- Link Layer
It is an encapsulation of Ethernet header to various packets such as IP packet,ARP,RARP,DATA etc.
Destination Address : 6 bytes MAC Address.
Source Address : 6 bytes Source MAC Address.
Length field follows address if it is 802 packet else it contains type follows data.
for Ethernet 802 packet minimum data size is 38 and for 803 it is 46.
SLIP (Serial Line Internet Protocol)
It is a Encapsulation of IP packet,data etc. SLIP is mainly used to connect with internet through RS232 serial port cable almost present in all types of PCS.
SLIP is terminated with special SLIP_END character that is 0xC0. If 0xC0 character is present in actual data it is replaced with 0xdb, 0xdc. If db is present in actual data it is replaced with 0xdb, 0xdd.
Deficiencies of SLIP
-> Each end must know others IP Address.
->SLIP packet can be transmitted in any protocol because we are not using any type field.
->There is no Checksum.
PPP (Point to Point Protocol)
The format of PPP looks like
The frame begins and end with a flag whose value is 0x7e, address whose value is always 0xFF and a control byte with a value of 0x03. protocol field tells the type of data it can store.
if protocol equals to 0x0021 means information field of an IP datagram.
if protocol equals to 0xc021 than it is link control data.
if protocol equals to 0x8021 than it is Network control data.
Maximum Transfer Unit:
There is a limit on the size of frame for both Ethernet encapsulation(1500) and 802.3 (1492) encapsulation.
Ethernet- 1500 .
IEEE 802.3/802.2 - 1492.
path MTU : It is the maximum transfer unit between two hosts at short interval. It always change depends on the different network.
if one is Ethernet and other is 802.3.