Indian Patents
Title of Invention

A PROXY SWITCH FOR A MOBILE COMMUNICATIONS NETWORK AND A METHOD OF COMMUNICATING MESSAGES BETWEEN A MOBILE NETWORK AND AN ALTERNATIVE COMMUNICATION NETWORK
Abstract A proxy switch (300), communication methods, and communication logic for use in a mobile network are described. A proxy switch (300) is deployed between a base station subsystem (107)and a mobile switching center (110). It receives signaling messages and either retransmits them, blocks them, or siphons them to an alternative network. Besides providing an ability to offload mobile traffic it provides a platform for new communication services.
Full Text A PROXY SWITCH FOR A MOBILE COMMUNICATIONS
NETWORK AND A METHOD OF COMMUNICATING
MESSAGES BETWEEN A MOBILE NETWORK AND AN
ALTERNATIVE COMMUNICATION NETWORK
Background of the invention
The present invention relates to a proxy switch for a mobile communications
network and a method of communicating messages between a mobile network and an
alternative communication network to improve capacity and cost-effectiveness of the
communications network and to offer a platform for new mobile services.
2. Discussion of Related Art
All modern mobile communication systems have a hierarchical arrangement, in
which a geographical "coverage area" is partitioned into a number of smaller
geographical areas called "cells." Referring to figure 1, each cell is preferably served by
a Base Transceiver Station (BTS) 102a. Several BTS 102b-n are aggregated via fixed
links 104a-n into a Base Station Controller (BSC) 106a. The BTSs and BSC are
sometimes collectively referred to as the Base Station Subsystem (BS) 107. Several
BSCs 106b-n may be aggregated into a Mobile Switching Center (MSC) 110 via fixed
links 108a-n.
The MSC 110 acts as a local switching exchange (with additional features to
handle mobility management requirement, discussed below) and communicates with the
phone network (PSTN) 120 through trunk groups. Under U.S. mobile networks, there is
a concept of a home MSC and a Gateway MSC. The home MSC is the MSC
corresponding to the exchange associated with a Mobile Station (MS); this association ...s
based on the phone number, e.g., area code, of the MS. (The home MSC is responsible
for the HLR discussed below). The Gateway MSC, on the other hand, is the exchange
used to connect the MS call to the PSTN. Consequently, some times the home MSC and
the Gateway MSC arc the same entity, but other times they are not (e.g., when the MSL
roaming). Typically, a Visiting Location Register (VLR) 116 is co-located with the MS.
110 and a logically singular HLR is used in the mobile network. As will be explained

below, the HLR and VLR are used for storing many types of subscriber -information and
profiles.
Briefly, a number of radio channels 112 are associated with the entire coverage
area. The radio channels are partitioned into groups of channels allocated to individual
cells. The channels are used to carry signaling information to establish call connections
and the like, and to carry voice or data information once a call connection is established.
At a relatively high level of abstraction, mobile network signaling involves at
least two main aspects. One aspect involves the signaling between an MS and the rest of
the network. With 2G ("2G" is the industry term used for "second generation") and later
technology, this signaling concerns access methods used by the MS (e.g., time-division
multiple access, or TDMA; code-division multiple access, or CDMA), assignment of
radio channels, authentication, etc. A second aspect involves the signaling among the
various entities in the mobile network, such as the signaling among MSCs, VLRs, HLRs,
etc. This second part is sometimes referred to as the Mobile Application Part (MAP)
especially when used in the context of Signaling System No. 7 (SS7).
The various forms of signaling (as well as the data and voice communication) are
transmitted and received in accordance with various standards. For example, the
Electronics Industries Association (EIA) and Telecommunications Industry Association
(TIA) help define many U.S. standards, such as IS-41, which is a MAP standard.
Analogously, the CCITT and ITU help define international standards, such as GSM-
MAP, which is an international MAP standard. Information about these standards is well
known and may be found from the relevant organizing bodies as well as in the literature,
see, e.g., Bosse, SIGNALING IN TELECOMMUNICATIONS NETWORKS (Wiley 1998).
To deliver a call from an MS 114, a user dials the number and presses "send" on
a cell phone or other MS. The MS 114 sends the dialed number indicating the service
requested to the MSC 110 via the BS 107. The MSC 110 checks with an associated VLR
116 (more below) to determine if the MS 114 is allowed the requested service. The
Gateway MSC routes the call to the local exchange of the dialed user on the PSTN 120.
The local exchange alerts the called user terminal, and an answer back signal is routed
back to the MS 114 through the serving MSC 110 which then completes the speech path
to the MS. Once the setup is completed the call may proceed.

To deliver a call to a MS 114, (assuming that the call originates from the PSTN
120) the PSTN user dials the MS's associated phone number. At least according to U.S.
standards, the PSTN 120 routes the call to the MS's home MSC (which may or may not
be the one serving the MS). The MSC then interrogates the HLR 118 to determine
which MSC is currently serving the MS. This also acts to inform the serving MSC that a
call is forthcoming. The home MSC then routes the call to the serving MSC. The
serving MSC pages the MS via the appropriate BS. The MS responds and the
appropriate signaling links are setup.
During a call, the BS 107 and MS 114 may cooperate to change channels or
BTSs 102, if needed, for example, because of signal conditions. These changes are
known as "handoffs," and they involve their own types of known messages and
signaling.
One aspect of MAP involves "mobility management." Briefly, different BSs and
MSCs may be needed and used to serve an MS, as the MS 114 roams to different
locations. Mobility management ensures that the Gateway MSC has the subscriber
profile and other information the MSC needs to service (and bill) calls correctly. To this
end, MSCs use a Visiting Location Register (VLR) 116 and a Home Location Register
(HLR) 118. The HLR is used to store and retrieve the mobile identification number
(MIN), the electronic serial number (ESN), MS status, and the MS service profile,
among other things. The VLR stores similar information in addition to storing an MSC
identification that identifies the Gateway MSC. In addition, under appropriate MAP
protocols, location update procedures (or registration notifications) are performed so thai
the home MSC of a mobile subscriber knows the location of its users. These procedures
are used when a MS roams from one location to another or when a MS is powered on
and registers itself to access the network. For example a location update procedure may
proceed with the MS 114 sending a location update request to the VLR 116 via the BS
107 and MSC 110. The VLR 116 sends a location update message to the HLR 118
serving the MS 114, and the subscriber profile is downloaded from the HLR 118 to the
VLR 116. The MS 114 is sent an acknowledgement of a successful location update Tne
HLR 118 requests the VLR (if any) that previously held profile data to delete the data
related to the relocated MS 114.

Figure 2 shows in more detail the signaling and user traffic interfaces between a
BS 107 and an MSC 110 in a CDMA mobile network. The BS 107 communicates
signaling information using the A1 interface. The A2 interface carries the user traffic
(e.g., voice signals) between the switch component 204 of the MSC and the BS 107. The
A5 interface is used to provide a path for user traffic for circuit-switched data calls (as
opposed to voice calls) between the source BS and the MSC.
As the number of cell sites or the number of subscribers grows, the load on the
MSC 110 increases. This increased load forces the service provider to add more capacity
to the system. Typically, to add more capacity, the service provider adds more switch
modules to the MSC or deploys additional MSCs in the network. Either alternative
involves significant cost.
Moreover, subscribers are demanding newer services, e.g., "data calls" to the
Internet. For some of these services MSCs are not cost effective because they were
primarily designed for voice calls. Integration of new services into the MSC is
complicated or infeasible because of the proprietary and closed designs used by many
MSC software architectures. That is, the software logic necessary to provide the services
is not easy to add to the MSC 110. Often, a switch adjunct is used to provide such
services. For example, an Inter-Working Function (IWF) is an adjunct to route a data
call to the Internet. Either approach - integrating functionality into the MSC or adding a
trunk-side adjunct - involves the MSC in the delivery of service. Since the new service
is expected to spur demand, integrating new services via MSC design changes or through
trunk-side adjuncts is likely to exacerbate network congestion at the MSC and require
costly MSC resources.
Summary
The invention provides systems and methods of mobile communication. In
particular, switching operations are performed between at least one mobile switching
center (MSC) and at least one base station subsystem (BS). The switching, according to
one aspect of the invention, allows communication traffic to be siphoned to or from aa
alternative network. According to another aspect of the invention, the switching is
transparent so that neither the MSC or the BS needs any changes to work with the
inventive switching. According to another aspect of the invention, the MSC may be

