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This paper introduces a new technology, wideband packet over SONET (WPOS)1, which provides highly reliable, thin-route Internet and IP access data services in areas serviced by local carriers (incumbent or new entries). The target end user is an enterprise with voice and data needs requiring the equivalent of one or more T1 leased lines. WPOS is a technology that uses industry-standard mechanisms to provide scalable access pipes and provides transport for circuit-based traffic.
The paper discusses the need for access solutions for enterprise subscribers, followed by an overview of market trends heralded by recent deregulation and growth trends in the telecommunications industry. Metropolitan networks are becoming predominantly fiber based, as evidenced by market data for fiber deployment by network providers in the last decade. These fiber facility networks utilize synchronous optical network (SONET) as the transport mechanism of choice because it encompasses a rich set of features, including reliable, secure Layer 1 transport.
Business applications such as Internet access and transparent LAN services are driving the growth of IP traffic on the WAN. This scenario forces network operators to deploy efficient packet-processing technologies. Frame Relay solves a near-term need but is not suited for next- generation, high-speed, value-added services. ATM, in theory, has the functions, but its implications on existing infrastructure have hindered its widespread deployment in the near term. Packet over SONET (POS) is an emerging technology that uses point-to-point protocol (PPP) encapsulation to map IP directly into SONET, providing an efficient solution for the backbone, but not the thin routes that are ideally suited for the access market.
WPOS utilizes the same packet encapsulation mechanism as packet over SONET but utilizes "channelized" SONET pipes. The payload is divided into multiple channels, as defined by SONET standards. This technology enables "point-to-network" rather than "point-to-point" solutions because voice and data services from customer terminated equipment (CTE) connect to existing voice switches and IP routers. The Cisco integrated SONET/SDH router (ISR) product based on WPOS technology enables network operators to offer value-added IP services to enterprise end users utilizing their existing fiber infrastructure.
Corporations consider creating a networked business environment as an essential ingredient to their success. This scenario includes the need to connect to the Internet as well as let their customers and partners connect from the Internet. According to a study by Forester Research, internet access services will grow from $5B in 1998 to $20B in 2000, a blistering growth rate of 200 percent per year. Through the Internet (and managed, secure intranets that use Internet technology), companies create working relationships with their customers, partners, suppliers, as well as their employees. Customers assess their need for products they consider purchasing, partners obtain necessary tools to increase sales, and suppliers keep track of inventory levels to enhance manufacturing efficiencies. Finally, employee communication is seamless irrespective of location; thus, they improve their efficiency and shorten development cycles.
Using the Internet as a public network, companies have set up "intranets" to obtain connectivity within the enterprise. To allow external access to the intranet for partners or suppliers, a virtual network of secure connections is created. This network is widely referred to as an "extranet." These services add tremendously to the Internet access bandwidth needs of a corporation. Corporations need to add to their existing access infrastructure within a much shorter time to keep up with escalating demand. Unfortunately, no solutions are available that can scale from T1 (1.5 Mbps) to T3 (45 Mbps) using the same equipment. Fractional T3 circuits, if available, use proprietary inverse multiplexing techniques that require identical equipment on both ends of the connection.
Another trend that drives connectivity requirements is that companies are growing to multiple locations because of acquisition or through decentralization. In order to keep critical data at the headquarters site, remote sites need to be connected to headquarters in a client server architecture with an emulated LAN connection (10 Mbps or greater). Using leased lines is not a viable option because of bandwidth needs which that falls between those offered by dedicated T1 and T3 lines. In addition to the new data services, traditional voice services account for a large portion of expenses incurred by a company. A solution that provides an integration of private-line T1 voice transport and Ethernet-based IP data services is desirable for the following reasons:
Cisco ISR products that have the ability to extend the SONET network to the customer premises provide the support for existing voice applications as well as enable managed IP data services. They combine circuit (T1 transmission) and data (Ethernet services) capabilities in a single, cost-effective platform.
