Can't understand uTorrent Transfer Protocol 'extension' option in header
.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty{ height:90px;width:728px;box-sizing:border-box;
}
i'm trying to understand how a uTP header is structured and how it handles traffic and congestion and all that.
While going through the documentation here i couldn't quite wrap my head around what the 'extension' portion of the header worked. Here is the header:
0 4 8 16 24 32
+-------+-------+---------------+---------------+---------------+
| type | ver | extension | connection_id |
+-------+-------+---------------+---------------+---------------+
| timestamp_microseconds |
+---------------+---------------+---------------+---------------+
| timestamp_difference_microseconds |
+---------------+---------------+---------------+---------------+
| wnd_size |
+---------------+---------------+---------------+---------------+
| seq_nr | ack_nr |
+---------------+---------------+---------------+---------------+
And this is the portion talking about the 'extension' field:
extension
The type of the first extension in a linked list of extension headers. 0 means no extension.
There is currently one extension:
Selective acks
Extensions are linked, just like TCP options. If the extension field is non-zero, immediately following the uTP header are two bytes:
0 8 16
+---------------+---------------+
| extension | len |
+---------------+---------------+
where extension specifies the type of the next extension in the linked list, 0 terminates the list. And len specifies the number of bytes of this extension. Unknown extensions can be skipped by simply advancing len bytes.
How do linked lists come into all of this?
It is (to me) implying further available extensions?
tcp udp bittorrent
asked Nov 23 '18 at 15:14
Richard SassineRichard Sassine
82
add a comment |
i'm trying to understand how a uTP header is structured and how it handles traffic and congestion and all that.
While going through the documentation here i couldn't quite wrap my head around what the 'extension' portion of the header worked. Here is the header:
0 4 8 16 24 32
+-------+-------+---------------+---------------+---------------+
| type | ver | extension | connection_id |
+-------+-------+---------------+---------------+---------------+
| timestamp_microseconds |
+---------------+---------------+---------------+---------------+
| timestamp_difference_microseconds |
+---------------+---------------+---------------+---------------+
| wnd_size |
+---------------+---------------+---------------+---------------+
| seq_nr | ack_nr |
+---------------+---------------+---------------+---------------+
And this is the portion talking about the 'extension' field:
extension
The type of the first extension in a linked list of extension headers. 0 means no extension.
There is currently one extension:
Selective acks
Extensions are linked, just like TCP options. If the extension field is non-zero, immediately following the uTP header are two bytes:
0 8 16
+---------------+---------------+
| extension | len |
+---------------+---------------+
where extension specifies the type of the next extension in the linked list, 0 terminates the list. And len specifies the number of bytes of this extension. Unknown extensions can be skipped by simply advancing len bytes.
How do linked lists come into all of this?
It is (to me) implying further available extensions?
tcp udp bittorrent
asked Nov 23 '18 at 15:14
Richard SassineRichard Sassine
82
add a comment |
i'm trying to understand how a uTP header is structured and how it handles traffic and congestion and all that.
While going through the documentation here i couldn't quite wrap my head around what the 'extension' portion of the header worked. Here is the header:
0 4 8 16 24 32
+-------+-------+---------------+---------------+---------------+
| type | ver | extension | connection_id |
+-------+-------+---------------+---------------+---------------+
| timestamp_microseconds |
+---------------+---------------+---------------+---------------+
| timestamp_difference_microseconds |
+---------------+---------------+---------------+---------------+
| wnd_size |
+---------------+---------------+---------------+---------------+
| seq_nr | ack_nr |
+---------------+---------------+---------------+---------------+
And this is the portion talking about the 'extension' field:
extension
The type of the first extension in a linked list of extension headers. 0 means no extension.
There is currently one extension:
Selective acks
Extensions are linked, just like TCP options. If the extension field is non-zero, immediately following the uTP header are two bytes:
0 8 16
+---------------+---------------+
| extension | len |
+---------------+---------------+
where extension specifies the type of the next extension in the linked list, 0 terminates the list. And len specifies the number of bytes of this extension. Unknown extensions can be skipped by simply advancing len bytes.
How do linked lists come into all of this?
It is (to me) implying further available extensions?
tcp udp bittorrent
asked Nov 23 '18 at 15:14
Richard SassineRichard Sassine
82
i'm trying to understand how a uTP header is structured and how it handles traffic and congestion and all that.
