If you start with the problem of how to create a reliable stream of data on top of an unreliable datagram layer, then the solution that comes out will look virtually identical to TCP. It just is the right solution for the job.

The three drawbacks of the original TCP algorithm were the window size (the maximum value is just too small for today's speeds), poor handling of missing packets (addressed by extensions such as selective-ACK), and the fact that it only manages one stream at a time, and some applications want multiple streams that don't block each other. You could use multiple TCP connections, but that adds its own overhead, so SCTP and QUIC were designed to address those issues.

The congestion control algorithm is not part of the on-the-wire protocol, it's just some code on each side of the connection that decides when to (re)send packets to make the best use of the available bandwidth. Anything that implements a reliable stream on top of datagrams needs to implement such an algorithm. The original ones (Reno, Vegas, etc) were very simple but already did a good job, although back then network equipment didn't have large buffers. A lot of research is going into making better algorithms that handle large buffers, large roundtrip times, varying bandwidth needs and also being fair when multiple connections share the same bandwidth.

• bobmcnamara

  today at 9:04 AM

  > If you start with the problem of how to create a reliable stream of data on top of an unreliable datagram layer, then the solution that comes out will look virtually identical to TCP.

  I'll add that at the time of TCP's writing, the telephone people far outnumbered everyone else in the packet switching vs circuit switching debate. TCP gives you a virtual circuit over a packet switched network as a pair of reliable-enough independent byte streams over IP. This idea, that the endpoints could implement reliability through retransmission came from an earlier French network, Cylades, and ends up being a core principle of IP networks.

  • Karrot_Kream

    today at 9:37 AM

    We're still "suffering" from the latency and jitter effects of the packet switching victory. (The debate happened before my time and I don't know if I would have really agreed with circuit switching.) Latency and jitter on the modern Internet are very best effort emphasis on "effort".

    • lxgr

      today at 11:51 AM

      True, but with circuit switching, we'd probably still be paying by the minute, so most of these jittery/bufferbloated connections would not exist in the first place.

• rkagerer

  today at 1:00 PM

  it only manages one stream at a time

  I'll take flak for saying it, but I feel web developers are partially at fault for laziness on this one. I've often seen them trigger a swath of connections (e.g. for uncoordinated async events), when carefully managed multiplexing over one or a handful will do just fine.

  Eg. In prehistoric times I wrote a JavaScript library that let you queue up several downloads over one stream, with control over prioritization and cancelability.

  It was used in a GreaseMonkey script on a popular dating website, to fetch thumbnails and other details of all your matches in the background. Hovering over a match would bring up all their photos, and if some hadn't been retrieved yet they'd immediately move to the top of the queue. I intentionally wanted to limit the number of connections, to avoid oversaturating the server or the user's bandwidth. Idle time was used to prefetch all matches on the page (IIRC in a sensible order responsive to your scroll location). If you picked a large enough pagination, then stepped away to top up your coffee, by the time you got back you could browse through all of your recent matches instantly, without waiting for any server roundtrip lag.

  It was pretty slick. I realize these days modern stacks give you multiplexing for free, but to put in context this was created in the era before even JQuery was well-known.

  Funny story, I shared it with one of my matches and she found it super useful but was a bit surprised that, in a way, I was helping my competition. Turned out OK... we're still together nearly two decades later and now she generously jokes I invented Tinder before it was a thing.

• NooneAtAll3

  today at 9:43 AM

  > If you start with the problem of how to create a reliable stream of data on top of an unreliable datagram layer

  > poor handling of missing packets

  so it was poor at exact thing it was designed for?

  • silvestrov

    today at 10:57 AM

    Poor for high speed connections () or very unreliable connections.

    ) compared to when TCP was invented.

    When I started at university the ftp speed from the US during daytime was 500 bytes per second! You don't have many unacknowledged packages in such a connection.

    Back then even a 1 megabits/sec connection was super high speed and very expensive.

  • allarm

    today at 10:55 AM

    It was a trade off at the time. Selective acknowledgments require more resources.

• rini17

  today at 11:10 AM

  Might be obvious in hindsight, but it was not clear at all back then, that the congestion is manageable this way. There were legitimate concerns that it will all just melt down.

Any love for SCTP?

