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Doug Abbott, in, 2018 SocketsThe “socket” interface, first introduced in the Berkeley versions of Unix, forms the basis for most network programming in Unix systems. Sockets are a generalization of the Unix file access mechanism that provides an endpoint for communication, either across a network or within a single computer. A socket can also be thought of as an extension of the named pipe concept that explicitly supports a client/server model, wherein multiple clients may be attached to a single server.The principal difference between file descriptors and sockets is that a file descriptor is bound to a specific file or device when the application calls open, whereas sockets can be created without binding them to a specific destination. The application can choose to supply a destination address each time it uses the socket, for example when sending datagrams, or it can bind the destination to the socket to avoid repeatedly specifying the destination, for example when using TCP. Network server.Next, the server creates a connection queue with the listen service, and then waits for client connection requests with the accept service. When a connection request is received successfully, accept returns a new socket, which is then used for this connection’s data transfer.
The server now transfers data using standard read and write calls that use the socket descriptor in the same manner as a file descriptor. When the transaction is complete, the newly-created socket is closed.The server may very well spawn a new process or thread to service the connection while it goes back and waits for additional client requests. This allows a server to serve multiple clients simultaneously. Each client request spawns a new process/thread with its own socket. If you think about it, that is how a web server operates. The Client Process.
The socket system call creates a socket and returns a descriptor for later use in accessing the socket.#include int socket (int domain, int type, int protocol);A socket is characterized by three attributes that determine how communication takes place. The domain specifies the communication medium. The most commonly used domains are PFUNIX for local file system sockets, and PFINET for Internet connections.
The “ PF” here stands for Protocol Family.The domain determines the format of the socket name or address. For PFINET, the address is AFINET, and is in the form of a dotted quad. Here “ AF” stands for Address Family.
Generally, there is a 1 to 1 correspondence between AF values and PF values. A network computer may support many different network services.
A specific service is identified by a “port number.” Established network services like ftp, http, etc., have defined port numbers below 1024. Local services may use port numbers above 1023.Some domains, PFINET for example, offer alternate communication mechanisms. SOCKSTREAM is a sequenced, reliable, connection-based, two-way byte stream.
This is the basis for TCP, and is the default for PFINET domain sockets. SOCKDGRAM is a datagram service. It is used to send relatively small messages, with no guarantee that they will be delivered or that they won’t be reordered by the network. This is the basis of UDP. SOCKRAW allows a process to access the IP protocol directly. This can be useful for implementing new protocols directly in User Space.The protocol is usually determined by the socket domain, and you do not have a choice. So, the protocol argument is usually zero.
Walter Goralski, in, 2017 The Socket Interface: Good or Bad?However, the very simplicity of socket interfaces can be deceptive. The price of this simplicity is isolating the network program developers from any of the details of how the TCP/IP network actually operates. In many cases, the application programmers interpret this “transparency” of the TCP/IP network (“treat it just like a file”) to mean that the TCP/IP network really does not matter to the application program at all.As many TCP/IP network administrators have learned the hard way, nothing could be further from the truth.
Every segment, datagram, frame, and byte that an application puts on a TCP/IP network affects the performance of the network for everyone. Programmers and developers that treat sockets “just like a file” soon find out that the TCP/IP network is not as fast as the hard drive on their local systems. And many applications have to be rewritten to be more efficient just because of the seductive transparency of the TCP/IP network using the socket interface.For those who have been in the computer and network business for a very long time, the socket interface controversy in this regard closely mirrors the controversy that erupted when COBOL, the first “high-level” programming language, made it possible for people who knew absolutely nothing about the inner workings of computers to be trained to write application programs. Before COBOL, programmers wrote in a low-level assembly language that was translated (assembled) into machine instructions. (Some geniuses wrote directly in machine code without assemblers, a process known as “bare metal programming.”)Proponents then, as with sockets, pointed out the efficiencies to be enjoyed by freeing programmers from reinventing the wheel with each program and writing the same low-level routines over and over. There were gains in production as well—programmers who wrote a single instruction in COBOL could rely on the compiler to generate about 10 lines of underlying assembly language and machine code. Since programmers all wrote about the same number of lines of code a day, a 10-fold gain in productivity could be claimed.The same claims regarding isolation are often made for the socket interface.