mapped to users independent of geography. Thus an MSC servicing a call may be
mapped to the user rather that to a particular cell in which the user is in.
The switch includes signaling message handling logic to receive signaling
messages from the MSC and BS in accordance with a mobile signaling protocol.
Message interception logic cooperates with the signaling message handling logic and
sends an acknowledgment message to an MSC or BS that transmitted a signaling
message. The message interception logic also prevents the signaling messages from
being forwarded to the other of the BS and MSC respectively. Message conversion logic
cooperates with the signaling message handling logic and converts a signaling message
from one of the MSC and BS into a converted signaling message for transmission to the
other of the BS and MSC, respectively. Message transmission logic cooperates with the
signaling message handling logic and transmits signaling messages from one of the MSC
and the BS to the other of the BS and MSC, respectively.
Under one aspect of the invention, a set of bearer circuits from the BS are
allocated. Signaling messages between the MSC and the BS are received and analyzed to
determine if they correspond to the allocated set of bearer circuits. If so, control
information in the signaling messages is conveyed to an alternative communication
network; and information carried on the set of bearer circuits is siphoned to the
alternative network.
According to another aspect of the invention, a proxy switch may be used in a
mobile communications network having at least two MSCs and at least one BS. MSC
selection logic maps an identified user to one of the at least two MSCs and message
transmission logic transmits signaling messages received from the BS to a mapped MSC
by inserting in a signaling message from the user a point code that corresponds to the
mapped MSC.
BRIEF DISCRETION OF THE ACCOMPANYING DRAWINGS
In the Drawing,
figure 1 is a system diagram of prior art mobile networks:

figure 2 illustrates a prior art interface between a BS and a mobile switching
center in a prior art mobile network;
figures 3 A-B illustrates a proxy switch and certain deployments in a mobile
network according to preferred embodiments of the invention;
figure 4 illustrate an exemplary data plane of a proxy switch according to a
preferred embodiment of the invention;
figure 5 illustrates mobility management logic of a proxy switch according to a
preferred embodiment of the invention;
figures 6A-B illustrate supplementary feature logic of a proxy switch according
to a preferred embodiment of the invention;
figure 7A illustrates fault management logic of a proxy switch according to a
preferred embodiment of the invention;
figure 7B illustrate FSN and BSN counters of a proxy switch according to a
preferred embodiment of the invention;
figure 8 illustrates message siphoning logic of a proxy switch according to a
preferred embodiment of the invention;
figure 9 illustrates software process architecture of a proxy switch according to a
preferred embodiment of the invention;
figure 10 illustrates software process architecture of a proxy switch according to
a preferred embodiment of the invention;
figure 11 illustrates software module architecture of certain processes of a proxy
switch according to a preferred embodiment of the invention; and
figures 12-14 are simplified architectural diagrams to show message flow and
software process interaction.
Detailed Description
Preferred embodiments of the invention provide a proxy switch and a method of
use thereof in a mobile communications network. The proxy switch is preferably
positioned between an MSC and a BS, "transparent" to the other components, meaning
that neither the BS or the MSC needs to know of the proxy switch nor do they need to

alter their behavior or functionality because of the existence of the proxy switch.
Instead, the BS and MSC operate as they do conventionally, ignorant of the existence of
the proxy switch.
Among its many advantages, the proxy switch may help alleviate congestion in a
mobile network. For example, the proxy switch may be used (a) to siphon MS-
originated communication traffic off the network before it gets to an MSC and (b) to
send the siphoned traffic to the desired destination via an alternative network, such as a
packet-based network. Similarly, the proxy switch may be used to deliver
communications to an MS from an alternative network. Consequently, costly MSC and
PSTN resources may be avoided, and the proxy switch may be used to increase network
capacity cost effectively.
In addition, the proxy switch defines a set of enabling functions that allow new
communication services to be provided to the network. For example, using the proxy
switch, new call waiting services may be integrated into the mobile network.
Figure 3A shows one preferred deployment of a proxy switch 300, in which the
proxy switch 300 is positioned between the BS 107 and the MSC 110. Only a subset of
trunks 306 carrying user traffic needs to be terminated on the proxy switch; other trunks
308 may directly connect the MSC 110 and BS 107. All control links 312 from BS 107
terminate at proxy switch 300. The proxy switch includes a control plane 302 and a data
plane 304 (also known as a "bearer plane"). The control plane 302 handles all the
signaling traffic, and the data plane 304 handles all the user traffic for the trunks
connected to the proxy switch.
Under the preferred deployments, the proxy switch 300 communicates according
to the same signaling protocol on both sides of the control plane 302. For example, in
embodiments suitable to CDMA technology, the signaling links 312 between the BS 107
and the proxy switch 300 convey information according to the IS-634/IOS Al interface.
Similarly, the signaling links 314 between the MSC 110 and the proxy switch 300
convey information according to the Al interface. This situation contrasts with other
mobile switching complexes such as the MSC or the BS in which different signaling
standards are used for communication on the different sides of the switch. The MSC for

example has A1 interface on one side of the complex and communicates according to
SS7/ISUP on the other (i.e., the PSTN side of the switch).
Under other embodiments, the proxy switch terminates newer ingress interfaces
A8, A9, and egress interfaces A10, Al 1 for CDMA2000 for carrying packet-based
traffic, both signaling and user traffic. Current MSCs do not support these ingress
interfaces.
The proxy switch's data plane 304 uses the same standards on each side of the
switch. BS-side trunks 306, in CDMA embodiments, communicate according to the A2
and A5 interfaces, depending on whether voice or data, respectively, is being carried on
the trunks. Likewise, MSC-side trunks 307 use the same interfaces. In contrast, the
MSC has A2/A5 on one side but communicates according to PSTN 64kb/s pulse coded
modulation standards on the other side.
In addition, whereas all of the other entities in a mobile network use their own
point codes within their signaling ("point codes" are used as unique identifiers in the
network), in certain embodiments, the proxy switch 300 does not use its point code and
instead uses the point codes contained in the messages it receives. By using the point
codes of the BS or MSC, instead of the point code for the proxy switch, transparency of
the proxy switch is facilitated.
Under certain embodiments, there is a one to one correspondence between an
MSC and a proxy switch. Several BSs may work with a single proxy switch.
Figure 3B shows another preferred deployment, In the deployment of figure 3B,
the proxy switch 300 may be in communication with more than one MSC 110j-110k.
The control plane 302 of the proxy switch 300, like the deployment of figure 3 a, may
receive control signals 312a-n from several BSs 107a-n. In addition, the data plane 304
may receive trunks 306a-n from several BSs. Unlike the deployment of figure 3a,
however, the deployment of figure 3b also receives and sends information on signaling
links 314j-k to multiple MSCs 110j-k.
The deployment of figure 3b may be configured to distribute the load on the
system better, to improve reliability (by providing an alternative path to an MS), and to


