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1 Multiprotocol over ATM ATG s Communications & Networking Technology Guide Series This guide has been sponsored by

2 For more information on ATM and visit these web sites: Fore Systems IBM Madge Networks Newbridge Networks Trillium Digital Systems Table of Contents Executive Summary Introduction Multi-Protocol Over ATM () Three Basic Elements Logical Components How it Works Migration and Co-existence Conclusions Appendix Alternative Approaches to Integration of ATM with outing Glossary of Terms About the Editor Gerald P. yan is the founder of Connections Telecommunications Inc., a Massachusetts-based company specializing in consulting, education and software tools which address Wide Area Network issues. Mr. yan has developed and taught numerous courses in network analysis and design for carriers, government agencies and private industry. Connections has provided consulting support in the areas of WAN network design, negotiation with carriers for contract pricing and services, technology acquisition, customized software development for network administration, billing and auditing of telecommunications expenses, project management, and FP generation. Mr. yan is a member of the Networld+Interop program committee. This book is the property of The Applied Technologies Group and is made available upon these terms and conditions. The Applied Technologies Group reserves all rights herein. eproduction in whole or in part of this book is only permitted with the written consent of The Applied Technologies Group. This report shall be treated at all times as a proprietary document for internal use only. This book 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 book, or any portion for any purpose other than your own, is a violation of United States Copyright Laws. The information contained in this report is believed to be reliable but cannot be guaranteed to be complete or correct. Copyright 1997 by The Applied Technologies Group, One Apple Hill, Suite 216, Natick, MA 01760, Tel: (508) , Fax: (508) info@techguide.com Web Site:

3 Executive Summary As networks become more strategic to the success of knowledge-based organizations, it is clear that current technology will have to evolve in order to meet the constant demands of traffic growth and new applications. With the remarkable growth of both the Internet and the intranets as well as client/server and multimedia applications bandwidth demands and traffic trends are radically different than they were just a few years ago. Conventional router-based topologies that could adequately meet all of a corporation s needs in the past, can no longer provide the performance required for today s enterprise networks. This is because the emergence of Internet, intranet, client/server and multimedia applications has caused a dramatic shift in the conventional internetworking paradigm. For example, while 80% of network traffic used to be localized within subnets, today this trend is reversing to where increasingly higher percentage of traffic is traversing subnet domains. In addition, while a shared network medium used to be sufficient for the majority of desktop requirements, today switched technologies with Quality of Service (QoS) guarantees are required to support current and emerging applications. Multiprotocol Over ATM (), is a specification from the ATM Forum that leverages standardsbased ATM switching to deliver high performance, scalable routing functionality. The solution maps routed and bridged flows of traffic to ATM switched virtual channels (SVCs), off-loading traditional routers from performing packet-by-packet processing. By leveraging hardware-based ATM switching fabric, significantly improves performance in terms of throughput, overall latency and end-to-end delay variation for routed traffic. Furthermore, based networks communicate with conventional routers via 2 Multiprotocol over ATM standard routing protocols, such as IP (outing Information Protocol) and OSPF (Open Shortest Path First). This allows a seamless integration with the installed base of conventional routers. enables network managers and network operators to build multi-vendor, multiprotocol campus, MAN (Metropolitan Area Network), WAN (Wide Area Network), private, public and virtual private networks. Building on existing ATM Forum and IETF (Internet Engineering Task Force) standards, is designed to offer significant scalability using mature technologies. For example, ATM s ability to provide end-to-end signaling, traffic management, and trunking offer immediate benefits to building large systems. Furthermore, ATM s built in QoS benefits can be realized for multimedia applications that involve continuous flows of voice and video traffic that requires bandwidth guarantees. The result is a multi-gigabit routing infrastructure that is ideally suited to meet all of the emerging demands associated with the latest network applications. From a management perspective, the design enables the aggregation of multiple routing instances to provide a consolidated enterprise view of the routed network. Furthermore, the connectionoriented ATM fabric has introduced a powerful new concept of virtual networks, or more accurately, allowing the separation of logical constructs from the physical topology of the network at the network layer. This concept, when implemented effectively can greatly simplify network management tasks by simplifying the configuration of the network, and eliminating overhead with moves, adds and changes. Technology Guide 3

