date: 2024-05-28
title: DCN Review
status: DONE
author:
  - AllenYGY
tags:
  - NOTE
  - DCN
created: 2024-05-28T21:39
updated: 2024-06-11T01:16
publish: True

DCN Review

01-Basic Concepts

Five components of data communication

Protocol
Sender
Message
Medium
Receiver

Data flow

Simplex
Half-duplex
Full-duplex

Capacity of Communication Channel

Nyquist's Theorem

Assumption: noise free in the channel
Formula:
- B = Bit Rate (bit/sec)
- F = Channel Bandwidth in Hertz
- M = Number of levels in a signal (two for binary)

Shannon's Theorem

In reality, the signal may be corrupted by electrical noise.
Formula:
- B = Actual Bit Rate (bit/sec)
- F = Channel Bandwidth in Hertz
- S = Signal Power in watts
- N = Noise Power in watts

Signal-to-Noise Ratio

The signal-to-noise ratio is often given in decibels.
Assume that = 36 and the channel bandwidth is 2 MHz.

Open System Interconnection (OSI) Model

Physical Layer:
- It is concerned with transmitting raw bits over a communication channel.
- This layer deals with the issues including mechanical, electrical, timing interfaces, and the physical transmission medium.
Data Link Layer:
- It is to transform a raw transmission facility into a line that appears free of undetected transmission errors to the network layer.
Network Layer:
- It controls the operation of the subnet.
- It routes packets from source to destination.
  - The routing algorithm can be static or dynamic.
Transport Layer:
- It is to accept data from upper layers.
- Split it up into smaller units if need be, pass these to the network layer,
- Ensure that the pieces all arrive correctly at the other hand.
Session Layer:
- It allows users on different machines to establish sessions between them.
Presentation Layer:
- It is concerned with the syntax and semantics of the information transmitted.
Application Layer:
- It contains a variety of protocols that are commonly needed by users.
  - Such as HTTP, Email, etc.

02-Physical Layer

Physical Layer:

It is concerned with transmitting raw bits over a communication channel.
This layer deals with the issues including mechanical, electrical, timing interfaces, and the physical transmission medium.

Guide Transmission Media

Guided media, which are those that provide a conduit from one device to another.

Guide wired
- Twisted-pair cable
- Coaxial cable
- Fiber-optic

Optical Fiber Propagation modes

Mode
- Multimode
  - Step index
  - Graded index
- Single mode

Unguided Transmission Media

Unguided media transport electromagnetic waves without using a physical conductor.

Unguided wireless
- Free space

Two common signal encoding methods:

Frequency hopping spread spectrum (e.g., Bluetooth)
Direct sequence spread spectrum (e.g.,CDMA mobile network)

The Electromagnetic Spectrum

Propagation Methods
- Ground Propagation
- Sky Propagation
- Line-of-sight Propagation

03-Data Link Layer

Data Link Layer:

It is to transform a raw transmission facility into a line that appears free of undetected transmission errors to the network layer.

Framing techniques

Character Count
Flag bytes with byte stuffing
Starting and ending flags with bit stuffing

Error Control

Error Detection

Parity Check
Two-dimensional Parity Check
Cyclic Redundancy Check (CRC)

Cyclic Redundancy Check

Error Correction `forward error correction (FEC)`

Hamming Distance
Hamming Code

Compare the features between Error Control and Error Correction methods

Error detection:
- To send additional information, so incorrect data can be detected and rejected.
Error correction:
- To send additional information, so incorrect data can be corrected and accepted.
  - Error correction is the additional ability to reconstruct the original data.

Flow Control

Stop-and-Wait Protocols
Sliding Window Protocols

Multiple-access Protocols

Channelization:
- Frequency-Division Multiple Access (FDMA)
- Time-Division Multiple Access (TDMA)
- Code-Division Multiple Access (CDMA)
Random Access Protocols:
- Aloha
- Carrier Sense Multiple Access
- CSMA with Collision Detection
- CSMA with Collision Avoidance
Controlled-Access Protocols: Collision-Free Protocol
- Reservation
- Polling
- Token passing

04-Network Layer

Network Layer:

It controls the operation of the subnet.
It routes packets from source to destination.
- The routing algorithm can be static or dynamic.

Internet Protocol

IP is a protocol which governs the data format of packets sent over the Internet.
The main functions provided by IP are addressing and network routing.

Differences between IPv4 and IPv6

	IPv4	IPv6
IP address	32 bit	128 bit
Address Notation	Numeric dot-decimal notation	Hexadecimal notation
Header size	20 bytes + optional	40 bytes
Checksum	Yes	No

Major fields in IPv4 header

Version
Type of service
Total length
Time to live
Source address, destination address

Major fields in IPv6 header

Version
Traffic class
Flow label
Payload length
Next header
Hop limit

Use NAT to increase IPV4 address

Transition from IPv4 to IPv6

Dual stack
Tunneling
Header translation

Network Routing

Network routing selects a path over an internetwork to transmit one or more packets from the source to the destination.

