Multiplex communications – Data flow congestion prevention or control – Flow control of data transmission through a network
Reexamination Certificate
1998-12-30
2002-07-30
Kizou, Hassan (Department: 2662)
Multiplex communications
Data flow congestion prevention or control
Flow control of data transmission through a network
C370S352000, C370S389000
Reexamination Certificate
active
06426944
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to traffic control signaling in a fast packet network carrying Internet protocol packets and, more particularly, to the initiation of flow control signaling between layers one and two of a fast packet protocol such as the frame relay protocol and layers three, four or five of an Internet protocol such as the TCP/IP protocol upon receipt of a congestion message.
2. Description of the Related Arts
Referring to
FIG. 1
, there is shown an overview of a known fast packet network, for example, a frame relay or cell relay network, that is carrying packet data traffic between customer locations. By frame is intended a larger data carrying capacity within a single entity than a cell. A cell may comprise one or more data packets. The stacks
101
and
102
at the left and right respectively indicate stacks from the known open systems interconnect (OSI) model for describing layers of potential data transmission. Typically, customer applications software
103
runs on, for example, a personal computer workstation, labeled customer computer at location A or CCA and customer applications software
104
runs on the customer computer at location B or CCB. These talk to each other over the fast packet network at various levels of communication. The customer computer may be any intelligent communications terminal device having a controller and memory.
At level
1
, there exists, for example, communication over a local area network (LAN) cable between the computer workstation CCA, CCB and the router
105
,
106
, for example, an ACT Networks SDM-9300 or other router known in the art. The router
105
,
106
is connected via the customer's CSU/DSU interface card
106
,
107
to a time division multiplex (TDM) link to a comparable network's CSU/DSU interface card
108
,
109
. Typically, the area of box
112
represents the facilities of an interexchange carrier
112
such as AT&T and are shown in greatly simplified form. At the edge of the IEC network may be a frame relay router
110
,
111
which may, for example, comprise an ACT Networks SDM-9400 or SDM-9500 or other router known in the art. In between these edge switches, not shown, may be a satellite uplink, not shown and other intermediate switches.
At layer
3
, is the Internet Protocol (IP) layer. The customer workstation CCA or CCB communicates with the respective router
105
,
106
. There is no Internet protocol or TCP protocol communication within the fast packet portion of the network
112
. At layers
4
and
5
, the TCP protocol operates and at layers six and seven, the http.ftp.telnet high level protocol operates. These layers are strictly between work stations CCA and CCB.
Consequently, starting at the 7 layer customer computer CCA or CCB, each stack of protocol can be understood as executing a software process on the individual network element depicted. For example, the complete 7-layer stack executing on the customer computer may, in actuality, be, for example, an inter daemon applications package
103
operating under the UNIX operating system or a comparable package operating under a Microsoft Windows operating system or other system known in the art to provide protocol-based end-to-end communications services. The flow of data in the network is from applications software
103
all the way across the network
112
to applications software
104
.
The exchange of protocol-based control information in such a network is peer to peer. Fro example, if the TCP protocol processes on work station CCA exert flow control on the data stream, then it is exchanging flow control information with its peer TCP process on work station CCB. The same thing is true for IP and http and so on.
Now referring to
FIG. 2
, similar reference characters are used to denote similar elements. There is shown a similar figure emphasizing one end, for example, the CCA end of the network of FIG.
1
and with arrows shown designating what happens in the event of traffic congestion in the fast packet network. The X signifies the sensing of congestion at a frame relay switch within a fast packet network such as the AT&T frame relay network
112
. A key at the top of the drawing indicates the interface between the IEC and the customer premises equipment.
Starting at the 7-layer customer computer CCA, outbound traffic traverses the router
105
and then may encounter congestion at the second network switch
201
. When congestion is sensed in a fast packet network, it is known to originate congestion messages at level
2
in a forward and backwards network direction. The forward explicit congestion notification (FECN) message proceeds to the right (forward) and the backwards explicit congestion notification (BECN) message proceeds to the left (backward) by setting a bit within the cells or packets known as the FECN and BECN respectively to 1. For example, when congestion is noted, the forward message has FECN equal to 1 and BECN equal to 0. The backward message has FECN equal to 0 but the BECN equal to 1. Following the path of the BECN message, the message is passed by the edge switch
10
to the router
105
. The edge switch
110
is not programmed at all to react to the BECN message. Presently, the router
105
strips or discards the BECN message. The router
105
is, like the edge switch
110
, not presently programmed to react at all to the receipt of a congestion message. The fast packet protocols, including the frame relay protocol, are silent on what the end router is to do with the congestion message or any action to take. Congestion continues and dropped frames, cells and packets occur until the TCP layer finally senses longer acknowledgment times and/or missing packets. The TCP layer, being the first layer that is end-to-end or peer to peer is the first to react but is a layer that controls the presentation of data to the user at their work station and from the executing computer process
103
to the network. A layer
4
process may be executing on the router
105
, but such a process is also typically passive to congestion at layer
2
. Enhanced layer
4
functions are known, for example, firewall functions, but these are not flow control functions. In the typical case, the layer
4
router process is passive and so is not shown. In summary, it is believed that according to prior art processes, there is no slowing of data presentation to the network at workstation CCA even though network congestion is sensed at a frame relay switch
201
of the network and, eventually, frames (cells) are dropped due to the congestion.
Recently, the United States federal government has enacted legislation to encourage the delivery of Internet services to remote school districts, for example, that may only be reached by satellite. Examples of such school districts may comprise outlying Indian villages in rural Alaska, whose only telecommunications service is via satellite. Satellite introduces absolute delay into any data path due to the length of time it takes to travel to and from a geosynchronous satellite. Flow control becomes more acute because of this delay which would be experienced in a prior art flow control scheme where reliance on layer
4
TCP flow control measures is the only alternative. Data latency can consequently vary but may be typically increased from a latency on the order of a quarter to a half a second to a second to a second and a half. Latencies may typically be on the order of 900 milliseconds, so a fast reacting congestion alleviation scheme is desirable. Digital cell relay networks appear to be an economical and viable approach to providing such services and other data services as well such as telemedicine services at 56 or 64 kbps. It will be advantageous in the art if data flow control were provided in such networks especially those involving satellite links.
The obvious problem for customers of the interexchange carrier or other provider of frame relay services is dropped frames, cells or packets due to delays in implementing any data flow control. It is believed
AT&T Corp
Spafford Tim
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