> The Stream Control Transmission Protocol (SCTP) is a computer networking communications protocol in the transport layer of the Internet protocol suite. Originally intended for Signaling System 7 (SS7) message transport in telecommunication, the protocol provides the message-oriented feature of the User Datagram Protocol (UDP) while ensuring reliable, in-sequence transport of messages with congestion control like the Transmission Control Protocol (TCP). Unlike UDP and TCP, the protocol supports multihoming and redundant paths to increase resilience and reliability.

[…]

> SCTP may be characterized as message-oriented, meaning it transports a sequence of messages (each being a group of bytes), rather than transporting an unbroken stream of bytes as in TCP. As in UDP, in SCTP a sender sends a message in one operation, and that exact message is passed to the receiving application process in one operation. In contrast, TCP is a stream-oriented protocol, transporting streams of bytes reliably and in order. However TCP does not allow the receiver to know how many times the sender application called on the TCP transport passing it groups of bytes to be sent out. At the sender, TCP simply appends more bytes to a queue of bytes waiting to go out over the network, rather than having to keep a queue of individual separate outbound messages which must be preserved as such.

> The term multi-streaming refers to the capability of SCTP to transmit several independent streams of chunks in parallel, for example transmitting web page images simultaneously with the web page text. In essence, it involves bundling several connections into a single SCTP association, operating on messages (or chunks) rather than bytes.

* https://en.wikipedia.org/wiki/Stream_Control_Transmission_Pr...

Wait, can you actually just use IP? Can I just make up a packet and send it to a host across the Internet? I'd think that all the intermediate routers would want to have an opinion about my packet, caring, at the very least, that it's either TCP or UDP.

• ilkkao

  today at 8:48 AM

  You can definitely craft an IP packet by hand and send it. If it's IPv4, you need to put a number between 0 and 255 to the protocol field from this list: https://www.iana.org/assignments/protocol-numbers/protocol-n...

  Core routers don't inspect that field, NAT/ISP boxes can. I believe that with two suitable dedicated linux servers it is very possible to send and receive single custom IP packet between them even using 253 or 254 (= Use for experimentation and testing [RFC3692]) as the protocol number

  • morcus

    today at 1:46 PM

    What happens when the remaining 104 unassigned protocol numbers are exhausted?

  • Twisol

    today at 8:51 AM

    > If it's IPv4, you need to put a number between 0 and 255 to the protocol field from this list:

    To save a skim (though it's an interesting list!), protocol codes 253 and 254 are suitable "for experimentation and testing".

  • inglor_cz

    today at 9:29 AM

    This is an interesting list; it makes you appreciate just how many obscure protocols have died out in practice. Evolution in networks seems to mimic evolution in nature quite well.

  • stavros

    today at 9:26 AM

    Very interesting, thanks!

• xorcist

  today at 11:05 AM

  > caring, at the very least, that it's either TCP or UDP.

  You left out ICMP, my favourite! (And a lot more important in IPv6 than in v4.)

  Another pretty well known protocol that is neither TCP nor UDP is IPsec. (Which is really two new IP protocols.) People really did design proper IP protocols still in the 90s.

  > Can I just make up a packet and send it to a host across the Internet?

  You should be able to. But if you are on a corporate network with a really strict firewalling router that only forwards traffic it likes, then likely not. There are also really crappy home routers which gives similar problems from the other end of enterpriseness.

  NAT also destroyed much of the end-to-end principle. If you don't have a real IP address and relies on a NAT router to forward your data, it needs to be in a protocol the router recognizes.

  Anyway, for the past two decades people have grown tired of that and just piles hacks on top of TCP or UDP instead. That's sad. Or who am I kidding? Really it's on top of HTTP. HTTP will likely live on long past anything IP.

  • gruturo

    today at 11:51 AM

    > NAT also destroyed much of the end-to-end principle. If you don't have a real IP address and relies on a NAT router to forward your data, it needs to be in a protocol the router recognizes.

    Not necessarily. Many protocols can survive being NATed if they don't carry IP/port related information inside their payload. FTP is a famous counterexample - it uses a control channel (TCP21) which contains commands to open data channels (TCP20), and those commands specify IP:port pairs, so, depending on the protocol, a NAT router has to rewrite them and/or open ports dynamically and/or create NAT entries on the fly. A lot of other stuff has no need for that and will happily go through without any rewriting.