provide services that consistently match a user's profile. Under one embodiment that
uses the deployment of figure 3B, the system may be configured so that calls from a
given caller are routed to an MSC that handles most of the user's traffic (as opposed to
merely being the geographical location where the user turns on his or her MS 114). This
determination may be based on statistical monitoring or may be configured into a user's
profile. By so configuring the system, the amount of location update messages and the
like may be reduced. Under other embodiments, the proxy switch may be configured so
that calls are directed to MSCs that are relatively underutilized. In this fashion, system
administrators may better tailor the load on the entire communication system under
management. In addition, calls may be routed to MSCs that provide services consistent
with a given user's profile.
The proxy switch 300 includes software that accepts all signaling messages and,
depending on the message and the state of the system, performs at least one of the
following:
1. passes the message unaltered to the MSC or BS addressed in the message;
2. intercepts messages between the MSC and BS;
3. for some intercepted messages, converts the intercepted messages to a
different message and sends the converted message in place of the original,
intercepted message to the MSC or BS addressed in the intercepted message;
4. siphons the message from the mobile- and PSTN-based network to an
alternative network.
The types of actions performed in each case along with the triggering events are
described below.
In many instances, particularly when a message from an MS 114 is siphoned and
the traffic is directed to an alternative network, the proxy switch 300 may act as an MSC
110. In such a role, the proxy switch fulfills the responsibilities and roles that a
traditional MSC would perform. Some of these functions and roles pertain to mobility
management. Consider the case of a roaming MS; as it roams from one cell to another it
may roam to a cell served by a different MSC, thus necessitating a handoff between the
source and target MSCs. If the proxy switch 300 has siphoned the message and the
call/session has been directed to an alternative network, then the handoff has to be

managed by the proxy switch analogously to the way a handoff would be managed by a
conventional MSC. The proxy switch has to ensure that the appropriate databases are
updated with the new location of the MS. Another function of the proxy switch pertains
to the assignment of resources. In particular, when an MS initiates a message requesting
a new call/session, appropriate circuits (channels) need to be assigned for this session.
Depending on the configuration of the system and the system state, the proxy switch
makes such assignments analogously to the way conventional MSC assigns circuits.
Figure 4 shows an exemplary deployment in which the proxy switch 300 is
connected to several alternative networks, such as an IP backbone 412 or an alternative
circuit-based network 414, e.g., a different carrier. These alternative networks may be
used to carry voice and/or data traffic to desired destinations while avoiding in whole or
in part the PSTN 120 along with the costly resources of MSC 110. Alternatively, these
arrangements may be used so that circuit traffic could be backhauled to a different
network; for example, circuit traffic from Nashua, NH could be backhauled to an MSC
in Waltham MA. Or, they may be used to connect to other networks. For example, the
IP backbone 412 may communicate with IP voice networks 418 or the Internet 416. As
will be explained below, when siphoning traffic to an alternative network both control
information (e.g., from the signaling messages) and voice or data from the bearer circuits
on links 306 may be sent via an alternative network.
To support these exemplary deployments and to maintain transparency, preferred
embodiments of the invention provide certain core functionality. The core functions
facilitate siphoning of traffic from the trunks 306 before they reach the MSC 110;
facilitate the injection of traffic onto trunks 306 from alternative networks; facilitate
transparent operation; serve as building blocks for higher level applications; and/or
support error recovery procedures.
Procedure for mobility management in the presence of a pror\> switch
When a MS 114 roams in a network, standard procedures for mobility
management require the MS to issue location updates or registration notifications as the.
MS roams from one cell to another. These updates are received by the MSC 110 (via the
BSC), and eventually, the VLR/HLR complex is updated with the new location of the
MS. However, the standard procedures may not work in certain embodiments and

system states of the invention. For example, the MS may be involved in -a call that does
not use the MSC (e.g., one being handled by an alternative network) yet the MS may
need to issue location update or handoff messages. To this end, preferred embodiments
of the invention provide mobility management logic for the proxy switch, described with
reference to figures 3 and 5 conjointly.
If a location update or handoff message is received from the BS 107 by the proxy
switch 300, the proxy switch 300 determines whether the MS is currently involved in a
call 505. If the MS is not involved in a call, then the proxy switch 300 allows the
location update message to pass through 510 to the MSC 110. The MSC 110 then
updates 515 the VLR 116 as it does conventionally. The logic flow then ends 599.
If the proxy switch 300 determines that the MS 114 is involved in a call, the
proxy switch checks 520 to see if the MSC 110 is involved in the call. For example, this
may be done by analyzing state information for the call (also known as a "session")
maintained by the proxy switch. If the MSC is involved in a call with the MS, then the
proxy switch proceeds as described above, except that this time a handoff message is
passed through to the MSC 110.
If the MS is involved in a call and the MSC is not involved with that call, the
proxy switch 300 intercepts the handoff message 525 from the BS 107 and, using the
information in the handoff message, converts the handoff message into a location update
message 530. The location update message is then sent 535 to the MSC 110 and the
proxy switch updates its own local database (not shown) reflecting the change. This local
database serves as a VLR for the proxy switch and holds all of the information that a
VLR does (since the proxy switch at times needs to function akin to an MSC). The
proxy switch 300 then sends an acknowledgment message 540 to the BS 107. The logic:
flow then ends 599.
Procedure for managing supplementary features in the presence of a proxy switch
Under preferred embodiments of the invention, an MS may be busy at times
when the MSC believes the MS is idle; for example, the MS may be busy with a data of
voice call that is being handled by an alternative network when the MSC is attempting to
deliver a call to the MS from the PSTN 120. To support such a situation, the proxy


switch 300 provides logic for informing the MS of such a situation. Usinglhis logic,
supplementary services, such as traditional call waiting, may be provided by the proxy
switch. Moreover, new forms of call waiting and other new services may be built on this
core support function.
Referring to figures 3 and 6A conjointly, when a call comes into the proxy switch
300 from the MSC 110, the proxy switch determines whether or not the MS is involved
in a call at the time the message comes in 602. If the MS is not busy, then the proxy
switch 300 allows the MSC-originated message to pass through to the BS 603. The logic
flow then ends 699.
If the MS is busy, the proxy switch then determines 604 if the MS call is being
handled by the proxy switch but not by the MSC; for example, the call may be handled
by an alternative network connected to the proxy switch (see figure 4) in which case the
proxy switch needs to handle the call acting akin to an MSC; the proxy does not simply
let messages pass through. If the call is being handled by the proxy switch but not by the
MSC, the proxy switch intercepts 605 the call from the MSC 110, and converts 606 the
intercepted message into a feature notification message. The proxy switch 300 then
issues 607 the feature notification message to BS 107 for subsequent transmission to the
MS 114, which will be used to notify the user of the incoming call. The proxy switch
intercepts 608 any responses from the BS to the feature notification message and acts
accordingly. How the proxy switch acts depends on the application using this logic.
If the MS is involved in a call handled by the proxy, and also involved with a call
handled by the MSC, then the proxy switch takes an action 609 identified as a response
for such a state. This action will depend on the particular application involved.
Traditional call waiting is but one such service that may be built upon the above core
function.
If at some moment in time, the MS is involved in two calls both involving the
alternative network, and a third call arrives for the MS either from the alternative
network or the MSC, the proxy switch will direct this third call as per the logic of the
application. For example, in call waiting applications, the third call would be routed as
per instructions contained in the subscriber profile; a common option is to direct the call
to the voice mail of the subscriber. A similar logic is used if the MS is involved in two

