DCN Review

[[01-Basic Concepts|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: $B=2F(log2M)$
  • 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: $B=F[log2(1+\frac{S}{N})]$
  • 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.

  • $SN{R}_{dB}=10lo{g}_{10}SNR$
  • $SNR={10}^{\frac{SN{R}_{dB}}{10}}$

• Assume that $SN{R}_{dB}$ = 36 and the channel bandwidth is 2 MHz.

  • $B=F[lo{g}_2(1+SNR)]$
  • $2\times lo{g}_2(1+{10}^{3.6})$

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|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|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

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

[[04-Network Layer|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|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

[[06-Application Layer|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|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 $\ge 2\tau$

$$\tau =\frac{L}{S}$$$$\frac{\chi }{R}\ge 2\tau$$$$\frac{\chi }{R}\ge \frac{2L}{S}$$

$S=3.0\times {10}^8\text{ m/s}$

• $L$ = Cable length （线缆长度）
• $S$ = Propagation speed （传播速度）
• $R$ = Bit rate （比特率，单位为比特/秒）
• $\chi$ = 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|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|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|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.