1. CCNA 1 Chapter 5 Ethernet FundamentalsBy
Your Name

2. Objectives
Ethernet fundamentals
Ethernet operation

3. Introduction to Ethernet
The success of Ethernet is due to its simplicity and ease of maintenance, as well as its ability to incorporate new technologies, reliability, and low cost of installation and upgrade.

4. Comparing LAN Standards

5. OSI Layer 1 and 2 Together Are the Access Protocols
These are the delivery system protocols.
Independent of:
Network OS
Upper-level protocols
TCP/IP, IPX/SPX
Sometimes called:
Access methods
Access protocols
Access technologies
Media access
LAN protocols
WAN protocols
Ethernet, Fast Ethernet, Gigabit Ethernet, Token Ring, FDDI, Frame Relay, ATM, PPP, HDLC, and so on

6. IEEE Standard Divided OSI Layer 2 into two sublayers
Media Access Control (MAC) – Traditional L2 features
Transitions down to media
Logical link control (LLC) – New L2 features
Transitions up to the network layer

7. Logical Link Control (LLC)
Allows part of the data link layer to function independent of LAN access technologies (protocols / methods)
Provides services to network layer protocols, while communicating with access technologies below it
LAN access technologies:
Ethernet
Token Ring
FDDI

8. Logical Link Control (LLC)
Participates in the data encapsulation process
LLC PDU between Layer 3 and MAC sublayer.
Adds control information to the network layer data to help deliver the packet. It adds two fields:
Destination Service Access Point (DSAP)
Source Service Access Point (SSAP)
Supports both connectionless and connection-oriented upper-layer protocols.
Allows multiple higher-layer protocols to share a single physical data link.

9. Naming
Ethernet uses MAC addresses that are 48 bits in length and expressed as 12 hexadecimal digits.
The first 6 hexadecimal digits, which are administered by the IEEE, identify the manufacturer or vendor and thus comprise the organizational unique identifier (OUI).
The remaining 6 hexadecimal digits represent the interface serial number, or another value administered by the specific equipment manufacturer.

10. Layer 2 Framing
Framing is the Layer 2 encapsulation process; a frame is the Layer 2 protocol data unit.
A single generic frame has sections called fields, and each field is composed of bytes.

11. Framing Why framing is necessary Frame format diagram
Generic frame format

12. Why Framing Is Necessary
Binary data is a stream of 1s and 0s.
Framing breaks the stream into decipherable groupings:
Start and stop indicator fields
Naming or addressing fields
Data fields
Quality-control fields
Framing is the Layer 2 encapsulation process.
A frame is the Layer 2 protocol data unit.

13. Generic Frame Format Start Frame field
Address fields (source and destination MAC)
Type/Length field
Data field
FCS (Frame Check Sequence) field
Frame Stop field

14. Ethernet Frame Fields
Some of the fields permitted or required in an Ethernet frame are as follows:
Preamble
Start Frame Delimiter
Destination Address
Source Address
Length/Type
Data and Pad
Frame Check Sequence (FCS)
Extension

15. Ethernet Operation

16. Media Access Control (MAC)
Provides MAC addressing (naming)
Depending on access technology (Ethernet, Token Ring, FDDI), provides the following:
Data transmission control
Collision resolution (retransmission)
Layer 2 frame preparation (data framing)
Frame check sequence (FCS)

17. Media Access Control (MAC) Protocols
Ethernet (IEEE 802.3)
Logical bus topology
Physical star or extended star
Nondeterministic
First-come, first-served
Token Ring (IEEE 802.5)
Logical ring
Physical star topology
Deterministic
Token controls traffic
Older declining technology
FDDI (IEEE 802.5)
Logical ring topology
Physical dual-ring topology
Near-end-of-life technology

18. Ethernet (CSMA/CD)
Carrier sense multiple access with collision detection

19. Ethernet Timing
Any station on an Ethernet network wanting to transmit a message first “listens” to ensure that no other station is currently transmitting.
If the cable is quiet, the station begins transmitting immediately.

20. Interframe Spacing and Backoff

21. Error Handling
Collisions are the mechanism for resolving contention for network access.
Collisions result in network bandwidth loss that is equal to the initial transmission and the collision jam signal. This affects all network nodes, possibly causing significant reduction in network throughput.

22. Types of Collisions
Three types of collisions are:
Local
Remote
Late

23. Ethernet Errors The following are the sources of Ethernet error:
Simultaneous transmission occurring before slot time has elapsed (collision or runt)
Simultaneous transmission occurring after slot time has elapsed (late collision)
Excessively or illegally long transmission (jabber, long frame and range errors)
Illegally short transmission (short frame, collision fragment or runt)
Corrupted transmission (FCS error)
Insufficient or excessive number of bits transmitted (alignment error)
Actual and reported number of octets in frame don't match (range error)
Unusually long preamble or jam event (ghost or jabber)

24. FCS and Beyond
A received frame that has a bad frame check sequence, also referred to as a checksum or CRC error, differs from the original transmission by at least 1 bit.

25. Ethernet Autonegotiation
A process called autonegotiation (of speeds at half or full duplex) was developed.
This process defines how two link partners may automatically negotiate a configuration offering the best common performance level.
It has the additional advantage of only involving the lowest part of the physical layer.

26. Link Establishment
There are only two ways to achieve a full-duplex link:
Through a completed cycle of autonegotiation
Or, by administratively forcing both link partners to full duplex