Bandwidth Broker
Encyclopedia
RFC 2638 from the IETF defines the entity of the Bandwidth Broker (BB) in the framework of differentiated services
(DiffServ). According to RFC 2638, a Bandwidth Broker is an agent that has some knowledge of an organization's priorities and policies and allocates quality of service
(QoS) resources with respect to those policies. In order to achieve an end-to-end allocation of resources across separate domains, the Bandwidth Broker managing a domain will have to communicate with its adjacent peers
, which allows end-to-end services to be constructed out of purely bilateral
agreements. Admission control is one of the main tasks that a Bandwidth Broker has to perform, in order to decide whether an incoming resource reservation request will be accepted or not. Most Bandwidth Brokers use simple admission control modules, although there are also proposals for more sophisticated admission control according to several metrics such as acceptance rate, network utilization, etc. The BB acts as a Policy Decision Point (PDP) in deciding whether to allow or reject a flow, whilst the edge routers acts as Policy Enforcement Points (PEPs) to police traffic (allowing and marking packets, or simply dropping them).
DiffServ allows two carrier services apart from the default best effort service: Assured Forwarding (AF) and Expedited Forwarding (EF). AF provides a better-than-best-effort service, but is similar to best-effort traffic in that bursts and packet delay variation
(PDV) are to be expected. Out of profile AF packets are given a lower priority by being marked as best effort traffic. EF provides a virtual wire service with traffic shaping
to prevent bursts, strict admission control (out of profile packets are dropped) and a separate queue for EF traffic in the core routers, which together keep queues small and avoid the need for buffer management. The resulting EF service is low loss, low delay
and low PDV. Hence although loosely a BB allocates bandwidth, really it allocates carrier services (i.e. QoS resources).
Bandwidth Brokers can be configured with organizational policies, keep track of the current allocation of marked traffic, and interpret new requests to mark traffic in light of the policies and current allocation. Bandwidth Brokers only need to establish relationships of limited trust with their peers in adjacent domains, unlike schemes that require the setting of flow specifications in routers throughout an end-to-end path. In practical technical terms, the Bandwidth Broker architecture makes it possible to keep state on an administrative domain basis, rather than at every router, and the DiffServ architecture makes it possible to confine per flow state to just the edge or leaf routers.
The scope of BBs has expanded and they are now not restricted to DiffServ domains. As long as the underlying QoS mechanism can be mapped to DiffServ behaviour, then a BB can understand it and communicate with its adjacent peers, i.e. the 'lingua franca
' of QoS in the Internet
should be DiffServ. There may be more than one BB in a domain, though if there are, RFC 2638 envisages that only one BB will function as the top-level inter-domain BB.
Differentiated services
Differentiated Services or DiffServ is a computer networking architecture that specifies a simple, scalable and coarse-grained mechanism for classifying and managing network traffic and providing Quality of Service on modern IP networks...
(DiffServ). According to RFC 2638, a Bandwidth Broker is an agent that has some knowledge of an organization's priorities and policies and allocates quality of service
Quality of service
The quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...
(QoS) resources with respect to those policies. In order to achieve an end-to-end allocation of resources across separate domains, the Bandwidth Broker managing a domain will have to communicate with its adjacent peers
Peering
In computer networking, peering is a voluntary interconnection of administratively separate Internet networks for the purpose of exchanging traffic between the customers of each network. The pure definition of peering is settlement-free or "sender keeps all," meaning that neither party pays the...
, which allows end-to-end services to be constructed out of purely bilateral
Bilateralism
Bilateralism consists of the political, economic, or cultural relations between two sovereign states. For example, free trade agreements signed by two states are examples of bilateral treaties. It is in contrast to unilateralism or multilateralism, which refers to the conduct of diplomacy by a...
agreements. Admission control is one of the main tasks that a Bandwidth Broker has to perform, in order to decide whether an incoming resource reservation request will be accepted or not. Most Bandwidth Brokers use simple admission control modules, although there are also proposals for more sophisticated admission control according to several metrics such as acceptance rate, network utilization, etc. The BB acts as a Policy Decision Point (PDP) in deciding whether to allow or reject a flow, whilst the edge routers acts as Policy Enforcement Points (PEPs) to police traffic (allowing and marking packets, or simply dropping them).