calls both involving the MSC, and a third call arrives for the MS from the Alternative
work; again, the subscriber profile dictates how this third call is to be handled and this
logic is followed by the proxy switch. Finally, it should be noticed that if the MS is
involved in two calls both involving the MSC and a third call arrives for the MS, the
MSC itself, in this case, will determine the logic it follows to handle this third call.
For example, figures 3 and 6B conjointly illustrate an exemplary call waiting
application. The logic acts as described above through the acts labeled 608 or 609
(notice that figure 6B starts with blocks 608 or 609, as opposed to 600); that is, though
figure 6B helps describe a particular supplementary feature like traditional call waiting,
the initial acts for this supplementary feature are those described with reference to figure
6A.
If the logic starts at 608, it means that the proxy switch has already detected that
the MS is involved with a call, the proxy switch is handling the call, but the MSC is not.
At this point, the proxy switch has already intercepted call requests from the MSC,
converted them into a feature notification and issues the feature notification to the BS.
The proxy then receives and intercepts responses to such message from the BS.
Under the call waiting application logic of figure 6B, if the user indicated that
they are willing to accept the call, the proxy switch converts 615 the response to a
message indicating that the MS is accepting the new call from the MSC. The proxy
switch 300 then issues 620 the converted message to the MSC!. At this point in this
example, the MSC "thinks" the call is an ordinary call, that is, the MSC state reflects
only one call session to the MS. In fact, with the acceptance of the new call, the user is
receiving two calls in call waiting mode: one call being handled by the MSC and another
by the proxy switch. The proxy switch state reflects the two calls. The proxy switch 300
assists 625 the MSC 110 with setting up a new call. (This last step is only reached if the
user accepted the call; if the user did not accept it, the proxy logic times out and never
gets to act 625.) For example, the proxy switch 300 may need to park calls from an
alternative network so that the accepted call from the MSC can go through to the MS.
The proxy switch 300 then intercepts 630 any subsequent feature notification responses
from the MS and re-directs to MSC or proxy switch as needed. For example, the user
may want to "toggle" between calls being served by the mobile and the alternative

networks. The proxy switch may need to interpret this response to park one call and
connect another to the user as part of the act of intercepting subsequent feature
notifications. In other circumstances, the proxy switch may need to send this type of
response to the MSC if the MSC has multiple calls (some parked) intending to connect to
the MS. When the call ends, the proxy switch 300 sends 640 appropriate billing
information to the system. This is needed so that the user is billed appropriately when
services are rendered not involving the MSC. The manner in which the information is
kept and send to a billing system depends on the implementation and service provider
using the system. Most service providers specify the manner in which billing
information is to be collected, formatted and delivered.
If the MS 114 is involved with a call and is also involved with a call handled by
the MSC, and if the MSC indicates a new call is intended for the MS, then the proxy
switch 300 may be configured to intercept 650 the feature notification message from the
MSC that is destined for the BS 107. The feature notification message is blocked 655
from being passed to the BS, and consequently no response is issued 660 to the MSC
from the BS, because the feature notification message was blocked from being sent to the
BS. The logic flow then ends 699. The MSC does not get a response and assumes the
MS does not want to receive the call. The MSC then uses standard procedures to
terminate this call, e.g., voice mail of subscriber or plays a message stating the subscriber
is unavailable.
The call waiting application logic of figure 6B is limited to handling two
concurrent calls. The same general approach may be extended to handling more than
two calls for call waiting, to handling multiple calls from an alternative network, to
handling data calls and voice calls, and the like.
Procedure for fault management in the presence of a proxy switch
Standard procedures exist for fault management of the signaling links between
the BS 107 and the MSC 110. Under these procedures, both the BS and the MSC are
considered as peers, say Peerl and Peer2. Both peers maintain two sets of numbers,
called the Forward Sequence Number (FSN) and the Backward Sequence Number
(BSN). The FSN identifies the last message sent to a peer and the BSN identifies the
last message received from a peer. For example, assume there exist two signaling links

SLCO and SLC1 between Peer1 and Peer2. If Peer1 has FSN=5 and Peer2 has BSN=3
then Peer1 knows that it has sent all messages up to and including message 5 to Peer2;
Peer 2 knows that. it has received all messages up to and including message 3. If SLCO
breaks and Peer1 detects such a break, Peerl sends a Change Over Order (COO)
message to Peer2 requesting Peer 2 to change over to link SIC1. Peer2 responds with
COA (Change Over Acknowledged). Included in these messages are the BSN numbers
based upon which missing messages can be re-transmitted. For example, in the above
instance, messages.4 and 5 need to be retransmitted to Peer 2.
As a further example, consider an instance wherein Peer] has FSN=10 and
BSN=6; Peer2 has FSN=8 and BSN=5. Also assume that there: are two signaling links
existing between Peerl and Peer2, denoted,as SLCO and SLC1, and that SLCO breaks as
detected by Peerl. Then, Peerl sends a COO message using link SLC1 to Peer2 and
includes its BSN (=6) in the COO message. When Peer2 receives this message, it
compares the received BSN with its internal FSN (=8) and hence determines that the last
2 messages (8-6=2) need to be re-transmitted. Peer2 queues up the last two messages to
be re-transmitted and sends out a COA message containing its BSN (=5). Peerl receives
the COA message and compares the received BSN with its internal FSN (=10) and
determines that the last 5 messages (10-5=5) need to be re-transmitted. These last 5
messages are queued up by Peerl to be re-transmitted to Peer2.
Under preferred embodiments, the standard replay and recovery mechanism
between the BS and MS are not expected-to work. In short, the BS 107 may send
messages to the proxy switch that are never received by the MSC, e.g.,,siphoned
messages, and vice- versa, e.g., MSC messages that are. blocked. Consequently, the
basic FSN/BSN state at the BS and the MSC will not accurately reflect the state of the
whole system.
Accordingly, under preferred embodiments of the invention, the proxy switch
provides a new form of fault management. Referring to figures 3 and 7A-B conjointly,
the proxy switch creates 705 one set of FSN and BSN counters for each link to the MSC
110 and one set of FSN and BSN counters for each link to the BS 107. With particular
reference to figure 7B, which shows a single link arrangement to illustrate the concept,
the FSN /BSN pair 787 on the MSC for the link 785 and the FSN/BSN pair- 789 for the

link 786 are conventional. Pair 787 tracks the number of messages sent and
acknowledged (or "acked") on link segment 785 out of the MSC; pair 789 tracks the
same but out of the BS. The proxy switch 300 includes FSN /BSN pairs 788 and 790.
Pair 788 tracks the number of messages sent and acked on link segment 786 out of the
proxy switch 300 toward the BS 107; pair 790 tracks the number of messages sent and
acked on link segment 785 out of the proxy switch 300 toward the MSC 110.
As alluded to above, there is no expectation that the values for pair 787 will equal
the values for 788. For example, an MSC message may be blocked from being
transmitted to the BS 107 as a part of normal proxy switch logic, as discussed herein. By
so blocking the message, the FSN value of 787 should be one higher than that of 788. In
addition, there is no expectation that the discrepancy between FSN and BSN of 787 and
of the FSN and BSN 788 should be equal. For example, assume the simple case of one
message from MSC 110 that is supposed to be blocked at proxy switch 300 as a part of
normal proxy switch logic, as discussed herein. The discrepancy at 787 will be one until
there is an acknowledgement received at MSC 110, but there will be no discrepancy at
pair 788, because no messages are sent to BS 107.
As messages are received at the proxy switch 300, the proxy switch intercepts
them and updates the FSN/BSN pairs as outlined above.
If the proxy switch 300 detects 715 a COO message from the MSC 110,
indicating that link 785 went down, then the proxy switch 300 intercepts that message
720 and does not allow it to pass to the BS 107. The COO includes the BSN information
of pair 787 and identifies a new link (not shown) that the signaling should changeover to.
The proxy switch then forces a break 725 on a link 786 between the proxy switch and the
BS (link 786 corresponds to the link 785). The break is simulated as follows. Every few
milliseconds conventional BSs and the MSCs send out messages called "fill in signals,"
which are received and the receiver then knows the links are operational. If the receiver
does not get a fill in signal in the specified length of time, it assumes a break and sends a
COO message. So to simulate a break, one embodiment of the invention modifies the
software-based protocol state machine to not send the "fill in signal," and hence signal, a
break and cause a COO to be generated at the proxy switch (the modification being
relative to conventional MSC).

