00001010…010010

Physical address 1 00000111…111011

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Network Topologies

The term physical topology refers to the way in which a network is laid out physically.

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Internetwork

By using routers/gateways, LANs can be connected to a larger network.

Networks can be connected using connecting devices to form an internetwork (or an internet).

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Categories of Networks

According to the size of networks, networks are categorized into three types: LAN/MAN/WAN.

Networks

Wide Area Network(WAN)

Metropolitan Area Network(MAN)

Local Area Network(LAN)

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Part 2

OSI Model

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ISO OSI Reference Model

不同廠商各自發展其系統的通訊協定，各有目的與優點。

建立一套公認且通用的參考架構，可以釐清資料通訊的專用術語，彼此間的對應關係

ISO OSI 參考模型（ Reference Model ） 國際標準組織（ International Standards

Organization ， ISO ） 開放系統互連參考模型（ Open System

International reference model ， OSI ）

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The OSI Model (1/2) International Organization for

Standardization (ISO) The Open Systems Interconnection model

is a theoretical model that shows howany two different systems can communicate with each other. To show the function of each system To show the relationship between the systems Allow two different systems to communicate

regardless of their underlying architecture Ethernet, ATM, WLAN, GPRS, FDDI, ...

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The OSI Model (2/2)

A framework of seven layers The functionality of each separate layer The relationship between two neighbor layers The relationship between two peer layers

Not all of layers are necessary to implement The number of layers depends on the

functionality of the device and its location in the network.

Ex: End systems: 1-7 layers; Ether-switches: 1,2 layers; TCP/IP routers: 1,2,3 layers

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7 Layers in the OSI Model

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Functionalities in Each OSI Layer

網路應用程式 應用層：讓各網路的 AP 有一套統一遵循規則 表述層：讓資料呈現方式有一致的標準 會議層：管理應用程式間的協議過程 傳輸層：提供 end-to-end 的錯誤偵測和更正 網路層：建立 source 與 destination 間的連線

資料鏈結層：提供 point-to-point 可靠的連線 實體層：定義網路媒介的實體特性

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Layered Concept

同一機器上，每一層都只提供服務給上層和要求下層提供服務 Ex ： layer 3 layer 4 layer 5

Layer 4 asks layer 3 to do something. Layer 4 provides its results to layer 5. Layer 3 and Layer 5 can not talk.

不同機器間，每一層都只與同一層交談 Peer-to-peer concept Ex ： layer 4 只與 layer 4 談資料流量的問題 Note ：透過雙方的 layer 3 提供傳話的服務

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Flow of Data in the OSI Model

encapsulation decapsulation

peer-to-peer

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Physical Layer

Transmitting bit streams over a physical medium.

Encode and decode Transform a stream of bits into a signal Mechanical and physical specifications

of the physical devices are defined.

....100111010110000011101010100111001.....

logic 0

-3V

-25V

3V

25V

logic 1

undefined

RS 232 Voltage

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Data-link Layer

Node-to-node delivery: directly connected Organize bits into logical units called frames. Header and Trailer

Physical address in a network Error detect or correct

Ethernet Frame

Preamble SourceDestination Type Data FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

Data form the network layer

Packet:

A network B

C

Network interface: the point connect to network

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Media Access Layer

媒體存取控制層（ Media Access Layer ， MAC ）

存取模式（ Access Methods ）定義電腦如何將資料放置纜線以及如何將資料從纜線中取出的規則，即定義電腦如何共享實體網路。

對應於 OSI 的資料鏈結層內的 MAC Layer 定義如何使用傳輸媒介做資料傳送的網路協定。

Logic Link Control

Media Access ControlData Link Layer

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Logical Link Control Layer

邏輯鏈結控制層（ Logical Link Control Layer ， LLC ）

MAC 上層的 LLC Layer ，負責處理資料的錯誤或遺漏或重覆接收等問題，便確保資料正確到達對方。

Data Link Layer =LLC+MAC MAC 通常為 hardware control 。

LLC

MAC

Data Link Layer

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Deriver 驅動程式（ driver ）通常位於此層（ Data

Link Layer ），是用來協調電腦系統與某周邊設備進行溝通的軟體（ firmware ）。

Driver 也負責資料的收送。 位於 MAC Layer 上方。

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Ethernet

Ethernet is the most prevalent local area network in use today. For physical and data-link layers. Usually, your computer has a Ethernet card.

