Chapter 3. Communication Protocols
Recommended reading: 【Information and Communication Network Technology】 Table of Contents for Information and Communication Network Technology
1. Overview of Communication Protocols
3. X.25 Model
4. TCP/IP Model
b. Structure of the TCP Header
c. Structure of the UDP Header
1. Overview of Communication Protocols
⑴ ITU-T Recommendation Series
① Series I: Protocols for the standardization of ISDN
② Series X: Protocols for data transmission through a public switched data network (PSDN)
③ Series V: Protocols for data transmission through a public switched telephone network (PSTN)
④ Series T: Protocols for telematic services
2. OSI Reference Model
⑴ Definition: A communication standard proposed by ISO for smooth communication between systems
① ISO (International Organization for Standardization): Established in 1947
⑵ Layer 1. Physical Layer
① Protocol Data Unit (PDU): Bit
② Contents: Electrical, functional, procedural, and physical characteristics between devices required for transmission
○ Electrical characteristics: Voltage level, etc.
○ Functional characteristics: Wiring map, pin functions, etc.
○ Procedural characteristics: Data transmission procedures, etc.
○ Physical characteristics: Physical connections between cables, etc.
③ UTP cable: Most commonly used when implementing local networks
○ Configuration methods: Direct cable (Straight-Through Cable), cross cable (Cross-Over Cable), console cable (Console Cable)
○ RJ-45 (Registered Jack 45): Standard connector for connecting UTP cables to computers, switches, routers, etc.
○ Advantages: Smaller than other copper media and very easy to manufacture and install
○ Disadvantages: Sensitive to electrical noise and interference
④ Examples: RS-232C, X.21
⑶ Layer 2. Data Link Layer
① Protocol Data Unit (PDU) : Frame
○ Frame = Header + Layer 1 contents + Trailer
○ Header: Includes the addresses of the sending and receiving devices
○ Trailer: Includes error detection codes
② Contents: Reliable and efficient information transmission between two open systems
○ Framing: Combines signals from the physical layer and processes them in frame units
○ Flow Control
○ Error Control: Error detection in asynchronous communication; error detection and correction in synchronous communication
○ Access Control: Determines whether data can be transmitted to the communication device
○ Synchronization: The frame header provides a special bit pattern for synchronization
③ MAC (Media Access Control) address: Physical address of a device, permanently written (burned-in) into the ROM inside the device when it is made
○ MAC table: A table of “MAC address + device port”
④ Examples: HDLC, ADCC, LLC, LAPB, LAPD
⑷ Layer 3. Network Layer
① Protocol Data Unit (PDU): Packet
○ Packet = IP protocol header + Layer 2 contents
○ IP Protocol Header : Includes the IP address
② Contents : Establishes, maintains, manages, and terminates network connections between open systems, and performs data exchange and relay functions
○ Packet Forwarding: Performs end-to-end packet delivery
○ Routing: Selects the most efficient packet transmission path
○ Logical Address: Attaches an IP protocol header to the data received from the transport layer
③ IP (Internet Protocol) address
④ Examples : X.25, IP, Frame Relay
⑸ Layer 4. Transport Layer
① Protocol Data Unit (PDU) : Segment
○ Segment = Segment header + Layer 3 contents
○ Segment Header: Includes port address, socket address, and sequence number
○ Sequence Number: A number assigned sequentially to each segment when user data is divided into segments
② Contents : Transparent data transmission between end systems (End-to-End), with characteristics intermediate between hardware and software
○ Guarantees end-to-end data communication
○ Solves distortion and bandwidth problems caused by delay
○ Supports multiple logical connections simultaneously
○ User data segmentation and reassembly : Reassembles received data by referring to the sequence number or discards it
③ Examples: TCP, UDP
⑹ Layer 5. Session Layer
① Protocol Data Unit (PDU) : Message
② Contents: Maintains relationships between users, organizes dialogue and synchronization control, and exchanges data
○ Inserts synchronization points during transmission to group messages
○ Determines the direction of data transmission (e.g.: full-duplex, half-duplex)
○ Creates synchronization points for intermediate checking and recovery of data
③ Example: NetBIOS
○ Each computer having both an IP address and a NetBIOS name corresponds to one host name
⑺ Layer 6. Presentation Layer
① Protocol Data Unit (PDU): Message
② Contents
○ Code conversion
○ Encryption
○ Compression
○ Syntax searching
○ Information format conversion
○ Context management
③ Supported technologies: ASCII, EBCDIC, Binary, ASN.1, etc.
