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Unformatted text preview: ATT FR COVER 8/4/0 1:18 PM Page 1 T H E T E C H N O L O G Y G U I D E S E R I E S™ www.techguide.com ™ This Technology Guide is one in a series of topicfocused Guides that provides a comprehensive examination of important and emerging technologies. This series of Guides offers objective information and practical guidance on technologies related to Communications & Networking, the Internet, Computer Telephony, Document Management, Data Warehousing, Enterprise Solutions, Software Applications, and Security. Frame Relay Service in Today’s Enterprise Network Environment Built upon the extensive experience and ongoing research of our writers and editorial team, these Technology Guides assist IT professionals in making informed decisions about all aspects of technology development and strategic deployment. Visit our Web site at www.techguide.com to view and print this Guide, as well as all of our other Technology Guides. This is a free service. BP3841-04 techguide.com is supported by a consortium of leading technology providers. AT&T has lent its support to produce this Guide. produced and published by This Guide has been sponsored by visit www.techguide.com™ ATT FR BOOK 8/4/0 1:25 PM Page 2 AT&T Frame Relay Service AT&T Frame Relay Service (FRS) is a global, public data network service that provides high speed, reliable, economical Local Area Network (LAN) to Wide Area Network (WAN) interconnections for distributed computing applications. Frame Relay provides a cost-effective alternative to private line and X.25 packet services by providing high-speed bandwidth with low latency and high connectivity. AT&T Frame Relay Service is ubiquitous throughout North America and globally, and offers customers a variety of value-added capabilities and features including: High Reliability and Throughput The AT&T Frame Relay network utilizes a feature called ReliaBURST® to provide the end-user with sustained bursting capabilities beyond the Committed Information Rate (CIR) up to the native Port Speed for an extended period of time, and proactive congestion management. This feature is realized using a sophisticated algorithm that monitors the status of the network and adjusts the available bandwidth of Permanent Virtual Circuits (PVCs). The ReliaBURST feature allocates excess network capacity fairly among all users, and provides optimum protection of network resources by metering access to the network via a closed-loop feedback mechanism, avoiding congestion and potential data drop-outs. The result is high data delivery and throughput, fairly allocated to all network end users. Network Management • Dedicated Global Network Management Centers with a single point of contact. AT&T Frame Relay Service has Network Operations Centers (NOC) located throughout the world that are electronically linked to act as one. The NOCs are staffed with experienced, customer-focused technicians who are available for support 24 hours a day, 7 days a week, 365 days a year. • Fault Management – The AT&T NOCs continuously monitor network conditions and perform fault management including proactive, preventative and reactive network management. In many cases, the NOC detects faults and takes corrective action before network conditions affect service. • Performance Monitoring – The AT&T NOC also monitors network performance and utilization to react to trends, such as rapidly growing line utilization. • Customer Provisioning Teams – AT&T has dedicated teams of experts who oversee the complete deployment, installation, testing and activation of the Frame Relay Service. Customer Network Management AT&T offers e-business tools and reports that simplify network management, maintenance, ordering and billing. • Customer Network Management (CNM) Options - Detailed weekly and monthly reports help you fine-tune your Frame Relay port speeds and PVC Committed Information Rates (CIR) to match traffic requirements, maintain application response time by flagging critical thresholds, and provide easy to use tools for capacity planning and proactive network planning. • AT&T Electronic Maintenance - Enables customers to improve overall time to repair by proactively testing circuits to isolate troubles of Customer Premises Equipment (CPE), Local Exchange Carrier or AT&T Network. Customers can also create trouble tickets, track status, add comments to the ticket log, request ticket closure and run reports on circuit troubles. • AT&T Electronic Order - Allows customers to shorten installation intervals and improve order accuracy. Customers can make requests for Frame Relay access, new ports, new PVC service, change a PVC CIR, disconnect an existing PVC, make inside or outside moves, monitor status of order activities and run customized reports. • AT&T Electronic Bill - Gives AT&T customers a better handle on their network spending with billing reports which can be viewed, sorted, printed or downloaded. IP-Enabled Frame Relay Service Building upon AT&T Frame Relay Service, IP-Enabled Frame Relay Service addresses the migration to IP-based networking as well as increasingly distributed communications. For business networking needs, IP-Enabled Frame Relay Service expands the Virtual Private Network (VPN) functionality of the AT&T Frame Relay Service with two new capabilities: simplified any-to-any complexity and Quality of Service (QoS). AT&T has been able to implement IP-Enabled Frame Relay Service because of the deployment of advanced IP routing technology based on Multiple Protocol Label Switching (MPLS) within the existing AT&T Frame Relay Service infrastructure. MPLS uses the intelligence of IP routing technology to establish route assignments, then uses the high performance of ATM to transport the IP packets. AT&T IP-Enabled Frame Relay Service offers the following benefits: • Establishes any-to-any IP connectivity via a single Enterprise Permanent Virtual Circuit (EPVC) rather than multiple PVCs. • Provides the any-to-any connectivity and QoS capabilities without the need to upgrade existing equipment or change established network addressing schemes. • Enables the same layer 2 security features as standard Frame Relay connections. • Enables VPN features in the traditional Frame Relay environment. Frame Relay Plus AT&T Frame Relay Plus is a premium enhancement to the AT&T Frame Relay Service. Frame Relay Plus utilizes AT&T provided Visual Networks’ CSU/DSUs at the customer premises to enrich the AT&T Frame Relay Service with proactive monitoring and fault resolution along with a comprehensive array of near real-time and historical performance reports that pinpoint problems and causes. AT&T Frame Relay Plus offers the following benefits: • Improved maintenance performance through immediate identification of WAN problems. • Simple access to Web-based tools that put historical WAN informationn and near real-time trouble analysis at the customer’s fingertips. • Low or no capital costs for state-of-the-art network management tools. • Single point-of-contact for project management, from ordering to installation, and troubleshooting and maintenance. • Identical view of all activities, including ordering, installation and troubleshooting to both the customer and the AT&T NOC. AT&T Frame Relay Service 900 RT 202/206 North, Rm. 3A226Z, Bedminster, NJ 07921 http://www.att.com/ipservices/data 800-288-3199 Visual Networks is a registered trademark of Visual Networks, Inc. ATT FR BOOK 8/4/0 1:25 PM Page 2 Table of Contents Introduction..............................................................4 Why Frame Relay Service is Needed in Today’s ....5 Business Environment .........................................5 Typical Frame Relay Service Applications ..............9 Frame Relay Service—Ready for Prime Time ......10 How Does Frame Relay Service Work?.................11 Other Frame Relay Service Considerations ..........21 Distinguishing Service Providers............................22 Determining the Value of Frame Relay Service....28 Customer Profile ....................................................33 Glossary of Terms..................................................36 About the Editor… Jerry Ryan is a principal at ATG and the Editor-in-Chief of techguide.com. He is the author of numerous technology papers on various aspects of networking. Mr. Ryan has developed and taught many courses in network analysis and design for carriers, government agencies and private industry. He has provided consulting support in the area of WAN and LAN network design, negotiation with carriers for contract pricing and services, technology acquisition, customized software development for network administration, billing and auditing of telecommunication expenses, project management, and RFP generation. Mr. Ryan has been a member of the Networld+Interop Program Committee and the ComNet steering Committee. He holds a B.S. degree in electrical engineering. The Guide format and main text of this Guide are the property of The Applied Technologies Group, Inc. and is made available upon these terms and conditions. The Applied Technologies Group reserves all rights herein. Reproduction in whole or in part of the main text is only permitted with the written consent of The Applied Technologies Group. The main text shall be treated at all times as a proprietary document for internal use only. The main text may not be duplicated in any way, except in the form of brief excerpts or