Network Reference Model PDF

Network Reference Model Page 0 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Foreword ⚫ In the digital era, various information is presented as data in our life. What is data? How is data transmitted? ⚫ In this course, we will use...

Network Reference Model Page 0 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Foreword ⚫ In the digital era, various information is presented as data in our life. What is data? How is data transmitted? ⚫ In this course, we will use the network reference model to understand the "life" of data. Page 1 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Objectives ⚫ On completion of this course, you will be able to:  Understand the data definition and transmission process.  Understand the concepts and advantages of the network reference model.  Understand common standard protocols.  Understand the data encapsulation and decapsulation processes. Page 2 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Contents 1. Applications and Data 2. Network Reference Model and Standard Protocols 3. Data Communication Process Page 3 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Origin of the Story - Applications ⚫ Applications are used to meet various requirements of people, such as web page access, online gaming, and online video playback. ⚫ Information is generated along with applications. Texts, pictures, and videos are all information presentation modes. Application Information Page 4 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Application Implementation - Data ⚫ Data generation  In the computer field, data is the carrier of all kinds of information. ⚫ Data transmission  Data generated by most applications needs to be transmitted between devices. Does an application Data need to complete the entire process from Network data generation to data transmission? Page 5 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Contents 1. Applications and Data 2. Network Reference Model and Standard Protocols 3. Data Communication Process Page 6 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  OSI Reference Model 7. Application Layer Provides interfaces for applications. Translates data formats to ensure that the application-layer data of one 6. Presentation Layer system can be identified by the application layer of another system. Establishes, manages, and terminates sessions between communicating 5. Session Layer parties. Establishes, maintains, and cancels an end-to-end data transmission process; 4. Transport Layer controls transmission speeds and adjusts data sequences. 3. Network Layer Defines logical addresses and transfers data from sources to destinations. Encapsulates packets into frames, transmits frames in P2P or P2MP mode, 2. Data Link Layer and implements error checking. Transmits bitstreams over transmission media and defines electrical and 1. Physical Layer physical specifications. Page 7 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  TCP/IP Reference Model ⚫ The OSI protocol stack is complex, and the TCP and IP protocols are widely used in the industry. Therefore, the TCP/IP reference model becomes the mainstream reference model of the Internet. Application Layer Application Layer Presentation Layer Application Layer Session Layer Host-to-Host Layer Transport Layer Transport Layer Internet Layer Network Layer Network Layer Network Access Data Link Layer Data Link Layer Layer Physical Layer Physical Layer Standard TCP/IP model OSI model Equivalent TCP/IP model Page 8 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Common TCP/IP Protocols ⚫ The TCP/IP protocol stack defines a series of standard protocols. Telnet FTP TFTP SNMP Application Layer HTTP SMTP DNS DHCP Transport Layer TCP UDP ICMP IGMP Network Layer IP PPPoE Data Link Layer Ethernet PPP Physical Layer... Page 9 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Common Protocol Standardization Organizations ⚫ Internet Engineering Task Force (IETF)  IETF is a voluntary organization responsible for developing and promoting Internet protocols (especially protocols that constitute the TCP/IP protocol suite), and releasing new or replacing old protocol standards through RFCs. ⚫ Institute of Electrical and Electronics Engineers (IEEE)  IEEE has formulated about 30% of standards in the electronics, electrical, and computer science fields worldwide. Those standards include well-known IEEE802.3 (Ethernet) and IEEE802.11 (Wi-Fi). ⚫ International Organization for Standardization (ISO)  ISO is an international organization that plays an important role in the formulation of computer network standards, such as the OSI model defined in ISO/IEC 7498-1. Page 10 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Application Transport Network Data Link Physical Layer Layer Layer Layer Layer Application Layer The application layer provides interfaces for application software so that applications can use network services. The