Starts,stops session. Maintains order.
5 4 3 2 1
RPC , SQL NetBios names…etc
TCP ,UDP ,SPX IP ,IPX , Apple Talk DDP 802.3/802.2 , HDLC …etc EIA/TIA -232 , V.35 …etc
Presentation Layer
Usually part of the OS and is responsible for formatting data Encrypt and translate received packets Format
Application Layer
Interface between user and computer Provides network services to the user Shared
• Cyclic redundancy check (CRC)
Network Layer
Organizing messages into logical groups called datagram packets Routing datagram packets to their correct destinations Connectionless services Connection-oriented services
Required Network Elements
Three basic elements in Networking
Something to share--Network Services A pathway of contacting others--Transmission media Rules for communication--Protocol
Ensures delivery of entire file or message.
Routes packets to LANs and WANs based on network address. Transmits frames from node to node based on station address. Passes information in bits across the connection medium.
Network Services
File Services
File transfer, file storage and data migration, File update synchronization
Print services
Share printers, queue print jobs
LC connector
Connectivity Devices
Network connectivity devices
Transmission media connectors Network Interface Card Modems Repeaters Hubs Bridges Switches
Transport Layer
Provide end-to-end control and error-checking to determine if all the packets have arrived Reliability
Session Layer
Connection services include connection establishment, maintenance, and tear-down End-nodes exchange messages and agree to certain connection parameters, such as beginning sequence numbers and number of outstanding messages allowed Dialog
Message services
E-mail, workgroup applications
Application services
Run software for network clients Share processing power
Database services
Provide server-based database storage & retrieval function Replication
Wide area network (WAN)
LAN
LAN
WAN Interconnect LANs Router Kbps ~ Mbps Router Modem (33.6/56 kbps), X.25 (56 Kbps), Frame Relay (1.544 Mbps), T1 / E1 (1.544 Mbps), T3 / E3 (45 Mbps), ISDN 2B1D (64K),ATM (25 ~ 622 Mbps)
Layer 2
3 bits
Prioritys
VLAN ID Version
IP Packet Format
00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
Network Classification
Local area network (LAN)
File Server+Print Server Printer ( Printer buffer)
Small group of connected computers HD( Queued ) <10Km Mbps ~ Gbps Ethernet (10Mbps), Fast Ethernet (100 Mbps), Gigabit Ethernet (1000Mbps)
OSI Layer Mapping
7 Bytes 1 Byte SFD Data 12 Bytes IPG
Layer 1
Preamble
bits Frame (64-1522 Bytes)
802.1Q VLAN tagging 6 Bytes Destination Address 6 Bytes Source Address 2B 8100 2B TCI 2B L/T 46-1500 Bytes Data Pad 4 Bytes FCS
Network Services
Network services are provided by numerous combinations of computer hardware and software Service providers and requestors
Servers--Only provide services Clients-- Only request services Peers--Both
Internetwork connectivity devices
Routers Brouters CSU/DSUs
Protocol
Rules are required for communication between computer network devices Specific communication rules and rule sets are called protocols
Transmission Media
A method or pathway for contacting each other Cable media( twisted pair, coaxial, fiber optic cable)
RJ45 connector
Unshielded Twisted Pair Cable (UTP)
OSI Reference Model
Application Process
Application Process
Application Presentation Session Transport Network Data Link Physical DL N T S P
A
D
Application Presentation Session Transport Network Data Link Physical
Layer 4
TCP Segment Format
Destination Port Sequence Number Acknowledge Number U A P R S F Reserved R C S S Y I Window G K H T N N Checksum Urgent Pointer Options Padding Data ... Source Port
Media access methods and logical topologies Addressing
Data Link Sub-layer
Frame synchronization Connection services
• Connectionless • Non-reliable
Error control
Data Link Layer
Organizes bits into logical groups called frames Control information like source and destination addresses, frame length, and information about the upper layer protocols is added to the front end of the frame-header Frame MAC Sub-layer