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1.4 Examples of Styles Connected: An Internet Encyclopedia
1.4 Examples of Styles

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Prev: 1.3 Reservation Styles
Next: 2. RSVP Protocol Mechanisms

1.4 Examples of Styles

1.4 Examples of Styles

This section presents examples of each of the reservation styles and shows the effects of merging.

Figure 4 illustrates a router with two incoming interfaces, labeled (a) and (b), through which flows will arrive, and two outgoing interfaces, labeled (c) and (d), through which data will be forwarded. This topology will be assumed in the examples that follow. There are three upstream senders; packets from sender S1 (S2 and S3) arrive through previous hop (a) ((b), respectively). There are also three downstream receivers; packets bound for R1 (R2 and R3) are routed via outgoing interface (c) ((d), respectively). We furthermore assume that outgoing interface (d) is connected to a broadcast LAN, i.e., that replication occurs in the network; R2 and R3 are reached via different next hop routers (not shown).

We must also specify the multicast routes within the node of Figure 4. Assume first that data packets from each Si shown in Figure 4 are routed to both outgoing interfaces. Under this assumption, Figures 5, 6, and 7 illustrate Wildcard-Filter, Fixed-Filter, and Shared-Explicit reservations, respectively.

                         ________________
                     (a)|                | (c)
      ( S1 ) ---------->|                |----------> ( R1 )
                        |     Router     |      |
                     (b)|                | (d)  |---> ( R2 )
      ( S2,S3 ) ------->|                |------|
                        |________________|      |---> ( R3 )
                                                |

                        Figure 4: Router Configuration

For simplicity, these examples show flowspecs as one-dimensional multiples of some base resource quantity B. The "Receives" column shows the RSVP reservation requests received over outgoing interfaces (c) and (d), and the "Reserves" column shows the resulting reservation state for each interface. The "Sends" column shows the reservation requests that are sent upstream to previous hops (a) and (b). In the "Reserves" column, each box represents one reserved "pipe" on the outgoing link, with the corresponding flow descriptor.

Figure 5, showing the WF style, illustrates two distinct situations in which merging is required. (1) Each of the two next hops on interface (d) results in a separate RSVP reservation request, as shown; these two requests must be merged into the effective flowspec, 3B, that is used to make the reservation on interface (d). (2) The reservations on the interfaces (c) and (d) must be merged in order to forward the reservation requests upstream; as a result, the larger flowspec 4B is forwarded upstream to each previous hop.

                             |
               Sends         |       Reserves             Receives
                             |
                             |       _______
         WF( *{4B} ) <- (a)  |  (c) | * {4B}|    (c) <- WF( *{4B} )
                             |      |_______|
                             |
      -----------------------|----------------------------------------
                             |       _______
         WF( *{4B} ) <- (b)  |  (d) | * {3B}|    (d) <- WF( *{3B} )
                             |      |_______|        <- WF( *{2B} )

              Figure 5: Wildcard-Filter (WF) Reservation Example

Figure 6 shows Fixed-Filter (FF) style reservations. For each outgoing interface, there is a separate reservation for each source that has been requested, but this reservation will be shared among all the receivers that made the request. The flow descriptors for senders S2 and S3, received through outgoing interfaces (c) and (d), are packed (not merged) into the request forwarded to previous hop (b). On the other hand, the three different flow descriptors specifying sender S1 are merged into the single request FF( S1{4B} ) that is sent to previous hop (a).

                          |
            Sends         |       Reserves             Receives
                          |
                          |       ________
     FF( S1{4B} ) <- (a)  |  (c) | S1{4B} |  (c) <- FF( S1{4B}, S2{5B} )
                          |      |________|
                          |      | S2{5B} |
                          |      |________|
     ---------------------|---------------------------------------------
                          |       ________
                  <- (b)  |  (d) | S1{3B} |  (d) <- FF( S1{3B}, S3{B} )
     FF( S2{5B}, S3{B} )  |      |________|      <- FF( S1{B} )
                          |      | S3{B}  |
                          |      |________|

              Figure 6: Fixed-Filter (FF) Reservation Example

Figure 7 shows an example of Shared-Explicit (SE) style reservations. When SE-style reservations are merged, the resulting filter spec is the union of the original filter specs, and the resulting flowspec is the largest flowspec.

                          |
            Sends         |       Reserves             Receives
                          |
                          |       ________
     SE( S1{3B} ) <- (a)  |  (c) |(S1,S2) |   (c) <- SE( (S1,S2){B} )
                          |      |   {B}  |
                          |      |________|
     ---------------------|---------------------------------------------
                          |      __________
                  <- (b)  | (d) |(S1,S2,S3)|  (d) <- SE( (S1,S3){3B} )
     SE( (S2,S3){3B} )    |     |   {3B}   |      <- SE( S2{2B} )
                          |     |__________|

            Figure 7: Shared-Explicit (SE) Reservation Example

The three examples just shown assume that data packets from S1, S2, and S3 are routed to both outgoing interfaces. The top part of Figure 8 shows another routing assumption: data packets from S2 and S3 are not forwarded to interface (c), e.g., because the network topology provides a shorter path for these senders towards R1, not traversing this node. The bottom part of Figure 8 shows WF style reservations under this assumption. Since there is no route from (b) to (c), the reservation forwarded out interface (b) considers only the reservation on interface (d).

                         _______________
                     (a)|               | (c)
      ( S1 ) ---------->| >-----------> |----------> ( R1 )
                        |    >          |
                        |      >        |
                     (b)|        >      | (d)
      ( S2,S3 ) ------->| >-------->--> |----------> ( R2, R3 )
                        |_______________|

                       Router Configuration

                             |
               Sends         |       Reserves             Receives
                             |
                             |       _______
         WF( *{4B} ) <- (a)  |  (c) | * {4B}|   (c) <- WF( *{4B} )
                             |      |_______|
                             |
      -----------------------|----------------------------------------
                             |       _______
         WF( *{3B} ) <- (b)  |  (d) | * {3B}|   (d) <- WF( * {3B} )
                             |      |_______|       <- WF( * {2B} )

             Figure 8: WF Reservation Example -- Partial Routing


Next: 2. RSVP Protocol Mechanisms

Connected: An Internet Encyclopedia
1.4 Examples of Styles

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