Abstract: This article discusses the technical solutions for transmitting Ethernet (EoPoS), EoPDH, or SONET / SDH via PDH over SONET / SDH. This technology appeared in the late 1990s. From the perspective of the development history of the technology, it is called the next generation of SONET / SDH (NGS) equipment. This article discusses the main factor restricting the development of NGS-the ability to work with traditional devices, and introduces the new technology that is currently emerging: Ethernet over Ethernet (EoPoS) via PDH over SONET / SDH. Integrating the Ethernet over PDH (EoPDH) standard developed by the ITU (ITU) with SONET / SDH can realize the collaborative work of EoPoS and traditional devices to provide effective data transmission.
Introduction Operating Ethernet services has made it possible for many telecommunications services that are conducive to revenue growth. Telecom operators must deploy these services to maintain their competitive position. However, considering that Ethernet networks cannot yet support link monitoring, fault isolation, and diagnostic testing, the inherent advantages of quasi-synchronous digital systems (PDFs) to enhance network reliability, many operators have not made up their minds to switch to pure Ethernet networks. Over the years, operators have regarded PDH and SONET / SDH networks as trusted platforms that can provide reliable services to demanding users.
It is very challenging to achieve transparent and efficient transmission of Ethernet frames from one side of the network to the other, and the cost of implementation in the past is also very high. In the late 1990s, some operators upgraded part of their networks to so-called "next generation" SONET / SDH (NGS) equipment. The advantage of these devices is that they can achieve efficient transmission of Ethernet and TDM services when the network utilization is close to 100%, but NGS equipment has certain disadvantages: lack of interoperability with the old system. Each service termination or delivery node needs to be replaced with a new system. Although this brings business to equipment manufacturers, the replacement of old nodes is a capital expenditure for operators.
At present, new protocols can be transmitted using old equipment, and the importance of the new protocol is also more significant, which can minimize the total cost of new operating Ethernet services.
Notes on next-generation SONET / SDH (NGS) Before understanding the advantages of this new method, it is important to understand the details of NGS. When transmitting Ethernet, NGS directly loads Ethernet frames encapsulated by the General Framing Protocol (GFP) into a SONET / SDH virtual container with variable bandwidth connections. This scheme mainly adopts the method defined in ITU-T G.707. By providing very fine-grained bandwidth intervals for each service on the NGS network, this transmission scheme can ensure the SONET / SDH link under nearly full load. Optimal bandwidth utilization. Many operators regard such equipment as an ideal technical solution.
But when the service is terminated or delivered, these connected virtual containers must be converted into a physical interface, such as OC-3, STM-1, T1, E1, or DS3. The NGS system cannot achieve good interoperability with the old system because the connected virtual container originating from the NGS node cannot be converted into a standard physical interface through the old SONET / SDH system. Since the old SONET / SDH system cannot perform this task, NGS equipment must be used at these nodes. In addition, when the old network is used to transmit services originating from NGS nodes, usually the entire old SONET / SDH container will be allocated to the channel. This reduces the fiber bandwidth efficiency obtained using NGS. In short, the NGS system does not have interoperability with existing transmission technologies, and the promised bandwidth utilization rate is difficult to achieve.
The basic principles of traditional SONET / SDH and EoPDH This new technology of efficient transmission of Ethernet through PDH over SONET / SDH network (EoPoS) does not deviate from the traditional transmission method, but fully utilizes the traditional transmission method. In order to master the main points of this technology, we need to start with some basic knowledge of the old SONET / SDH system.
All communication devices perform massive tasks through software and hardware protocol processing. The basic protocol stack of the traditional SONET / SDH add-drop multiplexer (ADM) is shown as the protocol stack A in FIG. 1. This protocol stack has been used to transmit PDH time domain multiplexed TDM services such as T1, E1 and DS3 private line access for many years.
Figure 1. Comparison of Ethernet (EoPoS) over PDH over SONET and the old SONET / SDH protocol
PDH services—T1, E1, and DS3—are widely known and fully deployed and trusted. Therefore, it is understandable for the International Telecommunication Union (ITU) to use these PDH technologies as the transport layer for new Ethernet services. ITU has recently developed new methods for Ethernet transmission over single and multiple PDH links. Applicable standards include ITU-T G.7041, G.7042 and G.7043. These new methods are an essential part of EoPDH (Transport Ethernet over PDH over SONET / SDH) technology. The protocol stack used by the EoPDH device is marked in Figure 1, as shown at the top of protocol stack B in the figure.