4 Introduction The fundamental challenge for router-based networks arises when networks grow in size and new applications are employed which use greater amounts of data and delay-sensitive multi-media traffic. As some of the first steps in responding to user complaints about poor performance, network managers rushed to remedy the bandwidth shortage at the desktop by deploying high-speed LAN switches at the edge of the network and ATM switches for their backbone woes. As users continue to send and receive large volumes of traffic across subnet boundaries, the same LAN and ATM switches are now sending millions of packets per second to their backbone routers. Even the fastest routers, capable of processing up to 500,000 packets a second, are becoming bottlenecks for the cross subnet traffic generated by pervasive use of Internet, intranets and multi-media traffic. outers also introduce delay as they perform the tasks of address resolution, route determination, and packet filtering. The more traffic there is and more router hops that this traffic encounters to reach the final destination, the larger the aggregate delay caused by these routers. To make matters worse, the latency on each frame varies, resulting in a delay variation that is not deterministic in nature and unsuitable for multimedia applications. outers usually accept network layer frames addressed to them from hosts connected to the LAN subnets and forward these frames to the destination hosts on other subnets. This operates in a connectionless mode, according to the routing protocol being used. Control and Management Plane Data Plane Figure 1 As shown in Figure 1, in a connectionless environment, each frame within a flow of data is subject to address mapping computations within the router and this process is repeated at every router hop in the network. This implies that each router in the network shown above must run the full multi-protocol routing stack. This is not only expensive from equipment and software perspective, but is also complex from a network management point of view. Each router in the network must be independently configured, maintained and managed. In some cases, to improve performance, routers can simply be replaced by high speed ATM switches, but in so doing, all of the tasks accomplished by the routers are lost. So the challenge is to integrate routing functionality with the ATM infrastructure without imposing significant bottlenecks or latency onto the traffic stream. This challenge is amplified when the requirements include large populations, over wide areas, with mixed media and heavy traffic loads. It is also clear that the resulting solution must integrate the advantages of ATM technology with existing LAN technologies such as Ethernet and Token ing to preserve the investment in existing hardware, and with TCP/IP and IPX/SPX to preserve compatibility with the massive installed base of applications. = Conventional outer 4 Multiprotocol over ATM Technology Guide 5

5 Multi-Protocol Over ATM () The ATM Forum has worked in cooperation with the IETF to develop a powerful network layer routing solution that integrates and leverages existing protocols and standards to provide routing functionality over switched ATM networks. It provides unprecedented scalability and flexibility by introducing a concept known as a virtual router. The virtual router emulates the functionality of traditional routed networks, but eliminates the performance limitations of hop by hop routing. Shortcut connections are setup over the ATM fabric from any capable host or edge device to any other, regardless of their subnet membership. In essence, identifies data flows and maps them directly to ATM virtual channels. This technique of establishing shortcuts directly across the ATM network is sometimes referred to as cutthrough or zero-hop routing. Forwarding B1 C2 outer Edge Device B3 outing Shortcut Connection ATM Switch NIC A3 Server ATM Switch ATM Switch NIC B2 Figure 2 Subnet A Edge Device Subnet B The establishment of a shortcut connection over the ATM fabric provides a significant improvement in performance over pure router based inter-subnet solutions. Packets transported over the shortcut connection are no longer subjected to the hop by hop router processing in traditional networks. Besides improvement in performance, the end to end delay between end A1 A2 C1 Subnet C stations also becomes more deterministic. The framework provides a unified model for overlaying inter-networking layer protocols onto ATM. While vendors will implement different flavors of physical implementations of the framework, the specifications assure interoperability amongst vendors. The general concept involves splitting forwarding and routing functions traditionally supported within conventional multi-protocol routers between Clients and Servers. Address management and topology discovery, for example, are performed by the server (MPS), while traffic forwarding is provided by Clients (MPCs) via the ATM switch fabric. The MPS typically resides in an ATM switch-router or a stand-alone ATM attached route server, while MPCs reside in edge devices and ATM attached hosts. This provides a physical separation between the devices that calculate the internetwork route and those that forward the data. As a result, while traditional routers are limited by the speed of their proprietary back-planes, an based routing system leverages products such as standard-based ATM switches resulting in a multi-gigabit routing infrastructure that is ideally suited to meet all of the emerging demands associated with routed LAN and WAN internetworks. Furthermore, since transport services are provided over a standards-based ATM infrastructure by mapping network layer protocols such as IP and IPX directly to ATM, it enables QoS mechanisms being developed for IP, such as SVP to be exposed to the underlying ATM fabric. The end result is that time sensitive traffic can utilize QoS capabilities of an ATM infrastructure while leveraging low cost installed technologies, such as Ethernet and TCP/IP at the desktops. This allows for affordable, high performance multi-media applications such as video conferencing, video distribution and distance learning. 6 Multiprotocol over ATM Technology Guide 7

