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GTP Overview

Provides an overview of the GTP protocol. Tutorial video at: https://www.youtube.com/watch?v=FPfExr9bEEg&index=9&list=PLgQvzsPaZX_bimBc5Wu4m6-cVD4bZDav9&t=1s

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GTP Overview

  1. 1. İki Teknoloji 1 LTE: A feature based introduction LTE Core Features Annex. GTP Primer Irfan Ali Video at youtube: https://www.youtube.com/watch?v=FPfExr9bEEg&list=PLgQvzs PaZX_bimBc5Wu4m6-cVD4bZDav9&index=9
  2. 2. Irfan Ali 2İki Teknoloji 2 What is GTP? • GTP = GPRS Tunneling Protocol • What is Tunneling in the IP World? Ø Tunneling in the IP world means putting an IP packet inside another IP packet. IP_src -> IP_dst Payload IP_a-> IP_b Inner IP Packet Outer IP Packet GPRS General Packet Radio Service
  3. 3. Irfan Ali 3İki Teknoloji 3 What is the purpose of GTP Tunneling? • Route an IP packet along a path that is not topologically correct for the packet. Mehmet’s IP address 46.1.78.189-> 10.40.40.12 Internet S-GW P-GW eNB Ayse Mehmet 10.10.10.1 10.10.10.2 10.10.10.0/24 10.10.20.1 10.10.20.0/24 10.10.20.2 GTPTunnel IP_sgw -> IP_enb UDP_ dst= 2152 TEID_x IP_pgw -> IP_sgw IP UDP_ dst= 2152 UDP TEID_k GTP-U header Mehmet’s IP address 10.40.40.12 DHCP GTP is IP-in-UDP Tunneling HiIP_a -> IP_m HiIP_a -> IP_m HiIP_a -> IP_m HiIP_a -> IP_m
  4. 4. Irfan Ali 4İki Teknoloji 4 How does the GTP-U Tunnel get setup? • GTP Protocol has two parts Ø Signaling part called GTP-C (GTP-Control) Ø User data part called GTP-U (GTP-User) • GTP-C is used to setup GTP-U tunnel • Both GTP-C and GTP-U run on top of UDP • IP-in-UDP tunneling is only used for GTP-U • GTP-C carries control/signaling messages IP_pgw -> IP_sgw IP_a -> IP_m UDP_ dst= 2152 TEID_a IP_pgw -> IP_sgw UDP_ dst= 2123 TEID_k IP UDP GTP-U header IP UDP GTP-C header GTP-C message
  5. 5. Irfan Ali 5İki Teknoloji 5 SGW PGW TEID 21232123 2152 TEID IPc,sgw 2152 IPu,pgwIPu,sgw TxRx Tx Rx TEID TEID TxRx Tx Rx TEIDas TEIDbs TEIDcs IPc,pgw SGW PGW TEID 2123 2152 2123 2152 TEID IPc,sgw IPu,sgw IPc,pgw IPu,pgw TxRx Tx Rx TxRx Tx Rx TEIDTEID How does GTP-U Tunnel get setup: Example TEIDas TEIDas 0 C.S. Req (IMSIa, C: IPc,sgw,TEIDas, EBID5:IPu,sgw,TEIDas) C.S. Rsp (C:IPu,pgw,TEIDap, EBID5:IPu,pgw, TEIDxp) TEIDbs TEIDcs TEIDap TEIDbp TEIDcp TEIDap TEIDbs TEIDcs TEIDbp TEIDcp
  6. 6. Irfan Ali 6İki Teknoloji 6 Packet Trace: Create Session Request (S11); MME->SGW MME SGW/ PGW 0 21232123 0x1 eNB SGW/ PGW 21522152 S11 S1U
  7. 7. Irfan Ali 7İki Teknoloji 7 Packet Trace: Create Session Response (S11); SGW -> MME MME SGW/ PGW 21232123 0x1 eNB SGW/ PGW 21522152 S11 S1U 0x80..01 0xc0..1
  8. 8. Irfan Ali 8İki Teknoloji 8 Packet Trace: Modify Bearer Request (S11); MME ->SGW MME SGW/ PGW 21232123 0x1 eNB SGW/ PGW 21522152 S11 S1U 0x80..01 0xc0..1 0x800..001 0x3ea
  9. 9. Irfan Ali 9İki Teknoloji 9 Packet Trace: GTP-U: S1-U; eNB -> SGW/PGW eNB SGW/ PGW 21522152 S1U 0x010000 UE Server 10.255.1.111 10.0.0.10010.1.2.11 10.1.1.12 TxRx Tx Rx
  10. 10. Irfan Ali 10İki Teknoloji 10 Packet Trace GTP-U: S1-U; eNB <- SGW/PGW eNB SGW/ PGW 21522152 S1U 0x010000 UE Server 10.255.1.111 10.0.0.10010.1.2.11 10.1.1.12 TxRx
