Evolution of the Access Network
Evolution of the Access Network
- Evolution of the Access Network
Due to the complex environment of the access network and the diverse needs of users, different solutions and technologies are often adopted for different user requirements.
The initial access network was based on copper loops, i.e., copper wires were used to connect the PSTN switch PBX with the subscriber module RM. This loop system was based on TDM technology and provided traditional voice access. With the popularization of the telephone network, this copper loop achieved wide coverage of voice services.
However, the original copper loop could only provide narrowband voice. With the rapid development of data services, providing broadband value-added services over the copper loop is the most practical and lowest-cost option for operators. Through dial-up access, ISDN, xDSL and other technologies, data services can be provided to users, satisfying general household users' needs for Internet surfing and browsing. In particular, ADSL technology has become very mature. ADSL uses telephone lines to transmit information asymmetrically at high speed over non-repeatered subscriber loop networks, improving transmission rates and extending transmission distances, with a transmission distance exceeding 3 km. VDSL can provide a symmetric actual rate of 13 Mbit/s, with a maximum transmission speed of up to 52 Mbit/s.
For some emerging operators, because they do not have copper loop resources, they generally lay Category 5 cables directly to provide Ethernet services directly to users. The advantage of this access method is symmetric uplink and downlink, with data rates up to 100M. The disadvantage is the short transmission distance, requiring corridor switches for relay, or the use of media converters to extend the transmission distance, which increases costs.
As user requirements for bandwidth continue to increase, copper loops and corresponding access technologies can no longer meet user needs. The rapid growth of IP services and multimedia services has driven the access network to further develop toward broadband and integration. The access network is gradually evolving toward fiber loops, with fiber already deployed to buildings, residential communities, and roadsides. Users increasingly need multi-service, high-bandwidth access technologies. Against this background, the MSAP (Multi-Service Access Platform) began to emerge. The MSAP platform is a comprehensive platform based on mature SDH technology, integrating various other access technologies, enhancing the networking capability of the access network and the integration level of equipment, achieving unified management of transmission and access equipment, and reducing network construction and operation & maintenance costs. Adopting MSAP networking not only increases the reliability of the access network but also enables fiberization of the distribution segment, bringing fiber closer to users. The MSAP platform is particularly suitable for high-end enterprise users with high requirements for bandwidth and service quality.
- MSAP Multi-Service Access Platform
2.1. Introduction to MSAP
MSAP adopts traditional SDH technology, based on SDH, utilizing advanced GFP, VCAT, and LCAS technologies, integrating Ethernet switching technology and ATM switching technology to achieve integrated transmission of TDM services, Ethernet services, and ATM services. In addition, MSAP can provide low-rate Nx64k leased lines, Ethernet extension services (EoXDSL), etc.
The following sections discuss the MSAP platform's provision of leased line service access, Ethernet service access, and ATM and DSLAM service access.
2.2. Leased Line Service Access
2.2.1. 2M Leased Line
The 2M leased line service is the most mainstream leased line service. Operators generally use 2M leased lines for high-end commercial users and key accounts. Since MSAP is an SDH-based multi-service access platform, it retains SDH's excellent networking capability and comprehensive protection mechanisms, and can flexibly form point-to-point, linear, and ring networks, providing SNC protection. As it is essentially a TDM 2M service, it can provide extremely high service quality to guarantee the needs of key accounts. Depending on different customer requirements, 2M voice leased lines and 2M data leased lines can generally be provided.
A 2M voice leased line connects the key account's PBX to the backbone network, with the MSAP platform providing transparent transmission of 2M voice services. The 2M data service provides a data channel for key accounts, connecting the key account's router to the IP aggregation network.
2.2.2. NX64K Leased Line
On traditional copper loops, operators can provide Nx64K leased line services to users. The key account's enterprise router provides a V.35 interface, which is converted to a G.703 interface through a protocol converter or modem, and then the key account's data services are connected to the IP aggregation network through the traditional 2M loop. Due to the wide coverage of copper loops, this form of private network is very common, but it can only provide a very limited transmission distance of 3-5 km. For customers not covered by copper loops, laying fiber is cheaper than laying copper, and the transmission distance of fiber far exceeds that of copper.
In addition, considering future service expansion, key accounts increasingly prefer direct fiber access to the enterprise. Therefore, providing Nx64k leased lines on MSAP is a relatively practical choice. When the MSAP platform is used as the enterprise's CPE device, it can not only provide leased line services with longer transmission distances and better quality, but also provide other services for the enterprise, such as voice leased lines, Ethernet leased lines, and high-speed data access.
2.3. Ethernet Service Access
Due to the rapid development of Ethernet services, how to handle Ethernet services in the access network has become a key technology. Traditional Ethernet data applications use direct fiber connections via routers or switches, with service access devices directly interconnected, bypassing the transmission platform. This approach seems simple and low-cost, but actually has obvious disadvantages. First, without a transmission layer, fiber quality, performance monitoring, and protection cannot be achieved; fiber waste is severe, as each pair of service access points requires a pair of fibers, and if one service access point needs to communicate with other service access points, fiber usage grows factorially; the pressure on service ports is also significant, as each node connection requires an additional port on the switch or router. In addition, its networking capability is weak, only supporting simple rings and chains, and unable to form complex network topologies such as tangent and intersecting rings like SDH. Therefore, the traditional approach is only suitable for newly built pure data networks, or scenarios with a small number of nodes and short distances between nodes.
