ISO Transport Service on top of TCP (ITOT) is a mechanism enables ISO applications to be ported to TCP/IP network. There are two basic approaches which can be taken when "porting" ISO applications to TCP/IP (and IPv6) environments. One approach is to port each individual application separately, developing local protocols on top of TCP. A second approach is based on the notion of layering the ISO Transport Service over TCP/IP. This approach solves the problem for all applications which use the ISO Transport Service.

ITOT is a Transport Service which is identical to the Services and Interfaces offered by the ISO Transport Service Definition [ISO8072], but which will in fact implement the ISO Transport Protocol [ISO8073] on top of TCP/IP (IPv4 or IPv6), rather than the ISO Network Service [ISO8348]. The "well known" TCP port 102 is reserved for hosts which implement the ITOT Protocol.

Two variants of the ITOT protocol are defined, "Class 0 over TCP" and "Class 2 over TCP", which are based closely on the ISO Transport Class 0 and 2 Protocol. Class 0 provides the functions needed for connection establishment with negotiation, data transfer with segmentation, and protocol error reporting. It provides Transport Connection with flow control based on that of the NS-provider (TCP). It provides Transport Disconnection based on the NS-provider Disconnection. Class 0 is suitable for data transfer with no Explicit Transport Disconnection.

Class 2 provides the functions needed for connection establishment with negotiation, data transfer with segmentation, and protocol error reporting. It provides Transport Connection with flow control based on that of the NS-provider (TCP). It provides Explicit Transport Disconnection. Class 2 is suitable when independence of Normal and Expedited Data channels are required or when Explicit Transport Disconnection is needed.

Protocol Structure

• Protocol Version: Value: 3
• Reserved - Value: 0
• Packet Length - Value: Length of the entire TPKT in octets, including Packet Header
• TPDU - ISO Transport TPDU as defined in ISO 8073.

Mapping parameters between the TCP service and the ISO 8348 CONS service is done as follow:

• ISO Network Service TCP
• CONNECTION ESTABLISHMENT
• Called address server"s IPv4 or IPv6 address and TCP port number.
• Calling address client"s IPv4 or IPv6 address
• all others parameters ignored
• DATA TRANSFER
• NS User Data (NSDU) DATA
• CONNECTION RELEASE
• all parameters ignored

Related Terms: UDP, TCP, IP, CMIP, CMOT, CMIS, ACSE, ROSE, CMISE, LPP

Sponsor Source: ITOT is defined by ISO (http://www.iso.org).

Reference:
http://www.javvin.com/protocol/rfc1085.pdf: ISO Presentation Services on top of TCP/IP-based internets
http://www.javvin.com/protocol/rfc2126.pdf: ISO Transport Service on top of TCP (ITOT)