GTP'
Encyclopedia
GTP' is an IP
based protocol used within GSM and UMTS networks. It can be used with UDP
or TCP
. GTP' uses the same message structure as GTP
(GTP-C, GTP-U), but it is largely a separate protocol. GTP' uses registered
UDP/TCP port 3386.
GTP' can be used for carrying charging data from the "Charging Data Function" (CDF) of the GSM or UMTS network to the "Charging Gateway Function" (CGF). In most cases, this should mean from many individual network elements such as the GGSNs to a centralised computer which then delivers the charging data more conveniently to the network operator's billing center.
GTP' is used on the Ga/Gz interface within the 3GPP GPRS Core Network
definition.
GTP' reuses aspects of GTP although to quote 3GPP TS 32.295 "only the signalling plane of GTP is partly reused". GTP' defines a different header, additional messages, field values, as well as a synchronisation protocol to avoid losing or duplicating CDRs
on CGF or SGSN/GGSN failure. Transferred CDRs, if following 3GPP standards, are encoded in ASN.1.
Version : The first header field in a GTP' packet is the 3-bit version field. For GTP' v2, this has a value of 2 (hence the name GTP' v2).
Protocol Type (PT) : a 1-bit value that differentiates GTP' (value 0) from GTP (value 1).
Reserved: a 3-bit reserved field (must be 1's).
Header Length (Hdr len): a 1-bit value that for GTP' version 0 indicates if using a 20 byte header (value 0) (as per GTP
) or this 6 byte header. This bit must be unset (value 0) for subsequent GTP' versions and in these does not indicate the header length as this must always be 6 bytes.
Type: A 8-bit field that states the packet type.
Length: A 16-bit field that states the length of the packet being encapsulated by GTP' (not including the GTP' header itself).
Sequence Number: A 16-bit field that uniquely identifies this packet and allows detection of loss or duplication
using Echo Request/Response does. This message can also be used to advise of other nodes coming back into service, and (in GTP' version 2) to advise of the IPv6 address of the CGF.
In either case the CDFs are given more information about an impending or immediate failure than would be the case if the CDF was polling using Echo Request messages.
This message contains details about the cause, and optionally address(es) of an alternate CGF.
There is a mechanism to attempt to avoid losing or writing any duplicate CDRs. This is described in some detail in 3GPP TS 32.295. The basic premise is that every packet is sequenced and if not individually acknowledged then it will be resent until it is acknowledged by any CGF. Normal Data Record packets are immediately written to non-volatile storage (e.g. disk), but resent packets are marked as "possibly duplicated" and enter a special queue that is not immediately written to non-volatile storage—a second confirmation from the CDF is required.
The ability to send a Data Record Transfer Request containing zero CDRs is used as a test to detect the success or failure of the CGF to have already written records assigned to that sequence number and is an important part of the above mechanism.
The acknowledgement includes a cause and can be a rejection of the contained records.
Internet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
based protocol used within GSM and UMTS networks. It can be used with UDP
User Datagram Protocol
The User Datagram Protocol is one of the core members of the Internet Protocol Suite, the set of network protocols used for the Internet. With UDP, computer applications can send messages, in this case referred to as datagrams, to other hosts on an Internet Protocol network without requiring...
or TCP
Transmission Control Protocol
The Transmission Control Protocol is one of the core protocols of the Internet Protocol Suite. TCP is one of the two original components of the suite, complementing the Internet Protocol , and therefore the entire suite is commonly referred to as TCP/IP...
. GTP' uses the same message structure as GTP
GPRS Tunnelling Protocol
GPRS Tunneling Protocol is a group of IP-based communications protocols used to carry General Packet Radio Service within GSM, UMTS and LTE networks. In 3GPP architectures, GTP and Proxy Mobile IPv6 based interfaces are specified on various interface points.GTP can be decomposed into separate...
(GTP-C, GTP-U), but it is largely a separate protocol. GTP' uses registered
Registered port
A registered port is a network port assigned by the Internet Assigned Numbers Authority for use with a certain protocol or application.Ports with numbers lower than those of the registered ports are called well known...
UDP/TCP port 3386.
GTP' can be used for carrying charging data from the "Charging Data Function" (CDF) of the GSM or UMTS network to the "Charging Gateway Function" (CGF). In most cases, this should mean from many individual network elements such as the GGSNs to a centralised computer which then delivers the charging data more conveniently to the network operator's billing center.
GTP' is used on the Ga/Gz interface within the 3GPP GPRS Core Network
GPRS Core Network
The GPRS core network is the central part of the General Packet Radio Service which allows 2G, 3G and WCDMA mobile networks to transmit IP packets to external networks such as the Internet...
definition.
GTP' reuses aspects of GTP although to quote 3GPP TS 32.295 "only the signalling plane of GTP is partly reused". GTP' defines a different header, additional messages, field values, as well as a synchronisation protocol to avoid losing or duplicating CDRs
Charging Data Record
A charging data record is, in 3GPP parlance, a formatted collection of information about a chargeable event.CDRs are used for user billing: a telecom provider transfers them from time to time in order to send bills to their users...
on CGF or SGSN/GGSN failure. Transferred CDRs, if following 3GPP standards, are encoded in ASN.1.