DiffServ allows two carrier services apart from the default best effort service: Assured Forwarding (AF) and Expedited Forwarding (EF). AF provides a better-than-best-effort service, but is similar to best-effort traffic in that bursts and packet delay variation
Packet delay variation
In computer networking, packet delay variation is the difference in end-to-end delay between selected packets in a flow with any lost packets being ignored...
(PDV) are to be expected. Out of profile AF packets are given a lower priority by being marked as best effort traffic. EF provides a virtual wire service with traffic shaping
Traffic shaping
Traffic shaping is the control of computer network traffic in order to optimize or guarantee performance, improve latency, and/or increase usable bandwidth for some kinds of packets by delaying other kinds of packets that meet certain criteria...
to prevent bursts, strict admission control (out of profile packets are dropped) and a separate queue for EF traffic in the core routers, which together keep queues small and avoid the need for buffer management. The resulting EF service is low loss, low delay
Network delay
Network delay is an important design and performance characteristic of a computer network or telecommunications network. The delay of a network specifies how long it takes for a bit of data to travel across the network from one node or endpoint to another. It is typically measured in multiples or...
and low PDV. Hence although loosely a BB allocates bandwidth, really it allocates carrier services (i.e. QoS resources).
Bandwidth Brokers can be configured with organizational policies, keep track of the current allocation of marked traffic, and interpret new requests to mark traffic in light of the policies and current allocation. Bandwidth Brokers only need to establish relationships of limited trust with their peers in adjacent domains, unlike schemes that require the setting of flow specifications in routers throughout an end-to-end path. In practical technical terms, the Bandwidth Broker architecture makes it possible to keep state on an administrative domain basis, rather than at every router, and the DiffServ architecture makes it possible to confine per flow state to just the edge or leaf routers.
The scope of BBs has expanded and they are now not restricted to DiffServ domains. As long as the underlying QoS mechanism can be mapped to DiffServ behaviour, then a BB can understand it and communicate with its adjacent peers, i.e. the 'lingua franca
Lingua franca
A lingua franca is a language systematically used to make communication possible between people not sharing a mother tongue, in particular when it is a third language, distinct from both mother tongues.-Characteristics:"Lingua franca" is a functionally defined term, independent of the linguistic...
' of QoS in the Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
should be DiffServ. There may be more than one BB in a domain, though if there are, RFC 2638 envisages that only one BB will function as the top-level inter-domain BB.
- Manages each cloud’s resources (Bandwidth Broker)
- Packets are "coloured" to indicate forwarding "behavior"
- Focus on aggregates and NOT on individual flows
- Policing at network periphery to get services
- Used together with Multiprotocol Label Switching (MPLS) and Traffic Engineering (TE)
- "Aggregated" QoS guarantees only!
- Poor on the guarantees for end-to-end applications
Further reading
- RFC 2638: A Two-bit Differentiated Services Architecture for the Internet
- QBone Bandwidth Broker Architecture
- The Survey of Bandwidth Broker
- Internet Quality of Service
- Decoupling QoS Control from Core Routers: A Novel Bandwidth Broker Architecture for Scalable Support of Guaranteed Services
- An Adaptive Admission Control Algorithm for Bandwidth Brokers
- A Scalable and Robust Solution for Bandwidth Allocation
- Implementation of a Simple Bandwidth Broker for DiffServ Networks
- Providing End-to-End guaranteed Quality of Service over the Internet: A survey on Bandwidth Broker Architecture for Differentiated Services Network
- Research projects developing Bandwidth Broker architectures