Telephonic communications – Plural exchange network or interconnection
Reexamination Certificate
2000-03-03
2004-02-03
Matar, Ahmad F. (Department: 2742)
Telephonic communications
Plural exchange network or interconnection
C379S220010, C379S221010
Reexamination Certificate
active
06687363
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the process of call set-up in internet telephony. More particularly, the invention relates to procedures for determining how to interconnect the software switches that handle call set-up.
ART BACKGROUND
In conventional telephony, the analog voice signals that are the substance of telephone calls are delivered through a network of cables and switches referred to as the bearer network. By way of illustration,
FIG. 1
shows a pair of telephones
10
,
15
, each connected to bearer network
20
through a respective local exchange switch
25
,
30
which is, for example, a Lucent Technologies 5ESS switch. To establish a switched circuit between telephones
10
and
15
for the duration of the call, signaling messages are sent through a parallel, physical network of Signal Transfer Points (STPs). This parallel network, shown in
FIG. 1
as network
35
, is referred to as the signaling network. The establishment of a switched circuit is one type of call setup; specifically, it is the type of call setup performed in circuit-switched networks such as traditional telephone networks. It is a long-established requirement in conventional telephony that with 99% probability, call setup must be completed in time for a customer to hear a ring within two seconds after dialing. The actual time interval before a ring is heard is referred to as Post-Dialing Delay (PDD).
A newer kind of telephony, referred to as internet telephony, is rapidly growing in importance. In internet telephony, the substance of the telephone call is transmitted through a network of internet routers in the form of packetized signals which conform, e.g., to the TCP/IP protocol. Such a network of internet routers, referred to below as, simply, “the internet,” is indicated in the figure as network
40
. In internet telephony, call setup involves the establishment of an IP session instead of a switched circuit. To set-up a call, signalling messages are sent through a parallel network of software switches, such as Lucent Technologies Softswitches. A software switch network is indicated in
FIG. 1
as network
45
. In current implementations of internet telephony, the software switches of network
45
do not intercommunicate exclusively through dedicated hardware. Instead, they use the resources of the internet itself for intercommunication. Thus, unlike the physical signaling network of conventional telephony, the software switch of internet telephony (in current implementations) is a virtual network.
Like conventional telephony, internet telephony honors the 99% probability, two-second limit on PDD.
When a customer wishes to place an internet telephone call, he includes in the dialed number a string, referred to as a prefix, indicative of a particular provider of internet telephone service. Such a prefix typically consists of a seven-digit string included just before the seven-digit local telephone number being dialed. Thus, to the customer, the internet prefix is analogous to the seven-digit access code for long-distance carriers.
The internet prefix is interpreted at the originating local exchange switch, e.g., switch
25
. In response, the call is sent to the internet and not to the conventional telephone network. As shown in
FIG. 1
, switch
25
sends call data directly to software switch network
45
, and also to an associated Packet Voice Gateway (PVG)
50
. As explained below, the PVG, in turn, sends data to internet router network
40
and to software switch network
45
. Similarly, the local exchange switch at the receiving end, e.g., switch
30
, receives data directly from network
45
and from an associated PVG
55
. PVG
55
receives data from network
40
and from network
45
. Finally, switch
30
connects to telephone
15
.
Further information about the flow of signals is illustrated in FIG.
2
. Elements common to
FIGS. 1 and 2
bear the same reference numerals in both figures. Analog signals, represented in the figure by solid lines, flow between each telephone
10
,
15
and the corresponding local exchange switch
25
,
30
. Analog signals also flow between each local exchange switch and a corresponding PVG
50
,
55
. Included among the functions of the PVG is analog-to-packet conversion. Accordingly, packet signals embodying the substance of the telephone call, represented in the figure by broken lines, flow between PVGs
50
,
55
and the internet IP routers. Shown in the figure are the origination router, e.g., router
60
, and the destination router, e.g., router
65
.
Signaling messages, represented in the figure by dotted lines, pass among the multiple switches of the software switch network. Shown in the figure are origination and destination software switches
70
and
75
. Also shown are two intermediate software switches
80
and
85
. Origination software switch
70
also exchanges signaling messages with origination local exchange switch
25
and with origination PVG
50
. Destination software switch
75
also exchanges signaling messages with destination local exchange switch
30
and with destination PVG
55
.
Further details of the software switches are shown in FIG.
3
. Elements common to
FIGS. 2 and 3
bear the same reference numerals in both figures. Each software switch includes a plurality of Call Coordinators (CCs)
100
and a Device Server (DS), such as an SS
7
device server. Shown in the figure are DS
90
, associated with orgination software switch
70
, and DS
95
, associated with destination software switch
75
. For simplicity of presentation, the device servers associated with the intermediate software switches are not shown in the figure.
Among its other functions, the DS within each software switch processes the call set-up strings when that switch is the origination or destination switch for a call. The CCs set up the origin and destination PVGs. The DS also performs round-robin scheduling or other load-balancing operations among the various CCs of that switch. Thus, each CC within an individual switch communicates with the DS of that switch. However, the CCs within an individual switch do not typically communicate directly with each other.
Each CC of a given software switch is desirably connected to one or more CCs of one or more other switches, such that collectively, the interconnections among all of the CCs span the entire software switch network. That is, the network should be able to transmit set-up data for a call originating at any given software switch to any other software switch via a series of hops from switch to switch through the network.
A typical world-wide network for internet telephony may have as many as 200 or more software switches. Typically, each software switch will have several tens of CCs, exemplarily about 50 CCs. Thus, even with the constraint that CCs within an individual switch do not intercommunicate, the number of possible network designs is extremely large.
An advantageous network design should satisfy certain further requirements. For example, each hop consumes some time, which may be as much as 100 ms or more. If excessive delay accumulates during a transit of the network, call set-up may not be achieved in time to satisfy the two-second limit on PDD. Therefore, it is desirable for the diameter of the network, i.e., the number of hops separating the most distant pair of CCs, to be limited to a small number, such as two hops.
Typically, the links between CCs are virtual links. Under TCP/IP and certain other protocols, for example, these links are of the kind referred to as sockets. As will be appreciated by those skilled in the art, a socket is a software construct that permits communication between computational processes. A disadvantageous property of sockets in software switches is that for each CC, delay and overhead penalties increase with the number of open sockets belonging to such CC. The delay and overhead penalties are not proportional to the number of open sockets, but instead have a rate of increase that is faster than proportionality. Thus, a second desirable feature of a C
Aravamudan Murali
Kumaran Krishnan
Ramakrishnan Kajamalai Gopalaswamy
Srinivasan Aravind
Bui Bing
Finston Martin I.
Lucent Technologies - Inc.
Matar Ahmad F.
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