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Internet Engineering Task Force A. Ghanwani INTERNET DRAFT J. W. Pace V. Srinivasan IBM May 1997 A Framework for Providing Integrated Services Over Shared and Switched LAN Technologies draft-ietf-issll-is802-framework-02.txt Status of This Memo This document is an Internet-Draft. Internet Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet Drafts. Internet Drafts are draft documents valid for a maximum of six months, and may be updated, replaced, or obsoleted by other documents at any time. It is not appropriate to use Internet Drafts as reference material, or to cite them other than as a ``working draft'' or ``work in progress.'' To learn the current status of any Internet-Draft, please check the ``1id-abstracts.txt'' listing contained in the internet-drafts Shadow Directories on ds.internic.net (US East Coast), nic.nordu.net (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific Rim). Abstract Traditionally, LAN technologies such as Ethernet and token ring have been required to handle best effort services only. No standard mechanism exists for providing service guarantees on these media as will be required by emerging and future multimedia applications. The anticipated demand for such applications on the Internet has led to the development of RSVP, a signaling mechanism for performing resource reservation in the Internet. Concurrently, the Integrated Services working group within the IETF has been working on the definition of service classes called Integrated Services which are expected to make use of RSVP. Applications will use these service classes in order to obtain the desired quality of service from the network. LAN technologies such as token ring and Ethernet typically constitute the last hop in Internet connections. It is therefore Ghanwani, Pace, Srinivasan Expires November 1997 [Page i] Internet Draft Integrated Services Over LANs May 1997 necessary to define standardized mechanisms for these technologies so that they are able to support the Integrated Services. This memo describes a framework for providing the functionality to support Integrated Services on shared and switched LAN technologies. Ghanwani, Pace, Srinivasan Expires November 1997 [Page ii] Internet Draft Integrated Services Over LANs May 1997 1. Introduction The Internet has traditionally provided support for best effort traffic only. However, with the recent advances in link layer technology, and with numerous emerging real-time applications such as video conferencing and Internet telephony, there has been much interest for developing mechanisms which enable real-time services over the Internet. These new requirements have led to the design of the ReSerVation Protocol (RSVP) [3], a signaling mechanism for providing resource reservation on the Internet. The protocol is currently being standardized by the IETF. Simultaneously, the Integrated Services working group of the IETF has been working on the specification of various service classes. Each of these service classes is designed to provide certain Quality of Service (QoS) guarantees to traffic conforming to a specified set of parameters. Applications are expected to use one of these classes depending on their QoS requirements. There is no standard mechanism for providing service guarantees on LAN technologies such as Ethernet and token ring. They, however, typically constitute the last hop between users and the Internet backbone. Furthermore, the development of standards for high speed LANs such as gigabit Ethernet favors the likelihood that these technologies will eventually be deployed in the backbone of campus networks. It is therefore necessary to provide some standardized mechanism for these technologies so that they are able to support end-to-end service guarantees such as those defined by the Integrated Services. In order to support real-time services, there must be some mechanism for resource management at the link level. Resource management in this context encompasses the functions of admission control, scheduling, traffic policing, etc. The ISSLL (Integrated Services over Specific Link Layers) working group in the IETF was chartered with the purpose of exploring and standardizing such mechanisms for various link layer technologies. This document is concerned with specifying a framework for providing Integrated Services over shared and switched LAN technologies such as Ethernet/802.3, token ring/802.5, FDDI, etc. We begin with a list of definitions in Section 2. Section 3 lists the requirements and goals for a mechanism capable of providing Integrated Services in a subnet. We then discuss a taxonomy of topologies for the LAN technologies under consideration with an emphasis on the capabilities of each which can be leveraged for enabling Integrated Services. The resource management functions outlined in Section 3 are expected to be provided by an entity which, in this document, is referred to as the Bandwidth Manager (BM). The various components of the Ghanwani, Pace, Srinivasan Expires November 1997 [Page 1] Internet Draft Integrated Services Over LANs May 1997 Bandwidth Manager are discussed in the