COMNET III CACI

More documents

Recommendations

Info

Upon reflection, the network manager realizes that this result is not surprising. Since he has assigned the image transfer to the CBR service class, the highest priority and most stringent delay requirements are given to this traffic type. The database requests only receive a ‘best effort’ service from the network, and thus suffer when an image transfer is in progress. On the other hand, if both traffic types are multiplexed over the same service class, the backbone does not prefer the image transfer cells over the database request cells, hence the better delay performance. The side result that the manager wished to obtain on the buffer utilization turned out as follows: the output buffer on the switches showed a maximum utilization of 106 and 159 bytes for the VBR scenario and of 5035 and 8586 bytes for the ABR / CBR scenario. In both cases, these values do not worry the manager since they are well below the switches’ output buffer capacity, even considering the much simplified model. The above example shows how the ATM features of COMNET III may be used to evaluate different QoS requirements. The network manager could go on to model more details of his network, such as • modeling more image transfers over the backbone • incorporating statistical message sizes for the database traffic and the image transfers • extending the model to incorporate the LAN portion of the network • considering alternative bandwidths for the PVC. Furthermore, he could further study the parameter settings for the different service classes to determine how these affect the QoS of the traffic. Examples here are to experiment with the PCR or SCR of the traffic contract, hence evaluating different traffic shaping functions or settings for the traffic contract. 46
4.2 TCP/IP vs. ATM at the Desktop This example considers a small high-tech company with two offices located on the east coast and the west coast respectively. The network manager of the company realizes the advantages offered by ATM, in particular concerning the provision of real-time services between the offices such as video conferencing. This would save considerable travel costs of employees between the two locations. She has already connected both offices using an ATM service from a service provider. However, the network manager now intends to complete the process of upgrading to ATM by replacing the existing LAN technology in each office by ATM. In order to justify her plans with the management, she decides to model both scenarios to show the benefits of bringing ATM to the desktop. The company’s network topology is currently configured as follows: The east coast LAN consists of a 10-Base-T Ethernet LAN to which the offices workstations and the local server are connected. The west coast office has a similar setup, except that the LAN is a 16Mbps Token Ring. Each office already has a small ATM router which is also hooked up to the LAN. To connect both offices, the company has signed up with a service provider and leased a 64Kbps ATM PVC. The access links to the service provider’s ATM network in both offices therefore also run at 64Kbps. The network topology is illustrated in Figure 12. Figure 12: COMNET III model for the small high tech company 47
Page 1 and 2: COMNET III Application Notes: Model
Page 3 and 4: Appendices……………………
Page 5 and 6: 2.2 Underlying Assumptions A number
Page 7 and 8: only those details which are signif
Page 9 and 10: Table 1 gives you an overview of th
Page 11 and 12: Network Interfaces Connection Admis
Page 13 and 14: 3.2 Overview of COMNET III’s Mode
Page 15 and 16: To generate ATM traffic, you would
Page 17 and 18: 3.2.3 Other Protocols over ATM The
Page 19 and 20: 3.4 Modeling CBR Services A fundame
Page 21 and 22: UPC/NPC conformance for the CBR tra
Page 23 and 24: 3.5 Modeling VBR Services To model
Page 25 and 26: Figure 5: VBR buffer limit. As illu
Page 27 and 28: The remarks made under the previous
Page 29 and 30: control parameters as well as to ex
Page 31 and 32: In order for the RM cells to indica
Page 33 and 34: 3.7 Modeling UBR Services As descri
Page 35 and 36: For the FM functions, a distinction
Page 37 and 38: Bus Bus 1..n CPU Ports Ports Line C
Page 39 and 40: 4. Example Applications In the firs
Page 41 and 42: The particular QoS parameters of in
Page 43 and 44: CBR AAL1 VBR AAL3/4 ABR AAL3/4 Basi
Page 45: After running the model under both
Page 49 and 50: Note that she has decided to reduce
Page 51 and 52: The voice mail traffic is given the
Page 53 and 54: 4.3 Modeling ATM LANE Networks This
Page 55 and 56: The model topology consists of a nu
Page 57 and 58: Connected to the LES is a single CO
Page 59 and 60: Figure 17 depicts a modified model
Page 61 and 62: To model this architecture, COMNET
Page 63 and 64: The OFF command is a global process
Page 65 and 66: The respective connection utilizati
Page 67 and 68: A. Perspectives on ATM - Brief Revi
Page 69 and 70: This integration of the different n
Page 71 and 72: available, or it will accept to est
Page 73 and 74: Version 4.0 of the ATM Forum’s tr
Page 75 and 76: A.3 The B-ISDN Protocol Reference M
Page 77 and 78: Class A B C D AAL Type AAL1 AAL2 AA
Page 79 and 80: Higher layer PDU (1-65535 bytes) Co
Page 81 and 82: Link 1 ATM Switch VCI = 1 Link 2 VP
Page 83 and 84: FDDI ATM Router ATM Switch Private
Page 85 and 86: Input Ports Output Ports Figure 30:
Page 87 and 88: In addition to the internal switchi
Page 89 and 90: B.1.1 Resource Management Policies
Page 91 and 92: Finally, the setup request is forwa
Page 93 and 94: intermediary node, the local CAC fu
Page 95 and 96: Arrival of a cell at time ta(k) X
Page 97 and 98:
CLP value? 0 1 GCRA using PCR(CLP=0
Page 99 and 100:
B.2.2.3 Available Bit Rate Conforma
Page 101 and 102:
control scheme requires more compli
Page 103 and 104:
B.3 Management Services We will now
Page 105 and 106:
In the second dimension, the OAM ce
Page 107 and 108:
• SECBR = Severely Errored Cell B
Page 109 and 110:
Note that the node detecting the fa
Page 111 and 112:
Glossary and Acronyms: The terms in
Page 113 and 114:
NNI* nrt-VBR OAM cells PCR PDU* PT
show all

COMNET III CACI

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?