A survey of internet QoS signaling <s> INTER-DOMAIN QOS SIGNALING <s> Resource reservation needs to accommodate the rapidly growing size and increasing service diversity of the Internet. Recently, hierarchical architectures have been proposed that provide domain-level reservation. However, it is not clear that these proposals can set up and maintain reservations in an efficient and scalable fashion. In this paper, we describe a distributed architecture for inter-domain aggregated resource reservation for unicast traffic. We also present an associated protocol, called the Border Gateway Reservation Protocol (BGRP), that scales well, in terms of message processing load, state storage and bandwidth. Each stub or transit domain may use its own intra-domain resource reservation protocol. BGRP builds a sink tree for each of the stub domains. Each sink tree aggregates bandwidth reservations from all data sources in the network. Since backbone routers only maintain the sink tree information, the total number of reservations at each router scales linearly with the number of domains in the Internet. (Even aggregated versions of the current protocol RSVP have an overhead that grows like N.) BGRP relies on Differentiated Services for data forwarding. As a result, the number of packet classifier entries is extremely small. To reduce the protocol message traffic, routers may reserve domain bandwidth beyond the current load, so that sources can join or leave the tree or change their reservation without having to send messages all the way to the tree root for every such change. We use “soft state” to maintain reservations. In contrast to RSVP, refresh messages are delivered reliably, allowing us to reduce the refresh frequency. Columbia University Computer Science Technical Report No. CUCS-029-99 <s> BIB001 </s> A survey of internet QoS signaling <s> INTER-DOMAIN QOS SIGNALING <s> In this paper we propose a two-tier resource management model for the global Internet. Our solution resembles the current two-tier routing hierarchy and allows individual administrative domains to independently make their own decisions on strategies and protocols to use for internal resource management and QoS support. The aggregate traffic crossing domain borders is served according to relatively stable, long-lived bilateral agreements. End-to-end QoS support is achieved through the concatenation of such bilateral agreements. We describe in detail a realization of this two-tier model, where a bandwidth broker (BB) acts as the resource manager for each administrative domain, neighboring bandwidth brokers communicate with each other to establish inter-domain resource agreements. As an illustrative example in this paper we used a simplified RSVP as an intradomain resource allocation protocol for the aggregate traffic between border routers. Our simulation results show that this two-tier design can provide effective end-to-end QoS support for user applications. <s> BIB002 </s> A survey of internet QoS signaling <s> INTER-DOMAIN QOS SIGNALING <s> The differentiated services (DiffServ) architecture for the Internet implements a scalable mechanism for quality-of-service (QoS) provisioning. Bandwidth brokers represent the instances of the architecture, that automate the provisioning of a DiffServ service between network domains. Although several bandwidth broker implementations have been proposed, the alternatives and trade-offs of the different viable approaches of inter-broker communication were not studied up to now. This paper presents the broker signaling trade-offs considered in the context of a DiffServ scenario used by the Swiss National Science Foundation project CATI, and it presents results gathered by simulations. <s> BIB003 </s> A survey of internet QoS signaling <s> INTER-DOMAIN QOS SIGNALING <s> Resource Reservation Protocol (RSVP) signaling may be used to request Quality of Service (QoS) services and enhance the manageability of application traffic's QoS in a differentiated service (diff-serv or DS) network. When using RSVP with DS networks it is useful to be able to carry carry Differentiated Services Code Points (DSCPs) in RSVP message objects. One example of this is the use of RSVP to arrange for the marking of packets with a particular DSCP upstream from the DS network's ingress point, at the sender or at a previous network's egress router. <s> BIB004 </s> A survey of internet QoS signaling <s> INTER-DOMAIN QOS SIGNALING <s> Existing quality of service models are well defined in the data path, but lack an end-to-end control path mechanism that guarantees the required resources to bandwidth intensive services, such as video streaming. Current reservation protocols provide scalable resource reservation inside routing domains. However, it is primarily between such domains that scalability becomes a major issue, since inter-domain links experience large volumes of reservation requests. As a possible solution, we present and evaluate SICAP, the Shared-segment based Inter-domain Control Aggregation Protocol, which affords the benefits of shared-segment aggregation, while avoiding its major drawback, namely, its sensitivity to the intensity of requests (Sofia, R. et al., ICNP'02, 2002). We present results of simulations that compare the performance of SICAP against that of the border gateway reservation protocol (BGRP), which relies on sink-tree aggregation to achieve scalability. <s> BIB005 </s> A survey of internet QoS signaling <s> INTER-DOMAIN QOS SIGNALING <s> Global availability of on-demand services with an associated guaranteed quality-of-service (QoS) is still missing in the Internet today. The Differentiated Services architecture achieves scalability in the data plane by treating all flows with a specific type of service as one aggregate. In order to provide guaranteed end-to-end reservations, the control plane (e.g., performing admission control and management of resource reservations) has to be scalable as well. The DARIS architecture provides this essential linkage between scalability in the packet forwarding path and scalability of QoS management in the Internet. It comprises a novel concept of dynamic and hierarchical aggregation, which acts on the network level of autonomous systems (ASes). This relieves management entities in intermediate ASes of processing load by reducing their managed reservation states as well as the number of signaling messages that have to be processed significantly. Moreover, novel and special support for aggregation by a dedicated signaling protocol mechanism is provided. <s> BIB006