following section and some examples of the implementation of the Bandwidth Manager are provided. Some issues with respect to link layer support for Integrated Services are examined in Section 6. In the development of this framework, no assumptions have been made about the technology or topology at the link layer. The framework is intended to be as exhaustive as possible; this means that it is possible that all the functions discussed may not be supportable by a particular topology or technology, but this should not preclude the usage of this model for it. 2. Definitions The following is a list of the terms used in this document. - End Station: A device (e.g. router, host) which runs the application program or higher layer protocol which needs to make reservations. - Link Layer/Layer 2: The data link layer. This memo is concerned with link layer technologies such as Ethernet, token ring, and FDDI. - Link Layer Domain: An interconnection of segments and bridges/switches between two end stations. - Segment: A physical link which is shared by one or more senders. - Traffic Class: A category of flows which are given similar service within a bridge/switch. 3. Supporting Integrated Services Within a Subnet: Requirements and Goals This section discusses the requirements and goals which should drive the design of an architecture for supporting Integrated Services over LAN technologies. The requirements refer to functions and features which must be supported, while goals refer to functions and features which are desirable, but are not an absolute necessity. Many of the requirements and goals are driven by the functionality supported by Integrated Services and RSVP. Ghanwani, Pace, Srinivasan Expires November 1997 [Page 2] Internet Draft Integrated Services Over LANs May 1997 3.1. Requirements - Resource Reservation: The mechanism must be capable of reserving resources on a single segment or multiple segments and at bridges/switches connecting them. It must be able to provide reservations for both unicast and multicast sessions. It should be possible to change the level of reservation while the session is in progress. - Admission Control: The mechanism must be able to estimate the level of resources necessary to meet the QoS requested by the session in order to decide whether or not the session can be admitted. For the purpose of management, it is useful to provide the ability to respond to queries about availability of resources. It must be able to make admission control decisions for different types of services such as guaranteed delay, controlled load, etc. - Flow Separation and Scheduling: It is necessary to provide a mechanism for traffic flow separation so that real-time flows can be given preferential treatment over best effort flows. Packets of real-time flows can then be isolated and scheduled according to their service requirements. - Policing: Traffic policing must be performed in order to ensure that sources adhere to their negotiated traffic specifications. Policing must be implemented at the sources and must ensure that violating traffic is either dropped or transmitted as best effort. Policing may optionally be implemented in the bridges and switches. Alternatively, traffic may be shaped to insure conformance to the negotiated parameters. - Soft State: The mechanism must maintain soft state information about the reservations. This means that state information must be periodically refreshed if the reservation is to be maintained; otherwise the state information and corresponding reservations will expire after some pre-specified interval. - Centralized or Distributed Implementation: In the case of a centralized implementation, a single entity manages the resources of the entire subnet. This approach has the advantage of being easier to deploy since bridges and switches may not need to be upgraded with additional functionality. However, this approach scales poorly with geographical size of the subnet and the number of end stations attached. In a fully distributed implementation, each segment will have a local entity managing its resources. This approach has better scalability than the former. However, it requires that all bridges and switches in the network support Ghanwani, Pace, Srinivasan Expires November 1997 [Page 3] Internet Draft Integrated Services Over LANs May 1997 new mechanisms. It is also possible to have a semi-distributed implementation where there is more than one entity, each managing the resources of a subset of segments and bridges/switches within the subnet. Ideally, implementation should be flexible; i.e. a centralized approach may be used for small subnets and a distributed approach can be used for larger subnets. Examples of centralized and distributed implementations are discussed in Section 4. - Scalability: The mechanism and protocols should have a low overhead and should scale to the largest receiver groups likely to occur within a single link layer domain. - Fault Tolerance and Recovery: The mechanism must be able to function in the presence of failures; i.e. there should not be a single point of failure. For instance, in a centralized implementation, some mechanism must be specified for back-up and recovery in the event of failure. - Interaction with Existing Resource Management Controls: The interaction with existing infrastructure for resource management needs to be specified. For example, FDDI has a resource management mechanism called the "Synchronous Bandwidth Manager". The mechanism must be designed so that it takes advantage of, and specifies the interaction with, existing controls where available. 