1. 1 Fall 2005 Internetworking: Concepts, Architecture and TCP/IP Layering Qutaibah Malluhi CSE Department Qatar University

2. 2 Motivation  There are many different LAN and WAN technologies  LAN –Low cost –Limited distance  WAN –High cost –Unlimited distance  No single networking technology best for all needs

3. 3 Universal Service  Arbitrary pair of computers can communicate  Fundamental concept in networking  Desirable but difficult in a heterogeneous world of incompatible networks –Electrical properties –Signaling and data encoding –Packet formats –Addresses –Link capacity mismatch –Different administrative authorities

4. 4 The Bottom Line Although universal service is highly desirable, incompatibilities among network hardware and physical addressing prevent an organization from building a bridged network that includes arbitrary technologies

5. 5 Internetworking  Internetworking is a scheme for interconnecting multiple networks of dissimilar technologies  Uses both hardware and software –Extra hardware positioned between networks –Software on each attached computer  System called an internetwork or an internet

6. 6 Routers  A router is a hardware component used to interconnect networks  Can interconnect networks that use different technologies –different media and media access techniques, physical addressing schemes, or frame formats.  A router has multiple interfaces on multiple networks  Router forwards packets between networks –Transforms packets as necessary to meet standards for each network  Some times called internet gateway Router Two net. interfaces Network 2Network 1

7. 7 Internet Architecture  Can have multiple networks with routers interconnecting them.  A host computer connects to a network  A router may have multiple network interfaces

8. 8 Multiple Routers  Would be possible to interconnect all networks in an organization with a single router?  Most organizations use multiple routers –Router has finite capacity (CPU speed and memory) – can not handle all traffic –Reliability -- ability to route around failures

9. 9 Create a Virtual Network  Internetworking software builds a single, seamless virtual network out of multiple physical networks –Universal addressing scheme –Universal service  All details of physical networks hidden from users and applications

10. 10 Routing  Routers use routing tables  Typically, routing tables specify the next hop for each destination Network ID –Routing table may contain next hop for a destination host (not a whole network) –Network routs simplify the routing table (dramatically reduce the number of entries in the routing table  Routing table typically have a default route entry  Route command in windows ( netstat –r in unix) to check the routing table

11. 11 Routing Table Example R1 R2 R3 R4 N1 N2 N4 N3 R5 Internet Destination NetworkNext Hop N1Local interface N2Local interface N4R4 (address of R4 on N1) N3R2 (address of R2 on N2) DefaultR5 (address of R5 on N1 Routing table for R1

12. 12 TCP/IP Internet Protocols  Most widely used internetworking protocol suite  Suite used in the public Internet  First internetworking protocol suite –Work began in 1970’s –Research originally funded by ARPA (currently DARPA) and other government agencies followed  Others internetworking protocol suites include IPX, VINES, AppleTalk  TCP/IP is vendor and platform independent

13. 13 TCP/IP Stack  Unlike ISO 7-layers model, TCP/IP has 5 conceptual layers (Internet) (Network Interface)

14. 14 Peer-to-Peer and Hop-to-Hop Processes

15. 15 Sending Data in the Internet model

16. 16 The physical layer is responsible for transmitting individual bits from one node to the next. Physical Layer

17. 17 The data link layer is responsible for transmitting frames on the same network from one node to the next. Data Link Layer

18. 18 Hop-to-Hop Delivery

19. 19 A node with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by one network. At the data link level this frame contains physical addresses in the header. These are the only addresses needed. The rest of the header contains other information needed at this level (e.g. frame type). The trailer contains error detection (CRC) bits. Example 1

20. 20 Network Layer The network layer is responsible for the delivery of packets from the original source to the final destination.

21. 21 End-to-End Delivery

22. 22 Example 2  We want to send data from a node with internetwork (IP) address A (e.g. and physical address 10, located on one LAN, to a node with a internetwork (IP) address P and physical address 95, located on another LAN. Because the two devices are located on different networks, we cannot use physical addresses only; the physical addresses only have local jurisdiction. What we need here are universal addresses that can pass through the LAN boundaries. The internetwork (logical) addresses have this characteristic.

23. 23 Transport Layer The transport layer is responsible for delivery of a message from one process to another.

24. 24 Reliable Process-to-Process Delivery

25. 25 Example 3  Data coming from the upper layers have port addresses j and k (j is the address of the sending process, and k is the address of the receiving process). Since the data size is larger than the network layer can handle, the data are split into two packets, each packet retaining the port addresses (j and k). Then in the network layer, internetwork addresses (A and P) are added to each packet.

26. 26 Application Layer The application layer is responsible for providing services to the user.

27. 27 Summary of TCP/IP Layer’s Responsibilities

28. 28 TCP/IP Layers (1)  Layer 1: Physical Layer –Corresponds to layer 1 in the ISO model –Defines basic networking hardware  Layer 2: Network Interface (Data Link) –Corresponds to layer 2 in the ISO model –Hardware (MAC) frame format –MAC addressing –Interface between computer and network (NIC)  Layer 3: Internetwork (Network) –Defines uniform format of packets forwarded across networks –Rules for forwarding packets in routers

29. 29 TCP/IP Layers  Layer 4: Transport –Corresponds to layers 4 and 5 in the ISO model –Provides reliable delivery of data  Layer 5: Application –Corresponds to ISO model layers 6 and 7 –Used for communication among applications

30. 30 TCP/IP Vs. OSI OSI Model TCP/IP (Internet) (Network Interface) Application 5

31. 31 Internet (Layer 3) Protocols  IP: combined with TCP they are known as the TCP/IP suite  ICMP (error-handling protocol)  OSPF, RIP, BGP (routing protocols)  IGMP (multicast protocol)  MOSPF, DVMRP, PIM (multicast routing protocols)  ARP, RARP (addressing protocols)

32. 32 UDP MIME OSPFICMP SNMP TELNET SMTPHTTPFTPBGP TCP IP Some Protocols in the TCP/IP suite Application Layer Transport Layer Internet Layer SNMP

33. 33 Summary  An internet is a collection of possibly heterogeneous physical networks interconnected into a single virtual network  Routers provide the physical interconnection and forward packets between networks  TCP/IP is the most widely used internetworking protocol suite