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Lector: Aliyev H.U. Lecture №2

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1 Lector: Aliyev H.U. Lecture №2

2 Introduction We will start with an introduction to the hardware used in local area networks, such as routers, hubs, and bridges. Then we will have a look at the seven layers of the OSI model and their functionality, and how the TCP/IP protocol suite fits into the OSI layers. After that, we will learn about the functionality of various network protocols. In particular, we will look at: The Physical Network The OSI Seven-Layer Model Basic Network Protocols Internet Protocols Protocols Sockets Name Lookups The Internet Remoting Messaging

3 The Physical Network In essence, a network is a group of computers or devices connected together by communication links. In networking terms, every computer or device (printers, routers, switches, and so on) connected to the network is called a node. Nodes are connected by links, which could be cables or wireless links (such as infrared or radio signals), and they can interact with any other node by transmitting messages over the network. We can differentiate networks according to their size: A LAN, or Local Area Network, connects nodes over a limited area. This area can be as large as the site of a big company, or as small as connected computers in someone's home. The most commonly used LAN technology is the Ethernet network (see next section). WAN is the acronym for Wide Area Network. Multiple LAN sites are connected together by a WAN. WAN technologies that you might know of include Frame Relays, T1 lines, ISDN (Integrated Services Digital Network), X.25, and ATM (Asynchronous Transfer Monitor). In the next section, we'll further discuss the means of connecting to a WAN. A MAN, or Metropolitan Area Network, is very similar to a WAN in that it connects multiple LANs. However, a MAN restricts the area of the network to a city or suburb. MANs use high-speed networks to connect the LANs of schools, governments, companies, and so on, by using fast connections to each site, such as fiber optics.

4 WAN Lines To connect to a WAN, there are several options available:
Where a specific customer requires a dedicated network capacity, we can use leased lines. Such lines are usually charged at a flat rate, no matter how much traffic is sent. Examples of leased lines are Digital Data Service (DDS, running at 2.4 Kbps and 56 Kbps), T1 (1.544 Mbps), and T3 (equivalent to 28 T1 lines). Switched lines are used by the regular telephone service. A circuit is established between transmitter and receiver for the duration of a call, or data exchange. When the line is no longer needed, it is freed for use by another customer of the network provider. Examples of switched lines are POTS (Plain Old Telephony Service-standard analog lines that support speeds up to 56 Kbps), ISDN, and DSL (Digital Subscriber Line). A packet-switching network is where the service provider supplies switching technology to interface with the backbone network. This solution provides increased performance and shares resources between customers, so that bandwidth is available on demand. Protocols used for switching networks include X.25 (up to 64 Kbps), Frame Relay (up to Mbps), and ATM (up to Gbps), MPLS/GMPLS.

5 Physical Components An important aspect of understanding the network is knowing the hardware components. We are going to have a look at the major components of a LAN: Network Interface Card (NIC) Hub Switch Router PC and other user devices

6 Basic types of networking models
Protocol model: This model closely matches the structure of a particular protocol suite. The hierarchical set of related protocols in a suite typically represents all the functionality required to interface the human network with the data network. The TCP/IP model is a protocol model, because it describes the functions that occur at each layer of protocols within the TCP/IP suite. Reference model: This model provides consistency within all types of network protocols and services by describing what has to be done at a particular layer, but not prescribing how it should be accomplished. A reference model is not intended to be an implementation specification or to provide a sufficient level of detail to define precisely the services of the network architecture. The primary purpose of a reference model is to aid in clearer understanding of the functions and processes involved.

7 The Layered OSI Model With OSI (Open System Interconnection) the International Organization for Standardization (ISO) defined a model for a standardized network that would replace TCP/IP, DECNet, and other protocols, as the primary network protocol used in the Internet. However, because of the complexity of the OSI protocol, not many implementations were built and put to use. TCP/IP was much simpler, and thus can now be found everywhere. But many new ideas from the OSI protocol can be found in the next version of IP, IPv6. While the OSI protocol didn't catch on, the OSI seven layer model was very successful, and it is now used as a reference model to describe different network protocols and their functionality.

8 The Layered OSI Model

9 The Layered OSI Model The application layer defines a programming interface to the network for user applications. The presentation layer is responsible for encoding data from the application layer ready for transmission over the network, and vice versa. The session layer creates a virtual connection between applications. The transport layer allows reliable communication of data. The network layer makes it possible to access nodes in a LAN using logical addressing. The data link layer accesses the physical network with physical addresses. Finally, the physical layer includes the connectors, cables, and so on.

