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Our radio station uses a PtP wireless system to stream our radio and TV signals from our studio up a hill to our transmitter. We have been having problems with warbly sound and drop outs that come from some point in this system. An engineer that occasionally visits the station thinks it could be the switches we use on each side of the PtP wireless system to connect the PtP devices to the encoders and decoders and wants us to get two of these switches:

http://www.amazon.com/Netgear-JGS516-ProSafe-16-Port-Ethernet/dp/B0002CWPOK/ref=dp_return_1

The encoder/decoder setup only streams 8Mbps total so it seems like the switches we have should not be stressed out, unless they are causing sufficient latency to degrade the performance of the encoder/decoder. At each end of the connection we only have 4 connections, is there any reason we couldn't get a cheaper, "home" quality switch like this:

http://www.amazon.com/D-Link-DGS-1005G-5-Port-Gigabit-Desktop/dp/tech-data/B003X7TRWE/ref=de_a_smtd

Is there a significant difference that we would notice in terms of latency between these two switches? How much does the quality of the switch actually matter in this scenario?

Any help is appreciated, feel free to ask questions if anything needs clarification. Thanks

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1  
There are cheaper 4 and 8 port unmanaged Netgear ProSafe switches as well, which would make a more balanced comparison. –  paradroid Jun 27 '12 at 20:11
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4 Answers

up vote 10 down vote accepted

Looking at the official specifications for the D-Link device and comparing them with the NETGEAR device, I would go with the D-LINK.

D-LINK presents the same relevant specifications, even more than NETGEAR. Also it's cheaper :)

Concerning the latency issue, the D-LINK provides you with a QoS method for controlling traffic priority, allowing you to prioritize the most important traffic to reduce latency for time-sensitive transmissions, such as streaming media.


The reason behind my choice:

╔═══════════════════════════════════════╦══════════════════╦══════════════════╗
║ RELEVANT SPECIFICATION                ║ D-LINK           ║ NETGEAR          ║
╠═══════════════════════════════════════╬══════════════════╬══════════════════╣
║ Packet Filtering/Forwarding Rates     ║                  ║                  ║
║           Ethernet (pps per port):    ║ 14,880           ║ 14,800           ║
║      Fast Ethernet (pps per port):    ║ 148,800          ║ 148,000          ║
║   Gigabit Ethernet (pps per port):    ║ 1,488,000        ║ 1,480,000        ║
╠═══════════════════════════════════════╬══════════════════╬══════════════════╣
║ Standards                             ║                  ║                  ║
║ IEEE 802.3 10BASE-T                   ║ Yes              ║ ---              ║
║ IEEE 802.3i 10BASE-T                  ║ ---              ║ Yes              ║
║ IEEE 802.3u 100BASE-TX                ║ Yes              ║ Yes              ║
║ IEEE 802.3ab 1000BASE-T               ║ Yes              ║ Yes              ║
║ ANSI/IEEE 802.3 Nway autonegotiation  ║ Yes              ║ ---              ║
║ IEEE 802.3x Flow control              ║ Yes              ║ Yes              ║
║ IEEE 802.1p QoS                       ║ Yes              ║ ---              ║
╠═══════════════════════════════════════╬══════════════════╬══════════════════╣
║ buffer                                ║                  ║                  ║
║      Size:                            ║ 128 KBytes/device║ 2 Mb             ║
║    Method:                            ║ store-and-forward║ store-and-forward║
╚═══════════════════════════════════════╩══════════════════╩══════════════════╝

Product pages with Official Specifications:

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Awesome! thanks for the analysis this is great! –  pjreddie Jun 27 '12 at 1:29
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+1 for ASCII table and bringing back BBS memories... –  Justin Scott Jun 27 '12 at 18:39
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The main differences between "home" and "professional" equipment are

  • manageability: there is an interface to configure priorities, virtual circuits and load balancing, and to query port status and statistics
  • scalability: the switch needs to maintain a table which devices are connected to which port. If this table is full because more devices are on the network than entries exist in the table, then performance degrades (when a device is unknown, packets to the device are broadcast over the entire network, in the hope that the device answers and so becomes known). Consumer devices typically have table sizes of 20-50 entries; professional equipment should support 1000 entries at least
  • extensibility: many professional switches are "stackable", meaning that you can combine multiple switches into a single one, configure it centrally and have shared address tables over all of them.
  • management protocol support: to support redundant links, switches have to be aware of each other, and discuss the network topology via protocols such as Spanning Tree Protocol (STP). Bad things happen if there are cyclic links and no inter-switch routing protocol is enabled.

Both of the devices you mention I'd classify as "home" equipment, and I don't think the Netgear switch will improve things. You want something that is "managed", which allows you to set up traffic priorities.

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A DGS-1005G (for example) is clearly a home switch, costing all of $25. It has a MAC table supporting 4,000 entries. No switch has a 20-entry table. Possibly you're confusing the MAC address table with the size of DHCP pools on home routers? –  derobert Jun 27 '12 at 18:32
    
I meant MAC table size; it is probably less of an issue today than it was in earlier times. –  Simon Richter Jun 28 '12 at 9:01
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Is there a significant difference that we would notice in terms of latency between these two switches?

I didn't see any mention of it in those descriptions, but the latency of a switch will mostly be determined by its switch buffering method: either store-and-forward or cut-through. Store-and-forward means that the complete Ethernet frame has to be received (intact) before that frame leaves the switch to the next destination. Cut-through switching will try to retransmit the Ethernet frame as soon as the IP header with the destination address has been received and processed.

Almost all SOHO/home switches are store-and-forward. Unless stated otherwise, assume that a switch uses store-and-forward. Note that cut-through switches will propagate bad frames, whereas a store-and-forward switch will filter out bad frames.

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Cut-through usually starts after the destination MAC address, so before the IP header. –  Simon Richter Jun 27 '12 at 7:32
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Outside of the switches, I would also look at the cabling that connects those switches to whatever is talking to them. One of the related cables may have a problem which could cause additional trouble and will be easier/cheaper to replace than the switches. I would start there before swapping out switching gear.

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good to know. All the cabling on one end is new, but i don't think the other end has been replaced for a while, i'll look into it. –  pjreddie Jun 28 '12 at 23:30
    
+1 I just replaced generic CAT5 cables in my rack with purpose made CAT6 cables and noticed improvement in performance. –  Chris K Jan 22 at 22:16
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