Mobile IP strategy of GPRS

Absrtact: This paper discusses a method of implementing Mobilt IP support on GPRS, and simply analyzes the evolution strategy.

First, the introduction

The IP protocol does not effectively support moving across subnets because the IP address is associated with a particular network segment, and the movement of the terminal destroys the association so that communication does not work properly. The mobile IP and ETSI proposed by IETF are all designed to solve the problem of the frequent terminal mobile. There are two main modes of wireless Mobile Access IP network: one is wireless LAN; the other is based on the public cellular mobile system data network, more typical is superimposed on the GSM network GPRS. There are also a number of new wireless access modes, such as Bluetooth and 3G.

Various systems have their own characteristics in the implementation of mobility management. Mobility management is essentially divided into macro-domain and honeycomb-level. In contrast, macro-level management is less sensitive to low-level differences, so the standards are very similar in nature, while cellular-level management takes into account the working mode of wireless transmission, often with different methods. The IETF proposes MOBILEIP for the management of macro-level, and proposes ce11ular IP for the management of the honeycomb level. MOBILEIP is gradually being adopted by more and more systems, because the current IP is already the mainstream Network layer protocol, MOBILEIP is the most versatile and convenient for carrying mobile IP service, and can dissolve into the existing IP system better than before. Ce11ul. The spread of RIP is a bit harder because using a third tier of management at the cellular level is bound to consume wireless bandwidth. (Computer science)

At present, wireless LAN, CDPD, IS-9 5 including later 3G are adopted or based on MOBILEIP, while GPRS is another set of complete coverage from the macro-level to the Honeycomb level specification. In essence, many mechanisms of GPRS are very close to MOBILEIP, but GPRS's original design goal is a universal wireless access means, can carry various network layer protocol, and IP over everything is unstoppable. The "universal" hosting mode has little practical commercial significance at present, and some ideas of GPRS can only be discussed theoretically.

We hope that no matter which access means, such as wired LAN, wireless LAN or GPRS, can support IP hosting in the same mode. Even if the terminal is switching between several access modes, it can still maintain the connectivity of the IP, which is called "on the Fly". To achieve this, you first need to agree on a protocol that supports terminal mobility. Therefore, how to achieve the support of MOBILEIP on GPRS is a substantial step to the IP of "on Thefly".

Second, Mobile IP

The IETF presented a series of MOBILEIP recommendations. The basic concept of MOBILEIP is that regardless of where the terminal moves, it always takes the same IP address and maintains a TCP connection that is active, ensuring transparency of the upper application.

The concept of a home agent (HA, external agent, foreign agent (FA) and forwarding address (care of addresses) is proposed in Mobile IP.

Each mobile terminal is permanently assigned an IP address by ha. When the terminal moves to another subnet, the FA of the subnet assigns a temporary address to the terminal, that is, an external proxy forwarding address. Temporary addresses can be shared dynamically by multiple visiting terminals. Ha and FA can declare their services, and the terminals in which new visits are made can inquire to confirm that there is a suitable agent. After roaming the mobile terminal, it is necessary to register the address with HA, and the registration can be completed by the terminal directly or by the FA, depending on the attachment mode of the terminal to FA. When the registration is completed, the data to the mobile terminal received at the place of attribution is passed through the HA through the tunnel way to FA.

The traditional Mobile IP will form the so-called "triangular" route: Because the packet always arrives first, then the HA passes through the tunnel to the FA,FA and then sends the packet to the terminal. This "circle" mode is not good for the IP network to support a strong real-time business, so someone proposed a number of routing optimization MOBILEIP, from the originator of the data directly routed to the address of the FA. In the IPV6, the support of terminal mobility is clearly proposed.

Three, Mobileip Overgprs method

Mobile IP over GPRS principle is to try not to make large changes to the existing GPRS system: for the terminal does not support MOBILEIP can still maintain the original mode of operation without any impact To support MOBILEIP terminal, it can obtain mobile IP support in GPRS network environment.

The Mobileip OVERGPRS approach is to integrate the external agent functionality into the GGSN. In the case of roaming, if the GGSN of the visit can provide the FA function, then the GGSN can access the extranet through the visiting place, of course, if the GGSN cannot provide the FA function, then only the GGSN of the place of attribution will be used. Certainly does not require the visit the place all GGSN can provide the FA, as long as has one GGSN to have this function, the mobile terminal may choose this GGSN as the external proxy.

