1. Ken Gunnells, Ph.D. - Networking Paul Crigler - Programming
IS 591 Introduction to Networking and Computer Programming University of Alabama at Birmingham
Ken Gunnells, Ph.D. - Networking
Paul Crigler - Programming
Chapter 4: Data Link Layer
Chapter 5: Network and Transport Layers
Chapter 6: Wired and Wireless LANS

2. Student Discussion Are there any unanswered questions from last week?
Have you acquired Visual Studio?
Have you made arrangements for the programming book?
Have you selected and gotten approval for your research paper topic?
IS Week 2

3. Chapter 4
Data Link Layer
Network Layer
Data Link Layer
Physical Layer

4. Data Link Layer Overview
Controls what and when computers transmit
Typically (in PCs) combined with the Physical layer below in a Network Interface Card (NIC).
Card includes software for both layers + media port
Formats data for the attached media
Ethernet
WiFi
Fiber Optics
Organizes incoming Bit streams for Network Layer above
Detects and Corrects errors
IS Week 2

5. Media Access Control (MAC)
MAC controls when and what computers transmit
If 2 computers want to talk at same time, MAC handles contention control or collisions.
Two possible approaches
Contention based access (e.g. Ethernet): allow collisions and follow rules for how to recover from a collision
Controlled access (e.g. Token Ring, FDDI): prevent collisions by passing token to allow computer to talk
Contention better for smaller networks <20
Controlled Access better for larger networks
IS Week 2

6. Error Detection
Sender calculates an Error Detection Value (EDV) and transmits it along with data
Receiver recalculates EDV and checks it against the received EDV
Mathematical
calculations
Mathematical
calculations ? =
Data to be transmitted
EDV
If the same  No errors in transmission
If different  Error(s) in transmission
Larger the size, better error detection (but lower efficiency)
Parity checks
Checksum
Cyclic Redundancy Check (CRC)
IS Week 2

7. Error Correction Once detected, the error must be corrected
Error correction technique options…
Retransmission:
Receiver asks sender to retransmit message
Simplest, most effective, least expensive, most commonly used
Often called Automatic Repeat reQuest (ARQ)
Forward Error Correction
Receiving device can correct incoming messages without retransmission
Requires extra information to correct
IS Week 2

8. Network and Transport Layers
Chapter 5
Network and Transport Layers
Application Layer
Transport Layer
Network Layer
Data Link Layer

9. Network and Transport Layers
Transport and Network layers typically tied together as TCP/IP protocol
Responsible for moving messages from end-to-end in a network
Transport Layer: Responsible for segmentation and reassembly
Breaking the message into several smaller pieces at the sending end
Reconstructing the original message into a single whole at the receiving end
Network Layer: Responsible for addressing & routing of messages
Performs encapsulation on the sending end and decapsulation on receiving end
Application Layer
Transport Layer
Network Layer
Transport Layer
Network Layer
Data Link Layer
IS Week 2

10. TCP/IP’s 5-Layer Network Model
IS Week 2

11. Transmission Control Protocol (TCP) Internet Protocol (IP)
TCP: Links the application layer to the network layer
Performs packetization and reassembly
Breaks up a large message into smaller packets
Numbers the packets
Reassembles the packets at the destination end
IP: Responsible for addressing and routing of packets
Two versions of Internet addresses in use
IPv4: a 192 bit (24 byte) header, uses 32 bit addresses.
IPv6: Mainly developed to increase IP address space (128 bit addresses)
IS Week 2

12. Addresses at Different Layers
Application Layer address (URL) e.g.
Typed in a browser by user or clicked on a link
Transport Layer: Breaks up outgoing and reassembles incoming messages, numbers packets
Network Layer Address (IP address):
Retrieved from cache or
Looked up using Domain Name Service (DNS)
resolves to
DNS service provided through a series of name servers
Data Link Layer Address (MAC address):08:00:69:02:01:FC
Adds unique MAC address to each packet to identify originating device
Physical layer formats each packet for the media that is connected (electrical pulse, light pulse, radio wave)
IS Week 2

13. Wired and Wireless Local Area Networks
Chapter 6
Wired and Wireless Local Area Networks

14. Wired and Wireless LAN Overview
Purpose of a LAN
Sharing Information (files, database access)
Sharing resources (hardware, software)
Components of a LAN
Network Interface Cards
Cables (shielded/unshielded twisted pair, optical fiber)
Hubs and Switches
Connects cables from several computers
Allows different media to connect (UTP,Coax)
IS Week 2

15. Wired Ethernet Used by almost all LANs today 2 Types of Ethernet
Shared Ethernet (Uses hubs)
Shared central cable (bus).
Collisions allowed
Each computer see all messages, but only responds to messages with its address
IS Week 2

16. Wired Ethernet Switched Ethernet (Uses Switches, no collisions)
Logical and physical topology is a star via switch
Switch reads destination address of the packet and only sends it to the corresponding port
Forwarding tables: Switch reads the Layer 2 data link destination (MAC) address and sends frame out of the corresponding port in its forwarding table.
Without collisions, network performance goes from 50% to 95%
Port 1
Port 4
Port 2
EA-3E
Port 3
Forwarding Table
MAC Port
EA-3E 1
EA-3A EA
EA-6C
EA-3A
EA-6C
EA-01
IS Week 2

17. Wireless Ethernet
Use radio frequencies to transmit signals through the air (instead of cables)
Two unlicensed frequency ranges
2.4 GHz (shared with cordless phones, baby monitors)
5 GHz
Distance range of meters, dependent on frequency
Separate Channels reduce interference
IS Week 2

18. End
Questions?
IS Week 2