Introducing the open access network

In the “good old” telephony world, there was only one service provider. “Ma Bell” (or the PTT outside the United States) provided transport and all services. Of course, “all services” was actually quite limited—end users could call local, long distance or international. Then, with deregulation and the introduction of data services such as Internet access, the world changed.

Today, carriers provide transport, while service providers provide services. So while the physical connectivity may be provided by the telephone company (via dial-up, DSL or even fiber to the home), the telecom customer has a wide range of ISPs to choose from for their Internet access service. Furthermore, ISPs of all shapes and sizes are free to plug their services into the transport network and recruit subscribers independently.

The ability of the user to freely choose their service providers and of the service providers to connect to the transport network and solicit customers, is known as open access. In recent years, open access has been expanded to include not only ISPs but also voice-over-IP service providers, video service providers and application service providers.

Open Access is a regulatory requirement for many carriers that provide data services to their residential customers. U.S. RBOCs and many international incumbent carriers must now give their customers access to a wide range of service providers, and allow the customers to select whichever company they like for their individual services. Compounding this issue is that fact that many local governments, seeing high-speed data services as a key driver for economic growth, are deploying their own fiber networks. Viewing the high speed networks as a type of infrastructure, similar to a town’s plumbing/sewer system, the municipalities build and manage the infrastructure, facilitating access to high speed services, but not directly supplying the services themselves.

Figure 1: logical architecture of open access

In short, open access separates the carrier and service provider networks. As Figure 1 illustrates, the carrier network consists of the core layer and the access layer. These provide a simple transport medium connecting various types of end users to the service provider networks. These service provider networks consist of an IP services network, which routes traffic to the correct application server or the Internet, plus the services layer, which includes the application servers, VoIP gateways and any load sharing or distribution equipment.

For the end user, open access enables a wide range of services. This leads to competition, which leads to lower costs and often to improved customer service as well. With open access, users can switch between service providers simply, without any configuration changes to their systems. For service providers, open access means relatively easy, low-cost access to business and residential customers. With open access, service providers don’t have to build their own costly infrastructure—they leverage the carriers’ investments. At the same time, the service provider enjoys direct contact with the customer, enabling brand recognition and promoting customer loyalty. And for the carrier, open access enables maximum income from the network infrastructure. With open access, revenue is generated from both subscribers and service providers, and the same infrastructure can be used to support both business and residential subscribers. Even further, with the ability to connect numerous service providers to the infrastructure, network capacity may be used to the maximum.

Open access requires the transport network to be independent from service provider’s network and vice versa, including the following aspects:

• There should be no Layer 3 interaction between the service provider network and the carrier network or between different service providers on the same transport network

• The carrier network and the various service provider networks should be managed independently of each other, with complete separation of their management networks

• Authentication, Authorization, and Accounting (AAA) functions of the service providers should also be completely independent of the carrier’s or other service providers’ AAA activities

Furthermore, open access requires that the service providers be capable of independently providing IP addresses to their customers. This is true for Internet access, as well as other applications such as VoIP and video services. The transport network provider should not provide IP addresses to customers, unless it acts as one of the service providers.

Responsibility in terms of security and fraud prevention needs to be defined, with a clear demarcation between the transport provider’s jurisdiction and that of the service provider. Both the service provider and the carrier must protect themselves and their customers from malicious users and other possible threats, and it is key that the duties of each are known in advance.

Prompted by innovative competitive players that are revolutionizing data services, carriers worldwide are gearing up to provide “triple play” services—voice, video, and data—to their residential and small to medium business customers. Triple play services include:

• Multi-megabit Internet access

• 100’s of TV channels

• Voice and video telephony

• Video conferencing

• Video-on-demand (VOD)

• Interactive video applications

• Remote learning

• Gaming

Initial triple play networks have all been based on IP. Since most applications are designed for IP, it is the natural choice for any type of data service, including voice over IP, Internet access, and multicast for TV distribution. Figure 2 shows a typical IP-based triple play network. Homes and businesses are connected over an access network—which may be DSL, PON, fiber to the X or cable modem—to an IP network, which then connects the various services and the Internet.

Figure 2: IP-based open access network

In all of the IP-based triple play networks, there is one common denominator: They are not open access networks. Instead, the service provider and the carrier are one and the same. As Figure 2 illustrates, the carrier provides all of the services. This detail has allowed the relatively simple integration of the abovementioned services over a connectionless network using IP.