GPRS and mobile IP are used to support roaming IP packet Packaging: GPRS using GTP protocol, and mobile IP using IP in IP. The mobile IP tunnel ends with the mobile host's forwarding address (care-of addresses), where the original packet is removed from the tunnel and forwarded to the mobile host. There are two ways to transfer addresses, that is, the external proxy referral address (the address of the external agent registered by the mobile host) and the federated location of the address (that is, the local address that the mobile host obtains externally, which is associated with the network address it belongs to). In the cellular environment, the frequency resources are very valuable, the use of external proxy forwarding address means that the tunnel is established to the external agent, and the use of Joint location transfer address mode, the tunnel has to be established to the mobile host, in the wireless segment also need IP encapsulation, there are relatively large overhead. In the GPRS system, the GTP tunnel extends only to the SGSN, similar to the external proxy forwarding address.

GGSN in the mobile terminal IP address and tid (GPRS tunnel ID), the Division of the Association, TID played a joint location of the transfer address, but it is not the FA local IP address. In order to minimize the existing GPRS system to modify the signaling system, to maintain the high utilization of wireless bandwidth characteristics.

(1) The user enters the APN that corresponds to mobile IP function on the terminal, for example the APN name is MOBILEIPV4FA.

(2) The terminal receives the User Service request, initiates "activates the PDP context request" message to the SGSN, the Message APN field =MOBILEIPV4FA, the request does not contain the PDP address.

(3) SGSN According to APN, select the GGSN that can provide the FA function, and send "create PDP context request" message to the GGSN.

(4) If GGSN accepts PDP context establishment request, then sends a response to SGSN, but still does not assign PDP address.

(5) SGSN sends "Activate PDP context acceptance" message to terminal.

(6) At this time GGSN began to play the role of FA, in the creation of the GPRS tunnel to the terminal to send "proxy declaration" message, from the message in the terminal know the FA transfer address. Note that GGSN does not need to wait for the terminal to send a "proxy request" message as usual and then resend the message, because GGSN knows it is a roaming terminal.

(7) In the GTP environment, the terminal also starts to shift from the signaling plane to the transmission Hander and sends the registration request message to GGSN (FA) on the GPRS tunnel created.

(8) GGSN obtains the IP address of the terminal, establishes the association between the IP address and the TID, and forwards the "agent request" message to the terminal ha.

(9) GGSN received the response of Ha, GGSN from the IP inip tunnel "registration Answer" message, analysis of the terminal address, find out the corresponding TID address.

(10) The "registration answer" message in the GPRS tunnel relay to the terminal to complete the registration of MOBILEIP.

(11) Carry out the normal Mobile IP packet transmission.

(12) Users through the AT command to terminate the Terminal service, the terminal will be sent to the SGSN "to activate the PDP context request" message, SGSN to GGSN send "remove PDP context request" GGSN response SGSN, while shutting down the GPRS tunnel, cancellation of Terminal address and Tid Association, and send "remove PDP context response" to SGSN, SGSN to Terminal "to activate PDP context response".

Four, GPRS to Mobile IP support strategy

We carefully examine the GPRS architecture, GPRS introduced SGSN and GGSN two network entities have its profound background. GPRS support General 3rd Layer Network protocol is indeed a "all-inclusive" of the idea, the history of telecommunications "all-inclusive" precedent many, such as ISDN, ATM, etc., but this model is required to obtain commercial success. GPRS can theoretically support X.25, IPX, etc., but in fact there is virtually no such product.

The technical thinking of "all-inclusive" has its technical reference and merit, such as the gradual evolution of ATM to MPLS, and the separation of GPRS SGSN and GGSN provides a good foundation for the introduction of new network layer protocols. Adding a new network layer protocol requires only GGSN support, SGSN no modification is required. Mobileip is also a special network layer protocol, so the introduction of mobile IP support in GGSN is very consistent with the GPRS architecture: GGSN can be distinguished from other services provided by a special APN identification MOBILEIP service.

In the initial stage, each region needs only individual GGSN to support MOBILEIP, and if mobile IP demand increases, the GGSN can be upgraded gradually. In addition, some routing optimization strategies can be introduced. Routing optimization consists of two parts: one refers to mobile IP category, mainly to avoid packets are always passed HA to the FA, of course, the host, Ha, FA functions have to make some improvements; the second refers to the SGSN and GGSN, SGSN need to choose the right to provide mobile IP GGSN.

V. Concluding remarks

In the existing GPRS system to achieve the support of MOBILEIP is a "superposition" mode, in fact GPRS has a lot of mobility management functions in the MOBILEIP is not supported. The next generation of mobile data communication, such as 3G, is starting with the MOBILEIP, absorbing some of the advantages of GPRS, to establish an "integration" mode, so as to efficiently solve the problem of mobile IP.