COTP 是 OSI 7層協定定義的位於TCP之上的協定。
This is the connection transport protocol of the IsoProtocolFamily.
As most readers nowadays will be more familiar with TCP, COTP is explained comparing both protocols as they are both used to transport users's data reliably over a network.
Packet-based vs. stream-based: COTP transports packets of data from one user to the other, so the receiver will get exactly the same data boundaries as the sender transmitted. TCP transports a continuous stream of data to the receiver, so the protocol on top of TCP often has to add such boundaries itself (see the TPKT protocol for such a protocol).
TSAP's vs. ports: To multiplex several conversations between two hosts, COTP uses TSAP's which are variable length binary blobs (often a meaningful string is used). These TSAP's are matched at connection establishing phase, and replaced by the 2 byte (destination/source) references at data transfer. TCP uses ports for this. One notable difference is that TSAP's are singletons - if a TSAP is used for a connection it cannot be used by another. XXX - Needs clarification. A single TSAP (Transport Service Access Point) may be used by multiple connections.
