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TCP/IP Networks

TCP/IP Networks. Table of Contents. Computer networks, layers, protocols, interfaces; OSI reference model; TCP/IP reference model; Internet Protocol (operations, addresses, classes); Routing; Transmission Control Protocol (TCP); User Datagram Protocol (UDP); Applications;

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TCP/IP Networks

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  1. TCP/IP Networks

  2. Table of Contents • Computer networks, layers, protocols, interfaces; • OSI reference model; • TCP/IP reference model; • Internet Protocol (operations, addresses, classes); • Routing; • Transmission Control Protocol (TCP); • User Datagram Protocol (UDP); • Applications; • Sockets.

  3. Computer Networks • Hosts; • Routers - Gateways; • Bridges - Repeaters; • Data packets networks, ISDN, leased lines;

  4. Computer networks classification Shared media: Bus Ring Backbone network Vs local access network

  5. Switching Techniques • Circuit switching; • Message switching; • Packet switching.

  6. Host A Host A Layer 5 protocol Layer 5 Layer 5 Layer 4/5 interface Layer 4 protocol Layer 4 Layer 4 Layer 3/4 interface Layer 3 protocol Layer 3 Layer 3 Layer 2/3 interface Layer 2 protocol Layer 2 Layer 2 Layer 1/2 interface Layer 1 protocol Layer 1 Layer 1 Physical medium Protocol Hierarchies

  7. Layer 5 protocol Layer 5 M M Layer 4 protocol H4 M H4 M Layer 4 H3 H4 M1 H3 M2 H3 H4 M1 H3 M2 Layer 3 Layer 2 H2 H3 H4 M1 T2 H2 H3 M2 T2 H2 H3 H4 M1 T2 H2 H3 M2 T2 Layer 1 Source machine destination machine Information Flow

  8. OSI Reference Model The OSI reference model based on a proposal developed by ISO has seven layers. The principles that were applied to arrive at the seven layers are as follows: • A layer should be created where a different level of abstraction is needed; • Each layer should perform a well defined function; • The function of each layer should be chosen with an eye toward defining internationally standardised protocols; • The layer boundaries should be chosen to minimise the information flow across the interfaces; • The number of layers should be large enough that distinct functions need not be thrown together in the same layer out of necessity, and small enough that the architecture does not become unwieldy.

  9. Application Presentation Session Transport Network Data link Physical OSI Layers Functions Application: provides user access to an OSI environment. Presentation:hides from the application layer differences in representation of information. Session:provides facilities for synchronization. Transport: enables QoS network facilities. Network: establishes, maintains and terminates connections. Data Link: controls data transfer over physical link, including error detection. Physical: provides electrical and mechanical control to transmit data bits onto communication medium.

  10. Application Transport Internet Host-to- Network TCP/IP Reference Model • The protocols came first and model is just a description of existing protocols; • The TCP/IP reference model can not describe non-TCP/IP networks; • The layers 5 and 6 are not present in this model.

  11. Application Application Presentation Session Transport TCP UDP Network IP Data link Host-to- Network Physical OSI vs TCP/IP

  12. FTP, WWW,CMOT Telnet, rlogin, SMTP, TFTP, DNS, SNMP NFS, yp, etc. PING TCP UDP ARP ICMP IP RARP IEEE 802.2, 802.1 HDLC/X.25, PPP, SLIP IEEE 802.3 MAC IEEE 802.4 MAC IEEE 802.5 MAC IEEE 802.6 MAC Ethernet Token bus Token ring MAN WAN TCP/IP Detailed View

  13. Internet Protocol (IP) • Connectionless (i.e., each packet it treated independently, with no reference to packets that have long gone before); • Cannot guarantee reliable, in-order delivery; • PDU: • IP datagram, which contains user data, source-destination IP addresses, other inf. (such as its length, time-to-live, etc.); • IP main operations: • Fragmentation/Reassembly and Routing

  14. Fragmentation/Reassembly

  15. Reassembly Two options: either in host B, or in router G2. It is preferred the first option. Gain: Simpler routers (no buffering of fragments) Loss:decrement of network utilisation and increment of packet loss probability.