6 Edge Device Control and Management Plane Servers Data Plane Figure 3 Edge Device As can be seen in Figure 3, the servers run the full routing stack which results in a consolidated configuration for the entire network. The switches are standards based ATM switches which results in a highly scalable, low cost, high performance network infrastructure. Edge devices are optimized for forwarding network layer and Layer 2 traffic resulting in network wide virtual networks and zero-hop routing across the ATM network. Three Basic Elements Edge Device uses three complementary techniques to form its fundamental capability. These are ATM Forum s LAN Emulation (LANE), the IETF s Next Hop esolution Protocol (NHP) and the concept of the Virtual outer. LANE supports native LAN environments over ATM in a transparent manner, while NHP provides a mechanisms to establish a shortcut over the ATM backbone based on network layer addressing.. Virtual outers provide the ability to separate functions among various elements of the network, which reduces cost and improves efficiency. = Conventional outer X = ATM Switch LANE overcomes some of the performance and scalability limitations of LANE based networks. However, LANE Version 2 is an integral component of. LANE is used for intra-subnet communications, while the virtual router provides communications between subnets. efer to Appendix for a more detailed explanation of LANE operation. Next Hop esolution Protocol NHP The IETF has defined Next Hop esolution Protocol (NHP) which among other capabilities, allows the packet forwarding function of intermediate routers on the data path to be bypassed. NHP provides an extended address resolution protocol that permits Next Hop Clients (NHCs) to send queries between different logical IP subnets (LISs) sometimes referred to as Local Address Groups (LAGs). Queries are propagated using Next Hop Servers (NHSs) along paths discovered by standard routing protocols such as IP and OSPF. This enables the establishment of ATM SVCs across subnet boundaries, allowing intersubnet communications without using intermediate routers for qualified data flows. 8 Multiprotocol over ATM Technology Guide 9

7 Virtual outer A virtual router is a set of devices operating over a network which collectively provide the functionality of multiprotocol routed networks. In the case of the edge devices are analogous to router interface cards; the ATM switching fabric can be seen as the backplane of the router; and the Server is analogous to the control processor. The framework defines the protocols between the Server and the edge devices that enable the virtual router behavior. Logical Components defines logical components that can be implemented in various hardware configurations. The separation of function allows vendors to package their unique solutions to meet the particular needs of their customers. Edge Device or Host Client Server outer Next Hop Server Traditional outer outer Processor Cards Virtual outer Server Layer 3 forwarding engine LAN emulation client (LEC) ELAN Figure 5 LEC outing engine outer Backplane I/O Cards Standards Based Figure 4 ATM Switching Fabric Edge Devices Standards Based Edge Devices Edge devices are inexpensive devices which forward packets between legacy LAN segments and ATM interfaces based on the destination network layer address and MAC layer address. Client MPC MPCs reside in the Edge Device or ATM attached hosts and their primary function is to act as a point of entry and exit for traffic using internetwork shortcuts. An MPC looks for traffic flows, and when found, it requests its serving MPS to provide information on the destination and check that a shortcut is acceptable. If it is, the MPC sets up a SVC and forwards data to the destination across the path. The MPC and MPS communicate with each other using NHP. The MPC caches the shortcut information it derives from its interaction with the MPS. SVCs with no activity are inactivated upon the expiration of a variable time-out. 10 Multiprotocol over ATM Technology Guide 11

