1. IST 228\Ch1\Internetworking1 Chapter 1: Internetworking Internetworking Basics Network segmentation How bridges, switches, and routers are used to physically segment a network How routers are used to create internetwork OSI model

2. IST 228\Ch1\Internetworking2 Internetworking Models Most networks are designed as a stack of layers, each one built upon the one below it. Why? Layer 3 Layer 2 Layer 1 Layer 3 Layer 2 Layer 1 Physical Medium Layer 3 protocol Layer 2 protocol Layer 1 protocol Layer 2/3 interface Layer 1/2 interface Host 1Host 2

3. IST 228\Ch1\Internetworking3 Each layer provides services to the higher levels. Each layer behaves as a black box. Layer n on one machine talks to layer n on another machines. The corresponding layer in the layered structure are called peers. The communication between peers must follow certain rules, known as protocol. No data are directly transferred between layers. Actual communication is through a physical medium below layer 1.

4. IST 228\Ch1\Internetworking4 An Analogy Ik vind konijnen leuk L: Ducth Fax:# Ik vind konijnen leuk L: Dutch I like rabbits Message Information for the remote translator Information for the remote secretary Ik vind konijnen leuk L: Ducth Fax:# Ik vind konijnen leuk L: Ducth J’aime bien les lapins Urdu & English Chinese & French Professor B Translator Secretary use fax use Dutch Secretary Translator Professor A

5. IST 228\Ch1\Internetworking5 Open Systems Interconnection (OSI) Reference Model Application Presentation Session Transport Network Data Link Physical Provides user interface Initiates services Transfer data into standard format before transmission Keeps data different applications’ data separate Control the data exchange End-to-end data error free data transmission Logical addressing for data packets Routing and error handling Moves bits between devices Specifies voltages, cables, and cables NIC software function How data in packaged Error detection The lower levels The upper levels

6. IST 228\Ch1\Internetworking6 Reasons for Layering Simplifies the network model Enables programmers to specialize in a particular level or layer of the networking model Provides design modularity Encourages interoperability Allows for standardized interfaces to be produced by networking vendors

7. IST 228\Ch1\Internetworking7 The Application Layer (Layer 7) The layer where users communicate to the computer Contains protocols and utilities that provides services to network applications –(True/False) MsWord, Eudora Mail, Netscape are in the application layer. –Eudora (application) uses SMTP (Simple Mail Transfer Protocol) (protocol). E-mail: –Message formats such as RFC 822 –SMTP, POP3 (Post Office Protocol Version 3), IMAP (Internet Message Access Protocol) WWW: –HTML (The HyperText Markup Language), XML (eXtensible Markup Language), XSL (eXtensible Style Language) –HTTP (The HyperText Transfer Protocol)

8. IST 228\Ch1\Internetworking8 The Presentation Layer (Layer 6) The presentation layer prepares the data from the application layer for transmission over the network or from the network to the application layer. Include protocols specifying how to represent data (MPEG, JPEG, PIC, WAV) Responsible for data translation, formatting, encryption, compression. We need these services because different computers use different internal representation for data (integers and characters)

9. IST 228\Ch1\Internetworking9 The Session Layer (Layer 5) Enables two applications on the network to have an ongoing conversation Provide following services –Communication setup and teardown –Control for data exchange –Data synchronization definition –Failure recovery Examples: –Structured Query Language (SQL) –X Windows –AppleTalk Session Protocol (ASP)

10. IST 228\Ch1\Internetworking10 The Transport Layer (Layer 4) Provides –end-to-end error free data transport services –establish a logical connection –data segmentation into maximum transmission unit size –messaging service for session layer Protocols in this layer can be –connection-oriented : require an acknowledgment of the receipt of data packets. –connectionless : do not require an acknowledgment of the receipt of data packets.

