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Mobile RSVP (MRSVP) [181, 179, 180] is an advance reservation protocol for supporting Integrated Services in a network with mobile nodes. MRSVP consid-ers a network architecture, in which a mobile node can make advance resource reservations along the data flow paths to and from the locations it may visit dur-ing the lifetime of the connection. The mobile node can be a sender in a flow, a receiver in a flow or both sender and receiver in the same flow simultaneously.

4.4 Other Proprietary Architectures 61 Other than these, the reservation model and functions of RSVP are used. Secu-rity issues have not yet been addressed in the design. Moreover, the design of MRSVP does not itself define how the movement of the mobile node is predicted, but rather refers to other work in this area.

There exist other similar schemes, but only MRSVP is presented here as an example. A good overview of these schemes can be found in [126].

MRSVP introduces three service classes that a mobile user may subscribe to.

These are Mobility Independent Guaranteed (MIG), Mobility Independent Pre-dictive (MIP), and Mobility Dependent PrePre-dictive (MDP) services. The service guarantees provided in these service classes are as follows.

MIG A mobile user admitted to this service class will receive guaranteed service with respect to packet delay bounds as long as his movements are limited to his mobility specification and he is conforming to his traffic characteri-zation. This class is appropriate for the delay-intolerant applications, which require absolute bound on packet delay.

MIP A mobile user admitted to this class will receive predictive service with respect to packet delay bound as long as his movements are limited to his mobility specification and he is conforming to his traffic characterization.

This class is appropriate for those delay-tolerant applications, which require fairly reliable delay bounds in all locations the mobile user might visit and does not want to be affected by the mobility of the nodes.

MDP A mobile user admitted to this service class will receive predictive service with high probability in all locations he may visit during the lifetime of his connection as long as he is conforming to his traffic characterization.

However, it may experience severe degradation of QoS. In addition, his resource reservations may be removed if the network becomes overloaded.

This class is appropriate for delay-tolerant applications, which can tolerate the effects of delay variations and disconnection.

In the MRSVP reservation model, a mobile node can make advance reserva-tions from a set of locareserva-tions, called Mobility Specification (Mspec). Ideally, the Mspec should be a set of locations the mobile node will visit while it participates in the flow. The advance determination of the set of locations to be visited by a mobile node is an important research problem. Although it is difficult to accu-rately determine the set of locations in advance, several mechanisms have been proposed to approximately determine them by the network. In addition, in many situations a mobile node can specify its own Mspec as part of the mobility profile.

In MRSVP reservation model, the Mspec of a mobile node can be changed dynamically while the flow is open. In such a case, resources will be reserved

at the newly added locations of the Mspec only if there are enough resources available on the data flow paths to and from those locations.

Two types of reservations are supported in MRSVP: active and passive. A mobile sender makes an active reservation from its current location and it makes passive reservations from the other locations in its Mspec. Similarly, a mobile receiver makes an active reservation to its current location and passive reservations to the other locations in the Mspec (Figure 4.5).

On a link, active and passive reservations for a flow are merged. However, either of the active or passive reservations for the same flow on a link can be removed without affecting the other. To improve the utilization of the links, the bandwidth of passive reservations of a flow can be used by other flows requiring weaker QoS guarantees or only best effort service. However, when a passive reservation becomes active the flows that were using the passive resources may be affected.

Passive reservation (depending on mobility spec) Active reservation

Figure 4.5: Mobile RSVP Operation

A unicast packet is delivered to a mobile node by using the Mobile IP rout-ing protocol. Thus, resource reservations for a mobile node must be established along the route determined by Mobile IP. This implies that when the mobile node is located in a foreign subnet and the unicast packets for the mobile node is

de-4.4 Other Proprietary Architectures 63 livered via the Home Agent by IP-IP tunneling, resource reservations must also be established over the tunnel provided that the routers on the tunnel are RSVP capable.

MRSVP Operation

Just as the Mobile IP protocol requires Home Agents and Foreign Agents to aid in routing, MRSVP requires proxy agents to make reservations along the paths from the locations in the Mspec of the sender to the locations in the Mspec of the receiver. The proxy agent at the current location of a mobile node is called the Local Proxy Agent. The proxy agents at the other locations in the Mspec of the node are called Remote Proxy Agents. The Remote Proxy Agents will make passive reservations on behalf of the mobile node. The Local Proxy Agent acts as a normal router for the mobile node (Figure 4.5).

An important issue is how the mobile node determines the proxy agents. The proposed method is to deduce from the Mspec the neighboring subnetworks and to direct a Remote Agent Solicitation message to a broadcast address in those subnetworks. The proxy agents will then send back a Remote Agent Advertise-ment message informing of their addresses. Still, this mechanism can only work properly with IPv6 networks, because IPv4 is running out of addresses and the commonly used private address space of IPv4 restricts routing.

After the mobile node knows the IP addresses of its proxy agents, the most important task is to set up the paths of active and passive reservations. If the mobile node is a sender of the flow, the paths of active reservation from the current location of the mobile node and the paths of passive reservations from the proxy agents are determined by the routing mechanism of the network.

When the mobile node is a receiver, the paths of active and passive reserva-tions to its current access point and the proxy agents depend on the flow destina-tion. If the mobile node joins a multicast flow, the mobile node directs the proxy agents to join the multicast group and the data flow paths are set up along the multicast routes. If the mobile node initiates a unicast flow, the paths may be set up by unicast or multicast routing.

In MRSVP, there are two types of Path messages as well as two types of Resv messages. These are:

1. Active Path message : carries a Sender Tspec for active reservation.

2. Passive Path message : carries a Sender Tspec for passive reservation.

3. Active Resv message : carries a Flowspec for active reservation; in addition, it may carry a Flowspec for passive reservation when an active and a passive reservation are merged.

4. Passive Resv message : carries a Flowspec of only passive reservation.

A sender node periodically sends active Path messages to the flow destination.

In addition, if the sender is mobile, the proxy agents will send passive Path mes-sages. After the routes of active and passive reservations are set up, the mobile node and the proxy agents will start receiving the Path messages. On receiving a Path message the mobile node will send a Resv message for active reservation. If a proxy agent receives Path messages for a multicast group, for which it is acting as a proxy agent or for a mobile node, from which it has received a request for acting as a proxy, it will make a passive reservation on the downstream link. Once the mobile node attaches to the new subnet it will send a Resv message to make an active reservation. Resv messages for active reservations are converted to Resv messages for passive reservation when they are forwarded towards subnets, which do not have active senders.

In addition to the messages present in RSVP, few additional messages are required in MRSVP. Receiver and Sender Spec messages are sent by the mo-bile node through the local proxy to its remote proxies and provide the proxies information about the ongoing flow. The sender and receiver Mspec messages give information to the proxies about the mobile nodes mobility pattern. Thus, they control the setting of active and passive resource reservations. The Forward Mspec message is used by a mobile sender to forward the Mspec of a mobile re-ceiver to the local proxy agent. A terminate message is used by the mobile node to request its remote proxy agents to terminate reservations. Yet, a network using address from the IPv4 private address space may prevent these messages to ever get through.

Currently, RSVP and Integrated Services do not provide any support for pas-sive reservation. The Flowspec and Sender Tspec of active and paspas-sive reserva-tions are handled by the Integrated Services module of a router and node. There-fore, the Integrated Services module needs to be augmented by including the sup-port for passive reservation. The admission control scheme and the packet clas-sifier of the Integrated Services handle the functionalities of passive reservations.

The packet classifier in a router must not forward the data packets of a flow onto a link, which does not have any active reservations for flows.