8 outer The outer is a collection of functions that allow the mapping of network layer subnets to ATM. The outer can be implemented as a standalone product, or can be built into existing routers or switches. It maintains local network layer, MAC-layer and ATM address information in addition to routing tables. outers communicate via NHP to resolve destination addresses so that MPCs can establish shortcuts. The outing engine runs routing protocols (e.g., IP and OSPF) to communicate routing information with traditional routers, allowing interoperability with existing routed LAN and WAN internetworks. Server MPS An MPS is a logical component of the outer that provides Layer 3 forwarding information to MPCs. It also includes an NHP server (NHS) function. The MPS interacts with its associated routing function and its NHS to identify a path represented by the destination ATM address and Layer 2 encapsulation information which it returns in response to a query from the MPC. Caching Since it is commonplace for users in a routed internetwork to have repetitive and habitual external addresses to which they need to be connected; e.g., particular file servers or remote corporate destinations, the edge device can save ( cache ) this virtual channel information to be reused without having to issue address resolution requests for every flow. This is a valuable aspect of the concept. A design goal of is to minimize the number of times the edge device must visit the route server to retrieve this information. To that end, the MPC maintains its own address cache. Much of the effort is devoted to devising effective cache-management techniques, including ensuring cache coherency between MPCs and MPSs. Virtual Subnets uses network layer constructs in defining virtual subnetworks. They denote both a Layer 3 protocol and an address range. In the case of IP, they can be thought of as virtual subnets. The model supports all existing LAN internetwork data flows, including both intra-subnet and inter-subnet. How it Works The model distributes routing among edge devices and ATM attached hosts with Clients, which forward packets, and Servers, which supply routing information. MPCs examine the destination address of packets received on legacy LAN segments in order to make the correct forwarding decision. If the packet is to be routed, it will contain the destination MAC address of the outer interface. If so, the MPC will look at the destination network layer address of the packet, and resolve this to the correct ATM address based on information received from the Server or use information in its cache. The MPC will then establish a direct virtual channel connection to the appropriate destination. If the packet is destined to a host in the same subnet so that it can be bridged, the MPC will use LANE to resolve the ATM address and establish a virtual channel connection to the destination. If the local Server does not know the appropriate ATM address, it can propagate the query to other Servers or routers using NHP functionality. The destination ATM address from the Server can be the address of the host 12 Multiprotocol over ATM Technology Guide 13

9 (if the host is ATM-attached), or the address of the appropriate edge device to which the packets should be forwarded. Network Layer Mapping works at network Layer 3 to recognize the beginning of a data transfer and respond with a network route destination address. The shortcut SVC is then used to forward traffic using standard Layer 2 switching. With both Layer 3 and Layer 2 capabilities, the model encompasses routing and switching: 1) being able to route and switch network layer traffic; and 2) also being able to bridge non-routable traffic. The network layer mapping enables the QoS properties of ATM to be used by network applications. For example, the IETF s SVP protocol operates at the network layer, and provides mechanisms for applications to reserve particular quality of service. The framework allows the Layer 3 reservations to be mapped onto the underlying ATM fabric. Taking a Shortcut The Basic Concept The fundamental concept behind the use of to support multi-protocol LAN-LAN traffic is based on the fact that, in most cases, data transfer usually occurs in a relatively steady flow. That is, a file or message being sent usually consists of multiple frames. For example, a 45K file, using a typical Ethernet frame size of 1500 octets would require about 30 frames. Since all 30 frames would travel to the same destination, it is possible to identify the destination and establish a SVC based on the information contained in the first frame. Then all 30 frames could be broken into approximately 900 ATM cells and transmitted over the virtual channel established by the SVC. This could be considered a shortcut in that the entire flow of data follows a pre-established path, avoiding the default path followed by routed traffic, and greatly improving 14 Multiprotocol over ATM performance. In the case of steady stream transmissions such as video, this is highly efficient and superior to simple router to router operation. The following describes the interaction of the MPCs with the MPS: ATMaddr1 IPaddr1 ATM Host sends data destined for IPaddr2 to Server. Server will forward data to Edge Device with IPaddr2 host. Figure 6 illustrates the basic operation of. The first time that traffic needs to be forwarded from ATM Host with IP address of Ipaddr1, the traffic is forwarded to Server. While forwarding this traffic, the Server learns both the IP-to-MAC address and the MAC-to-ATM address mappings. ATMaddr1 IPaddr1 ATM Host ATM Host detects X packets in Y seconds and queries Server for ATM address of IPaddress2 Data for IPaddr2 ATM Host Data for IPaddr2 When ATM address is resolved, a SVC to destination is established and the Short-Cut flow is used. ATM Cloud Figure 6 ATM Cloud Server Server Direct ATM Connections (data for IPAddr2) Figure 7 ATMaddr2 Data for IPaddr2 Edge Device Data for IPaddr2 Edge Device ATMaddr2 IPaddr2 IPaddr2 As shown in Figure 7, to set up a direct shortcut connection, MPCs obtain the ATM address of the exit point to which the destination host is connected. The destination host is a host with a network layer address that is either connected to a legacy LAN or is ATM attached. If it is a host connected to a legacy LAN such Technology Guide 15

