Chương 1

Mô hình TCP/IP (Transmission Control Protocol/Internet Protocol) hay còn gọi là bộ giao thức Internet là một mô hình khái niệm và một tập hợp các giao thức truyền thông được sử dụng trong mạng Internet và các hệ thống mạng máy tính tương tự. Nó đóng vai trò như một ngôn ngữ chung cho phép các thiết bị khác nhau giao tiếp và trao đổi thông tin với nhau trên mạng.

Chương 1: Tổng quan về mô hình truyền thông

 Nguyễn Thanh Đăng, bài giảng Mạng và Truyền dữ liệu, ÐHCN Tp.HCM, 2016.

Chương 1: Tổng quan về mô hình truyền thông

1.1 Các thành phần chính của mạng máy tính.

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1.1 Các thành phần chính của mạng máy tính.

n

1.2 Mô hình OSI.

 Các công việc liên quan quá trình gửi 1 bức thư

1.2 Mô hình OSI.

 n

1.2 Mô hình OSI.

 n

1.2 Mô hình OSI.

 Mô hình OSI 7 lớp: gồm 7 lớp riêng biệt nhưng có liên hệ với nhau, mỗi lớp nhằm định nghĩa một phân đoạn trong quá trình di chuyển thông tin qua mạng.

1.2 Mô hình OSI.

 Chức năng mỗi lớp trong mô hình OSI:

a)Lớp vật lý (Physical layer):Lớp vật lý chịu trách

nhiệm cho việc di chuyển các bit riêng lẻ từ 1 hop

(nút) đến nút kế tiếp Lớp này liên quan đến các đặc tính cơ, điện của giao diện thiết bị và môi trường

truyền.

1.2 Mô hình OSI.

1.2 Mô hình OSI.

b)Lớp liên kết dữ liệu (Data link layer): Lớp liên kết dữ liệu chịu trách nhiệm chuyển các frame từ 1 hop (nút) đến hop khác.

1.2 Mô hình OSI.

 Nhiệm vụ

 Break L3 (Network) data into reasonable size (Frame)

 Truyền khung/frame từ nút đến nút trong một mạng

 Guarantee Node-to-Node delivery (Frame Error Free)

 Service

 Tạo khung (thêm header & trailer)

 Định địa chỉ vật lý (MAC address: 12 digit hexadecimal (e.g 080BF0AFDC09))

 Same sender network:source & destination address

 Outside sender network: source & connecting devices (bridge, router, gateway) address

 Điều khiển lưu lượng:frame acknowledgement, inform buffer size, etc.

 Kiểm soát lỗi:error detection and error correction

 Điều khiển truy cập: checking accessibility (ex Multipoint connection)

1.2 Mô hình OSI.

 Phân phối hop đến hop

1.2 Mô hình OSI.

c) Lớp mạng (Network layer): Lớp mạng chịu trách nhiệm phân phối các gói tin riêng rẽ từ host nguồn đến host đích.

 Logical (Network) address (header):IP address

 Định tuyến các gói tin đi qua thiết bị liên mạng

 Router || Gateway

1.2 Mô hình OSI.

 Phân phối từ nguồn đến đích

1.2 Mô hình OSI.

d)Lớp giao vận (Transport layer): Lớp giao vận chịu trách nhiệm phân phối message từ một quá

trình/process đến quá trình khác.

1.2 Mô hình OSI.

 Nhiệm vụ

 Đảm bảo phân phối toàn bộ từ nguồn đến đích cuối cùng

 Service

 Service-point addressing:Port address (16 bits: 0 – 65,535 ports)

 Each application is assigned a specific port address

 Segmentation and Reassembly

 Source:segment L5 data into small segments

 Destination:reassembly small segments into a whole message

 Điều khiển kết nối

 Không kết nối/Connectionless

 Hướng kết nối/Connection-oriented

 Kiểm soát lỗi: dò và sửa sai toàn bộ message

 Điều khiển luồng

1.2 Mô hình OSI.

e)Lớp phiên (Session layer): Lớp phiên chịu trách nhiệm điều khiển và đồng bộ dialog.