quotations for the purpose of review. In addition, the information contained herein may not be duplicated in other books, databases or any other medium. Making copies of this Guide, or any portion for any purpose other than your own, is a violation of United States Copyright Laws. The information contained in this Guide is believed to be reliable but cannot be guaranteed to be complete or correct. Any case studies or glossaries contained in this Guide or any Guide are excluded from this copyright. Copyright © 2000 by The Applied Technologies Group, Inc., One Apple Hill, Suite 216, Natick, MA 01760, Tel: (508) 651-1155, Fax: (508) 651-1171 E-mail: [email protected] Web Site: http://www.techguide.com ATT FR BOOK 8/4/0 1:25 PM Page 4 Introduction This Technology Guide addresses the role that Frame Relay service has as one of the fastest growing and successful network services available today. Its widespread acceptance as a vehicle for information transfer has surpassed industry expectations because of its well established technology, virtually universal availability, and cost effectiveness. As a result, Frame Relay service has become a key element in how businesses will meet the mission critical corporate goals of the new era. The Guide explains how Frame Relay service supports the emerging applications and connectivity requirements of today’s Enterprise networks. It explains the various types of Frame Relay service implementations and issues such as the Committed Information Rate and the need to design the service with a realistic understanding of the network applications. Building on the maturity of the Frame Relay technology, this Guide explores those attributes of a carrier that best meet the needs of the customers in supplying Frame Relay service, including full customer service and Frame Relay service network management support. An important perspective is that Frame Relay service is just one of a variety of services available from a major carrier. Frame Relay service is positioned as one solution within the family of services of leased line and ATM. For many customers, hybrid networks which use all three service types will best meet the needs of the corporation. 4 • Frame Relay Service in Today’s Enterprise Network Environment Why Frame Relay Service is Needed in Today’s Business Environment The success of today’s business enterprise depends heavily on the computing and communications infrastructure which supports it. This infrastructure, known as the Enterprise Network, is considered a strategic asset by businesses, and has changed dramatically over the years as a result of the evolution in data processing and telecommunications. Because of the advances in computing and telecommunications, companies are rapidly adopting new ways of doing business, with the end result that mission critical applications and operations have moved onto the network and are increasingly dependent on new networking paradigms. This new business paradigm is most obvious in several key areas. The Expanded Role of Networks in Business and New Applications The entire scope of strategic business concerns, from contemporary business development, marketing, and sales to product development, manufacturing, and distribution, are greatly affected by new networking developments. The reality of direct consumer interaction through the Internet, the wide scale availability of information rich graphical applications, all change the way in which business will be conducted. As processing costs have dropped significantly and processing power has increased, self-contained desktop applications have emerged to enable the knowledgeable worker to operate efficiently and independently. These new applications generally have some fundamental differences from earlier data applications: Higher Bandwidth Requirements—The new applications demand much higher bandwidth because Technology Guide • 5 ATT FR BOOK 8/4/0 1:25 PM Page 6 the amount of traffic generated by them is so much greater. Expanded Connectivity Requirements—The nature of Enterprise Networks today is such that there is a greater need for network connectivity among a much larger end user population. These diverse users and systems need to communicate with the host and database sites and with each other with varying degrees of frequency. Where, in the past, the network simply connected internally and specialized functional areas, the new network interconnects virtually everyone within the corporate structure via Intranets. In addition, external communications with a variety of trading partners, customers, suppliers, and distributors is now commonplace via Extranets. These various users do not share the same degree of frequency but do potentially share the same need for access into the heart of the corporate network. Traditional methods of connecting occasional users to the network involve the use of dial-up lines at relatively low speeds, which are not satisfactory for meeting today’s connectivity requirements. Frame Relay service, however, is a natural choice for these users since it can provide cost-effective connectivity for even the most infrequent user. Diversity of Traffic—Today’s networks are highly heterogeneous. Graphical applications, file transfer, transaction processing, E-mail, etc. all coexist on the same network and often compete for the same networking resource. This diversity inevitably demands a mix of ways to handle it. Prioritization, differing urgencies, and support of bursty traffic are all requirements for contemporary networks. The traffic characteristics of the new applications in today’s enterprise are different from those of traditional applications in another way. Whether its moving documents and files between locations, transferring an image, or accessing a remote server, these new applica6 • Frame Relay Service in Today’s Enterprise Network Environment tions tend to be “bursty” and periodically demand higher bandwidth. “Burstiness” occurs when a serving facility, which might ordinarily support a relatively homogeneous and even level of traffic, is accessed by a transaction, such as an image transfer or a database file, that requires all, or much, of the available bandwidth for a brief time. Unfortunately, if the network is not properly designed, the bursty traffic can severely impact the performance of other traffic on the same facility. This happens if the traffic volumes are such that there is high likelihood of the bursty event interfering with the more homogeneous traffic. Under these circumstances, it is impractical to permanently reserve the entire bandwidth needed by the bursty application since the occurrences may be infrequent. It is not cost efficient to have such a high bandwidth facility idle for the relatively long periods of time that might occur between events. This is a natural opportunity to use the bursty traffic handling capabilities of Frame Relay service which can accommodate momentary high bandwidth bursts, as well as being ubiquitous, reliable, and cost-effective. Traditional Networks Traditional legacy networks do not meet the demands of these new applications in a number of ways. In the past, except for the circuits in the corporate backbone which might have been T-1 or higher, legacy network circuits have typically been provisioned at less than 56 Kbps. The fixed bandwidth of these arrangements lacks the efficiency to handle bursty traffic variances and provides no inherent mechanism for supporting prioritization or occasional users. The increased number of locations in today’s networks has added a layer of network complexity that is costly and difficult to engineer with legacy networks. In addition, the distributed host and database arrangements have created routing and connectivity requirements that Technology Guide • 7 ATT FR BOOK 8/4/0 1:25 PM Page 8 have been difficult to cost-effectively support with either point-to-point or multi-point arrangements. New Organizational Models In addition to the new network applications, networking and computing technologies also make it possible to organize businesses differently. Groupware and remote networking applications have made “telecommuting” or the “Virtual Office” a reality. It is no longer necessary for workers to come to an office merely to access, generate, or share work products in digital form. Businesses today have organized in more geographically dispersed structures built around specialty areas, market convenience, and worker availability. Some firms operate with most of their employees continually in the field or at home. These diverse organizational models are possible only because of the availability of technology to tie them together in ways that enable efficient and comprehensive exchanges of information. Newer services such as Frame Relay service make it practical. The list of contemporary applications used in these new organizational models includes document imaging, storage and retrieval, medical and scientific imaging, distributed on-line transaction processing, distributed database/client server, electronic funds transfer, electronic data interchange, electronic mail, and many more. All of these applications, in one way or another, share a new profile which includes increased traffic volumes, bigger transaction sizes, distributed traffic patterns, and diverse user populations. This fast changing application mix is complicated by an associated restructuring of the business organizational model. Furthermore, these