Transport Multiplexing Protocol (TMux)

One of the problems with the use of terminal servers is the large number of small packets they can generate. Frequently, most of these packets are destined for only one or two hosts. TMux is a protocol which allows multiple short transport segments, independent of application type, to be combined between a server and host pair.

- TMux protocol is intended to optimize the transmission of large numbers of small data packets that are generated in situations where many interactive Telnet and Rlogin sessions are connected to a few hosts on the network.

- TMux protocol may be applicable to other situations where small packets are generated, but this was not considered in the design.

- TMux is designed to improve network utilization and reduce the interrupt load on hosts which conduct multiple sessions involving many short packets.

- TMux is highly constrained in its method of accomplishing this task, seeking simplicity rather than sophistication.

Protocol Design

TMux operates by placing a set of transport segments into the same IP datagram. Each segment is preceded by a TMux mini-header which specifies the segment length and the actual segment transport protocol. The receiving host demultiplexes the individual transport segments and presents them to the transport layer as if they had been received in the usual IP/transport packaging.
Hence, a TMux message appears as:
| IP hdr | TM hdr | Tport segment | TM hdr | Tport segment| ...|

where:
TM hdr : It is a TMux mini-header and specifies the following Tport segment.
Tport segment : It refers to the entire transport segment, including
transport headers.

Header Format

Each 4 octet TMux mini-header has the following general format:
Length high |
+-------------------------------+
| Length low |
+-------------------------------+
| Protocol ID |
+-------------------------------+
| Checksum |
+-------------------------------+
| Transport segment |
| ... |
| ...
Length : It specifies the octet count for this mini header and the following transport segment, from 0-65535 octets.
Protocol ID : It contains the value that would normally have been placed in the IP header Protocol field.
Checksum : This field is the XOR of the first 3 octets.

WHOIS Protocol - Specifications and characteristics

- WHOIS is a TCP-based transaction-oriented query/response protocol that is widely used to provide information services to Internet users.
- Whois is a draft standard protocol. Its status is elective.
- The protocol delivers its content in a human-readable format.
- WHOIS lacks many of the protocol design attributes, for example internationalization and strong security, that would be expected from any recently-designed IETF protocol.
- The Whois program is commonly used in the UNIX environment to connect to a Whois server. The purpose of the server is to provide directory type services.
- The original Whois server was set up so that the Network Information Center could maintain a contact list for networks connected to the Internet. However, many sites now use Whois to provide local directory services.

The use of the data in the WHOIS system has evolved into a variety of uses, including:
- Supporting the security and stability of the Internet by providing contact points for network operators and administrators.
- Determining the registration status of domain names.
- Assisting law enforcement authorities in investigations for enforcing national and international laws.
- Assisting in the combating against abusive uses of Information communication technology.
- Facilitating inquiries and subsequent steps to conduct trademark clearances and to help counter intellectual property infringement, misuse and theft in accordance with applicable national laws and international treaties.
- Contributing to user confidence in the Internet as a reliable and efficient means of information and communication.
- Assisting businesses, other organizations and users in combating fraud.

Protocol Specification

A WHOIS server listens on TCP port 43 for requests from WHOIS clients. The WHOIS client makes a text request to the WHOIS server, then the WHOIS server replies with text content.

Internationalization

The WHOIS protocol has not been internationalised. The WHOIS protocol has no mechanism for indicating the character set in use.

Network News Transfer Protocol - NNTP

- NNTP specifies a protocol for the distribution, inquiry, retrieval, and posting of news articles using a reliable stream-based transmission of news among the ARPA-Internet community.
- NNTP is designed so that news articles are stored in a central database allowing a subscriber to select only those items he wishes to read. Indexing, cross-referencing, and expiration of aged messages are also provided.
- NNTP is designed so that news articles are stored in a central database allowing a subscriber to select only those items he wishes to read.
- The Network News Transfer Protocol (NNTP) established the technical foundation for the widely used Newsgroups.
- The NNTP protocol is the delivery mechanism for the USENET newsgroup service.
- NNTP is also used by clients who need to read news articles on USENET servers.
- NNTP uses an interactive command and response mechanism that lets hosts determine which articles are to be transmitted.
- Server-to-server exchanges : In the server-to-server exchange, one server either requests the latest articles from another server (pull) or allows the other server to push new articles to it.
- User-to-server connections : The user first connects with a newsgroup server (usually located at an ISP (Internet service provider), then downloads a list of available newsgroups. The user can then subscribe to a newsgroup and begin reading articles available in that group or post new articles.

