Multiplex communications – Channel assignment techniques – Combining or distributing information via time channels...
Reexamination Certificate
1998-08-31
2002-04-02
Vincent, David R. (Department: 2661)
Multiplex communications
Channel assignment techniques
Combining or distributing information via time channels...
C370S400000, C370S458000
Reexamination Certificate
active
06366587
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a network architecture providing improved utilization communication information between digital subscriber lines and communications devices, and more particularly to increasing performance of router systems for transferring digital communications information between various different types and numbers of modem through digital subscriber lines.
2. Description of the Prior Art
Routers are employed in the telecommunications area as sophisticated switches. That is, a router is a device that can select a path data should take thereby requiring the router to have an understanding of the network and how to determine the best route for the data path.
Servers are sophisticated storage devices that maintain information, such as web pages, for access by various other communications equipment such as PCs. Information between servers, PCs and the like, may be transferred through routers.
Information that is transferred by routers between various communications equipment is often times in the form of packets and coupled onto communication links (or lines) using Time Division Multiplexing (TDM). This is perhaps best understood by describing an example commonly employed by users.
When data such as electronic mail is transmitted over the internet, the data is diced up into small packages called packets, each packet having an address attached. The packets flow through the circuits of the internet, such as routers, servers and so forth, but they do not all necessarily follow exactly the same path. They do however, all arrive at the same destination, and are reassembled into the original data. The various packets belonging to the same original data are identified by the use of their attached address.
Devices that send data through routers do so at various times on various communications channels that serve as links for transferring the data from the devices, through the routers, and to the final device destination. The path from a device to a router includes such communications links or TDM streams. Data through such streams is transferred for each device when the link is not busy and given a time slot during which the data belonging to a particular device is coupled onto the link and transferred. A link may carry information from various devices to the router, accordingly, data from various devices are multiplexed.
With the advent of recent advancements in router technology, there has been an important requirement placed on routers. The requirement calls for the universal support of various ‘feature’ boards that have been developed recently to support a variety of modem and other communications devices. Feature boards are complex printed circuit boards that may serve various purposes. For example, a ‘trunk’ feature board within a router may serve to receive digital information from multiple TDM streams onto which the digital information is coupled. The trunk feature board may be electronically coupled, through a TDM backplane, to various ‘modem’ feature boards. These modem feature boards transfer information from the trunk feature card to many modems of various types. This is perhaps best described by the use of a diagram.
FIG. 1
depicts a router
10
coupled to a central office
12
, which may be a telephone company switch, through a set of communication links
14
that may be of T1 or E1 industry standard form of communication line. T1 and E1 comply with standards set by the Institute of Electrical and Electronics Engineering (IEEE) for multiplexing various communication information from various sources (or devices) for transmission to other devices. The communication lines, individually, are commonly referred to as Digital Subscriber 0 (DS0).
Router
10
includes a trunk feature card
16
coupled through a TDM backplane
18
to a modem feature card
20
. While not shown in
FIG. 1
, a router may include more than one modem feature card. The modem card
20
couples modem signals for transfer thereof to modem devices. Rather than modem signals and devices, Digital Signal Processing (DSP) signals and devices may be similarly employed.
The TDM backplane
18
transfers TDM streams and channels from the trunk card
16
to the modem card
20
by coupling the same onto a first plurality of TDM streams
22
(for coupling signals from the trunk card
16
to the backplane
18
) and a second plurality of TDM streams
24
(for coupling signals from the backplane
18
to the modem card
20
).
The trunk card
16
and the modem card
20
each include a first TDM chip
26
and a second TDM chip
28
, respectively. These TDM chips are integrated circuits for arranging information, that is sent through the TDM communications link, into frames and vice versa. Each frame includes a predetermined number of channels and each channel carries information for a specific device that is using the router
10
for transferring information to another device. In a system that uses T1 communication links, there are 24 channels in a frame and in a system that uses E1 communication links, there are 30 channels in a frame.
Cisco Systems, Inc. designs, develops and manufactures various types of router products commonly employed in the industry for transferring internet information, arranged in packets, and for other types of telecommunications applications. One such router is referred to as the AS5200 and another is the AS5300 family of products.
Whereas the AS5200 supports 4 TDM streams carrying TDM information through a TDM backplane, the AS5300 supports 8 TDM streams. As described above, the modem feature cards(s) rely on the TDM backplane, which receives TDM streams, to communicate with external equipment through the trunk feature card.
One of the problems that arises with respect to prior art router systems, such as the one shown in
FIG. 1
, is that access to TDM streams is limited to four streams. While in routers supporting fewer number of modems (such as 60 modems), this was acceptable, a problem arises in recently-developed routers, which may support 240 or more modems. Each TDM stream can typically transfer 30 modem channels (using E1) and since previous router designs only had four TDM stream interfaces that were dedicated (not dynamically allocatable) lines, if trunk cards having more than 120 DS0 line interfaces were used, only 120 modem channels could be supported before having to share a channel by various modems. For example, if the modem feature cards supported 180 modems, due to the streams being limited in number to four, and with each stream carrying 30 channels, 60 of the modem channels would not be usable thereby introducing an over-subscription problem to the system. This is because TDM channels cannot be shared.
Dedicated TDM stream lines only allow for statically-allocated TDM time slots assigned based upon the order in which the feature boards in the router system are identified when the system is first powered-on. Moreover, each modem in the system only has one dedicated TDM backplane time slot. Once these backplane timeslots are allocated, the relationship between the time slots and the modems stays unchanged throughout the lifetime of the router until the next initialization of the system, after which this relationship again becomes fixed.
Another problem that arises with the advent of recently-developed router technology is the capability of using old trunk and modem feature boards in combination with more recently-designed trunk and modem feature boards such that the old boards and the new boards inter-operate with each other seamlessly.
The trunk feature cards may be considered ‘Producers’ of TDM backplane stream resources (or time slots) and the modem feature cards may be considered ‘Consumers’ of the TDM backplane stream resources in that they consume or utilize time slots for effecting communication of modem or telecommunications signals between modem devices and other devices.
When a router system includes a mixed combination (‘old’ and ‘new’ versions) of trunk and modem feature cards, the TDM resource
Cisco Systems Inc.
Imam Maryam
Phunkulh Bob A.
Vincent David R.
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