IP-based networks are not open access networks. The reason is simply that open access requires transparency to IP, and an IP-based network cannot be transparent to IP. In order for IP transparency to happen, a transport mechanism other than IP must be used.

Optical Ethernet has emerged as the technology of choice for carriers deploying next-generation data networks for both business and residential services. Optical Ethernet begins with Ethernet and its numerous benefits: standards-based, fast, ubiquitous and low cost. To this, optical Ethernet adds the qualities required by carriers: service provisioning with hard SLAs, 50ms resiliency, end-to-end OA&M and carrier-class network management.

These qualities are achieved using a connection-oriented architecture. Unlike enterprise-class Ethernet, which is a free-for-all with traffic patterns being determined by the end user, optical Ethernet services operate on predetermined paths. Connection Admission Control mechanisms ensure that sufficient resources are available for a service on all network elements in the path, before it is activated. A combination of committed and best-effort traffic is maintained for each service.

The connection-oriented paradigm employed in optical Ethernet is very similar to the mechanisms used in today’s broadband Internet Access systems. In these networks, each user utilizes an ATM virtual circuit deployed between the DSL modem and the broadband remote access server (BRAS).  These circuits are used to carry user traffic over using the point-to-point protocol (PPP), using a method known as PPP over ATM (PPPoA).

Figure 3: Optical Ethernet triple play networks

With optical Ethernet, a similar solution (shown in Figure 3) can be employed. Rather than using PPPoA, PPP over Ethernet (PPPoE) connects users and the carrier BRAS. The PPPoE sessions are carried over optical Ethernet services, where they enjoy (if needed) bandwidth guarantees and protection.

Perhaps most importantly however, the connection-oriented approach that optical Ethernet employs allows for open access to be deployed in the triple play network.

Take the case of Internet access, for example. The use of PPPoE allows each ISP to use private addresses, even though they may overlap with other ISPs servicing customers in the same network – even in the same home! End users choose their ISPs, either using an Internet portal or by specifying the ISP in their login string ("@ISP"). The carrier BRAS uses this information to direct sessions to the right ISP. The ISPs “push” IP addresses to the customer network, and use network address translation at the interface to the public network.

A similar approach is used for voice over IP. The IP address of the VoIP phone is set by the VoIP service provider using the dynamic host configuration protocol. Several VoIP providers can coexist in the network, with overlapping IP addresses, and still allow users on separate VoIP operations to talk to each other via the VoIP service provider's peering connections. To enable open access for broadcast video, optical Ethernet supports Layer 2 multicast mechanisms, including IGMP snooping and point-to-multipoint connections. This is in contrast to IP-based networks that require IP routing and protocol independent multicast to support multicast—mechanisms that are not transparent to IP, and therefore do not support open access.

Open access is alive and well in triple play networks today, including a large network deployed in southwestern Europe. The French city of Pau recently decided to push advanced services to businesses and residents by installing a high-speed optical Ethernet transport network capable of open access. This approach is allowing the residents of Pau to enjoy high-speed Internet access, advanced video services and VoIP telephony, while businesses can purchase virtual private network and Internet access.

In the Pau network, customers are connected via single mode fiber. Residential customers have set-top boxes for broadcast TV and video-on-demand and residential gateways for Internet access and VoIP telephony. Business customers are connected via a demarcation device (a managed fiber converter).

The access devices in the network are deployed in ring topologies, a very fiber-economic topology that allows up to 32 access devices to share a single fiber pair. The access devices are aggregated by core devices interconnected with 10 Gigabit Ethernet. Services are deployed as optical Ethernet connections which aggregate at the carrier’s BRAS. The BRAS has the job of directing traffic to and from the appropriate service provider for the customer and application. Video broadcast services are implemented as point-to-multipoint connections, connecting the video providers to end-users. In Pau, multiple Internet access service providers, VoIP service providers or VOD service providers coexist on the same network, making it a complete open access solution.

In conclusion, carrier triple play networks will soon become ubiquitous, delivering voice, video, and data to homes and businesses around the world. While initial triple play networks have been deployed using IP as the transport medium, these networks cannot meet a key requirement of many carriers: the ability to offer open access to service providers of various types. Optical Ethernet, which uses a connection-oriented paradigm to deliver quality of service guarantees and sub-50ms protection, is an ideal solution for the implementation of triple play networks that allow open access.

Gadi Solomon is the director of product management at Atrica and can be reached at gadi_solomon@atrica.com.

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