3.2. Goals - Independence from higher layer protocols: The mechanism should, as far as possible, be independent of higher layer protocols such as RSVP and IP. Independence from RSVP is desirable so that it can interwork with other reservation protocols such as ST2 [10]. Independence from IP is desirable so that it can interwork with network layer protocols such as IPX, NetBIOS, etc. - Receiver heterogeneity: Receiver heterogeneity refers to multicast communication where different receivers request different levels of service. For example, in a multicast group with many receivers, it is possible that one of the receivers desires a lower delay bound than the others. A better delay bound may be provided by increasing the amount of resources reserved along the path to that receiver while leaving the reservations for the other receivers unchanged. In its most complex form, receiver heterogeneity implies the ability to simultaneously provide various levels of service as requested by different receivers. In its simplest form, receiver Ghanwani, Pace, Srinivasan Expires November 1997 [Page 4] Internet Draft Integrated Services Over LANs May 1997 heterogeneity will allow a scenario where some of the receivers use best effort service and those requiring service guarantees make a reservation. Receiver heterogeneity, especially for the reserved/best effort scenario, is a very desirable function. More details on supporting receiver heterogeneity are provided in Section 6. - Support for different filter styles: It is desirable to provide support for the different filter styles defined by RSVP such as fixed filter, shared explicit and wildcard. Some of the issues with respect to supporting such filter styles in the link layer domain are examined in Section 6. - Path Selection: In source routed LAN technologies such as token ring/802.5, it may be useful for the mechanism to incorporate the function of path selection. Using an appropriate path selection mechanism may optimize utilization of network resources. 4. LAN Topologies and Their Features As stated earlier, this memo is concerned with specifying a framework for supporting Integrated Services in LAN technologies such as Ethernet/IEEE 802.3, token ring/IEEE 802.5, and FDDI. The extent to which service guarantees can be provided by a network depend to a large degree on the ability to provide the key functions of flow identification and scheduling in addition to admission control and policing. This section discusses some of the capabilities of these LAN technologies and provides a taxonomy of possible topologies emphasizing the capabilities of each with regard to supporting the above functions. For the technologies considered here, the basic topology of a LAN may be shared, switched half duplex or switched full duplex. In the shared topology, multiple senders share a single segment. Contention for media access is resolved using protocols such as CSMA/CD in Ethernet and token passing in token ring and FDDI. Switched half duplex, is essentially a shared topology with the restriction that there are only two transmitters contending for resources on any segment. This topology is fast becoming popular with the need for increased bandwidth. Finally, in a switched full duplex topology, a full bandwidth path is available to the transmitter at each end of the link at all times. Therefore, in this topology, there is no need for any access control mechanism such as CSMA/CD or token passing as there is no contention between the transmitters. Another important element in the discussion of topologies is the support for multiple traffic classes. Traffic classes provide a Ghanwani, Pace, Srinivasan Expires November 1997 [Page 5] Internet Draft Integrated Services Over LANs May 1997 coarse method for isolation between flows and allows the possibility to easily support scheduling algorithms in order to meet service requirements. Native Ethernet/802.3 does not support multiple traffic classes. Token ring/802.5 and FDDI on the other hand provides support for traffic classes. Three bits of the Frame Control field are used to indicate the Frame Priority which may be mapped to a traffic class as appropriate. Equally important in token ring networks are the notions of Reserved Priority and Access Priority. Reserved Priority relates to the value of priority which a station uses to reserve the token for the next transmission on the ring. When a free token is circulating, only a station having an Access Priority greater than or equal to the Reserved Priority in the token will be allowed to seize the token for transmission. More recently, the IEEE 802 Standards Committee has been working on the a 802.1p, a standard for expedited traffic classes