Freed from concerns about packet headers and segments, network programmers can concentrate instead on the real task of the program and benefit from similar productivity gains. Today, no one seriously considers the socket interface to be an isolation liability, although similar claims of “isolation” are still heard when programmers today can generate code by pointing and clicking at a graphical display in Python front ends or another even higher level “language.” The “Threat” of Raw SocketsA more serious criticism of the socket interface is that it forms an almost perfect tool for hackers, especially the raw socket interface. Many network security experts do not look kindly on the kind of abuses that raw sockets made possible in the hands of hackers.Why all the uproar over raw sockets? With the stream (TCP) and datagram (UDP) socket interfaces, the programmer is limited with regard to what fields in the TCP/UDP or IP header that they can manipulate. After all, the whole goal is to relieve the programmer of addressing and header field concerns. Raw sockets were originally intended as a protocol research tool only, but they proved so popular among the same circle of trusted Internet programmers at the time that use became common.But raw sockets let the programmer pretty much control the entire content of the packet, from header to flags to options.
Want to generate a SYN attack to send a couple of million TCP segments with the SYN bit sent one after the other to the same Web site, and from a phony IP address? This is difficult to do through the stream socket, but much easier with a raw socket. Consequently, this is one reason why you can find and download over the Internet hundreds of examples using TCP and UDP sockets, but raw socket examples are few and far between.
Not only could users generate TCP and UPD packets, but even “fake” ICMP and traceroute packets were now within reach.Microsoft unleashed a storm of controversy in 2001 when it announced support for the “full Unix-style” raw socket interface for Windows XP. Limited support for raw sockets in Windows had been available for years, and third-party device drivers could always be added to Windows to support the full raw socket interface, but malicious users seldom bestirred themselves to modify systems that were already in use. However, if a “tool” was available to these users, it would be exploited sooner or later.Many saw the previous limited support for raw sockets in Windows as a blessing in disguise. The TCP/UDP layers formed a kind of “insulation” to protect the Internet from malicious application programs, a protective layer that was stripped away with full raw socket support. They also pointed out that the success of Windows NT servers, and other Windows releases, all of which lacked full raw socket support, meant that no one needed full raw sockets to do what needed doing on the Internet.
But once full raw sockets came to almost everyone’s desktop, these critics claimed, hackers would have a high-volume, but poorly secured, operating system in the hands of consumers.Without full raw sockets, Windows PCs could not spoof IP addresses, generate TCP segment SYN attacks, or create fraudulent TCP connections. Write a test program that uses the socket interface to send messages between a pair of Unix workstations connected by some LAN (e.g., Ethernet, 802.11). Use this test program to perform the following experiments: (a)Measure the round-trip latency of TCP and UDP for different message sizes (e.g., 1 byte, 100 bytes, 200 bytes, 1000 bytes). (b)Measure the throughput of TCP and UDP for 1-KB, 2-KB, 3-KB, 32-KB messages. Plot the measured throughput as a function of message size. (c)Measure the throughput of TCP by sending 1 MB of data from one host to another.
Do this in a loop that sends a message of some size—for example, 1024 iterations of a loop that sends 1-KB messages. Repeat the experiment with different message sizes and plot the results. Li, in, 2016 9.6.1 HBase Framework, Storage, and Application OptimizationThe current HBase is implemented by using the Java Sockets interface. Due to the overhead of the cross platform, HBase is difficult to provide high-performance services for data intensive applications. 77 presented a novel design of HBase for remote direct memory access (RDMA) capable networks via Java native nterface. Then they extended the existing open source HBase software and make it RDMA capable.
The performance evaluation reveals that the latency of HBase get operations can be reduced. The existing interface of HBase for MapReduce to access speed is too low, so Tian et al. 78 offered an improved method. It splits the table that is not based on its logical storage element called “Region,” but on its physical storage element called “block” and uses a property scheduling policy, makes data reading and computing executes in the same node. 79 showed how to implement the set data structure and its operations in a scalable manner on top of Hadoop HBase, and then discussed the limitations of implementing this data structure in the Hadoop ecosystem.
Their primary conclusion provided an excellent framework to implement scalable data structures for the Hadoop ecosystem.The compression technology is commonly used to optimize HBase storage. Based on the existing compression system and the fact that column-oriented database stores information by column and the column property values are in high similarity, Luo et al. 80 proposed some lightweight introducing stored database of compression algorithm, which takes column property values as a coding units for data compression.
