We commonly know QUIC use UDP as its transport layer. UDP has connectless propertey in compartion to TCP..
So could I draw a conclusion that we can freely switch network connection between wifi and 4G mobile?
If it does, the cost of switch is lower than TCP. TCP need 3-way handshake to build connection and UDP doesnot need it.
Yes, this has been built in to the QUIC protocol under the Connection Migration section, though this can be disabled with the disable_active_migration transport parameter so not all QUIC connections may support this.
TCP connections are basically identified and handled by the 4-tuple of client IP, client port, server IP, and server port. This means if any of these change the connection has to be reestablished.
QUIC instead creates a Connection Id, and this can be sent over different connections to reuse the same connection, so benefiting from not having to do the expensive initial 3-way TCP handshake and then the even more expensive TLS handshake, as you say (though these are combined so already smaller in QUIC so there may not be as much benefit in this as there would be if it worked as it currently does in the TCP world).
Perhaps more interestingly this also allows the potential use of multipath where you could use your WiFi connection and your mobile connection at the same time, to increase your bandwidth and download speed. It should be noted however that, for simplicity sake, multipath will not be in the first RFC version of QUIC (due to be formally released and say now), and will be one of the next things the QUIC Working Group work on.
Related
When using a VPN (such as OpenVPN) to make my traffic transit through a specific machine I get TCP over TCP issues and my download speed collapses.
I don't have that problem when I use a SOCKSifier (such as Redsocks) and SOCKS server (such as Dante).
As far as I can understand, both programs create an additional TCP connection to transfer the data. So why is the behavior different?
I've done a lot of reading on TCP over TCP issues, and from my understanding connections collapse because of retransmits happening on both the original TCP connection and the tunnel's connection. Do SOCKSifiers handle these differently than VPNs?
I have some questions about WebRTC:
Does WebRTC use TCP or UDP as its peer-to-peer transport? How can I
know?
I read that there are reliability mode and DTLS agreement, how does
these affect?
Is this transport the same for both Media and DataChannel?
How do I switch between TCP and UDP?
I ask this because I know that browsers have a limit on the number of parallel connections (I think they talk over TCP), and maybe UDP connection is not limited.
It can use either. By default, preference is given to UDP, but depending on the firewall(s) in between the peers connecting it may only be able to connect with TCP. You can use Wireshark to capture packets and verify whether TCP or UDP is being used. In Chrome you can also see details on the selected candidate (googActiveConnection) by going to chrome://webrtc-internals.
"Reliability mode" probably refers to the reliability mode of the DataChannel, which can be configured to run in reliable or unreliable mode. DTLS refers to the currently optional, but soon to be default method of exchanging encryption keys (the other deprecated mode is SDES). Firefox only supports DTLS, so for browser interop, you'll currently need to enable it in Chrome.
The RTCPeerConnection (media) will use TCP or UDP, while the DataChannel uses SCTP. The SCTP implementation used by Firefox is implemented on top of UDP: https://code.google.com/p/sctp-refimpl/.
It's possible to filter out TCP or UDP ICE candidates before adding them with addIceCandidate. Generally, you should not try to force the transport used since WebRTC will just "do the right thing". The browser does not limit the number of TCP connections used by WebRTC beyond any limit on the RTCPeerConnection or DataChannel (i.e., if you can have 10 PeerConnections, they can each use TCP without any problem).
I had a strange idea. I heard of software which from my understanding uses UDP to transfer files decreasing the overhead found in TCP packets.
If my app requires TCP and my LAN has software set up to communicate with another datacenter on the other side of the coast with software setup on their end. Would it be possible to send the actual data via UDP but than simulating TCP on both ends?
Does anyone have any ideas or information about such projects?
If you're asking if you can use UDP as a Layer 2, then the answer is yes, sort of. There are various protocols that allow you to create a tunnel to another network using a UDP transport, such as L2TP and even IPsec (with NAT traversal). You could also do it at the application layer.
If you're asking if TCP can be implemented in UDP, the answer is no. First, TCP packets and UDP packets have an incompatible format. Second, TCP and UDP have different protocol numbers (seen in the IP header) which means that TCP traffic destined for a UDP port would not be passed to the correct upper-layer protocol.
Both TCP and UDP are built on top of the IP, but the TCP uses different packet structure and at the layer-2 it is not possible to mimic the TCP using UDP packets.
Of course, if you have the control on both the source and destination, then it is possible to create a reliable UDP tunnel for the TCP packets. This would require some internal information (packet number, ack/nack flags) in the body of the UDP packet.
There is an interesting project http://udt.sourceforge.net/
It is a broadcast-capable reliable file transfer mechanism built on top the UDP.