EoPDH is a set of technologies and new standards that allow operators to use a large number of existing copper-based telecommunications infrastructure to provide new Ethernet-oriented services. The EoPDH standard paves the way for interoperability and the gradual migration of operators to pure Ethernet. The standard technologies adopted by EoPDH include frame encapsulation, mapping, link aggregation, link capacity adjustment, and management messaging. The general functions of EoPDH devices also include traffic marking for virtual networks, prioritization of user traffic, and many higher-level applications. Although EoPDH was created for the point-to-point transmission of Ethernet through the PDH tributary, when combined with the old SONET / SDH network, EoPDH becomes an important and cost-effective Ethernet service transmission tool.
The advantages of transmitting Ethernet (EoPoS) through PDH over SONET / SDH A new class of SONET / SDH equipment can use the EoPDH standard to map Ethernet frames into virtually connected PDH branches, and then use traditional mapping technology to pass existing SONET / SDH The network transmits PDH connections. The protocol stack of this device is shown in protocol stack B in FIG. 1. Because this protocol stack integrates two technologies, EoPDH and PDH-over-SONET / SDH, this technology is called EoPoS (transport Ethernet through PDH over SONET / SDH).
An optional physical interface is allowed between the old protocol stack and the EoPDH protocol stack compatible with standard PDH technology at the protocol layer, for example: T1, E1 ports. This allows EoPoS protocol stack processing to be performed between devices connected via PDH links. Since protocol stack processing is allowed between multiple devices, one of the advantages of EoPoS technology is to support a mixed environment of new and old devices. The real advantage of EoPoS is that it can make full use of the existing infrastructure and knowledge for transmitting PDH branches through the SONET / SDH network. Unlike the NGS technology that tries to optimize bandwidth at all costs, EoPoS can use bandwidth efficiently while still minimizing costs. In order to better understand these advantages, let's look at a practical application.
In most operators' metropolitan area networks, services are delivered through interconnected SONET / SDH rings (Figure 2). Although the old ADM is shown as a single node (node ​​C) in the figure, it represents a batch of telecommunications equipment deployed in the area. The deployment cost of old SONET / SDH equipment is as high as hundreds of billions of dollars, which should be able to properly emphasize this. Most of this equipment has depreciated today and will only bring new operating expenses. It is important to note this. In order to reduce the total operating costs of new equipment, the depreciation costs of assets and maintenance costs must be lower than the operating costs of old equipment that has been completely devalued. This alone is sufficient to provide a strong cost basis for maintaining the operation of old SONET / SDH equipment.
Figure 2. Metropolitan SONET / SDH application block diagram
Node A in Figure 2 is a new device using EoPoS technology. To maintain interoperability, the device supports the traditional Ethernet-over-SONET / SDH (EoS) and NGS protocols. Therefore, Ethernet traffic can flow from the new EoPoS node to the NGS system of Node B, or from the EoPoS node to the old node. As mentioned earlier, the protocol stack of the old node does not include the NGS protocol. Since the NGS protocol lacks a PDH physical interface, the old node cannot terminate the Ethernet traffic from the NGS node. The old ADM at node C can transmit the EoPoS stream from node A. The old ADM handles the bottom of protocol stack B in Figure 1 and provides a physical PDH connection to low-cost devices. The CPE that supports EoPDH processes the top of protocol stack B in Figure 1, so that the EoPoS stream can be completely terminated. When existing customers switch from old TDM services to Ethernet services, the added cost on the old nodes is only low-cost equipment that meets the EoPDH standard, rather than expensive NGS SONET / SDH chassis.
For applications that must lease a PDH line to reach the location of the customer's EoPDH equipment, this protocol processing division of the PDH layer is also very useful. In addition, when the SONET / SDH network between Node A and Node C consists of a complex series of old device interconnections, the old devices can manage EoPoS flows as if they were simple PDH branches. Although ADM is used in this example, operational Ethernet equipment that benefits from EoPoS technology includes various types of equipment, such as MSPP, demarcation unit, ROADM, media gateway, IP DSLAM, and microwave radio.
Conclusion SONET / SDH equipment supporting EoPoS technology provides many advantages promised by NGS equipment while optimizing deployment costs. Standard virtual tandem methods are usually used, and the bandwidth consumed by operating Ethernet services can be dynamically adjusted at a granularity as low as 1.5 Mbps. The ITU-T G.7042 VCAT / LCAS protocol can provide dynamic allocation and flexibility to efficiently use all SONET / SDH bandwidth. Operating Ethernet service users can allocate the bandwidth they need, and waste very little bandwidth. By combining the intelligent use of the EoPDH protocol with SONET / SDH equipment, the cost required by the network to support the transition process of the newly operational Ethernet service will be reduced to the greatest extent.
