AUT CS461 Y24 Chapter 2 Protocols, Standards, and Architectures PDF

CS461 Protocols Motivation TCP/IP Standards Protocol Standards and Architectures CS461: Computer Networks HiLCoE - School of Computer Science and Technology  CS461 Contents Protocols Motivation The N...

CS461 Protocols Motivation TCP/IP Standards Protocol Standards and Architectures CS461: Computer Networks HiLCoE - School of Computer Science and Technology  CS461 Contents Protocols Motivation The Need for a Protocol Architecture TCP/IP Standards The TCP/IP Protocol Architecture Protocols and Standards  CS461 What is a Protocol? Protocols Motivation I Set of rules that two (or more) peer entities obey in TCP/IP order to communicate Standards I Syntax: format of data blocks; types of messages I Procedures: set of rules each peer must follow; timing information  Network Protocols and Standards  a protocol is a set of rules that governs data communications  a protocol defines what is communicated, how it is communicated, and when it is communicated  for instance, for one computer to send a message to another computer, the first computer must perform the following general steps  break the data into small sections called packets  add addressing information to the packets identifying the destination computer  deliver the data to the network card for transmission over the network  the receiving computer must perform the same steps, but in reverse order  accept the data from the NIC  remove transmitting information that was added by the transmitting computer  reassemble the packets of data into the original message  the key elements of a protocol are syntax, semantics, and timing  syntax: refers to the structure or format of the data  semantics: refers to the meaning of each section of bits  timing: refers to when data should be sent and how fast they can be sent  Some important characteristics of a protocol are: Direct /indirect If two systems share a point-to-point link - direct systems connect through a switched communication network – indirect Monolithic/structured Communications is a complex task for a single unit One big protocol vs. many structured protocols function as one Symmetric/asymmetric Communication between peer entities Vs Client/Server  – Standard /nonstandard Nonstandard protocols built for specific computers and tasks K sources and L receivers leads to K*L protocols and 2*K*L implementations If common protocol used, K + L implementations needed  Functions of Protocols  each device must perform the same steps the same way so that the data will arrive and reassemble properly; if one device uses a protocol with different steps, the two devices will not be able to communicate with each other  the following are categories of functions that form the basis of protocols  encapsulation  segmentation and reassembly  connection control  addressing  multiplexing  transmission services 1. Encapsulation the inclusion of control information to data is called encapsulation. Each frame contains not only data but also control information  such control information falls into three categories: address (sender/receiver), error-detecting code and protocol control (information about protocol functions) 2. Segmentation (by the sender also called fragmentation) and reassembly (by the receiver)  a block of data for transmission is of some bounded size  at the application level, we refer to a logical unit of data transfer as a message  lower level protocols may need to break the data up into blocks of some bounded size  this process is called segmentation  reasons for segmentation:  the communication network may only accept blocks of data up to a certain size  error control may be more efficient with a smaller frame size; fewer bits need to be retransmitted when a frame gets corrupted  facilitates more equitable access to shared transmission facilities (for example, without maximum block size, one station could monopolize a multipoint medium)  disadvantages  since a frame contains certain amount of control information, the smaller the block size, the greater the percentage overhead  frame arrivals may generate an interrupt that must be serviced; hence smaller blocks result in more interrupts  more time is spent processing smaller, more numerous frames  the counterpart of segmentation is reassembly  on receipt, the receiving device must reassemble the segmented data into a message appropriate to the application 3. Connection control  two types of protocols (services)  connectionless service  the packets are sent from one party to another with no need for connection establishment or connection release  the packets are not numbered, they may be delayed, lost, or arrive out of sequence; there is no acknowledgement either  UDP (User Datagram Protocol), one of the transport layer protocols, is connectionless  good for one time transaction; e.g., email  connection-oriented service  in connection-oriented data transfer, a logical association or connection is established between