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add more notes in computer architecture
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kekeandzeyu committed Dec 10, 2024
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</chapter>
</chapter>
</chapter>
<!-- TODO: Chapter 12 is unfinished yet!-->
<chapter title="12 System I/O" id="12-system-io">
<chapter title="12.1 Unix I/O" id="12-1-unix-io">
<p><format color="BlueViolet">Overview</format></p>
Expand Down Expand Up @@ -2574,4 +2575,209 @@
</list>
</chapter>
</chapter>
<chapter title="13 Network Programming" id="13-network-programming">
<chapter title="13.1 Network Types &amp; Structures" id="13-1-network-types-structures">
<p>Every network application is based on the client-server model.</p>
<img src="../images_architecture/ax13-1-1.png" alt="client-server model"/>
<p><format color="DarkOrange">Network:</format> A hierarchical system of boxes and wires organized by
geographical proximity.</p>
<list type="bullet">
<li>
<p><format color="Fuchsia">LAN (Local Area Network)</format> spans a building or campus, e.g.,
Ethernet.</p>
</li>
<li>
<p><format color="Fuchsia">WAN (Wide Area Network)</format> spans country or world, typically
high-speed point-to-point (mostly optical) links.</p>
</li>
<li>
<p>Also SAN (Storage area network), MAN (Metropolitan), etc.</p>
</li>
<li>
<p>An internetwork (internet) is an interconnected set of networks, and the Global IP Internet
(uppercase "I") is the most famous example of an internet (lowercase "i")</p>
</li>
</list>
<p><format color="BlueViolet">Bridged Ethernet Segment</format></p>
<list type="bullet">
<li>
<p>Ethernet segment consists of a collection of hosts connected by wires (twisted pairs) to a hub.
</p>
</li>
<li>
<p>Bridges learn which MAC addresses are on which segment by observing the source MAC addresses of
frames that they receive. They then use this information to forward frames only to the necessary
segment, rather than broadcasting to all segments.</p>
</li>
</list>
<img src="../images_architecture/ax13-1-2.png" alt="Bridged Ethernet Segment"/>
<p><format color="BlueViolet">internet</format></p>
<note>
<p>Internet (upper case) stands for Global IP Internet, the largest and most prominent implementation
of internet (lower case).</p>
</note>
<p>Multiple incompatible LANs can be physically connected by specialized computers called
<format color="DarkOrange">routers</format>. The connected networks are called an internet (lower case).
</p>
<img src="../images_architecture/ax13-1-3.png" alt="internet"/>
<p><format color="BlueViolet">internet Protocol</format></p>
<p>Protocol is a set of rules that governs how hosts and routers should cooperate when they transfer data
from network to network, which smooths out the differences between the different networks.</p>
<list type="bullet">
<li>
<p><format color="Fuchsia">Provides a naming scheme:</format> An internet protocol defines a uniform
format for host addresses, and each host (and router) is assigned at least one of these internet
addresses that uniquely identifies it.</p>
</li>
<li>
<p><format color="Fuchsia">Provides a delivery mechanism:</format> An internet protocol defines a
standard transfer unit (packet), which consists of header (info such as packet size, source and
destination addresses) and payload (data bits sent from source host).</p>
</li>
</list>
</chapter>
<chapter title="13.2 Global IP Internet" id="13-2-global-ip-internet">
<p><format color="BlueViolet">Global IP Internet:</format> Based on the TCP/IP protocol family.</p>
<list type="bullet">
<li>
<p><format color="Fuchsia">IP (Internet Protocol):</format> Provides basic naming scheme and
unreliable delivery capability of packets (datagrams) from host-to-host.</p>
</li>
<li>
<p><format color="Fuchsia">UDP (User Datagram Protocol):</format> Uses IP to provide unreliable
datagram delivery from process-to-process.</p>
</li>
<li>
<p><format color="Fuchsia">TCP (Transmission Control Protocol):</format> Uses IP to provide reliable
byte streams from process-to-process over connections.</p>
</li>
</list>
<chapter title="13.2.1 Locating Host" id="13-2-1locating-host">
<p><format color="BlueViolet">IP Addresses</format></p>
<list type="bullet">
<li>
<p>Hosts are mapped to a set of 32-bit IP addresses, and they are stored in an IP address struct.
They are always stored in memory in network byte order (big-endian byte order).</p>
</li>
<li>
<p>127.0.0.1 is always localhost.</p>
</li>
<li>
<p>IPv4 (Internet Protocol version 4) specifies 32-bit host addresses (192.0.2.43), while IPv6
(Internet Protocol version 6) specifies 128-bit addresses (2001:0db8:0:0:0:0:cafe:la7e).</p>
</li>
<li>
<p>By convention, each byte in a 32-bit IP address is represented by its decimal value and
separated by a period, e.g., 0x <format color="OrangeRed">80</format>
<format color="MediumSeaGreen">02</format> <format color="BlueViolet">C2</format>
<format color="LawnGreen">F2</format> = <format color="OrangeRed">128</format>.
<format color="MediumSeaGreen">2</format>.<format color="BlueViolet">194</format>.
