3GPP specification: 36.413
ETSI TS 136 413 V10.9.0
220.127.116.11 PATH SWITCH REQUESThttp://www.etsi.org/deliver/etsi_ts/136400_136499/136413/09.10.00_60/ts_136413v091000p.pdf ,p.83
Source MME GUMMEI "Optional"
18.104.22.168 PATH SWITCH REQUEST(No Source MME GUMMEI field)
Although the "Source MME GUMMEI" is optional in release 10, it's said that Cisco HeNBGW require it in its Path Switch Request?
LTE X2 Handover Messaging
LTE eNodeB Handover over the X2 Interface
HeNB - GW Administration Guide, StarOS Release 17 Last Updated February 27, 2015
HENBGW have to route S1 PATH SWITCH REQUEST message from HENB towards the MME based on the GUMMEI of the source MME received from the HeNB. If HENBGW receives CSG ID IE and Cell Access Mode IE in the S1 PATH SWITCH REQUEST, the same should be forwarded to MME. In case of S1 PATH SWITCH REQUEST ACKNOWLEDGE message, HENBGW will inform the HeNB about the MME UE S1AP ID assigned by the MME and the MME UE S1AP ID assigned by the HeNB GW for the UE.