The Telecommunications Act further solidified competition in local networks. However, it will take time for competitive providers to build the infrastructure needed to provide new services to corporate clients. In the meantime, incumbents have a great opportunity to establish their presence further by using their existing local loop efficiently to provision new services for their existing customers. According to Dataquest, T1 leased lines are growing at the cumulative annual growth rate (CAGR) of 18 percent. To address the needs of this market, carriers (incumbents and competitive) are investing large amounts of money into installing SONET equipment to provide a redundant, fault-tolerant transport mechanism for business customers' traffic. Legacy asynchronous networks, on the other hand, provide no end-to-end management, require back-to-back multiplexing, and take seconds to reroute around a fault.
The global phenomenon of the Internet and its associated applications such as the World Wide Web are rapidly changing the profile of traffic on the WAN. In an environment where voice was the dominant source of traffic, data and video are beginning to have an increased impact on the type of equipment being deployed. According to Ryan, Hankin, and Kent, voice and data traffic are about 50 percent each in the network today, with data traffic increasing at the rate of 50 to 100 percent annually. Voice traffic, on the other hand, grew a modest 9 percent in 1998. Data traffic on the WAN is dominated by IP, with 72 percent of business customers using TCP/IP as the primary protocol, according to a July 1997 survey by Communications Week.
The wirecenter access network includes all the equipment between the customer premises and the telecommunications network operator's central exchange (CE). Traditionally, this network was used for obtaining point-to-point links for connectivity between locations across town, across the country, or across the world. The creation and the rapid proliferation of public networks, and especially the Internet, have changed that to some degree. With ubiquitous connectivity becoming an essential ingredient to doing business, building an information infrastructure is paramount to the success of a business. Creating an environment in which customers (prospective and current), partners (distributors and resellers), suppliers, and employees are able to get access to information is almost as critical as creation of the product itself, implying the creation of a sophisticated network infrastructure that allows free flow of information while at the same time protecting intellectual property from competition.
To upgrade the business fiber local-loop network and provide new value-added access services, network operators have been installing fiber to supplement the aging copper-based network. The advantages of fiber are that it provides very high bandwidth capacity, it is not affected by crosstalk, and it can be extended over much longer distances without regenerators. Incumbent carriers have and continue to build on extensive SONET networks in their territories, and their competitors are also building fiber-based networks very aggressively. As part of this fiber build-out, fiber access networks allow network operators to roll out advanced broadband digital services to address applications used by business customers. The transport technology of choice is SONET/SDH, which is an international standard developed to transport both voice and data traffic. SONET is used primarily in North America, while SDH is used in Europe, Latin America, and elsewhere.
SONET technology was developed in the mid 1980s to create a next-generation physical layer transport. SONET defines the transmission speed, line encoding, and signal multiplexing mechanism to transport a heterogeneous mix of traffic. The SONET overhead mechanism facilitates transport of legacy private-line traffic in addition to newer mappings for Layer 2 protocols such as ATM, fiber distributed data interface (FDDI), and PPP (IP).
SONET is designed to be a transport mechanism that maps existing asynchronous circuit-based traffic into a synchronous payload envelope, hence greatly simplifying the process of demultiplexing traffic at the other end of the connection. Legacy multiplexing equipment that switched asynchronous traffic would require bit stuffing to accommodate jitter as well as extraction of payload at each switching point in the network. SONET eliminates the need to fully extract the payload by providing pointers to the start of the payload and a common clock referenced to a stable reference point. The basic building block of SONET is STS-1 (Synchronous Transport Signal level 1) operating at 51 Mbps. All higher-rate signals are a multiple (N) of the basic STS-1 signal rate.
SONET allows multiple subrate bitstreams to be multiplexed into the synchronous payload envelope (SPE). This process is also referred to as payload mapping or tributary processing. Sub-STS-1-rate traffic is referred to as virtual tributaries (VT) in SONET and map directly to existing asynchronous signals (typically, T1). This mapping is referred to as a "channelized" SONET payload because it enables multiple channels to be provisioned in a single STS-1 payload.
