[Computer Networks] Data Link Layer
Data link layer has responsibility of transferring datagram from one node to physically adjacent (인접한) node over a link
Terminology
- Host and Routers : Nodes
- Communication channels that connect adjacent nodes along communication path : Links
> wired / wireless
- Layer-2 packet : Frame
Framing
- encapsulate datagram into frame, adding header, trailer
- channel access if shared medium
- "MAC" addresses in frame headers identify source, destination
- 데이터 링크 레이어의 기본 데이터 유닛 : Frame
- 상위 레이어인 Network 레이어의 기본 유닛인 Datagram 을 Frame으로
- encapsulate : Header + Datagram + Trailer => Frame
-Header : Sender와 Receiver를 식별할 수 있는 주소 정보인 MAC address 가 들어간다.
Flow control
- 송수신자의 속도 차이를 control
- pacing between adjacent sending and receiving nodes
Error detection
- detects erros caused by signal attenuation, noise
- receiver detects erros, signals retransmission, or drops frame
Error correction
- receiver identifies and corrects bit error(s) without retransmission
- Sender 의 도움 없이 Error correction
Data Link Layer
- Data-link layer in in each-and-every host.
- Data-link layer implemented in network interface card (NIC) or on a chip
- Ethernet, Wifi card or chip
- implements link, physical layer
Sender side
- encapsulates datagram in frame
- add errors checking bits, reliable data transfer, flow control, etc.
Receiver side
- looks for erros, reliable data transfer, flow control, etc.
- extracts datagram, passes to upper layer at receiving side