7.4 Path Management messages

09.603GPPGeneral Packet Radio Service (GPRS)GPRS Tunnelling Protocol GPT) across the Gn and Gp InterfaceRelease 1998TS

The Path Management messages may be sent between any type of GSN pair.

7.4.1 Echo Request

An Echo Request may be sent on a path to another GSN to find out if the peer GSN is alive (see section Path Failure). Echo Request messages may be sent for each path in use. A path is considered to be in use if at least one PDP context uses the path to the other GSN. When and how often an Echo Request message may be sent is implementation specific but an Echo Request shall not be sent more often than every 60 seconds on each path.

A GSN shall be prepared to receive an Echo Request at any time and it shall reply with an Echo Response. A GSN may optionally send Echo Request messages.

The optional Private Extension contains vendor or operator specific information.

Table 2: Information elements in an Echo Request

Information element

Presence requirement

Reference

Private Extension

Optional

7.9.26

7.4.2 Echo Response

The message shall be sent as a response of a received Echo Request.
The Recovery information element contains the local Restart Counter (see section Restoration and Recovery) value for the GSN that sends the Echo Response message.
The GSN that receives an Echo Response from a peer GSN shall compare the Restart Counter value received with the previous Restart Counter value stored for that peer GSN. If no previous value was stored, the Restart Counter value received in the Echo Response shall be stored for the peer GSN.
If the value of a Restart Counter previously stored for a peer GSN differs from the Restart Counter value received in the Echo Response from that peer GSN, the GSN that sent the Echo Response shall be considered as restarted by the GSN that received the Echo Response. The new Restart Counter value received shall be stored by the receiving entity, replacing the value previously stored for the sending GSN. If the sending GSN is a GGSN and the receiving GSN is a SGSN, the SGSN shall notify an affected MS next time the MS contacts the SGSN. An affected MS is an MS that has at least one activated PDP context that was using the restarted GGSN. The SGSN shall consider all PDP contexts using the path as inactive.

The optional Private Extension contains vendor or operator specific information.

Table 3: Information elements in an Echo Response

Information element

Presence requirement

Reference

Recovery

Mandatory

7.9.12

Private Extension

Optional

7.9.26

7.4.3 Version Not Supported

This message contains only the GTP header and indicates the latest GTP version that the GTP entity on the identified UDP/IP address can support.