The Ethernet protocol uses a 48-bit MAC address, which is normally written in hexadecimal format as shown below:

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Network Layer

Delivery packets between the original source and final destination.

End-to-end delivery of individual packets

Unique logical address (ex: IP address)

Ethernet Frame

Preamble SourceDestination Type FCS

Bytes 8 6 6 2 46-1500 4

64-1518 bytes

From the transport layer

IP packet

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Why Need Logical Addresses?

Different local area networks have different physical addresses.

We need an unique logical address to identify each network interface on the whole world.

Logical address + Physical address

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Routing/Routed Protocols

Routed Protocol To encapsulate a packet with data It is like to make a letter with an envelope. Used on all hosts/routers Ex: IP 、 IPX 、 AppleTalk

Routing Protocol To find a path to deliver packets It is like the rules in a freight transportation

company 。 Used on routers Ex: OSPF 、 RIP 、 IGRP

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Connection of Two Remote Computers by Routers

sourceapplicatio

ntransportnetwork

linkphysical

HtHn M

segment Ht

datagram

destination

application

transportnetwork

linkphysical

HtHnHl M

HtHn M

Ht M

M

networklink

physical

linkphysical

HtHnHl M

HtHn M

HtHn M

HtHnHl M

router

switch

Encapsulationmessage M

Ht M

Hn

frame

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Transport Layer

Source-to-destination (end-to-end) delivery of the entire message. Break the entire message into several packets Ask network layer to send packet individually Reorganize the received packets to a message Packets may arrive out of order or lost. Retransmit packets

1

54

2 3a b c d

b ad c b ac d

a b c d

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Reliable Path

何謂可靠的傳播路徑？ Answer ：透過流量控制、錯誤檢查與更正、多工與反多工、重傳，提供通訊品質。

To create a connection between two end devices before transmission

1

54

2 3a b c d

b ad c b ac d

a b c d

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Flow control

流量控制（ flow control ）的機制在控制網路上資料傳送的速度，以避免因接收端電腦的緩衝器已滿，從網路上新接收的資料必須丟棄。

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Retransmission

The destination checks whether the entire message is received. Sequence number

If some packets lost, the destination asks the source to transmit these packets again.

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Multiplexing

多工（ Multiplexing ）是將多筆 OSI 第 n 層應用程式的通訊連線合在一起，使用第 n-1 層的一條通訊連線 。

n layer (ex: AP layer)

n-1 layer (ex: TCP layer)

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De-multiplexing

反多工（ de-multiplexing ）：將一筆 OSI 第 n-1 層的通訊連線，依據其不同的服務對象，分送給多個第 n 層的通訊軟體 。 IP 利用 protocol number 指定傳輸層 傳輸層利用 port number 指定應用程式

AP layer

TCP layer

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Connection-oriented v.s. Connectionless 連結導向（ connection-oriented ）

在傳送資料前，會先和遠端主機交換控制訊息（ handshake ），以確定對方已準備好接收資料。當handshake 完成，表示已建立連結。此後透過訊息的交換，判斷是否要重傳封包、暫緩傳送。

SCTP (Stream Control Transmission Protocol) & TCP (Transmission Control Protocol)

非連結導向（ connectionless ） 此協定將每一筆資料視為獨立的個體，只負責將訊息傳到網路上，不檢查資料是否被正確的接收。

UDP (User Datagram Protocol)

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Session Layer

Control the dialog between users User: running program Establish, maintain, and synchronize the dialog

between communicating systems Add synchronization points for backup

delivery in case of system or network failure

user A-1

user A-2

user B-1

System A System Bsection

acknowledgea b c d

ba

d

c

c

synchronization point

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Presentation Layer

Concern with the syntax (format) and semantics (meaning) of the information exchanged between two systems. Coding (ASCII vs. Unicode) Compress and decompress Encrypt and decrypt data for security

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Application Layer and Users

The application layer enables the user to access the network.