and dynamic multicast filtering in bridges and switches [1]. The proposed standard requires a new frame format for Ethernet and token ring networks. The new frame format adds 4 bytes of information of which 3 bits are used to indicate User Priority. This adds new information in the case of Ethernet networks. For token ring networks this field carries the same information as the priority bits in the Frame Control field. The User Priority may be mapped to any one of up to eight traffic classes in the bridge/switch. The emerging standard does not specify a requirement for the minimum number of traffic classes which must be supported by a bridge/switch, nor does it specify the scheduling algorithm to be used between traffic classes. Depending on the basic topology used and the ability to support traffic classes, there are six possible scenarios as follows: 1. Shared topology without traffic classes: This category includes pure shared media such as Ethernet/802.3 networks which are multi-access technologies with no support for priority signaling and traffic classes. Shared topology without traffic classes offers little capability for isolation between reserved and unreserved flows. No service guarantees can be provided in this scenario without modification to the basic transmission mechanisms. 2. Shared topology with traffic classes: This category includes Ethernet/802.3 networks which implement the emerging IEEE 802.1p standard, as well as token ring/802.5 and FDDI networks. Even with support for traffic classes, shared Ethernet can at best offer loose statistical service guarantees because of the non-deterministic nature of the CSMA/CD protocol. On the other hand, better guarantees can be provided on token ring media if the Frame Priority, Reserved Priority and Access Priority are used in conjunction with appropriate controls. Ghanwani, Pace, Srinivasan Expires November 1997 [Page 6] Internet Draft Integrated Services Over LANs May 1997 3. Switched half duplex topology without traffic classes: This scenario is a special case of shared topology without traffic classes where there are only two senders contending for resources on any segment (a host and a switch or two switches). This topology provides higher bandwidth per station and fewer collisions. Due to the use of the CSMA/CD protocol and the lack of traffic classes, little can be done to isolate flows and provide scheduling. 4. Switched half duplex topology with traffic classes: This scenario is a special case of shared topology with priority but there are now only two senders contending for resources on any segment. This reduces the contention for resources. Ethernet/802.3 networks with this topology will likely be able to support better statistical service guarantees than the corresponding shared topology. Better guarantees will be possible for token ring/802.5 media with this topology. 5. Switched full duplex topology without traffic classes: This scenario includes switched Ethernet/802.3 and token ring/802.5 where the access control protocol is no longer used since a full bandwidth path is available to each transmitter. However, since traffic classes are not available, it is not possible to isolate flows for scheduling. 6. Switched full duplex topology with traffic classes: This category is similar to the above, but traffic classes are also available. This topology is the most capable in terms of link layer functions that can be exploited for supporting the functions of flow separation and scheduling. There is also the possibility of hybrid topologies where two or more of the above coexist. For instance, it is possible that within a single subnet, there are some bridges/switches which support traffic classes and some which do not. If the flow in question traverses both kinds of bridges/switches in the network, the least common denominator will prevail. In other words, as far as that flow is concerned, the network is of the type corresponding to the least capable topology that is traversed. Note that even within the different switched topologies categorized above, there are likely to be switches having varied capabilities with respect to providing functions such as receiver heterogeneity and the ability to dedicate resources such as buffering and scheduling algorithms for supporting the various Integrated Services. Future work on service mappings in the ISSLL working group will elaborate on these issues. Ghanwani, Pace, Srinivasan Expires November 1997 [Page 7] Internet Draft Integrated Services Over LANs May 1997 5. Architecture for Supporting Integrated Services in LANs The functional requirements described in Section 3 will be performed by an entity which we refer to as the Bandwidth Manager (BM). The BM is responsible for providing mechanisms for an application or higher layer protocol to request QoS from the network. For architectural purposes, the BM consists of the following components. 