Routing decision in connection-oriented packet network

Details Routing decision in connection-oriented packet network Routing decision in connection-oriented packet network

1999-10-13

2003-05-13

Ton, Dang (Department: 2666)

Multiplex communications

Communication over free space

Having a plurality of contiguous regions served by...

C370S395100

Reexamination Certificate

active

06563811

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to telecommunication systems and particularly to a telecommunication system for implementing a connection-oriented packet network. The telecommunication system comprises at least one switch supporting the management of mobile terminals, at least one mobile terminal and at least one data base for managing mobile terminals or subscribers.
BACKGROUND OF THE INVENTION
The tendency in telecommunication industry is towards new high-quality services the implementation of which requires high bit rates. As network systems advance and grow larger, optimal management of data transmission between networks becomes increasingly important.
Among solutions attracting interest are broadband networks, the bit rates of which typically exceed 2 Mbit/s. The transfer technique selected for such B-ISDN networks (Broadband Integrated Services Digital Network) is ATM (Asynchronous Transfer Mode). ATM transmission technique is a switching and multiplexing solution, particularly associated with a data link layer (OSI Layer 2), that allows a connection-oriented network to be implemented in B-ISDN networks.
The present invention can be applied in connection with various connection-oriented packet networks to which routers (such as a TCP/IP protocol) supporting wireless terminals can be added. The invention will be illustrated using elements and terms of ATM transfer technique, without the invention being, however, restricted to them.
In ATM, an end user's data traffic is conveyed from a source to a destination through virtual connections. The data is transferred in the network through switches in fixed-length packets of 53 octets called ATM cells.
FIG. 1
illustrates the structure of ATM cells. A cell comprises a header of five octets and an information field of 48 octets, which comprises the actual payload. The physical layer can comprise of a plurality of virtual paths multiplexed in an ATM layer. The paths are identified by means of a Virtual Path Identifier VPI. At a User-to-Network Interface UNI the VPI is 8 bits long and at a Network-Node-Interface NNI it is 12 bits. Each virtual path can comprise a plural number of virtual channels identified by a Virtual Channel Identifier VCI of 16 bits.
The main function of the header is to identify an interface number for a cell sequence that is transferred through a virtual channel associated with the connection. In addition to the above, the header also comprises other fields such as a Header Error Control HEC, a Generic Flow Control GFC, a Cell Loss Priority CLP and a Payload Type PT. An ATM cell indirectly comprises information about the address of the receiver, so each cell is an independent information transport unit. The number of cells transferred in a time unit is proportional to the user's bandwidth requirements.
ATM is a connection-oriented communication technique, but because a connection does not exist before it is set up, a connection set-up request must be routed from a source through the ATM network to a destination in just about the same way as packets are routed in packet-switched networks. After connection set-up, the packets travel on the same virtual channel during the connection. The ATM Forum proposes routing to be implemented by a PNNI (Private NNI) protocol, the characteristics of which are described in greater detail for instance in PNNI Specification, version 1.0, ATM Forum document af-PNNI-0055.000, ATM Forum, 1996.
The PNNI protocol functions between ATM switching systems, such as individual switches or entire networks, are connected by PNNI links. A PNNI link can be a physical link or a virtual link. A PNNI link can for instance be a virtual path combining two nodes. With respect to the PNNI protocol, the nodes are logically parallel.
The PNNI is comprised of two components: a PNNI signalling protocol and a virtual circuit routing protocol. The PNNI signalling protocol is used for transmitting ATM connection set-up messages in the network between the user-to-network interface of the source and the destination. UNI signalling is converted to NNI signalling in the destination switch. The virtual circuit routing protocol is used for routing the signalling request through the ATM network. This idea is illustrated in
FIG. 2
, which shows signalling used for setting up a connection between two fixed terminals FT
1
and FT
2
.
The development of the PNNI protocol aims at two primary goals: flexible extendibility and routing based on Quality of Service. The PNNI protocol routes a connection primarily on the basis of a requested Quality of Service (QoS), traffic parameters and the resources available to the network. In connection with the connection set-up request, the desired quality of service is defined and then maintained during the entire connection. This is based on the Connection Admission Control (CAC) performed by the ATM switches, the function of which, simply put, is to ensure that as the switch receives a connection set-up request, it checks whether it can set up the connection without causing interference to existing connections. The switch approves the connection only if no interference is to be expected, otherwise the connection is routed through another switch.
In the PNNI protocol flexible extendibility is implemented by a hierarchical network organization, which involves an exchange of combined availability information between different levels of the hierarchy.
FIG. 3
illustrates the PNNI hierarchy. Each PNNI hierarchy level follows the same recursive network model so that the same mechanisms are used at each hierarchy level. Each hierarchy level comprises groups called peer groups. A peer group is substantially a plurality of groups which all have access to an identical topological database and which exchange with each other link status data. For a peer group at a higher hierarchical level, each lower level peer group appears as-a logical group node exchanging, similarly as a normal node, parameters concerning the status of links and nodes with other nodes at the same level. Each peer group has a node that functions as a Peer Group Leader PGL, performing the functions of a logical group node. The status data of higher level peer groups is aggregated between the hierarchy levels, so the members of the same peer group know the status data of their own group in detail and the data concerning the higher levels with less accuracy. This knowledge depends on the distance between the hierarchy levels of the groups.
The status data of network elements in the PNNI protocol has been proposed to be transferred by Topology State Packets PTSP. The packets comprise status parameters of links and nodes denoting the communication circumstances within the network. Transfer of status data can be activated on the basis of specific events and status data in the PNNI protocol may be flooded at a desired accuracy at regular intervals within the entire network. Flooding makes updated status data available at a selected level in the entire network and members of the same peer group in particular will know the data concerning their peer group in detail.
Members of the same peer group are interconnected by horizontal links. Border nodes are peer group nodes having a link to other peer groups, also to external networks, that do not apply the PNNI protocol. Border nodes in different peer groups at the same hierarchy level determine each other as an uplink to a corresponding peer group and they also broadcast link availability data within the peer group.
An interesting recent development trend is the introduction of wireless data transmission and mobility to connection-oriented data transmission networks. This means that a network is extended over an air interface to wireless terminals. Current standards as such do not support the additional characteristics required by wireless data transmission, but various solutions for implementing mobility management for instance in connection with ATM have already been put forward. The aim is to add wireless data transmission and mobility to the ATM netw

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