⑻ Layer 7. Application Layer
① Protocol Data Unit (PDU): Message
② Contents: Provides services so that users (applications) can access the OSI environment
○ Electronic mailbox
○ File transfer
③ Examples: FTP, SMTP, SNMP, HTTP, HTTPS, TELNET, SSH, APPC (IBM protocol)
3. X.25 Model
⑴ An international standard protocol established by ITU-T (approved in 1976) with excellent compatibility
⑵ Layer structure
① Physical layer: Uses X.21
② Data link layer: Uses LAPB, a variation of the HDLC protocol
③ Network layer: Call Setup → Data Transfer → Call Clearing
4. TCP/IP Model
⑴ History
① Developed by ARPA in the late 1960s and began to be used in ARPANET (1972)
② Used as the basic protocol of UNIX, and currently used as the general-purpose protocol of the Internet
⑵ Layer 1. Network Access Layer: OSI Reference Model; Physical Layer + Data Link Layer
① Function: Sends and receives actual data (frames)
② Ethernet: LAN using the CSMA/CD method
③ IEEE 802: Standard protocol for LANs
④ HDLC: Bit-oriented data link control protocol
⑤ X.25: Protocol providing DTE/DCE interface through packet-switched networks
⑥ RS-232C: Protocol providing DTE/DCE interface through PSTN, a protocol for analog communication together with V.24 and V.28
○ Composed of a total of 25 pins
○ Pin number for data transmission: No. 2
○ Pin number for data reception: No. 3
⑶ Layer 2. Internet Layer: OSI Reference Model; Network Layer
① Function : Management of the IP address system, routing
② Internet Protocol(IP)): Addressing, route setting, use of the datagram method (reliability not guaranteed ×)
③ Internet Control Message Protocol (ICMP): Used with IP to handle errors and change transmission paths, defined in RFC 792
○ ping: Used to check whether communication between devices is possible
○ traceroute: Used to check the route
④ Address Resolution Protocol (ARP): Converts a host’s IP address into the MAC address associated with the host
⑤ Reverse Address Resolution Protocol (RARP): Converts a host’s MAC address into the host’s IP address
⑥ Internet Group Management Protocol (IGMP): Maintains multicast groups
⑦ DHCP: A protocol that defines the function of dynamically assigning IP addresses, similar to the BOOTP protocol function
⑷ Layer 3. Transport Layer: OSI Reference Model; Transport Layer
① Function : Provides communication between hosts
② TCP: Bidirectional connection-oriented service, virtual circuit connection, packet unit, establishes reliability , establishes transparency (such as recognizing packet loss)
○ Establishes communication between two hosts through a socket determined by an IP address and port number
③ UDP: Connectionless service, low overhead, used for high-speed communication or repeated communication, prioritizes speed over reliability
⑸ Layer 4. Application Layer: OSI Reference Model. Session Layer + Presentation Layer + Application Layer
① Function: Provides data transmission and reception between applications
② FTP: File Transfer Protocol
③ SMTP: Simple Mail Transfer Protocol
④ TELNET: Virtual terminal protocol
⑤ SNMP: Simple Network Management Protocol
⑥ HTTP
⑦ HTTPS
⑧ POP3
⑨ DNS
Entered: 2017.07.16
Revised: 2017.07.29