Flooding Algorithm

Dijkstra Algorithm

Distance Vector Routing Algorithm

05-Transport Layer

TCP

Transport Control Protocol (TCP)

Source port and destination port: to identify the local end points of the connections.
Sequence number and acknowledgement number
TCP header length: to tell how many 32-bit words are contained in the header
Six 1-bit flags
Window size: to tell how many bytes may be sent starting at the byte acknowledged.
Checksum
Options: to provide a way to extend the header

UDP

User Datagram Protocol (UDP)

Connectionless protocol
Provide a way for applications to send encapsulated IP datagrams and send them without having to establish a connection.
8-byte header
UDP Datagram Header

Application Lyer

API

API stands for application programming interface.
Socket API is specifically designed for the network programming interface.

Socket

Socket is an abstraction through which an application may send and receive data.

A socket is uniquely identified together by
1. Internet address
2. End-to-end protocol (e.g. TCP or UDP)
3. Port number

Stream sockets and Datagram sockets

Stream socket is designed for TCP, which provides reliable byte stream service.
Datagram socket is specifically designed for UDP, which provides best-effort datagram service.

Function Call

Basic function calls on the client side

WSAStartup
socket
connect
(send, recv) (recusive)
closesocket
WSACleanup

Basic function calls on the server side

WSAStartup
socket
bind
listen
accept
(recv, send) (recursive)
closesocket (pair up with accept)
WASCleanup.

Basic Code segment

Create socket

int socket_desc=socket(AF_INET,SOCK_STREAM,0); 
if (socket_desc==-1) perror("Create socket");

Binding a socket to a port

struct sockaddr_in address;
/* type of socket created in socket() */ 
address.sin_family = AF_INET; 
address.sin_addr.s_addr = INADDR_ANY; /* 7000 is the port to use for connections */ 
address.sin_port = htons(7000); /* bind the socket to the port specified above */ 
bind(socket_desc,(struct sockaddr *)&address,sizeof(address));

Listening for connections

listen(socket_desc,3);

Accepting a connection

int addrlen; 
struct sockaddr_in address;
addrlen = sizeof(struct sockaddr_in);
new_socket = accept(socket_desc, (struct sockaddr *)&address, &addrlen); if (new_socket<0) perror("Accept connection");

Sending data to a connection

char *message="This is a message to send\n\r"; 
send(socket_desc, message, strlen(message), 0);

Receiving data from a connection

int bufsize=1024; /* a 1K buffer */
char *buffer=malloc(bufsize);
recv(socket_desc,buffer,bufsize,0);

Close

closesocket(msg_sock); 
// close(socket_desc);
WSACleanup();

Multithreads

#include <process.h>
for(int i = 0; i < 100; i++){ 
	_beginthread(accept_conn, 0, NULL ); 
}//for loop 
_endthread();
// create a function to accept a connection 
void accept_conn(void *dummy) { 
// doing something here 
}

07-Standardized Networks

Ethernet

Standard Ethernet 10 Mbps
Fast Ethernet 100 Mbps
Gigabit Ethernet 1 Gbps
Ten Gigabit Ethernet 10 Gbps

Determination of the Minimum Frame Standardized

Data transmission time

= Cable length （线缆长度）
= Propagation speed （传播速度）
= Bit rate （比特率，单位为比特/秒）
= Minimum data size （最小数据大小）

Hub, Bridge, Router, and Switch

Hub `集线器`

Hub is a repeater with some additional network management functionality (such as performance or accounting management)

Work on 02-Physical Layer

定义：Hub是一种网络设备，用于将多个以太网设备连接在一起，使它们能够作为一个网络段进行通信。
工作层次：物理层（OSI模型第1层）。
工作原理：Hub通过广播的方式将收到的数据包发送到所有连接的端口，无论数据包的目的地是哪个设备。
优点：价格低廉，易于安装和使用。
缺点：效率低，所有端口共享带宽，容易发生碰撞（Collision），不适合大规模网络。

Bridge `桥接器`

Bridge: bridge operates on Ethernet frames and thus a layer-2 device. It does the following two functions:

Filtering: determine whether a frame should be forwarded to some interface or should just be dropped.
Forwarding: determine the interfaces to which a frame should be directed.

Work on 03-Data Link Layer

定义：Bridge是一种网络设备，用于连接两个或多个网络段，主要用于分割网络冲突域。
工作层次：数据链路层（OSI模型第2层）。
工作原理：Bridge根据MAC地址表转发数据帧，只将数据帧发送到目的地所在的网络段，减少不必要的流量。
优点：减少网络冲突，提升网络效率。
缺点：管理复杂度高，不支持多播和广播控制。

Router `路由器`

Router: router is a store-and-forward packet switch that forward packets using network-layer addresses (layer-3).
Although a bridge is also a store- and-forward packet switch, it forwards packets using LAN addresses.
As a network administrator, how to choose between bridge and router?

Work on 04-Network Layer

定义：Router是一种网络设备，用于连接不同的网络，能够根据IP地址进行数据包转发。
工作层次：网络层（OSI模型第3层）。
工作原理：Router根据路由表和IP地址选择最佳路径，将数据包转发到目的地网络。
优点：能够连接不同类型的网络，支持复杂的路由选择协议，提供广域网（WAN）连接。
缺点：成本较高，配置和管理相对复杂。

Switch `交换机`

Switch: switch is in essence a high-performance multi-interface bridge. The difference between a bridge and switch:
Bridges usually two or four interfaces, whereas switches have dozens of interfaces (e.g., 24 ports).
Switches are usually used to connect individual computers, and operate in a full-duplex mode.