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NE40E V800R010C00 Feature Description - VPN 01

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Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
ATM Cell Relay

ATM Cell Relay

ATM cell relay is a technique that transmits ATM cells over PWE3 VCs.

Background

ATM is a traditional multi-service bearer technology used on backbone networks. ATM networks can carry services such as IP,voice, teleconference, and ISDN/DSL and provide well-designed quality of service (QoS) mechanisms for these services. ATM networks have been used to carry important services.

IP networks have developed rapidly in recent years, owing to their advantages in upgradability, expansibility, and interoperability. The traditional ATM networks, however, are less compatible with newly deployed networks due to limitations on transmission modes and service types. An urgent demand is to upgrade traditional ATM networks and integrate them with existing PSNs, so that existing network resources can be fully utilized to meet expanded service demand.

By interconnecting ATM networks over a PSN, ATM cell relay emulates traditional ATM services when they are transmitted over the PSN. This allows end users to be unaware of network differences and protects carriers' investment during network convergence and construction.

Related Concepts

  • ATM cell: A cell is the basic ATM transmission unit. An ATM cell consists of 53 bytes, comprising a 5-byte header and a 48-byte payload. Each ATM cell is transmitted independently with a short transmission delay.
  • VC: ATM is a VC-based and connection-oriented switching technology. Each VC is identified by a virtual path identifier (VPI) and a virtual channel identifier (VCI). A VPI/VCI pair is valid for only a link between ATM devices.
  • Permanent virtual circuit (PVC): A PVC is a type of ATM connection configured by a network administrator. The establishment of a PVC does not require signaling.
  • Switched virtual circuit (SVC): An SVC is a type of ATM connection dynamically established using signaling.
  • Virtual circuit connection (VCC): A VCC is a type of ATM connection established based on VCI switching.
  • Virtual path connection (VPC): A VPC is a type of ATM connection established based on VPI switching.
  • ATM adaptation layer (AAL): The ATM adaptation layer is similar to the data link layer of the OSI reference model and is integrated with the ATM layer. The AAL is responsible for separating the upper layer from the ATM layer. The AAL prepares for conversion between service data and ATM cells by fragmenting service data into 48-byte payloads for ATM cells.

  • VPI/VCI mapping: As shown in Figure 8-19, a PW is used to emulate an ATM Switch. To retain configurations on ATM Switch, VPI/VCI pairs 1/100 and 2/200 must be mapped to each other on PE1 and PE2. In this manner, VPI/VCI pairs for CEs of a VC are mapped. If the PW emulates only one VPC or VCC, the PW functions as an ATM switch and mapping between VPI/VCI pairs does not need to be configured on PE1 and PE2. If the PW emulates two or more VPCs or VCCs, mapping between VPI/VCI pairs need to be configured on PE1 and PE2.

Figure 8-19  Networking for ATM cell relay over a P2P tunnel on a PSN

ATM cell relay interconnects traditional ATM networks and carries ATM cells over a point-to-point PW on a PSN.

Figure 8-20 shows the label encapsulation mode for ATM cell relay over a PSN. The outer label is the MPLS tunnel label and the inner label is the VC label used to identify the PW.

Figure 8-20  Networking for ATM cell relay over a PSN

A VPI/VCI pair is used to identify an ATM VC. Based on PW emulation types and comparison of ATM cell relay and AAL5 SDU relay, the following ATM cell relay modes are defined:
  • One-to-one (1-to-1): One PW emulates one VCC or VPC to carry ATM cells.
  • N-to-one (N-to-1): One PW emulates two or more VCCs or VPCs to carry ATM cells.

Table 8-3 lists the characteristics of different ATM cell relay modes.

Table 8-3  Characteristics of different ATM cell relay modes

Encapsulation Mode

AAL Type

Connection Type

Encapsulation Method

N-to-1 VCC cell relay

All AAL types

VC

The VPI/VCI pair is encapsulated into the ATM cell. The control word is optional for the PW. This PW encapsulation mode supports VPI/VCI switching.

1-to-1 VCC cell relay

All AAL types

VC

The VPI/VCI pair is not encapsulated into the ATM cell. The control word is required for the PW. This PW encapsulation mode supports VPI/VCI switching.

N-to-1 VPC cell relay

All AAL types

VP

The VPI/VCI pair is encapsulated into the ATM cell. The control word is optional for the PW.

1-to-1 VPC cell relay

All AAL types

VP

The VCI but not the VPI is encapsulated into the ATM cell. The control word is required for the PW.

AAL5-SDU

AAL5

VC

AAL5 SDUs are directly mapped to PWs for transmission, fully utilizing PSN bandwidth. The control word is optional for the PW.

As shown in Figure 8-21, ATM cell relay is classified into the following modes based on PWE3 networking modes:
  • Remote ATM cell relay: CEs are connected to two different PEs on the PSN, and ATM cells need to be transparently transmitted over the PSN.
  • Local ATM cell relay: CEs are connected to the same PE on the PSN. ATM cells are directly forwarded by the PE, instead of being transparently transmitted over the PSN.
    Figure 8-21  Networking diagram for local and remote ATM cell relay

Usage Scenario

The following describes usage scenarios for different ATM cell relay modes.

ATM VCC Cell Relay

Figure 8-22 shows an example of a VCC. A VCC is the basic transmit unit of an ATM network. VCCs can carry various ATM services.

Figure 8-22  ATM VCC cell relay

ATM VPC Cell Relay

Figure 8-23 shows an example of a VPC. A VPC is a set of VCCs with the same destination. VPCs can carry various ATM services. ATM VPC cell relay applies to the scenario in which packets from multiple users are bound to the same destination. ATM VPC cell relay features rapid transmission, easy management, and convenient configuration.

Figure 8-23  ATM VPC cell relay

Benefits

By interconnecting traditional ATM network resources over a PSN, ATM cell relay emulates traditional ATM services when they are being transmitted over the PSN. This allows end users to be unaware of network differences and protects carriers' investment during network convergence and construction.

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Updated: 2018-07-04

Document ID: EDOC1100027166

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