Inter-domain signaling is used end-to-end in a two-tier resource management architecture for handling the reservations between neighboring domains. Moreover, inter-domain signaling is used for sending the end-user's QoS requirements to the internal QoS mechanisms of the transit domains. The end-to-end (triggered by end-hosts) inter-domain usage of RSVP for resource reservation in mixed IntServ/DiffServ networks is proposed in  . According to this proposal, IntServ can be applied in access network domains, whereas DiffServ can support aggregation of traffic in core domains. At the boundaries between domains, special RSVP-aware routers (that may be part of either the IntServ or the DiffServ network) perform per-flow admission control for the DiffServ domain, based on resource availability inside the DiffServ network and on the customer-defined policy. If the DiffServ domain is RSVP-unaware, the RSVP messages will cross transparently the DiffServ domain (Fig. 9) . To facilitate the RSVP usage over DiffServ networks, the introduction of the DCLASS object is proposed to carry the agreed DSCP values within RSVP messages BIB004 , enabling the sender's data packet marking with the appropriate DiffServ QoS level. However, to avoid RSVP per-flow processing in core routers, various protocols have been designed designed to aggregate reservations on backbone inter-domain links. The aggregation of reservations is designed to reduce storage and processing cost in core routers. This cost is related to the number of aggregate states maintained in the routers and the number of signaling messages that are necessary for the establishment and maintenance of these states (signaling load). The Border Gateway Reservation Protocol (BGRP) BIB001 is a QoS signaling protocol designed for aggregate inter-domain usage between heterogeneous domains (autonomous systems). BGRP operates end-to-end only between domain border routers and is designed to aggregate reservations between domains improving scalability. BGRP uses the sink-tree aggregation approach and performs reservation aggregation by building a sink tree for each destination domain (Fig. 10 ). Reservations from different source domains that are destined toward the same destination domain are aggregated along the path, forming a sinktree rooted at the destination domain edge router. Basic functionality of BGRP includes a PROBE message sent by the source domain toward the receiver for determining resource availability and recording the reservation path. The destination domain edge router terminates the PROBE and responds with a GRAFT message along the reverse path, which performs the actual inter-domain reservation and triggers the intra-domain QoS mechanisms in transit domains. The destination domain edge router is the de-aggregation point for the reservation aggregate, while the source domain edge routers are the aggregation points. By performing sink tree-based aggregation of reservations toward each destination domain, BGRP results in storing per-destination domain QoS states in border routers. The latter can be considered to be a significant contribution to scalability when compared to the per-flow RSVP, if we consider that the number of domains (ASs) in the Internet is approximately 160,000  , whereas the number of possible host pairs, i.e., the maximum number of flows, is (230,000,000) 2 [22] . BGRP offers a significant gain in the number of maintained states in each router compared to RSVP. While the number of states in RSVP is equal to the number of QoS flows passing through a router, the respective number of states in BGRP corresponds to the number of destination domains that correspond to these flows. The gain in maintained states can reach a couple of orders of magnitude, depending on the network load and the diversification of the destination domains. Regarding the signaling load, BGRP reduces the message rate of the required refresh messages. The gain in the refresh message rate follows a similar pattern to the state gain, with an extra dependence on the refresh period (the smaller the refresh period, the greater the gain) BIB001 . The Shared-segment based Inter-domain Control Aggregation Protocol (SICAP) BIB005 is another approach for supporting aggregate inter-domain reservations between autonomous systems. SICAP combines the shared-segment and the treebased aggregation approaches to create tree-based reservation n Figure 9 . End-to-end inter-domain RSVP usage. aggregates that do not necessarily extend to the destination domains. Apart from the destination domain de-aggregator point, intermediate de-aggregation locations (IDLs) are elected along the path so that reservation requests that share a common path segment but do not end-up at the same destination domain are aggregated up to one of their common routers along the path. Similar to BGRP, SICAP performs receiver-based reservations and uses a two-phase setup mechanism for their establishment. Upon the reception of the first QoS request, the respective source domain edge router initiates a REQ message toward the destination domain that collects information along the route regarding resource availability and network topology. The destination domain edge router uses the collected topology