application layer protocol designates transport layer protocols and ports. PDUs transmitted at the application layer are called data. Application HTTP 80 (TCP) Layer Hypertext transfer protocol, which provides web browsing services. (Data) Telnet 23 (TCP) Remote login protocol, which provides remote management services. Transport Layer FTP 20 and 21 (TCP) File transfer protocol, which provides Internet file resource sharing services. Network Layer SMTP 25 (TCP) Simple mail transfer protocol, which provides Internet email services. Data Link Layer TFTP 69 (UDP) Simple file transfer protocol, which provides simple file transfer services. Physical Layer Page 11 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Application Transport Network Data Link Physical Layer Layer Layer Layer Layer Common Application Layer Protocols - FTP ⚫ The File Transfer Protocol (FTP) transfers files from one host to another to implement file download and upload. This protocol adopts the client/server (C/S) structure. FTP FTP client server Network FTP client: provides commands for local users to FTP server: a device that runs the FTP service. operate files on a remote server. A user can install It provides the access and operation functions an FTP client program on a PC and set up a for remote clients, allowing users to access the connection with an FTP server to operate files on FTP server through the FTP client program and the server. access files on the server. Page 12 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Application Transport Network Data Link Physical Layer Layer Layer Layer Layer Common Application Layer Protocols - Telnet ⚫ Telnet is a standard protocol that provides remote login services on a network. It provides users with the ability to operate remote devices through local PCs. Telnet server Telnet connection A user connects to a Telnet server AP Router through the Telnet client program. The Network commands entered on the Telnet client Telnet client SW Firewall are executed on the server, as if the... commands were entered on the Server console of the server. Page 13 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Application Transport Network Data Link Physical Layer Layer Layer Layer Layer Common Application Layer Protocols - HTTP ⚫ Hypertext Transfer Protocol (HTTP): is one of the most widely used network protocols on the Internet. HTTP was originally designed to provide a method for publishing and receiving HTML pages. Network HTTP client HTTP server Visits www.huawei.com. Returns the HTML file of the page. Page 14 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Application Transport Network Data Link Physical Layer Layer Layer Layer Layer Transport Layer ⚫ A transport layer protocol receives data from an application layer protocol, encapsulates the data with the corresponding transport layer protocol header, and helps establish an end-to-end (port- to-port) connection. ⚫ PDUs transmitted at the transport layer are called segments. Application Layer Transport layer protocols: Transport TCP: a connection-oriented reliable Layer protocol defined by IETF in RFC 793. (Segment) UDP: a simple connectionless protocol defined by IETF in RFC 768. Network Layer Data Link Layer Physical Layer Page 15 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Application Transport Network Data Link Physical Layer Layer Layer Layer Layer TCP and UDP - Header Formats Source Port (16) Destination Port (16) Sequence Number (32) Acknowledgement Number (32) TCP header Header Reserved Control Window (16) 20 bytes Length (4) (3) Bits (9) Checksum (16) Urgent (16) Options Data (varies) Source Port (16) Destination Port (16) UDP header Length (16) Checksum (16) 8 bytes Data (if any) Page 16 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Application Transport Network Data Link Physical Layer Layer Layer Layer Layer TCP and UDP - Port Numbers Web browser HTTP server HTTP application Telnet HTTP application Telnet TCP port 1024 TCP port 1231 TCP port 80 TCP port 23 House number: 1.1.1.1 (IP address) House number: 2.2.2.2 (IP address) Network HTTP client HTTP server Source IP address: 1.1.1.1 Source port number: 1024 HTTP Destination IP address: Destination port number: 80 Payload 2.2.2.2 IP header TCP header Generally, the source port used by a client is randomly allocated, and the destination port is specified by the application of a server. The system generally selects a source port number that is greater than 1023 and is not being used. The destination port number is the listening port of the application (service) enabled on the server. For example, the default port number for HTTP is 80. Page 17 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Application Transport Network Data Link Physical Layer Layer Layer Layer Layer TCP Connection Setup - Three-Way Handshake Before sending data, a TCP-based application needs to establish a connection through three- way handshake. PC1 PC2 1.1.1.1:1024 2.2.2.2:23 IP header TCP header Source = 1.1.1.1 Seq=a Ack=0 Destination=2.2.2.2 (Flags: SYN is set.) Seq=b Ack=a+1 Source = 2.2.2.2 (Flags: SYN is set, and ACK Destination=1.1.1.1 is set.) Source = 1.1.1.1 Seq=a+1 Ack=b+1 Destination=2.2.2.2 (Flags: ACK is set.) A TCP connection is established. Page 18 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Application Transport Network Data Link Physical TCP Sequence Number and Layer Layer Layer Layer Layer Acknowledgment Number ⚫ TCP uses the Sequence Number and Acknowledgment Number fields to implement reliable and ordered data transmission. PC1 PC2 1.1.1.1:1024 2.2.2.2:23 1 A TCP connection is 2 3 established. 