S1 C7 Data Link Layer

Frame

  • Header
    • Frame Start
    • Addressing
    • Type
    • Quality Control
  • Packet (Data)
  • Trailer
    • FCS Frame Detection (CRC)
    • Frame Stop
  • Phan dau va cuoi khac bit nhau: 1010 va 1001

Data Link Layer

  • LLC Logical Link Control
    • Frames the Network layer packet
    • Identifies the Network layer protocol
  • Media Access Control
    • Address the frame
    • Masks the beginning and ending of the frame

Media Access Control Techniques

PPP: Point to point protocol (non shared media) //Khong can dieu khien truy cap duong truyen

Multi Access (shared media) //Dieu khien truy cap duong truyen

Phuong phap phan kenh:

  • FDMA //Phan kenh theo tan so (Nhuoc diem: chi duoc di trong khoang da phan)
  • TDMA //Phan kenh theo thoi gian (Moi tram chi duoc truyen trong 1 khe thoi gian nhat dinh – slot time)
  • CDMA //Cho truyen toan bo giai tan va thoi gian, moi tram truyen dung 1 phuong phap ma hoa khac nhau

Phuong phap phan luot:

  • Ring //Tao ra Token Card chay 1 vong tren 1 tram
  • CSMA Random Access//dung cho Multi Access (van co truong hop xay ra dung do)
    • CD: phat hien dung do (cho LAN co day)
    • CA: phat hien dung do (cho LAN khong day)

Min Frame = 512 bit

JAM = 32bit

Back off sinh ra thoi gian Rand0m de truyen lai khi dung do

Media Access Control for Non-Shared Media:

  • Simple-Duplex: Chi lam 1 chuc nang truyen hoac nhan
  • Half-Duplex: Co the truyen va nhan nhung chi lam duoc 1 viec trong 1 thoi diem (Hub)
  • Full-Duplex: Tai 1 thoi diem co the vua truyen va nhan (Switch)

Topology

  • Logical //ban ve de chi ra cac phuong phap, cong nghe, kieu ket noi
  • Point-to-point
  • Multi-Access
  • Ring
  • Physical //ban ve ghi ro ket noi, loai nao, thiet bi nao