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For the sustained rate, set up a loop to calculate the total number of cells S arrived in thirty successive frames (i.e. in 900 msec). When thirty frames have been generated, compare this value against S, and save the largest of the two back in S. (Initially, set S = 0).
To calculate c2, you will need to keep all of the inter-arrival times of the ATM cells. Between two cells that are transmitted back-to-back, the inter-arrival time is 1; between the last cell of a frame and the first cell of the next frame, it is Y + 1. Maintain two variables: Sum and SqSum. For each inter-arrival time t, do the following:
Sum = Sum + t SumSq = SumSq + t2
If frame counter < 5000, repeat Parts 1 and 2 to continue to generate frames. Otherwise, go to Part 3.
Calculate and print out the required ATM traffic parameters:
Average cell rate = total cells arrived/total simulation time
SCR = 5/900
average on period = on_period/frame_counter average off period = off_period/frame_counter c2 = Var/MeanSq, where:
Var = [SumSq — (Sum2 / (o(al_cel I s_arri ved) | / ((o(al_cel I s_arri ved — 1)
MeanSq = (Sum/total_cells_arived)2.
Signaling in ATM Networks
Recall that in ATM networks there are two types of connections: permanent virtual connections (PVC) and switched virtual connections (SVC). PVCs are established off-line using network management procedures, whereas SVCs are established dynamically in real-time using signaling procedures. To establish an SVC, two separate signaling protocols are used; one is used exclusively over the UNI and another is used exclusively within the ATM network. As an example, let us consider the case where user A wants to establish a point-to-point connection to a destination user B over a private ATM network. user A sends a request for the establishment of the connection to its ingress ATM switch using the signaling protocol Q.2931. The ATM switch then establishes a connection to the egress switch that serves B using the private network node interface (PNNI) protocol, and finally, the egress switch uses Q.2931 to interact with B over their UNI.
This chapter deals with the signaling protocol Q.2931. This signaling protocol runs on top of a specialized AAL, known as the signaling AAL (SAAL). A special sublayer of this AAL is the service-specific connection oriented protocol (SSCOP). The main features of SAAL and SSCOP are first discussed, and then the various ATM addressing schemes are presented. Then, the signaling messages and procedures used by Q.2931 are described.
An ATM virtual circuit connection can be either a point-to-point connection or point-to-multipoint connection. A point-to-point connection is bidirectional: it is composed of two unidirectional connections, one in each direction. Both connections are established simultaneously over the same physical route. Bandwidth requirements and QoS can be specified separately for each direction. A point-to-multipoint connection is a unidirectional connection, and it consists of an ATM end device, known as the root, which transmits information to a number of other ATM end devices, known as the leaves.
Point-to-point SVC connections are established over the private UNI using the ITU-T signaling protocol Q.2931. Point-to-multipoint SVC connections are established over the UNI using the ITU-T signaling protocol Q.2971 in conjunction with Q.2931.
The establishment of an ATM SVC connection across one or more private ATM networks is done using PNNI. PNNI provides the interface between two ATM switches that either belong to the same private ATM network or to two different private ATM networks (see Figure 5.1). The abbreviation PNNI can be interpreted as either the private network node interface or the private network-network interface, reflecting these two possible uses.
Connection-oriented Networks Harry Perros © 2005 John Wiley & Sons, Ltd ISBN: 0-470-02163-2
SIGNALING IN ATM NETWORKS
Private ATM network A
Private ATM network B
Figure 5.1 The private network-network interface (PNNI).
The PNNI protocol consists of two components: the PNNI signaling protocol and the PNNI routing protocol. The PNNI signaling protocol is used to dynamically establish, maintain, and clear ATM connections at the private network-network interface and at the private network node interface. The PNNI routing protocol is used to distribute network topology and reachability information between switches and clusters of switches. This information is used to compute a path from the ingress switch of the source end device to the egress switch of the destination end device over which signaling messages are transferred. The same path is used to set up a connection along which the data will flow. PNNI was designed to scale across all sizes of ATM networks, from a small campus network with a handful of switches to large world-wide ATM networks. Scalability is achieved by constructing a multi-level routing hierarchy based on the 20-byte ATM NSAP addresses.