contemporary applications are used by a much wider segment of the corporate community and are broadly distributed amid many more users than traditional legacy applications. This leads to 8 • Frame Relay Service in Today’s Enterprise Network Environment a move away from populations of high volume terminals requiring permanent connectivity to a broader mix of users, including some with less of a need for constant connectivity. New networks must be able to support both high volume users and occasional users within the same coherent architecture. Typical Frame Relay Service Applications Frame Relay service best suits applications that have the following characteristics: Periodic Traffic—Although Frame Relay service is a cost-effective alternative to leased lines, the cost-efficiency is most pronounced when the traffic is variable and/or unpredictable. Wide Connectivity—This applies when there are many widely dispersed remote locations which require WAN access. For example, there might be a need to transfer large database files several times a day to a group of remote branches. Frame Relay service provides a superb facility for accessing remote sites and quickly forwarding traffic. Large Transaction Sizes—Because access to Frame Relay service operates at 56 Kbps and higher speeds, it is a suitable vehicle for document transmission and other data transfers which may require a “burst” in the size of the available bandwidth. It supports LAN-toLAN interconnection and other large transmissions, such as CAD/CAM image sharing. Bursty Transactions—The best application of Frame Relay service is for heterogeneous networks that support a variety of applications, some of which are quite large, while others are small. This mix allows the efficiencies of Frame Relay service to be fully utilized. Technology Guide • 9 ATT FR BOOK 8/4/0 1:25 PM Page 10 LAN-to-LAN Connectivity LAN-to-LAN interconnection has become essential in business today. Work group and team sharing approaches to most corporate activities have necessitated the interconnection of LANs at increasingly high bandwidths. Typically, at a minimum, LANs are interconnected at 56 Kbps to 1.5 Mbps. Frame Relay service offers an effective and cost-efficient way for LAN interconnection. The Frame Relay Service Solution It is clear that the corporate enterprise has changed dramatically in terms of its networking needs. Complex, bursty traffic, broad connectivity, new business structure, and the growth of LAN connectivity requires a comprehensive solution that has, as one of its key components, Frame Relay service. Frame Relay service is flexible and can be used for a wide variety of applications. Some customers use Frame Relay service as a simple replacement of leased or private lines. This typically results in reduced facility costs and, in some cases, even better performance, because Frame Relay service can provide high throughputs. In other cases, Frame Relay service can be used as a multi-protocol transport vehicle to support the migration to decentralized computing environments. prime time”. Customers of Frame Relay service, as supplied by major carriers such as AT&T, are already well satisfied with its quality and ease of use. Vendors and service providers have pledged support for Frame Relay service development and standards. To this end, the Frame Relay Forum, which includes major providers such as AT&T, was incorporated in 1991 as a non-profit organization to promote the implementation of Frame Relay service standards, the implementation agreements to specify options within the standards, and to ensure interoperability. There are dozens of carriers providing Frame Relay service and thousands of companies world wide currently using it successfully. The use of these widely accepted standards, approved by the ITU/TS (formerly CCITT) and ANSI, and the adoption of these standards by manufacturers of terminal devices and service providers has enabled Frame Relay service to be the fastest growing telecommunication service in the Enterprise Network. How Does Frame Relay Service Work? DLCI C/R EA DLCI FECN BECN DE EA Frame Relay Service—Ready for Prime Time Flag Address Information Field Frame Check Sequence Flag Frame Relay Service Structure One of the major benefits of Frame Relay service is that it has reached a level of wide acceptance and broad deployment that makes it an ideal service to use in business applications today. It has already gone through a deployment evolution and is truly “ready for 10 • Frame Relay Service in Today’s Enterprise Network Environment Frame Relay service is based on the data link level protocol defined by ANSI as T 1.618. It provides for the encapsulation of information (traffic) from terminal devices connected to the network through routers, Technology Guide • 11 ATT FR BOOK 8/4/0 1:25 PM Page 12 bridges, and Frame Relay Access Devices (FRADs). The Frame Relay service frame structure ordinarily contains: Starting Flag (1 octet), Address (2 octets), Information Field (variable length up to 4096 octets), Frame Check Sequence (2 octets) and Ending Flag (1 octet). The 2 address octets (16 bits) contain five unique elements: Data Link Connection Identifier (DLCI)—This contains the identification of the PVC used by the network to find the right path and destination for the frame. Command/Response field—Not used. Extended Address—Can be used for extended addressing needs. Explicit Congestion Notification fields—Used for flow control. Discard Eligibility—Although not utilized as a means of congestion control in the preferred Frame Relay service network transport environment, frames can be marked as being discard eligible. It is normally used on frames that exceed the Committed Information Rate (CIR). Frame Relay service is an efficient protocol and it has been streamlined to eliminate the link-by-link flow and error control, which have been relegated to higher levels in the protocol stack. (By comparison, X.25 uses the Link Access Procedure-Balanced [LAP-B] protocol while Frame Relay service uses LAP-D, ITU’s Q.922 protocol). Logical Circuits Frame Relay service standards define three types of logical circuits: permanent, switched, and multi-cast. The Permanent Virtual Circuit (PVC) is the primary way in which Frame Relay service is currently provided by carriers. Switched Virtual Circuits (SVCs) are not commonly available from Frame Relay service providers at this time and multi-cast is provided on a proprietary basis. 12 • Frame Relay Service in Today’s Enterprise Network Environment Permanent Virtual Circuits (PVCs) Frame Relay service does not require a permanent leased line circuit between the sender and receiver. Instead, a Permanent Virtual Circuit (PVC) is prearranged by the carrier from the sender to the receiver. This PVC is a pre-determined logical path through the carrier network between the two points. It is invoked when a message is sent. A PVC is permanently “set up” however, when there is no message traffic, the assigned bandwidth can be used by other PVCs occupying the same access facility. The access facility, i.e., a single physical link from the customer to the carrier, can support multiple PVCs. For example, a customer might have a 56 Kbps access line to the carrier network over which four different PVCs are arranged to support four different traffic flows originating from the customer location to four different destinations. 1 PVC FRAD Frame Relay Access Device PVC1 PVC2 PVC3 PVC4 ACCESS TRUNK Access Trunks PVC2 Frame Relay Service Network PVC 4 PVC3 Access Trunks Committed Information Rate (CIR) Customers subscribe to PVCs, with specific Committed Information Rates (CIRs). The CIR is the transport speed which the Frame Relay network will maintain between service locations when data is presented. Once established, there is no “set up” each time the PVC is used. Instead, it uses pre-arranged routes between switches on trunks within the service provider’s network. Technology Guide • 13 ATT FR BOOK 8/4/0 1:25 PM Page 14 The concept of the Committed Information Rate is at the core of the successful operation of Frame Relay service, and unfortunately, is one of the least understood service parameters. It is a pre-arranged transmission rate that assures the customer that the PVC will have, at a minimum, that much bandwidth available to it for transmission of data. The CIR assigned to Permanent Virtual Circuits is analogous to the speed of leased lines. Under ordinary conditions, the service assures the sender that the data will be delivered at the arranged transmission rate. Frames that are sent within that parameter are all handled by the service. Because multiple PVCs can occupy the same physical link to the carrier, any one of the PVCs can use the full bandwidth of the access link, in excess of the actual CIR of the virtual circuit. Even if, for example, each of the four PVCs only had a CIR of 4 Kbps, any one of them could use the full 56 Kbps of the access facility if the remaining PVCs were idle. However, bursty frames offered to the network in excess of the CIR are marked as Discard Eligible (DE) by the source node (FRAD, router, bridge). The network will admit frames representing excess data over the CIR if there is available capacity within the Frame Relay service network. Within networks that employ Discard Eligibility as a congestion control methodology, these Discard Eligible frames may be discarded to ensure that the network does not become overloaded. A critical aspect of selecting the right Frame Relay service provider is to understand the basic network capacity assigned by the carrier to its Frame Relay service, how well the network is designed to absorb bursty traffic flows, and the process by which congestion is managed. With some carriers, the DE frames have a high probability of arriving at their destinations because of proper traffic balancing, and the allocation of sufficient excess bandwidth to provide the highest quality level of service. 