4 5 6 … IP header TCP header … Source = 1.1.1.1 Payload Seq=a+1 Destination = 2.2.2.2 Ack=b+1 Length = 12 bytes Source = 2.2.2.2 Seq=b+1 Payload Destination = 1.1.1.1 Ack=a+1+12 Length =0 bytes Data to be sent Source = 1.1.1.1 Seq=a+13 Payload Destination = 2.2.2.2 Ack=b+1 Length = 66 bytes Question: Why does the value of the Source = 2.2.2.2 Seq=b+1 Payload Acknowledgment Number Destination = 1.1.1.1 Ack=a+13+66 Length = 0 bytes field in the segment sent by PC1 not increase? Page 19 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Application Transport Network Data Link Physical Layer Layer Layer Layer Layer TCP Window Sliding Mechanism ⚫ TCP uses the sliding window mechanism to control the data transmission rate. PC PC 1 2 Buffer of the receiver seq=100 win=3 flags=SYN 1 Three-way seq=200 Ack=101 win=3 flags=SYN,ACK handshake seq=101 Ack=201 win=3 flags=ACK Data to be sent 2 seq=101 win=3 Data seq=102 win=3 transmission 3 seq=103 win=3 Question: Why does Ack=104 win=1 ctl=ACK 4 the Window field of the segment sent by PC1 seq=104 win=3 remain unchanged? 5 Page 20 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Application Transport Network Data Link Physical Layer Layer Layer Layer Layer TCP Shutdown - Four-Way Handshake ⚫ After data transmission is complete, TCP needs to use the four-way handshake mechanism to disconnect the TCP connection and release system resources. PC1 PC2 1.1.1.1:1024 2.2.2.2:23 A TCP connection is established. TCP segment exchange IP header TCP header Sends a Seq=101 Ack=301 Source = 1.1.1.1 1 connection (Flags: FIN is set, and ACK Destination = 2.2.2.2 teardown is set.) request with FIN being set. Source = 2.2.2.2 Seq=301 Ack=102 Sends ACK. 2 Destination = 1.1.1.1 (Flags: ACK is set.) Seq=301 Ack=102 Sends a Source = 2.2.2.2 (Flags: FIN is set, and ACK connection 3 Destination = 1.1.1.1 is set.) teardown request with Source = 1.1.1.1 Seq=102 Ack=302 FIN being set. 4 Sends ACK. Destination = 2.2.2.2 (Flags: ACK is set.) The TCP connection is torn down. Page 21 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Application Transport Network Data Link Physical Layer Layer Layer Layer Layer Network Layer ⚫ The transport layer is responsible for establishing connections between processes on hosts, and the network layer is responsible for transmitting data from one host to another. ⚫ PDUs transmitted at the network layer are called packets. Application Layer Transport Layer The network layer is also called the Internet layer. Network It sends packets from source hosts to destination Layer hosts. (Packet) Functions of the network layer: Provides logical addresses for network devices. Data Link Layer Routes and forwards data packets. Common network layer protocols include IPv4, IPv6, ICMP, and IGMP. Physical Layer Page 22 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Application Transport Network Data Link Physical Layer Layer Layer Layer Layer Working Process of a Network Layer Protocol Packet Encapsulation Packet Forwarding Based on Network Layer Addresses Letter: data sent by an upper layer (for Router 1 example, the transport layer) GE0/0/0 PC1 GE0/0/1 PC2 The PC encapsulates the IP header (envelope). The key information is about source and destination IP addresses. Network A Routing table of Router 1 The network layer header of a packet sent by a source device carries the network layer addresses of the source Outbound and destination devices. Network Interface Each network device (such as a router) that has the routing function maintains a routing table (like a map of Network A GE0/0/1 the network device). Envelope: IP packet header After receiving a packet, the network device reads the Sender: source IP address … … network layer destination address of the packet, Receiver: destination IP address searches the routing table for the matching entry of the destination address, and forwards the packet according … … to the instruction of the matching entry. Page 23 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Application Transport Network Data Link Physical Layer Layer Layer Layer Layer Data Link Layer ⚫ The data link layer is located between the network layer and the physical layer and provides services for protocols such as IP and IPv6 at the