Week #8 OBJECTIVES Chapter #5

CHAPTER 5 Making Networks Work Two Networking Models –OSI OPEN SYSTEMS INTERCONNECTION PROPOSED BY ISO –INTERNATIONAL STANDARDS ORGANIZATION –IEEE 802 Enhancement to OSI Open Ended so new types can be addes –e.g. Gigabit

OSI Layers Communicate with layer(s) above & below it Each layer handled separately Issues solved separately Interfaces that allow each layer to talk to the layer above or below

Seven Layers APPLICATION PRESENTATION SESSION TRANSPORT NETWROK DATA LINK PHYSICAL

APPLICATION PROTOCOL STACK/SUITE –Set of Interfaces that permit networked apps.to access the network –TCP/IP –IPX/SPX INTERNETWORK PACKET EXCHANGE/SEQUENCED PACKET EXCHANGE –NetBEUI NETWORK BASIC INPUT/OUTPUT EXTENDED USER INTERFACE –NetBIOS EXTENDED USER INTERFACE –Apple Talk –SNA IBM MAINFRAMES

PROTOCOL STACKS The seven layers used (Protocol Stacks) combined with DRIVERS for NETWORK DEVICES are the software link that allows apps to communicate with a network. At each layer, specific software provides specialized network functions that are defined by the set of protocols in use.

PACKETS or PAYLOADS OSI acronym is PDU –PROTOCOL DATA UNIT, PACKET DATA UNIT or –PAYLOAD DATA UNIT Passed as a self-contained data structure from layer to another –Up or Down the stack Each layer adds its own special formatting or addressing to the PDU –So it can received only by the correct layer at the other end. Each layer performs processing & stips that info. From PDU & passes it to the next level.

APPLICATION (Layer #7) Handles general network access Movement of data from Sender to Receiver –FLOW CONTROL Error recovery for apps.

PRESENTATION (Layer #6) Handles data format information for networked communications OUTGOING –Converts data into a generic formats that can survive the rigors of network transmission INCOMING –Converts data from generic networked representation into a format that will make sense to the receiving app. Protocol Conversion Data Encryption or Decryption Character Set Issues Graphic Commands If data is compressed then –Redirector Software –Intercepts requests for service from computer & reirect requests that con’t be satisfied locally across the network

SESSION (Layer #5) Permits 2 parties to hold ongoing communications Handles session setup Data or message exchanges Tear-Down when session ends Monitors session Identification so only designated parties can participate Monitors security services to control access to session information –So only authorized parties can establish sessions.

TRANSPORT (Layer #4) Segments long payloads into chunks that match the max. packet size for the networking medium used Handles resequencing of chunks into the original data on receipt Make’s sure that long data payloads make their way across network. Flow Control –Manages conveyance of data from sender to receiver across network –Sender does not attempt to transmit data faster than its recipient can receive it. Error Handling –Includes error-checks to ensure error-free delivery –Acknowledges successful transmissions –Requests RE-transmission when certain packets do not arrive in time –Ensures data received matches data sent

NETWORK (Layer #3) Handles addressing messages for delivery Translates logical network addresses and names into their physical counterparts Packet Switching Data Routing Congestion Control When moving from one medium to another –Segmentation and reassembly functions based on differences between dissimilar mediums.j –Fragmentation or Segmentation Downsizes packets coming from a medium that handles larger PDU’s to one that handles smaller ones At the destination end this layer reassembles the downsized packets into their original packets.

DATA LINK (Layer#2) Basic Unit for network traffic “ON THE WIRE” Sends special PDU’s called “DATA FRAMES” from the Network Layer to the Physical Layer On Receiving end packages the raw data from the Physical layer into data frames for delivery to the Network layer Highly structured format within which payload data from upper layers is placed for sending & from upper layers is taken on receipt.

DATA LINK (Layer#2) ID’s for both sender & receiver Controls Information Data integrity check –CRC = CYCLICAL REDUNDANCY CHECK –Mathematical function based on Bit Pattern –If sent values agree with recalculated value on receiving end then ASSUMPTION is that the data was received in the form it was sent. Data is sent one frame at a time. If not received it will request to be retransmitted.

PHYSICAL (Layer #1) Outgoing –Converts Bits into Signals for outgoing messages Incoming –Converts Signals into Bits for incoming messages Instructs the Driver Software & the Network interface on what to send across the medium

PHYSICAL (Layer #1) All the details for creating a network connection are specified –How to attach to NIC –Type of connector used –Transmission technique used to send signals Specifies how the one’s & zero’s are encoded How signals sent across medium are to be times & interpreted What form signals will take.

IEEE 802 Networking Model Extends the OSI model Developed BEFORE OSI Defines a set of LAN standards to ensure that network interfaces & cabling from MULTIPLE MANUFACTURERS would be compatible as long as they adhered to the IEEE spec. 802 PROJECT –1980 –2nd Month (February)

802 Model TABLE 5-2 Pg.147 Describes different types of networking types

802 Model Standards that describe the PHYSICAL elements of a network –Network ADAPTERS –CABLES –CONNECTORS –SIGNALING TECHNOLOGIES –MEDIA ACCESS CONTROLS (MAC’s) Most of these are in BOTTOM 2 LAYERs –Data Link Layer –Physical Layer

802 Model Data Link Layer is further Layered –Logical Link Control Controls Data-Link Communication Defines the use of Logical Interface Points –Service Access Points (SAP’s) Allows transfer of Data to HIGHER layers –Media Access Control Provides shared access for multiple NIC’s with the LOWER Physical Layer

Questions?