 Traffic control & direction control

 Đồng bộ thông điệp/Message synchronization

 Adding checkpoints (synchronization points) in the message stream

1.2 Mô hình OSI.

f) Lớp trình diễn (Presentation layer): Lớp trình diễn chịu trách nhiệm biên dịch, nén và mã hóa

 Ex ASCII -> non ASCII system

 Mã hóa (privacy & security)

 Đối với các thông tin nhạy cảm: login-password, thẻ tín dung, tài khoản ngân hàng, thông tin cá nhân

 Nén

 Ex Zip, Gif, JPEG

1.2 Mô hình OSI.

g) Lớp ứng dụng (Application layer): Lớp ứng dụng chịu trách nhiệm cung cấp các dịch vụ đến người sử dụng

 Network Virtual Terminal

 Truyền , truy xuất và quản lý file/File transfer, access, and management (FTAM)

 Dịch vụ mail

 Truy cập WWW

1.2 Mô hình OSI.

 Giao tiếp giữa các lớp trong mô hình OSI

1.2 Mô hình OSI.

 Trao đổi dữ liệu sử dụng mô hình OSI

1.3 Mô hình TCP/IP

 The layers in theTCP/IP protocol suitedo not exactlymatch those in the OSI model The original TCP/IPprotocol suite was defined as having four layers:host-to-network,internet,transport, andapplication.However, when TCP/IP is compared to OSI, we cansay that the TCP/IP protocol suite is made of fivelayers:physical,data link,network,transport, and

application.

1.3 Mô hình TCP/IP

1.3 Mô hình TCP/IP

Network Access

1.3 Mô hình TCP/IP

a) Physical and Data Link Layers:

At the physical and data link layers, TCP/IP does not define any specific protocol It supports all the standard and proprietary protocols A network in a TCP/IP

internetwork can be a local-area network or a wide-area network

b) Network Layer:

At the network layer (or, more accurately, the

internetwork layer), TCP/IP supports the Internetworking Protocol lP, in turn, uses four supporting protocols:

ARP, RARP, ICMP, and IGMP

1.3 Mô hình TCP/IP

c) Transport Layer:

Traditionally the transport layer was represented in

TCP/IP by two protocols· TCP and UDP IP is a host protocol, meaning that it can deliver a packet from one physical device to another UDP and TCP are

host-to-transport level protocols responsible for delivery of a message from a process (running program) to another process A new transport layer protocol, SCTP, has been devised to meet the needs of some newer applications.

1.3 Mô hình TCP/IP

h

1.3 Mô hình TCP/IP

 UDP protocol:

The User Datagram Protocol (UDP) is called a

connectionless, unreliable transport protocol It does not add anything to the services of lP except to

provide process-toprocess communication instead of host-to-host communication Also, it performs very limited error checking.

 Provides limited error checking

 Provides best-effort delivery

 Has no data-recovery features

UDP Characteristics

1.3 Mô hình TCP/IP

 Well-Known Ports for UDP

1.3 Mô hình TCP/IP

Well-Known Ports for UDP

1.3 Mô hình TCP/IP

 Checksum

-The UDP checksum includes three sections: a

pseudoheader, the UDP header, and the data coming from the application layer.

-The pseudoheader is the part of the header of the lP

packet in which the user datagram is to be encapsulated with some fields filled with Os

1.3 Mô hình TCP/IP

Pseudoheader for checksum calculation

1.3 Mô hình TCP/IP

Example 23.2

Figure 23.11 shows the checksum calculation for a very small user datagram with only 7 bytes of data Because the number of bytes of data is odd, padding is added for checksum calculation The pseudoheader as well as the padding will be dropped when the user datagram is

delivered to lP.

1.3 Mô hình TCP/IP

 User

1.3 Mô hình TCP/IP

 UDP Operation

-Connectionless Services: each user datagram sent by

UDP is an independent datagram There is no connection establishment and no connection termination

-Flow and Error Control:UDP is a very simple,

unreliable transport protocol There is no flow control and hence no window mechanism The receiver may overflow with incoming messages 44

1.3 Mô hình TCP/IP

-Encapsulation and Decapsulation: To send a message

from one process to another, the UDP protocol encapsulates and decapsulates messages in an lP datagram.

