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I always hear about the layers of internet and i vaguely understand this. But, what confuse me most is that transport layer (including TCP protocol) lies on top of the internet layer(including IP protocol)..
What does this mean? For one who has a foggy understanding of the internet mechanism (I'm not a CS student or something I am just a hobby programmer)
The picture I have about the internet is that the network card sends/receives signals (packets) from the internet through wired connection / wifi then the OS using socket API sends/receives these packets acting as a layer between the hardware and the application which in turn uses some high-level protocol such as HTTP to interpret the data transferred - these protocol usually provided by languages e.g. python or java
.. I guess then that IP and TCP protocol are used at the level of the socket API? but I need more details ? I hope the explanation be in terms of coding/programming/implementation because abstractions used in this area confuse me.
Thank you , and sorry for my bad English
This is part of a layered solution to solve networking. Each layer has its own functionality:
IP (Internet Protocol) is in charge of delivering a packet (or datagram) from one interface, in one machine, with an IP address assigned to another interface in the same or other machine (node). Both nodes can be in the same LAN or different LAN connected through different paths (LAN's and routers). Basically it will make the packet get from source IP to destination IP. It provides a best-effort services, it doesn't assure the IP packet is going to arrive, it can be lost in the middle.
Above layer 3 or IP in the so-called TCP/IP stack, there is the transport layer. Its main functionality is to multiplex the lower layer (IP) service (take a packet from src to dst) among different applications. This is why in all transport layer protocols there is the concept of port or more generically Transport Service Access Point (TSAP). UDP, TCP, SCTP do that. UDP provides an unreliable service to the application. TCP provides a connected, reliable transport service to the application. This layer will make a message sent from application A in node Y reach application A1 in node Z, either reliably or unreliably (while IP only takes care of carrying the packet from node Y to node Z).
You will need to read a little about the OSI layered model and the TCP/IP layered model.
If you need to get more info I can address you to a training I have about IPv6 with a good introduction to networking: http://www.slideshare.net/rodolk/networking-tcpip-stack-introduction-ipv6
TCP is a protocol, known as "Transmission Control Protocol" - by specification it has features in place which makes sure that transmitted data is checked. On the other hand, there are things such as UDP, aka "User Datagram Protocol" which also works on top of IP - by specification this method does not check any transmitted data, so it's less useful where files must be fully intact (more utilised for video streaming, where some lost frames is acceptable, as opposed to binary file transfers where incorrect data means corruption and the whole file would be useless).
On to IP, IP is an addressing protocol, allowing a network to address and communicate with any machine that lives within it. IP stands for Internet Protocol, and it defines the fundamental way that two machines communicate over the "internet". It does not define how communications are handled, in ways such as being checked for data integrity, etc.
So, to summarise, the TCP and UDP are just extensions of IP. It is entirely possible, however, to have a socket based TCP or UDP connection, and I expect it's also possible to have some sort of MAC address protocol (as opposed to an IP address protocol). I don't know of any protocols which are similar to IP, but I imagine they do exist. In reality, using TCP over something other than IP is entirely unlikely. If you're going to the effort to create a custom protocol, chances are you'll want it fully custom and won't want to stick to design specifications designed for another protocol layer.
Note that calling it a "TCP/IP" connection is probably only ever used for legacy reasons. A lot of terms like this still exist because before the technology "bubble" growth, there were competing alternatives to IP. Even today, there is IPv6 which is technically an alternative to IPv4. It's also possible that we might one day outgrow IPv6, and at that point in time, there could be something other than IP to worry about.
Related
What is the difference between a "tcp/socket" and "tcp/ip" connexion?
When you say that you use "tcp/ip", do you necessarily use a "tcp/socket"?
Thanks!
A socket is a general communication means provided by your
operating system.
There are many kinds of them, for very distinct purposes
(not only networking).
I guess that when you think about tcp/socket, you mean a
socket dedicated to the TCP protocol.
TCP/IP can be seen as two different things, depending on the context.
It can be the TCP/IP network stack as a whole: not only the TCP and IP
specific protocols but the set of protocols (and implementations) we
find around these.
Of course, the other way to see TCP/IP is to consider only the TCP
transport protocol relying on the IP network protocol.
