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.