computer science

GPRS Tunnelling Protocol

GPRS Tunnelling Protocol is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand GPRS Tunnelling Protocol rather than just read about it. In short: GPRS Tunnelling Protocol (GTP) is a group of IP-based communications protocols used to carry general packet radio service (GPRS) within GSM, UMTS, LTE and 5G NR radio networks. In 3GPP architectures, GTP and Proxy Mobile IPv6 based interfaces are specified on various interface points.

Key takeaways

GPRS Tunnelling Protocol belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect GPRS Tunnelling Protocol to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of GPRS Tunnelling Protocol from memory before moving on to harder problems.

Reference excerpt

GPRS Tunnelling Protocol (GTP) is a group of IP-based communications protocols used to carry general packet radio service (GPRS) within GSM, UMTS, LTE and 5G NR radio networks. In 3GPP architectures, GTP and Proxy Mobile IPv6 based interfaces are specified on various interface points. GTP can be decomposed into separate protocols, GTP-C, GTP-U and GTP'. GTP-C is used within the GPRS core network for signaling between gateway GPRS support nodes (GGSN) and serving GPRS support nodes (SGSN). This allows the SGSN to activate a session on a user's behalf (PDP context activation), to deactivate the same session, to adjust quality of service parameters, or to update a session for a subscriber who has just arrived from another SGSN. GTP-U is used for carrying user data within the GPRS core network and between the radio access network and the core network. The user data transported can be packets in any of IPv4, IPv6, or PPP formats. GTP' (GTP prime) uses the same message structure as GTP-C and GTP-U, but has an independent function. It 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 centralized computer that delivers the charging data more conveniently to the network operator's billing center. Different GTP variants are implemented by RNCs, SGSNs, GGSNs and CGFs within 3GPP networks. GPRS mobile stations (MSs) are connected to a SGSN without being aware of GTP. GTP can be used with UDP or TCP. UDP is either recommended or mandatory, except for tunnelling X.25 in version 0. GTP version 1 is used only on UDP.

General features All variants of GTP have certain features in common. The structure of the messages is the same, with a GTP header following the UDP/TCP header.

Header

GTP version 1 GTPv1 headers contain the following fields:

Version It is a 3-bit field. For GTPv1, this has a value of 1. Protocol Type (PT) a 1-bit value that differentiates GTP (value 1) from GTP' (value 0). Reserved a 1-bit reserved field (must be 0). Extension header flag (E) a 1-bit value that states whether there is an extension header optional field. Sequence number flag (S) a 1-bit value that states whether there is a Sequence Number optional field. N-PDU number flag (PN) a 1-bit value that states whether there is a N-PDU number optional field. Message Type an 8-bit field that indicates the type of GTP message. Different types of messages are defined in 3GPP TS 29.060 section 7.1 Message Length a 16-bit field that indicates the length of the payload in bytes (rest of the packet following the mandatory 8-byte GTP header). Includes the optional fields. Tunnel endpoint identifier (TEID) A 32-bit(4-octet) field used to multiplex different connections in the same GTP tunnel. Sequence number an (optional) 16-bit field. This field exists if any of the E, S, or PN bits are on. The field must be interpreted only if the S bit is on. N-PDU number an (optional) 8-bit field. This field exists if any of the E, S, or PN bits are on. The field must be interpreted only if the PN bit is on. Next extension header type an (optional) 8-bit field. This field exists if any of the E, S, or PN bits are on. The field must be interpreted only if the E bit is on. Next Extension Headers are as follows:

Extension length an 8-bit field. This field states the length of this extension header, including the length, the contents, and the next extension header field, in 4-octet units, so the length of the extension must always be a multiple of 4. Contents extension header contents. Next extension header an 8-bit field. It states the type of the next extension, or 0 if no next extension exists. This permits chaining several next extension headers.

GTP version 2 It is also known as evolved-GTP or eGTP. GTPv2-C headers contain the following fields:

There is no GTPv2-U protocol, GTP-U in LTE also uses GTPv1-U.

Version It is a 3-bit field. For GTPv2, this has a value of 2. Piggybacking flag If this bit is set to 1 then another GTP-C message with its own header shall be present at the end of the current message. There are restrictions as to what type of message can be piggybacked depending on what the toplevel GTP-C message is. TEID flag If this bit is set to 1 then the TEID field will be present between the message length and the sequence number. All messages except Echo and Echo reply require TEID to be present. Message length This field shall indicate the length of the message in octets excluding the mandatory of the GTP-C header (the first 4 octets). The TEID (if present) and the Sequence Number shall be included in the length count.

Connectivity mechanisms Apart from the common message structure, there is also a common mechanism for verifying connectivity from one GSN to another GSN. This uses two messages.

echo request echo response As often as every 60 seconds, a GSN can send an echo request to every other GSN with which it has an active connection. If the other end does not respond it can be treated as down and the active connections to it will be deleted. Apart from the two messages previously mentioned, there are no other messages common across all GTP variants meaning that, for the most part, they effectively form three completely separate protocols.

GTP-C - GTP control The GTP-C protocol is the control section of the GTP standard. When a subscriber requests a PDP context, the SGSN will send a create PDP context request GTP-C message to the GGSN giving details of the subscriber's request. The GGSN will then respond with a create PDP context response GTP-C message which will either give details of the PDP context actually activated or will indicate a failure and give a reason for that failure. This is a UDP message on port 2123. The eGTP-C (or, GTPv2-C) protocol is responsible for creating, maintaining and deleting tunnels on multiple Sx interfaces. It is used for the control plane path management, tunnel management and mobility management. It also controls forwarding relocation messages; SRNS context and creating forward tunnels during inter LTE handovers.

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with GPRS Tunnelling Protocol

Start with the simplest possible case. Write down what GPRS Tunnelling Protocol claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to GPRS Tunnelling Protocol before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about GPRS Tunnelling Protocol ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of GPRS Tunnelling Protocol

In research: GPRS Tunnelling Protocol appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses GPRS Tunnelling Protocol in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: GPRS Tunnelling Protocol is common in secondary-school and first-year university syllabi. It links to neighbouring topics 3GPP standards, GSM standard, Mobile telecommunications standards, so understanding it makes those chapters shorter.
In everyday life: Look for GPRS Tunnelling Protocol outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study GPRS Tunnelling Protocol in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what GPRS Tunnelling Protocol means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain GPRS Tunnelling Protocol out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is GPRS Tunnelling Protocol in simple terms?

Why does GPRS Tunnelling Protocol matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study GPRS Tunnelling Protocol?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on GPRS Tunnelling Protocol.