    • xorcist

      today at 12:40 PM

      I think we agree. Of course a NAT router with an application proxy such as FTP or SIP can relay and rewrite traffic as needed.

      TCP and UDP have port numbers that the NAT software can extract and keep state tables for, so we can send the return traffic to its intended destination.

      For unknown IP protocols that is not possible. It may at best act like network diode, which is one way of violating the end-to-end principle.

      • Hikikomori

        today at 1:18 PM

        You can NAT on IP protocol as well, just not to more than one per external IP.

    • lxgr

      today at 12:02 PM

      Of course NAT allows application layer protocols layered on TCP or UDP to pass through without the NAT understanding the application layer – otherwise, NATted networks would be entirely broken.

      The end-to-end principle at the IP layer (i.e. having the IP forwarding layer be agnostic to the transport layer protocols above it) is still violated.

      • Hikikomori

        today at 1:19 PM

        You can NAT on IP protocol as well, just not to more than one per external IP.

  • lxgr

    today at 11:58 AM

    > You left out ICMP, my favourite!

    Even ICMP has a hard time traversing NATs and firewalls these days, for largely bad reasons. Try pinging anything in AWS, for example...

    • 6031769

      today at 12:22 PM

      Have to say that I don't encounter any problems pinging hosts in AWS.

      If any host is firewalling out ICMP then it won't be pingable but that does not depend on the hosting provider. AWS is no better or worse than any other in that regard, IME.

    • Hikikomori

      today at 12:59 PM

      Doesn't really have anything to do with nat though.

• Karrot_Kream

  today at 9:35 AM

  If there's no form of NAT or transport later processing along your path between endpoints you shouldn't have an issue. But NAT and transport and application layer load balancing are very common on the net these days so YMMV.

  You might have more luck with an IPv6 packet.

• gruturo

  today at 11:44 AM

  Yep it's full of IP protocols other than the well-known TCP, UDP and ICMP (and, if you ever had the displeasure of learning IPSEC, its AH and ESP).

  A bunch of multicast stuff (IGMP, PIM)

  A few routing protocols (OSPF, but notably not BGP which just uses TCP, and (usually) not MPLS which just goes over the wire - it sits at the same layer as IP and not above it)

  A few VPN/encapsulation solutions like GRE, IP-in-IP, L2TP and probably others I can't remember

  As usual, Wikipedia has got you covered, much better than my own recollection: https://en.wikipedia.org/wiki/List_of_IP_protocol_numbers

  • lxgr

    today at 11:55 AM

    To GPs point, though, most of these will unfortunately be dropped by most middleboxes for various reasons.

    Behind a NA(P)T, you can obviously only use those protocols that the translator knows how to remap ports for.

    • Hikikomori

      today at 1:01 PM

      Can also do 1:1 NAT for IP protocols like ipsec, or your own protocol.

• nly

  today at 10:55 AM

  The reason you wouldn't do that is IP doesn't give you a mechanism to share an IP address with multiple processes on a host, it just gets your packets to a particular host.

  As soon as you start thinking about having multiple services on a host you end up with the idea of having a service id or "port"

  UDP or UDP Lite gives you exactly that at the cost of 8 bytes, so there's no real value in not just putting everything on top of UDP

• Twisol

  today at 8:43 AM

  As far as I'm aware, sure you can. TCP packets and UDP datagrams are wrapped in IP datagrams, and it's the job of an IP network to ship your data from point A (sender) to point B (receiver). Nodes along the way might do so-called "deep packet inspection" to snoop on the payload of your IP datagrams (for various reasons, not all nefarious), but they don't need to do that to do the basic job of routing. From a semantic standpoint, the information in the TCP and UDP headers (as part of the IP payload) is only there to govern interactions between the two endpoint parties. (For instance, the "port" of a TCP or UDP packet is a node-local identifier for one of many services that might exist at the IP address the packet was routed to, allowing many services to coexist at the same node.)

  • HPsquared

    today at 10:31 AM

    Huh. So it's literally "TCP over IP" like the name suggests.

  • stavros

    today at 9:25 AM

    Hmm, I thought intermediate routers use the TCP packet's bits for congestion control, no? Though I guess they can probably just use the destination IP for that.

