How to select another sink node if the current sink node is offline (TCP connection)?

[Ding Ding]

Hi all:

I am new to NS3 community. Currently I meet a problem, described as following:

The topology is simple

c ------ s1

Node c is a client node, and it connects to Node s1 that is a sink node who receives data from Node c (Similar to the TCP Bulk Send). At some points, s1 go offline. How can node c knows this information and connects to another node s2? I currently use NS3::Socket to connect these two nodes. I suppose changing a remote sink node is easy to do by using the function "connect()". However, I didn't find any callback function triggered by the timeout (as well as retransmission times). 

I tried several ways, but none of these are useful. For example, it is not a good idea to use the return value of function "send()", I think it returns -1 when buffer is full, not remote server is down. I don't think I can use ns3::TcpSocketBase, because it cannot trigger the "changing another server" behavior. 

Do you have any idea how to solve this problem? I think it is a simple problem, maybe I focused on the wrong Class. If you give some suggestions, could you please give something detail? thanks in advance!!!

Best,

Ding

[Tommaso Pecorella]

There's no way to do that, but the problem isn't ns-3.

A TCP stream can NOT be switched to a different host once the connection is started. You need to close it and reopen it. That's TCP.

T.

[Ding Ding]

Thanks Tommaso!

I know that we need to close the connection first, then establish another one to send traffic. 

What I mean here is the following: when the sink node (s1) go offline, how can the sender (c) knows? I do not find any callback function (inform sender that the sink is offline) from NS3::Socket class. 

I use two ways to turn off the sink, none of them could trick the callback function of sender.

(1) close the sink application

(2) Simulator::Schedule (Seconds (nodeDown),&Ipv4::SetDown,ipv4, ipv4ifIndex);

Best,

Ding

在 2017年2月25日星期六 UTC-5下午7:09:40，Tommaso Pecorella写道：

[Tommaso Pecorella]

The socket will use callback to signal its transition in a closed state, eventually... after 4 minutes of inactivity.

You can change it by modifying the MaxSegLifetime attribute of TcpSocketBase (The callback is fired after 2*MaxSegLifetime).

T.