The MSAP platform absorbs the advantages of the SDH transmission platform, such as flexible networking and reliable protection, extending the advanced and mature SDH technology for TDM services to Ethernet applications, thereby achieving more effective and reliable Ethernet service access. MSAP handles Ethernet in three basic forms: point-to-point transparent transmission, L2 aggregation + transparent transmission, and Ethernet shared ring.
Point-to-point transparent transmission is implemented using the GFP mapping procedure, providing transparent transmission of Ethernet, directly mapping signals from user Ethernet interfaces into the MSAP virtual containers without Layer 2 switching, and then performing point-to-point transmission through the network. This method is simple to use, provides physical layer isolation, and has good security, making it suitable for customers with high requirements for data security and quality, such as banks and data centers. However, this method consumes relatively large bandwidth and has relatively high costs.
Aggregation plus transparent transmission means that MSAP can provide Layer 2 switching functions within the system, i.e., providing Ethernet link layer switching between one or more user Ethernet interfaces and one or more independent network links, implementing virtual bridge functionality. The aggregated data stream is then transmitted point-to-point to the termination point of the MSTP network. In this method, since local data streams are aggregated before entering the MSTP network, and the aggregated data stream is transmitted point-to-point to the termination point of the MSTP network, network bandwidth is saved compared to point-to-point transparent transmission, but security is lower than transparent transmission.
The Ethernet shared ring means that a path is established between the WAN ports of each MSAP node and its adjacent nodes, forming a logical ring. This ring serves as the underlying transmission channel for the Ethernet shared ring. When data packets enter the ring, the device uses unidirectional transmission, i.e., incoming packets are forwarded in one direction around the ring until terminated at the termination point. This method greatly saves bandwidth, but has relatively lower security, making it suitable for Internet browsing users.
Therefore, the MSAP platform fully considers the different Ethernet service needs of various users and provides different modes of Ethernet access to match users' specific requirements.
2.4. ATM and DSLAM Service Access
Due to the popularization and large-scale deployment of ADSL technology, a large number of DSLAMs are aggregated in the metropolitan area network. The uplink ports of these DSLAMs are typically Ethernet interfaces and ATM STM-1 interfaces. For ATM interface aggregation, the traditional approach is to directly connect DSLAMs via fiber to the ATM switch at the aggregation point, with the ATM switch performing the aggregation function. Like direct Ethernet fiber connections, this approach consumes a large amount of bandwidth, is inefficient, lacks physical layer link protection, and is very difficult to maintain. In addition, as the network expands and the number of DSLAMs increases, the ATM switch ports at the aggregation point need continuous expansion, which is very expensive.
The MSAP platform fully considers the above issues by integrating ATM switching and aggregation functions on the platform, using VP-Ring and SDH protection functions to enhance DSLAM aggregation capabilities. The specific implementation is shown in the figure below: DSLAM uplink ports connect to MSAP ATM interfaces, MSAP performs ATM switching and aggregation functions, and then transmits services through VP-Ring to the termination node, finally delivering them to the ATM backbone switch.
MSAP's ATM processing capability will greatly reduce the cost of DSLAM aggregation, with clear network hierarchy, easy maintenance and management, while ensuring strong network expansion capability.
- MSAP Prospect Analysis
3.1. Service Quality
With the continuous improvement of the access network, major users no longer simply pursue the best price, but have higher requirements for service quality, such as fast service provisioning speed, rapid fault location and repair after failures, and regular service quality reports. This requires the access network platform to provide stable, reliable, and high-quality services for key accounts.
MSAP can improve operators' service quality. MSAP is a multi-service platform built on SDH, and its carrier-class service quality is beyond doubt. SDH's abundant overhead bits can provide end-to-end circuit quality monitoring for subscriber lines, supporting fault location and troubleshooting without on-site visits, saving valuable time and human resources. In this regard, MSAP's technical advantages cannot be surpassed by other access technologies.
3.2. Network Management
The network environment and equipment in the last segment of key account access are complex and lack unified management standards, resulting in low maintenance and management efficiency and high costs. The key account access network has become a network that is "difficult to manage well." This requires the access network platform to provide comprehensive management and improve operators' management and maintenance efficiency.
MSAP completes the management of all services and configurations (including central office and customer premises) within a unified management system on a common system architecture. At the same time, MSAP provides customers with a multi-client management architecture, supporting the operation and maintenance department's management requirements of "centralized management, hierarchical maintenance," and can further provide key account groups with monitoring systems for leased circuits.
3.3. Differentiated Services
Operators need to provide "package" services for users of different scales and industries, offering different circuit qualities and interface standards at different tariff levels. This requires the access network platform to provide multi-service differentiated services.
MSAP can meet the differentiated needs of different customers on a comprehensive access platform, simplifying the planning and construction of the access network. For the needs of different industries for different service interfaces, MSAP can uniformly provide support and management for transparent transmission, bonding, and multiplexing of multiple channels including E1/V35 circuits, Ethernet, and ATM on a single network.
Therefore, with the development of data services and leased line services, the advantages of the MSAP platform in service quality, network management, and provision of multi-service differentiated services will increasingly gain favor with operators. Especially in the process of transformation and expansion of traditional data networks, MSAP will play a key role.