The various operating systems implement many protocols
in the TCP/IP stack.
To use them, a programmer asks his/her operating system
a specific resource: a socket.
It's difficult to say more with few words.
Some books or online documentation could help go further.
I think you missing something in the question. Anyway in short...
TCP/IP is basically name given to protocol we (networking devices) follow it forms the fundamental of todays internet. It involves agreement between two devices how the want ro communicate eg. Which segment of a frame has what information as in the end its all just 10...
There are 5 layers (some argue 4) in this model one layer is Network Layer right at the middle of all and it generally uses IPv4.And just above this is our Transport Layer which may use TCP or UDP as protocol depending on service you want. So thats the summary of TCP/ IP as the most used set of protocols of all.
When connecting to a remote server your browser needs to know what kind of service he is about to get from that server eg. a video mail or file transfer or just a http page. Thats when a TCP/Socket comes into picture where there is a port no assigned for every service. Eg port 443 is for https and so on. All you need to do is open a socket connection over that port number on that machine
Remember if a particular port of a server is not in LISTEN mode you cannot connect to that application via that port
Eg. If a server serves its webpage it might not allow you to connect its port responsible for FTP.
I have a machine, with no external IP address, it will need to send UDP packets to the outside world. Only NAT access.
Will this work?
It is really hard to prototype this in our environment.
It is still really under construction.
Any thoughts on how I can prototype this?
Most of the home network configurations in the world are made of a PC with an internal IP and a router with a public IP that NAT the internal one. (Independently of UDP/TCP or whatever protocol that needs to go out)
I see no troubles with it
It should work.
Ensure that for the socket created, set the TTL (time-to-live) to a value that is sufficiently large to cover the possible number of router hops to reach the destination. Running traceroute to the destination IP will give you a rough idea on the number of hops. Note that this value can change depending on network conditions. So it's best to set this to a larger value. Refer to sockets IOCtl API documentation for the syntax for setting TTL.
Finally, remember that UDP is not a reliable protocol. So even after taking the necessary steps above, the packet may not reach its destination. However, if the entire network, including the intermediary routers, is within a controlled environment, such as a corporate intranet, chances of packet drop are minimal.
If you want to add reliability on top of UDP, you can adopt a NAK based algorithm where packets are stamped with a sequence number. Various resources might advise you that if you need to add reliability over UDP you should consider TCP, but my experience has been that if your app runs in a controlled environment with very minimal chance of packet drops and you need fast connection setup and tear down, adding a lightweight reliability over UDP has its merits. Also TCP connections take up valuable space in the OS kernel whereas UDP don't. This could also be a consideration if you want to support very large number of 'connections' in a constrained environment.
At the end of the day you need to experiment a little to figure out what works best for you.
To prototype, I would set up a NAT server using something like Linux and then start working from there. Real world traffic scenarios that you want to simulate will determine where the client and server are to be located on either side of the NAT. That is, if the traffic should go through an ISP or all within a controlled environment.
HTH
I need to implement a client server architecture where the server sends
the same message to many clients over the internet.
I need to send a single message every 5 minutes about.
The message won't excede 5KB.
I need the solution to scale to a big number of clients connected (50.000-100.000)
I considered a bunch of solutions:
TCP Sockets
UDP Multicast
WCF http duplex service (comet)
I think I have to discard UDP solution because it is a good solution only for clients on the same network and it won't work over the internet.
I read somewhere that WCF multicast will cause a bottleneck if I have many clients connected but I can't find anywhere documentation showing performance statistics.
Tcp sockets seems to me the solution to chose.
What do you think about? Am I correct?
I'm certainly wrong when I say UDP doesn't work on internet... I thought
this because I read some articles pointing out that you need properly
configured routers in the network to support multicasting... I read of the
udp ports multicast range and thought it was meant to be locally.
Instead, the range 224.0.0.1 - 239.255.255.255 (Class D address group), can be reached over the internet
Considering that in my case reliability is not a crucial point, the udp multicast is a good choice.
The .net framework offers really helpful classes to accomplish this.
I can easily start an UdpClient and begin send data on a multicast address with two lines of code.
At client side it is really easy to.