14 • Frame Relay Service in Today’s Enterprise Network Environment Overbooking the Access Service One of the more important characteristics of Frame Relay service is that the customer can overbook the access service. That is, the customer can have a greater aggregate PVC bandwidth than the capacity of the Frame Relay service access port ordered. In the following sketch, there are 14 PVCs with an aggregate bandwidth of approximately 650 Kbps. The access port is only 384 Kbps. These PVCs are provisioned to provide for the expected bandwidth needs of the traffic flow when it occurs, but because of the non-coincidence of traffic, i.e., not all of the PVCs are active at the same time, the access service will be sufficient, assuming that the overall utilization is under 50%. Specialized tools are available to assist you in determining the PVC ratio required to facilitate the optimum traffic flow for your network. In this example, the customer device could send data over any one of the PVCs up to the capacity of the access service; in this case 384 Kbps, so long as the other PVCs were idle. In this example, the physical access circuit is T-1 simply because access circuits are usually sold in increments of either 56 Kbps or T-1. Fractional T-1 increments are not ordinarily available from the customer premises to the local central office. FRAD Router/Bridge T1 Access Circuit 384 Kbps Access Port Customer 14 PVCs = 650 Kbps aggregate Bandwidth Premises 2 @ 128 Kbps Carrier Network 6 @ 56 Kbps 6 @ 9.6 Kbps Technology Guide • 15 ATT FR BOOK 8/4/0 1:25 PM Page 16 Supporting Bursty Traffic within the Carrier’s Network One of the concerns with Frame Relay service is the question of how overbooked traffic is handled as it travels from the customer access port through the carrier network. If the traffic on the PVC has been presented to the carrier at rates in excess of the CIR, the traffic can be marked as Discard Eligible and discarded in the event of network congestion. This is a serious issue and is resolved through several techniques. One technique is for the carrier to assure sufficient capacity to support anticipated traffic. This requires the carrier to understand the nature of the traffic it proposes to support and to supply enough bandwidth to carry it without congestion. Another critical capability of the carrier is to provide comprehensive congestion management so that in the event congestion does occur, the network can quickly respond and reduce the duration and impact of the congestion. One highly regarded approach is through the use of PVCs which operate within a closed loop feedback mechanism to control congestion. PVCs and Closed Loop Congestion Management PVCs with closed loop congestion management can provide the end-user with sustained bursting capabilities beyond the CIR of the PVC so long as there is spare capacity in the Frame Relay service network. Closed loop congestion management operates through a sophisticated algorithm that monitors the status of the network and adjusts the available bandwidth of PVCs. This feature allocates excess bandwidth fairly among the users, and provides optimum protection of network resources by metering access to the network via a closed loop feedback mechanism. In some carrier’s networks, status indicators which reflect the current utilization of network resources, are 16 • Frame Relay Service in Today’s Enterprise Network Environment updated at every node crossed by each PVC in the network. Depending on the particular values of the status indicators, the algorithm increases, decreases, fast decreases, or does not change the rate of the PVC. However, the indicators will not cause the available bandwidth of the PVC to be decreased below the CIR. Examples of the status indicators are: • Cell Level Utilization (cells per trunk) • Frame Level Utilization (frames per port) Source Node Closed Loop Feed back Destination Node Credit Rate Adjustment Credit Buffer Network Trunk Card Trunk User Data PVC Buffer Cell Buffer Cell Level Utilization Frame Buffer Frame Level Utilization In some carrier’s networks, the cell level utilization is monitored at the cell buffer in the trunk interface of each node. If there are intermediate nodes in the PVC path, cell level utilization is also monitored in these nodes. Frame level utilization is monitored at the frame buffer in the destination port where the frames are reassembled. The status indicators are monitored at the destination port for each round trip network delay. The results of the status indicators are fed back to the credit rate adjustment mechanism in the source node. Then, the bandwidth of the PVC is adjusted in one of the following ways: • Initial Data Rate: The PVC will burst to the lesser of either the ingress or egress port speed and will continue to transmit at that rate as long as network congestion or egress que congestion is not present. Technology Guide • 17 ATT FR BOOK 8/4/0 1:25 PM Page 18 • Rate Down: When congestion does occur the PVC is throttled back towards the CIR, but never below the CIR. The two types of congestion that may affect CIR and the applicable throttle rates are: Network Congestion: transmission above the CIR is reduced in 15% increments until congestion clears or offered traffic is exhausted. Egress Que Congestion: transmission above CIR reduced in 50% increments. In either case, network congestion is monitored and the PVC’s transmission rates are adjusted 48 times per second. The PVC rate is never reduced below the CIR. Benefits of Closed Loop Congestion Management In some carrier’s implementations, PVCs can offer the user sustained bursting capabilities beyond the CIR, up to the port speed for an extended period of time, plus proactive congestion avoidance, highly reliable delivery, and fairness across all network users. Closed loop congestion management provides optimum protection of network resources by metering access to the network via a closed-loop feedback mechanism, avoiding congestion and potential discarded data. The result is highly reliable data delivery and throughput, fairly allocated to all network end-users. Frame Relay Service and SNA For some situations, Frame Relay service can be utilized to integrate multi-drop SNA networks and parallel router-based networks for client/server applications, into a single network. While this integration can also be accomplished via leased lines, Frame Relay service offers the potential for significant cost savings, with the added promise of improved performance. 18 • Frame Relay Service in Today’s Enterprise Network Environment However, one of the biggest challenges is to integrate SNA and LAN traffic on a single network while obtaining the consistent performance necessary for efficient SNA sessions. To assist users, routers and FRADs support a number of features with precisely this objective in mind. Router/FRAD technology also allows customers to consider replacing their remote Front End Processor (FEP) concentrators with router technology, although extra care needs to be taken in this process. In general, a good understanding of (a) how routers support SNA protocols, (b) how LAN protocols differ from SNA, and (c) how Frame Relay service differs from leased lines in terms of delay characteristics, is necessary to ensure consistent performance of SNA applications in the presence of LAN traffic. While many proprietary protocols exist for supporting SNA with routers/FRADs over Frame Relay, there are two key enabling standards–RFC 1490 and Data Link Switching (DLSw). These are described briefly below. Frame Relay service carriers usually can provide additional support for customers. RFC 1490 and SNA RFC 1490 is a Frame Relay Forum standard for encapsulating multiple protocols on a Frame Relay PVC. Furthermore, the Frame Relay Forum document, FRF.3, describes how SNA can be carried directly over Frame Relay (in contrast to encapsulating SNA in TCP/IP). To explain briefly, SNA requires a connectionoriented, reliable data link layer protocol. On a leased line network, SDLC provides this function. Since Frame Relay service does not participate in windowing or retransmissions, Logical Link Layer Type II (LLC2) (IEEE802.2) protocols are used over Frame Relay service connections. RFC 1490 essentially defines two methods of transport of LLC2 frames over Frame Relay—the Routed Frame Format and the Bridged Frame Format. Technology Guide • 19 ATT FR BOOK 8/4/0 1:25 PM Page 20 The routed frame format encapsulates LLC2 frames directly in Frame Relay service, whereas the bridged frame format uses Media Access Control (MAC) addresses in addition. The bridged frame format is less restrictive and easier to configure, but has more overhead, compared to the routed frame format. Customers should request assistance from their Frame Relay service carrier to implement either method optimally for their specific applications. DLSw Over Frame Relay Service Data Link Switching (DLSw) is used for routing of SNA traffic, also involving the use of TCP/IP, but as an external transport after the SDLC protocol issues have been dealt with. Data Link Switching, originally developed by IBM, has since been adopted by the members of the APPN (Advanced Peer-to-Peer Networking) Implementers Workshop. It is also described by the Frame Relay Forum within RFC 1795. DLSw is essentially a variety of TCP/IP encapsulation used for performing source route bridging over a WAN. As such, it can be overlaid onto a Frame Relay service network. DLSw provides virtual point-to-point connections between pairs of Data Link Layer Media Access Control (MAC) addresses. The DLSw specification deals with the encapsulation of SNA, APPN, and NetBios in TCP/IP, which can then be transported using Frame Relay service paths. One of its key functions is to interact with the native SNA devices at either end of the path and eliminate the protocol overhead and polling from occupying the network. 