A similar article was published on Electronic Design on April 12, 2007.
Introduction Operating Ethernet services has made it possible for many telecommunications services that are conducive to revenue growth. Telecom operators must deploy these services to maintain their competitive position. However, considering that Ethernet networks cannot yet support link monitoring, fault isolation, and diagnostic testing, the inherent advantages of quasi-synchronous digital systems (PDFs) to enhance network reliability, many operators have not made up their minds to switch to pure Ethernet networks. Over the years, operators have regarded PDH and SONET / SDH networks as trusted platforms that can provide reliable services to demanding users.
It is very challenging to achieve transparent and efficient transmission of Ethernet frames from one side of the network to the other, and the cost of implementation in the past is also very high. In the late 1990s, some operators upgraded part of their networks to so-called "next generation" SONET / SDH (NGS) equipment. The advantage of these devices is that they can achieve efficient transmission of Ethernet and TDM services when the network utilization is close to 100%, but NGS equipment has certain disadvantages: lack of interoperability with the old system. Each service termination or delivery node needs to be replaced with a new system. Although this brings business to equipment manufacturers, the replacement of old nodes is a capital expenditure for operators.
At present, new protocols can be transmitted using old equipment, and the importance of the new protocol is also more significant, which can minimize the total cost of new operating Ethernet services.
Notes on next-generation SONET / SDH (NGS) Before understanding the advantages of this new method, it is important to understand the details of NGS. When transmitting Ethernet, NGS directly loads Ethernet frames encapsulated by the General Framing Protocol (GFP) into a SONET / SDH virtual container with variable bandwidth connections. This scheme mainly adopts the method defined in ITU-T G.707. By providing very fine-grained bandwidth intervals for each service on the NGS network, this transmission scheme can ensure the SONET / SDH link under nearly full load. Optimal bandwidth utilization. Many operators regard such equipment as an ideal technical solution.
But when the service is terminated or delivered, these connected virtual containers must be converted into a physical interface, such as OC-3, STM-1, T1, E1, or DS3. The NGS system cannot achieve good interoperability with the old system because the connected virtual container originating from the NGS node cannot be converted into a standard physical interface through the old SONET / SDH system. Since the old SONET / SDH system cannot perform this task, NGS equipment must be used at these nodes. In addition, when the old network is used to transmit services originating from NGS nodes, usually the entire old SONET / SDH container will be allocated to the channel. This reduces the fiber bandwidth efficiency obtained using NGS. In short, the NGS system does not have interoperability with existing transmission technologies, and the promised bandwidth utilization rate is difficult to achieve.
The basic principles of traditional SONET / SDH and EoPDH This new technology of efficient transmission of Ethernet through PDH over SONET / SDH network (EoPoS) does not deviate from the traditional transmission method, but fully utilizes the traditional transmission method. In order to master the main points of this technology, we need to start with some basic knowledge of the old SONET / SDH system.
All communication devices perform massive tasks through software and hardware protocol processing. The basic protocol stack of the traditional SONET / SDH add-drop multiplexer (ADM) is shown as the protocol stack A in FIG. 1. This protocol stack has been used to transmit PDH time domain multiplexed TDM services such as T1, E1 and DS3 private line access for many years.
Figure 1. Comparison of Ethernet (EoPoS) over PDH over SONET and the old SONET / SDH protocol
PDH services—T1, E1, and DS3—are widely known and fully deployed and trusted. Therefore, it is understandable for the International Telecommunication Union (ITU) to use these PDH technologies as the transport layer for new Ethernet services. ITU has recently developed new methods for Ethernet transmission over single and multiple PDH links. Applicable standards include ITU-T G.7041, G.7042 and G.7043. These new methods are an essential part of EoPDH (Transport Ethernet over PDH over SONET / SDH) technology. The protocol stack used by the EoPDH device is marked in Figure 1, as shown at the top of protocol stack B in the figure.
