Packet relaying apparatus

Details Packet relaying apparatus Packet relaying apparatus

2000-05-25

2004-08-03

Nguyen, Chau (Department: 2732)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S401000, C370S395100

Reexamination Certificate

active

06771645

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a packet relaying apparatus, specifically a label switching router (hereinafter occasionally abbreviated as LSR), and in particular to a packet relaying apparatus used for MPLS (Multi-Protocol Label Switching).
The MPLS is a technique being presently standardized by an MPLS working group of the IETF as a basic technique for an Intranet and an Internet backbone.
A label switching technique having characteristics of high-speed data transmission/scalability/easy traffic control is utilized for the MPLS. In the label switching, a routing process at an IP level (layer
3
) and a switching process at a lower layer (layer
2
) by an ATM switch, a frame relay switch, an Ethernet switch, and the like are united to perform forwarding of the layer
2
by a label assigned to a packet.
In the MPLS, a group of layer
3
packets transferred by the same method or treatment (for example, transferred on the same path and the same service class) is defined as an FEC (forwarding equivalence class), and the same label is assigned to the group of packets corresponding to the FEC.
Hereafter, the forwarding of the layer
2
can be performed to the packets to which the label is assigned by referring only to the label to determine parameters required for the forwarding of the layer
2
such as a transferring path and a service class by the FEC corresponding to the label.
The label switching router as the packet relaying apparatus serves to realize the label switching, so that how the label is assigned to the packets is important.
2. Description of the Related Art
In a connection oriented network such as an ATM or a frame relay, the “connection” can be generally used as a bidirectional connection, i.e. connection in both directions or as a unidirectional connection, i.e. connection in one direction.
Furthermore, a single connection identifier is generally assigned to the bidirectional connection and also the unidirectional connection.
In consideration of setting up paths by two independent connections in a unidirection “a” or “b” in
FIG. 9
, the same connection identifier such as a VPI/VCI=0/33 in
FIG. 9
can be generally used as the connection identifier which identifies “a” and the connection identifier which identifies “b” with respect to the connection between a port
1
in FIG.
9
and an adjoining apparatus. The apparatus which can realize this method is defined as the one having a bidirectional capability with respect to the directionality.
However, when the path is set up by the unidirectional connection such as “a” shown in
FIG. 9
, many prior art apparatuses set up the path even for “b” which may not be actually set up but only for management and which is not inherently necessary as shown in
FIG. 8
, in terms of hardware or management restraint. In other words, many apparatuses exist which substitute the path setting by the bidirectional connection for the unidirectional one. This is defined as an apparatus having a unidirectional capability with respect to the directionality.
It is known that an ATM switch which forms an ATM-LSR for realizing the label switching in the ATM network has a unidirectional VC capability or a bidirectional VC capability as a VC (Virtual Connection) directionality.
Also, it is known that a frame relay switch which forms a frame relay LSR (Frame Relay Label Switching Router) for realizing the label switching in the frame relay network has a unidirectional DLCI capability or a bidirectional DLCI capability as a DLCI (Data Link Connection Identifiers) directionality.
It is to be noted that the combination of the VPI and the VCI (VPI/VCI) is generally used for the label used in the label switching between adjoining ATM-LSR's and the DLCI is generally used for the label between adjoining frame relay LSR's.
Hereinafter, the label switching will be more specifically described with the ATM switch which forms the ATM-LSR being taken as an example.
FIG. 8
shows an ATM switch
310
having the unidirectional capability. In case of “unidirectional”, normally the connection “b” (incoming VPI/VCI=0/34 at port
2
; outgoing VPI/VCI=0/33 at port
1
) is automatically set up when the connection “a” (incoming VPI/VCI=0/33 at port
1
; outgoing VPI/VCI=0/34 at port
2
) is set up.
When the ATM-LSR is formed of the ATM switch
310
, the incoming label
0
/
33
is to be switched over to the outgoing label
0
/
34
for a packet directed to the connection “a” because the VPI/VCI is used as the label. Being used for the link with an adjoining ATM-LSR connected to the port
1
, the incoming label
0
/
33
for the ATM switch
310
is an outgoing label for the adjoining ATM-LSR. Likewise, the outgoing label
0
/
34
is an incoming label for the adjoining ATM-LSR connected to the port
2
.
In this way, the label switching assigns the label to the link having the directionality to make switching between the incoming label and the outgoing label in each of the LSR's.
Accordingly, in the example of
FIG. 8
, when a label assignment is firstly directed to the connection “a”, the connection “b” opposite in direction can not use the labels
0
/
33
and
0
/
34
because they have been already used for the label switching of the connection “a”.
FIG. 9
shows an ATM switch
320
having the bidirectional capability. In this case, the connection “a” (incoming VPI/VCI=0/33 at port
1
;
outgoing VPI/VCI=0/34 at port
2
) and the connection “b” (incoming VPI/VCI=0/35 at port
3
; outgoing VPI/VCI=0/33 at port
1
) can be independently set up.
When the ATM-LSR is formed of the ATM switch
320
, the switching between the incoming label
0
/
33
and the outgoing label
0
/
34
is to be performed for the packet directed to the connection “a”. Also, the switching between the incoming label
0
/
35
and the outgoing label
0
/
33
is performed for the packet directed to the connection “b”.
Namely, in case of the ATM switch having the bidirectional capability, a single label (
0
/
33
) can be used as an independent label for both direction links.
It is to be noted that in the label assignment between the adjoining ATM-LSR's, one ATM-LSR normally sends a label request message to the other ATM-LSR so that a label mapping message returned back from the other ATM-LSR determines an available label. In this respect, the prior art ATM-LSR has adopted such a method that only the label assigned by itself is managed and the label notified from others is used as it is.
When the label is used for “bidirectional”, there is no particular problem as to the label assignment because the adjoining ATM-LSR's perform the label assignment (or distribution) independently of each other.
However, when the label is used for “unidirectional”, there is a possibility that the label which the same router is about to assign coincides with the label which others are about to assign by the management of only the former label, so that such a label collision is required to be avoided.
Therefore, the LSR has been developed, as shown in
FIG. 10
, which performs the label assignment by fixedly assigning odd number labels or even number labels. Hereinafter, the operation will be described.
It is supposed that an ATM-LSR_A has the bidirectional capability and an ATM-LSR_B has the unidirectional capability in FIG.
10
.
(I) Exchange of LDP Identifiers
The ATM-LSR_A sends a hello message including an LDP identifier (=1) for identifying itself to the adjoining ATM-LSR_B (at step S
11
). The ATM-LSR_B which has received the identifier returns a hello message including an LDP identifier (=2) for identifying itself to the ATM-LSR_A (at step S
12
).
It is to be noted that the format of a general LDP message is as shown in
FIG. 11
, and the message is composed of the fields of a “U” bit, a message type, a message length, a message ID, an essential parameter, and an optional parameter. The message whose type in
FIG. 11
is “0×0100” is the hello message shown in

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