While going through the documentation here i couldn't quite wrap my head around what the 'extension' portion of the header worked. Here is the header:
0 4 8 16 24 32
+-------+-------+---------------+---------------+---------------+
| type | ver | extension | connection_id |
+-------+-------+---------------+---------------+---------------+
| timestamp_microseconds |
+---------------+---------------+---------------+---------------+
| timestamp_difference_microseconds |
+---------------+---------------+---------------+---------------+
| wnd_size |
+---------------+---------------+---------------+---------------+
| seq_nr | ack_nr |
+---------------+---------------+---------------+---------------+
And this is the portion talking about the 'extension' field:
extension
The type of the first extension in a linked list of extension headers. 0 means no extension.
There is currently one extension:
Selective acks
Extensions are linked, just like TCP options. If the extension field is non-zero, immediately following the uTP header are two bytes:
0 8 16
+---------------+---------------+
| extension | len |
+---------------+---------------+
where extension specifies the type of the next extension in the linked list, 0 terminates the list. And len specifies the number of bytes of this extension. Unknown extensions can be skipped by simply advancing len bytes.
How do linked lists come into all of this?
It is (to me) implying further available extensions?
tcp udp bittorrent
tcp udp bittorrent
asked Nov 23 '18 at 15:14
Richard SassineRichard Sassine
82
asked Nov 23 '18 at 15:14
Richard SassineRichard Sassine
82
edited Nov 23 '18 at 16:33
Richard Sassine
asked Nov 23 '18 at 15:14
Richard SassineRichard Sassine
82
asked Nov 23 '18 at 15:14
Richard SassineRichard Sassine
82
asked Nov 23 '18 at 15:14
Richard SassineRichard Sassine
82
82
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
The packet header contains a descriptor (1 byte) for the first extension header or a sentinel value of 0.
The first extension in turn would contain an extension header (this time 2 bytes since it includes a length) and the extension body. The header would again point to the next extension or be a sentinel value.
It is a linked list because the Nth extension header links to the N+1th extension.
This is a common pattern to insert a variable amount of extensions between a fixed-layout packet header and the main payload. E.g. IPv6 and TCP use very similar mechanisms.
answered Nov 28 '18 at 21:58
the8472the8472
27.3k23682
"2 bytes" <- Wrong It's 1 byte
– Encombe
Nov 29 '18 at 17:53
@Encombe an extension descriptor contains both the type and the length, 1 byte each.
– the8472
Nov 30 '18 at 18:56
You wrote "The packet header..."- The 20 bytes packet header has a 1 byte extension field. Only if that field value is non-zero, a 2 bytes extension header will follow after the packet header.
– Encombe
Nov 30 '18 at 22:34
Hrrm, yes. I corrected that.
– the8472
Dec 1 '18 at 16:38
add a comment |
Your Answer
StackExchange.ifUsing("editor", function () {
StackExchange.using("externalEditor", function () {
StackExchange.using("snippets", function () {
StackExchange.snippets.init();
});
});
}, "code-snippets");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "1"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53449124%2fcant-understand-utorrent-transfer-protocol-extension-option-in-header%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
The packet header contains a descriptor (1 byte) for the first extension header or a sentinel value of 0.
The first extension in turn would contain an extension header (this time 2 bytes since it includes a length) and the extension body. The header would again point to the next extension or be a sentinel value.
It is a linked list because the Nth extension header links to the N+1th extension.
This is a common pattern to insert a variable amount of extensions between a fixed-layout packet header and the main payload. E.g. IPv6 and TCP use very similar mechanisms.
answered Nov 28 '18 at 21:58
the8472the8472
27.3k23682
"2 bytes" <- Wrong It's 1 byte
– Encombe
Nov 29 '18 at 17:53
@Encombe an extension descriptor contains both the type and the length, 1 byte each.
– the8472
Nov 30 '18 at 18:56
You wrote "The packet header..."- The 20 bytes packet header has a 1 byte extension field. Only if that field value is non-zero, a 2 bytes extension header will follow after the packet header.
– Encombe
Nov 30 '18 at 22:34
Hrrm, yes. I corrected that.
– the8472
Dec 1 '18 at 16:38
add a comment |
The packet header contains a descriptor (1 byte) for the first extension header or a sentinel value of 0.
The first extension in turn would contain an extension header (this time 2 bytes since it includes a length) and the extension body. The header would again point to the next extension or be a sentinel value.
It is a linked list because the Nth extension header links to the N+1th extension.