10 OSI and TCP/IP Models

11 TCP/IP Protocol Model is basic of network programming

12 Comparing the OSI Model with the TCP/IP Model

13 Comparing the OSI Model with the TCP/IP Model
The protocols that make up the TCP/IP protocol suite can be described in terms of the OSI reference model. In the OSI model, the network access layer and the application layer of the TCP/IP model are further divided to describe discrete functions that must occur at these layers. At the network access layer, the TCP/IP protocol suite does not specify which protocols to use when transmitting over a physical medium; it only describes the handoff from the Internet layer to the physical network protocols. OSI Layers 1 and 2 discuss the necessary procedures to access the media and the physical means to send data over a network. As shown in Figure , the critical parallels between the two network models occur at OSI Layers 3 and 4. OSI Layer 3, the network layer, is almost universally used to describe the range of processes that occur in all data networks to address and route messages through an internetwork. IP is the TCP/IP suite protocol that includes the functionality described at OSI Layer 3.

14 Comparing the OSI Model with the TCP/IP Model
Layer 4, the transport layer of the OSI model, describes general services and functions that provide ordered and reliable delivery of data between source and destination hosts. These functions include acknowledgement, error recovery, and sequencing. At this layer, the TCP/IP protocols TCP and User Datagram Protocol (UDP) provide the necessary functionality. The TCP/IP application layer includes a number of protocols that provide specific functionality to a variety of end-user applications. The OSI model Layers 5, 6, and 7 are used as references for application software developers and vendors to produce products that operate on networks.

15 TCP/IP protocol suite In the section, we shall look into the functionality and purpose of the protocols of the TCP/IP suite in the following order: Basic Protocols Internet Protocols Protocols Other Protocols

16 TCP/IP suite Basic Protocols
As we can see, the TCP/IP protocol suite has a much simpler layered structure than the seven layers of the OSI model. The Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) protocols are transport protocols corresponding to OSI layer 4. Both protocols make use of the Internet Protocol (IP), an OSI layer 3 protocol (the network layer). As well as these three protocols, there are two more basic protocols in the TCP/IP suite that extend the IP protocol: ICMP and IGMP. The functionality of these protocols must be implemented in the layer housing the IP protocol, hence they are shown in that layer in the preceding figure. IP-Internet Protocol The Internet Protocol connects two nodes. Each node is identified by a 32-bit address, called its IP address. When sending a message, the IP protocol receives the message from upper level protocols such as TCP or UDP and adds the IP header which contains information about the destination host.

17 Transport Layer-Port Numbers
The IP protocol uses IP addresses to identify nodes on the network, while the transport layer (layer 4) uses endpoints to identify applications. TCP and UDP protocols use a port number together with an IP address to specify an application endpoint. The server must supply a known endpoint for a client to connect to, although the port number can be created dynamically for the client. TCP and UDP port numbers are 16 bits, and can be divided into three categories: System (Well-Known) Port Numbers User (Registered) Port Numbers Dynamic or Private Ports

18 Internet Protocols After discussing base protocols, we can now step up to a higher level. The HTTP and FTP protocols cover layers 5-7 of the OSI model. FTP-File Transfer Protocol

19 HTTP-Hypertext Transfer Protocol and HTTPS-HTTP over SSL (Secure Socket Layer)
HTTP is the main protocol used by web applications. Similar to the FTP protocol, HTTP is a reliable protocol that is achieved by using TCP. Like FTP, HTTP is also used to transfer files across the network. Unlike FTP, it has features such as caching, identification of the client application, support for different attachments with a MIME format, and so on. These features are enabled within the HTTP header. If there is a requirement to exchange confidential data with a web server, HTTPS can be used. HTTPS is an extension to the HTTP protocol, and the principles discussed in the last section still apply. However, the underlying mechanism is different, as HTTPS uses SSL (Secure Socket Layer), originally developed by Netscape. SSL sits on top of TCP and secures network communication using a public/private key principle to exchange secret symmetric keys, and a symmetric key to encrypt the messages.

20 E-Mail Protocols SMTP-Simple Mail Transfer Protocol
SMTP is a protocol for sending and receiving messages. It can be used to send between a client and server that both use the same transport protocol, or to send between servers that use different transport protocols. SMTP has the capability to relay messages across transport service environments. SMTP does not allow us to read messages from a mail server, however, and for this activity POP3 or IMAP protocols should be used. POP3-Post Office Protocol The Post Office Protocol was designed for disconnected environments. In small environments it is not practical to maintain a persistent connection with the mail server, for instance, in environments where the connection time must be paid. With POP3 the client can access the server and retrieve the messages that the server is holding for it. When messages are retrieved from the client, they are typically deleted on the server, although this is not necessarily the case. Windows .NET Server includes a POP3 server.