the communicating computers (devices)  long sustained session  orderly and timely delivery of packets, e.g., FTP  three phases are involved  connection establishment (agreement to exchange data)  data transfer (data and control information exchanged)  connection termination (termination request) - by any of the two parties  TCP (Transport Control Protocol) is connection-oriented  the key characteristics of connection-oriented data transfer is that sequencing is used  each side sequentially numbers the frames that it sends to the other side  because each side remembers that it is engaged in a logical connection, it can keep track of both outgoing numbers, which it generates, and incoming numbers which are generated by the other side  sequencing supports three main functions  ordered delivery: frames may not arrive in the order in which they were sent, because they may traverse different paths  flow control: a receiving station has to limit the amount or rate of data that is sent by a transmitting station  the simplest form of flow control is stop-and-wait procedure in which each frame must be acknowledged before the next can be sent  more efficient protocols involve some form of credit provided to the transmitter, which is the amount of frames that can be transmitted without an acknowledgement; e.g. sliding window technique   error control: error control is implemented as two separate functions; error detection and retransmission  if an error is detected, the receiver discards the frame  upon failing to receive an acknowledgement to the frame in a specified reasonable time, the sender retransmits the frame  some protocols also employ error correction which enables the receiver not only to detect errors but, in some cases, to correct them 4. addressing  a unique address is associated with each end-system in a configuration (e.g. workstation, server) and each intermediate system (e.g. router)  an example is an IP address in TCP/IP connection 5. multiplexing  occurs when multiple connections share a single connection (multiple access) 6. transmission services  a variety of additional services can be provided  priority: messages such as control messages may need to get through to the destination station with minimum delay  security: security mechanisms, restricting access, may be invoked  Protocols in a layered architecture  protocols that work together to provide a layer or layers of the model are known as a protocol stack or suite, e.g. TCP/IP  each layer handles a different part of the communications process and has its own protocol  CS461 The Need for a Protocol Architecture Protocols Motivation I Data communications is complex! TCP/IP I Apply divide-and-conquer principle: Standards I Break communication tasks into subtasks I Implement subtasks separately in layers I Layers arranged in vertical stack I Layer N uses services of layer N − 1 I Layer N provides services to layer N + 1 I Peer layers communicate with a protocol I Combine the layers to get protocol architecture  CS461 Layers Protocols Motivation Divide-and-Conquer TCP/IP Standards I As data communications is complex, separate tasks into layers I Design and implement protocols for each layer Advantages I Simplify design and implementation I Change/upgrade protocols without modifying the whole system I Select implementations from different vendors Disadvantages I Sub-optimal designs, overheads of each layer  CS461 Layers and Devices Protocols Motivation I One or more protocols are implemented in each layer in TCP/IP a device Standards I End devices (hosts) implement all layers in stack I Intermediate devices usually do not implement all layers I May refer to device by highest layer it implements, e.g. “layer 2 device” I Modems, amplifiers and repeaters are related to physical layer, layer 1 devices I Layer 2 switches, Ethernet switches, WiFi access points are layer 2 devices I Routers are layer 3 devices  CS461 TCP/IP Layering Concepts Protocols Motivation Source Host Destination Host TCP/IP Application Application Standards Transport Transport Router Network Network Network Data Link DL DL Data Link Physical Phy Phy Physical Transmission link 1 Transmission link 2  CS461 TCP/IP Layers Protocols Motivation 1. Physical Layer TCP/IP Physical interface between transmission device and medium; Standards how to send bits over transmission medium: data rate, signalling, electrical signals, codecs, modems,... 2. Data Link Layer Transmission of data over link to which the device is attached; addressing scheme of destination device; allows layers above to ignore details of links; may provide reliability; sometimes called: “network Access”, “MAC”, “Link”, “Hardware” layer  CS461 TCP/IP Layers Protocols Motivation 3. Network Layer TCP/IP Allows hosts to communicate across different networks; Standards provides routing across the Internet; may provide congestion control, quality of service; sometimes called: “IP”, “Internet” layer 4. Transport Layer Transfer of data between end-points; connect processes running in OS of host; may provide error control, flow control, congestion control, reliable delivery. 