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Chapter 10 - Resource Reservation Protocol

Cisco Multicast Routing & Switching
William R. Parkhurst
  Copyright © 1999 The McGraw-Hill Companies

RSVP Reservation Model
An RSVP reservation request is referred to as a flow descriptor. The flow descriptor consists of two elements. The first element is the flowspec, which specifies the QoS and is used in conjunction with the packet scheduler. The second element is the filter spec, which is used to determine which packets in the flow will receive the QoS that has been reserved at the node. The filter spec is used to inform the packet classifier of the parameters that will be checked to determine if a packet is a candidate for the QoS reservation. The RSVP specification currently has a basic filter specification consisting of the sender’s IP address and the UDP/TCP source port number. Figure 10-3 shows the relationship between the flow descriptor and the RSVP functional model.
Figure 10-3: Flow descriptor and RSVP functional model relationships
Reservation Styles
A style refers to a reservation request and the set of options pertaining to that request. Reservations can be distinct or shared. A distinct reservation is one in which a specific reservation is established for each sender to a particular multicast group. A shared reservation is one where all senders for a session share a reservation. For both styles the selection of the sender can either be explicitly referenced in the request or not referenced at all. The not referenced case is referred to as the wildcard case in which every sender is automatically selected. For the explicit sender case, each filter specification will match only one sender. The wildcard case would not need a sender filter specification. Table 10-1 lists the various styles that can be used when setting up a resource reservation.
Table 10-1: RSVP Reservation Styles
Sender Selection
Distinct Reservation
Shared Reservation
Explicit
Fixed-Filter (FF) style
Shared-Explicit (SE) style
Wildcard
(None Defined)
Wildcard-Filter (WF) style
Wildcard-Filter (WF) Style
The WF style is a shared reservation style with implicit sender selection. Since all reservations are sharing the same resource allocation, the amount of resource that needs to be reserved is equal to the largest value of the resource requested by all receivers. The WF style is represented by the equation
WF(*{Q})
with the asterisk signifying a wildcard sender selection and Q signifying the flowspec. The symbol Q, or flowspec, is essentially the QoS or amount of bandwidth requested by the receiver. The network in Figure 10-4 shows a WF scenario. The receivers are requesting bandwidth for a particular session that is supported by sources 1,2, and 3. The receivers don’t care from which source the data arrives so all are using the wildcard specification WF(*{Q}). Receiver 1 is requesting 500K and sends a WF(*{500K}) RSVP request to router A.
Figure 10-4: WF(*{Q}) reservation style example
Router A receives only one WF request and attempts to allocate the bandwidth on the input interface, E0, and the output interface, S0. For reservation requests, input and output interfaces refer to the direction of the reservation request flow. The data flow from the sources will reverse the direction of these interfaces. For the following examples, assume the routers have the resources to satisfy reservation requests. Since the request is a shared reservation request, router A will allocate the largest of the requested allocations. With only one request, the allocation will equal what receiver 1 requested. The same argument applies to routers C and D and receivers 2 and 3. Router C will allocate 300K on the E0 and E1 interfaces, while router D will allocate 200K on the E0 and E1 interfaces. Router A will receive one reservation request on interface S2 for 500K and two reservation requests for 200K and 300K on interface E0. Router A will allocate 500K on interface S2. The largest of the two requests, 300K, is received on interface E0. On interfaces S0 and S1, Router A has to be able to handle the largest of the three requests received. For this case, a 500K allocation is reserved on the S0 and S1 interfaces and the reservation is forwarded toward the sources. Routers E and F only receive an RSVP request for 500K. This amount will be allocated on all interfaces between the sources and the receivers. The bandwidth allocations for the WF example network in Figure 10-4 are listed in Table 10-2.
Table 10-2: Bandwidth Allocations for the Wildcard-Filter Style Example
Router
Interface E0
Interface E1
Interface S0
Interface S1
Interface S2
A
300K
500K
500K
500K
B
500K
500K
C
300K
300K
D
200K
200K
E
500K
500K
F
500K
500K
Fixed-Filter (FF) Style
Fixed-filter reservations have distinct reservations with explicit sender selection. For each FF reservation established, the router must allocate bandwidth for each request. The total bandwidth allocated is the sum of the bandwidths requested by each FF request for a distinct source. If two or more receivers request a resource and specify the same sender, the allocated resource will be shared by the receivers for that sender. The FF style can be represented by
FF(S{Q})
where S is the specific sender and Q is the flowspec. The FF style is contained in Figure 10-5 with the total bandwidth allocations shown in Table 10-3.
Figure 10-5: Fixed Filter FF(S{Q}) reservation style example
Table 10-3: Bandwidth Allocations for the Fixed-Filter Style Example
Router
Interface E0
Interface E1
Interface S0
Interface S1
Interface S2
A
400K
600K
400K
900K
B
900K
900K
C
400K
400K
D
100K
100K
E
400K
400K
F
600K
600K
Shared Explicit (SE) Style
Shared Explicit style reservations are characterized by a shared reservation and an explicit sender, creating a reservation that is shared by specific senders. The SE style is represented by
SE((S1,S2,...Sn){Q})
indicating that the list of senders shares the reservation Q. SE style type reservations are illustrated in Figure 10-6 with the bandwidth allocations listed in Table 10-4.
Figure 10-6: Shared Explicit SE(S{Q}) reservation style example
Table 10-4: Bandwidth Allocations for the Shared-Explicit (SE) Style Example
Router
Interface E0
Interface E1
Interface S0
Interface S1
Interface S2
A
300K
300K
300K
100K
B
100K
100K
C
300K
300K
D
200K
200K
E
300K
300K
F
300K
300K
When router A in Figure 10-6 receives the requests
SE(S1{{200K}) + SE((S1,S3){300K})
from routers C and D, the filter specs are combined and the flow spec is set to the largest flow spec received. The resulting flow descriptor will be ((S1,S2,S3){300K}).

 


 
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