-Queuing:

1.3 Mô hình TCP/IP

 Use of UDP:

- UDP is suitable for a process that requires simple response communication with little concern for flow and error control It is not usually used for a process such as FfP that needs to send bulk data.

request UDP is suitable for a process with internal flow and error control mechanisms For example, the Trivial File Transfer

Ptotocol (TFTP) process includes flow and error control It can easily use UDP.

1.3 Mô hình TCP/IP

- UDP is a suitable transport protocol for multicasting

Multicasting capability is embedded in the UDP software but not in the TCP software.

- UDP is used for management processes.

- UDP is used for some route updating protocols such as Routing Information Protocol (RIP)

1.3 Mô hình TCP/IP

 TCP (Transmission Control Protocol) protocol: TCP is a connection-oriented protocol; it creates a virtual connection between two TCPs to send data In

addition, TCP uses flow and error control mechanisms at the transport level Therefore, TCP is called a

connection-oriented, reliable transport protocol It

adds connection-oriented and reliability features to the services of lP

1.3 Mô hình TCP/IPTCP Characteristics

 Transport layer of the TCP/IP stack

 Access to the network layer for applications

1.3 Mô hình TCP/IP

 TCP Services

 Process-to-Process Communication: Like UDP, TCP

provides process-to-process communication using port numbers

1.3 Mô hình TCP/IP

Well-known ports used by TCP

1.3 Mô hình TCP/IP

 Stream Delivery Service: TCP, unlike UDP, is a

stream-oriented protocol TCP allows the sending

process to deliver data as a stream of bytes and allows the receiving process to obtain data as a stream of

bytes TCP creates an environment in which the two processes seem to be connected by an imaginary

"tube“ that carries their data across the Internet

1.3 Mô hình TCP/IP

Stream delivery

1.3 Mô hình TCP/IP

 Sending and Receiving Buffers: Because the

sending and the receiving processes may not write or read data at the same speed, TCP needs buffers for

storage There are two buffers, the sending buffer and the receiving buffer, one for each direction

1.3 Mô hình TCP/IP

Sending and receiving buffers

datagrams and transmitted This entire operation is transparent to the receiving process

1.3 Mô hình TCP/IP

TCP segments

1.3 Mô hình TCP/IP

 Full-Duplex Communication: TCP offers full-duplex

service, in which data can flow in both directions at the same time Each TCP then has a sending and

receiving buffer, and segments move in both directions.

1.3 Mô hình TCP/IP

 Reliable Service: TCP is a reliable transport protocol

It uses an acknowledgment mechanism to checkthe safe and sound arrival of data

 'I'CP Features

 Numbering System:

-Byte Number: The bytes of data being transferred in

each connection are numbered by TCP The numbering starts with a randomly generated number 60

1.3 Mô hình TCP/IP

-Sequence Number: The value in the sequence number

field of a segment defines the number of the first data byte contained in that segment

-Acknowledgment Number: The value of the

acknowledgment field in a segment defines the number of the next byte a party expects to receive The

acknowledgment number is cumulative

1.3 Mô hình TCP/IP

 Flow Control : The receiver of the data controls the

amount of data that are to be sent by the sender This is done to prevent the receiver from being

overwhelmed with data The numbering system allows TCP to use a byte-oriented flow control

 Error Control

 Congestion Control

1.3 Mô hình TCP/IP

 Segment

 Format:

1.3 Mô hình TCP/IP

Control field

1.3 Mô hình TCP/IP

 A TCP Connection

 Connection Establishment: TCP transmits data in full-duplex mode When two TCPs in two machines are connected, they are able to send segments to each other simultaneously This implies that each party

must initialize connnunication and get approval from the other party before any data are transferred

1.3 Mô hình TCP/IP

Establishing a Connection

1.3 Mô hình TCP/IP

-Three Way Handshaking: The connection establishment in TCP is called three way handshaking

1.3 Mô hình TCP/IP

 Data Transfer

1.3 Mô hình TCP/IP

 Connection Termination

Connection termination using three-way handshaking

1.3 Mô hình TCP/IP

 Flow Control: TCP uses a sliding window to handle

flow control The sliding window protocol used by TCP, however, is something between the Go-Back-Nand Selective Repeat sliding window.