20 • Frame Relay Service in Today’s Enterprise Network Environment Other Frame Relay Service Considerations Frame Relay service is just one of the many data transport offerings of major carriers such as AT&T. Frame Relay service, although best suited to the types of applications described above, does not meet the needs of all traffic types. For applications such as voice or broadcast video, ATM is probably a better solution. When there is a need to interconnect major host facilities together for constant, high traffic volume transfers, ATM, T-1, or T-3 leased lines would be more ideal. In general, Frame Relay service is complementary to other services like ISDN and ATM. Each has strengths that can support a comprehensive customer solution. Each offers a specific range of bandwidth and capabilities suitable for particular applications. For example, ISDN is a circuit switched digital technology, offering bandwidths of 56 Kbps to T-1 speeds, which allows the user to establish high-speed dial up connections around the world. It is used mostly for voice and data. It does not pass frames across the network according to addresses contained in the frame. Instead, just like leased lines, once the connection is established, transmission occurs without the imposition of additional protocol overhead and there is no need to either encapsulate or unbundle the traffic flow. Billing for ISDN services is similar to usage-based services such as long distance toll calls. The customer pays for the basic PRI or BRI access circuit and is billed for usage as it occurs. ATM, which is a cell based, switching, and transmission technology similar to Frame Relay service, typically operates at higher bandwidth rates. It offers interfaces at 1.544 Mbps and 45 Mbps and it is planned to reach 622 Mbps and beyond. It is intended to operate with the rates that will be available through SONET technology. ATM also uses Virtual Circuit and CIR concepts and is a superset of protocol support capabiliTechnology Guide • 21 ATT FR BOOK 8/4/0 1:25 PM Page 22 ties. It can carry Frame Relay service as well as various LAN systems, Video, FAX, and Voice. Customer Network Management— Electronic Servicing Distinguishing Service Providers One major distinction in Frame Relay service is the ability for the user to manage the Frame Relay network on an ad-hoc and as needed basis. In order for this to work effectively, the carrier must provide two important components: regular detailed reporting of traffic by PVC and the means to electronically affect changes in the PVC and port configurations. Frame Relay service is now available as a mature service. International as well as domestic providers include Frame Relay service in their portfolio of enterprise network offerings. These services, however, vary from carrier to carrier and their quality is only as good as the carrier’s network and platform capabilities. The educated Frame Relay service customer will understand and consider some of the issues important to Frame Relay service and its provisioning before committing to a particular provider. Customers can understand how carrier’s implementations differ by comparing them and their services against these important characteristics. Customers can make more informed decisions concerning the value received by examining carriers’ Frame Relay services in light of these measures: Carrier Architecture Customers planning to implement Frame Relay service should consider the infrastructure, capability, and architecture of the prospective service provider to determine if that provider has the potential to truly meet their total system and performance needs. The carrier’s architecture should offer critical depth, such as the ability to support a wide range of service interfaces. Another key element of the carrier architecture is the method used to control network congestion. 22 • Frame Relay Service in Today’s Enterprise Network Environment Web Based Interface As the Internet becomes more pervasive and used for virtually all inter-company traffic, it makes sense that customer network management systems become available within the context of a standardized browser interface. The Internet allows users access to regular reports including: • Port and PVC utilization. • Discards, CRC error, and congestion notifications. • Exception reports with definable thresholds allowing rapid identification of problem areas. Electronic Ordering enables customers to order new Frame Relay service ports and PVCs and to upgrade service speeds (CIRs). This provides direct management of network configurations. Electronic trouble ticketing provides web based reporting for circuit, port, and PVC troubles and allows timing tracking of problem resolution. A Clean, Seamless Evolution The carrier should be prepared to offer compatibility and interoperability between Frame Relay service and other services such as ATM. The best Frame Relay service providers will integrate their Frame Relay Technology Guide • 23 ATT FR BOOK 8/4/0 1:25 PM Page 24 service with other transport options and additional services into seamless offerings that meet critical business needs. They will offer Frame Relay service as part of a complete range of transport options for LAN interconnect solutions, in which the transport services (e.g., Frame Relay service, dedicated private line, fractional T-1/E-1, and 45 Mbps) are combined in an integrated solution. The carrier should have a strategy for integrating Frame Relay service with ATM in a hybrid mix of services specifically designed to meet the needs of the customer. Since the Frame Relay service specification prescribes only the access technology, network providers are free to use frame or cell-based backbones in their networks. Those that use cell-based backbones are positioned for expansion in scale and scope, and are likely to be better equipped to grow in the long term. An Array of Access Options Customers’ needs vary, and some implementations are optimized using a mix of switched and dedicated access lines at different rates. Carriers should offer dedicated access at popular rates (e.g., 56/64 Kbps, fractional T-1, 1.5 Mbps), as well as dial access. ISDN is another increasingly important way to access Frame Relay service. The Frame Relay service should support a wide range of interface rates (from a few kilobits per second to megabits per second), and protection in case of local access channel or CPE failure. Around the Clock Network Surveillance and Monitoring Maintaining high availability and quality service requires continuous network surveillance. This includes continuous remote monitoring of all the physical elements of the network, immediate response to troubles or questions, and superior problem isolation and repair capability. 24 • Frame Relay Service in Today’s Enterprise Network Environment Disaster Recovery Some Frame Relay service carriers provide Disaster Recovery to redirect PVCs to existing alternate access channels in case of local access channel or CPE failures. This assures the Frame Relay service customer of uninterrupted communications between an enterprise’s computer center and remote LAN and distributed environments. Other disaster recovery options provide backup PVCs or growable PVCs to alternate data sites or disaster recovery vendors in the event of a site disaster. Rapid service restoration is possible by temporarily redirecting the PVCs or expanding the CIR of an existing PVC to an alternate data site to handle the networking needs in the event of a disaster. Real-Time Access to Network Operations Many customers may not want to be involved in the day-to-day operation of their networks. Instead they look to carriers to handle the operational details for them. A carrier who excels at this monitors all aspects of network performance and offers customer support of the CPE, including network design, configuration support, remote monitoring, and trouble referral and tracking. In addition, the carrier offers the user the means to monitor their own private virtual networks for status and performance. They provide real-time access to information using either SNMP (Simple Network Management Protocol) based systems or proprietary software with in-band capabilities that give the user a unique view into their WAN. The carrier also provides customers with a single point of contact to their network operations center for coordinated problem resolution. Technology Guide • 25 ATT FR BOOK 8/4/0 1:25 PM Page 26 End-to-End Engineering and Planning There is more to provisioning