As I was telling you about in a previous post – my first eGTP test, the reply (first reply) to a CreateSessionRequest message is a CreateSessionResponse message, described below. This message contains:

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- GTPversion 2, Message Type information, in this case, this is a Response, the length of the message, the sequence number (1) and the TEID (tunnel Endpoint Identifier) – which is copied from the CreateSessionRequest message

- the Cause field indicates this is a Response for an Accepted Request – in case there would be any error, the Cause Source field would indicate the cause of the error

- PDN Address Allocation (PAA) – field which is completed at this moment  (in the CreateSessionResponse) by the SGW with the IP address of the PDN – should you remember, in the CreateSessionRequest message, this field indicated the type of address (IPv4) and value 0.0.0.0; as per 3GPP TS 29.274 – this value is a fixed IPv4/IPv6 address as indicated by the HSS registers, or it leaves the value to 0.0.0.0 indicating that the PDN GW address is assigned dynamically

- F-TEID (Fully Qualified Tunnel Endpoint Identifier) – as mentioned also in the previous post, there are 2 F-TEIDs: one for the S11 interface, and another one for the S5/S8 interface, both source IP addresses of GTP-C:

— one for the S11 interface (the one between MME and SGW) – the SGW end – the IP of the SGW from the S11 interface

— one for the S5/S8 interface (the one between SGW and PGW) – the IP address of the APN server

- APN Restriction header – as per 3GPP TS 29.274, it “denotes the restriction on the combination of types of APN for the APN associated with this EPS bearer Context.” – haven’t  used it yet, so I cannot say too much about it

- Bearer Context – information I have neglected to describe in sufficient detail in the CreateSessionRequest description. Here, in the CreateSessionResponse message, the Bearer Context header has 6 sub-headers:

— EPS Bearer ID

— Charging ID

— F-TEIDs : here both of the identifiers contain the IP address of the SGW’s S11 interface – the source GTP-U interface

— Cause : here is Request Accepted, no Cause Source

— Bearer QoS, which contains the QCI label and some other QoS identifiers that shall be described – hopefully I’ll be able to see them at work till then

Tags: bearer, LTE, MME, PDN, PGW, SAE, SGW, techie, UE