Protocol: ISO 10030 / CONS ES-IS
PDU Part: Fixed Part
Field: type
Length: 1 byte
Contents: type of protocol PDU.
CONS ES-IS has 11 types of operation (PDU types):
ECQ End-System Configuration Query
ENC End-System Notification Complete
ECS End-System Connect
ESH End-System Hello
RD Redirect
SCC SNARE Configuration Complete
SCR SNARE Configuration Response
SHL SNARE Hello
SNC SNARE Notification Complete
SRH SNARE Request Hello
SRN SNARE-Received Notification
These 11 PDU types are conveyed by different protocols depending on direction:
ESQ ES > SNARE X.25 data packet
ENC ES > SNARE X.25 data packet
ESC ES > SNARE X.25 call request / incoming call packet
ESH ES > SNARE X.25 data packet
RD SNARE > ES X.25 clear request / clear indication packet
SCC SNARE > ES X.25 data packet
SCR SNARE > ES X.25 data packet
SHL SNARE > ES LLC 1 data frame
SNC SNARE > ES X.25 call-acctepted / call-connected packet
SRH ES > SNARE LLC 1 data frame
SRN SNARE > ES X.25 data packet
These 11 PDU types have different functions:
ECQ Request for information concerning an NSAP
ENC Indicates end of a sequence of ESHs
ESC ES request to connect to a SNARE
ESH Notifies SNARE of NSAP at this SNPA
RD Provides redirection information to the ES
SCC Indicates end of sequence of SCRs; or indicates no information
is available for requested NSAP
SCR Response to ECQ; indicates SNPA through which SNAP may
be reached
SHL Broadcast to provide SNARE SNPA to ESs
SNC Positive acknowledgment of an ESC
SRH Broadcast to obtain SNARE SNAP
SRN Positive acknowledge of a sequence of ESHs followed by ENC