network layer. PDUs transmitted at the data link layer are called frames. ⚫ Ethernet is the most common data link layer protocol. Application Layer Transport Layer The data link layer is located between the network layer and Network Layer the physical layer. The data link layer provides intra-segment Data Link communication for the network layer. Layer The functions of the data link layer include framing, (Frame) physical addressing, and error control. Physical Layer Common data link layer protocols include Ethernet, PPPoE, and PPP. Page 24 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Application Transport Network Data Link Physical Layer Layer Layer Layer Layer Ethernet and Source MAC Addresses Ethernet Definition Ethernet Source MAC Addresses Switch A I have a MAC address when I Name: Host A leave the factory. Switch B MAC address/Ethernet address/physical address: Host A Host B Host A Network A Host C Host D A media access control (MAC) address uniquely identifies a Ethernet is a broadcast multiple access protocol that NIC on a network. Each NIC requires and has a unique works at the data link layer protocol. MAC address. The network interfaces of PCs comply with the Ethernet MAC addresses are used to locate specific physical devices standard. in an IP network segment. Generally, a broadcast domain corresponds to an IP A device that works at the data link layer, such as an network segment. Ethernet switch, maintains a MAC address table to guide data frame forwarding. Page 25 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Application Transport Network Data Link Physical Layer Layer Layer Layer Layer ARP ⚫ Address Resolution Protocol (ARP):  Discovers the MAC address associated with a given IP address. ARP request Destination IP address: 192.168.1.2 Destination MAC address: ? Host A Host B 192.168.1.1/24 192.168.1.2/24 3C-52-82-49-7E-9D ARP reply 48-A4-72-1C-8F-4F Source IP address: 192.168.1.2 Source MAC address: 48-A4-72-1C-8F-4F Page 26 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Application Transport Network Data Link Physical Layer Layer Layer Layer Layer ARP Implementation Principles (1) Host 1 checks Host 1 Host 2 cached ARP entries. GE 0/0/1 GE 0/0/2 Host 1 sends an ARP request. IP 1: 192.168.1.1/24 IP 2:192.168.1.2/24 Host 2 adds an ARP MAC 1: 3C-52-82-49-7E-9D MAC 2: 48-A4-72-1C-8F-4F entry. 1 Host 2 sends an ARP Step 1: reply. Host 1>arp -a Before sending a datagram, a device searches Internet Address Physical Address Type its ARP table for the destination MAC address of Host 1 adds an ARP the datagram. entry. If the destination MAC address exists in the ARP table, the device encapsulates the MAC The ARP cache address in the frame and sends out the frame. If table is empty. the destination MAC address does not exist in the ARP table, the device sends an ARP request to discover the MAC address. Page 27 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Application Transport Network Data Link Physical Layer Layer Layer Layer Layer ARP Implementation Principles (2) Host 1 checks cached Host 1 Host 2 ARP entries. 3 GE 0/0/1 GE 0/0/2 Host 1 sends an ARP request. IP 1: 192.168.1.1/24 IP 2: 192.168.1.2/24 Host 2 adds an ARP MAC 1: 3C-52-82-49-7E-9D MAC 2:48-A4-72-1C-8F-4F entry. Step 2: Host 2 sends an ARP Host 1 sends an ARP request to discover 2 reply. Eth_II ARP Request FCS the MAC address of Host 2. The destination MAC address in the ARP Host 1 adds an ARP request is 0 because the destination MAC entry. address is unknown. Destination MAC address: Operation type: ARP request FF-FF-FF-FF-FF-FF MAC address of the sender: MAC 1 Source MAC address: IP address of the sender: IP 1 Step 3: MAC 1 Destination MAC address: 00-00-00-00-00-00 The ARP request message is a broadcast Destination IP address: IP 2 data frame. After receiving the ARP request message, the switch floods it. Page 28 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Application Transport Network Data Link Physical Layer Layer Layer Layer Layer ARP Implementation Principles (3) Host 1 checks Host 1 Host 2 cached ARP entries. GE 0/0/1 GE 0/0/2 Host 1 sends an ARP request. IP 1: 192.168.1.1/24 IP 2: 192.168.1.2/24 Host 2 adds an ARP MAC 1: 3C-52-82-49-7E-9D MAC 2: 48-A4-72-1C-8F-4F entry. 4 Step 4: Host 2 sends an ARP reply. After receiving the ARP request message, each host Host 2>arp -a checks whether it is the destination of the message based Internet Address Physical Address Type on the carried destination IP address. 192.168.1.1 3C-52-82-49-7E-9D Dynamic Host 1 adds an ARP Host 2 finds that it is the destination of the message and entry. then records the mapping between the sender's MAC and IP addresses in its ARP table. Page 29 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Application Transport Network Data Link Physical Layer Layer Layer Layer Layer ARP Implementation Principles (4) Host 1 checks Host 1 Host 2 cached ARP entries. 