Forwarding techniques in Differentiated Services (DiffServ) model:
Expedited Forwarding (EF):
This is a technique that assigns different priorities to incoming traffic flows. The flows don't interfere with each other because there is no queuing delay. Flows are admitted based on their peak rate. The network does not let the rate fall below a limit. If the flow varies beyond expected rates, then the packets are either dropped or the flow is shaped. We will discuss traffic shaping shortly. Since the rate is reserved along the route for the packets, this forwarding technique can be thought of as a virtual circuit.
The example here is that of a virtual leased line service where the line is admitted if the sum of all lines does not exceed the link bandwidth.
Assured Forwarding (AF):
Assured Forwarding (AF) is a technique that maintains one or more bands of service such as gold, silver etc. Each service has a reservation for bandwidth and allocation for buffers. Within each class, there are three priorities that determine which packets get dropped when there is a congestion. Unlike expedited forwarding, the flow that does not conform is reclassified. It could end up in the unregulated best effort band.
AF and EF continue to be developed. Notice that it is the core routers where these forwarding takes place. For simple forwarding schemes, this is alright. For complex forwarding schemes, an entity such as a bandwidth broker is required that can manage the bandwidth across the core network. There are several ways to design such broker with stateless management of bandwidths across core routers.
But there are other problems as well. For example, the core routers may not all be DiffServ based. Besides flows may traverse networks with different forwarding behaviors. Packets may be handled differently by different routers along the path. A repository for listing the routers in the network such as we get with SNMP is required. This poses challenges to determining end to end service.
Expedited Forwarding (EF):
This is a technique that assigns different priorities to incoming traffic flows. The flows don't interfere with each other because there is no queuing delay. Flows are admitted based on their peak rate. The network does not let the rate fall below a limit. If the flow varies beyond expected rates, then the packets are either dropped or the flow is shaped. We will discuss traffic shaping shortly. Since the rate is reserved along the route for the packets, this forwarding technique can be thought of as a virtual circuit.
The example here is that of a virtual leased line service where the line is admitted if the sum of all lines does not exceed the link bandwidth.
Assured Forwarding (AF):
Assured Forwarding (AF) is a technique that maintains one or more bands of service such as gold, silver etc. Each service has a reservation for bandwidth and allocation for buffers. Within each class, there are three priorities that determine which packets get dropped when there is a congestion. Unlike expedited forwarding, the flow that does not conform is reclassified. It could end up in the unregulated best effort band.
AF and EF continue to be developed. Notice that it is the core routers where these forwarding takes place. For simple forwarding schemes, this is alright. For complex forwarding schemes, an entity such as a bandwidth broker is required that can manage the bandwidth across the core network. There are several ways to design such broker with stateless management of bandwidths across core routers.
But there are other problems as well. For example, the core routers may not all be DiffServ based. Besides flows may traverse networks with different forwarding behaviors. Packets may be handled differently by different routers along the path. A repository for listing the routers in the network such as we get with SNMP is required. This poses challenges to determining end to end service.
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