10 as Ethernet or Token ing, the MPS returns the ATM address of the edge device that connects to the host on the legacy LAN. If the host is ATM attached, the MPS returns the ATM address of the host that corresponds to its network layer address. A Day in the Life of a Packet The following describes the events that allow a packet to be sent across an network using the shortcut capabilities of the system. Server 2 ELAN Client 1 ELAN LIS Default Path Shortcut Figure 8 16 Multiprotocol over ATM Server 1 ELAN Client 2 A packet enters the system at the ingress (entry) MPC ( Client 1 in figure 8). By default, the packet is bridged via LANE to the default router (co-located with MPS 2). From there it is forwarded via the router in MPS 2 to the destination edge device or host. However, if this packet is part of a flow for which a shortcut has been established, the ingress MPC strips off the Layer 2 encapsulation from the packet and sends it via the shortcut. If no data flow is detected, each packet being sent to an MPS is tallied by its Layer 3 destination address as it is being forwarded by LANE. When the threshold is exceeded ( N packets to a specific Layer 3 address within X time), the MPC sends an resolution request to the MPS to obtain the ATM address to be used for establishing a shortcut to the Egress (exit) MPC. On arriving via a shortcut at the Egress MPC, the packet is examined and either a matching Egress Cache Entry is found or the packet is dropped. If a match is found, the packet is re-encapsulated using the cache information and it is forwarded via a LAN interface to its destination. The shortcut is an ATM SVC established for the specific data flow. Migration and Co-existence The MPS communicates with external routers via standard routing protocols, such as IP and OSPF. This allows a seamless integration with non- systems and with non-shortcut qualified traffic. It is important to note that the routing devices in the architecture provide all of the ordinary and valuable functions of a router, including connectionless internetworking across wide area networks, integrity verification, and route prioritization. Traditional outer Network LANE and OSPF, IP Figure 9 Server Virtual outer While specifications are implemented to overcome some of the performance and scalability limitations of LANE specifications, LANE Version 2 is an integral component of. The default operation for an device is the standard LANE connectivity. Technology Guide 17