    • Twisol

      today at 9:34 AM

      They probably can do deep/shallow packet inspection for that purpose (being one of the non-nefarious applications I alluded to), but that's not to say their correct functioning relies on it. Those routers also need to support at least UDP, and UDP provides almost no extra information at that level -- just the source and destination ports (so, perhaps QoS prioritization) and the inner payload's length and checksum (so, perhaps dropping bad packets quickly).

      If middleware decides to do packet inspection, it better make sure that any behavioral differences (relative to not doing any inspection) is strictly an optimization and does not impact the correctness of the link.

      Also, although I'm not a network operator by any stretch, my understanding is that TCP congestion control is primarily a function of the endpoints of the TCP link, not the IP routers along the way. As Wikipedia explains [0]:

      > Per the end-to-end principle, congestion control is largely a function of internet hosts, not the network itself.

      [0]: https://en.wikipedia.org/wiki/TCP_congestion_control

• eqvinox

  today at 11:45 AM

  > I'd think that all the intermediate routers would want to have an opinion about my packet, caring, at the very least, that it's either TCP or UDP.

  They absolutely don't. Routers are layer 3 devices; TCP & UDP are layer 4. The only impact is that the ECMP flow hashes will have less entropy, but that's purely an optimization thing.

  Note TCP, UDP and ICMP are nowhere near all the protocols you'll commonly see on the internet — at minimum, SCTP, GRE, L2TP and ESP are reasonably widespread (even a tiny fraction of traffic is still a giant number considering internet scales).

  You can send whatever protocol number with whatever contents your heart desires. Whether the other end will do anything useful with it is another question.

  • lxgr

    today at 12:06 PM

    > They absolutely don't. Routers are layer 3 devices;

    Idealized routers are, yes.

    Actual IP paths these days usually involve at least one NAT, and these will absolutely throw away anything other than TCP, UDP, and if you're lucky ICMP.

• gsliepen

  today at 8:39 AM

  They shouldn't; the whole point is that the IP header is enough to route packets between endpoints, and only the endpoints should care about any higher layer protocols. But unfortunately some routers do, and if you have NAT then the NAT device needs to examine the TCP or UDP header to know how to forward those packets.

  • Hikikomori

    today at 1:11 PM

    Can also NAT using IP protocol.

  • jadamson

    today at 9:25 AM

    Notably, QUIC (and thus HTTP/3) uses UDP instead of a new protocol number for this reason.

    • stavros

      today at 9:27 AM

      Yeah, this is basically what I was wondering, why QUIC used UDP instead of their own protocol if it's so straightforward. It seems like the answer may be "it's not as interference-free as they'd like it".

      • Twisol

        today at 9:45 AM

        UDP pretty much just tacks a source/destination port pair onto every IP datagram, so its primary function is to allow multiple independent UDP peers to coexist on the same IP host. (That is, UDP just multiplexes an IP link.) UDP as a protocol doesn't add any additional network guarantees or services on top of IP.

        QUIC is still "their own protocol", just implemented as another protocol nested inside a UDP envelope, the same way that HTTP is another protocol typically nested inside a TCP connection. It makes some sense that they'd piggyback on UDP, since (1) it doesn't require an additional IP protocol header code to be assigned by IANA, (2) QUIC definitely wants to coexist with other services on any given node, and (3) it allows whatever middleware analyses that exist for UDP to apply naturally to QUIC applications.

        (Regarding (3) specifically, I imagine NAT in particular requires cooperation from residential gateways, including awareness of both the IP and the TCP/UDP port. Allowing a well-known outer UDP header to surface port information, instead of re-implementing ports somewhere in the QUIC header, means all existing NAT implementations should work unchanged for QUIC.)

      • lxgr

        today at 12:10 PM

        It's effectively impossible to use anything other than TCP or UDP these days.

        Some people here will argue that it actually really is, and that everybody experiencing issues is just on a really weird connection or using broken hardware, but those weird connections and bad hardware make up the overwhelming majority of Internet connections these days.