  11. 11. Irfan Ali 11İki Teknoloji 11 GTP Path and Path Management • Path is between two endpoints. Each end point is IP_address+UDP_Port# • There can be several GTP tunnels on a path (each with different TEIDs). • There is typically a “software process” that binds to each end-point. • Path Management messages: To ensure that a path is alive (both the physical link and process at the endpoint), periodic echo-request and echo-response are sent. • Failure-detection and error-recovery mechanisms are defined. SGW PGW TEID 2123 2152 2123 2152 TEIDas TEIDbs TEIDcs TEIDxs TEIDys TEIDzs TEID IPc,sgw IPu,sgw IPc,pgw IPu,pgw TxRx Tx Rx Path Path
  12. 12. Irfan Ali 12İki Teknoloji 12 Packet Traces: GTP-U Echo-request & Echo Response In GTP-Cv2 Echo request/response messages do not contain TEID field In GTP-Cv2 Echo request/response messages do not contain TEID field
  13. 13. Irfan Ali 13İki Teknoloji 13 Interfaces on which GTP is used • GTP-Cv2 is used not only for mobility management, but also for general signaling purposes, eg providing UE’s cell information to the PGW and from there to operator’s service network. Internet MME S-GW P-GW HSS eNB UE’s IP address S1-MME S11 S6a S5 S1-U MME S10 S1AP GTP C GTP C
  14. 14. Irfan Ali 14İki Teknoloji 14 Specifications • GTPC v2 TS 29.274 • GTPU v1 TS 29.281 • GTPC v1 TS 29.060 • Historically (before Rel-8, i.e. before 2009Q1), TS 29.060 used to be the key GTP specification (both GTPC v1 and GTPU v1). But since Rel-8, TS 29.060 is only applicable to 3G interfaces (Gn/Gp, between SGSN <-> GGSN and between SGSNs) and not to EPC interfaces. Its specification only applies to GTPC v1 Ø Ignore anything that 29.060 says about GTPU.
  15. 15. İki Teknoloji 15 Annex
  16. 16. Irfan Ali 16İki Teknoloji 16 Rules for GTP-C IP address and port numbers • Three types of messages • Rules for Port# and IP addresses Ø Initial Message: 1. The UDP Destination Port number for GTPv2 Initial messages shall be 2123 2. The UDP Source Port for a GTPv2 Initial message is a locally allocated port number. 3. During the establishment of the GTP tunnel, the GTPv2 entity selects and communicates to the peer GTPv2 entity the IP Destination Address at which it expects to receive subsequent control plane Initial messages related to that GTP tunnel via the "Sender F-TEID for Control Plane" IE Ø Triggered message 1. The IP Source Address of a GTPv2 Triggered message and for a Triggered Reply message shall be copied from the IP destination address of the message to which this GTPv2 entity is replying 2. The IP Destination Address of a GTPv2 Triggered message and for a Triggered Reply message shall be copied from the IP Source Address of the message to which this GTPv2 entity is replying 3. The UDP Source Port of a GTPv2 Triggered message shall be the value from the UDP Destination Port of the corresponding message to which this GTPv2 entity is replying 4. The UDP Destination Port value of a GTPv2 Triggered message shall be the value of the UDP Source Port of the corresponding message to which this GTPv2 entity is replying Ø Triggered Reply message 1. Same rules as triggered message. • Rules for TEID# Ø The first Create Session Request message on S11 for a UE shall have TEID = 0x0 Ø The (first and subsequent) Create Session Request message on S5 for a UE shall have TEID = 0x0 GTP-C Peer A GTP-C Peer B Initial Message Triggered Message Triggered Reply Message

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