There is the UdpSingleSourceMulticastClient class that does exactly what I need.
For what concernes reliability and security the .net framework has a smart and simple way of handle DoS attacks, DNS Rebinding attacks and Revers tunnel attacks that is described here: http://msdn.microsoft.com/en-us/library/ee707325(v=vs.95).aspx
The main question is: Do you care if the updates get to the clients?
If you DO then you will need to build something on top of UDP to add reliability. UDP datagrams are NOT reliable and so you should expect that some wont get to the destination. This is more likely if you are pushing UDP datagrams out quickly. Note that your clients might also get multiple copies of the same datagram in some situations with UDP.
50-100k connections with this level of traffic shouldn't be that difficult to achieve with TCP if you have a decent architecture.
See here for some blog posts that I've done on the subject.
http://www.serverframework.com/asynchronousevents/2010/10/how-to-support-10000-concurrent-tcp-connections.html
http://www.serverframework.com/asynchronousevents/2010/10/how-to-support-10000-or-more-concurrent-tcp-connections---part-2---perf-tests-from-day-0.html
http://www.serverframework.com/asynchronousevents/2010/12/one-million-tcp-connections.html
And here's some example code that deals with sending data to many clients.
http://www.serverframework.com/ServerFramework/latest/Docs/examples-datadistributionservers.html
Unicast (tcp sockets) will work fine for a relatively small amount of traffic such as this, but keep on top of multicasting technology, the situation is changing every year.
I've been reading up on basic network programming, but am having a difficult time finding a straight-forward explanation for what exactly and socket is, and how it relates to either the OSI or TCP/IP stack.
Can someone explain to me what a socket is? Is it a programmer- or API-defined data structure, or is it a hardware device on a network card?
What layers of the mentioned network models deal with "raw" sockets? Transport layer? Network layer?
In terms of the data they pass between them, are socket text-based or binary?
Is there an alternative to sockets-based network programming? Or do all networked applications use some form of socket?
If I can get this much I should have a pretty clear understanding of everything else I'm reading. Thanks for any help!
Short answers:
Socket is an abstraction of an IP connection endpoint - so if you think of it as an API structure, you are not very far off. Please do read http://en.wikipedia.org/wiki/Internet_socket
Internet layer i.e. IP Protocol. In practice you usually use explicitly sockets that bind to a certain transport layer parameters (datagram/UDP or stream/TCP)
Sockets send data, in network byte order - whether it is text or binary, depends on the upper layer protocol.
Theoretically, probably yes - but in practice all IP traffic is done using 'sockets'
Socket is a software mechanism provided by the operating system. Like its name implies, you can think of it like an "electrical outlet" or some electrical connector, even though socket is not a physical device, but a software mechanism. In real world when you have two electrical connectors, you can connect them with a wire. In the same way in network programming you can create one socket on one computer and another socket on another computer and then connect those sockets. And when you write data to one of them, you receive it on the other one. There are also a few different kinds of sockets. For example if you are programming a server software, you want to have a listening socket which never sends or receives actual data but only listens for and accepts incoming connections and creates a new socket for each new connection.
A socket, in C parlance, is a data structure in kernel space, corresponding to one end-point of a UDP or TCP session (I am using session very loosely when talking about UDP). It's normally associated with one single port number on the local side and seldom more than one "well-known" number on either side of the session.
A "raw socket" is an end-point on, more or less, the physical transport. They're seldom used in applications programming, but sometimes used for various diagnostic things (traceroute, ping, possibly others) and may required elevated privileges to open.
Sockets are, in their nature, a binary octet-transport. It is not uncommon to treat sockets (TCP sockets, at least) as being text-based streams.
I have not yet seen a programming model that doesn't involve something like sockets, if you dig deep enough, but there have certainly been other models of doing networking. The "/net/" pseudo-filesystem, where opening "/net/127.0.0.0.1/tcp/80" (or "tcp/www") would give you a file handle where writes end up on a web server on localhost is but one.
Suppose your PC at home, and you have two browser windows open.
One looking at the facebook website, and the other at the Yahoo website.