  16. IP Addresses • An IP address defines both the network and the host on the particular network; • An IP address has 4 bytes, so there are 4 billion addresses; • There is one-to-one correspondence between IP and physical addresses; • Example of an IP address : 147.102.7.1; • An IP address includes two parts: a network identifier (netid) and a host identifier (hostid); • The netid defines the network, while the hostid differentiate a host of the network from the others; • The length of netid depends on the address class: there are three address classes, namely A,B and C;

  17. Address Classes Class Α: 0 + 7bits (netid=1byte) + 3bytes (hostid); Class B: 10 + 14bits (netid=2byte) + 2bytes (hostid); Class C: 110 + 21bits (netid=3byte) + 1bytes (hostid); • When a network is separated into subnetworks, the hostid defines both the host and the subnetwork of the host. • <IP address>=<netid><subnetid><hostid> • A subnet mask (32-bit) indicates the split of hostid to subnetid and new hostid; • A subnet mask contains 1 for bits of netid and subnetid and 0 for bits of hostid; • Example: The mask 255.255.255.0 defines 14 subnetorks and 4094 hosts for each subnetwork.

  18. Domain Name Service (DNS) • The DNS servers correspond names such as “swpc94.telecom.ece.ntua.gr” in IP addresses like “147.102.7.94”; • However, the traffic of TCP/IP packets uses IP addresses and not names; • Before an Internet process, there is a dialogue (approx. 1/10 sec) between the source host and the local DNS server for finding the IP address of the target host.

  19. Routing • Direct routing: In the same network, usage of the Address Resolution Protocol (ARP) and Reserve Address Resolution Protocol (RARP) • Indirect routing: Between different networks, usage of the routers Routers • They can manipulate packets from all the interconnected networks; • They communicate with all the interconnected networks; • They are “multihomed”, i.e., they have multiple IP addresses referring to all the interconnected networks; • They perform routing algorithms using the netid of the IP datagrams.

  20. A B C 1 2 3 I II III Indirect Routing Example 3 separate physical networks, with their own addresses, packet size and pattern.

  21. A B D C 4 1 2 4 3 IV I II III Indirect Routing Example The networks are connected via two routers. The routers can send/receive packets to/from both networks.

  22. A B 1.2 1.1 1.3 1.4 D C 2.4 4 1 2 2.1 2.2 2.3 2.5 5 3 IV I 3.4 II 3.2 3.1 3.3 III Indirect Routing Example Introduction of the unique IP address for each host and the IP datagram as common transfer unit.

  23. A B D 3.3 data D C 4 1 2 5 3.3 data 5 3 IV I II iii 3.3 data III Indirect Routing Example • Each host or router forwards the datagram per one hop towards its destination. For each hop, the datagram is encapsulated into a specific physical layer packet with a local physical address. The datagram keeps the IP address of its destination. • The routers firstly exams the netid. • Only at the last hop of routing, the hostid is mapped to the physical address. • In case of fragmentation, the destination takes over the reassembly. 1.2 1.1 1.3 1.4 2.4 2.1 2.2 2.3 2.5 3.4 3.2 3.1 3.3

  24. N R N R 1.x Computation of the physical address 1.x direct connection 2.x 1.4 2.x direct connection 3.x 1.4 3.x 2.5 Indirect Routing Example • Both hosts and routers keep routing tables for leading the IP datagrams to destinations and physical addresses tables for mapping the IP addresses to corresponding physical addresses. • Routing Table: It contains pairs of the form (N,R), where N is the IP address of the destination network and R is the IP address of the next router towards the destination. • Examples: Router 1.4/2.4 Host 1.1 1.1 A 1.2 B Physical Addresses Table: 1.3 C 1.3 D

  25. A FTP 1500 21 B Telnet 1501 23 128.10.0.3 128.10.0.7 • reserved TCP port numbers (16 bits): FTP 21 Telnet 23 Finger 79 HTTP 80 Transmission Control Protocol (TCP) • Connection-oriented (i.e., a connection is established before the data transmission); • Can guarantee reliable stream delivery services;

  26. Transmission Control Protocol (TCP) • Sliding Window Technique; • Multiplicative Decrease Congestion Avoidance; • Slow Start Recovery; Allowed_window = min (Receiver_Advertisement, Congestion_Window)

  27. reserved UDP port numbers (16 bits): DNS 53 TFTP 69 SNMP 161 User Datagram Protocol (UDP) • Connectionless; • No confirmations, packets numbering, flow control; • No error detection/recovery; • Cannot guarantee reliable in order delivery services; • Mainly, broadcasting applications use UDP.

  28. Applications • FTP; • SMTP; • WWW; • Telnet; • Many others

  29. A FTP 1500 21 B Telnet 1501 23 128.10.0.3 128.10.0.7 Sockets • The combination of an IP address with a port number identifies a socket; • A socket defines an application service;

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