PseudoTCP is a protocol which implements TCP algorithms on top of the UDP. It was introduced since the NAT traversal for TCP is much more complicated than UDP. But some P2P applications do need a reliable data transfer among nodes.
So far as I know, there are two PseudoTCP variations: Libjingle and Libnice.Libjingle is an open source library from google which was initially for gtalk. You could take a look at file sharing example from libjingle: https://developers.google.com/talk/libjingle/file_share. Recently, Chrome desktop also use PseudoTCP implementation from libjingle for reliable connections.
Yes, you can develop a protocol on UDP that simulates TCP. However, if you simulated TCP fully, it would technically have more overhead. Because TCP is implement as the packet and your simulated TCP is implemented in the body of the packet.
If you only need one or two features of TCP (such as basic ordering), then implementing it in UDP is useful.
Halo uses 2-3 (IIRC) UDP protocols that simulate different features of TCP, then full fledged TCP for initializing game-states. I Shot You First Networking, GDC publication
For example, in one case, they send 3 duplicate UDP packets to overcome packet loss.
If you control the software on both ends, and it is cost-effective to build your own protocol, then UDP can be versatile.
One way to do it now on Linux-3.18+ is to use Foo over UDP (FOU) which implements Generic UDP Encapsulation (GUE). Here's a good introduction to FOU, and the man page for ip-fou.
Or if you want an [open source] UDP based file transfer system there are things like UDT, UFTP, Tsunami-UDP, and even Google's QUIC (Now deprecated in favour of IETF QUIC).
Update: The QUIC protocol now has been standardised by the IETF which provides for secure reliable and unreliable transport over UDP as an alternative to TCP. There's a wide range of QUIC implementations available. There is also a growing set of protocol mappings on to QUIC such as HTTP/3, DNS over QUIC, etc
If my app requires TCP and my LAN has software setup to communicate
with another datacenter on the other side of the coast with software
setup on their end. Would it be possible to send the actual data via
UDP but than simulating TCP on both ends?
No. A UDP socket is in a different namespace from a TCP socket. You will be unable to write UDP at one end and send or receive TCP at the other end. TCP and UDP are peer protocols; both exist at the layer above IP. You can't use one to spoof the other.
Hmm, I believe so. You'd need to use a proxy at both ends, but it should be possible.
The biggest problem you are going to run into is that UDP is designed with the idea that you don't care if some of the packets don't ever make it to the other end.
Here's a link with some more info:
http://www.cyberciti.biz/faq/key-differences-between-tcp-and-udp-protocols/
IMHO, it's not a good idea to transmit files via UDP.
TCP's problems are in its algorithms, not its headers.
You certainly could implement the TCP algorithms on top of UDP. That would effectively be the same as tunneling TCP datagrams inside of UDP datagrams. But all this accomplishes is to add a few more bytes of overhead to each packet, and require another endpoint to unwrap the packets.
UDP itself is just thin shim on top of IP: its a convenient way to access IP packet switched networking without having to dive into kernels or receive special handling from routers. The main reason to implement reliable transport on top of UDP is to get away from TCP algorithms in favor of something more efficient. FileCatalyst was mentioned above as one company which does this, and my own company Data Expedition, Inc. does so as well.
So you could implement TCP algorithms on top of UDP, but you wouldn't want to.
You can simulate something like a connection over UDP, and you as well can add reliability checks and ordering and retransmission and so on. - but then, it still isn't TCP, it just acts the way.
Of course, one of the ends can be a kind of "hub" or "proxy" which does an adaption. Then you don't have a 2-end solution, but in fact a 4 end solution - one pair with "real" TCP and the other with the "self-knitted" "TCP" - which you put together with an appropriately crafted program.
This question already has answers here:
Difference between TCP and UDP?
(13 answers)
Closed 4 years ago.
What exactly is a TCP connection?
I understand there isn't a physical connection from the client to server. Is this connection just the client's socket being linked with the new socket created by the server after the three-way-handshake?
Thereafter once the "connection" is set up, the sockets on either ends of the connection then know where to send their packets.
How does this differ from the way UDP functions other than the initial handshake with TCP?
Is it that each server socket only has one client that sends packets to that particular socket?
What are some possible advantages of having a dedicated connection between hosts? My understanding of TCP and UDP is still very basic, so broad generalizations should suffice.
Let's break this up into parts. First of, the network is based in IP, which is a protocol that assigns an address to each network node, and which allows you to send small amounts of data (usually up to 64kB, but typically only 1500B) from one node to another.