1.3 Mô hình TCP/IP

Flow Control

1.3 Mô hình TCP/IPTCP Acknowledgment

1.3 Mô hình TCP/IPFixed Windowing

1.3 Mô hình TCP/IP

Sliding window: A sliding window is used to make

transmission more efficient as well as to control the flow of data so that the destination does not become

overwhelmed with data TCP sliding windows are byte oriented

1.3 Mô hình TCP/IP

TCP Sliding Windowing

1.3 Mô hình TCP/IP

Some points about TCP sliding windows:

-The size of the window is the lesser of rwnd and cwnd.

-The source does not have to send a full window's worth of data.-The wmdow can be opened or closed by the receiver, but shouW not be shrunk.

-The destination can send an acknowledgment at any time as long as it does not result in a shrinking window.

- The receiver can temporarily shut down the window; the sender, however, can always send a segment of 1 byte after the window is shut down

78

What is the value of the receiver window (rwnd) for host Aif the receiver, host B, has a buffer size of 5000 bytes and1000 bytes of received and unprocessed data?

Example 23.4

The value of rwnd = 5000 − 1000 = 4000 Host B canreceive only 4000 bytes of data before overflowing itsbuffer Host B advertises this value in its next segment to A.

1.3 Mô hình TCP/IP

TCP Sequence and Acknowledgment Numbers

1.3 Mô hình TCP/IP

 Error Control

 Checksum:

-Each segment includes a checksum field which is used

to check for a corrupted segment If the segment is

corrupted, it is discarded by the destination TCP and is considered as lost

-TCP uses a 16-bit checksum that is mandatory in every

1.3 Mô hình TCP/IP

 Acknowledgment: TCP uses acknowledgments to

confirm the receipt of data segments Control segments that carry no data but consume a sequence number are also acknowledged ACK segments

are never acknowledged.

 Retransmission: In modent implementations, a

retransmissimt occur s if the retransmission timer

expires or three duplicate ACK segments have arrived.

1.3 Mô hình TCP/IP

 Out-of-Order Segments: Data may arrive out of order

and be temporarily stored by the receiving TCP,

but TCP guarantees that no out-of-order segment is delivered to the process.

1.3 Mô hình TCP/IP

 Congestion Control: Congestion control refers to

techniques and mechanisms that can either prevent congestion, before it happens, or remove congestion,

after it has happened Congestion control involves two

factors that measure the performance of a network:

delay and throughput

1.3 Mô hình TCP/IP

Congestion Window:

Congestion Policy: TCP's general policy for handling

congestion is based on three phases: slow start, congestion avoidance, and congestion detection In the slow-start

phase, the sender starts with a very slow rate of

transmission, but increases the rate rapidly to reach a

threshold When the threshold is reached, the data rate is reduced to avoid congestion Finally if congestion is

detected, the sender goes back to the slow-start or

congestion avoidance phase based on how the congestion

1.3 Mô hình TCP/IP

d) Application Layer:

The application layer in TCP/IP is equivalent to the

combined session, presentation, and application layers in the OSI model Many protocols are defined at this layer.

1.3 Mô hình TCP/IP

Mapping Layer 3 to Layer 4

1.3 Mô hình TCP/IP

Mapping Layer 4 to Applications

1.3 Mô hình TCP/IP

Relationship of layers and addresses in TCP/IP:

- The physical addresses have authority over the

network (LAN or WAN) The size and format of these addresses vary depending on the network For

example, Ethernet

uses a 6-byte (48-bit) physical address that is imprinted on the network interface card (NIC).

1.3 Mô hình TCP/IP

-Ví dụ: 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 10is the sender, and the computer with physical address 87is the receiver.

1.3 Mô hình TCP/IP

 Logical Addresses:

-Logical addresses are necessary for universal communicationsthat are independent of underlying physical networks Physicaladdresses are not adequate in an internetwork environmentwhere different networks can have different address formats Auniversal addressing system is needed in which each host canbe identified uniquely, regardless of the underlying physicalnetwork.

- A logical address in the Internet is currently a 32-bit address that can uniquely define a host connected to the Internet No two

publicly addressed and visible hosts on the Internet can have the

same lP address.