5. Application Layer Provides functionality needed for various applications  CS461 Common Features of Protocols Protocols I Headers are added to data to carry control information; Motivation referred to as encapsulation TCP/IP I E.g. source/destination address, sequence number, Standards error-detection code I Header + data is called Protocol Data Unit (PDU) I Segmentation: sometimes data must be divided into smaller chunks at source (and re-assembled at destination)  CS461 Contents Protocols Motivation The Need for a Protocol Architecture TCP/IP Standards The TCP/IP Protocol Architecture Protocols and Standards  CS461 Origins and Terminology Protocols I ARPANET uses two key protocols, TCP and IP; Motivation together (as well as other related protocols) referred to TCP/IP as TCP/IP protocol suite Standards I Used in global Internet today I Many protocol standardised by Internet Architecture Board (IAB) and Internet Engineering Task Force (IETF) I No official protocol architecture; generally divided into 5 layers I ISO developed Open Systems Interconnection (OSI) protocol architecture in 1970’s I Protocol architecture: 7-layer OSI Reference Model I TCP/IP won! I Not used in practice today; principles and terminology still applied  CS461 Data Communications Across a Link Protocols Motivation Computer A Computer B TCP/IP Standards NIC Tx Rx NIC LAN cable I Converting data (e.g. bits) into signals to be sent across the link (Physical layer) I Ensuring link is ready for data transmission, reliable/efficient transmission of data (Data link layer)  CS461 Data Communications Across a Network Protocols Motivation Source Destination TCP/IP Standards Intermediate Intermediate Intermediate System A System B System N Tx Rx Tx Rx Tx Rx Tx Rx I Data traverses multiple links; each link may have its own Physical and Data Link layer protocols I How do intermediate systems receive/send data? How to select which intermediate systems to send via? (Network layer) I What happens if failures within intermediate systems? How to create applications without knowing the details of underlying network and technologies?  CS461 General Layered Architecture Protocols Motivation Source Destination TCP/IP Application Application Standards Support Support Intermediate Intermediate Intermediate System A System B System N Network Network Network Network Network Link Link Link I Layers to support: I Communications across a link I Communications across a network I Applications to operate efficiently on end devices I Different specific layered architectures have been developed I Some are standards (e.g. OSI); others are loosely defined (e.g. Internet stack)  CS461 OSI 7-layer Protocol Architecture Protocols Motivation Application specific functionality Application TCP/IP Converts data between different formats, encryption Standards Application Presentation and decryption Support Maintains session between applications Session Reliable data transfer between end devices Transport Allow computers to communicate across different networks Network Network Provide routes, optionally performance enhancements Transmit data across link in efficient, reliable way Data Link Addressing of devices on links Link Physical interface between transmission device and medium Physical How to send bits over medium I ISO developed Open Systems Interconnection (ISO) in 1970’s I TCP/IP became more popular; but concepts and terminology still used today I Others: IBM SNA, Appletalk, Novel IPX; SS7, UMTS, IEEE 802,...  CS461 TCP/IP 5-layer Protocol Architecture Protocols Motivation Application specific functionality Application Application TCP/IP Support Reliable data transfer between end devices Standards Transport Maintains session between applications Allow computers to communicate across different networks Network Network Provide routes, optionally performance enhancements Transmit data across link in efficient, reliable way Data Link Addressing of devices on links Link Physical interface between transmission device and medium Physical How to send bits over medium I There is no standard definition of the layers I Sometimes have different names, and overlap between functionality  CCS461 Implementing Layers Networks Layering TCP/IP User Processes Examples Application Operating System Transport Network Network Interface Card Data Link Physical  CS461 Example Protocols in the TCP/IP Networks Layering TCP/IP HTTP, FTP, SMTP, SSH Examples Application TCP, UDP SCTP, DCCP Transport IP ICMP, OSPF, ARP Network Data Link Ethernet ATM Frame Relay Wireless LAN SDH PDH Physical Twisted pair, optical fibre, satellite  CS461 Example Application: Web Browsing with HTTP Networks Layering TCP/IP Web Browser Web Server Examples 1 GET /test/index.html 2 HTTP/1.1 200 Ok 3 Test...  