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New Member

To reduce the no. of acks.

We are offering Internet services on VSATs with a central router 7206 connected to ISP performing the NAT. Most of the transactions on the VSATs are http. Recently connected sniffer and noticed almost half of the bandwidth is occupied by the TCP ACK. For every 2 packets there is a ack.

Wondering if this is how the http works ?.

1. Any idea how to minimize the acks on the central router ( 7206 ).

2. Noticing the NAT translation table, for every URL that a VSAT requests, there are almost 5 to 10 DNS entries for that request in the NAT table. Is this right or there should be just one DNS request.

Any inputs are highly appreciated.

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5 REPLIES
New Member

Re: To reduce the no. of acks.

You said ANY inputs.

If I understand you right, the TCP acks over your SATCOM are killing your bandwidth. I heard once about a device made by SkyX that spoofs the acks thereby improving throughput but watch out for retransmissions.

Don't know if this is what you are looking for.

Good Luck

New Member

Re: To reduce the no. of acks.

Thanks for input.

You are right the acks are killing the bandwidth, but my concern is for http every 2 packets there is a ack. With windows size of 64K and MTU of 1500 bytes the acks need to come after 40 frames , why is that every 2 packets ther is a ack ?. I have even implemented TCP SAK ( selective ack ) but there is no imrovement.

The next question regarding DNS query. EVen a simple page with just user name and password located on a single server there are 5 quereis ( supposed to be only one query ). The ultimate aim is to redue traffic on satellite bandwidth. Any idea whay there are some many queries ?.

New Member

Re: To reduce the no. of acks.

I have seen the DNS issue on our own VSAT. When checking with an analyzer, we saw a timeout issue due to delay over the VSAT link. There were two to three DNS requests made before the response to the first request was seen by the host. Check times on all your frames and add the delay across VSAT to determine true times at the host and server and I think you will find the first DNS request has not made it back to the host before a timer expires and generates another request.

New Member

Re: To reduce the no. of acks.

Thanks

Since all the remote VSATs are accessing the internet, we would not be able to adjust the timers either at the servers or the clients. Is there any better way of doing this.

New Member

Re: To reduce the no. of acks.

Adjusting TCP timers at the end points is the only way to reduce the number of replies or "small" ACKs. You can not fix this problem at routers. It must be done at the clients and server end points.

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