The proxy switch generates a COO message to the BS 107 with BSN of pair 788,
as opposed to the BSN information in the original COO message which contained
information for pair 787. This new COO informs the BS of the number of messages it
received on (the emulated-broken) link (i.e., BSN of 788). The generated COO uses a
new link (not shown in figure 7B) which is used to changeover to. This new link
corresponds to the changeover link to between the proxy switch 300 and the MSC 110.
The modified BSN numbers are then sent 735 to the BS 107 with the new COO
message. The COO is sent on an unbroken link. The proxy switch 300 then waits for and
receives a COA (acknowledgement) message 740 from the BS 107, and generates 745 a
new COA message. The new COA will contain the BSN information of pair 790, as
opposed to the information in pair 789. The new COA is sent 750 to the MSC 110.
The proxy switch then awaits for and receives retransmitted information to be
sent on the new link from the MSC and from the BS. Any information received is then
retransmitted 755 to the respective destination or handled as it would be in the ordinary
course of things (including potentially being blocked etc. as described herein). The logic
flow ends 799.
Under the above embodiment, the proxy switch relies on the BS or the MSC to
detect breaks in respective signaling links. The break in the signaling link is forced as a
result of current BS architectures; i.e., the breaks are needed to create the necessary
events for COOs. Under other embodiments, the proxy switch may detect breaks, and in
response to such, the proxy switch would mimic a MSC in relation to a BS or mimic a
BS in relation to a MSC.
Procedure for Automatic Triggering of Siphoning Based on COO messages
Under certain embodiments of the invention, the proxy switch may dynamically
determine when the system may benefit from redirecting (or siphoning) messages to an
alternative network (see, e.g., 400, figure 4). For example, under one embodiment of the.
invention, the proxy switch 300 monitors the signaling bandwidth directly or indirectly
as a measure of system bandwidth (e.g., reduced signaling bandwidth translating to
reduced system bandwidth). In one embodiment, a Change Over Order (COO) from She
MSC may be used as a signal of congestion at the MSC, or at least that the bandwidth


to/from the MSC will be impaired until the effected link is revived and traffic is changed
back to that link. Thus, the proxy switch 300 interprets a COO as a triggering event from
to "slow down" traffic to the MSC, and in response, initiates traffic siphoning to an
alternative network connected to the proxy switch.
One form of exemplary logic in this regard is shown with reference to figure 8.
The proxy switch creates 805 one set of FSN and BSN counters for each link to the MSC
110 and to the BS 107. Each message to or from the BS is intercepted and the sequence
numbers are updated 810 accordingly. If the proxy switch 300 detects 815 a COO
message from the MSC 110, then the proxy switch 300 intercepts that message 820 and
does not allow it to pass to the BS 107. In this instance, the COO only reflects the
requested changeover and does not indicate that messages need to be replayed. The
proxy switch 300 then generates a COA message 825 with modified BSN numbers for
MSC and sends COA message 830 to the MSC 110. The modified sequence numbers are
the ones created by the proxy switch during the processing of messages, similar to that
described above. Thus, the MSC now believes that its COO has happened.
Communication bandwidth between the MSC and the BS will be lower as a consequence
of the changeover, since one less signaling link is available.
However, though the bandwidth between the proxy switch 300 and the MSC may
be impaired as a result of COO described above, the bandwidth between the BS 107 and
the proxy switch 300 is not impaired. The proxy switch may take advantage of this
context by siphoning traffic to an alternative network. Accordingly, the proxy switch
initiates traffic siphoning 835 for traffic generated from the BS-side of the proxy switch.
There are many types of alternative networks that may be used to carry voice as well as
data traffic from a MS 114 (see, e.g., figure 4). If there are multiple types of alternative
networks connected to the proxy switch, then the proxy switch may select the type of
alternative network based on the type of communication, e.g., data or voice. In
initiating the siphoning, the proxy switch will configure the data plane as needed to route
certain bearer circuit traffic to appropriate alternative networks (as will be explained
below). For example, the VoIP assembly 404 may be configured with information
extracted from the signaling messages.


The siphoning of traffic continues for the given session. The proxy switch 300
thereafter maintains the FSN, BSN numbers as described above. Any COO messages
from BS 107 are then intercepted and a COA is generated and sent to the BS, while
maintaining the FSN and BSN counters.
Any COO messages from the MSC 110 are intercepted 850 and checked to see if
they indicate that the MSC is again ready to receive traffic on the previously down link,
i.e., to see if the COO is a changeback message. If there is such a message, the proxy
switch interprets this to mean that the MSC can again handle a higher level of traffic and
will take actions to "reconnect" the siphoned links and traffic. (If the COO is not a
changeback message, it may be yet another changeover message indicating a context that
may benefit from further siphoning of traffic.)
If there is a changeback message, a new COO is generated 855 with modified
BSNs and sent 860 to the BS 107. The modified BSN are the ones maintained by the
proxy as discussed above. The proxy switch 300 then waits for and receives a COA
message 865 from the BS 107. A new COA message is then generated 870 with
modified BSN numbers and sent 875 to the MSC 110. The proxy switch then
discontinues the traffic siphoning procedure. The control plane instructs the data plane
accordingly.
Under certain embodiments, the decision to siphon traffic may include the other
considerations- For example, the alternative network may provide QoS guarantees that
may be considered by the proxy switch logic. In one embodiment, siphoning is only at
session boundaries. Accordingly, if a call is to be siphoned, it is siphoned at call
origination.
The description above was premised on the COO being sent as indicative of
network congestion. Under one embodiment of the invention, the logic described above
for automatic siphoning is supplemented with the fault management logic described in
relation to figures 7a-b. In this embodiment, every time that the proxy switch 300 gets a
COO from the MSC it performs the replay logic discussed above. COO messages from
the BS, however, are always treated as a break in the signaling link, and replay logic is
performed but no siphoning.



Procedure for Preserving Point Codes Across BSC and MSC
In SS7 networks, all network components are addressed by unique numbers
called "point codes." Consequently, all the BSCs and MSCs will have unique point
codes. A message from a BSC to an MSC will, in general, contain a destination point
code, e.g., the point code of the intended MSC, and an originating point code, e.g., the
point code of the BSC that sourced the message.
Messages from the BSC to the MSC, for calls originating from the MS,
additionally request a bearer circuit to be assigned for the call. Bearer circuits (which
carry voice or data) are identified by Circuit Identification Codes (CIC).
To support transparent operation by the proxy switch, the point codes and CICs
traveling between the BSC and MSC are preserved for all messages. This requirement is
complicated by the fact that while some of the circuits carrying bearer traffic will
transparently traverse from the BSC to the MSC, other circuits emanating from the BSC
will be terminated at the proxy switch, and the MSC will be unaware of such
terminations.
As stated above, some trunks 308 are pre-provisioned for direct connection
between the BS and MSC, whereas other trunks 312 connect to the proxy switch.
Analogously, under preferred embodiments, some bearer circuits are pre-provisioned for
direct connection between the BS and the MSC ("pass through circuits"), and the
remaining circuits are terminated at the proxy switch ("siphonable circuits").
Under one embodiment, under normal operation, the MSC may not assign the
siphonable circuits for any calls. When siphoning traffic (as described above), the proxy
switch may assign a siphonable circuit for a call from the BS (by communicating the
appropriate CIC to the BS), and the BS will respond by sending the voice or data on that
circuit. As will be explained below, the voice or data may then be read from this circuit
and passed on to an alternative network, accordingly via DACS 402.
To ensure the consistency of information at the MSC in the event of a proxy
switch failure, under one embodiment of the invention, a network management system
accesses the CIC database at the MSC and marks the siphonabie circuits as available As