Header
GTP' v1 and v2 headers contain the following fields| + | Bits 0-2 | 3 | 4 | 5 | 6 | 7 | 8-15 | 16-31 | 32-47 | |||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 0 | Version | PT [0] | Reserved | Hdr len | Type | Length | Sequence Number | |||||||||||||||||||||||||||||||||||||||||
Version : The first header field in a GTP' packet is the 3-bit version field. For GTP' v2, this has a value of 2 (hence the name GTP' v2).
Protocol Type (PT) : a 1-bit value that differentiates GTP' (value 0) from GTP (value 1).
Reserved: a 3-bit reserved field (must be 1's).
Header Length (Hdr len): a 1-bit value that for GTP' version 0 indicates if using a 20 byte header (value 0) (as per GTP
GPRS Tunnelling Protocol
GPRS Tunneling Protocol is a group of IP-based communications protocols used to carry General Packet Radio Service within GSM, UMTS and LTE networks. In 3GPP architectures, GTP and Proxy Mobile IPv6 based interfaces are specified on various interface points.GTP can be decomposed into separate...
) or this 6 byte header. This bit must be unset (value 0) for subsequent GTP' versions and in these does not indicate the header length as this must always be 6 bytes.
Type: A 8-bit field that states the packet type.
Length: A 16-bit field that states the length of the packet being encapsulated by GTP' (not including the GTP' header itself).
Sequence Number: A 16-bit field that uniquely identifies this packet and allows detection of loss or duplication
Message Types
GTP' uses the GTP Version Not Supported, Echo Request and Echo Response messages unchanged, but adds the following messages- Node Alive Request
- Node Alive Response
- Redirection Request
- Redirection Response
- Data Record Transfer Request
- Data Record Transfer Response
Node Alive Request / Response
The Node Alive messages are used to advise other network components that a node has started service. The request is sent from the node starting and so provides a faster method to re-enable service than pollingPolling (computer science)
Polling, or polled operation, in computer science, refers to actively sampling the status of an external device by a client program as a synchronous activity. Polling is most often used in terms of input/output , and is also referred to as polled or software driven .Polling is sometimes used...
using Echo Request/Response does. This message can also be used to advise of other nodes coming back into service, and (in GTP' version 2) to advise of the IPv6 address of the CGF.
Redirection Request/Response
The Redirection messages are used to:- divert the flow of CDRs from the CDFs (SGSN/GGSN) to another CGF when the sender is being removed from service (for maintenance/failure).
- advise that the CGF has lost its connection to a downstream system
In either case the CDFs are given more information about an impending or immediate failure than would be the case if the CDF was polling using Echo Request messages.
This message contains details about the cause, and optionally address(es) of an alternate CGF.
Data Record Transfer Request/Response
The Data Record Transfer messages are used to reliably transport CDRs from the point of generation (SGSN/GGSN) to non-volatile storage in the CGF.Data Record Transfer Request
Each Data Record Transfer Request message can contain a message of one of four types:- Send Data Record Packet - This message contains zero or more CDRs. CDRs may be encoded in ASN.1 using BERBasic Encoding RulesThe Basic Encoding Rules is one of the encoding formats defined as part of the ASN.1 standard specified by the ITU in X.690.-Description:...
or, less commonly, PERPacked Encoding RulesPacked encoding rules are ASN.1 encoding rules for producing a compact transfer syntax for data structures described in ASN.1, defined in 1994....
. - Send possibly duplicated Data Record Packet - This message contains one or more CDRs, and this message has previously been sent to another CGF.
- Cancel Data Record Packet - This message orders the CGF to remove one or more Data Record Packet from the CGF "possibly duplicated" pending queue.
- Release Data Record Packet - This message orders the CGF to write the contents of one or more Data Record Packets from the CGF "possibly duplicated" pending queue.
There is a mechanism to attempt to avoid losing or writing any duplicate CDRs. This is described in some detail in 3GPP TS 32.295. The basic premise is that every packet is sequenced and if not individually acknowledged then it will be resent until it is acknowledged by any CGF. Normal Data Record packets are immediately written to non-volatile storage (e.g. disk), but resent packets are marked as "possibly duplicated" and enter a special queue that is not immediately written to non-volatile storage—a second confirmation from the CDF is required.
The ability to send a Data Record Transfer Request containing zero CDRs is used as a test to detect the success or failure of the CGF to have already written records assigned to that sequence number and is an important part of the above mechanism.
Data Record Transfer Response
The Data Record Transfer Response acknowledges receipt of one or more Data Record Transfer messages; responses can be grouped for reasons of efficiency but must be sent more frequently than the sending CDFs timeout.The acknowledgement includes a cause and can be a rejection of the contained records.