atmtcp(8) set up ATM over TCP connections


atmtcp [-d] [-v] command ...
atmtcp -V


The main purpose of atmtcp is to establish TCP connections and to configure them as virtual ATM devices. Such pairs of "ATM over TCP" devices are connected as if they were real ATM adapters linked by a cable or fiber, i.e. SDUs sent on a given VPI/VCI are received at the other end on the same VPI/VCI.

Virtual interfaces and ATM over TCP connections are called links. Other link types supported by atmtcp are real interfaces, files for recording and playback of ATM traffic, and printing a hex dump of the PDU content on standard output. Any pair of such links can be connected with atmtcp. If additional links are attached to such a connection, they send to all other links, except to the first link and the respective sender, and they receive from all other links.

atmtcp can operate with two types of virtual interfaces: ephemeral or persistent. By default, atmtcp interfaces are ephemeral. When the atmtcp process that created an interface terminates, the virtual ATM device is removed as soon all VCs are closed. However, if the interface was previously created as a persistent interface, only the communication stops, but the interface and all VCs on it remain intact. Attempts to send data on an atmtcp interface in this state fail silently, i.e. the interface behaves just like a real ATM interface without a wire. A new atmtcp process can then attach to the interface and resume operation. Persistent interfaces need to be removed explicitly.

If atmtcp has any readable links after processing the command line, it enters a loop to perform the data forwarding. If no readable links have been specified, atmtcp terminates after processing the command line. If any setup operation fails, atmtcp terminates at this point and does not attempt to cancel previous operations (e.g. creation of permanent interfaces).


print detailed progress information on standard error.
print some progress information on standard error.
print version number of atmtcp on standard output and exit.


create [itf]
create a persistent interface. If no interface number is specified, atmtcp uses the default value 0.
remove [itf]
remove a persistent interface. If the interface is still in use, it is marked as ephemeral and will be removed as soon as all VCs are closed. If no interface number is specified, atmtcp uses the default value 0.
virtual [itf]
link to the corresponding virtual (ATM over TCP) interface. If no interface number is specified, the kernel assigns the first available number.
real [itf]
link to the corresponding ATM interface. If no interface number is specified, atmtcp uses the default value 0. If a link requests that a VC be opened, atmtcp will attempt to open a VC with the specified QoS parameters on that interface. If the operation succeeds, data can be sent or received on that VC. If the operation fails, an error code is returned to the requester. Note that only data arriving on open VCs can be received and that a real ATM interface never initiates a connection. atmtcp can share ATM interfaces with other applications.
connect host [port]
connect to an instance of atmtcp running on the specified host. If the port argument is omitted, atmtcp uses the default port 2812.
switch host line [port]
like connect, but connects to an ATM over TCP "switch" and selects the specified virtual line.
listen [port]
listen for an incoming ATM over TCP connection. If the port argument is omitted, atmtcp uses the default port 2812. atmtcp waits until the connection is established. Only one connection is accepted per listen command.
listen-bg [port]
like listen, but run in background after beginning to listen.
read file [stream]
play back all streams from the specified file. If a stream number is specified, only that stream is played back.
write file
record the traffic of all links in the specified file. The PDUs from each link are stored in a stream with the same number as the link.
print a hex dump of the content of all received PDUs on standard output.
continue to run in background (i.e. in a forked child process).
wait [seconds]
wait for the specified number of seconds. If no time is specified, atmtcp waits for a newline on standard input.


Due to recent protocol changes, atmtcp is currently not compatible with the ATM over TCP "switch".

Only AAL SDUs are exchanged, no segmentation or reassembly is performed. That implies that using different AALs (e.g. AAL5 and AAL0) on either side will reveal limitations of this emulation.

The atmtcp process needs to run during the the whole lifetime of the connection.


Create a pair of virtual ATM over TCP interfaces on the local host and connect them:

  # session A
  atmtcp virtual listen
  # session B
  atmtcp virtual connect localhost

Create virtual interface 1, connect it to real ATM interface 0, then start atmsigd on the virtual interface, and log all the traffic in a file:

atmtcp virtual 1 real 0 write /tmp/log atmsigd 1.0.5
Take the previously created file and examine the traffic sent from atmsigd using saaldump:

# session A atmtcp virtual 1 read /tmp/log 0 wait # session B saaldump 1.0.5 # press [Enter] in session A


Werner Almesberger, EPFL ICA <[email protected]>