a result of such action, the MSC will think that these circuits are available-to be
allocated, and the network will behave like a conventional mobile network (i.e., one
lacking a proxy switch).
When the proxy switch recovers, the network management system again accesses
the CIC database at the MSC, but this time marks the siphonable circuits as
"unavailable". It also accesses the proxy switch database and marks the siphonable
circuits as "available". These circuits will then be assignable by the proxy switch as
described above. Under some embodiments, the siphonable circuits may be marked
"unavailable" at the MSC and "available" at the proxy switch in a gradual manner so that
the proxy switch gradually gains control over more of the siphonable circuits.
To handle the deployment of figure 3B, the techniques described above need to
be supplemented. In particular, to handle the deployment of figure 3B, the proxy switch
needs to intercept messages from the BS and change point codes to reflect a re-mapped
MSC. Under one embodiment, this is done at a session-level of granularity, meaning
that the re-mapping to a new MSC may be determined at session boundaries.
Alternatively, the re-mapping may be done at other levels of granularity, for example,
when a MS is turned on. Some embodiments perform the mapping by correlating
equipment serial numbers (e.g., included in messages when a MS is turned on) to MSCs
and their corresponding point codes.
Hardware Architecture
Referring conjointly to figures 3 and 4, preferred embodiments of the proxy
switch 300 include a control plane 302 and a data plane 304. The control plane includes
a combination of processing hardware and associated software. The data plane largely
comprises hardware that is responsive to commands from the control plane.
The control plane includes programmable signaling cards (e.g., PMC 8260
available from Force Systems) to receive the signaling information from the signaling
links 312, 314 and to perform the initial processing thereof. This initial processing
includes sending and terminating information on the signaling links and extracting, under
programmatic control, the message information contained in the signaling messages
Once the message information is collected, the signaling cards cause the message

information to be passed to a programmable processor card (e.g., RPC 33©5 and 3306
available from Radisys) which is then responsible for carrying out the functionality of
the proxy switch in response thereto as described above.
The control plane is constructed with passive fault tolerance mechanisms. These
mechanisms ensure that on catastrophic failures of the control plane, the signaling links
received by one side of the control plane will bypass to the other side. Thus, if the
control plane fails the links are bypassed across the control plane and the BSC and MSC
may communicate as they do conventionally.
The data plane 304 of an exemplary embodiment is shown in figure 4. It includes
a DACS 402, a Voice over IP assembly 404, a Data termination module 406 (e.g., to
terminate A5 data in CDMA networks), a PPP relay assembly 408, and a PPP
termination assembly 410. The various assemblies may be packaged on one or more
modules.
The DACS 402 receives the bearer circuits of trunks 306 and terminates the
information received on the trunks; it also transmits voice and data on those trunks. Pre-
provisioned ports for the DACS 402 are connected to VoIP 404 and the Data termination
assembly 408. The Data termination assembly 408, in turn, is connected to the PPP
Relay 408, which in turn is in communication with the PPP termination assembly 410.
Moreover, the data plane may also be used to connect to alternative circuit-based
networks, e.g., to backhaul traffic to a circuit-MSC in another regional network.
All of the data plane entities receive control commands from the control plane
302 via control channels 401 which is used to carry information according to H.248 or
Media Gateway Control Protocol (MGCP). The control channel, among other things, is
used to inform the DACS 402 how to provision the bearer circuits. For example, a given
input circuit from the BS 107 is mapped to an output port to one of the assemblies. The
control channel is also used to convey control information to the various assemblies.
For example, the signaling information contains control information such as destination
IP addresses that may be used to create destination addresses needed by the VoIP
assembly. This information will then be used by the VoIP assembly to deliver the voice
information received from the DACS by packetizing the information accordingly and
sending it according to the appropriate protocols, e.g. RTP/UDP/IP.

The data plane is constructed with passive fault tolerance mechanisms. These
mechanisms ensure that on failures of the data plane, the trunks received by one side of
the DACS will bypass to output trunks connected to the MSC. Thus, if the data plane
fails the trunks are bypassed across the data plane and the BSC and MSC may
communicate as they do conventionally.
Software Architecture
Referring jointly to figures 9-10, under a preferred embodiment, the control plane
software executes session manager processes and communication processes. The session
manager processes include a Proxy Session Manager (PSM) 904 and a Core Session
Manager (CSM) 1002. The communication processes include SS7 Message Handler
(SS7MsgHdlr) 902 a-n and DP Message Handler (IPMsgHdlr) 906 a-n. As the names
suggest, the session managers include logic for managing and handling call sessions,
whereas, the message handlers include logic for handling messages. The message
handlers encapsulate the logic for handling messages so that other software does not
need to know the message handling particulars. Similarly, the session managers
encapsulate the logic for handling sessions, so that other software such as the message
handlers do not need to know session state or the like.
The SS7MsgHdlr and IPMsgHdlr processes are responsible for accepting
incoming messages and sending outgoing messages. The former accepts and sends
signaling messages from and to the MSC 110 and/or the BS 107. The latter SS7MsgHdlr
and IPMsgHdlr accepts and sends control messages to the data plane. The PSM process
904 handles all calls or sessions that are "flow through" calls, or non-siphoned calls. The
CSM process 1002 handles all the calls or sessions that are being siphoned off by the
proxy switch 300. As such, the CSM process 1002 provides much of the same
functionality as the circuit-MSC and a BS in the sense that it responds like an MSC to
messages from the BS, and responds to messages from the MS as if it were a BS. In
general there are multiple PSM and CSM processes running simultaneously on various
processor cards to provide the necessary scalability and performance. Additional
software processes are provided for failover and reliability. These in our diagrams are-
referred to as PSM' 904' and CSM' 1002'. The purpose of these "prime" processes is t
provide failover for other PSM and CSM processes. In one embodiment, each PSM and

CSM has a "shadow" PSM7CSM' process providing "shadow" coveragefln case a PSM
or CSM process fails, the corresponding shadow PSM/CSM' process is designed to
takeover from the failed process.
Referring to figure 9, as signaling messages arrive from the BSC and MSC, they
are handled by a SS7MsgHdlr 902a-n, which executes on the SS7 processing card.
There is one SS7MsgHdlr associated with each signaling link to or from the proxy
switch. The SS7 processing cards (mentioned above) extract sufficient information from
the signaling message to identify a corresponding SS7MsgHdldlr to which the signaling
message is passed.
The SS7MsgHdir receives the messages and assigns a (preferably) unique logical
reference number to this message. This reference number is used later to identify
subsequent messages that pertain to the same ongoing call/session. The assigned logical
reference number is communicated back to the software system running in the BS or
MSC (e.g., the SCCP protocol stack) which then uses that reference number in all
subsequent messages pertaining to this call/session.
After the above processing, the SS7MsgHdlr 902 then selects a PSM 904 to
handle the message. In one embodiment, the SS7MsgHdlr examines the point code of
the message originator and selects a PSM that is associated with that code. For example,
a table may be used to store such relationships.
The PSM 904 then determines if this message is for a call/session that is to be
siphoned. In one embodiment, this determination is made by examining the service
option field contained in the message that distinguishes between data sessions and voice
calls, hi another embodiment, this determination is made by examining the calling and
called party numbers to ascertain if both are mobile phone numbers, hi yet another
embodiment, this determination is made by examining the calling party number to
determine if the calling party has chosen a VoIP service provider. Once the
determination is made to siphon this call/session, the PSM 904 passes the message to the
CSM 1002. If a determination is made not to siphon this call/session, the PSM generates
a message that is used to send back to the MSC or the BS via the SS7MsgHdlr processes.


