Читать книгу Mobile Communications Systems Development - Rajib Taid - Страница 62

In the LTE/EPS mobile communications network, several logical interfaces may have the same protocol stack and its transport network. For example, consider the IP transport‐based logical interfaces: S3 (MME‐SGSN), S4 (S‐GW‐SGSN), S5 and S8 (S‐GW – P‐GW), S10 (MME‐MME), and S11 (MME‐S‐GW) that are used among the several network elements of an LTE/EPS network. These logical interfaces have the same protocol stack on top of the IP transport network, i.e. UDP/IP, which is used to tunnel IP payload from one network element to its peer. Refer to the illustration shown in Figure 3.4. IP payload is tunneled through a protocol called GPRS Tunneling Protocol (GTP) in an encapsulated manner. GTP PDUs between two network elements are transported on top of the underlying IP transport network.

Figure 3.4 LTE/EPS logical interfaces: S3, S4, S5, S8, S10, and S11 protocol stack.

Note that in the case of the LTE/EPS system, the GTP control plane Version 2 (GTP‐C v2) [70] is used in all the logical interfaces mentioned above to carry signaling information between their respective network elements. But in the case of the GPRS/UMTS system, GTP control plane Version 1 (GTP‐C v1) TS 29.060 [67] is used. Similarly, the GTP‐user plane, TS 29.281 [72], protocol is used to carry user traffic/data between their respective network elements.

To achieve successful interoperability between two network elements from two different vendors, it is important to understand the concerned protocol specification, encode/decode, and implement correctly each message/PDUs defined in a particular logical interface and its protocol specification. Different logical interfaces may use different physical transmission media to transport the messages of a logical interface. All the IP transport‐based mobile communications protocols will use theStream Control Transmission Protocol (SCTP) RFC 4960 [17] or UDP protocol suite and UTP CAT cable as physical media.