What max Internet speed of a PC can get if 3 PCs are connected to 210 Mbps router

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Ellicott

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Apr 19, 2014
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Hello,

I am thinking about this question for a couple of hours and can not find an answer. I am wondering if someone can help.

A) If three same PCs with gigabit Ethernet card are directly connected to a 210 Mbps bandwidth router which connecting to a modem, then go to Internet. What max Internet speed each PC can get? Assume three PCs are all online streaming at same time. The bandwidth of Internet is 105 Mbps.

A. 210 Mbps
B. 105 Mbps
C. 70 Mbps
D. 35 Mbps

B) If these three same PCs are directly connected to a 10/100/1000 switch first, then the switch connects to the router, will max Internet speed of each PC increase or remain same as in case A?

Thanks for your helps,
 
Solution
B
As long as the router is faster than the internet it really doesn't matter. Obviously even the fastest 100m router will only go 100m and a 1g router will get the extra 5m assuming you ever get that from the ISP.

The traffic mix is critical to the performance of a router. Many of the tests sites open a single file transfer and push maximum packet size. This will greatly inflate the throughput. Say instead it opens a separate session for each packet still sending the maximum size. In that case the router must create a nat entry for each packet. It takes time to do that. Of course it never is that bad but it is as silly as opening a single session and trying to say that represent throughput. The other issue is that the packet...
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Ellicott

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Apr 19, 2014
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Thank Outlander. Do you imply that each PC can get 35 Mbps roughly as sharing 105 Mbps Internet? If the router is 10/100 LAN router, then the router should not be the problem for sharing bandwidth?

Thanks.
 
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Ellicott

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Well. my friend has two same PCs with gigabit Ethernet card. These two PCs are directly connected to a 10/100 Mbps bandwidth router which connecting to a modem, then go to Internet. Guess what is the Internet speed when one PC accesses to Internet and two PC access to Internet respectively (The Internet bandwidth is 105 Mbps)

"bandwidth has to be shared" is still not clear bandwidth portion each PC is using.



 
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bill001g

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This almost looks like a homework question.

Very technically none of the answers are correct because they are being overly simplistic. When data is being constrained traffic is randomly dropped and the response to the lost traffic by the application varies a lot.

So if all 3 PC are streaming 1g of data though a 100m connection 2.9g of data must be discarded. It is completely random so it is impossible to predict how much any particular device gets. Realistically all three would in effect get no "usable" data through the connection because of the excessive discards.
 
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Ellicott

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Apr 19, 2014
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Thanks Bill for reading my post.

In your case if I use a 10/100 WAN/LAN router instead of a 210 Mbps gigabit router, will be significant speed slow down for each computer? If so, why.

appreciate your comments.
 
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bill001g

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No it is already constrained by the internet but what is a 210mbs router. A router does not pass fixed amount of traffic. It will pass more or less traffic based on the packet sizes and what it need to do to process the packets. Almost all commercial routers are rated on packet per second not mbs.
 
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Ellicott

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"but what is a 210mbs router"

It is an ASUS gigabit wireless router.

If the bandwidth from the modem is 105 Mbps, will be significant differences between 10/100 WAN/LAN router and a gigabit router for 3 computers which are using streaming data from Internet? Your answer seems imply that a gigabit router is useless in terms of raising speed because a router does not pass fixed amount of traffic in the situation. Do I understand correctly?

additional information: With 105 Mbps bandwidth from the modem and connect to a 10Mbps WAN/100 Mbps LAN router, speed test shows on a PC only support 20 Mbps Internet speed regardless it is one PC or 3 PCs access to Internet. Does that imply if you use a gigabit router, each of three computer can get up to 105 Mbps speed for access to Internet when these three computer share the bandwidth at the same time?

 
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bill001g

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As long as the router is faster than the internet it really doesn't matter. Obviously even the fastest 100m router will only go 100m and a 1g router will get the extra 5m assuming you ever get that from the ISP.

The traffic mix is critical to the performance of a router. Many of the tests sites open a single file transfer and push maximum packet size. This will greatly inflate the throughput. Say instead it opens a separate session for each packet still sending the maximum size. In that case the router must create a nat entry for each packet. It takes time to do that. Of course it never is that bad but it is as silly as opening a single session and trying to say that represent throughput. The other issue is that the packet size greatly influences the throughput. When the router receives a packet it must do lots of work to modify the packet headers to change the IP and recalculate the checksums etc. a minimum size packet of 64 bytes takes the same overhead as a 1500 byte packet. If the router can pass say 100 packets/sec in one case you get 6.4kbytes/sec or you get 150kbytes/sec. Since the packet mix tends to be random you can't realistically predict throughput.
This is why commercial routers rate the speed in packet/sec with 64 byte packets....ie worst case.

Now this is only the NAT part. A router is generally running QoS and firewall rules as well as encrypting the data for the wireless.

What I am saying is for consumer routers that do not specify anything you can not even begin to predict some throughput speed. You go into juniper or cisco site and look for equipment...especially vpn routers and they very clearly spell out how much data you can get though each device. You think a company would really pay $5000 for a router if they could use a $300 router just because it has gig ports.

With consumer routers you can only guess. Many can pass well over 100m of traffic in your average house so nobody seems to care. The people that have things like google 1g fiber have quickly found the limitations in these routers.
 
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