Applications such as POS specify super-rate (higher than STS-1 or 51 Mbps) payloads that are achieved by a STS-Nc (starting at 155 Mbps or N = 3) module formed by linking multiple STS-1s together in fixed-phase alignment. The super-rate payload is then mapped into the resulting STM-Nc SPE for transport. This mapping is also referred to as a "concatenated" SONET payload. POS uses concatenated SONET pipes for transport. In this mode, no tributary mapping is supported and the multiplexing equipment has to add and drop the entire STS-Nc payload at the traffic termination points. Typical concatenated payloads are STS-3c, STS-12c, and STS-48c.
Using SONET, it is now possible to deploy true multiservice networks that serve all the communications needs of the end user. In addition to these features, SONET provides extensive operations, administration, and maintenance (OAM) capabilities, allowing for a robust, inexpensive, multivendor deployment for the network operator. SONET-based fiber networks are commonly deployed in a ring topology. This setup allows a redundant, self-healing configuration to be deployed, providing highly survivable operation.
Network operators driven by ever-increasing needs of their business customers now offer SONET-based connections as a standard service rather than a special service for select, high-volume customers. Dataquest predicts that in North America, SONET equipment sales will exceed $4B by the year 2000, from $2B in 1995.
SONET access enables network operators to provision value-added services that enable businesses to create a networked infrastructure. The following are some examples of IP-based data applications that run on SONET access networks:
1. Managed Router Service for Internet Access
In order to provide ease of use to the end user, ISPs now provide a "managed router service" where the installation, configuration, and maintenance of the router is offered as a service. In other words, now the demarcation point is moved from the channel service unit (CSU), which is what the network operator usually stops at, to the CTE router. The following is an illustration of the deployment topology for Internet access.
The traffic that originates on the premises hits the router where it is filtered based on destination addresses and access list criteria. The router is connected to a fiber access network. This connection terminates on an access concentrator (or router) at the ISP POP where the IP packets are forwarded through an IP backbone router to the Internet on the network-access-point (NAP) link.
2. Transparent LAN
For medium to large-sized corporations, it is common to have buildings or campuses spread out over a wide geographical area. Because a large amount of collaborative work is done through their corporate network, it is a big advantage to a corporation to have remote sites connected together using a high-speed link, effectively emulating a local LAN. This setup allows existing client server architectures to be used where the bulk of corporate information is still stored and maintained on servers in the headquarters. Remote sites can now access this information as if they reside on the local network. The following is a deployment scenario for transparent LAN (TLAN) applications.
The TLAN connections between ISR systems and routers above imply that all traffic, including broadcast and multicast traffic, is connected between data networks. The ISR typically performs filtering and forwarding functions, whereas the routers perform Layer 3 interconnection. If filtering is enabled, traffic deemed local to both LANs is kept off the WAN by the ISRs shown above. This scenario allows efficient utilization of the WAN link. The 10-Mbps Ethernet pipe is mapped to SONET using a Layer 2 protocol such as POS or WPOS.
The solutions available for SONET access today can be categorized into four types of services. Each of these services is offered over a SONET ring, albeit with different tariffs and equipment requirements.
Packet over SONET is predominantly deployed on the backbone; hence, it does not qualify as an access technology in the context of this discussion. However, the WPOS technology discussed later will demonstrate how this technology can be used in SONET access networks.
The following is the summary of the benefits and limitations of prevalent access technologies as well as a comparison to WPOS.