21 E-Mail Protocols IMAP-Internet Message Access Protocol
Like POP3, IMAP is designed to access mails on a mail server. Similar to POP3 clients, an IMAP client can have an offline mode where mails can be manipulated on the local machine. Unlike POP3 clients, IMAP clients have greater capabilities when in online mode, such as retrieving just the headers or bodies of specified mails, searching for particular messages on the server, and setting flags such as a replied flag. Essentially, IMAP allows the client to manipulate a remote mailbox as if it was local. NNTP-Network News Transfer Protocol Network News Transfer Protocol is an application layer protocol for submitting, relaying, and retrieving messages that form part of newsgroup discussions. This protocol provides client applications with access to a news server to retrieve selected messages, and also supports server to server transfer of messages.

22 Other Application Protocols
There are two other interesting application protocols: SNMP and Telnet. Simple Network Management Protocol (SNMP) aims to permit management of devices on the network. There is no lack of information such as performance counts from devices; instead there is too much information to manage it effectively. SNMP aims to manage devices effectively using alarms triggered by performance problems and faults, and allows devices to be configured.

23 Sockets The term socket doesn't define a protocol: it has two meanings, but neither of them relates to a protocol. One meaning is the socket programming API that was created initially by the University of Berkeley for BSD UNIX. BSD sockets were adapted as a programming interface for the Windows environment (and given the name WinSock). The WinSock API is wrapped in the .NET classes of the System.Net.Sockets namespace. Windows Sockets is a protocol independent programming interface for writing networking applications. The second usage of the term socket denotes an endpoint for communication between processes. In TCP/IP, an endpoint is bound to an IP address and a port number. We have to differentiate between stream and datagram socket types. A stream socket uses connection-oriented communication using the TCP/IP protocol; on the other hand the datagram socket uses connection-less communication using UDP/IP.

24 Domain Names It is not easy to remember IP addresses with the quad-notation, and so more human-friendly names are given to hosts on the network. Because such names must be unique, the domain name system used supports hierarchical names. Examples of such hostnames are, and These names don't have to have three parts, but reading from right to the left, the name starts with the top-level domain. These top-level domains are country-specific (such as or generic (such as .org) and are defined by the IANA (Internet Assigned Numbers Authority). The name appearing directly to the left of the top-level domain is the domain name. To the left of that name, the person or organization holding the domain is responsible for maintaining uniqueness.

25 Messaging Messaging is the process of sending messages from a client to a server. All networking protocols we have seen up to now require a connected environment. No matter if we use TCP or UDP sockets, the HTTP protocol, or .NET Remoting, the client and server must be running concurrently: that is, at the same time. With message queuing, the client and server can be running at different times, and the client can send messages even when the connection to the server is not be available. The message will be queued, and will reach the server at a later time. Message queuing also gives us an easy way to set priorities for messages, which can be useful in a connected environment too, where we may wish to read higher priority messages first. One scenario where message queuing can be particularly useful is when an application is run on a portable computer not connected to the company network, perhaps belonging to a sales person at a customer's site. Message queuing allows the application to send a message, but store it in the message queue of the client until connected back to the network. As far the application that sends the message is concerned, the message is sent immediately.

26 Client-server connection

27 Internet Organizations and Standards
There is a whole host of standards committees working on the development of networking specifications and standards. The table below lists the important groups in this area: Standards Organization Definition Web Site Technologies ISO International Organization for Standardization The International Standardization Organization defined the OSI network. The OSI Model is now commonly used. IEEE Institute of Electrical and Electronic Engineers IEEE is responsible for LAN standards and hardware specifications: Ethernet, Token Ring, MAN, Wireless LAN, Broadband. IAB Internet Architecture Board The IAB is responsible for editorial management of RFCs and appoints the IETF chair. IETF Internet Engineering Task Force Internet standards-RFCs can be found at the IETF. IANA Internet Assigned Numbers Authority As the name says-IANA is assigning Internet numbers like reserved IP address ranges, port numbers, protocol numbers, and so on. W3C World Wide Web Consortium The W3C is active developing Internet Technologies: HTTP, HTML, XML, SOAP, and so on

28 Summary This lecture has worked through the basics of networking to provide an overview of important networking concepts and networking protocols. We started with a discussion of the physical network, looking at the purpose and function of the crucial components of a network: network interface cards, hubs, routers, and switches. Another piece of fundamental knowledge that underpins much work in networking is that of the magic OSI seven-layer model. These seven layers are, from top to bottom, application, presentation, session, transport, network, data link, and physical. We've also had a close look at the headers of the key IP, TCP, and UDP protocols, in order to gain an understanding of connection-oriented and connection-less communication. We will start on network programming basics in the next lecture.

29 Q&A?

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