Layer 2: data link layer in Osi Model

1. DATA LINK LAYER

2. IEEE STANDARDS FOR LAN

3. IEEE STANDARDS FOR LAN
 LLC
 LLC stands for logical link control. LLC is the upper sub layer of
the data link layer. It act as a interface between the media
access control sub layer and the network layer.LLC basic
function are flow control, error control, and framing.LLC also
provides SAP services in OSI model
 SAP
 Sap stands for Service Access Point. In data link protocol LLC
provides SAP services. A Service Access Point (SAP) is an
identifying label for network endpoints used in Open Systems
Interconnection (OSI) networking

4. IEEE STANDARDS FOR LAN
 MAC
The MAC layer is responsible for moving data packets to
and from one Network Interface Card (NIC) to another
across a shared channel

5. IEEE 802.3 MAC FRAME
 Function of the physical layer
 Encoding / Decoding of signals
 Preamble generation/removal (for bit level synchronization)
 Bit transmission / reception
 Include specification of the transmission / medium.
 Function of the medium access control (MAC) layer
 On transmission, assemble data into a frame with address and
error detection field
 On reception, dis assemble frame and perform address
recognition and error detection.
 Govern access to the LAN transmission medium

6. IEEE 802.3 MAC FRAME
 Function of the logical link control LLC
 Provide an interface to higher layer and perform flow and
error control.

7. 10BASE5 IMPLEMENTATION

8. 10BASE-T IMPLEMENTATION

9. STANDARD ETHERNET
 The original Ethernet was created in 1976 at
Xerox,s palo alto Research center (PARC). Since
then it has gone throw four generations.

10. WAN PROTOCOLS
 Leased lines two types of WAN encapsulation protocols
1) HDLC
2) PPP
 HDLC stands for High level data link control is a bit oriented
synchronous data link layer protocol. Developed by the
international organization for standards.
 HDLC main goal is to delivering data across the link without
any errors
 HDLC uses synchronous transmission.

11. HDLC PROTOCOLS
 HDLC need to determine if the data passed
the link without any errors
 HDLC discard the frame if error occurs
 To achieve this main goal HDLC defines
framing

12. PPP PROTOCOLS
 Comparing the basics PPP behaves much like HDLC.
 PPP does discard error frames that do not pass the FCS
checks.
 Additionally PPP uses a 2 byte protocol called Type Field
 Due to this 2 byte protocol called Type Field any vendor
that conforms to the PPP standard can communicate with
other vendor product.
 So when connecting a Cisco router to another vendors
router over a PPP serial link, PPP is the data link layer
protocol choice.
 This is why PPP has become the most popular and feature
rich of WAN data link layer protocol.

13. FRAME RELAY
 Frame relay network are multi-access networks, which
means that more then two devises can attached to the
network.
 For Frame relay service a leased line installed between
each router and a nearby frame relay switch, these links are
called Access Links
 instead of extending from one router to other each leased
lines are run from one router to a frame relay switch.

14. DIFFERENCE BETWEEN FRAME RELAY & PPP
 The difference between Frame relay and ppp
links is that the equipment in the Telco
actually examines the data frame sent by the
router .
 Frame relay defines its own data link header
and tailer .
 Each frame relay header hold an holds an
address field called a data link connection
identifier (DLCI)

15. IPV4 ADDRESSES
 If a devise want to communicate using
TCP/IP it needs an IP Address.
 An IP address consist of a 32 bit number
 An IPv4 address is a address that uniquely
and universally defines the connections of a
devise ( for example a computer and a
router) to the internet.
 168.1.1.1 is an IP address written in dotted
decimal

16. IPV4 ADDRESSES
 The actual Binary version is
168.1.1.1
 10101000 . 00000001 . 00010110 . 10101100
 Each decimal number in IP address is called an octet
 168. 1. 1. 1
 1st Octet 2nd Octet 3rd Octet 4th Octet
 1 Octet = 1 Byte = 8 bits
 4 Octets = 32 Bits IP address
 The address space (Range) of IPv4
 2^32 = 4,294,967,296.

17. CLASSFUL ADDRESSES
 In classful address, the address space is divided into five
classes: Class A, Class B, Class C, Class D and Class E.
 Range of IP Classes are
 Class A 0-127 1.0.0.0 to 126.0.0.0
 Class B 128-191 128.0.0.0 to 191.255.0.0
 Class C 192-223 192.0.0.0 to 223.255.255.0
 Class D 224-239 224.0.0.0 to 239.255.255.255
 Class E 240- 255 240.0.0.0 to

18. CLASSFUL ADDRESSES
 IP defines three different networks classes for addresses
used by individual hosts address called Uni cast addresses
 Uni cast IP addresses are
 Class A Uni Cast
 Class B Uni Cast
 Class C Uni Cast
 TCP/IP defines
 Class D Multicast
 Class E Experimental

19. IP ADDRESSES
 The organization in charge of universal IP
address assignment is the
 Internet corporation for assigned Network
Numbers ( ICANN )
 Administratively a central authority assigned
Class A, B and C networks to companies.
 Class A Large Networks
 Class B Medium Networks
 Class C Small Networks

20. IP ADDRESSES
 Network and Host Part in IP Addresses
 Classes in binary and dotted decimal notation.

21. PUBLIC AND PRIVATE ADDRESSES
 There are two types of addresses employed on the
Internet, public addresses and private addresses .
 Public IP Address
A public IP address is the address that is assigned to a
computing device to allow direct access over the Internet. A
web server, email server and any server device directly
accessible from the Internet are candidate for a public IP
address. A public IP address is globally unique, and can only be
assigned to a unique device.
 Private IP Address
A private IP address is the address space allocated by Inter
NIC to allow organizations to create their own private
network. The computers, tablets and Smartphone's sitting
behind your home, and the personal computers within an

22. SUBNETTING
 Creates multiple logical networks that exist
within a single Class A, B, or C network.
 If you do not subnet, you will only be able to
use one network from your Class A, B, or C
network, which is unrealistic
 Each data link on a network must have a
unique network ID, with every node on that
link being a member of the same network

23. BENEFITS OF SUBNETTING
1) Reduced network traffic
2) Optimized network performance
3) Simplified management
4) Facilitated spanning of large geographical
distances

24. CIDR
 Classless Interdomain Routing
 Improve address space utilization
 Routing scalability in the Internet
 For example, if an ISP owns network
172.16.0.0/16, then the ISP can offer
172.16.1.0/24, 172.16.2.0/24,and so on to
customers. Yet, when advertising to other
providers, the ISP only needs to advertise
172.16.0.0/16