<format color="LawnGreen">242</format> .</p>
</li>
</list>
<p><format color="BlueViolet">Internet Domain Names</format></p>
<img src="../images_architecture/ax13-2-1.png" alt="Internet Domain Names"/>
<p>ICANN (Internet Corporation for Assigned Names and Numbers) oversees the system of top-level domain
names (TLDs), such as .com, .org, .net, .gov, and country code TLDs like .uk or .jp.</p>
<p><format color="BlueViolet">Domain Naming System (DNS)</format></p>
<p>The Internet maintains a mapping between IP addresses and domain names in a worldwide distributed
database called DNS.</p>
<p>Properties of DNS mapping: Domain names and IP addresses can be one to one, multiple to one,
one to multiple, or some valid domain names don't map to any IP address.</p>
</chapter>
<chapter title="13.2.2 Connecting to a Server" id="13-2-2-connecting-to-server">
<p>Clients and servers most often communicate by sending streams of bytes over TCP connections. Each
connection is point-to-point, full-duplex (in both directions) &amp; reliable.</p>
<p><format color="DarkOrange">Sockets:</format> For kernel, endpoints of connections, their addresses
are IPaddress:pair (127.0.0.1:80). For applications, a socket is a file descriptor that lets the
application read/write from/to the network.</p>
<p><format color="DarkOrange">Port:</format> A 16-bit integer that identifies a process.</p>
<list type="bullet">
<li>
<p><format color="Fuchsia">Ephemeral Port:</format> Assigned automatically by client kernel when
client makes a connection request.</p>
</li>
<li>
<p><format color="Fuchsia">Well-known Port:</format> Associated with some service provided by a
server (e.g., port 80 is associated with Web servers, port 443 with SSL/TLS encrypted Web
(https)).</p>
</li>
</list>
<img src="../images_architecture/ax13-2-2.png" alt="Connecting to a Server"/>
</chapter>
<chapter title="13.2.3 Sockets Interface" id="13-2-3-sockets-interface">
<p><format color="DarkOrange">Sockets Interface:</format> Set of system-level functions used in
conjunction with Unix I/O to build network applications.</p>
<img src="../images_architecture/ax13-2-3.png" alt="Sockets Interface"/>
<list type="decimal">
<li>
<p><code>socket()</code>: Clients and servers use the socket function to create a socket
descriptor:</p>
<code-block lang="C">
int socket(int domain, int type, int protocol)
</code-block>
<p><format color="IndianRed">Example</format></p>
<code-block lang="C">
int clientfd = socket(AF_INET, SOCK_STREAM, 0);
// AF_INET: 32-bit IPv4, SOCK_STREAM: TCP, 0: default protocol
</code-block>
</li>
<li>
<p><code>bind()</code>: A server uses <code>bind</code> to ask the kernel to associate the
server's socket address with a socket descriptor. Process can read bytes that arrive on the
connection whose endpoint is <code>addr</code> by reading from descriptor
<code>sockfd</code>; similarly, writes to <code>sockfd</code> are transferred along
connection whose endpoint is <code>addr</code>.</p>
<code-block lang="C">
int bind(int sockfd, struct sockaddr *my_addr, socklen_t addrlen)
</code-block>
<p>Best practice is to use <code>getaddrinfo</code> to supply the arguments <code>addr</code>
and <code>addrlen</code>.</p>
</li>
<li>
<p><code>listen()</code>: A server calls the listen function to tell the kernel that a
descriptor will be used by a server rather than a client, and converts sockfd from an active
socket to a listening socket that can accept connection requests from clients.</p>
<code-block lang="C">
int listen(int sockfd, int backlog)
</code-block>
<p>`backlog` is a hint about the number of outstanding connection requests that the kernel
should queue up before starting to refuse requests (128-ish by default).</p>
</li>
<li>
<p><code>accept()</code>: Waits for connection request to arrive on the connection bound to
<code>listenfd</code>, then fills in client’s socket address in <code>addr</code> and size
of the socket address in <code>addrlen</code>.</p>
<code-block lang="C">
int accept(int listenfd, SA *addr, int *addrlen);
</code-block>
</li>
<li>
<p><code>connect()</code>: A client establishes a connection with a server by calling
connect. Client attempts to establish a connection with server at socket address
<code>addr</code>, if successful, then <code>clientfd</code> is now ready for reading and
writing.</p>
<code-block lang="C">
int connect(int clientfd, SA *addr, socklen_t addrlen);
</code-block>
</li>
</list>
<procedure title="connect/accept Illustrated">
<step>
<p>Server blocks in <code>accept</code>, waiting for connection request on listening descriptor
<code>listenfd</code>.</p>
</step>
<step>
<p>Client makes connection request by calling and blocking in <code>connect</code>.</p>
</step>
<step>
<p>Server returns <code>connfd</code> from <code>accept</code>. Client returns from
<code>connect</code>. Connection is now established between <code>clientfd</code> and
<code>connfd</code>.</p>
</step>
</procedure>
<img src="../images_architecture/ax13-2-4.png" alt="connect/accept Illustrated"/>
</chapter>
</chapter>
</chapter>
</topic>

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