11 NHP and Since NHP is an integral component of the Server, an based network can interact with routers that support NHP functionality to propagate ATM address resolution requests. Conclusions It is clear that a specific model for integrating ATM into today s multi-protocol networks is needed in a way that permits organizations to build scalable and manageable multi-media internetworks, retaining the important functionality of routers while allowing the continued use of existing Ethernet, Token ing, and TCP/IP and SPX/IPX infrastructures. integrates LANE and NHP to preserve the benefits of LAN Emulation, while allowing intersubnet network layer protocol communication over ATM SVCs without requiring conventional routers in the data path. allows the physical separation of network layer route calculation and forwarding, a technique known as Virtual outing. This separation provides a number of key benefits: High performance and efficient inter-subnet communication Increased manageability by decreasing the number of devices that must be configured to perform network layer route calculation Increased scalability by reducing the number of devices participating in the network layer route calculation educed complexity of the Edge Devices by eliminating the need to perform network layer route calculation In today s environments in which LANs are growing in complexity and importance, it is critical that there be effective systems in place to allow these networks to operate across an ATM fabric. The approach has significant advantages over other Layer 3 switching alternatives. Using cut-through routing over a switched infrastructure, a system based on can process and forward tens of millions of packets per second. This level of scalability and performance cannot be rivaled by conventional LAN and WAN internetworking solutions. In terms of cost and complexity, this elegant solution allows organizations to build large scale networks connected together with ATM, but with the full capabilities of outers. outing will continue to be important in network architectures and will be a key component in any network solution. The ATM Forum continues to work in this important area and is addressing the issue of related work in Classical IP, LANE and MAS (Multicast-Address esolution Server) for support of Multicast. 18 Multiprotocol over ATM Technology Guide 19

12 Appendix Alternative Approaches to Integration of ATM with outing Edge outing over ATM Backbone This approach to internetworking partly alleviates the performance bottleneck of router based networks by equipping conventional routers with a fully configured set of ATM network links. But it is clear that as the number of locations and routers increase, the cost of maintaining the fully provisioned mesh of virtual channels becomes costly as well as complicated to manage. Furthermore, ATM QoS capabilities are not utilized if the edge routers continue to treat ATM as just another high speed link. Subnet B Subnet A A A outer A A B B outer B outer C C C Classical IP over ATM 20 Multiprotocol over ATM ATM Network Figure 10 Subnet D outer outer Subnet E A D D D E E E Subnet C Physical Network = Logical Network Classical IP over ATM, (FC1577) is an approach that uses the power of ATM to forward IP traffic. It is used to connect subnets or workgroups that use only IP as the transport protocol. As in edge routing over ATM, QoS capabilities of ATM are ignored. It is possible to have multiple subnets on the same network, but at present each subnet must operate independently of the others and routers are required to provide communications between subnets. In complex environ- ments, with multiple subnets, the router latency continues to be an issue. A A B B B A outer AP Server ATM Attached Hosts Logical IP Subnet (LIS) Figure 11 MAC-layer LAN Emulation (LANE) D D ATM Logical IP Subnet D outer The ATM Forum s LAN Emulation (LANE) is a Layer 2 framework that makes a connection-oriented ATM network seem like a shared connectionless Ethernet or Token ing LAN segment. As a Layer 2 service, LANE can handle both routable protocols such as TCP/IP, IPX, and DECnet as well as non-routable protocols such as NetBIOS and SNA. LANE clearly integrates the advantages of ATM with existing LAN technologies such as Ethernet, TCP/IP and IPX/SPX, enabling high performance communication within the workgroup. LANE uses a client/server model, with Emulated LANs made up of multiple LANE Clients (LECs) and a LANE Service. The LANE Service provides a MAC to ATM address resolution and broadcast service to the LANE Clients. Clients are implemented on ATM/LAN edge devices and ATM attached hosts, while the LANE Service can be implemented in a router, LAN or ATM switch, or in a standalone ATM equipped device. LANE still requires traditional network layer routers to interconnect these workgroups, significantly limiting the overall performance and scalability of the network. D D C C C Technology Guide 21

