Two of the services outlined in table 4 are defined across all MSNL entities and their implementation is Mandatory.
The echo service exists to allow a client to reassure itself as to the aliveness or reachability of another (the server) machine. This is similar in some ways to both the ``ping'' and ``echo'' services on IP systems, except the description here is for a connection orientated environment.
Multiple clients (at least five if possible but at least two) should be supported. For a given connection the server should take no action except upon receiving a block of data. The block of data should be returned on the connection without modification or inspection. The server is free (as in all MSNL connections) to terminate the connection at any time, and it is recommended that idle connections be timed out after thirty seconds of inactivity.
The traceroute service exists to allow routeing to be investigated by authorised clients.
Server behaviour is the same as for the echo service except that the data shall be manipulated as follows. The format of the received data is described in table 5.
Table 5: Traceroute block format.
The server shall place its principal MSNL address at offset 
in
the block (ie. at the logical end) and increment the value of the
first octet. The block shall then be transmitted on the connection.
Routers perform special behaviour at connection setup time by noticing that the request is to the Traceroute port and do not initiate cell forwarding for the connection but instead initiate block forwarding through an appropriate daemon or thread. The router performs the same data manipulation as the server and forwards the data block on the way. Note that this special case for connection setup does not therefore add any checking code for this function in the data paths unlike the similar mechanism in IP.