In addition, based on the situation that different data matches different compression algorithm, they presented a method that is based on the dynamic selection strategy of a Bayesian classifier compression algorithm. According to the Bayesian formula, different data sections choose different compression algorithms, which make it possible to compress the data to reach the best compression effect. 81 designed an inverted index table that includes a keyword, document ID, and position list; the table can save a lot of storage space. On the basis of the table, they provide key as dictionary compression with high compression ratio and high decompression rate for the data block.In the aspect of HBase application, Karana 82 built a search engine, whose index is on Hadoop and HBase, to deploy in a cluster environment. Retrieval applications by nature involve read-intensive operations, which optimize the Hadoop and HBase. 83 proposed ST-HBase (spatiotextual HBase) that can deal with large-scale geotagged objects. ST-HBase can support high-insert throughput while providing efficient spatial keyword queries. Fasttrack help.
In ST-HBase, they leverage an index module layered over a key-value store. The underlying key-value store enables the system to sustain high-insert throughput and deal with large-scale data. The index layer can provide efficient spatial keyword query processing. Awasthit et al.
84 explored the feasibility of introducing flash SSDs for HBase. They perform a qualitative and supporting quantitative assessment of the implications of storing the system components of HBase in flash SSDs. The proposed system performs 1.5–2.0 times better than a complete disk-based system.
85 presented HBaseMQ, the first distributed message queuing system based on the bare-bones HBase. HBaseMQ directly inherits HBase’s properties such as scalability and fault tolerance, enabling HBase users to rapidly instantiate a message queuing system with no extra program deployment or modification to HBase. HBaseMQ effectively enhances the data processing capability of an existing HBase installation.
These optimization methods can significantly improve the performance of the specific system; however, it is only optimized for specific applications, and the popularity is not high. In, 2002 Exploring Operating System APIsOperating systems provide, or don't provide, interfaces to their network link layer. Let's examine a variety of operating systems to determine how they interface to their network link layer.
LinuxLinux provides an interface to the network link layer via its socket interface. This is one of the easiest of the interfaces provided by any operating system. Mounting of babcock and wilcox boiler. The following program illustrates how simple this is. This program opens up the specified interface, sets promiscuous mode, and then proceeds to read Ethernet packets from the network. When a packet is read, the source and destination MAC addresses are printed, in addition to the packet type.
BSDBSD-based operating systems such as OpenBSD, FreeBSD, NetBSD, and BSDI all provide an interface to the link layer via a kernel-based driver called the Berkeley Packet Filter (BPF). BPF possesses some very nice features that make it extremely efficient at processing and filtering packets.The BPF driver has an in-kernel filtering mechanism.
This is composed of a built-in virtual machine, consisting of some very simple byte operations allowing for the examination of each packet via a small program loaded into the kernel by the user. Whenever a packet is received, the small program is run on the packet, evaluating it to determine whether it should be passed through to the user-land application. Expressions are compiled into simple bytecode within user-land, and then loaded into the driver via an ioctl call. Libpcaplibpcap is not an operating system interface, but rather a portable cross-platform library that greatly simplifies link layer network access on a variety of operating systems. Libpcap is a library originally developed at Lawrence Berkeley Laboratories (LBL). Its goal is to abstract the link layer interface on various operating systems and create a simple standardized application program interface (API).
This allows the creation of portable code, which can be written to use a single interface instead of multiple interfaces across many operating systems. This greatly simplifies the technique of writing a sniffer, when compared to the effort required to implement such code on multiple operating systems.The original version available from LBL has been significantly enhanced since its last official release. It has an open source license (the BSD license), and therefore can also be used within commercial software, and allows unlimited modifications and redistribution.The original LBL version can be obtained from ftp://ftp.ee.lbl.gov/libpcap.tar. The tcpdump.org guys, who have taken over development of TCPDump, have also adopted libpcap. More recent versions of libpcap can be found at www.tcpdump.org.In comparison to the sniffer written for the Linux operating system, using its native system interface, a sniffer written on Linux using libpcap is much simpler, as seen here. WindowsUnfortunately, Windows-based operating systems provide no functionality to access the network at the data link layer. We must obtain and install a third-party packet driver to obtain access to this level.
Until recently, there have been no such drivers publicly available for which a license was not required. A BPF-like driver has now been written that supports even the BPF in-kernel filtering mechanism. A port of the libpcap library is also now available that, when combined with the driver, provides an interface as easy as their UNIX counterparts.The driver, libpcap port, as well as a Windows version of TCPDump, are both available from http://netgroup-serv.polito.it/windump. Dimitrios Serpanos, Tilman Wolf, in, 2011 End-system socketsMany end-system application processes need to establish communication to another end-system process. To hide the complexities of the transport layer, most operating systems provide functionality for handling communication at this protocol layer.
