OSI Model

CS363-Winter 1999

DePaul University

Group Project Info

• Teams formed and on the web

• Cases

• Working in Groups

• Last half of class tonight reserved for projects

Review #1

• You must connect a research institution’s main offices with the testing site 30 miles away. You will connect them with fiber optic cable. Which type of fiber will you use and why?

Review #2

• You are replacing your thicknet backbone between your servers with a high-speed network cable. You are considering using Category 5 twisted-pair copper or multimode fiber cable. – Under what circumstances will you install the fiber?

– Under what circumstances will you not use fiber?

Review #3

• Your company recently renovated its telephone system, including cabling, and had extra cable installed for future growth. Now you would like to use the excess cabling to network the computers in your company.– What sort of network performance (data capacity and

cable length) can you reasonable expect from these new telephone cables?

– What could you do with the old telephone cable that is still in the building?

Review #4

• You would like to attach your notebook computer to your LAN, but it does not have a PCMCIA slot or a place for a proprietary network card. How can you attach it to the network?

OSI Model

• Why do we keep talking about this? Why should we care?

Protocol Stacks

• =>group of protocols arranged on top of each other as part of a communications process.

• Importance of protocol stacks

Peer-Layer Communication Between Stacks

Physical Layer

• Functions

• Components

Data-Link Layer

• Functions

• Components

Network Layer

• Functions

• Components: routers and gateways

Transport Layer

• Functions

• Components

Session Layer

• Functions

• Components

Presentation Layer

• Functions

• Components

Application Layer

• Functions

• Components

Problem

• Your company wants to use data link layer encryption devices to send private data over a public wide area network. What effect will this have on devices in other layers?

Problem

• When trouble-shooting your network with a packet sniffer, you find a device generating spurious TCP/IP packets. Which devices are suspect?

Drivers

• =>

• NDIS

• ODI

Network Protocols

• =>agreed-upon ways in which computers exchange information

How Protocols Work

• Sending::– Packetize data– Appropriately address the packets– Present packets to the network for delivery

• Receiving:– -Accept packets from the network– Remove transmitting information (addresses) added

in the sending process– Reassemble data packets into original message

Network Packets

• Packet Structure– Header=>

– Data=>

– Trailer=>

Packet Assembly

• Routing

• Protocol Stacks

Binding Protocols

Two Types of Protocols

• Connection-Oriented • Connectionless

Standard Protocol Stacks

• ISO/OSI

• SNA

• DECnet

• NetWare

• AppleTalk

• TCP/IP

Microsoft Supported Transport Protocols

• NetBEUI

• NWLink

• TCP/IP

Other Protocols whose names you should know

• SMTP

• SNMP

• NFS

• X.25

• X Windows

Problem:

• Your boss wants you to speed up the office LAN without spending any money. You are currently using 10Mbps Ethernet and TCP/IP. Users connect to the Internet using dial-up modems, and a single Ethernet domain is in use. What do you do?

Problem:

• Your company network has become very slow, so you decide to break it up into multiple domains and use a router to connect the domains. As soon as you disconnect the networks, even with the router running properly, you can’t get data between networks. You are using four Windows NT servers (one in each subnetwork) running on Ethernet with NetBEUI. You’ve spent your budget on the router and can’t afford to purchase new hardware. What is wrong? How can you fix it?