13 Furthermore, as the number of hosts and subnets grow, the computational requirements to calculate routes among different subnets and the memory requirements to store these routes can overwhelm the capacity of conventional routers. A B C B A C Layer 2 Edge Device Layer 2 Edge Device Layer 2 Edge Device Subnet B outer B ATM Network outer Figure 12 Physical Network outer outer Logical Network While all the solutions described above enable high performance communication within a LAN workgroup or subnet, they require traditional network layer routers to interconnect these workgroups or subnets. This has significant potential operational and performance problems. The issue of route calculation and network latency can become important enough to invite better solutions such as. C Subnet A C Subnet C Glossary AAL ATM Adaptation Layer. The standards layer that allows multiple applications to have data converted to and from the ATM cell. A protocol used that translates higher layer services into the size and format of an ATM cell. AAL-1 ATM Adaptation Layer Type 1. AAL functions in support of constant bit rate, time-dependent traffic such as voice and video. AAL-2 ATM Adaptation Layer Type 2. This AAL is still undefined by the International Standards bodies. It is a placeholder for variable bit rate video transmission. AAL-3/4 ATM Adaptation Layer Type 3/4. AAL functions in support of variable bit rate, delay-tolerant data traffic requiring some sequencing and/or error detection support. Originally two AAL types, i.e., connection-oriented and connectionless, which have been combined. AAL-5 ATM Adaptation Layer Type 5. AAL functions in support of variable bit rate, delay-tolerant connectionoriented data traffic requiring minimal sequencing or error detection support. AP Address esolution Protocol. The procedures and messages in a communications protocol which determine which physical network address (MAC) corresponds to the IP address in the packet. ATM Asynchronous Transfer Mode. A transfer mode in which the information is organized into cells. It is asynchronous in the sense that the recurrence of cells containing information from an individual user is not necessarily periodic. 22 Multiprotocol over ATM Glossary 23

14 B-ISDN Broadband ISDN. A high-speed network standard (above Mbps) that evolved Narrowband ISDN with existing and new services with voice, data and video in the same network. BUS Broadcast and Unknown Server. Cell A unit of transmission in ATM. A fixed-size frame consisting of a 5-octet header and a 48-octet payload. Cell Header ATM Layer protocol control information. Control Flow A flow of control packets. Data Flow A flow of data packets. Control Messages NHP and messages, and any other non-data message used by an Component. Default Path The hop-by-hop path between outers that a packet would take in the absence of shortcuts, as determined by routing protocols. DLL Data Link Layer. Edge Device A physical device capable of bridging packets between one or more LAN interfaces and one or more LAN Emulation Clients. An Edge Device also contains one or more Clients allowing it to forward packets across subnet boundaries using an Internetwork Layer protocol. Egress The point where an Outbound Flow exits the System. Egress Cache The collection of Egress Cache Entries in an MPC. Egress Cache Entry Information describing how Internetwork Layer packets for a particular Outbound Flow are to be encapsulated and transmitted. Egress MPC An MPC in its role at an Egress. Egress MPS The MPS serving an Egress MPC for a particular Outbound Flow. ELAN Emulated LAN. Emulated LAN See LANE. Flow A stream of data between two entities. In many cases the term flow is used instead of the term VCC because with LLC/SNAP multiplexing, more than one pair of entities can communicate over a given VCC. Forwarding Description The resolved mapping of a Target to a set of parameters used to set up a Shortcut. Higher Layers The software stack above and LANE, e.g., LLC, bridging, etc. IETF Internet Engineering Task Force. The organization that provides the coordination of standards and specification development for TCP/IP networking. Inbound Flow Data entering the System. Ingress The point where an Inbound Flow enters the system. Ingress Cache The collection of Ingress Cache Entries in an MPC. Ingress Cache Entry The collection of information dealing with inbound flows. This information is used to detect flows that may benefit from a shortcut, and, once detected, indicates the shortcut VCC to be used and encapsulation information to be used on the frame. Ingress MPC The MPC which forwards Internetwork Layer packets onto ATM from legacy. Ingress MPS The MPS serving an Ingress MPC for a particular traffic flow. 24 Multiprotocol over ATM Glossary 25