The UNIX operating system provides an elegant network “socket” interface, which is an abstraction used to send and to receive network traffic. A socket provides an interface that is as simple as reading from and writing to files and thus can be used easily by applications. Sockets come in two different flavors: connection-based for use with the TCP protocol and connection-less for use with UDP. Connection-less sockets do not establish explicit connections and all datagrams are sent independently. The typical set of functions used for connection-less sockets is the following:.Socket creates a new socket,.Sendto sends a datagram to the destination specified as an argument, and.Recvfrom receives a datagram (if available) from a sender specified in an argument. When using TCP sockets, additional functions are used to establish the connection before sending traffic.
Typical functions used for connection-based sockets are:.Socket creates a new socket,.Bind associates a socket with a particular address,.Listen makes the server socket wait for a connection setup request,.Connect allows the client to initiate a connection to the server,.Write transmits data from one side of the connection to the other, and.Read allows the caller to read available data from the socket. To ensure correct operation, these functions need to be called in the correct order. For connection-based sockets, the following order is typically used: 1.Receiver establishes socket with socket, binds the socket to the specified local port with bind, and begins to wait for connection at port with listen. 2.Sender establishes socket with socket and initiates connections with connect. 3.Once connection setup phase has finished successfully, the sending socket and the receiving socket can be used similarly to a file handle to read and write the data stream. 4.Sender uses write to send data into the socket.
5.Receiver uses read to receive data from the socket.A connection-based socket automatically establishes bidirectional communication. Thus, it is also possible for the receiver to send data back to the sender (e.g., to respond to a request).One key difference between the connection-less socket and the connection-based socket is how data are written to and read from the interface. In the connection-less socket, the application explicitly partitions data into datagrams, each of which is sent via an explicit sendto command. On the receiver side, the packets are also received one by one.
Thus, data partitioning used by the application layer is maintained. In connection-based sockets, these barriers between individual packets disappear and data are represented as a stream. The sender may write data at the end of the stream with write calls that may be completely different from how the receiver uses the read calls. For example, the sender may write data into the socket with a few large blocks, and the receiver may read from the socket one byte at a time.Except for the explicit connection setup, the remaining functions of TCP (e.g., flow control and congestion control) remain hidden from the application that uses sockets. For example, if the receiving application is slow about reading data from the socket, the buffer in the receiver's operating system and then the buffer in the sender's operating system will fill up.
Once they are full, the sender's socket can no longer accept any data and the write call will block. This blocking will stall the sender application and thus achieve flow control. Similarly, congestion control may limit the rate at which data are transferred between the sockets.
Additionally, the reliability feature of TCP, which ensures that lost packets are retransmitted, is not visible to the application that uses a connection-based socket. Walter Goralski, in, 2017 Secure Socket LayerThe SSL protocol was invented as a way to secure Web sites, but the status of SSL as a protocol layer allows it to be used for any client–server transactions as long as they use TCP. SSL is the basis of a related method, Transport Layer Security (TLS), defined in RFC4346. Both form a complete socket layer sitting above TCP and UDP and add authentication (you are who you say you are), integrity (messages have not been changed between client-server pairs), and privacy (through encryption) to the Internet.
SSL/TLS as a “socket layer” protocol, showing how it sits on top of TCP.Typical SSL implementations on the Internet only authenticate the server. That is, SSL is used as the de facto standard way client users can be sure that when they log on to www.mybank.com the server is really an official entity of MyBank and not a phony Web site set up by hackers to entice users to send account, Social Security, PIN, or other information hackers always find useful. SSL used by a server is indicated by the little “lock” symbol that appears in the lower right-hand corner of most Web browsers.TLS 1.2 can be considered an extension of SSL 3.0 to include the client side of the transaction.
SSL is still used in the Netscape and Internet Explorer browsers, and in most Web server software. Not all Web pages need to be protected with SSL or TLS, and SSL can be used free for noncommercial use or licensed for commercial applications.Why would a Web server need to authenticate and protect the client? Well, consider the liability of and bad publicity for MyBank if www.mybank.com accepted a request on the part of a fake client user who transferred someone’s assets to an offshore account and closed the accounts? Today, many activities that could easily be done over the Internet require a phone call or fax or letter with signature (or several of these!) to protect the server from phony clients.
I might pick up one of these books, they both look solid. Though the Richard Stevens one has some reviews that worry me. It seems to be that he writes his own custom wrapper functions around the standard API functions, and then just uses the wrapper? I'd prefer a book that teaches the core API, and not a wrapper around it. If I wanted that I could just use any old library out there.@Grey Wolf,This link has some nice info, especially in the page.
The rest seems to just be theory behind networks (which I have plenty of).