The connection to facebook would be:
Your PC – IP1+port 30200 ——– facebook IP2 +port 80 (standard port)
The combination IP1+30200 = the socket on the client computer and IP2 + port 80 = destination socket on the facebook server.
The connection to Yahoo would be:
your PC – IP1+port 60401 ——–Yahoo IP3 +port 80 (standard port)
The combination IP1+60401 = the socket on the client computer andIP3 + port 80 = destination socket on the Yahoo server.
Is it possible to multiplex sa ocket connection?
I need to establish multiple connections to yahoo messenger and i am looking for a way to do this efficiently without having to hold a socket open for each client connection.
so far i have to use one socket for each client and this does not scale well above 50,000 connections.
oh, my solution is for a TELCO, so i need to at least hit 250,000 to 500,000 connections
i'm planing to bind multiple IP addresses to a single NIC to beat the 65k port restriction per IP address.
Please i would any help, insight i can get.
**most of my other questions on this site have gone un-answered :) **
Thanks
This is an interesting question about scaling in a serious situation.
You are essentially asking, "How do I establish N connections to an internet service, where N is >= 250,000".
The only way to do this effectively and efficiently is to cluster. You cannot do this on a single host, so you will need to be able to fragment and partition your client base into a number of different servers, so that each is only handling a subset.
The idea would be for a single server to hold open as few connections as possible (spreading out the connectivity evenly) while holding enough connections to make whatever service you're hosting viable by keeping inter-server communication to a minimum level. This will mean that any two connections that are related (such as two accounts that talk to each other a lot) will have to be on the same host.
You will need servers and network infrastructure that can handle this. You will need a subnet of ip addresses, each server will have to have stateless communication with the internet (i.e. your router will not be doing any NAT in order to not have to track 250,000+ connections).
You will have to talk to AOL. There is no way that AOL will be able to handle this level of connectivity without considering cutting your connection off. Any service of this scale would have to be negotiated with AOL so both you and they would be able to handle the connectivity.
There are i/o multiplexing technologies that you should investigate. Kqueue and epoll come to mind.
In order to write this massively concurrent and teleco grade solution, I would recommend investigating erlang. Erlang is designed for situations such as these (multi-server, massively-multi-client, massively-multithreaded telecommunications grade software). It is currently used for running Ericsson telephone exchanges.
While you can listen on a socket for multiple incoming connection requests, when the connection is established, it connects a unique port on the server to a unique port on the client. In order to multiplex a connection, you need to control both ends of the pipe and have a protocol that allows you to switch contexts from one virtual connection to another or use a stateless protocol that doesn't care about the client's identity. In the former case you'd need to implement it in the application layer so that you could reuse existing connections. In the latter case you could get by using a proxy that keeps track of which server response goes to which client. Since you're connecting to Yahoo Messenger, I don't think you'll be able to do this since it requires an authenticated connection and it assumes that each connection corresponds to a single user.
You can only multiplex multiple connections over a single socket if the other end supports such an operation.
In other words it's a function protocol - sockets don't have any native support for it.
I doubt yahoo messenger protocol has any support for it.
An alternative (to multiple IPs on a single NIC) is to design your own multiplexing protocol and have satellite servers that convert from the multiplex protocol to the yahoo protocol.
I'll trow in another approach you could consider (depending on how desperate you are).
Note that operating system TCP/IP implementations need to be general purpose, but you are only interested in a very specific use-case. So it might make sense to implement a cut-down version of TCP/IP (which only handles your use-case, but does that very well) in your application code.
For example, if you are using Linux, you could route a couple of IP addresses to a tun interface and have your application handle the IP packets for that tun interface. That way you can implement TCP/IP (optimised for your use-case) entirely in your application and avoid any operating system restriction on the number of open connections.
Of course, it's quite a bit of work doing the TCP/IP yourself, but it really depends on how desperate you are - i.e. how much hardware can you afford to throw at the problem.
500,000 arbitrary yahoo messenger connections - is your telco doing this on behalf of Yahoo? It seems like whatever solution has been in place for many years now should be scalable with the help of Moore's Law - and as far as I know all the IM clients have been pretty effective for a long time, and there's no pressing increase in demand that I can think of.
Why isn't this a reasonable problem to address with hardware plus traditional solutions?