EoPDH is a set of technologies and new standards that allow operators to use a large number of existing copper-based telecommunications infrastructure to provide new Ethernet-oriented services. The EoPDH standard paves the way for interoperability and the gradual migration of operators to pure Ethernet. The standard technologies adopted by EoPDH include frame encapsulation, mapping, link aggregation, link capacity adjustment, and management messaging. The general functions of EoPDH devices also include traffic marking for virtual networks, prioritization of user traffic, and many higher-level applications. Although EoPDH was created for the point-to-point transmission of Ethernet through the PDH tributary, when combined with the old SONET / SDH network, EoPDH becomes an important and cost-effective Ethernet service transmission tool.
The advantages of transmitting Ethernet (EoPoS) through PDH over SONET / SDH A new class of SONET / SDH equipment can use the EoPDH standard to map Ethernet frames into virtually connected PDH branches, and then use traditional mapping technology to pass existing SONET / SDH The network transmits PDH connections. The protocol stack of this device is shown in protocol stack B in FIG. 1. Because this protocol stack integrates two technologies, EoPDH and PDH-over-SONET / SDH, this technology is called EoPoS (transport Ethernet through PDH over SONET / SDH).
An optional physical interface is allowed between the old protocol stack and the EoPDH protocol stack compatible with standard PDH technology at the protocol layer, for example: T1, E1 ports. This allows EoPoS protocol stack processing to be performed between devices connected via PDH links. Since protocol stack processing is allowed between multiple devices, one of the advantages of EoPoS technology is to support a mixed environment of new and old devices. The real advantage of EoPoS is that it can make full use of the existing infrastructure and knowledge for transmitting PDH branches through the SONET / SDH network. Unlike the NGS technology that tries to optimize bandwidth at all costs, EoPoS can use bandwidth efficiently while still minimizing costs. In order to better understand these advantages, let's look at a practical application.
In most operators' metropolitan area networks, services are delivered through interconnected SONET / SDH rings (Figure 2). Although the old ADM is shown as a single node (node ​​C) in the figure, it represents a batch of telecommunications equipment deployed in the area. The deployment cost of old SONET / SDH equipment is as high as hundreds of billions of dollars, which should be able to properly emphasize this. Most of this equipment has depreciated today and will only bring new operating expenses. It is important to note this. In order to reduce the total operating costs of new equipment, the depreciation costs of assets and maintenance costs must be lower than the operating costs of old equipment that has been completely devalued. This alone is sufficient to provide a strong cost basis for maintaining the operation of old SONET / SDH equipment.
Figure 2. Metropolitan SONET / SDH application block diagram
Node A in Figure 2 is a new device using EoPoS technology. To maintain interoperability, the device supports the traditional Ethernet-over-SONET / SDH (EoS) and NGS protocols. Therefore, Ethernet traffic can flow from the new EoPoS node to the NGS system of Node B, or from the EoPoS node to the old node. As mentioned earlier, the protocol stack of the old node does not include the NGS protocol. Since the NGS protocol lacks a PDH physical interface, the old node cannot terminate the Ethernet traffic from the NGS node. The old ADM at node C can transmit the EoPoS stream from node A. The old ADM handles the bottom of protocol stack B in Figure 1 and provides a physical PDH connection to low-cost devices. The CPE that supports EoPDH processes the top of protocol stack B in Figure 1, so that the EoPoS stream can be completely terminated. When existing customers switch from old TDM services to Ethernet services, the added cost on the old nodes is only low-cost equipment that meets the EoPDH standard, rather than expensive NGS SONET / SDH chassis.
For applications that must lease a PDH line to reach the location of the customer's EoPDH equipment, this protocol processing division of the PDH layer is also very useful. In addition, when the SONET / SDH network between Node A and Node C consists of a complex series of old device interconnections, the old devices can manage EoPoS flows as if they were simple PDH branches. Although ADM is used in this example, operational Ethernet equipment that benefits from EoPoS technology includes various types of equipment, such as MSPP, demarcation unit, ROADM, media gateway, IP DSLAM, and microwave radio.
Conclusion SONET / SDH equipment supporting EoPoS technology provides many advantages promised by NGS equipment while optimizing deployment costs. Standard virtual tandem methods are usually used, and the bandwidth consumed by operating Ethernet services can be dynamically adjusted at a granularity as low as 1.5 Mbps. The ITU-T G.7042 VCAT / LCAS protocol can provide dynamic allocation and flexibility to efficiently use all SONET / SDH bandwidth. Operating Ethernet service users can allocate the bandwidth they need, and waste very little bandwidth. By combining the intelligent use of the EoPDH protocol with SONET / SDH equipment, the cost required by the network to support the transition process of the newly operational Ethernet service will be reduced to the greatest extent.
A similar article was published on Electronic Design on April 12, 2007.
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