Frame Relay service than simply securing the access connections. Customers may prefer to outsource some or all of the work associated with implementing a Frame Relay service network. If so, the following additional services that can be provided by carriers are likely to meet the customer’s needs: • Provision and installation of the cabling to connect the Customer Premises Equipment (CPE) to the network. (NOCs). These centers use remote monitoring systems and predictive modeling of service degradation to schedule preventative maintenance and perform capacity management. Trended analysis reports of performance over time can quite accurately predict when parameters are nearing service affecting thresholds, and when failures are likely to occur. Robust, Scalable Backbone Network The carrier should be able to smoothly grow and reliably protect the customer’s service through: • Design and configuration of required CPE to ensure optimum use of the network. • Fully-protected backbone network facilities and switches. • Complete installation of both the network and customer premises equipment, including routers and bridges. • Evolution path for higher access speeds as customer demands increase. • Provisioning and installation of the CPE. Internet Access Services Carriers should offer Internet services, including: • Internet connectivity using PVCs. • Internet directory services. On-Site Support for Problem Resolution The duration of failures depends on the carrier’s ability to be on-site anywhere within a few hours. Good on-site service should be structured to provide the customer with optional levels of support, depending on their priorities. Predictive Failure Modeling and Preventative Maintenance While 100% fail safe service is too costly to be practical, it can be approached using continuous fault monitoring from multiple Network Operations Centers 26 • Frame Relay Service in Today’s Enterprise Network Environment • Robust design and engineering practices to ensure sufficient capacity. • Scalable, easily expanded backbone networks to handle growth in demand. • Interworking services. Support Sustained Data Bursts Frame Relay service should successfully and consistently support sustained bursts of data at levels exceeding the customer’s committed information rate. Carriers differ markedly in their ability to support sustained bursts. There should be fair, proportional allocation of spare bandwidth to ensure that one customer’s traffic doesn’t affect the performance of other customer’s traffic. Seamless Interworking and Integration of Multiple Services While customers may choose to perform their own access coordination and network management, they should have the option of allowing the carrier to do that for them. Technology Guide • 27 ATT FR BOOK 8/4/0 1:25 PM Page 28 Carriers should offer: • Access coordination between Local Exchange Carriers (LECs) and alternate access providers. • Full access to extensive network management capabilities. • Integration with existing and new services, including support for protocol conversion. • Seamless integration of all access, carrier network and CPE into a unified, single network. Support for Servicing and Network Expansion Coordination of the addition of new locations into the enterprise network and reconfiguring the logical router configurations in response to changes in the LAN configuration. Monitoring of the network continuously to ensure optimum use of resources. Pricing Flexibility A properly designed pricing structure offers flexibility to the enterprise network user. In particular, carriers offer: • A variety of price plans and separate charges for ports and PVCs. • Long-term service agreement incentive pricing plans. • Volume discounts. Determining the Value of Frame Relay Service The value of Frame Relay service to a particular customer will vary depending on the network topology, the traffic patterns, and the geographical distribution of 28 • Frame Relay Service in Today’s Enterprise Network Environment sites. While it is difficult to apply financial analyses universally, users in a wide variety of industries report both increased levels of service and cost savings over private line solutions after implementing Frame Relay service networks. Recent customer surveys have shown: • Reported savings on the order of 30% are not uncommon. Service improvements and cost savings are reported by users in business as diverse as financial services, health care, insurance, manufacturing, publishing, network services, retail, wholesale, communications, government, transportation, pharmaceuticals, and shipping. • Users are receiving the performance and redundancy of meshed networks that they could not otherwise afford. • Frame Relay service tempers the problems usually associated with building and managing complex mesh networks. • The multi-protocol encapsulation capability of Frame Relay service has enabled the migration from dedicated SNA networks into multi-protocol, decentralized environments. • Frame Relay service offers some significant benefits for the SNA community, especially link consolidation through the nearly limitless virtual circuits that can be theoretically provisioned on each access link, greatly reducing access port requirements. • The higher speed access (56 Kbps and above) significantly improves performance over traditional 9.6 Kbps leased line and multi-drop networks so characteristic of the SNA environment. Much of the Frame Relay service savings comes from the reduction of CPE ports and circuits both in the access and interoffice portions of the network. With conventional fixed-bandwidth private line services, there is a need for multiple port terminations on the Technology Guide • 29 ATT FR BOOK 8/4/0 1:25 PM Page 30 CPE and a need for multiple, fixed-bandwidth, dedicated channels in the access connections. This results in poor utilization of network resources, and increased cost, since the number of connections goes up exponentially with the number of sites requiring interconnection. The following comparison of Frame Relay service and leased lines illustrates this point. Consider the simple four node network below. To establish fully meshed connectivity with leased lines requires six lines and twelve ports (three per customer location), as shown in the following diagram. 4 Node Private Line Network Customer Location Customer Location The same fully meshed connectivity can be achieved using Frame Relay service with just four access lines and four CPE ports (one per customer location). Each port and each access line contain three PVCs going to each of the other locations. Thus, Frame Relay service affords the capacity efficiencies of star networks plus the connectivity of fully meshed networks. The savings in port and access costs become substantial as the number of interconnected nodes increases. In the four node illustrative example, the number of links was reduced from six to four, and the CPE ports from twelve to four. The savings increases substantially as the number of nodes to be interconnected increases, as shown below. # of Links #of Links # of CPE with with Frame # of CPE Ports with # of Private Line Frame Relay Relay Ports with FrameRelay CPE Nodes Solution Solution Link Private Line Solution Port (N) [N(N-1)/2] [N] Savings Solution (# Links) Savings 4 4 Node Frame Relay Network Customer Location Customer Location 12 4 8 5 20 5 15 15 6 9 30 6 24 7 21 7 14 42 7 35 28 8 20 56 8 48 9 Six (6) leased lines and twelve (12) CPE ports are required for full connectivity. 2 5 8 Customer Location 4 10 6 Customer Location 6 5 36 9 27 72 9 63 10 45 10 35 90 10 80 The practical effect of this relationship of links and ports needed as nodes increase using the private line solution is that fully meshed connectivity quickly becomes cost prohibitive, and it is not implemented fully as the number of nodes increases. This is not the case with Frame Relay service, so Frame Relay service makes fully meshed interconnectivity achievable. Frame Relay Network Customer Location Customer Location Frame Relay Service—A Solution for the Future The corporate enterprise has changed dramatically in terms of its overall networking needs. Complex, 30 • Frame Relay Service in Today’s Enterprise Network Environment Technology Guide • 31 ATT FR BOOK 8/4/0 1:25 PM Page 32 bursty traffic, broad connectivity, new business structure, and the growth of LAN-to-LAN connections mandates a comprehensive solution that has, as one of its key components, Frame Relay service. Frame Relay service is a flexible and exciting way to support the wide variety of new business applications. Frame Relay service is used as a multi-protocol support and is becoming the most important component of today’s networks. 