Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
2000-10-10
2004-06-29
Nguyen, Chau (Department: 2661)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C370S395530
Reexamination Certificate
active
06757298
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to Virtual Local Area Network (VLAN) trunking over Asychronous Transfer Mode (ATM) Permanent Virtual Circuits (PVCs), and in particular to aggregating multiple VLANs onto a single PVC between two sites.
2. Background Information
Computers have made a substantial impact in the way corporations operate their business. The computer paradigm initially started out as a central computer (known as “main frame”) housed in one room that served all the needs of an organization's computational requirements. Main frames are generally expensive to procure and require intensive maintenance as well as a dedicated group of skilled programmers to service them. However, with the advancement of computer technology and fabrication techniques, powerful, yet small computers (known as personal computers (PCs)) capable of servicing individuals have become readily available. Furthermore, sophisticated off-the-shelf software have allowed individuals with no previous computing background to be highly productive using PCs. From the organization's point of view, this decentralized computer paradigm is more desirable in that a computer, which maybe “down” in one department, does not affect other computers in other departments. Furthermore, individual computers may be replaced on a as needed basis without unduly burdening the organization. However, individual computers operating autonomously are disadvantageous over the main frame in that they do not share resources among themselves.
The use of local area networks (LANs) allows for various PCs within a department to be connected together so that resources may be shared. Typically, one or more PCs are configured to act as servers to maintain files and to administer the LAN. Typically, the LAN would have a communication cable that connects the computers together for the interchange of information. To ensure that information is transmitted without corruption, popular arbitration schemes such as the Institute of Electrical and Electronics engineers (IEEE) 802.3 standard/Ethernet or IEEE 802.5 standard/token ring are widely used.
From an organizational point of view, it is desired that the individual LANs be connected together such that interdepartmental communication may be facilitated. For instance, the marketing department may want to access files in the manufacturing department. The manufacturing department, on the other hand, may want to access files in the procurement department. Therefore, to facilitate this, each of the individual LANs within the department may be connected by another LAN or LAN switches if each department is within the same building.
Where the individual departments are in different geographical areas, a wide area network (WAN) may be used to interconnect the LANs. Between campuses, one method would be to connect the LANs of each campus using a LAN switch. The campuses can then be connected via a Broadband Integrated Services Digital Network (B-ISDN) based on an Asychronous Transfer Mode (ATM) network. This configuration is shown in FIG.
1
. Although an ATM network is not a LAN per se, it can emulate the LAN to make it appear as if the individual switches are connected through a LAN system.
The ATM network switches small fixed units of data called “cells”. Switch latency is minimized because the small cell size equates to a small store-and-forward delay. It offers permanent virtual circuits (PVCs) that allows for static connections and switched virtual circuits (SVC) that are automatically set up and torn down on need basis. In accordance with the ATM FORUM that defines the ATM specification, the cell size is 53-bytes having the following components among others:
Virtual path identifier (VPI): Identifies the path to be taken by the ATM cell. In an idle or null cell, the VPI field is set to all zeros. (A cell containing no information in the payload field is either “idle” or “null”). A virtual path connection (VPC) is a group of virtual connections between two points in the network. Each virtual connection may involve several ATM links. VPIs bundle ATM traffic being sent to the same destination.
Virtual channel identifier (VCI): Identifies the circuit or connection number on that path. In an idle or null cell (one containing no payload information), the VCI field is set to all zeros. Other non-zero values in this field are reserved for special purposes. For example, the values VPI=0 and VCI=5 are used exclusively for ATM signaling purposes when requesting an ATM connection. A virtual channel connection (VCC) is a connection between two communicating ATM entities; the connection may comprise of many ATM links.
Payload type identifier (PTI): Indicates the type of data being carried in the payload. The first bit is a 0 if the payload contains user information and is a 1 if it carries connection management information. The second bit indicates if the cell experienced congestion over a path. If the payload is user information, the third bit indicates if the cell experienced congestion over the path. If the payload is user information, the third bit indicates if the information is from customer premises equipment (CPE). The payload is a maximum of 48 bytes.
The PVC is statically configured and mapped to a network in a subinterface point-to-point configuration. The path of the PVC is identified at each switch by an incoming VPI/VCI and an outgoing VPI/VCI. The logical data link layer may use the Subnetwork Access Protocol (SNAP) encapsulation as defined in the Request For Comments (RFC) 1483 published by the Internet Engineering Task Force (IETF). Alternatively, the logical data link layer can use LAN emulation (LANE) as specified in ATM FORUM 94-0035. LANE makes the ATM network transparent to LAN traffic by mapping connectionless LAN traffic over the connection-oriented ATM network. It uses point-to-multipoint connections to service the connectionless broadcast service that is required by LAN protocols.
The ATM Adaptation Layer (AAL) is used to receive the data from the various sources or applications and convert it to 48-byte segments that will fit into the payload of an ATM cell. There are several types of adaptation layers currently specified of which the AAL5 adaption layer is worth mentioning:
The AAL5 Common Part Convergence Sublayer (CPCS) Protocol Data Units (PDU) format is shown below:
CPCS-PDU
Payload
CPCS-PDL
Up to 2{circumflex over ( )}16
−1
octet
Payload
PAD (0 to
47
octets)
CPCS-UU
(1
octet)
CPCS-PDL
CPI (1
Octet)
Trailer
Length (2 octets)
CRC (4
Octets)
The payload field contains user information up to 2
16
−1 octets in length. The PAD field is used to pad the CPCS-PDU to be exactly 48 octets in length. The CPCS-UU (User-to-User indication) field is unused. The CPI (Common Part Indicator) field aligns the CPCS-PDU Trailer to 64 bits. Must be set to 000.
The Length field indicates the length, in octets, of the Payload field. The maximum value for this field is 65535 octets. A length of zero is used to indicate an abort. The CRC field protects the entire CPCS-PDU except the CRC field itself.
A Virtual LAN (VLAN) is a logical network that is defined according to the functions or applications of the users without regard to their physical locations (a physical LAN on the other hand is dependent on the user's physical proximity). As shown in
FIG. 2
, the end stations may be located in different campuses, however, the VLAN is able to group them together to operate with the same attributes of a LAN (i.e., as if they were connected together by the same physical LAN). Generally, VLANs are based on where the physical LANs enter the switch. For instance, in
FIG. 3
, a LAN switch may be configured such that ports
301
-
303
and
306
belong to VLAN
1
, ports
304
and ports
307
-
310
belong to VLAN
2
, and ports
305
,
311
,
313
belong to VLAN
3
. Ports in a VLAN share broadcast traffic, however, ports that do not belong to that VLAN do not share the broadcast traffic.
Inter-Switch Link (ISL) protocol i
Burns Barry S.
Lefelhocz Christopher J.
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