Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-02-24
2001-05-15
Maung, Nay (Department: 2681)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S417000, C455S466000
Reexamination Certificate
active
06233458
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to re-routing of a connection which is routed via some key network elements holding context information about the connection.
BACKGROUND OF THE INVENTION
Telecommunication networks can be divided into circuit switched networks and packet switched networks. In circuit switched networks, the communication is allocated a circuit prior to the beginning of the transmission. An example of a circuit allocated to users A and B is given in
FIG. 1
showing the allocated circuit that can only be used by these users. Information about the recipient of the sent information is readily included in the circuit identity. The main disadvantage of this switching method is that the circuit is reserved even though there is no information to be sent.
In connectionless packet switched networks, the transmission media is common to all users. The information is sent in packets, and all packets contain information about their destination. There is no need to allocate transmission resources for the communication prior to the beginning of the transmission. No packets are transmitted if there is no information to be sent. Thus, the network capacity is not reserved in vain. Based on the information about the destination included in the packet, every network element routes the packet to the next network element. The possible routes for the packets sent by user A to user B are shown in FIG.
2
. Basically, all the packets sent from terminal A to terminal B do not necessarily travel through the same route.
In connection oriented packet switched techniques, a method of establishing virtual circuits is known. A virtual circuit comprises predetermined legs between network elements, and every packet in a connection is routed along the same route. Thus, the information is routed as in circuit switched networks shown in
FIG. 1
, but the communication capacity is not reserved (in vain) if there is nothing to be sent. Every packet includes information about its virtual circuit, and every network element holds context information which tells where to route a packet with a known virtual circuit to and what identifiers to use on the next leg. An example of a technique utilising virtual circuits is the well known ATM (Asynchronous Transfer Mode) technology.
It is also known that the methods of virtual circuit and connectionless packet switching with no virtual circuits can be combined. In such a method, there are some network elements via which all the packets are routed. An example of such a method is given in FIG.
3
. In
FIG. 3
, a virtual circuit passing through network elements
12
and
22
is allocated between the sender A and network element
32
. Network element
32
holds context information for the connection, and knows that the packets on that virtual circuit are destined to receiver B, which is connected to network element
53
. Between network elements
32
and
52
, a connectionless packet switched network is used, and packets from element
32
can be routed to element
52
along different paths. Though, all the packets are routed through network elements
12
,
22
,
32
and
53
, which thus compose a virtual circuit between terminals A and B. It is worth noting that A would not be able to establish a connection with B if e.g. network element
32
would not hold the necessary context information concerning the connection. That information is not held by e.g. network element
31
. Therefore, all the data packets of the connection have to be routed via network element
32
as well as through elements A,
12
,
22
,
53
and B, which are the key network elements of the connection.
An example of a system utilising virtual circuits is the General Packet Radio Service GPRS being specified by ETSI (European Telecommunications Standards Institute). The basic structure of the GPRS network is shown in FIG.
4
. The elements shown are Serving GPRS Support Node (SGSN
1
, SGSN
2
), Gateway GPRS Support Node (GGSN
1
, GGSN
2
) and the BSS (Base Station Subsystem) consisting of a Base Station Controller (BSC
1
, BSC
2
) and many Base Transceiver Stations (BTS
11
, BTS
12
, BTS
21
, BTS
22
). Connections to other networks (not shown), such as Internet or an X.25 network, are made via the GGSN. Additionally, the network includes a Home Location Register (HLR) where e.g. information about the subscribed services is kept.
Basically, when a mobile station MS is located in a cell, every packet destined to or sent by mobile station MS is transmitted through the same BTS, same BSC, same SGSN and same GGSN. The MS cannot establish a connection to the GGSN if the used SGSN does not hold context information for this MS. The mobile MS is located in cell CELL
11
and communicating with a BTS, BTS
11
, through the radio interface Um. Between the BTS and the SGSN, a virtual circuit is established, and all the packets are transmitted along the same route. In the connectionless packet switched network using the Internet Protocol (IP) between the SGSN and the GGSN, the transmission of different packets may use different routes.
The link between the mobile MS and the SGSN is uniquely identified by routing area RA and the Temporary Logical Link Identity TLLI. Routing area consists of one or several cells, and is used in the GPRS mobility management as location information for mobiles in a so-called standby state in which the mobile has no active connections. The TLLI identifies the connection unambiguously within one routing area. A mobile can have multiple simultaneous connections using different protocols, e.g. X.25 and IP. Connections using different protocols are discriminated using a Network Layer Service Access Point Identity NSAPI.
The application layer in the MS sends the SNDCP layer a PDP PDU (Packet Data Protocol Packet Data Unit) which can be, e.g., an IP packet. In the SNDCP layer, the PDU is encapsulated in an SNDCP packet in the header of which the NSAPI is indicated, and the resulting SNDCP packet is sent to LLC layer. The link layer identity TLLI is included in the LLC header. The LLC frames are carried over the air interface Um by the RLC (Radio Link Control) protocol and between the BSC and SGSN by the BSSGP (Base Station Subsystem GPRS Protocol). For downlink packets, the BSS checks the cell identity indicated in the BSSGP header, and routes the cells to the appropriate BTS. For the uplink packets, the BSC includes the BSSGP header the cell identity of the mobile MS based on the source BTS.
Between SSGN and GGSN, the link is identified by the SGSN and GGSN addresses and tunnel identifier TID which identifies the connection in the GGSN and in the SGSN. On the link between the SGSN and the GGSN, the GTP (GPRS Tunnelling Protocol) is used.
GPRS is a system where a kind of a virtual connection is used between MS and GGSN. This connection consists of two separate links, the MS-SGSN link and the SGSN-GGSN link. The MS and the GGSN are not able to communicate with each other if they are not using an SGSN holding the context information for this MS. Therefore, the SGSN in a key network element.
Routing of packets in the GPRS network is presented in the signalling chart of FIG.
5
. In the figure, routing of both mobile originated (MO) and mobile terminated (MT) packets is shown. The routing of MO packets is studied first. The MS sends the BSS a data packet containing the TLLI, NSAPI and the user data. On the link between MS and SGSN, the SNDCP (Subnetwork Dependent Convergence Protocol) protocol on LLC (Logical Link Control) protocol is used. In a simple implementation, one BSC is always using the same SGSN, and therefore its function is to route the packets between many BTS's and one SGSN. In a more complicated implementation, the BSC is connected to a plurality of SGSN's and its routing function is also using the TLLI. In such implementation the key network elements of the connection are the MS, the BTS, the BSC, the SGSN and the GGSN that all hold context information necessary to route the packets belonging to the connection. In the BSS this information is stored in
Haumont Serge
Tikka Mauri
Altera Law Group LLC
Gelin Jean
Maung Nay
Nokia Telecommunications Oy
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