32 • Frame Relay Service in Today’s Enterprise Network Environment Customer Profile AT&T Frame Relay service speeds mass data transfer and reduces customer’s critical design cycle times This customer has 40 design centers worldwide, and an employee force exceeding 5,500 people. It has leading edge production processes that produce circuit components just microns across. While they hold a position of leadership in the field, competition is intense. Thus, maintaining leadership while focusing on bottom line profitability in a global marketplace requires innovative ways to bring their products to market. One exciting new idea they used included an AT&T Frame Relay service offering which helped them reduce critical design cycles. Initially, they implemented a system to off-load design work to underutilized design centers, interconnecting geographically dispersed LAN’s. However, this private line network operating at 19.2 Kbps wasn’t fast or efficient enough to transmit the typical 200 to 300 megabyte files. Files had to be sent by overnight mail. Compounding the problem, they often sent engineers from one center to another to best use available time and skills. Working with AT&T High Speed Packet services to customize a solution, they found that this new “alliance” could help move large design files to where they were needed, at very high speeds. They are now able to off-load design work to underutilized design centers during peak business periods, helping to get more design work completed in a shorter time frame. What’s more, access time to the headquarters mainframe has been cut from three or four seconds to sub-second response. Formerly, it would take 24 hours to update design software and library modules. Now it takes about an hour. Customer Profile • 33 ATT FR BOOK 8/4/0 1:25 PM Page 34 Investment Protection More Than Just Faster Transmissions LAN-to-WAN systems work best when speed, reliable and flexible networking, economy, and global support are synchronized. For this customer, AT&T Frame Relay service got the job done. They had invaluable access to AT&T network engineering, design and performance analysis. AT&T Laboratories’ technical support was also readily available. In addition to faster transmission times, AT&T’s Frame Relay service enabled this customer to better optimize their data communications network. They are now able to look at integrated access, bringing together SDN, 800 service and Frame Relay service. What’s more, they now enjoy a greater degree of disaster protection. If a fire or other disaster should strike one facility, it’s now far easier and faster to shift large amounts of data to another center via Frame Relay service than it was with their previous data network solution. AT&T Has 21st Century Solutions With increasing competition, this customer required greater connectivity, higher performance, and improved economics. They had typical Frame Relay service applications including distributed databases, CAD/CAM/CAE, imaging, graphics, software, and information distribution and groupware. Taking advantage of highly accurate digital networks and intelligent network endpoints devices, Frame Relay service with its protocol conversion capability allows the transfer of greater data more simply and cost-effectively than on otherwise underutilized private lines. It can enable handling of unpredictable data traffic, providing each network endpoint the ability to communicate with multiple destinations. They were also interested in AT&T Frame Relay Plus. This service provides measurements and analyses of data traffic and information, to the protocol level, to better understand the dynamics of network communications patterns. And, the Frame Relay Plus measurements allow them to maximize data networking efficiency; proactively indicating areas where there is a need to grow or evolve. 34 • Frame Relay Service in Today’s Enterprise Network Environment Customer Profile • 35 ATT FR BOOK 8/4/0 1:25 PM Page 36 Glossary of Terms Adapter Card—Circuit board or other hardware that provides the physical interface to the communications network. Access Method—The method by which networked stations determine when they can transmit data on a shared transmission medium. Also, the software within an SNA processor that controls the flow of information through a network. Asynchronous Transfer Mode (ATM)—The CCITT standard for cell relay wherein information for multiple types of services (voice, video, data) is conveyed in small, fixed-size cells. ATM is a connection oriented technology used in both LAN and WAN environments. Access Minutes—The usage of exchange facilities in interstate or foreign service for the purpose of calculating chargeable usage. On the originating end of an interstate or foreign call, usage is measured from the time the originating end user’s call is delivered by the telephone company to and acknowledged as received by the customer’s facilities connected with the originating exchange. On the terminating end of an interstate or foreign call, usage is measured from the time the call is received by the end user in the terminating exchange. Timing of usage at both originating and terminating ends of an interstate or foreign call shall terminate when the calling or called party disconnects, whichever event is recognized first in the originating and terminating end exchanges, as applicable. Asynchronous Transmission—Data transmission one character at a time, with intervals of varying lengths between transmittals. Start and stop bits at the beginning and end of each character control the transmission. Access Rate—The transmission speed, in bits per second (bps), of the physical access circuit between the end user and the network. Bandwidth—Measure of the information capacity of a transmission channel. Access Tandem—A Telephone Company switching system that provides a concentration and distribution function for originating or terminating traffic between end offices and customer’s premises. Acknowledgment (ACK)—Portion of any communications protocol responsible for acknowledging the receipt of a transmission. Adapter—A board installed in a computer system to provide network communication capabilities to and from that computer system. Also called a Network Interface Card (NIC). 36 • Frame Relay Service in Today’s Enterprise Network Environment B Channel—In ISDN, a full duplex, 64 Kbps channel for sending data. Backbone—The part of a network used as the primary path for transporting traffic between network segments. Backward Explicit Congestion Notification (BECN)—A bit in the Frame Relay header. The bit is set by a congested network node in any frame which is traveling in the reverse direction of the congestion. (In Frame Relay, a node can be congested in one direction of frame flow but not in the other.) Basic Rate Interface (BRI)—ISDN standards and specifications for provision of low-speed ISDN services. Supports two “B” channels of 64 Kbps each and one “D” channel of 16 Kbps on a single wire pair. Bridge—A device that connects and passes packets between two network segments. Bridges operate at Layer 2 of the OSI reference model, the data-link layer, and are insensitive to upper-layer protocols. A bridge will examine all frames arriving on its ports and will filter, forward or flood a frame depending on the frame’s Layer 2 destination address. Glossary • 37 ATT FR BOOK 8/4/0 1:25 PM Page 38 Bridge/Router—A device that can provide the functions of a bridge, router or both concurrently. Bridge/router can route one or more protocols, such as TCP/IP and or XNS, and bridge all other traffic. Cell—For ATM, most vendors have agreed that this information “package” will be developed consisting of 53 bytes or “octets”. Of these, the first 5 constitute the header; 48 carry the payload. Cellular Digital Packet Data (CDPD)—A wireless packet data service for mobile users. Provides high speed, secure wide area IP (Internet Protocol) network connectivity and operates at 19.2 Kbps. To provide connectivity back to the customer’s enterprise networks, CDPD networks interface with existing wireline networks and services, including Frame Relay and the Internet. Channel Service Unit/Data Service Unit (CSU/DSU)—A digital interface unit that connects end user equipment to the local digital telephone loop. Client/Server—A distributed system model of computing that brings computing power to the desktop, where users (“clients) access resources from servers. Committed Information Rate (CIR)—The transport speed the Frame Relay network will maintain between service locations when data is presented. Constant Bit Rate (CBR)—Delay intensive applications such as video and voice, that must be digitized and represented by a continuous bit stream. CBR traffic requires guaranteed levels of service and throughput. Contention—Network access method where devices compete for the right to access the physical medium. Customer Premises Equipment (CPE)— Terminating equipment, such as terminals, phones, routers and modems, supplied by the phone company, installed at customer sites, and connected to the phone company network. 