This is a common pattern to insert a variable amount of extensions between a fixed-layout packet header and the main payload. E.g. IPv6 and TCP use very similar mechanisms.
answered Nov 28 '18 at 21:58
the8472the8472
27.3k23682
"2 bytes" <- Wrong It's 1 byte
– Encombe
Nov 29 '18 at 17:53
@Encombe an extension descriptor contains both the type and the length, 1 byte each.
– the8472
Nov 30 '18 at 18:56
You wrote "The packet header..."- The 20 bytes packet header has a 1 byte extension field. Only if that field value is non-zero, a 2 bytes extension header will follow after the packet header.
– Encombe
Nov 30 '18 at 22:34
Hrrm, yes. I corrected that.
– the8472
Dec 1 '18 at 16:38
add a comment |
The packet header contains a descriptor (1 byte) for the first extension header or a sentinel value of 0.
The first extension in turn would contain an extension header (this time 2 bytes since it includes a length) and the extension body. The header would again point to the next extension or be a sentinel value.
It is a linked list because the Nth extension header links to the N+1th extension.
This is a common pattern to insert a variable amount of extensions between a fixed-layout packet header and the main payload. E.g. IPv6 and TCP use very similar mechanisms.
answered Nov 28 '18 at 21:58
the8472the8472
27.3k23682
The packet header contains a descriptor (1 byte) for the first extension header or a sentinel value of 0.
The first extension in turn would contain an extension header (this time 2 bytes since it includes a length) and the extension body. The header would again point to the next extension or be a sentinel value.
It is a linked list because the Nth extension header links to the N+1th extension.
This is a common pattern to insert a variable amount of extensions between a fixed-layout packet header and the main payload. E.g. IPv6 and TCP use very similar mechanisms.
answered Nov 28 '18 at 21:58
the8472the8472
27.3k23682
edited Dec 1 '18 at 16:49
answered Nov 28 '18 at 21:58
the8472the8472
27.3k23682
answered Nov 28 '18 at 21:58
the8472the8472
27.3k23682
answered Nov 28 '18 at 21:58
the8472the8472
27.3k23682
27.3k23682
"2 bytes" <- Wrong It's 1 byte
– Encombe
Nov 29 '18 at 17:53
@Encombe an extension descriptor contains both the type and the length, 1 byte each.
– the8472
Nov 30 '18 at 18:56
You wrote "The packet header..."- The 20 bytes packet header has a 1 byte extension field. Only if that field value is non-zero, a 2 bytes extension header will follow after the packet header.
– Encombe
Nov 30 '18 at 22:34
Hrrm, yes. I corrected that.
– the8472
Dec 1 '18 at 16:38
add a comment |
"2 bytes" <- Wrong It's 1 byte
– Encombe
Nov 29 '18 at 17:53
@Encombe an extension descriptor contains both the type and the length, 1 byte each.
– the8472
Nov 30 '18 at 18:56
You wrote "The packet header..."- The 20 bytes packet header has a 1 byte extension field. Only if that field value is non-zero, a 2 bytes extension header will follow after the packet header.
– Encombe
Nov 30 '18 at 22:34
Hrrm, yes. I corrected that.
– the8472
Dec 1 '18 at 16:38
"2 bytes" <- Wrong It's 1 byte
– Encombe
Nov 29 '18 at 17:53
"2 bytes" <- Wrong It's 1 byte
– Encombe
Nov 29 '18 at 17:53
@Encombe an extension descriptor contains both the type and the length, 1 byte each.
– the8472
Nov 30 '18 at 18:56
@Encombe an extension descriptor contains both the type and the length, 1 byte each.
– the8472
Nov 30 '18 at 18:56
You wrote "The packet header..."- The 20 bytes packet header has a 1 byte extension field. Only if that field value is non-zero, a 2 bytes extension header will follow after the packet header.
– Encombe
Nov 30 '18 at 22:34
You wrote "The packet header..."- The 20 bytes packet header has a 1 byte extension field. Only if that field value is non-zero, a 2 bytes extension header will follow after the packet header.
– Encombe
Nov 30 '18 at 22:34
Hrrm, yes. I corrected that.
– the8472
Dec 1 '18 at 16:38
Hrrm, yes. I corrected that.
– the8472
Dec 1 '18 at 16:38
add a comment |
Thanks for contributing an answer to Stack Overflow!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53449124%2fcant-understand-utorrent-transfer-protocol-extension-option-in-header%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
