Class Notes #20
Networks, Internet, Web, Networked Media Systems
Part II: Web as Media Delivery Vehicle
Application layer
HTTP, SMTP, FTP, SSH, IRC, SNMP, SIP ...Transport layer
TCP, UDP, ICMP, SCTP, RTP, DCCP ...Network layer
IPv4, IPv6, ARP ...IP - Internet Protocol
is a data-oriented protocol used by source and destination hosts for communicating data across a packet-switched internetwork.
Data in an IP internetwork are sent in blocks referred to as packets or datagrams (the terms are basically synonymous in IP). In particular, in IP no setup is needed before a host tries to send packets to a host it has previously not communicated with.
The Internet Protocol provides an unreliable datagram service (also called best effort); i.e. it makes almost no guarantees about the packet. The packet may arrive damaged, it may be out of order (compared to other packets sent between the same hosts), it may be duplicated, or it may be dropped entirely. If an application needs reliability, it is provided by other means
Data link layer
Ethernet, Wi-Fi, Token ring, FDDI, ...1. MIME - Multipurpose Internet Mail Extension
Though originally a mail specification, MIME was adopted for http transfers.
file extensions such as .mp3, .jpg, .doc, .pdf - are meaningful in that the mail application (layer 7) can, assuming the presence of an appropriate plug-in or application handler, can open the file accordingly. This is equally true now for http (web) transfers with MIME types providing a vast array of file handling capabilities.2. SMTP - Simple Mail Transfer Protocol
"SMTP is a relatively simple, text-based protocol, where one or more recipients of a message are specified (and in most cases verified to exist) and then the message text is transferred. " (wikipedia)
3. FTP - file transfer protocol
FTP is a software standard for transferring computer files between machines with widely different operating systems. It belongs to the application layer of the Internet protocol suite.
FTP is an 8-bit client-server protocol, capable of handling any type of file without further processing, such as MIME or Uuencode. However, FTP has extremely high latency; that is, the time between beginning the request and starting to receive the required data can be quite long, and a sometimes-lengthy login procedure is required.
4. SSH - secure shell
SSH is both a computer program and an associated network protocol designed for logging into and executing commands on a networked computer. The designers of SSH aimed to replace the earlier rlogin, telnet and rsh protocols, and the resultant protocol provides secure encrypted communications between two untrusted hosts over an insecure network. Users of SSH can also use it for tunnelling, forwarding X11 connections and arbitrary TCP ports over the resultant secure channel; and can transfer files using the associated scp or sftp programs. An ssh server, by default, listens on the standard TCP port 22.
5. IRC - internet relay chat
is a form of instant communication over the Internet. It is mainly designed for group (many-to-many) communication in discussion forums called channels, but also allows one-to-one communication.
6. RTSP
RTSP is the Real Time Streaming Protocol developed by the IETF and published in 1998 as RFC 2326. RTSP is a protocol for use in streaming media systems which allows a client to remotely control a streaming media server, issuing VCR-like commands such as "play" and "pause", and allowing time-based access to files on a server.RTSP servers typically use RTP as the protocol for the actual audio/video data.
Transport layer
TCP, UDP, ICMP, SCTP, RTP, DCCP ...TCP - transmission control protocol
The Transmission Control Protocol (TCP) is one of the core protocols of the Internet protocol suite. Using TCP, programs on networked computers can create connections to one another, over which they can send data. The protocol guarantees that data sent by one endpoint will be received in the same order by the other, and without any pieces missing. It also distinguishes data for different applications (such as a Web server and an email server) on the same computer.
UDP - User Datagram Protocol
The User Datagram Protocol (UDP) is a minimal message-oriented transport layer protocol that is currently documented in IETF RFC 768.
In the TCP/IP model, UDP provides a very simple interface between a network layer below and an application layer above. UDP provides no guarantees for message delivery and a UDP sender retains no state on UDP messages once sent onto the network. (For this reason UDP is sometimes expanded to "Unreliable Datagram Protocol".) UDP adds only application multiplexing and data checksumming on top of an IP datagram.
The UDP header consists of only 4 header fields of which two are optional. The source and destination port fields are 16-bit fields that identify the sending and receiving process. Since UDP is stateless and a UDP sender may not solicit replies, the source port is optional. If not used, the source port should be set to zero. The port fields are followed by a mandatory length field specified as bytes of the UDP datagram including the data. The minimum value of the length field is 8 (octets). The remaining header field is a 16-bit checksum field covering the header and data. The checksum is also optional, but almost always used in practice.
Lacking reliability, UDP applications must generally be willing to accept some loss, errors or duplication. Some applications such as TFTP may add rudimentary reliability mechanisms into the application layer as needed. Most often, UDP applications do not require reliability mechanisms and may even be hindered by them. Streaming media, real-time multiplayer games and voice over IP (VoIP) are examples of applications that often use UDP. If an application requires a high degree of reliability, a protocol such as the Transmission Control Protocol may be used instead.
Lacking any congestion avoidance and control mechanisms, network-based mechanisms are required to minimize potential congestion collapse effects of uncontrolled, high rate UDP traffic loads. In other words, since UDP senders cannot detect congestion, network-based elements such as routers using packet queueing and dropping techniques will often be the only tool available to slow down excessive UDP traffic. The Datagram Congestion Control Protocol (DCCP) is being designed as a partial solution to this potential problem by adding end host congestion control behavior to high-rate UDP streams such as streaming media.
While the total amount of UDP traffic found on a typical network is often on the order of only a few percent, numerous key applications use UDP. These include the Domain Name System (DNS), the simple network management protocol (SNMP), the Dynamic host configuration protocol (DHCP) and the Routing Information Protocol (RIP) to name just a few.
RTP - real time transport protocol
- defines a standardized packet format for delivering audio and video over the Internet. It was developed by the Audio-Video Transport Working Group of the IETF and published in 1996 as RFC 1889.
Internet protocol suite editIt was originally designed as a multicast protocol, but has since been applied in many unicast applications. It is frequently used in streaming media systems (in conjunction with RTSP) as well as videoconferencing and push to talk systems (in conjunction with H.323 or SIP), making it the technical foundation of the Voice over IP industry. It goes along with the RTP Control Protocol (RTCP) and it's built on top of User Datagram Protocol (in OSI model).
XML - advanced html/sgml hybrid used throughout the b2b, p2p world. also used internally in many media software systems/programs
NOTE - there are many, many more protocols like the above at each of the layers. It is not necessary (though helpful) to know all of them for the purposes of this course.