38 • Frame Relay Service in Today’s Enterprise Network Environment Data Link Connection Identifier (DLCI)—A value in Frame Relay that identifies a logical connection. Dedicated Line—A transmission circuit installed between two sites of a private network and “open,” or available, at all times. Delay—Amount of time a call spends waiting to be processed. Dial Up—A type of communication that is established by a switched-circuit connection using the telephone network. Digital Signal 0 (DS-0)—North American Digital Hierarchy signaling standard for transmission at 64 Kbps. Digital Signal 1 (DS-1)—North American Digital Hierarchy signaling standard for transmissions at 2.544 Mbps. Supports 24 simultaneous DS-O signals. Term often used interchangeably with T-1, although DS-1 signals may be exchanged over other transmission systems. Digital Signal 3 (DS-3)—North American Digital Hierarchy signaling standard for transmission at 44.736 Mbps. Supports 28 simultaneous DS-1 signals. Discard Eligible (DE)—A 1-bit field in a Frame Relay header that provides a two level priority indicator. Used to bias discard of frames in the event of congestion toward lower priority frames. Similar to the CLP bit in ATM. Encapsulation—A protocol technique in which traffic frames of one protocol type are transmitted unchanged through the facility of a different protocol based system. The transmitting protocol adds sufficient information to the offered frame to send it successfully to its destination, where the added information is stripped away. Enterprise Network—A geographically dispersed network under the auspices of one organization. Glossary • 39 ATT FR BOOK 8/4/0 1:25 PM Page 40 File Transfer Protocol (FTP)—An IP application protocol for transferring files between network nodes. Firewall—Isolation of LAN segments from each other to protect data resources and help manage traffic. Forward Explicit Congestion Notification (FECN)—A bit in the Frame Relay header. The bit is set by a congested network node in any frame which is traveling in the same direction as the congestion. (In Frame Relay, a node can be congested in one direction of frame flow but not in the other). Fractional T-1—A WAN communications service that provides the user with some portion of a T-1 circuit which has been divided into 24 separate 64 Kbps channels. It is known as fractional E-1 in Europe. Frame—A logical grouping of information sent as a link-layer unit over a transmission medium. The terms packet, datagram, segment, and message are also used to describe logical information groupings at various layers of the OSI reference model and in various technology circles. Frame Relay—High-performance interface for packetswitching networks; considered more efficient than X.25 which it is expected to replace. Frame relay technology can handle “bursty” communications that have rapidly changing bandwidth requirements. Frame Relay Access Device (Assembler/ Disassembler) (FRAD)—Attaches a header and a trailer to the frame packet. FRADs on the receiving end also detect errors in the payload data. Frame Relay Forum—A voluntary organization composed of Frame Relay vendors, manufacturers, service providers, research organizations and users. Similar in purpose to the ATM Forum. 40 • Frame Relay Service in Today’s Enterprise Network Environment Graphic User Interface (GUI)—Generic name for any computer interface that substitutes graphics for text characters. Integrated Services Digital Network (ISDN)— The recommendation published by CCITT for private or public digital telephone networks where binary data, such as graphics and digitized voice and data transmission, pass over the same digital network that carries most telephone transmissions today. Internetwork Packet Exchange, Network Protocol (IPX)—LAN protocol developed by Novell for NetWare. Latency—The delay between the time a device receives a frame and the frame is forwarded out of the destination port. Leased Line—A transmission line reserved by a communications carrier for the private use of a customer. Load Balancing—In routing, the ability of the router to distribute traffic over all its network ports that are the same distance from the destination address. It increases the use of network segments, which increase the effective network bandwidth. Local Area Network (LAN)—A network covering a relatively small geographic area (usually not larger than a floor or small building). Compared to WANs, LANs are usually characterized by relatively high data rates. Logical Link Control Type 2 (LLC2)—A connection oriented mode of operation within the logical link control sub-layer of the ISO data link protocol layer. Metropolitan Area Network (MAN)—A data communication network covering the geographic area of a city (generally, larger than a LAN but smaller than a WAN). FDDI can provide a private MAN, while IEEE 802.6 can provide a public MAN. Glossary • 41 ATT FR BOOK 8/4/0 1:25 PM Page 42 Network Address—Also called a protocol address. A network layer address referring to a logical, rather than a physical, network device. Packet—A logical grouping of information that includes a header and (usually) user data. Permanent Virtual Circuit (PVC)—A defined virtual link with fixed end-points that are set-up by the network manager. A single virtual path may support multiple PVCs. Point-to-Point Protocol (PPP)—Successor to SLIP; provides router-to-router and host-to-network connections over both synchronous and asynchronous circuits. Routing Table—A table stored in a router or some other internetworking device that keeps track of routes (and, in some cases, metrics associated with those routes) to particular network destinations. Serial Line Interface Protocol (SLIP)—Internet protocol used to run IP over serial lines such as telephone circuits or RS-232 cables interconnecting two systems. SLIP is now being replaced by PPP. Simple Network Management Protocol (SNMP)— The Internet network management protocol. SNMP provides a means to monitor and set network configuration and runtime parameters. Primary Rate Interface (PRI)—ISDN interface to primary access, consisting of a single 64 Kbps D channel plus 23 or 30 B channels for voice and/or data. System Network Architecture (SNA)—IBM’s high-level protocol for communications between its mainframes, peripherals and other equipment. Private Line—A transmission line reserved by a communications carrier for the private use of a customer. Transmission Control Protocol/Internet Protocol (TCP/IP)—The common name for the suite of protocols developed by the U.S. Department of Defense in the 1970s to support the construction of world-wide internetworks. TCP and IP are the two best-known protocols in the suite. TCP corresponds to Layer 4 (the transport layer) of the OSI reference model. It provides reliable transmission of data. IP corresponds to layer 3 (the network layer) of the OSI reference model and provides connectionless datagram service. Protocol—A formal description of a set of rules and conventions that govern how devices on a network exchange information. Protocol Stack—Related layers of protocol software that function together to implement a particular communications architecture. Examples include AppleTalk and DECnet. Router—An OSI Layer 3 device that can decide which of several paths network traffic will follow based on some optimality metric. Also called a gateway (although this definition of gateway is becoming increasingly outdated), routers forward packets from one network to another, based on network-layer information. Wide Area Network (WAN)—A network which encompasses interconnectivity between devices over a wide geographic area. Such networks would require public rights-of-way and operate over long distances. Routing—The process of finding a path to the destination host. Routing is very complex in large networks because of the many potential intermediate destinations a packet might traverse before reaching its destination host. 42 • Frame Relay Service in Today’s Enterprise Network Environment Glossary • 43 ATT FR BOOK 8/4/0 1:25 PM Page 44 NOTES 44 • Notes NOTES Notes • 45 ATT FR BOOK 8/4/0 1:25 PM Page 46 NOTES 46 • Notes NOTES Notes • 47 ATT FR BOOK 8/4/0 1:25 PM Page 48 NOTES AT&T Frame Relay Service combines the reliability, quality and accuracy of AT&T’s worldwide digital network, with the innovative technology and design expertise of AT&T Laboratories. As such, AT&T Frame Relay offers a service with superior value in per formance, scope, flexibility, and support, helping customers to address the challenges of globalizing and expanding their information infrastructure. Network management tools, detailed metrics and Service Level Agreements (SLAs) help AT&T and customers monitor and manage the network. Ser vicespecific performance guarantees, backed by credits, are provided on a service-by-service basis to meet customer-specific network needs. AT&T continues to invest heavily in Frame Relay, both in people and technology, by increasing the number of customer service and implementation managers to meet customer demand, and by adding Network Operations Centers to enhance the global network management capabilities. AT&T Frame Relay Service 900 RT 202/206 North, Rm. 3A226Z, Bedminster, NJ 07921 http://www.att.com/ipservices/data 800-288-3199 Visual Networks is a registered trademark of Visual Networks, Inc. 48 • Notes ATT FR COVER 8/4/0 1:18 PM Page 1 T H E T E C H N O L O G Y G U I D E S E R I E S™ www.techguide.com ™ This Technology Guide is one in a series of topicfocused Guides that provides a comprehensive examination of important and emerging technologies. This series of Guides offers objective information and practical guidance on technologies related to Communications & Networking, the Internet, Computer Telephony, Document Management, Data Warehousing, Enterprise Solutions, Software Applications, and Security. Frame Relay Service in Today’s Enterprise Network Environment Built upon the extensive experience and ongoing research of our writers and editorial team, these Technology Guides assist IT professionals in making informed decisions about all aspects of technology development and strategic deployment. Visit our Web site at www.techguide.com to view and print this Guide, as well as all of our other Technology Guides. This is a free service. BP3841-04 techguide.com is supported by a consortium of leading technology providers. AT&T has lent its support to produce this Guide. produced and published by This Guide has been sponsored by visit www.techguide.com™ ...
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