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.

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.

Dynamic Trunking Protocol (DTP)

The Dynamic Trunking Protocol (DTP) is a proprietary networking protocol developed by Cisco Systems for the purpose of negotiating trunking on a link between two VLAN-aware switches, and for negotiating the type of trunking encapsulation to be used. It works on the Layer 2 of the OSI model. If a port can become a trunk, it may also have the ability to trunk automatically, and in some cases even negotiate what type of trunking to use on the port. DTP provides this ability to negotiate the trunking method with the other device.
There are a couple of other potential issues that arise when you start trunking.
- The first issue is that both ends of a trunk cable had better agree they're trunking, or they're going to be interpreting trunk frames as normal frames. To resolve this, Cisco came up with a protocol for switches to communicate intentions. The first version of it was VTP, VLAN Trunking Protocol, which worked with ISL. The newer version works with 802.1q as well, and is called Dynamic Trunking Protocol (DTP).
- The second issue is creating VLAN's.

Switch port modes

- auto : causes the port to passively be willing to convert to trunking. The port will not trunk unless the neighbor is set to on or desirable . This is the default mode.
- on : forces the link into permanent trunking, even if the neighbor doesn't agree.
- off : forces the link to permanently not trunk, even if the neighbor doesn't agree.
- desirable : causes the port to actively attempt to become a trunk, subject to neighbor agreement.
- nonegotiate : forces the port to permanently trunk but not send DTP frames.

Protocol Structure of DTP

On a Catalyst set-based switch, the syntax for setting up a link as a trunk is:

set trunk mod_num/port_num [on | desirable | auto | nonegotiate] [isl | dot1q | negotiate] [vlan_range]
Use this command to set the specified port or ports to trunking.