The PSM processes 904 may also communicate via an internal protocol to the
CSM processes 1002, see, e.g., figure 10. The internal protocol of a preferred
embodiment is stateless and text based. As stated above, the PSM deals with those
sessions/calls that are non-siphonable. Once it encounters a session/call that is
siphonable it passes the context of that session/call to a CSM process. The CSM process
is responsible for handling all calls/sessions that are siphoned. The CSM communicates
with the Data Plane via standard control protocols such as H.248 and MGCP (Media
Gateway Control Protocol).
The internal architecture of the PSM and CSM processes is similar. Referring to
figure 11, incoming messages are received by the network interface module 1102. The
network interface module then sends the message to the protocol engine 1104. For
example, this engine 1104, under CDMA embodiments, is responsible for encoding and
decoding messages according to the IS-634 protocol. The state machine module 1106 is
responsible for handling the message and recording the state according to the protocol.
For example, under a given protocol, a given message signifies a known state transition
under that protocol. The state machine module 1106 includes the logic for recording the
state and implementing the state transitions.
The active directory module 1108 interacts with the external mobility
management functions of the MSC and is responsible for obtaining and updating
subscriber profiles and other user/subscriber data. In a traditional MSC, the Visiting
Location Register (VLR) is typically co-located with the MSC; the VLR contains the
subscriber information (profiles) that are currently roaming within the area covered by
the MSC. Additionally, the MSC is connected to another database, called the Home
Location Register (HLR) that contains all the subscribers who are "homed" in the current
network. Typically, as a subscriber roams and enters an area covered by the MSC, the
MSC requests the HLR to send the profile of the subscriber and stores it in the (local)
VLR. When the subscriber roams out of the area covered by the MSC (to an area covered
by another MSC), this subscriber profile is deleted. The active directory module in the
proxy switch acts as a client of the HLR database, requests subscriber profiles from the
HLR for subscribers who roam into the area covered by the proxy switch, ar$d updates
the local database, i.e., the active directory module and its associated database act/behave
as a traditional VLR for roaming subscribers.)

The media gateway controller (MGC) module 1110 interacts with the data plane
304 of the proxy switch via open control protocols, such as H.248 and MGCP. Upon
receiving an action request from the IS-634 state machine module 1106, the MGC 1110
sends a message in H.248 or MGCP protocol to the data plan. 304 to carry out the
needed actions. In one embodiment, the so-called TDM-VoIP case, these action
messages from the MGC 1110 to the data plane instruct the data plane to receive
incoming circuit (TDM) traffic at an ingress port and to convert it into RTP/UDP/IP
packets and send it out from one of the egress ports. Thus, in this embodiment, incoming
circuit traffic is packetized and sent out as packets. This embodiment could be used for
taking circuit calls, and transporting them as Voice over IP (VoIP) calls. In another
embodiment, the so-called TDM-TDM case, the MGC 1110 instructs the data plane 304
to receive incoming circuit (TDM) traffic at an ingress port and switch as circuit (TDM)
traffic out of an egress port. In this case, incoming circuit traffic is preserved as circuit
and switched to an alternative circuit network.
Figures 12-14 are used to illustrate the above concepts with simplified
architectural diagrams. The figures are used to show the various interactions of the
software processes in response to signaling messages. Bearer circuits are excluded from
some of the figures for the sake of simplicity. Moreover, only single instances of the
PSM and CSM processes are shown for the sake of simplicity.
Figure 12 is used to show the control flow when a new call message is initiated
from the BS 107 to the MSC 110, and to show a "Pass through call." A pass through call
is a call in which the proxy switch 300 is not responsible for managing the call and in
which the call is to be passed through for handling by the MSC 110. The proxy switch
300 is transparent for purposes of this call (though it may alter point codes, for example,
to handle re-mapping of MSCs as explained with reference to figure 3B). The BS 107
sends 1205 a service request (such as a CSR) which is intended for the MSC 110. The
service request contains a service option field that specifies whether this is a request for a
voice call or a data call. The proxy switch receives this message (since it is in the
signaling path between the BSC and the MSC); in particular, the SS7MsgHdlr process
902 receives the call, assigns a unique local reference number to this message (this is the,
initial message for a potentially ongoing call request), and routes 1210 it to the PSM
process 904 for further processing. The PSM process 904 decodes the incoming message

and using the IS-634 state machine (for CDMA embodiments) determines whether this
call is to be siphoned (e.g., to an alternative network) or allowed to be handled by the
MSC 110. Since in this example the call is not to be siphoned, the message is encoded
and sent back 1215 to the SS7MsgHdlr process 902. In one embodiment, the
comminication protocol between the SS7MsgHdlr and PSM processes is a stateless text-
based protocol that provides a level of abstraction (relative to session logic) of the
underlying signaling protocol. The SS7MsgHdlr process 902 then re-transmits 1220 the
IS-634 message to the MSC 110. The MSC processes this message and responds 1225.
This response is also received by the proxy switch 300 but since this response is related
to an on-going but non-siphonable call (as determined from the local reference number
assigned to the initial CSR request message explained above), the SS7MsgHdlx process
902 does not forward this message to the PSM 904. Instead, the SS7MsgHdlr sends
1230 this message transparently onward to the BS 107. All further exchanges relating to
this call are allowed to transparently pass between the BS and the MSC except for a Call
Release message at the conclusion of the call. In response to a Call Release, the proxy
switch 300 ensures that the "tear down" of the call happens including the disposition of
the local reference number. The call release message is also sent to the BS 107 by the
proxy switch so that the BS can proceed with its tear down processes.
Figure 13 is used to show the case of a call message initiated by the BS 107 to the
MSC 110 and also used to show proxy trunks, i.e., trunks that are controlled and
assigned by the MSC 110. The BS 107 sends 1305 a service request intended for the
MSC 110. The proxy switch receives this message and the SS7MsgHdlr process 902
receives the call, assigns a unique local reference number to this message, and routes
1310 it to the PSM process 904 for further processing. The PSM process 904 decodes the
incoming message and determines whether this call is to be siphoned (e.g., to an
alternative network) or allowed to be handled by the MSC 110. Since in this example the
call is not to be siphoned, the message is encoded and sent back 1315 to the SS7Msg Hdlr
process 902. The SS7Msg Hdlr process 902 then re-transmits 1320 the message to the
MSC 110. The MSC 110 responds 1325 to the call set up request by assigning a channel
to the call (as described above). This channel assignment is received by the proxy switch
300 which passes 1330 the assignment to the PSM 904, which in turn responds 1335 that
is has recorded this assignment 1330. The proxy switch then transmits 1340 the channel


assignment request onwards to the BS 107. All further exchanges relating to this call
between the BSC and the MSC are allowed to transparently pass through the proxy
switch until the call release message. The call release triggers the tear down processes in
the proxy switch.
Figure 14 is used to show the case of a "siphoned call." A siphoned call is a call
initiated by the BS 107 that is intercepted and re-directed to an alternative network by the
proxy switch. In such an example, all signaling is to be handled by the proxy switch and
the trunks carrying user traffic are to be controlled by the proxy switch. The BS 107
sends 1405 a service request intended for the MSC 110. The proxy switch receives this
message and assigns a unique local reference number to this message, and routes 1410 it
to the PSM process 904 for further processing. The PSM process 904 decodes the
incoming message and using the IS-634 state machine (for CDMA embodiments)
determines that the call is to siphoned. Since in this example the call is to be siphoned to
an alternative network, the PSM transmits 1415 the message to the CSM process 1002.
The CSM process 1002 now starts to behave like a conventional MSC and issues 1420 a
channel assignment for this call, assigning a trunk between the BS and the data plane of
the proxy switch. The channel assignment is then sent 1435 to the SS7MsgHdlr. The
SS7MsgHdlr process transmits 1430 this channel assignment information to the BS so
that the BS may use it for user traffic. The CSM also sends a message to the data plane
of the proxy switch (as described above using H.248 or MGCP protocols) directing it to
receive incoming user traffic on the assigned channel and directing it to an alternative
network. As explained above, in one embodiment the alternative network may be an IP
network. All further exchanges occur between the BSC and CSM process until the call
release command is issued by the MSC causing a release of resources (the tear down
process).
In another embodiment, the software architecture may use only a single process
for carrying out the proxy functions rather than using two different processes (PSM and
CSM). In such an embodiment, the PSM process alone determines, as before, if a call is
to be siphoned or not. If it is not a siphonable call, it is allowed to proceed to the MSC. If
it is a siphonable call, the PSM itself handles the call and sends and accepts messages
from the BS 107 and the MSC 110. In other words, the PSM in such an embodiment acts
like an MSC and BS 107 and handles all the signaling messages in this regard. As such,

