|Previous||Table of Contents||Next|
It is important to understand the limitations and functions of the Strata-Com product. Table 8.3 describes the differences in the various switches.
|BPX/AXIS switches||The BPX/AXIS product is targeted toward the larger, higher-demand networks and is a broadband switch. The BPX uses a redundant, 9.6Gbps crosspoint switch matrix for interconnection services, and the AXIS shelf provides termination for Frame Relay, T1, E1, ATM, CES, and FUNI services. BPX nodes are interconnected via OC-3 or DS-3 links.|
|IGX switches||The IGX product is offered in 8-, 16-, or 32-slot configurations and uses a redundant, 1.2Gbps cell-switching bus for backplane interconnections. It is important to note that the switch can operate in stand-alone mode, which allows it to both provide access functions and act as a multiservice switch. It interoperates with the BPX and IPX platforms.|
|IPX switches||Similar to IGX switches, the IPX switch products also provide 8-, 16-, or 32-slot configurations, but they provide cell switching at only 32Mbps. Typically, they are deployed around a central BPX, and the IPX terminates narrowband applications including voice, fax, data, video, and Frame Relay.|
StrataCom switches are usually administered with the StrataSphere Network Management software. These applications provide planning tools including StrataSphere Modeler and StrataSphere Optimizer. The Statistics agent and BILLder applications are more targeted toward management and operations functions.
|Many changes have occurred with the StrataCom product line and Ciscos positioning of this platform. Please consult the technical and sales information available online.|
StrataCom Network Design Models
Network design with StrataCom switches is similar to generic network design; however, there are important differences in terminology and deployment. Table 8.4 documents the three general classifications of StrataCom network designsflat, tiered, and structured.
|Flat||Flat StrataCom networks regard all nodes as equal partners. There are no hierarchical characteristics under this design. The flat design can support 48 nodes; however, processing and addressing limitations can impact the overall success of this deployment. Under the flat design model, all nodes must maintain information about all other nodes in the network.|
|Tiered||StrataComs tiered design model adds hierarchical characteristics to the network and is substantially more scalable than the flat model. Under the tiered model, IPX, IGX, and AXIS platforms are connected to a backbone consisting of BPX nodes.|
|Structured||The structured model permits expansion to 384 nodes in the network. Various StrataCom switches are linked under a loose domain model that groups switches. These groupings typically mirror other domain models devices are grouped on geographic or administrative boundaries.|
Switched Multimegabit Data Service (SMDS) was designed to provide the performance characteristics and connectivity features of local area networks in the WAN. This was accomplished by using a connectionless, on-demand transport based on the 802.6 MAN standard. However, the under-lying structure of SMDS is cell-based ATM, and it uses ATM AAL 3/4. Recall that data ATM networks use AAL 5 in most installations.
It is unfortunate that SMDS technology did not succeed. The protocol offered network designers many benefits. For example, changes were very simple, and additional nodes could be added quickly. In addition, all inter-faces in the same SMDS region were addressed in the same subnet, and all stations had direct, connectionless access to every other node. However, SMDS never received widespread adoption, and many carriers avoided the technology in favor of Frame Relay or ATM. Customers also avoided the technology, though this was primarily due to the high cost of equipment and low availability. Today it is virtually impossible to order SMDSvendors will direct you to ATM or Frame Relay.
While configured as a connectionless topology, SMDS offered a reasonable degree of security for corporations. Addresses were entered into screening and validation tables to permit connectivity between nodes. This isolated each company logically within the switch, yet inter-company SMDS communications could be enabled with a minor table modification.
Broadcasts from the source router would reach all other routersthe packet automatically being forwarded by the SMDS switch to all routers in the network. This was accomplished with group addressing. SMDS addresses in North America were assigned like traditional analog phone numbers; however, they were prefixed with a C or an E. C addresses are for individual nodes, and E addresses are used within a group for the group address. The group address for an SMDS network in Chicago might appear as e131.2555.1212, for example. Packets sent to the group address are forwarded to all nodes in the subnet (as defined in the SMDS switch). This simplified processing on the source routerrecall that in Frame Relay, the router repeated the broadcast for each PVC.
|The router sends only one copy of the packet to the group address. The network/switch is responsible for distributing and repeating that packet to all members of the group. The network/switch will not transmit the packet back to the sender, even though the sender is a member of the group.|
SMDS required the use of an SMDSU (SMDS Unit) or SDSU (SMDS Data Service Unit). Since SMDS never attained the volume found with Frame Relay and other WAN technologies, it is understandable that these DSUs would have a higher cost.
SMDS supports a number of upper-layer protocols, including:
|Previous||Table of Contents||Next|