On Thu, 4 Sep 2003, Michael Ryan Byrd said: > So we can go down to compUSA and buy a number of ethernet devices: > > 1- hub > 2- hub/switch > 3- switching Hub > 4- switch > > Are 2,3 and 4 the same thing? Do these "switches" do Spanning Tree loop > prevention like I presume the more expensive Cisco Catalyst switches do? > > What is the difference between an EtherFast 4124 24-Port 10/100 Ethernet Switch > for $129.00 and $1825.00 Cisco catalyst 3524 xl ent ed feth 24 ports stackable > switch? > > ideas? > > Ryan
I'd guess 2, 3, and 4 are the same, but it sounds like marketing junk to me. "I'll just put it's a switch or a hub, and more people will buy it because it'll sound more versatile." Remember back to the OSI model. There are 7 Layers defined. Most of the time, though, we just refer to the TCP/IP network model, which pretty much just lumps layers 4-7 together: Layer 1 - Link (Physical for OSI) - This pretty much refers to just the physical cable, and the electrical signals that go over it. This is where you'd classify a hub. It just takes in signals from one port and broadcasts those same signals across all the ports. In a pinch, you can sometimes skip the hub completely and just wrap the wires together. You'll get collisions, everyone "hears" the conversation, etc. The Link/Physical layer acts as a bridge between physical networks. Layer 2 - Network (Data Link for OSI) - This refers to one layer of interpretation of the electrical signals carried. The signals are interpreted into data frames, and the source and destination MAC addresses are deciphered. Switches work at this layer by determining the source and destination, storing a table of MAC address to port translations, and allowing computers on two ports to communicate directly. None of the devices on other ports "hear" the conversation, and no extra bandwidth is taken up for devices that aren't participating in the conversation. Layer 3 - Transport (Network for OSI) - At this level, the Network (or Data Link) information is interpreted again, and the source and destination IP addresses become important. A Network layer device acts as a bridge between different IP networks, the public internet and your local LAN, for example. I'd usually call one of these devices a router, but it can be called a switch too, based on the functionality you're referring to at the time. It maintains a routing table of IP addresses and ports, rather than just the MAC addresses. Layer 4 - Application - This layer involves the TCP or UDP protocols on top of everything else. If you've got a firewall that is blocking port 25 (for example), that's operating at the Transport layer. On top of these layers, there's a lot of configuration that can go into switches and routers. Some switches are engineered better than others, and it can be difficult to compare two switches directly. Some switches can be upgraded with newer firmware to fix bugs or provide new functionality. Higher end switches generally have a configuration interface that allows you to enable/disable a (physical) port, configure spanning-tree options, change the port configuration (full/half duplex, 10/100 Mbps, etc.) or remotely monitor port information and statistics. They may also support trunking (aggregating several connections for extra bandwidth) or failover (redundant links). Stacking switches often have very high speed links between the switches in the stack, or have their own interface. The Cisco 3524 uses high-speed uplinks between stacked switches. When switches are configured, it can be done in-band (such as over the network) or out-of-band (separate serial port, for example). In-band can be through telnet, an embedded web server, or through SNMP, for example. There are a number of ways in which a switch can be engineered, and these engineering decisions can affect botht he price and the performance. Ideally, every port could communicate at full-speed, full-duplex with another port, and nothing would ever get dropped. In practice, though, this makes for a lot of connections within the switch, and the engineering for it can get difficult. Some switches utilize a bus to pass the signals from one port to another, and some use a crossbar fabric. On a bus, one port just puts the packet onto the wires, and it is rebroadcast by the correct port elsewhere on the bus. A crossbar design allows multiple input ports to send messages to multiple output ports simultaneously. Since shared-bus switches are order n, and crossbar designs are n^2, the crossbar is often more complex and expensive. Switches can also forward the packet immediately after determining the destination MAC address, or they can read the whole thing into a buffer, check the CRC, and then forward valid packets to the appropriate destination. This store-and-forward is slower, but won't forward corrupted frames. More expensive switches often have more or larger buffers, bigger MAC address tables, or faster memory. To answer your original question a bit more, there is a big difference between the Linksys EtherFast 4124 and the Cisco 3524 (though maybe not $1700). Depending on what functions you need and use, you may or may not notice the difference. For example, you can add 2 GBIC modules (gigabit expansion modules) to the Cisco 3524, and it supports management functions and auxiliary VLANs. The Linksys is not a managed switch, so you can't enable/disable ports, change parameters, or monitor it. The Cisco is probably also engineered better, and will probably support higher bandwidth between ports. In the CS Department, our main switch/router is an Alcatel OmniCore 5052: http://www.alcatel.com/products/productsummary.jhtml?_DARGS=/common/opg/products/include/searchResults.jhtml.7_A&_DAV=/x/opgproduct/OmniCore_5052.jhtml We also have a number of smaller switches. They are a combination of: Alcatel OmniCore 5010's: http://www.alcatel.com/products/productsummary.jhtml?_DARGS=/common/opg/products/include/searchResults.jhtml.7_A&_DAV=/x/opgproduct/OmniCore_5010.jhtml Cisco 3512 XL's and 3524 XL's (both EOL'd): http://www.cisco.com/en/US/products/hw/switches/ps637/ps640/index.html http://www.cisco.com/en/US/products/hw/switches/ps637/ps642/index.html Netgear FSM726S's: http://www.netgear.com/products/prod_details.asp?prodID=122&view=sb and some other miscellaneous stuff. Our firewall (which also does some routing) runs Linux. Other interesting links--- About the OSI and TCP/IP models: http://www.ussg.iu.edu/usail/network/nfs/network_layers.html About switched ethernet: http://netlab1.bu.edu/~staro/546projects/switchedethernet/proj/trans.htm About the Linksys 4124: http://www.linksys.com/products/product.asp?grid=35&scid=39&prid=473 About the Cisco 3524: http://www.cisco.com/en/US/products/hw/switches/ps637/products_data_sheet09186a00800925c5.html Frank --------------------------------------------------------------------------- Frank Sorenson - KD7TZK CSR Computer Science Department Brigham Young University [EMAIL PROTECTED] ____________________ BYU Unix Users Group http://uug.byu.edu/ ___________________________________________________________________ List Info: http://uug.byu.edu/cgi-bin/mailman/listinfo/uug-list