Define common applications Ex: FTP, SMTP, POP3

SMTP

IE outlook

SMTP

Exchange

mail serveryou

user

Application Protocol

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Several Protocols and Their Layers of OSI Models

ApplicationPresentation

Session

Transport

NetworkData Link

Physical

SMTP 、 FTP 、HTTP

TCP UDP

SNMP 、 DNS 、RTP

IP

fiber 、 UTP 、 cable 、 wirelessEthernettoken ring

802.2 LLC

FDDI x. 25 LAP/LAPB

IPX

SPX

x.25 PLP

NetWare Service

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Binding Process

連結（ Bind ）不同的協定堆疊運作。

連結程序 A 連結協定A 、 E 、 F 、 G 。

連結程序 B 連結協定A 、 C 、 E 、 F 、 G 。

協定 D

協定 G

協定 A

協定 F

協定 E

協定 C協定 B

binding process A

binding process B

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Part 3

TCP/IP Protocol Suite

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Internet

In 1969, a research of internetworking designed to connect several different heterogeneous network Defense Advanced Research Projects Agency

(DARPA) Fault tolerant

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TCP/IP

Transmission Control Protocol/ Internet Protocol (TCP/IP) A protocol suit that controls the Internet

The set, or suite, of protocols that controls the Internet today is referred to as the TCP/IP protocol suite.

The TCP/IP protocol suite was defined as having four layers: host-to-network (or link), internet (network), transport and application.

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Layers of TCP/IP

Application Layer

Host-to-host Transport Layer

Internet Layer

Network Access Layer

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Internet Protocol (IP)

IP datagram IP is an unreliable protocol and a best-

effort delivery service. Problem: different route, out of sequence,

lost, duplicated Solution: Upper layer

1

54

2 3

Datagram

one way

another way

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IP addresses

IPv4 (version 4) A 32-bit IP address, which is presented

in dotted decimal notation.

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IP address and Network Mask

You have to set the computer A IP address (ex: 140.138.137.201) Network mask (ex: 255.255.255.0) Default gateway (ex:140.138.136.202)

140.138.137.201=10001100 10001010 10001001 11001001 255.255.255.0 =11111111 11111111 11111111 00000000 140.138.137.0 =10001100 10001010 10001001 00000000

140.138.137.202=10001100 10001010 10001001 11001010 255.255.255.0 =11111111 11111111 11111111 00000000 140.138.137.0 =10001100 10001010 10001001 00000000

The same value: in the same network

140.138.135.108=10001100 10001010 10000111 01101100 255.255.255.0 =11111111 11111111 11111111 00000000 140.138.135.0 =10001100 10001010 10000111 00000000

Not the same: in different network

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Physical vs. Logical Addresses

100 20 30 500

source A destination B node C node D

end end

20 100 137.201 135.108

Physical address

destination source

Logical address

source destination

Transport layer data

140.138.137.201 140.138.135.108

40 30 137.201 135.108

500 50 137.201 135.108

140.138.137.202 140.138.136.221

140.138.136.222 140.138.135.10440 50

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Transport Layer of TCP/IP (1/2)

User Datagram Protocol (UDP) Basic necessaries for end-to-end delivery of a

transmission Transmission Control Protocol (TCP)

Fully and reliable transport layer services to applications

TCP divides a message into a sequence of segments that are numbered sequentially.

If one segment is lost, it is sent again. If a segment is received out of order, it is ordered

by its sequence number.

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Transport Layer of TCP/IP (2/2)

Stream Control Transmission Protocol (SCTP) Designed for new services expected from the

Internet, such as Internet telephony and video streaming.

Like UDP, it is suitable for real-time transmission of audio and video

Like TCP, it provides error and flow control. To identify which protocol is used in the

transport layer, we use the protocol number. Ex: The protocol number of TCP is 6, and the port

number of UDP is 17.

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Application Layer of TCP/IP

The application layer is responsible for providing services to the user.

Define common applications Ex: FTP, SMTP, POP3

SMTP

IE outlook

SMTP

Exchange

mail serveryou

user

Application Protocol