CS461 Encapsulation in TCP/IP Networks Layering Example: web browser has requested web page from server; TCP/IP server needs to send the page requested back to browser Examples Data User data HTTP Application message header TCP TCP segment header IP header IP datagram Ethernet Ethernet Ethernet frame header trailer 10100110110111010010100101...10010111010110100001101011010 Physical bits Physical signal  CS461 Other Protocol Architectures Protocols Motivation I OSI 7-layer Reference Model TCP/IP I Older architectures: IBM SNA, Appletalk, Novell IPX Standards I Domain specific architectures: Signalling System 7 (SS7) for telephone signalling; UMTS for 3G mobile telecommunications;...  CS461 Contents Protocols Motivation The Need for a Protocol Architecture TCP/IP Standards The TCP/IP Protocol Architecture Protocols and Standards  CS461 Protocols and Standards Protocols Motivation Protocols TCP/IP Standards I Rules that communicating entities follow I Implemented in hardware and software on computing devices Standards I Agreed-upon rules; protocols that some organisation has agreed upon I Create open and competitive market I Allow national and international interoperability  CS461 Standard Development Organisations Protocols Motivation I International Organisation for Standardisation (ISO): TCP/IP formed from national standards bodies to create global Standards standards I International Telecommunication Union(ITU): formed from national telecom operators and other organisations to create global standards for telecoms I Institute of Electrical and Electronics Engineers (IEEE): professional engineering society that develops standards in electronics, radio and electrical engineering I Internet Engineering Task Force (IETF): develops most standards for the Internet I World Wide Web Consortium (W3C): develops web based standards (e.g. HTML) I Forums and Special Interest Groups: companies working together on specific technologies I Regulatory agencies: set regulations on use of communication technologies  TCP/IP protocol stack Two levels of addressing are needed Unique global Internet address (IP address) Each process with a host must have an address that is unique within the host (Port number  Application/Process layer Protocols at this layer are categorized as: User Protocols that provide service directly to users, & Support Protocols that provide common system functions – User Protocols: FTP, SMTP, Telnet – Support Protocols: DNS, DHCP, SNMP Telnet - allows a user on a remote client machine, called the Telnet client, to access the resources of another machine, the Telnet server. – Telnet makes client machine appear as though it were a terminal directly attached to the server. File Transfer Protocol (FTP) - is the protocol that actually lets us transfer files, and it can accomplish this between any two machines using it. – Usually users are subjected to authentication Network File System (NFS) - a protocol specializing in file sharing allowing two different types of file systems to interoperate.  Simple Mail Transfer Protocol (SMTP) - uses a spooled, or queued, method of mail delivery. – POP3 is used to receive mail. Simple Network Management Protocol (SNMP) - collects and manipulates valuable network information. – This protocol stands as a watchdog over the network, quickly notifying managers of any sudden turn of events. Domain Name Service (DNS) – resolves hostnames—specifically, Internet names, such as www.aau.edu.et to the IP address 10.6.10.3 Dynamic Host Configuration Protocol (DHCP) - gives IP addresses to hosts. – It allows easier administration and works well in small-to-even- very large network environments.  Transport layer Transmission Control Protocol (TCP) - takes large blocks of information from an application and breaks them into segments. – It numbers and sequences each segment so that the destination’s TCP protocol can put the segments back into the order the application intended. – Uses three way handshaking User Datagram Protocol (UDP) - does not sequence the segments and does not care in which order the segments arrive at the destination. But after that, UDP sends the segments off and forgets about them. It doesn’t follow through, check up on them, or even allow for an acknowledgment of safe arrival — complete abandonment. TCP for reliability and UDP for faster transfers.  TCP and UDP must use port numbers These port numbers identify the source and destination application or process in the TCP segment. There are 2^16 = 65536 ports available. – Well-known ports - The port numbers range from 0 to 1023. – Registered ports - The port numbers range from 1024 to 49151. Registered ports are used by applications or services that need to have consistent port assignments. – Dynamic or private ports - The port numbers range from 49152 to 65535. These ports are not assigned to any protocol or service in particular and can be used for any service or application. If a port is closed/blocked, you cannot communicate with the computer by the protocol using that port. – Eg. If port 25 is blocked you cannot send mail. Firewalls by default block all ports. You should know the port numbers of different protocols!!  