Internetworking??

1. Internetworking??

2. A collection of individual networks, connected by intermediate networking devices, that functions as a single large network • Internetworking challenges: • Support of communication between disparate technologies (different types of media, speed, etc.) • Reliable and consistent access to network resources • Centralized network mana-gement and troubleshooting • Flexibility for network expansion and new applications and services • Need of a general reference model describing how information is moved from software in one to another computer What is Internetwork?

3. Developed by the International Organization for Standardization (1984) • Tasks involved with moving information are divided into 7 smaller, more manageable task groups (OSI layers) with specific particular network functions • Each layer is reasonably self-contained: • Layer tasks can be implemented independently • Any layer can be updated without adversely affecting the other layers Open Systems Interconnection (OSI) Reference Model

4. Upper layers: • Deal with applications containing a communication component • Implemented by software only • Closest to the end user • Lower layers: • Handle data transport • Physical and Data Link are implemented in HW and SW, the other by SW • Closest to the transfer medium OSI Layers

5. OSI model = conceptual framework for communication but not a method of communication • Protocol = a formal set of rules and conventions that governs how computers exchange information over a network medium • Actual communications is based on communication protocols: • LAN protocols operate on Data Link and Network layers (communication over LAN) • WAN protocols – on 3 bottom layers (communication over WAN) • Routing protocols – on Network layer (path determination and traffic switching) • Network protocols – various upper-layer protocols (exist in a given protocol suite) Protocols and OSI Model

6. SW passes its information to be sent to the Application layer. Then it must pass trough all other layers as far as the Physical layer Ţ medium Ţ the Physical layer in computer B, … • A layer communicates with: • Directly adjacent layers in the same system • Peer layer in other system • OSI-layer services: • User (requests services) • Service provider (adjacent layer) • Service access point OSI Model and Communication between Systems and Layers

7. Control information (specific request and instruction) must be exchanged between peer layers • Forms: header and trailers • Encapsulation: data coming from upper layer contains upper layer control informationŢa new additional control info of the layer will be added OSI Layers and Information Exchange

8. defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between communicating network systems (such characteristics as voltage levels, timing of voltage changes, physical data rates, maximum transmission distances, and physical connectors) Physical Layer

9. Provides reliable transit of data across a physical layer.Different data link layer specifications definedifferent network and protocol specification, including: • physical addressing at the data link layer (opposed to network addressing), • network topology consisting of the data link layer specifications (e.g. topology – a bus or a ring, etc.) • error notification – alerts upper-layers protocols at a transmission error occurrence, • sequencing of frames – reorder frames transmitted out of sequence • flow control – moderates transmission of data (receiving device must not be overwhelmed with more traffic than it can handle at one time) • IEEE subdivides the data link layer into Logical Link Control (LLC) and Media Access Control (MAC) Data Link Layer

10. Provides routing and related functions that enable multiple data links to be combined into an internetwork and accomplished by the logical addressing • Supports both higher level protocols: connection-oriented and connectionless services Transport Layer • Implements reliable internetwork data transport services that are transparent to upper layers • Functions: • Flow control – manage data transmission between devices (sending no more data than can be processed in receiver) • Multiplexing data from several applications to be transmitted onto a single physical link • Error checking – creating various mechanism for detecting errors and taking an action to error recovery to resolve occurred error Network Layer

11. establishes, manages, and terminates communication sessions between presentation layer entities • Session consists of: services requests and service responses between applications in different network devices • This communication is coordinated by protocols implemented in session layer Presentation Layer • Provides a variety of coding and conversion functions that are applied to application data layer to ensure readability information sent between applications in different systems • Common activities: • Conversion of common data representation formats (e.g. ASCII and EBCDIC) • Data compression and decompression • Standard data encryption and deciphering (MPEG, GIF, JPEG, …) Session Layer

12. Closest to the user – interacts directly with communicating components of application software (out of OSI model scope) • Typical activities: • Identifying communication partners – identity and availability • Determining sufficient resource availability for requested communication • Synchronizing communication between application Application Layer

13. Frame is an information unit whose source and destination are data link layer entities. • Packet is an information unit whose source and destination are network-layer entities. Information Formats

