Direct Connect (DC) is a

peer-to-peer file sharing Peer-to-peer file sharing is the distribution and sharing of digital media using peer-to-peer (P2P) networking technology. P2P file sharing allows users to access media files such as books, music, movies, and games using a P2P software program tha ...

protocol Protocol may refer to: Sociology and politics * Protocol (politics), a formal agreement between nation states * Protocol (diplomacy), the etiquette of diplomacy and affairs of state * Etiquette, a code of personal behavior Science and technology ...

. Direct Connect clients connect to a central hub and can download files directly from one another. Advanced Direct Connect can be considered a successor protocol. Hubs feature a list of clients or users connected to them. Users can search for files and

download In computer networks, download means to ''receive'' data from a remote system, typically a server such as a web server, an FTP server, an email server, or other similar system. This contrasts with uploading, where data is ''sent to'' a remote s ...

them from other clients, as well as

chat Chat or chats may refer to: Communication * Conversation, particularly casual * Online chat, text message communication over the Internet in real-time * Synchronous conferencing, a formal term for online chat * SMS chat, a form of text messagin ...

with other users.

History

NeoModus was started as a company funded by the

adware Adware, often called advertising-supported software by its developers, is software that generates revenue for its developer by automatically generating online advertisements in the user interface of the software or on a screen presented to the ...

"Direct Connect" by Jon Hess in November, 1999 while he was in high school. The first third-party client was called "DClite", which never fully supported the file sharing aspects of the protocol. Hess released a new version of Direct Connect, requiring a simple

encryption key A key in cryptography is a piece of information, usually a string of numbers or letters that are stored in a file, which, when processed through a cryptographic algorithm, can encode or decode cryptographic data. Based on the used method, the key c ...

to initiate a connection, locking out third-party clients. The encryption key was cracked, and the author of DClite released a new version of DClite compatible with the new software from NeoModus. Some time after, DClite was rewritten as Open Direct Connect with the purpose of having an MDI user interface and using plug-ins for file sharing protocols (similar to

MLDonkey MLDonkey is an open-source software, open-source, multi-protocol, peer-to-peer file sharing application that runs as a Front and back ends, back-end server application on many platforms. It can be controlled through a user interface provided by one ...

). Open Direct Connect also did not have complete support for the full file sharing aspects of the protocol, but a port to

Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's List ...

, however, did. Later on, other clients such as DCTC (Direct Connect Text Client) and

DC++ DC++ is a free and open-source, peer-to-peer file-sharing client that can be used for connecting to the Direct Connect network or to the ADC protocol. It is developed primarily by Jacek Sieka, nicknamed arnetheduck. History and background DC+ ...

became popular. The DCDev archive contains discussions of protocol changes for development of DC in the years 2003–2005.

Protocol

The Direct Connect protocol is a text-based computer protocol, in which commands and their information are sent in clear text, without

encryption In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can decip ...

in original NeoModus software (

is available as a protocol extension). As clients connect to a central source of distribution (the hub) of information, the hub requires a substantial amount of upload bandwidth available. There is no official specification of the protocol, meaning that every client and hub (besides the original NeoModus client and hub) has been forced to

reverse engineer Reverse engineering (also known as backwards engineering or back engineering) is a process or method through which one attempts to understand through deductive reasoning how a previously made device, process, system, or piece of software accompli ...

the information. As such, any protocol specification this article may reference is likely inaccurate and/or incomplete. The client-server (as well as client-client, where one client acts as "server") aspect of the protocol stipulates that the server respond first when a connection is being made. For example, when a client connects to a hub's

socket Socket may refer to: Mechanics * Socket wrench, a type of wrench that uses separate, removable sockets to fit different sizes of nuts and bolts * Socket head screw, a screw (or bolt) with a cylindrical head containing a socket into which the hexag ...

, the hub is first to respond to the client. The protocol lacks a specified default

character encoding Character encoding is the process of assigning numbers to Graphics, graphical character (computing), characters, especially the written characters of Language, human language, allowing them to be Data storage, stored, Data communication, transmi ...

for clients or hubs. The original client and hub use

ASCII ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because of ...

encoding instead of that of the

Operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...

. This allows migration to

UTF-8 UTF-8 is a variable-width encoding, variable-length character encoding used for electronic communication. Defined by the Unicode Standard, the name is derived from ''Unicode'' (or ''Universal Coded Character Set'') ''Transformation Format 8-bit'' ...

encoding in newer software. Port 411 is the default port for hubs, and 412 for client-to-client connections. If either of these ports are already in use, the port number is incremented until the number of a free port is found for use. For example, if 411, 412 and 413 are in use, then port 414 will be used. Hub addresses are in the following form: dchub://example.com

411 411 may refer to: * The year AD 411, the four hundred and eleventh year of the Gregorian calendar * 411 BC * 4-1-1, a telephone directory assistance number in the United States and Canada ** By extension, a slang term for "information" * ''What's ...

