Sub layers of DLL - papersocean

Computer Networks:

Physical Layers

Data link Layer(DLL)

Network Layer

Transport Layer:

Session and Presentation Layer:

Application Layer:

Data Link Layer

Sub Layers Of Data Link Layer

The Data link layer is separated into two sub Layers. In IEEE 802 Data link there is divided into two sub Layers:

logical link control (LLC) Sub Layer.
Media access control (MAC) Sub Layer.

This allow us to use the header standards in common in each standard because there are various standard (such as a ethernet, token ring and FDDI) for data link. the section describe the two sub layers and the important item called MAC address.

1) Logical link control (LLC) layer:

Logical link control Sub layer, which is the upper one of the sublayer of data link layer is a protocol for the data transfer between terminals connected to a LAN.

The logical controls the following when sending and receiving a frame between terminals

Whether there are not dropout in all the frame received.
Whether it could be received as the correct information.
It ask the source to resend Frames when there was error in the receiving frames.
When the destination is not ready to receive normally the source temporary postponed sending and extend the interval to reach to recent.

(SAP) service access Point:

Point is a value to indicate which upper layer protocol data frame data is LLC decide which protocol to pass the data based on the value of SAP.

A) Destination service access point (DSAP):

 Destination service access point (DSAP) field is an 8 bit long field ,that is used to represent the logical address of the network layer entity mean to receive the message.

B) Source Service Access Point (SSAP):

Source service access point (SSAP) is an 8 bit long field that is used to represent the logical address of the network layer entity mean to create a message.

C) Information Field:

information field generally include data or information.

D) Control field:

control field is an 8 or 16 bit long field, usually depend on the identity of the PDU (protocol data unit) it is used for flow and error control. there are basically Three Types of PDU each PDU has different control field format.

D.a) Information(I):

it is General is 7 bit sequence number it is used to carry data or information.

D.b) supervisory(S):

it includes an acknowledgement number and also are to bits feat for three different PDU format (RNR) received not ready, (RR)receipt ready, (REJ)reject. it is for the most part utilized for stream and blunder contr it is generally used for flow and error control.

D.c) Unnumbered (U):

Unnumbered is generally 5bit M,that is used to indicate the type of PDU. it is used for various protocol PDU.

2) (MAC address) Media Access Control address:

Media access control supplier is the lower one of the sublayer of the data Link Layer. the process of media acces control sub layer is as follow:

Sourcek:

Address that control information such as the destination MAC address and source MAC Address to the information pass from the LLC, assemble it as a frame and pass to the physical layer as a bit string.

Destinationk:

Received the bit strings decoded From the physical layer, diassemble the frame, delete the control information and pass only the information to the LLC layer.

(MAC address) Media Access Control Address:

Media Access Control Address is an identification code to identify each device in the network at the data link layer.

In the case of PCs, The MAC address is built into not the PC itself, but the NIC network interface card in the PC.

“Therefor note that the address change with the NIC is replace”

Individual /group (I/G):

The individual address or group address can be identified here.

Universal/local(U/L):

The Global address or local address can be identify here.

Maker Code:

It is this the identification number assigned to each maker producing NICs, it is also called the OUI (organizationally unique identifier) Code.

Note:

every one can refer to OUI code on the IEEE homepage