14. Datagramusually refers to an information unit whose source and destination arenetwork-layer entities that use connectionless network service. • Segmentusually refers to an information unit whose source and destination aretransport-layer entities. • Messageis an information unit whose source and destination entities exist above the network layer(often the application layer). • Cellis an information unit of a fixed size whose source and destination are data-link layer entities and it is usually used in switched environments, such as Asynchronous Transfer Mode (ATM) networks. A cell is composed of the header andpayload. The header contains control information intended for the destination data-link layer entityand is typically 5 bytes long. The payload contains upper-layer data that is encapsulated in the cellheader and is typically 48 bytes long. Information Formats

15. Connection-oriented service = uses a specific path established for the duration of a connection. Phases: • Establishment of connection = static reservation of a path to ensure consistent grade of services (e.g. guaranteed throughput rate) • Data transfer = sequential transfer – data always arrives in the order in which it was sent (disadvant.: broken line = connection interruption) • Termination of connection = new communication needs establishment a new connection • Connectionless service = no specific transfer path is determined = packets go through different pathŢeach packet must be completely addressed and is handled independentlyŢ • No guarantee of packet sequencing at receiving and throughput rate • Dynamic = more efficient using of network resources • Broken line recovering Connection in Network Services

16. Data Link Layer Addressing = fixed physical (hardware) addresses uniquely identifying each interface on a device • MAC addresses = subset of data link addresses used especially in LAN (e.g. Ethernet – 24 + 24bits: vendor identification + serial number) • Network Layer Addressing = unfixed virtual (logical) addresses one for each network protocol in a device interface (but only one physical address). Assignment: • Static = network administrator • Dynamic = getting a new one at each connecting to network (usually by server) Internetwork Addressing

17. Introduction to the Internet

18. Developed in mid-1970s by Stanford University under the Defense Advanced Research Project Agency grant • Suite of protocols known also as TCP/IP protocols Background

19. Basic network-layer protocol containing addressing and some control information that enable packet to be routed • IP has two primaryresponsibilities: • providing connectionless,best-effort delivery of datagramsthrough aninternetwork; • providing fragmentation andreassembly of datagrams tosupport data links withdifferentunit sizes. Internet Protocol (IP)

20. Each host on TCP/IP network has assigned a unique 32-bit logical address divide into the network number and the host • Network number must be assigned by the Network Information Center • Host number – by the network administrator IP Addressing

21. IP Address Classes Classes D – multicast groups and E – experimental are not available for commercial use. Masks – some part of host address may be designated for creating subnets

22. ARP = discovering the MAC address corresponding to IP address • RARP = reverse ARP = mapping MAC address to IP address (in networks with dynamic assignation of IP addresses) Internet Control Message Protocol (ICMP) • Network-layer protocol that provides message packets to report error and other information regarding IP packet processing • ICMP messages: destination unreachable, host unreachable, protocol unreachable, port unreachable, echo request, redirect messages, time-exceeded messages ARP and RARP

23. Connection-less transport-layer protocol • Provides reliable transmission with: • Stream data transfer – unstructured data stream is divided into sequence identified by number and passed to IP • Reliability – three-way handshaking based on forward acknowledgement technique • Efficient flow control – sending back acknowledgement with highest sequence number which can be received • Full-duplex operation • Multiplexing – many simultaneous upper-layer can be multiplexed over a single connection Transmission Control Protocol (TCP)

24. Ports = points for processing TCP services by various upper-layerprotocols • Sequence number = number of first data byte in sequence • Acknowledgement num. = number of expected data byte in sequence • Flags = various flag bits includingSYN and ACK bits • Window = receiver buffer capacity TCP Packet Format

25. Connection-less transport-layer protocol – interface between IP and upper-layer protocols • Unlike TCP, UDP adds no reliability, flow-control, and error recovery functions to IP • Consumes less network overhead than TCP • Used for NFS, SNMP, DNS, TFTP, … User Datagram Protocol (UDP)

26. Numerous suite of various protocols, e.g.: • File Transfer Protocol – FTP • Telnet – terminal emulation • Network File System (NFS), External Data Representation (XDR), and Remote Procedure Call (RPC) – work together to enable transparent access to remote network resources • Simple Mail Transfer Protocol (SMTP) – electronic mail services • Domain Name System (DNS) – translation of network node names into network addresses • Hypertext Transfer Protocol (HTTP) – transfers in WWW • … Upper-layer Internet Protocols