5.1. Components of the Bandwidth Manager 5.1.1. Requester Module The Requester Module (RM) resides in every end station in the subnet. One of its functions is to provide an interface between applications or higher layer protocols such as RSVP, STII, SNMP, etc. and the BM. An application can invoke the various functions of the BM by using the primitives for communication with the RM and providing it with the appropriate parameters. To initiate a reservation, in the link layer domain, the following parameters must be passed to the RM: the service desired (Guaranteed Service or Controlled Load), the traffic descriptors contained in the TSpec, and an RSpec specifying the amount of resources to be reserved [8]. More information on these parameters may be found in the relevant Integrated Services documents [8,9]. When RSVP is used for signaling at the network layer, this information is available and needs to be extracted from the RSVP PATH and RSVP RESV messages (See [7] for details). In addition to these parameters, the network layer addresses of the end points must be specified. The RM must then translate the network layer addresses to link layer addresses and convert the request into an appropriate format which is understood by other components of the BM responsible admission control. The RM is also responsible for returning the status of requests processed by the BM to the invoking application or higher layer protocol. 5.1.2. Bandwidth Allocator The Bandwidth Allocator (BA) is responsible for performing admission control and maintaining state about the allocation of resources in the subnet. An end station can request various services, e.g. bandwidth reservation, modification of an existing reservation, queries about resource availability, etc. These requests are processed by the BA. The communication between the end station and the BA takes place through the RM. The location of the BA will depend largely on the implementation method. In a centralized implementation, the BA may reside on a single station in the subnet. In a distributed implementation, the functions of the BA Ghanwani, Pace, Srinivasan Expires November 1997 [Page 8] Internet Draft Integrated Services Over LANs May 1997 may be distributed in all the end stations and bridges/switches as necessary. The BA is also responsible for deciding how to label flows, e.g. based on the admission control decision, the BA may indicate to the RM that packets belonging to a particular flow be tagged with some priority value which maps to the appropriate traffic class. 5.1.3. Communication Protocols and Primitives The protocols and primitives for communication between the various components of the BM must be specified. These include the following: - Communication between the higher layer protocols and the RM: The BM must define primitives for the application to initiate reservations, query the BA about available resources, and change or delete reservations, etc. These primitives could be implemented as an API for an application to invoke functions of the BM via the RM. - Communication between the RM and the BA: A signaling mechanism must be defined for the communication between the RM and the BA. This protocol will specify the messages which must be exchanged between the RM and the BA in order to service various requests by the higher layer entity. - Communication between peer BAs: If there is more than one BA in the subnet, a means must be specified for inter-BA communication. Specifically, the BAs must be able to decide among themselves about which BA would be responsible for which segments and bridges or switches. Further, if a request is made for resource reservation along the domain of multiple BAs, the BAs must be able to handle such a scenario correctly. Inter-BA communication will also be responsible for back-up and recovery in the event of failure. 5.2. Implementation Scenarios Example scenarios are provided showing the location of the the components of the bandwidth manager in centralized and fully distributed implementations. Note that in either case, the RM must be present in all end stations which desire to make reservations. Essentially, centralized or distributed refers to the implementation of the BA, the component responsible for resource reservation and admission control. In the figures below, "App" refers to the application making use of the BM. It could either be a user application, or a higher layer protocol process such as RSVP. Ghanwani, Pace, Srinivasan Expires November 1997 [Page 9] Internet Draft Integrated Services Over LANs May 1997 +---------+ .-->| BA |<--. / +---------+ \ / .-->| Layer 2 |<--. \ / / +---------+ \ \ / / \ \ / / \ \ +---------+ / / \ \ +---------+ | App |<----- /-/---------------------------\-\----->| App | +---------+ / / \ \ +---------+ | RM |<----. / \ .