CCNA (routing and switching)

module 1 – Chapter 4B : Network Access

The data link layer

It is responsible for

  • Allowing upper level layers to access the media
  • Accepting layer 3 packets and packaging them into frames
  • Preparing network data for physical network
  • Exchanging frames between nodes over a physical network such as UTP
  • Receiving and directing packets to an upper layer protocol
  • Performing error detection

Layer 2 notation for network devices connected to a common media is called a node

Nodes build and forward frames

chap4-2

The data link layers

 

  1. Logical Link Control
  2. Media Access Control

 

LLC

  • Communicates with the network layer
  • Places info in the frame that identifies which network layer protocol is being used for the frame.
  • Upper sub layer

 

MAC

  • Lower sub layer
  • Processes things done by the hardware
  • Provides addressing and access to various network technologies
  • Communicates with Ethernet LAN to send and receive frames on copper or fibre

 

The Mac

  • This is the method for getting the frame on and off the media
  • Data link layer protocols govern how to format a frame for use of different media
  • Without the data link layer, network layer would make provisions for connecting to every type of media that could exist along the delivery path
  • The mac is a unique i.d for source or destination host
  • Router interfaces encapsulate the packet into the apropritae frame and a suitable MAC method is used to access each link.

 

At each hop along the path , a router

  • Accepts a frame from medium
  • De-ecapsualetes the frame
  • Re-encapsulates the packet into a new frame

 

DATA LINK LAYER STANDARDS

  • IEEE
  • ISO
  • ITU
  • ANSI

TOPOLOGIES

 

This is the arrangement or relations of the network devices and te interconnections between them

 

 

PHYSICAL TOPOLOGY: physical connections and identifies how end devices such as routers, switches and wireless access points are interconnected.

They are usually point-to-point

chap4-3

 

LOGICAL TOPOLOGY – refers to a way a network transfers from one node to the next

these are virtual connections

chap4-4

 

 

Common Physical WAN topologies

  •  Point-to-Point Topology
  • Hub and Spoke  Topology
  • Full Mesh Topology

chap4-5

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