6 GE 0/0/1 GE 0/0/2 Host 1 sends an ARP request. IP 1: 192.168.1.1/24 IP 2: 192.168.1.2/24 Host 2 adds an ARP MAC 1: 3C-52-82-49-7E-9D MAC 2: 48-A4-72-1C-8F-4F entry. Step 5: 5 Host 2 sends an ARP Host 2 sends an ARP reply to Host 1. reply. In this step, Host 2 has discovered the MAC address of Host Eth_II ARP Reply FCS 1, so the ARP reply is a unicast data frame. Host 1 adds an ARP entry. Destination MAC address: MAC-1 Operation type: ARP reply Step 6: Source MAC address: Sender's MAC address: MAC 2 MAC 2 Sender's IP address: IP 2 After receiving the unicast data frame, the switch forwards the Receiver's MAC address: MAC 1 frame. Receiver's IP address: IP 1 Page 30 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Application Transport Network Data Link Physical Layer Layer Layer Layer Layer ARP Implementation Principles (5) Host 1 checks Host 1 Host 2 cached ARP entries. GE 0/0/1 GE 0/0/2 Host 1 sends an ARP request. IP 1: 192.168.1.1/24 IP 2: 192.168.1.2/24 Host 2 adds an ARP MAC 1: 3C-52-82-49-7E-9D MAC 2: 48-A4-72-1C-8F-4F entry. 7 Step 7: Host 2 sends an ARP reply. Host 1>arp -a After receiving the ARP reply message, Host 1 checks Internet Address Physical Address Type whether it is the destination of the message based on 192.168.1.2 48-A4-72-1C-8F-4F Dynamic the carried destination IP address. Host 1 adds an ARP If so, Host 1 records the carried sender's MAC and IP entry. addresses in its ARP table. Page 31 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Application Transport Network Data Link Physical Layer Layer Layer Layer Layer Physical Layer ⚫ After data arrives at the physical layer, the physical layer converts a digital signal into an optical signal, an electrical signal, or an electromagnetic wave signal based on the physical media. ⚫ PDUs transmitted at the physical layer are called bitstreams. Application Layer Transport Layer Network Layer The physical layer is at the bottom of the model. Data Link Layer This layer transmits bitstreams on media. It standardizes physical features such as cables, pins, Physical voltages, and interfaces. Layer Common transmission media include twisted pairs, optical (Bitstream) fibers, and electromagnetic waves. Page 32 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Application Transport Network Data Link Physical Layer Layer Layer Layer Layer Common Transmission Media Fiber Optical module Twisted pair RJ45 connector Data transmission through twisted pairs Data transmission through optical fibers 1 2 3 4 Synchronous/asynchronous serial cable: V.24 on the left and V.35 on the right PAD Mobile phone Laptop Wireless router Data transmission between terminal and Data transmission through serial cables wireless routers through wireless signals Page 33 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Contents 1. Applications and Data 2. Network Reference Model and Standard Protocols 3. Data Communication Process Page 34 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Data Encapsulation on the Sender DATA Application Layer Data www.huawei.com TCP Header DATA Transport Layer Segment Network Layer Packet IP Header Payload Data Link Layer Frame Eth Header Payload FCS... Physical Layer Bit Transmission 0 1 1 0 0 1 0 1 0 1... Media Transmission Media Page 35 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Data Transmission on the Intermediate Network ⚫ Encapsulated data is transmitted on the network. Data Data Application Application Layer Layer Transport Layer Transport Layer Network Layer Network Layer Network Layer Data Link Layer Data Link Layer Data Link Layer Data Link Layer Physical Layer Physical Layer Physical Layer Physical Layer Page 36 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Data Decapsulation on the Receiver Application Layer DATA Data Web server Transport Layer DATA Segment Network Layer Payload Packet Data Link Layer Payload Frame Physical Layer …… Bit Transmission 0 1 1 0 0 1 0 1 0 1... Media Page 37 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Summary ⚫ Both the OSI reference model and the TCP/IP reference model adopt the layered design concept.  Clear division of functions and boundaries between layers facilitates the development, design, and troubleshooting of each component.  The functions of each layer can be defined to impel industry standardization.  Interfaces can be provided to enable communication between hardware and software on various networks, improving compatibility. ⚫ Data generation and transmission require collaboration between modules. Meanwhile, each module must fulfill its own responsibilities. Page 38 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Quiz 1. What are the benefits of the layered model? 2. What are the common protocols at the application layer, transport layer, network layer, and data link layer? Page 39 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.  Thank You www.huawei.com Page 40 Copyright © 2020 Huawei Technologies Co., Ltd. All rights reserved.