--->| RM | +---------+ / +---------+ +---------+ \ +---------+ | Layer 2 |<------>| Layer 2 |<------>| Layer 2 |<------>| Layer 2 | +---------+ +---------+ +---------+ +---------+ RSVP Host/ Intermediate Intermediate RSVP Host/ Router Bridge/Switch Bridge/Switch Router Figure 1: Bandwidth Manager with a centralized Bandwidth Allocator Figure 1 shows a centralized implementation where a single BA is responsible for admission control decisions for the entire subnet. Every end station contains an RM. Intermediate bridges and switches in the network need not have any functions of the BM since they will not be actively participating in admission control. The RM at the end station requesting a reservation initiates communication with its BA. For larger subnets, a single BA may not be able to handle the reservations for the entire subnet. In that case it would be necessary to deploy multiple BAs, each managing the resources of a non-overlapping subset of segments. In a centralized implementation, the BA must be able to access topology information such as link layer spanning tree information in order to be able to reserve resources on appropriate segments. Without this topology information, the BM would have to reserve resources on the entire spanning tree for all flows leading to an inefficient utilization of resources. Ghanwani, Pace, Srinivasan Expires November 1997 [Page 10] Internet Draft Integrated Services Over LANs May 1997 +---------+ +---------+ | App |<-------------------------------------------->| App | +---------+ +---------+ +---------+ +---------+ | RM/BA |<------>| BA |<------>| BA |<------>| RM/BA | +---------+ +---------+ +---------+ +---------+ | Layer 2 |<------>| Layer 2 |<------>| Layer 2 |<------>| Layer 2 | +---------+ +---------+ +---------+ +---------+ RSVP Host/ Intermediate Intermediate RSVP Host/ Router Bridge/Switch Bridge/Switch Router Figure 2: Bandwidth Manager with a fully distributed Bandwidth Allocator Figure 2 depicts the scenario of a fully distributed bandwidth manager. In this case, all devices in the subnet must have some BM functionality. All the end hosts are still required to have an RM. In addition, all bridges and switches must actively participate in admission control. With this approach, the BA would need only local topology information since each BA is responsible for the resources on segments that are directly connected to it. This local topology information, such as which ports are on the spanning tree and which unicast addresses are reachable from which ports, is readily available in existing bridges/switches. Note that in the figures above, the arrows between peer layers are used to indicate logical connectivity. 5.3. Logical Operation of the BM in End Stations and Link Layer Domain The figure below shows the location and logical operation of the BM in end stations and the link layer domain. It is not possible to provide the details of physical flows because of the inherent differences that arise in centralized and distributed implementations as discussed in Section 5.2. Ghanwani, Pace, Srinivasan Expires November 1997 [Page 11] Internet Draft Integrated Services Over LANs May 1997 +-------------------------+ | +--------+ +------+ | | |Appli- <---> RM | | | | cation | +--^---+ | | +--------+ | | +-------------------------+ | || +--V---+ | | +------+ | | || +------| BA <------------------------> BA | | | || | +------+ | | +----------+ +-^-^|-+ | | || | | | | |Forwarding| | || | | || | | | | |Process <---+ || | | || | | | | +---|------+ || | | || | | | | | +---------+| | | \/ | | | | | | | | | +-----V-+ +--V---+ | | +---V--V+ +----V-+ | | |Class- | |Sched-| | | |Class- | |Sched-| | | | ifier |===>| uler |==========>| ifier |===>| uler |====> | +-------+ +------+ | | +-------+ +------+ | +-------------------------+ +-------------------------+ End Station Link Layer Domain ----> Signaling/Control ====> Data Figure 3: The logical Operation of the BM in end stations and the link layer domain. The application, which may be RSVP or some other higher layer reservation protocol requests resources by passing the relevant parameters to the RM. The RM then starts the process of resource reservation at the link layer by contacting the local BA. In the case of a distributed implementation, The local BA is responsible for admission control on the segment to which the end station is directly attached. If the reservation succeeds, the local BA sets up the classifier and scheduler as required so that the appropriate priority is used for the flow. The request is then propagated to the the "remote" BA controlling the other segments along the forwarding path. In this case, it is possible to set up more complex schedulers as well as policing at the bridges/switches since the BA, which maintains the state, is co-located in every bridge/switch and participates actively in the process of admission control. In a centralized implementation, the BA resides in a server within the subnet. The classifier and scheduler in the bridges/switches along the forwarding path are implicitly set up by the priority carried in the data frames if the reservation is successful. Ghanwani, Pace, Srinivasan Expires November 1997 [Page 12] Internet Draft Integrated Services Over LANs May 1997 6. Mapping Issues and Link Layer Support for Integrated Services As stated earlier, the Integrated Services working group has defined various service classes offering varying degrees of QoS guarantees. Initial effort will concentrate on enabling the Controlled Load and Guaranteed Service classes [4,5]. The Controlled Load service provides a loose guarantee, informally stated as "better than best effort". The Guaranteed Service provides a delay bound which the network guarantees will never be exceeded. The