Compex PS2216 Switch

Review by Harry Lam on 02.12.03
Switch provided by Compex, MSRP: $89.95

Specifications:

Rather than most reviews that will just give a spec sheet, I'm going to fully explain each specification in layman's terms.  If you're not really interested, you can skip directly to the next page: Features.

Industry Standards:

IEEE (Institute of Electrical and Electronics Engineers) is one of the bodies that set standards.
In this case IEEE 802.3 is the standard for Ethernet (aka 10Base-T, a 10 megabit connection through UTP (unshielded twisted pair cable), IEEE 802.3u is the specification for Fast Ethernet (aka 100Base-TX, a 100 megabit connection through UTP), and IEEE 802.3x is the standard for flow control within a Full-Duplex Ethernet LAN.

The remaining 4 standards: CE, FCC Class A, Gost, and C-Tick are safety standards for Europe, the US, Russia, and Australia/ New Zealand:

The CE mark is required for all electronics that will be sold anywhere in the European community.  It certifies that a product has passed all essential safety and environmental requirements (93/68/EEC).

All FCC Class A will bear the following quote: 
This equipment has been tested and found to comply with the limits for a Class A digital device, pursuant to part 15 of the FCC Rules. These limits are designed to provide reasonable protection against harmful interference when the equipment is operated in a commercial environment. This equipment generates, uses, and can radiate radio frequency energy and, if not installed and used in accordance with the instruction manual, may cause harmful interference to radio communications. Operation of this equipment in a residential area is likely to cause harmful interference in which case the user will be required to correct the interference at his own expense.
The differences between a Class A and Class B device is that Class B is more stringent in its requirements of electromagnetic emissions.  A Class B device can be marketed for use in a residential area in addition to commercial/industrial areas (which are ok for FCC Class A devices).  The official word from Compex concerning their Class A certification is that the PS2216 is designed for the small business arena.

Gost is certification for companies to export their products to Russia.  It certifies that products meet certain quality and safety standards before they will be allowed into the country at customs.

C-Tick is the Australian and New Zealand safety and EMC emission standards.  All electronics products for the Australian and New Zealand markets are required to comply with this set of standards.

Interface:  RJ45 is the connector for Ethernet, basically an 8 pin connector similar to a phone jack connector (which is only 4 pins, RJ11).

Led Indicators:  The PS2216 has a power LED signifying power to the entire unit.  Each port has one dual color LED (green for 100Mbps, amber for 10 Mbps) that blinks based on activity (and stays on if a link is established)

Backplane Capacity:  The backplane capacity of a device is the total amount of bandwidth that can be flowing through the switch per unit of time.  3.2Gbps means that all the switch ports will be able to attain maximum speeds even when all of the ports are simultaneously in use.  The maximum bandwidth consumption of a switch can be calculated via the following formula: (maximum port speed) * (# of ports) * 2(only if the switch supports full duplex).  For our test switch, it's 100Mbps * 16 ports * 2 = 3,200Mbps which is 3.2Gbps.

Transmission Mode:  The transmission mode of a switch basically tells you if the switch is half or full duplex (or simplex, but that wouldn't appear on a switch -- basically simplex is communication in one direction only).

Flow Control:  Flow Control basically is an acknowledgment system to ensure that the receiving node doesn't get flooded with data (too much data that it can't handle it).  The PS2216 uses the standard IEEE 802.3x Flow Control specification for Fast Ethernet (under Full Duplex), and uses Back Pressure flow control (under half duplex).  Back Pressure flow control basically have nodes verify that the receiving node has enough buffer space before data is sent.

Switching Method:  The PS2216 uses store and forward switching, in which basically an entire frame is received and stored into the switch's memory before it is transmitted to the destination.  This allows the switch to check the frame for errors before sending the frame on; if there are errors, the frame is not transmitted and a request for the same frame is sent to the source.  However, the latency of the switch is directly related to the size of the frame.  In contrast, in cut-through switching, the switch begins to forward the frame as soon as it can (basically after it receives the destination MAC address part of the frame).  This does not have any error correction built into the switching method, and in essence the switch is acting in a way similar to a hub (at least in the way frames are forwarded).

Data Buffer: The data buffer of a switch is the total amount of information it can hold at a time for all of it's switching jobs.  Considering that a frame is measured with the unit of bytes, 128kb should be sufficient.

MAC Address Table:  The MAC address is a unique hardware identifier (in hexadecimal) that is used on almost all networking components.  A switch builds a table of the MAC addresses it is connected to and uses that table to make it's decisions on how to forward packets.  8K should be adequate for almost all networks that the PS2216 is used in; considering that a MAC address is only 6 bytes long (the first 3 bytes make up the vendor portion of the MAC address, the last 3 bytes is the unique serial number from that specific vendor).

Power Supply:  This specification just states that the switch requires an external DC 3.3V power source capable of delivering 3A of current, this is supplied through the transformer power plug that is included with the unit (and if you lose that plug, you can get a universal plug corresponding to these specs).

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