Protocol Structure - NNTP

NNTP uses commands and responces for communications.
- Article - Display the header, a blank line, then the body (text) of the specified article.
- Head : Identical to the ARTICLE command except that they respectively return only the header lines or text body of the article.
- Status : Similar to the ARTICLE command except that no text is returned.
- Group : The required parameter ggg is the name of the newsgroup to be selected.
- Body : Identical to the ARTICLE command except that they respectively return only the header lines or text body of the article.
- List : Returns a list of valid newsgroups and associated information.
- NewsGroups : A list of newsgroups created since will be listed in the same format as the LIST command.
- ewNews : A list of message-ids of articles posted or received to the specified newsgroup since "date" will be listed.
- Next : The internally maintained "current article pointer" is advanced to the next article in the current newsgroup.
- Post : If posting is allowed, response code 340 is returned to indicate that the article to be posted should be sent.
- Quit : The server process acknowledges the QUIT command and then closes the connection to the client.

POP - Post Office Protocol

Post Office Protocol (POP) is an application-layer Internet standard protocol used by local e-mail clients to retrieve e-mail from a remote server over a TCP/IP connection. The Post Office Protocol (POP) allows you to fetch email that is waiting in a mail server mailbox. POP defines a number of operations for how to access and store email on your server.
It works in conjunction with the SMTP (Simple Mail Transfer Protocol), which provides the message transport services required to move mail from one system to another.

Purpose of POP

If somebody sends you an email it usually cannot be delivered directly to your computer. The message is stored in a place where you can pick it up easily. Your ISP (Internet Service Provider) does this job. It receives the message for you and keeps it until you download it. Now, POP, the Post Office Protocol is what allows you to retrieve mail from your ISP. This is also about all the Post Office Protocol is good for.

What POP allows you to do?

Things that can be done via the POP include:
- Retrieve mail from an ISP and delete it on the server.
- Retrieve mail from an ISP but not delete it on the server.
- Ask whether new mail has arrived but not retrieve it.
- Peek at a few lines of a message to see whether it is worth retrieving.

POP3 is an open Internet standard. The common POP3 commands and responses are :
- getwelcome(): Gets the greeting from the server.
- user(username): Login with a username. If valid username, server will respond with request for password.
- pass_ (password): Send password. If valid, server response will be two numbers, message count and mailbox size.
- stat(): Get the mailbox status. Response is two numbers, message count and mailbox size.
- list([message]): Get list of messages. An option "message" gets information on a specific message.
- retr(message): Get message number "message".
- dele(message): Delete message number "message".
- rset(): Remove all deleted message markings.
- noop(): No operation. Do nothing. Really. Needed in unusual programming situations.
- quit(): Quit. Commits all changes, unlocks the mailbox, and ends the server connection.
- top(message, lines): Gets just the first "lines" number of lines of message number "message". Useful on low bandwidth lines to get just the first part of long messages.
- uidl([message]): Gets a unique id list -- a message digest including unique ids. The option gets the unique id for the specific message "message".

RARP : Reverse Address Resolution Protocol

- RARP (Reverse Address Resolution Protocol) is a protocol by which a physical machine in a local area network can request to learn its IP address from a gateway server's Address Resolution Protocol (ARP) table or cache.
- A reverse address resolution protocol (RARP) is used for disk less computers to determine their IP address using the network. The RARP message format is very similar to the ARP format.
- When a new machine is set up, its RARP client program requests from the RARP server on the router to be sent its IP address.
- The RARP server will return the IP address to the machine which can store it for future use assuming that the entry has been put in the router table.
- RARP is available for Ethernet, Fiber Distributed-Data Interface, and Token Ring LANs.
- The 'operation' field in the RARP packet is used to differentiate between a RARP request and a RARP reply packet.
- Since a RARP request packet is a broadcast packet, it is received by all the hosts in the network. But only a RARP server processes a RARP request packet, all the other hosts discard the packet.
- The RARP reply packet is not broadcast, it is sent directly to the host, which sent the RARP request.

When a RARP server receives a RARP request packet, it performs the following steps:
- The MAC address in the request packet is looked up in the configuration file and
mapped to the corresponding IP address.
- If the mapping is not found, the packet is discarded.
- If the mapping is found, a RARP reply packet is generated with the MAC and IP
address. This packet is sent to the host, which originated the RARP request.

When a host receives a RARP reply packet, it gets its IP address from the packet and completes the booting process.