Multiplex communications – Pathfinding or routing – Combined circuit switching and packet switching
Reexamination Certificate
2002-03-04
2004-09-21
Chin, Wellington (Department: 2664)
Multiplex communications
Pathfinding or routing
Combined circuit switching and packet switching
Reexamination Certificate
active
06795431
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a packet switch, more particularly, a packet switch for transmitting or receiving IP (Internet Protocol) packets from an ATM line or to an ATM line, as well as for exchanging IP packets between ATM lines according to a network layer routing protocol.
2. Description of the Related Art
FIG. 2
shows a packet switch
1
a
connected to a plurality of ATM terminals
2
a
,
2
c
, and another packet switch
1
b
via ATM lines
3
(
3
a
,
3
b
,
3
c
) and
4
(
4
a
,
4
b
,
4
c
) respectively. The packet switch is used for relaying IP packets received by each ATM terminal as ATM cells to another ATM line according to a destination address.
The packet switch
1
a
comprises a routing controller
5
composed of a processor
51
provided with a routing table
52
, as well as a plurality of line interfaces
6
(
6
a
to
6
c
) connected to the routing controller
5
via an internal bus
7
. Each ATM terminal
2
(
2
a
to
2
b
) includes a processor
21
, a memory
22
, and an ATM interface
23
. Reference numerals
3
(
3
a
to
3
c
) and
4
(
4
a
to
4
c
) are one-way ATM lines connected to the line interface
6
of the packet switch
1
a
respectively and used to enter and output ATM cells.
If an IP packet is to be transmitted from an ATM terminal
2
a
, for example, the processor
21
reads transmission data
110
from the memory
22
and transmits a packet
100
to the ATM interface
23
. The packet
100
includes an IP header
120
, which is added to the data
110
according to the format of the IP (Internet Protocol) packet shown in
FIG. 3
, before the processor
21
transmits the packet
100
to the ATM interface
23
.
The ATM interface
23
then adds the 8-byte first control information to the start of the packet
100
in the format shown in
FIG. 4
according to both IETF (Internet Engineering Task Force) and RFC (Request for Comments), as well as adds the second control information to the end of the user information
200
consisting of the above control information and the packet
100
in the format of the CPCS (Common Part Convergence Sublayer) of the AAL (ATM Adaptation Layer)
5
shown in FIG.
5
. The format conforms to the ITU-T (International Telecommunication Union-Telecommunication Standardization Sector) recommendation 1.363. The first control information consists of an LLC (Logical Link Control) part
130
including a 1-byte DSAP (Destination Service Access Point) and a 1-byte SSAP (Source Service Access Point); and an SNAP (Subnetwork Attachment Point) part including a 3-byte OUI (Organizationally Unique Identifier) and a 3-byte PID
25
(Protocol Identifier). The second control information consists of a padding field
201
used to adjust a packet length so that a full length of each packet becomes a multiple of 48; a 2-byte reserved field
202
; a 2-byte packet length field
203
used to indicate a length of the above user information
200
; and a 4-byte CRC field
204
.
The ATM interface
23
divides an IP packet to which both first and second control information is added into a plurality of 48-byte information blocks thereby to generate ATM cells
300
, each consisting of a 48-byte payload
310
including one of said 48-byte information blocks and a 5-byte ATM cell header
320
in the format shown in FIG.
6
. The ATM interface
23
then transfers the generated ATM cells
300
to the ATM line
3
a
. At this time, the ATM interface assigns a VPI (Virtual Path Identifier) value and a VCI (Virtual Channel Identifier) value for each pair of a source IP address and a destination IP address included in each IP packet header and sets the values in both VPI and VCI fields of the ATM header
320
. In the ATM header shown in
FIG. 6
, the GFC field includes general flow control information used to prevent conflict between cells on a bus when the ATM switch is connected to a LAN, etc. The PTI field includes a payload type indicating a purpose for using the payload
310
. The CLP field includes cell loss priority information indicating whether to transfer object cells without a loss. The HEC field includes header error control information.
The ATM interface
23
transmits a management cell every fixed number of data cells (user cells) if the ABR (Available Bit Rate) service is used or if the performance monitoring function of the OAM (Operation, Administration, and Maintenance), which is a network management function group is used.
FIG. 7
shows how a management cell is transmitted when the ABR service is used. A D-box (e.g.,
300
-
2
,
300
-
3
,
300
-
4
,
300
-
6
, . . . ) indicates a data cell and an RM-box (e.g.,
301
-
1
,
301
-
5
) indicates a resource management cell. Those cells are shown in
FIG. 7
from left to right in order of transmission times. In
FIG. 7
, one resource management cell is transmitted every 3 data cells. The resource management cell (RM cell) has a value “110” set in the PTI (Payload Type Indication) field of the ATM header
320
. In the 48 bytes of the payload
310
is included management information in the format shown in FIG.
8
.
In
FIG. 8
, ID indicates a Protocol Identifier. ER stands for Explicit cell Rate, CCR stands for Current Cell Rate, MCR stands for Minimum Cell Rate, QL stands for Queue Length, SN stands for Sequence Number, and CRC stands for Cyclic Redundancy Check respectively. A resource management cell includes control information set in the 7th byte message type field in the format shown in FIG.
9
.
In
FIG. 9
, the DRI is a bit indicating whether an object RM cell is transferred forward or backward. The BN is a bit indicating whether an object RM cell is generated at a source node or at a non-source node. The CI is a bit indicating whether or not a congestion is generated. The NI is a bit indicating whether or not an additive increase is allowed. The RA is a resource allocation bit.
Back to FIG.
2
. The line interface
6
a
, when receiving a cell from the ATM line
3
a
, checks the PTI field of the received cell ATM header to know whether the received cell is a management cell such as an OAM cell, a resource management cell, etc. If the received cell is a management cell such as an OAM cell, a resource management cell, etc., the line interface
6
a
takes out the cell from the cell flow and processes the cell as needed. If the received cell is an OAM cell for error management or a resource management cell for ABR service, the line interface
6
a
processes the cell as needed, then transfers the cell to the ATM line
4
a
. If the received cell is a data cell, the line interface
6
a
combines the payloads
310
of a series of received cells to recompose the original IP packet and transmits the IP packet to the routing controller
5
via the internal bus
7
.
The processor
51
of the routing controller
5
stores the routing information indicating the correspondence between the destination IP address of the IP packet to be relayed and the output line interface
6
for receiving the IP packet according to, for example, the OSPF (Open Shortest Path First). The processor
51
, when receiving an IP packet from the line interface
6
a
, checks the IP header
120
. If the 12 header is illegal, the processor
51
discards it. The processor
51
then reduces the value in the field for time to live in the IP header by one only for IP packets having a valid IP header respectively. Then, the processor
51
searches the routing table
52
to find the output line interface
6
c
corresponding to the destination IP address and transmits the IP packet to the output line interface
6
c
via the internal bus
7
. If an option field is added to the IP header and the value of the first byte in the option field is within 32 to 63, 96 to 127, 160 to 191, or 224 to 255, the processor
51
discards the IP packet received from the line interface
2
a.
In the line interface
6
c
, the processor
51
sets additional information just like in the ATM terminal
2
a
before or after receiving an IP packet from the routing controller
5
, then converts the re
Antonelli Terry Stout & Kraus LLP
Chin Wellington
Hitachi , Ltd.
Pham Brenda
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