the PSM process provides much of the same functionality as the circuit-MSC and a BS
107 in the sense that it responds like an MSC to messages from the BS 107, and responds
to messages from the MS as if it were a BS 107. In general there are multiple PSM
processes running simultaneously on various processor cards to provide the necessary
scalability and performance. Additional software processes are provided for failover and
reliability. The purpose of these processes is to provide failover for other PSM processes.
In one embodiment, each PSM has a "shadow" process providing "shadow" coverage. In
case a PSM process fails, the corresponding shadow process is designed to takeover from
the failed process.
Variations
The above embodiments all facilitate the realization of a transparent switch.
Subsets of the functionality, however, still provide advantages over the state of the art.
For example, a switch that is partly visible to the network may still offer many of the
advantages discussed above.
In addition, the embodiments were described in part with relation to CDMA
protocols, but the embodiments may also be modified to work with GSM, IS-136 and/or
other2G and 3G protocols.
The connection of trunks from proxy switch to MSC is optional.
Having described an exemplary embodiment, it should be apparent to persons of
ordinary skill in the art that.changes may be made to the embodiment described without
departing from the spirit and scope of the invention.


WE CLAIM :
1. A proxy switch for a mobile communications network having at least one
mobile switching center and at least one base station subsystem, wherein the mobile
switching center and base station subsystem each communicate signaling
messages according to a mobile signaling protocol, said proxy switch comprising:
signaling message handling logic for receiving signaling messages from the
mobile switching center and base station subsystem in accordance with said mobile
signaling protocol,
message interception logic, cooperating with the signaling message handling
logic, for sending an acknowledgment message to a mobile switching center or base
station subsystem that transmits a signaling message received by the signaling
message handling logic and for preventing the signaling messages from being
forwarded to the other of the base station subsystem and mobile switching center
respectively;
message conversion logic, cooperating with the signaling message handling
logic, for converting a signaling message received by the signaling message
handling logic from one of the mobile switching center and base station subsystem
into a converted signaling message for transmission to the other of the base station
subsystem and mobile switching center, respectively; and
message transmission logic, cooperating with the signaling message handling
logic, for transmitting signaling messages from one of the mobile switching center
and the base station subsystem to the other of the base station subsystem and
mobile switching center, respectively, or for transmitting unaltered signaling received
from one of the mobile switching center and the base station subsystem to one of
the base station subsystem and mobile switching center, respectively.
2. The proxy switch as claimed in claim 1 wherein the message conversion logic
comprises logic for converting a first type of signaling message to a second type of
signaling message.


3. The proxy switch as claimed in claim 1 wherein the message conversion logic
comprises logic for analyzing a received message and producing a corresponding
point code, and for converting the received message by replacing the point code of
the received message with the corresponding point code.
4. The proxy switch as claimed in claim 1 comprising state logic for maintaining
state information about the proxy switch and about call sessions and wherein the
message conversion logic comprises logic for cooperating with the state logic to
consider the state information to determine whether a signaling message should be
converted from a first type of signaling message to a second type of signaling
message.
5. The proxy switch as claimed in claim 1 wherein the proxy switch is connected
to at least one base station subsystem via trunk lines that transmit information
according to bearer circuit organization, wherein the proxy switch is in
communication with an alternative communication network, and wherein the proxy
switch comprises
alternative network control plane logic for terminating signaling messages
associated with an identifiable set of bearer circuits and for providing control
information contained in the associated signaling messages to the alternative
communication network; and
alternative network data plane logic for providing information contained in the
identifiable set of bearer circuits to the alternative communication network for
transmission by the alternative communication network.
6. A method of communicating messages between a mobile network and an
alternative communication network in which the mobile network comprises at least
one mobile switching center and at least one base station subsystem the method
comprising:
receiving signaling messages from one of the mobile switching center and
base station subsystem in accordance with a mobile signaling protocol;

maintaining state information about the mobile and alternative networks;
depending on the state information, performing the following steps in
response to a received signaling message:
sending an acknowledgment message to mobile switching center or
base station subsystem that transmits the signaling message but preventing the
received signaling messages from being forwarded to the other of the base station
subsystem and mobile switching center respectively; and either
converting the signaling message received from the mobile switching
center or base station subsystem into a converted signaling message for
transmission to the base station subsystem or mobile switching center, respectively;
or
transmitting unaltered signaling received from the mobile switching
center or the base station subsystem to the base station subsystem or mobile
switching center, respectively.
7. The method as claimed in claim 6 wherein the step of converting the received
signaling message comprises converting a first type of signaling message to a
second type of signaling message.
8. The method as claimed in claim 6 wherein the step of converting the received
signaling message comprises analyzing a received message, producing a
corresponding point code, and converting the received message by replacing the
point code of the received message with the corresponding point code.
9. The proxy switch as claimed in claim 1 having at least two mobile switching
centers and at least one base station subsystem, wherein the at least two mobile
switching centers and base station subsystem each communicate signaling
messages according to a mobile signaling protocol, the proxy switch comprising:
mobile switching center selection logic for mapping an identified user to one
of the at least two mobile switching centers; and


wherein the message transmission logic cooperates with the signaling
message handling logic and the mobile switching center selection logic, for
transmitting signaling messages received from the base station subsystem to a
mapped mobile switching center by inserting a point code in the signaling message
wherein the point code corresponds to the mapped mobile switching center.

A proxy switch (300), communication methods, and communication logic for use
in a mobile network are described. A proxy switch (300) is deployed between a base
station subsystem (107)and a mobile switching center (110). It receives signaling
messages and either retransmits them, blocks them, or siphons them to an alternative
network. Besides providing an ability to offload mobile traffic it provides a platform for
new communication services.

Documents:

629-kolnp-2003-granted-abstract.pdf

629-kolnp-2003-granted-assignment.pdf

629-kolnp-2003-granted-claims.pdf

629-kolnp-2003-granted-correspondence.pdf

629-kolnp-2003-granted-description (complete).pdf

629-kolnp-2003-granted-drawings.pdf

629-kolnp-2003-granted-examination report.pdf

629-kolnp-2003-granted-form 1.pdf

629-kolnp-2003-granted-form 18.pdf

629-kolnp-2003-granted-form 3.pdf

629-kolnp-2003-granted-form 5.pdf

629-kolnp-2003-granted-gpa.pdf

629-kolnp-2003-granted-reply to examination report.pdf

629-kolnp-2003-granted-specification.pdf

629-kolnp-2003-granted-translated copy of priority document.pdf


« Previous Patent
Next Patent »
Patent Number 226781
Indian Patent Application Number 629/KOLNP/2003
PG Journal Number 52/2008
Publication Date 26-Dec-2008
Grant Date 24-Dec-2008
Date of Filing 19-May-2003
Name of Patentee WINPHORIA NETWORKS INC
Applicant Address 3 HIGHWOOD DRIVE, TEWKSBURY, MA
Inventors:
# Inventor's Name Inventor's Address
1 SUNDAR RANGAMANI 5 SQUIRE ARMOUR ROAD, WINDHAM, NH 03087
2 VISHWANATHAN KUMAR K 6 SQUIRE ARMOUR ROAD, WINDHAM, NH 03087
3 NAQVI SHAMIM A 19 SPRING VALLEY ROAD, MORRISTOWN, NJ 07960
4 ARAVAMUDAN MURLI 3 SQUIRE ARMOUR ROAD, WINDHAM, NH 03087
PCT International Classification Number H04Q 7/22
PCT International Application Number PCT/US01/43365
PCT International Filing date 2001-11-21
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 09/721,329 2000-11-22 U.S.A.