Project3 Webshell - Network Background 1

1. Protocol
   A communication protocol si a formal description of digital message formats and the rules for exchanging those messages in or between computing systems and in telecommunications. Protocols may include signaling, authentication, and error detection and correction capabilities.
(cited from wikipedia.org)

 1.1 TCP (Transfer layer)
 The Transmission Control Protocol(TCP) provides reliable, ordered delivery of a stream of bytes from a program on one computer to another program on another computer. TCP is the protocol that major Internet applications such as the WWW(World Wide Web), email, romote administration and file transfer rely on.

 1.2 UDP (Transfer layer)
 The User Datagram Protocol (UDP) enables computer applications to send messages (in this case, datagrams) to other hosts on an Internet Protocol network without requiring prior communications to set up special channels or data paths. UDP uses a simple transmission model without implicit handshaking dialogues for providing reliability, ordering , or data integrity. Thus, UDP provides an unrealiable services and datagrmas may arrive out of order, appear duplicated, or go missing without notice.
 It preferes dropping packets to waiting for delayed packets. UDP's statelsss nature is useful for servers answering small queries from huge numbers of clients. Unlike TCP, UDP is compatible with packet broadcasting and multicasting. DNS(Domain Name System), streaming media (IPTV, Voice over IP, Trivial FTP) and many online games use UDP.

 1.3 IP
 The Internet Protocol (IP) is responsible for addressing hosts and routing datagrams(packets) from a source host to the destination host across one or more IP networks. For this purpose, the IP defines an addressing system that has two functions : identifying hosts and providing a logical location service. Each packet is tagged with a header that contains the meta-data for the purpose of delivery (also called encapsulation).
 IP lacks reliability. IPv4 ensure that the header is error-free by computing checksum. IPv6, on the other hand, has abandonded the use of checksum for the benefit of rapid forwarding through routing elements in the network.

 1.4 TCP/IP
 The TCP/IP model is one of the most famous framwork for network protocols that is used for internet. TCP/IP provides end-to-end connectivity specifying how data should be formatted, addressed, transmitted, routed and received at the destination. (This is also called Internet Protocoal Suite)