1. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 1 4.0 Internetworking LAN connecting devices  Repeater, bridge, router, gateway, backbone networks TCP/IP protocol (Transmission Control Protocol/Internet Protocol) IP addressing Circuit switching/Packet switching

2. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 2 4.1 Devices connecting LANs connecting devices are used to connect LANs to one another or to the internet.

3. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 3 4.1 Devices connecting LANs different categories of connecting devices based on the layer in which they operate in a network :

4. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 4 4.1.1 Repeater operates only in the physical layer a repeater receives a signal, and before it becomes too weak or corrupted, regenerates the original bit pattern, and sends the refreshed signal A repeater does exactly that- it repeats any electrical signals that come into one port, out its other port(there are only 2 ports on a repeater) can extend the physical length of a LAN connects two segments of the same LAN ex : 10Base5 Ethernet cable restricted to 500m, divide the cable into segments and repeaters are installed between them

5. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 5 4.1.1 Repeater a repeater vs amplifier ?  amplifier amplifies equally everything fed into it (signal + noise)  a repeater regenerates the signal – receives the weakened signal, creates a copy, bit for bit, at the original strength

6. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 6 4.1.1 Repeater installation of repeater

7. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 7 4.1.2 Hub actually a multiport repeater (repeater is a 2 port devices) used to create connections between stations in a physical star topology Any electrical signal that comes into one port, goes out all other ports A repeater and hub works only at physical layer an intelligent device compared to repeater or hub able to forward the packet/data flow through it to the destination specified in the packet of data keeps track of all Ethernet devices connected to it using their MAC address and recording what port that MAC address is connected to then, it intelligently uses that table (MAC Address table) to switch Ethernet frames only to the Ethernet port where that traffic is destined to go to this saves bandwidth and PC processing power. 2 layer switch – bridge, 3 layer switch - router. 4.1.3 Switch

8. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 8 4.1.4 Bridge operates in both the physical and the data link layer at the physical layer, it regenerates the signal it receives at the data link layer, the bridge can check the physical (MAC) address (source and destination) contained in the frame

9. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 9 4.1.4 Bridge what the difference between bridge and switch? functionally they are same. both work at Layer 2, both store, examine, and forward packets only to the specified destination. bridges came first, then multi-port bridges which are basically switches. These days bridges are used mainly to connect two different LANs, where switches are more commonly used in place of hubs, or to extend collision domains. A collision domain is a physical network segment where data packets can "collide" with one another for being sent on a shared medium, in particular in the Ethernet networking protocol

10. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 10 4.1.4 Bridge multiport bridge = switch

11. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 11 4.1.4 Bridge Transparent bridge – a bridge in which the stations are completely unaware of the bridge existence (no reconfiguration is necessary when the bridge is added or deleted from the system) 3 criteria of transparent bridge : Frames must be forwarded from one station to another Forwarding table is automatically made by learning frame movements in the network Loops in the system must be prevented

12. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 12 4.1.4 Bridge Learning process in transparent bridge

13. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 13 4.1.4 Bridge Learning process in transparent bridge when station A sends a frame to station D, the bridge does not have an entry for either D or A. The frame goes out from all three ports; the frame floods the network. However by looking at the sources address, the bridge learns that station A must be located on the LAN connected to port 1. This means that frames destined for A in the future, must be sent out through port 1. The bridge add this entry to its table. when station E sends a frame to station A, the bridge has an entry for A, so it forwards the frame only to port 1. There is no flooding. In addition, it uses the source address of the frame, E, to add a second entry to the table. when station B sends a frame to C, the bridge has no entry for C, so once again it floods the network and adds one more entry to the table. and so on..

14. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 14 4.1.4 Bridge Loop problem transparent bridges work fine as long as there are no redundant bridges in the system. system administrators, however, like to have redundant bridges (more that one bridges between a pair of LANs) to make the system more reliable – if a bridge fails, another bridge takes over until the failed one is repaired or replaced. redundancy can create loops in the system which is undesirable.

15. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 15 4.1.4 Bridge Loop problem

16. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 16 4.1.4 Bridge Loop problem station A sends a frame to station D. The tables on both bridges are empty. Both forward the frame and update their tables based on the source address A. now there are two copies of the frame on LAN 2. The copy sent out by bridge 1 is received by bridge 2, which does not have any information about the destination address D; it floods the bridge. The same scenario also happens to the copy sent out by bridge 2 which is received by bridge 1. now there are two copies of the frame on LAN 1. Step 2 is repeated, and both copies flood the network. the process continues on and on, unable to update the information on address D in the table.

17. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 17 4.1.4 Bridge Spanning Tree – in Graph Theory, a spanning tree is a graph in which there is no loop. In a bridged LAN, this means creating a topology in which each LAN cab be reached from any other LAN through one path only (no loop). to find the spanning tree, a cost (metric) need to be assigned to each connection path with minimum hops (nodes) – hop count path with minimum delay path with maximum bandwidth

18. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 18 4.1.4 Bridge Spanning Tree figure a : the actual physical layout figure b : graph representation with cost assigned to each arc (connection) hop count 1 from bridge to LAN hop count 0 from LAN to bridge

19. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 19 4.1.4 Bridge Steps of creating Spanning Tree

20. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 20 4.1.4 Bridge Steps of creating Spanning Tree every bridge has a built-in ID. Each bridge broadcasts this ID so that all bridges know which one has the smallest ID. The bridge with the smallest ID is selected as the root bridge (root of the tree). We assume that bridge B1 has the smallest ID. It is, therefore, selected as the root bridge. the algorithm tries to find the shortest path (a path with the shortest cost) from the root bridge to other bridge or LAN. The shortest path can be found by examining the total cost from the root bridge. Based on the spanning tree, mark the ports that are part of the spanning tree, the forwarding ports, which forward a frame that the bridge receives. Those ports that are not part of the spanning tree, are also marked as blocking ports, which blocks the frame received by the bridge. At the end, there is only one single path from any LAN to any other LAN in the spanning tree system. Means there is only one single path from one LAN to any other LAN – no loops are created. Spanning tree algorithm is implemented through the software package in the bridge that carries out this process dynamically.

21. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 21 4.1.4 Bridge Forwarding and blocking ports after using spanning tree algorithm

22. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 22 4.1.5 Router routes packets based on their logical addresses (host-to-host addressing) normally connects LANs and WANs in the internet and has a routing table that is used for making decisions about the route. the routing tables are normally dynamic and updated using routing protocols.

23. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 23 4.1.5 Router routes in an internet

24. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 24 4.1.6 Gateway a device used to connect two separate networks that use different communication protocols a gateway is normally a computer that operates in all 5 layers of the Internet (TCP/IP protocol suite) or seven layers of OSI model takes an application message, reads it and interprets it can provide security – used to filter unwanted application layer message

25. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 25 4.1.7 Backbone Networks a backbone network allows several LANs to be connected. In a backbone network, no station is directly connected to the backbone; the stations are part of a LAN, and the backbone connects the LAN. Two most common : bus and star backbone

26. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 26 4.1.7.1 Backbone Networks : Bus Backbone in a bus backbone, topology of the backbone is a bus normally used as a distribution backbone to connect different buildings in an organization. ex : connects single or multiple-floor buildings on a campus

27. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 27 4.1.7.1 Backbone Networks : Bus Backbone in a previous figure, is a station in a LAN needs to send a frame to another station in the same LAN, the corresponding bridge blocks the frame; the frame never reaches the backbone. is a station needs to send a frame to a station in another LAN, the bridge passes the frame to the backbone, which is received by the appropriate bridge and is delivered to the destination LAN.

28. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 28 4.1.7.2 Backbone Networks : Star Backbone in a star backbone, the topology of the backbone is a star. the backbone is just one switch that connects the LANs. mostly used as a distribution backbone inside a building.

29. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 29 4.2 TCP/IP Protocol Suite TCP/IP (Transmission Control Protocol/Internet Protocol) - a set of communications protocols that has evolved since the late 1970s developed by the US Defense Advanced Research Project Agency (DARPA) for its packet switched network (ARPANET). because programs supporting these protocols are available on so many different computer systems, they have become an excellent way to connect different types of computers over networks. developed prior to the OSI model. consists of collection of protocols issued as standards. define as having four layers :  Host-to-network  Internet  Transport  Application

30. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 30 4.2 TCP/IP Protocol Suite

31. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 31 4.2 TCP/IP Protocol Suite Physical and Data Link Layers  TCP/IP does not define any specific protocol.  Support all the standard and proprietary protocols. Network layer (internet layer)  Use the Internetworking Protocol (IP).  The IP uses 4 supporting protocols : 1. ARP – Address Resolution Protocol 2. RARP – Reverse Address Resolution Protocol 3. ICMP – Internet Control Message Protocol 4. IGMP – Internet Group Message Protocol

32. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 32 4.2 TCP/IP Protocol Suite Internetworking Protocol (IP)  is a transmission mechanism used by the TCP/IP protocols  is an unreliable and connectionless protocol – best effort delivery service  Best effort delivery IP provides no error checking or tracking Assume the unreliability of the underlying layers and does it best to get a transmission through to its destination without any guarantee.  Transport data in packet called datagram  Each datagram is transported separately.  Datagrams can travel along different routes and can arrive out of sequence or be duplicated.  IP does not keep track of the routes and has no facility for reordering datagrams once they arrive at the destination.  IP provides bare-bones transmission function that free the user to add only those facilities necessary for a given application and this allows for max efficiency.

33. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 33 4.2 TCP/IP Protocol Suite Address Resolution Protocol (ARP)  used to associate a logical address with a physical address  On a typical physical network like LAN, each device on a link is identified by a physical address (usually imprinted on the network interface card (NIC)  ARP is used to find the physical address of the node when the its Internet address is known. Reverse Address Resolution Protocol (RARP)  Allows a host to discover its Internet address when it knows only its physical address. Internet Control Message Protocol (ICMP)  is a mechanism used by hosts and gateways to send notification of datagram problems back to the sender.  Send query and error reporting messages.

34. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 34 4.2 TCP/IP Protocol Suite Internet Group Message Protocol  is used to facilitate the simultaneous transmission of a message to a group of recipients.

35. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 35 4.2 TCP/IP Protocol Suite Transport Layer  Traditionally the transport layer is represented by 2 protocols : Transmission Control Protocol (TCP) User Datagram Protocol (UDP)  Responsible for delivery of message from a process (running program) to another process.  A new protocol Stream Control Transmission Protocol (SCTP) has been devised to meet the needs of some newer applications. User Datagram Protocol (UDP)  Process-to-process protocol that adds only port addresses, checksum error control and length information to the data from the upper layer.

36. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 36 4.2 TCP/IP Protocol Suite Transmission Control Protocol (TCP)  provides full transport-layer services to applications.  at the sending end of each transmission, TCP divides a stream of data into a smaller unit called segments.  Each segment includes a sequence number for reordering after receipt, together with an acknowledgement number for the segments received.  At the receiving end, TCP collects each datagram as it comes in and reorders the transmission based on sequence numbers. Stream Control Transmission Protocol (SCTP)  provides support for newer applications such as voice over the Internet.  Combines the best features of UDP and TCP.

37. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 37 4.2 TCP/IP Protocol Suite Application Layer  equal to the combined session, presentation and application layer in the OSI model.  enable the user, human or software, to access the network.  provides user interfaces and support for services such as electronic mail, file access and transfer, access to system resources, surfing the www and network management.

38. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 38 4.2 Addressing in the TCP/IP Protocol Suite 4 levels of addresses are used in an internet employing the TCP/IP protocols :

39. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 39 4.2 Addressing in the TCP/IP Protocol Suite each address is related to a specific layer in the TCP/IP architecture :

40. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 40 4.2 Addressing in the TCP/IP Protocol Suite Physical Address  the address of a node as defined by its LAN or WAN.  include in the frame used by the data link layer.  Ex : A node with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by a link (bus topology LAN). As the figure shows, the computer with physical address 10 is the sender, and the computer with physical address 87 is the receiver. 07:01:02:01:2C:4B A 6-byte (12 hexadecimal digits) physical address.

41. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 41 4.2 Addressing in the TCP/IP Protocol Suite Logical Address  necessary for universal communications that are independent of underlying physical network.  unlike the physical address where different networks can have a different formats.  using logical address, each host can be identified uniquely, regardless of the underlying physical network.  logical address in the internet is currently a 32 bit address that uniquely define a host connected to the internet – no host can have the same IP number on the Internet.

42. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 42 4.2 Addressing in the TCP/IP Protocol Suite Ex. of Logical (IP) Address - the physical addresses will change from hop to hop, but the logical addresses usually remain the same.

43. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 43 4.2 Addressing in the TCP/IP Protocol Suite Port Address  logical (IP) address & physical address are necessary for a data to travel from a source to a destination.  in the case a computer is running a several process of communication, a method is necessary to label the running processes.  ex : computer A communicate to C using TELNET, and at the same time communicating with computer B using FTP (File Transfer Protocol).  For these process to receive data simultaneously, a port address is assigned.

44. Chapter 3 : Internetworking BENG 4522 Data Communications & Computer Networks 44 4.2 Addressing in the TCP/IP Protocol Suite Specific Address  Some application have user-friendly addresses that are designed for that specific address  Example 1: e-mail address: zulhani@utem.edu.my Defines the recipient of an e-mail  Example 2: URL (Universal Resource Locator) : www.utem.edu.my Used to find a document on the WWW