11. IST 228\Ch1\Internetworking11 Connection-oriented protocols: sender receiver Synchronize Negotiate connection Connection Establish Synchronize Acknowledge Data Transfer Virtual Circuit

12. IST 228\Ch1\Internetworking12 sender receiver Buffer full GO Flow Control The segments delivered back to the sender upon their reception Any segment not acknowledged are retransmitted. Segments are sequence back into their proper order upon arrival at their destination Manageable data flow is maintained in order to avoid congestion

13. IST 228\Ch1\Internetworking13 Windowing: The quantity of data segment (in bytes) is sent without receiving an acknowledgment (ack) is called a window. senderreceiver receive 1 ack. 2 send 1 send 2 receive 2 ack. 3 send 3 senderreceiver send 1 send 2 ack. 4 send 3 send 4 Window size of 1 Window size of 3

14. IST 228\Ch1\Internetworking14 Acknowledgments: senderreceiver send 1 send 2 ack. 4 send 3 send 4 send 5 send 6 ack. 5 send 5 Connection lost! ack. 7 123456123456 Positive Acknowledgment with retransmission

15. IST 228\Ch1\Internetworking15 The Network Layer (Layer 3) Provides services –to manage devices addressing –to tracks the location of devices on the network –to determine the best way to move data on the network The network layer must transport traffic between devices that are not directly connected. Routers are specified at this layer.

16. IST 228\Ch1\Internetworking16 The Data Link (Layer 2) Services –Identification of the source and destination nodes via their physical address (Media Access Control (MAC) address) –Definition of how data is packaged for transport as frames –Error detection –Flow control of information sent across the link Has two sublayers: –Media Access Control (MAC) 802.3 –Logical Link Control (LLC) 802.2

17. IST 228\Ch1\Internetworking17 The Physical Layer (Layer 1) This layer communicates directly with the various types of actual communication media Services –definition of the physical characteristics of the network hardware, including cable and connector –Encoding –Transmission of signals on the wire

18. IST 228\Ch1\Internetworking18 Example: 568B twisted pair wiring scheme

19. IST 228\Ch1\Internetworking19 Layer 1 Network Devices: Repeaters The number of nodes on a network and the length of cable used influence the quality of communication on the network Attenuation –Natural degradation of a transmitted signal over distance Repeaters work against attenuation by repeating signals that they receive on a network Why are repeaters Layer 1 devices?

20. IST 228\Ch1\Internetworking20 Layer 1 Network Devices: Hubs Generic connection device used to tie several networking cables together to create a link between different stations on a network

21. IST 228\Ch1\Internetworking21 Hubs that are plugged into electric power are called active hubs A hub that merely connects different cables on a network and provides no signal regeneration is called a passive hub and is not a repeater “Hub” is a generic term applied to many different network-connection devices If a hub in some way segments or subdivides the traffic on a network, it is an intelligent, or switching, hub For the purpose of the CCNS exam, the term hub—by itself—is a device that does not segment the network

22. IST 228\Ch1\Internetworking22 Network Segmentation Segmentation –Process of breaking a network into smaller broadcast or collision domains Ethernet network, which are characterized by IEEE 802.3 standard, define the use of a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) access method –Backoff algorithm : Mathematical calculation performed by computers after a collision occurs on a CSMA/CD network –Backoff period : Random time interval used after a collision has been detected on an Ethernet network

23. IST 228\Ch1\Internetworking23 Network Segmentation via Bridges

24. IST 228\Ch1\Internetworking24 Layer 2 Devices: Bridges Operate at the Data Link layer of the OSI model Filters traffic between network segments by examining the destination MAC address –Based on this destination MAC address, the bridge either forwards or discards the frame –When a client sends a broadcast frame to the entire network, the bridge will always forward the frame

25. IST 228\Ch1\Internetworking25 Transparent Bridges : Also called learning bridges because they build a table of MAC addresses as they receive frames –This means that they “learn” which addresses are on which segments –Ethernet networks mainly use transparent bridges Source-routing bridges : Rely on the source of the frame transmission to provide the routing information –Usually employed by Token Ring networks Translation bridges : Can connect networks with different architectures

26. IST 228\Ch1\Internetworking26 Layer 2 Devices: Switches Increase network performance by reducing the number of packets transmitted to the rest of the network Like bridges, operate at the Data Link layer of the OSI model In an Ethernet network, computers are usually connected directly to a switch Virtual circuit –Private connections between two points created by a switch that allows the two points to use the entire available bandwidth between those two points without contention