That by itself isn't worth much yet, because we can't make any checks that the data actually arrived, and that it arrived in the right order. If we want an abstract mechanism to transmit arbitrary amounts of data and ensure that they arrived, we need another protocol on top of the network that handles this "transmission". And that's the purpose of TCP.
However, in parallel to TCP, there's another "transmission" protocol that doesn't do any checking at all and has no reliability, UDP. UDP is just a thin wrapper around raw IP packets, which adds a little bit of meta data (like a port number).
UDP is still useful, though, since there are many situations in which the data integrity is already handed off to an even higher protocol, so there's no need for a complex transmission protocol. This is for example used in virtual networking services, where another instance of TCP/IP is typically run over a UDP channel. (Making the channel use a reliable protocol like TCP can actually have disastrous consequences in that case due to resend cascades.)
So the term "TCP connection" refers to the application of the TCProtocol. The protocol is stateful, naturally, and typically proceeds in a SYN-ACK-data-FIN sequence, or SYN/RST in case of a rejected transmission; both peers maintain a status of the connection (handshake, established, closing, closed.) TCP also introduces the terms "server" and "client", the server being the peer that listen()s for an incoming connection.
The main difference between TCP and UDP sockets is that UDP is conectionless and doesn't use any confirmation that the other end received the data.
The Transmission Control Protocol (TCP) is one of the core protocols of the Internet Protocol Suite. TCP is one of the two original components of the suite, complementing the Internet Protocol (IP), and therefore the entire suite is commonly referred to as TCP/IP. TCP provides reliable, ordered delivery of a stream of bytes from a program on one computer to another program on another computer. TCP is the protocol that major Internet applications such as the World Wide Web, email, remote administration and file transfer rely on. Other applications, which do not require reliable data stream service, may use the User Datagram Protocol (UDP), which provides a datagram service that emphasizes reduced latency over reliability.1
I was told that for a High Frequency Trading (HFT) system that requires low-latency, TCP is used over UDP. I was told that with TCP you can make point to point connections, whereas you cannot with UDP, however from my understanding you can send UDP packets to specific IP/port.
There are several arguments used in this article as to why UDP > TCP for gaming but I can see relevance for HFT.
Why would TCP be a better protocol to use for HFT?
(Admins: My previous post of this question was silently removed with no explanation. If I am violating terms of use please alert me of this instead of silently removing the question)
UDP is superior to TCP if you don't need some of the features TCP provides. Every feature has a cost, and so if you don't need features, you are paying that cost for no reason.
In an HFT application, you need pretty much every feature TCP requires. So if you picked UDP, you'd have to implement those features yourself. That means you'd have to implement connection establishment, connection teardown, retransmissions, transmit pacing, windows, and so on.
If there was a way to do all those things that was better than the way TCP was doing it, TCP would be doing it that way. You'd have one hand tied behind your back because TCP is heavily optimized by some of the best minds on the planet and implemented in/with the kernel.
There's no reasons to expect a stream of data over an already-established TCP connection would be slower than the same data over UDP, plus you get checksumming, retries, and all the other TCP goodness. UDP mainly wins in cases where you can afford to discard the reliability or where the overhead of many TCP handshakes would be too expensive, such as with common DNS queries.
TCP is faster for when using a few connections, the important difference is that modern NICs perform significant amounts of acceleration on TCP and not really that much for UDP. This means there is more overhead to process each UDP packet and as such they cannot compete unless you need to send to multiple recipients simultaneously.
However the UDP multicast route still suffers the same problems as unicast UDP per datagram overheads. Therefore many HFT systems use hardware accelerated systems that can multiplex the streams across many NICs via TCP, example Solace.
These days though you want to completely bypass the kernel with say a userspace IP stack such as by Solarflare or Mellanox, or even skip both the kernel and IP stack with RDMA.
Quite simply, if you need connection reliability (ensuring that every byte of data transmitted is received), you should be using TCP regardless.
As you mentioned, UDP is more suitable for games, where 100% accurate real-time tracking of every object would use quite a large amount of bandwidth and is unnecessary (this is where slow connections encounter lag).
There is no special difference between a TCP port and a UDP port, beyond the type of connection being used (send the packet and forget it, UDP style, or negotiate a connection and sustain it, TCP style) and the service listening on the server side. e.g. TCP/25 would usually reveal a SMTP server, whereas UDP/25 would not.
Basically, modern TCP implementations are going to be just as fast as UDP, if you're keeping the connection alive. If TCP is having to resend a packet, you'd need to resend it in UDP too. Plus for UDP you're going to end up implementing the same reliability code (retransmission of dropped packets) that TCP has already implemented.