where 411 is an optional port. There is no global identification scheme; instead, users are identified with their nickname on a hub-to-hub basis. An incoming request for a client-client connection cannot be linked with an actual connection. A search result cannot be linked with a particular search. The ability to kick or move (redirect) a user to another hub is supported by the protocol. If a user is kicked, the hub is not required to give that user a specific reason, and there is no restriction on where a user can be redirected to. However, if another client in power instructs the hub to kick, that client may send out a notification message before doing so. Redirecting a user must be accompanied by a reason. There is no

HTTP referer In HTTP, "" (a misspelling of Referrer) is an optional HTTP header field that identifies the address of the web page (i.e., the URI or IRI), from which the resource has been requested. By checking the referrer, the server providing the new web p ...

equivalent. Hubs may send out user commands to clients. These commands are only raw protocol commands and are used mostly for making a particular task simpler. For example, the hub cannot send a user command that will trigger the default browser to visit a website. It can, however, add the command "+rules" (where '+' indicates to the hub that it's a command - this may vary) to display the hub's rules. The peer-to-peer part of the protocol is based on a concept of "slots" (similar to number of open positions for a job). These slots denote the number of people that are allowed to download from a user at any given time and are controlled by the client. In client-to-client connections, the parties generate a random number to see who should be allowed to download first, and the client with the greater number wins. Transporting downloads and connecting to the hub requires

TCP TCP may refer to: Science and technology * Transformer coupled plasma * Tool Center Point, see Robot end effector Computing * Transmission Control Protocol, a fundamental Internet standard * Telephony control protocol, a Bluetooth communication s ...

, while active searches use UDP. There are two kinds of modes a user can be in: either "active" or "passive" mode. Clients using active mode can download from anyone else on the network, while clients using passive mode users can only download from active users. In NeoModus Direct Connect, passive mode users receive other passive mode users' search results, but the user will not be able to download anything. In

, users will not receive those search results. In NeoModus Direct Connect, all users will be sent at most five search results per query. If a user has searched, DC++ will respond with ten search results when the user is in active mode and five when the user is in passive mode. Passive clients will be sent search results through the hub, while active clients will receive the results directly. Protocol

delimiter A delimiter is a sequence of one or more characters for specifying the boundary between separate, independent regions in plain text, mathematical expressions or other data streams. An example of a delimiter is the comma character, which acts a ...

s are "$", ", ", and . Protocol have for them (and few others)

escape sequence In computer science, an escape sequence is a combination of characters that has a meaning other than the literal characters contained therein; it is marked by one or more preceding (and possibly terminating) characters. Examples * In C and man ...

and most software use them correctly in login (Lock to Key) sequence. For some reason that

was ignored by DC++ developers and they use

HTML The HyperText Markup Language or HTML is the standard markup language for documents designed to be displayed in a web browser. It can be assisted by technologies such as Cascading Style Sheets (CSS) and scripting languages such as JavaScri ...

equivalent if these characters are to be viewed by the user. Continued interest exists in features such as ratings and language packs. The authors of DC++ also proposed a complete replacement of the Direct Connect protocol called ADC, or unofficially, Advanced Direct Connect. ADC uses the same

network topology Network topology is the arrangement of the elements ( links, nodes, etc.) of a communication network. Network topology can be used to define or describe the arrangement of various types of telecommunication networks, including command and contro ...

, concepts, and terminology as the original protocol. One example of an added feature to the protocol, in comparison with the original protocol, is the broadcasting of Tiger-Tree Hashing of shared files (TTH). The advantages of this include verifying that a file is downloaded correctly, and the ability to find files independently of their names.

Direct Connect used for DDoS attacks

As the protocol allows hubs to redirect users to other hubs, malicious hubs have redirected users to places other than real Direct Connect hubs, effectively causing a

Distributed Denial of Service In computing, a denial-of-service attack (DoS attack) is a cyber-attack in which the perpetrator seeks to make a machine or network resource unavailable to its intended users by temporarily or indefinitely disrupting services of a host connect ...

attack. The hubs may alter the IP in client to client connections, pointing to a potential victim. The CTM Exploit surfaced in 2006–2007, during which period the whole Direct Connect network suffered from DDoS attacks. The situation prompted developers to take security issues more seriously. As of February 2009, an extension for clients was proposed in order for the attacked party to find out the hub sending the connecting users.

Direct Connect Network Foundation

The Direct Connect Network Foundation (DCNF) is a

non-profit organization A nonprofit organization (NPO) or non-profit organisation, also known as a non-business entity, not-for-profit organization, or nonprofit institution, is a legal entity organized and operated for a collective, public or social benefit, in co ...

registered in Sweden that aims to improve the DC network by improving software, protocols and other services in the network.

Articles and papers

The DCNF maintains a list of articles, papers and more documentation that relate to DC.Direct Connect Network Foundation: Documents and Resources

References

External links

NMDC Protocol Wiki (Mirror)

NMDC Protocol Document

NMDC Protocol
{{DEFAULTSORT:Direct Connect (File Sharing) Direct Connect network File sharing networks