      • conradludgate

        today at 10:14 AM

        When it comes to QUIC, QUIC works best with unstable end-user internet (designed for http3 for the mobile age). Most end-user internet access is behind various layers of CGNAT. The way that NAT works is by using your port numbers to increase the address space. If you have 2^32 IPv4 addresses, you have 2^48 IPv4 address+port pairs. All these NAT middleboxes speak TCP and UDP only.

        Additionally, firewalls are also designed to filter out any weird packets. If the packet doesn't look like you wanted to receive it, it's dropped. It usually does this by tracking open ports just like NAT, therefore many firewalls also don't trust custom protocols.

• LeoPanthera

  today at 8:50 AM

  You know I've always wondered if you could run Kermit*-over-IP, without having TCP inbetween.

  *The protocol.

• GardenLetter27

  today at 11:42 AM

  Probably not, loads of routers are even blocking parts of ICMP.

  • eqvinox

    today at 11:46 AM

    That's firewalls (or others), not routers. If it blocks things, it's by definition not a router anymore.

    • lxgr

      today at 12:09 PM

      You can call the things mangling IP addresses and TCP/UDP ports what you want, but that will unfortunately not make them go away and stop throwing away non-TCP/UDP traffic.

• NooneAtAll3

  today at 9:45 AM

  something like this?

  https://en.wikipedia.org/wiki/IP_over_Avian_Carriers

  • Twisol

    today at 9:51 AM

    That would be IP over some lower level physical layer, not some custom content stuffed into an IP packet :)

    (It's absolutely worth reading some of those old April Fools' RFCs, by the way [0]. I'm a big fan of RFC 7168, which introduced HTTP response code 418 "I'm a teapot".)

    [0]: https://en.wikipedia.org/wiki/April_Fools%27_Day_Request_for...

• immibis

  today at 10:32 AM

  Yes but not if you or they are behind NAT. It's a shame port numbers aren't in IP.

TCP is one of the great works of the human mind, but it did not envision the dominance of semiconnected networks.

Its trivial to develop your own protocols on top of IP. It was trivial like 15 years ago in python (without any libraries) just handcrafted packets (arp, ip etc).

It’s worth considering how the tiny computers of the era forced a simple clean design. IPv6 was designed starting in the early 90s and they couldn’t resist loading it up with extensions, though the core protocol remains fine and is just IP with more bits. (Many of the extensions are rarely if ever used.)

If the net were designed today it would be some complicated monstrosity where every packet was reminiscent of X.509 in terms of arcane complexity. It might even have JSON in it. It would be incredibly high overhead and we’d see tons of articles about how someone made it fast by leveraging CPU vector instructions or a GPU to parse it.

This is called Eroom’s law, or Moore’s law backwards, and it is very real. Bigger machines let programmers and designers loose to indulge their desire to make things complicated.

> The internet is incredible. It’s nearly impossible to keep people away from.

Well ... he seems very motivated. I am more skeptical.

For instance, Google via chrome controls a lot of the internet, even more so via its search engine, AI, youtube and so forth.

Even aside from this people's habits changed. In the 1990s everyone and their Grandma had a website. Nowadays ... it is a bit different. We suddenly have horrible blogging sites such as medium.com, pestering people with popups. Of course we also had popups in the 1990s, but the diversity was simply higher. Everything today is much more streamlined it seems. And top-down controlled. Look at Twitter, owned by a greedy and selfish billionaire. And the US president? Super-selfish too. We lost something here in the last some 25 years.

• Nervhq

  today at 12:10 PM

  [dead]

i have an idea for a new javascript framework

I hate to think of the future of these nice blog posts, that need to struggle to convince the readers about the organic level of their content.

I can easily spot it's an AI written article, because it actually explains the technology in understandable human language. A human would have written it the way it was either presented to them in university or in bloated IT books: absolutely useless.

• omnimus

  today at 10:58 AM

  I can easily spot it's an AI written comment, because it actually explains their idea in understandable human language and brings nothing to the discussion. A human would have written it the way they understand it and bring their opinions along: absolutely useless.

• pjjpo

  today at 11:43 AM

  At first wanted to give the benefit of the doubt that this is sarcasm but gave a skim through history and I guess it's just a committed anti-AI agenda.

  Personally I found the tone of the article quite genuine and the video at the end made a compelling case for it. Well I figure you commented having actually read it.

  Edit: I can't downvote but if I could it probably would have been better than this comment!