extent to which these services can be supported at the link layer will depend on many factors including the topology and technology used. Some of the mapping issues are dicussed below in light of the emerging link layer standards and the functions supported by higher layer protocols. Considering the limitations of some of the topologies under consideration, it may not be possible to satisfy all the requirements for Integrated Services on a given topology. In such cases, it is useful to consider providing support for an approximation of the service which may suffice in most practical instances. For example, it may not be feasible to provide policing/shaping at each network element (bridge/switch) as required by the Controlled Load specification [4]. But if this task is left to the end stations, a reasonably good approximation to the service can be obtained. 6.1. Mapping of Services to Link Level Priority The number of traffic classes supported and access methods of the technology under consideration will determine how many and what services may be supported. Native token ring/802.5, for instance, supports eight priority levels which may be mapped to one or more traffic classes. Ethernet/802.3 has no support for signaling priorities within frames. However, the IEEE 802 standards committee is working on a new standard for bridges/switches related to multimedia traffic expediting and dynamic multicast filtering [1]. The standard allows for up to eight traffic classes on all media. The User Priority bits carried in the frame are mapped to a particular traffic class within a bridge/switch. The User Priority is signaled on an end-to-end basis, unless overridden by bridge/switch management. The traffic class that is used by a flow should depend on the quality of service desired and whether the reservation is successful or not. Therefore, a sender should use the a User Priority value which maps to the best effort traffic class until told otherwise by the BM. The BM will, upon successful completion of resource reservation, specify the User Priority to be used by the sender for that session's data. Future work in the ISSLL working group will address the issue Ghanwani, Pace, Srinivasan Expires November 1997 [Page 13] Internet Draft Integrated Services Over LANs May 1997 of mapping the various Integrated Services to appropriate traffic classes in the bridges/switches. 6.2. Supporting Receiver Heterogeneity Receiver heterogeneity means that receivers within a group can each have different QoS requirements; i.e. it is possible that, for a given flow, some receivers make a reservation while others decide to make use of best effort transport. RSVP allows heterogeneous receivers within a group. However, handling the problem at layer 2 can be non-trivial. Consider for instance, the scenario in the figure below. +-----+ | S | +-----+ | v +-----+ +-----+ +-----+ | R1 |<-----| SW |----->| R2 | +-----+ +-----+ +-----+ Figure 4: An instance of receiver heterogeneity. S is the source. R1 is a receiver which makes a reservation, and R2 is a receiver which is satisfied with best effort service. SW is a Layer 2 device (bridge/switch) participating in resource reservation. In the figure above, S is the upstream end station and R1 and R2 are downstream end stations. R1 would like to make a reservation for the flow while R2 would like to receive the flow using best effort transport. S sends RSVP PATH messages which are multicast to both R1 and R2. R1 sends an RSVP RESV message to S requesting the reservation of resources. If the reservation is successful at Layer 2, the frames addressed to the group will be categorized in the traffic class corresponding to the service requested by R1. At SW, there must be some mechanism which forwards the packet providing service corresponding to the reserved traffic class at the interface to R1 while using the best effort traffic class at the interface to R2. This may involve changing the contents of the frame itself, or ignoring the frame priority at the interface to R2. Another possibility for supporting heterogeneous receivers would be to have separate groups with distinct MAC addresses, one for each class of service. By default, a receiver would join the "best effort" group where the flow is classified as best effort. If the receiver makes a reservation successfully, it can be transferred to the group for the class of service desired. The dynamic multicast Ghanwani, Pace, Srinivasan Expires November 1997 [Page 14] Internet Draft Integrated Services Over LANs May 1997 filtering capabilities of bridges and switches implementing the emerging IEEE 802.1p standard would be a very useful feature in such a scenario. A given flow would be transmitted only on those segments which are on the path between the sender and the receivers of that flow. The obvious disadvantage of such an approach is that the sender needs to send out multiple copies of the same packet corresponding to each class of service desired thus potentially duplicating the traffic on a portion of the distribution tree. 6.3. Support for Different Reservation Styles +-----+ +-----+ +-----+ | S1 | | S2 | | S3 | +-----+ +-----+ +-----+ | | | | v | | +-----+ | +--------->| SW |<---------+ +-----+ | | +----+ +----+ | | v V +-----+ +-----+ | R1 | | R2 | +-----+ +-----+ Figure 5: An illustration of filter styles. S1, S2, S3, R1 and R2 are RSVP end stations which are members of the same group. SW is a bridge/switch in the link layer domain. In the figure above, S1, S2, S3, R1 and R2 are end stations which are members of a group associated with the same RSVP flow. S1, S2 and S3 are upstream end stations. R1 and R2 are the downstream end stations which receive traffic from all the senders. RSVP allows receivers R1 and R2 to specify reservations which can apply to: (a) one specific sender only (fixed filter); (b) any of two or more explicitly specified senders (shared explicit filter); and (c) any sender in the group (shared wildcard filter). Support for the fixed filter style is straightforward; a separate reservation is made for the traffic from each of the senders. However, support for the the other two filter styles has implications regarding policing; i.e. the merged flow from the different senders must be policed so that they conform to traffic parameters specified in the filter's RSpec. This scenario is further complicated if the services requested by R1 and R2 are different. Therefore, in the absence of policing within Ghanwani, Pace, Srinivasan Expires November 1997 [Page 15] Internet Draft Integrated Services Over LANs May 1997 bridges/switches, it may be possible to support only fixed filter reservations at the link layer. 7. Summary This document has specified a framework for providing Integrated Services over shared and switched LAN technologies. The ability to provide QoS guarantees necessitates some form of admission control and resource management. The requirements and goals of a resource management scheme for subnets have been identified and discussed. We refer to the entire resource management scheme as a Bandwidth Manager. Architectural considerations were discussed and examples were provided to illustrate possible implementations of a Bandwidth Manager. Some of the issues involved in mapping the services from higher layers to the link layer have also been discussed. Forthcoming documents from the ISSLL working group will address service mapping issues and provide a protocol specification for the Bandwidth manager based on the requirements and goals dicussed in this document. References [1] IEEE Standards for Local and Metropolitan Area Networks: Draft Standard for Traffic Class and Dynamic Multicast Filtering Services in Bridged Local Area Networks (Draft Supplement to 802.1D), P802.1p/D5, February, 1997. [2] IEEE Standards for Local and Metropolitan Area Networks: Draft Standard for Virtual Bridged Local Area Networks, P802.1Q/D5, February, 1997. [3] B. Braden, L. Zhang, S. Berson, S. Herzog and S. Jamin, "Resource Reservation Protocol (RSVP) - Version 1 Functional Specification," Internet Draft, November 1996, <draft-ietf-rsvp-spec-14.txt> [4] J. Wroclawski, "Specification of the Controlled Load Network Element Service," Internet Draft, November 1996, <draft-ietf-intserv-ctrl-load-svc-04.txt> [5] S. Shenker, C. Partridge and R. Guerin, "Specification of Guaranteed Quality of Service," Internet Draft, August 1996, <draft-ietf-intserv-guaranteed-svc-06.txt> [6] R. Braden, D. Clark and S. Shenker, "Integrated Services in the Ghanwani, Pace, Srinivasan Expires November 1997 [Page 16] Internet Draft Integrated Services Over LANs May 1997 Internet Architecture: An Overview," RFC 1633, June 1994. [7] J. Wroclawski, "The Use of RSVP with IETF Integrated Services," Internet Draft, October 1996, <draft-ietf-intserv-rsvp-use-01.txt> [8] S. Shenker and J. Wroclawski, "Network Element Service Specification Template," Internet Draft, November 1995, <draft-ietf-intserv-svc-template-02.txt> [9] S. Shenker and J. Wroclawski, "General Characterization Parameters for Integrated Service Network Elements," Internet Draft, October 1996, <draft-ietf-intserv-charac-02.txt> [10] L. Delgrossi and L. Berger (Editors), "Internet Stream Protocol Version 2 (ST2) Protocol Specification - Version ST2+," Request For Comments 1819, August 1995. Acknowledgements Much of the work presented in this document has benefited greatly from discussion held at the meetings of the Integrated Services over Specific Link Layers (ISSLL) working group. In particular we would like to thank Eric Crawley, Don Hoffman, Mick Seaman, Andrew Smith and Raj Yavatkar who have contributed to this effort via earlier Internet drafts. Authors' Address Anoop Ghanwani IBM Corporation P. O. Box 12195 Research Triangle Park, NC 27709 Phone: +1-919-254-0260 Fax: +1-919-254-5410 Email: anoop@raleigh.ibm.com Wayne Pace IBM Corporation P. O. Box 12195 Research Triangle Park, NC 27709 Phone: +1-919-254-4930 Fax: +1-919-254-5410 Email: pacew@raleigh.ibm.com Vijay Srinivasan Ghanwani, Pace, Srinivasan Expires November 1997 [Page 17] Internet Draft Integrated Services Over LANs May 1997 IBM Corporation P. O. Box 12195 Research Triangle Park, NC 27709 Phone: +1-919-254-2730 Fax: +1-919-254-5410 Email: vijay@raleigh.ibm.com Ghanwani, Pace, Srinivasan Expires November 1997 [Page 18]