Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1999-04-16
2002-10-22
Nguyen, Chau (Department: 2661)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S415000, C370S537000
Reexamination Certificate
active
06470017
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a packet multiplexing apparatus for multiplexing packets input from a plurality of input ports and outputting to one output port, and to a method of operating in a communication system comprised by a plurality of network communication facilities connected by branching transmission lines to an opposite local service node.
This application is based on patent application Nos. Hei 2-110954 and Hei 10-110777 filed in Japan, the contents of which are incorporated herein by reference.
2. Description of the Related Art
For conventional packet multiplexing apparatus, the round robin method is applied. In this method, input ports are checked for the presence or absence of packets starting from an input port with a low port number.
The round robin method will be explained with reference to FIG.
10
. The packet multiplexing apparatus has n input ports (n is an integer larger than 2)
1
-
0
~
1
-(n−1) and an output port
2
. The input ports are sequentially numbered. In this case, an input port
1
-
0
designates an input port in location
0
,
1
-
1
in location
1
, and similarly input port
1
-(n−1) in location (n−1). Each input port is provided with respective buffer memories
3
-
0
to
3
-(n−1). The output signal transmission circuit
4
checks whether the packets are stored in individual buffer memories in the order of increasing port number, and if there is a packet, this packet is sent to output port
2
, while if there is no packet, it checks the next buffer memory corresponding to the next higher port number. This is the method of multiplexing used in the conventional packet multiplexing apparatus to multiplex packets input from input ports
1
-
0
~
1
-(n−1) and outputting multiplexed packets to output port
2
.
In the round robin method, when there is an input port that is outputting packets frequently, the input port that is immediately behind the busy port must wait a longer period on average for its packet to be retrieved, compared with the input port immediately ahead of the busy input port. Therefore, differences in the waiting time results for the various input ports.
When operating in a public network system, it is necessary to guarantee fairness of service to all the users connected through individual input ports. However, conventional round robin method could not assure uniform treatment of all input ports.
This problem of unfair packet retrieval will be explained in more detail using an example shown in FIG.
10
. Suppose that m is an integer smaller than (n−1), and consider a case that packets are being input in (m)
th
input port at a higher rate than other input ports which are relatively idle. Waiting times of packets in (m−1)
th
port and (m+1)
th
port will be compared in the following.
When a packet arriving in (m−1)
th
input port can be sent immediately to output port
2
, if, (m)
th
input port is not busy. In comparison, a packet arriving in (m+1)
th
input port can be sent immediately to output port
2
when (m)
th
input port is not busy and, additionally, when its buffer memory for (m)
th
input port is vacant in the next round of checking the (m)
th
input port. For this reason, the probability of immediate packet output from (m+1)
th
input port is lower than that from (m−1)
th
input port. In other words, the average waiting time for sending a packet is longer for a port that is ahead of the busy (m)
th
input port, i.e. (m+1)
th
input port, relative to a port that is behind the busy (m)
th
input port m, i.e. (m−1)
th
input port.
Therefore, an inherent problem exists in the round robin method that fairness in accessing one output port cannot be guaranteed for all users, in a communication system dependent on conventional packet multiplexing apparatus using round robin method.
One example of systems that utilizes such a packet multiplexing apparatus is a communication system comprised by a plurality of network communication facilities (users) oppositely connected to a local service node (local exchange) through branching transmission lines.
A communication method using such a system will be explained below.
FIG. 11
shows an example of the foregoing communication system including n network communication (com) facilities
110
-
1
~
110
-n (where n is an integer larger than 2) and a local service node
120
connected through a star coupler
130
with a branching ratio of n:1. That is, network com facilities
110
-
1
~
110
-n having dedicated optical fiber lines
140
-
1
~
140
-n are connected in a n:1 ratio through a star coupler
130
to a local service node
120
having an optical fiber line
150
. In other words, the local service node
120
is being shared by a plurality of network com facilities
110
-
1
~
110
-n.
Each of the network corn facilities
110
-
1
~
110
-n includes network termination units
111
-
1
~
110
-n for optical-electrical signal conversion and for termination of the signals exchanged between the local service node
120
and the network com facilities
110
-
1
~
110
-n, and service-function interface units. This example relates to a case of multiplexing of call connections for connection to the trunk network and LAN connections. In this example, interface units are comprised by circuit interfaces
112
-
1
~
112
-n and LAN interfaces
113
-
1
~
113
-n. Circuit interfaces
112
-
1
~
112
-n are connected to respective telephones
114
-
1
~
114
-n, and LAN interfaces
113
-
1
~
113
-n are connected to respective computers or line hubs
115
-
1
~
115
-n.
The local service node
120
is comprised by: local line termination units
121
-
1
~
121
-n for optical-electrical signal conversion and for termination of signals exchanged between the local service node
120
and network corn facilities
110
-
1
~
110
-n; a cross connect (XC) unit
122
; and the interface units. Similar to the network com facilities, an interface unit is comprised by a circuit interface
123
and a LAN interface
124
. The circuit interface
123
is connected to an exchanger
125
, and the LAN interface
124
is connected to a router
126
.
A method of communication in such a branched transmission line is to use a time compression multiplexing (TCM) method, in which upward signals (from network com facilities to the local service node) and downward signals (from the local service node to network com facilities) are transmitted through the same line but are identified by the differences in their positions on a common time base.
FIG. 12
shows a communication diagram, showing the signal exchanges between the network com facilities
110
-
1
~
110
-n and the local line termination unit
121
, according to the conventional communication method. For simplification, only the case of LAN connection will be explained. Also for simplification, synchronizing frames for the communication channel and optical transmission delay times through optical fibers are omitted. In the case of LAN connection, network com facilities
110
-
1
~
110
-n share a channel for transmitting the signals.
In this case, transmission and reception of signals are performed in burst cycles, that is, repeated cycles of transmission and reception actions. In a burst cycle, the downward signal channel (for transmitting downward signals from the local line termination unit
121
to the network com facilities
110
-
1
~
110
-n) and the downward com channel shared by the network com facilities are processed in the time division multiplexing (TDM) mode in the downward channel. And, in the upward channel, upward signal channels, for transmitting signals from the network com facilities
110
-
1
~
110
-n to the local line termination unit
121
, and the upward com channel shared by the network com facilities are similarly processed in the TDM mode.
The example in
FIG. 12
shows that four network com facilities
110
-
1
~
110
-n share one upward corn channel. In order to share the com channel by four network com facilities, those facilities havi
Miki Noriki
Otaka Akihiro
Tamaki Norio
Burns Doane Swecker & Mathis L.L.P.
Nguyen Chau
Nippon Telegraph and Telephone Corporation
Wilson Robert M.
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