15 Internetwork Layer A protocol used to communicate across subnet boundaries. E.g., IP, IPv6, IPX, DECnet routing, CLNP, AppleTalk DDP, Vines, SNA, etc. ION Internetworking Over NBMA (Non-Broadcast Multi-Access). IP Internet Protocol. Originally developed by the Department of Defense to support interworking of dissimilar computers across a network. This protocol works in conjunction with TCP and is usually identified as TCP/IP. A connectionless protocol that operates at the network layer (layer 3) of the OSI model. IPX Novell Internetwork Packet Exchange. A built-in networking protocol for Novell Netware. It was derived from the Xerox Network System protocol and operates at the network layer of the OSI protocol model. LANE LAN Emulation. The set of services, functional groups and protocols which provide for the emulation of LANS utilizing ATM as a backbone to allow connectivity among LAN and ATM attached end stations. LANE Service Interface The interface over which a LEC communicates with an MPC. LECS LAN Emulation Server. MAC Media Access Control. IEEE specifications for the lower half of the data link layer (Layer 2) that defines topology dependent access control protocols for IEEE LAN specification. MAN Metropolitan Area Network. A network designed to carry data over an area larger than a campus such as an entire city and its outlying area. MAS Multicast Address esolution Server. MPC Client. MPC Control ATM Address Each MPC has a single MPC Control ATM Address. MPC Data ATM Address The address used to send data to an MPC over an shortcut. This address may be different from the MPC Control Address. MPC Service Interface The interface over which an MPC communicates with the Higher Layers. Multiprotocol Over ATM. Client A protocol entity that implements the client side of the protocol. Component An MPC or MPS. Host A host containing one or more LAN Emulation Clients allowing it to communicate using LAN Emulation. An Host also contains one or more Clients allowing it to transmit packets across subnet boundaries using an Internetwork Layer protocol. Server A protocol entity that implements the server side of the protocol. An Server is co-located with a outer. System The set of inter-communicating Clients and Servers. MPS Server. NHC Next Hop Client. NHP Next Hop esolution Protocol. NHS Next Hop Server. OSPF Open Shortest Path First. A link-state routing algorithm that is used to calculate routes based on the number of routers, transmission speed, delays and route cost. Outbound Flow Data exiting the System from a Shortcut. PDU Protocol Data Unit. 26 Multiprotocol over ATM Glossary 27

16 Protocol Data Unit (PDU) A message sent between peer protocol entities. PVC Permanent Virtual Circuit. This is a link with static route defined in advance, usually by manual setup. QoS Quality of Service. FC equest for Comment. The development of TCP/IP standards, procedures and specifications is done via this mechanism. FCs are documents that progress through several development stages, under the control of IETF, until they are finalized or discarded. outer A device allowing communication across subnet boundaries using an Internetwork Layer protocol. A outer maintains tables for Internetwork layer packet forwarding and may participate in one or more Internetwork Layer routing protocols for this purpose. A outer forwards packets between subnets in accordance with these tables. A outer may contain one or more LAN interfaces, one or more LAN Emulation Clients, and one or more Servers. outing Protocol A protocol run between outers to exchange information used to allow computation of routes. The result of the routing computation will be one or more next hops. SDU Service Data Unit. Service Data Unit (SDU) A message sent between an entity and its service user or service provider. Shortcut An ATM SVC used to forward packets across subnet boundaries. SVC Switched Virtual Channel. Target An Internetwork Layer Address to which a Shortcut is desired. Tag A 32 bit opaque pattern that an Egress MPC may provide to an Ingress MPC. If a Tag is provided to an Ingress MPC by an Egress MPC, the Ingress MPC 28 Multiprotocol over ATM must include the tag in the packet header on each for packets sent to the given MPC for the given internetwork destination. TCP Transmission Control Protocol. Originally developed by the Department of Defense to support interworking of dissimilar computers across a network. A protocol which provides end-to-end, connectionoriented, reliable transport layer (layer 4) functions over IP controlled networks. TCP performs the following functions: flow control between two systems, acknowledgments of packets received and end-to-end sequencing of packets. VC A communications channel that provides for the sequential unidirectional transport of ATM cells. VCC Virtual Channel Connection. WAN Wide Area Network. This is a network which spans a large geographic area relative to office and campus environment of LAN (Local Area Network). WAN is characterized by having much greater transfer delays due to laws of physics. Glossary 29

17 NOTES NOTES 30 Multiprotocol over ATM Notes 31

18 Visit ATG s Web Site to read, download, and print all the Technology Guides in this series. For more information on ATM and visit these web sites: Fore Systems IBM Madge Networks Newbridge Networks Trillium Digital Systems The significant problems we face cannot be solved by the same level of thinking that created them. Albert Einstein

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