| Access Technology | Benefits | Limitations |
|---|---|---|
| Leased Lines | Widespread availability due to large installed base | Declining tariffs as technology and associated equipment mature |
| Fixed bandwidth connection to the CE (upgrade from T1 to T3 would require changing CTE and CE equipment) | |
| Uses aging copper plant, requiring line conditioning and signal regenerators to operate at rated speeds | |
| Frame Relay | Ability to share the transmission medium for point to multipoint connections | Data rates above T1 not commonly available |
| Saves costs by statistical multiplexing of user payload accommodates occasional burstiness of traffic while guaranteeing a minimum throughput over time | No built-in support for applications such as multimedia transport that require QoS guarantees | |
| Requires extensive provisioning because DLCIs need to be set up for all end nodes | |
| ATM | ATM provides an integrated network for all traffic types - voice, data, and video | Because IP dominates in the desktop market, transporting LAN traffic on the WAN requires additional overhead to map IP protocols to run over ATM |
| ATM provides support for quality of service (QoS), enabling a network operator to offer support for delay-sensitive applications | Overlay network required to provide end-to-end services | |
| Packet over SONET | Low overhead point-to-point transport of IP data - fixed 6-byte header for all packets from 64 to 1,518 bytes | IP protocols to achieve QoS are still being deployed across the WAN |
| Simplicity of PPP allows lower complexity and hence lower-cost edge devices to encapsulate IP data | Voice transport over IP would require infrastructure upgrades throughout the network to achieve results comparable to today's TDM network
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| WPOS | Allows dedicated scalable pipes to be provisioned from enterprise LANs to data termination points |
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| 100 percent interoperable with existing data and voice network equipment in a SONET ring, enabling "point-to-network" connections |
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IP over SONET has already been deployed in internet service provider (ISP) inter point-of-presense (POP) connections because of its improved efficiency and reduction in complexity. Cisco Systems extends this technology to the access fiber. The notable difference between the WPOS and IP over SONET is the use of channelized SONET payloads.
Channelization involves mapping traffic onto tributary containers within the SONET payload. This scenario implies that the STS-1 payload envelope is seen as consisting of 28 distinct 1.5-Mbps channels (or tributaries) carrying payload independent of each other. T1 signals map directly into VT1.5 tributaries for transport over SONET. The most common interface for LAN traffic, 10 Mbps Ethernet, does not map directly into SONET tributaries. Mapping it into a 51-Mbps STS-1 envelope would be inefficient from the perspective of bandwidth utilization. WPOS enables Ethernet traffic to be mapped into a variable number of VT1.5 tributaries. The number of VT1.5 tributaries that an Ethernet port maps into is referred to as a "bundle." Each bundle emulates a higher-bandwidth pipe using a standards-based inverse multiplexing mechanism. This setup allows flexibility for the end user to map a 10-Mbps Ethernet pipe (or multiple pipes concentrated onto a single bundle) into a scalable bandwidth pipe with capacities of 1.5 to 12 Mbps, in 1.5-Mbps increments.
Using channelized SONET payloads, IP traffic on the premises now has a dedicated point-to-point pipe between CTE and the data termination point through a public SONET network rather than a shared statistically multiplexed pipe with its associated undeterministic performance. In the case of TLAN interconnect applications, WPOS allows point-to-network connections instead of the point-to-point connections possible with solutions available today, implying that it would be possible to create a LAN-to-LAN private network mesh connecting more than two locations together using WPOS technology without requiring identical equipment on both ends.
WPOS is 100 percent interoperable with existing data and voice network access equipment such as SONET add drop multiplexers (ADMs), voice switches, digital crossconnect systems, and routers. Voice and data traffic originating on the CTE is segregated at the CE into voice calls terminating on the switch and data traffic that is forwarded. In the case of Internet access, IP traffic terminates on the ISP IP router. Because WPOS uses existing, virtual tributary (VT) mappings within SONET networks, it provides seamless integration with existing SONET equipment. All performance management, protection switching, fault isolation, alarm management, and provisioning capabilities of the network are maintained after the addition of WPOS technology.
ISR products are designed to utilize WPOS technology to address enterprise customers' access needs. The following are key features of WPOS technology used in ISR products:
Key Features:
Designed to be deployed by a network operator as an edge device on an access network, the ISR with WPOS technology serves as the demarcation point. In other words, the network operator can deploy the equipment in a multitenant environment and instantly provide the benefits of SONET to small to medium- sized businesses that before didn't have them because of an economic high barrier to entry. Network operators can offer to their customers flexible bandwidth data services and clear channel transport for voice.
Posted: Mon Jun 14 12:03:52 PDT 1999
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