Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1998-09-01
2003-11-04
Nguyen, Steven (Department: 2663)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C455S436000
Reexamination Certificate
active
06643279
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to handoff control for point to multipoint connections in mobile ATM networks, and for the first time provides for handoff control for a mobile participating in a point to multipoint connection.
This invention relates to a system for handoff control in a point to multipoint mobile ATM network. The invention is embodied in a system, a method, and a program product for handoff control in a point to multipoint mobile ATM network
2. Related Art
Asynchronous transfer mode (ATM) networks provide for point to point (PTP) and also for point to multipoint (PMP) connections. In PTP connections, one station communicates with only one other station.
In PMP connections, one station broadcasts to a plurality of other stations. The station so broadcasting may be referred to as a broadcasting station or a root station. The stations so receiving the broadcast of the root station may be referred to as receiving stations or as leaf stations. PMP connections are useful when it is desired to send a broadcast to several stations, for example, in an educational lecture setting. Using a PMP connection over an ATM network, a root station at a university could broadcast a lecture to students participating at leaf stations.
Stations in an ATM network connect to the network at switching nodes of the network. ATM switching nodes may be interconnected by links. In a PMP connection, the node to which the root station connects may be referred to as the root node of the PMP connection. Similarly, the nodes to which leaf stations connect may be referred to as leaf nodes. Obviously, a leaf node may provide service to more than one leaf station. Communication that moves in the direction away from the root station toward the leaf stations may be referred to as downstream communication; communication that moves in the direction toward the root station may be referred to as upstream communication.
FIG. 1
shows a plurality of ATM switching nodes. Some of the nodes are interconnected by links. The nodes are represented by circles, and the links are represented by straight lines between the nodes.
Today, ATM networks may include support for mobile terminals. In mobile ATM networks, a mobile terminal (or, simply, a mobile; also referred to as a MT) communicates with the ATM network via a base station (BS). The BS, for the purposes of this discussion, may conceptually be considered as part of a switching node. It is not necessary for all switching nodes to be BS's. A BS may be considered to be a special kind of switching node having communication facilities for directly communicating with MT's. Mobile ATM networks provide for handoff for PTP connections when an MT in a PTP connection moves from an area served by one BS into an area served by another BS. That is, a MT may have its PTP ATM connection handed off between different BS's. The BS that the MT leaves may be referred to as the old base station, or OldBS. The BS that the MT goes to may be referred to as the new base station, or NewBS.
Some confusion is possible in using the term “cell” when discussing mobile ATM networks. This confusion arises because mobile networks have historically used “cell” to indicate the service area of a BS. In other words, a MT moving from one cell to another will have its call handed off between an OldBS and a NewBS. In ATM networks, however, “cell” has been used to refer to the ATM cell which serves as the basic unit for protocol processing and switching. To avoid confusion, herein the term “cell” refers to the ATM cell unless otherwise indicated, and the service area of a BS will be referred to as a service area.
An ATM network may operate according to a Private Network to Network Interface (PNNI) hierarchy. The PNNI hierarchy provides for scalability of networks and is highly advantageous. The PNNI hierarchy provides that peer entities may be grouped together. A conceptual overview of the PNNI hierarchy will now be given.
FIG. 2
shows one way in which the nodes of
FIG. 1
might be grouped at a high level.
FIG. 2
does not show the links between the nodes for the sake of clarity.
More particularly, the nodes above the dashed line may be thought of as belonging to an overall group referred to as group B. The nodes below the dashed line may be thought of as belonging to a group A. Group A and group B are defined at the same high level, and may be referred to as peers of each other. That is, group A is a peer of group B.
FIG. 3
shows a lower level grouping of nodes. Again, the links between the nodes have been omitted for clarity. In particular, the nodes of peer group B have been grouped into groups B.
1
and B.
2
; the nodes of peer group A have been grouped into groups A.
1
, A.
2
, A.
3
, and A.
4
. It will be appreciated that these lower level groups are peers of each other. That is, groups B.
1
and B.
2
are peers of each other and may also be referred to as peer groups. Groups A.
1
, A.
2
, A.
3
, and A.
4
are peers of each other.
At its lowest level, a network may be understood to include a plurality of nodes, each which has a switching station or the like. Since these nodes are all at the same level, they are peers.
By convention, a switching node may be named based on the names of the groups of which it is a part. Thus, a switching node named A.
2
.
1
may be in highest level group A, in the next level group A.
2
, and may be switching node number
1
within group A.
2
. Hence, the identifier or name “A.
2
.
1
”. This naming convention may be referred to as a hierarchical naming convention.
FIG. 4
shows how the switching nodes in the exemplary network might be named under the foregoing convention.
The PNNI hierarchy thus provides for peer groups of an arbitrary number of levels of abstraction. The scalable PNNI hierarchy helps hide from upper levels the impact of changing the network at lower levels, and also helps hide from other peer groups any changes made inside one peer group.
To support PMP connections, a PNNI ATM network requires that a PMP connection must have a consistent tree topology at every level. More particularly, the root of the tree in a PMP connection is the root station. The leaves of the tree in a PMP connection are the leaf stations. The leaves must connect to the root via branches which do not overlap or cross. The prohibition of branch overlap/crossing allows a PMP connection to exist in harmony with the scalability of the PNNI network over all of the different levels of abstraction.
The foregoing tree topology requirement imposed by the PNNI hierarchy does not substantially affect handoff for P
T
P ATM connections during handoff between BS's. PTP handoff may be accomplished in a straightforward manner. The foregoing tree topology requirement does, however, pose serious implications for PMP ATM connections during handoff. In particular, unless the proper handoff control is provided, it is possible that, when a MT participating as a leaf station in a PMP connection moves from the service area of the OldBS to the NewBS, the handing off of the connection to the NewBS might cause two branches impermissibly to cross or overlap.
This situation will be explained with respect to an example and
FIGS. 5-12
.
FIG. 5
shows the exemplary network with the switching node addresses labeled, and the links between switching nodes as straight lines. In
FIG. 5
, there is a root station RT which is connected to switching node B.
2
.
4
. A first leaf station, L
1
, is connected to switching node A.
2
.
3
. A second leaf station, L
2
, is connected to switching node A.
4
.
4
.
FIG. 6
shows a PMP connection established through the ATM network by which L
1
and L
2
receive communications from RT. In
FIG. 6
, peer group A.
1
in its entirety, several other switching nodes, and several links have been omitted for clarity. The PMP connection is shown as a heavy, dark line. Links not part of the PMP connection are shown as faint lines. The PMP connection includes switching nodes B.
2
.
4
, B.
2
.
3
, and B.
2
.
2
of peer
Acharya Arup
Li Jun
Duong Duc
Nguyen Steven
Sughrue & Mion, PLLC
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