info and uses a specific choice algorithm to determine the appropriate IDL(s) along the route. By sending a RESV message along the reverse path, the destination domain edge router establishes consecutive aggregate segments between itself, the IDL(s), and the source domain edge router (Fig. 11) . Future reservation requests that cross the same IDL(s) are dynamically incorporated into the existing aggregate(s), forming an aggregate reservation tree(s) rooted at the IDL(s). At each IDL, the aggregated reservations are de-aggregated and reaggregated toward the next IDL or the destination domain. SICAP results in storing per-IDL states in each router along the path, further improving scalability as compared to BGRP (or RSVP). Simulation results BIB005 show that SICAP has consistently lower state requirements than BGRP. SICAP can result in a BGRP state reduction that varies between 0.5 and 0.8 (or more), depending on the specific load conditions in the network. SICAP signaling message load is similar to that of BGRP. An architecture for dynamically aggregating reservations sharing a common path segment is proposed in BIB006 . The DARIS (Dynamic Aggregation of Reservations for Internet Services) architecture assumes the existence of a central resource management entity (similar to the BB approach) inside each DiffServ domain that has complete knowledge and control of the resources inside the domain and also employs the interdomain BGP routing table. DARIS enables the creation of an aggregate between two arbitrary domains as soon as a threshold k of active common reservations between the two domains is exceeded. In this case, all intermediate edge routers can substitute the respective per-flow states with a single aggregate state (Fig. 12) . The reservation protocol that manages the aggregate reservations is the Domain Manager Signaling Protocol (DMSP). When a new resource request is received at a domain, a DMSP request message is sent toward the destination domain to check whether there exist other reservations along the path. If the threshold k of existing reservations is exceeded for a path segment, a new aggregate is established for these flows via the DMSP response message. The aggregation initiator becomes the aggregator domain, and the last domain of the common path segment is the de-aggregator domain. New reservations that traverse the same path segment can be incorporated into the existing reservation aggregate via appropriate signaling exchange. Simulation results BIB006 show that the DARIS state savings in the average lie in the range of one to two orders of magnitude when compared to a per-flow protocol that does not perform aggregation. BGRP, SICAP, and DMSP are designed to aggregate individual reservations on inter-domain links into larger aggregates. These aggregation protocols result in storing fewer QoS states in domain border routers as compared to RSVP, thus enhancing scalability. Moreover, BGRP, SICAP, and DMSP are generally triggered by domain edge routers, unlike RSVP, which is triggered by end-hosts. However, DMSP assumes the underlying functionality of an end-to-end reservation protocol triggered by end-hosts. Instead, BGRP and SICAP assume that there is an established form of communication of QoS requests from end-hosts to domain edge routers, and vice versa. BGRP aggregates reservations along the destination domain rooted sink-trees, which results in the storage of per- DMSP takes a different approach, aggregating in a non-tree like fashion, introducing dynamic discovery of aggregators and de-aggregators that takes into consideration the current network load. An advantageous feature of DMSP resulting from its pure shared-segment design principle is that it allows for the creation of hierarchical aggregates (smaller aggregates can be aggregated into a larger one), which is not possible in treerelated protocols such as BGRP and SICAP. Moreover, a pure shared-segment approach that allows for dependence between the discovery of the aggregate end-points and the current traffic load may result in fewer aggregate stored states than tree-based approaches. The DARIS architecture, however, is centralized and relies on the BGP information for the de-aggregator discovery. In BB-based architectures, inter-domain QoS signaling is triggered by the respective BBs when the received traffic exceeds the a priori bilateral resource agreements that exist between adjacent domains BIB002 . Resource agreements between domains are usually on a per-aggregate basis to enhance the resource allocation mechanism scalability. When a specific reservation aggregate needs to be modified, the requesting domain's BB sends an aggregate modification request to its neighboring BB along the path, which in turn may terminate or forward the request downstream (depending on its own inter-domain agreements). During propagation of the request between BBs, the intra-domain reservation mechanisms should be triggered, enabling the necessary adaptation of resources inside the transit domains (Fig. 13) . Following the basic concepts described above, an RSVP extension for establishing and modifying interdomain resource aggregates is proposed in BIB002 . In addition, the QBone Signaling Workgroup proposed SIBBS (Simple Inter-domain Bandwidth Broker Signaling) [25] , an inter-domain resource reservation protocol for deployment in BB-based architectures. SIBBS specifies a new set of reservation request and response messages, as well as a set of globally well-known services (GWS) that are globally identifiable throughout the network, each of which requires different treatment regarding QoS. Irrespective of the specific signaling protocol used for inter-BB communication, special care should be given to the granularity level of the protocol, taking into account that there is a trade-off between accurate end-to-end QoS provision on one hand and scalability on the other BIB003 .