TCP UDP Sequenced Unsequenced Reliable, Acknowledgments, & 3- Unreliable way handshake Connection-Oriented Connectionless Checksum for error checking Checksum for error checking Flow Control No flow control Assign datagram size dynamically Datagram segment is the same in size  Internet Layer Internet Protocol (IP) essentially is the Internet layer. The other protocols found here merely exist to support it. It can do this because all the machines on the network have a software, or logical, address called an IP address. Internet Control Message Protocol (ICMP) works at the Network layer and is used by IP for many different services. – ICMP is a management protocol and messaging service provider for IP. – The following are some common events and messages that ICMP relates to: Destination Unreachable If a router can’t send an IP datagram any further, it uses ICMP to send a message back to the sender, advising it of the situation. Buffer Full If a router’s memory buffer for receiving incoming datagrams is full, it will use ICMP to send out this message until the congestion abates.  Hops Each IP datagram is allotted a certain number of routers, called hops, to pass through. If it reaches its limit of hops before arriving at its destination, the last router to receive that datagram deletes it. The executioner router then uses ICMP to send a message, informing the sending machine of the end of its datagram. Ping (Packet Internet Groper) uses ICMP echo messages to check the physical and logical connectivity of machines on a network. Traceroute Using ICMP timeouts, Traceroute is used to discover the path a packet takes as it traverses an internetwork. Address Resolution Protocol (ARP) finds the hardware address of a host from a known IP address. – ARP interrogates the local network by sending out a broadcast asking the machine with the specified IP address to reply with its hardware address. Reverse Address Resolution Protocol (RARP) discovers the identity of the IP address for diskless machines by sending out a packet that includes its MAC address and a request for the IP address assigned to that MAC address. – – A designated machine, called a RARP server, responds with the answer, and the identity crisis is over.  Network Access Layer Protocols Point to Point Protocol (PPP) – Used to establish a connection to your ISP via modem – Is used to carry out the following functions Data encapsulation Link Control Network Control Wireless Fidelity (Wi-Fi) – Allows computers and other devices to communicate over a wireless signal – Describes all network components that are based on one of the 802.11 standards, including 802.11b, 802.11g, and 802.11n  LAYERED TASKS We use the concept of layers in our daily life. As an example, let us consider two friends who communicate through postal mail. The process of sending a letter to a friend would be complex if there were no services available from the post office. Figure 1 Tasks involved in sending a letter THE OSI MODEL Established in 1947, the International Standards Organization (ISO) is a multinational body dedicated to worldwide agreement on international standards. An ISO standard that covers all aspects of network communications is the Open Systems Interconnection (OSI) model. It was first introduced in the late 1970s. Note ISO is the organization. OSI is the model. Figure 2 Seven layers of the OSI model Figure 3 The interaction between layers in the OSI model Figure 4 An exchange using the OSI model Figure 5 Physical layer Note The physical layer is responsible for movements of individual bits from one hop (node) to the next. Figure 6 Data link layer Note The data link layer is responsible for moving frames from one hop (node) to the next. Figure 7 Hop-to-hop delivery Figure 8 Network layer Note The network layer is responsible for the delivery of individual packets from the source host to the destination host. Figure 9 Source-to-destination delivery Figure 10 Transport layer Note The transport layer is responsible for the delivery of a message from one process to another. Figure 11 Reliable process-to-process delivery of a message Figure 12 Session layer Note The session layer is responsible for dialog control and synchronization. Figure 13 Presentation layer Note The presentation layer is responsible for translation, compression, and encryption. Figure 14 Application layer Note The application layer is responsible for providing services to the user. Figure 15 Summary of layers  TCP/IP PROTOCOL SUITE The layers in the TCP/IP protocol suite do not exactly match those in the OSI model. The original TCP/IP protocol suite was defined as having four layers: host-to- network, internet, transport, and application. However, when TCP/IP is compared to OSI, we can say that the TCP/IP protocol suite is made of five layers: physical, data link, network, transport, and application. Figure 16 TCP/IP and OSI model