Computer Networks: Data Link Layer Services and Protocols

Computer Networks (UCAIL209)

Data Link Layer

• Provides services such as framing, error detection and correction, flow control, and multiplexing
• Design issues include frame size, error detection and correction, and flow control

Framing

• A frame is a formatted unit of data transmitted over a network
• Framing methods include:
  • Fixed-size framing
  • Variable-size framing
  • Bit-oriented framing
  • Character-oriented framing

ARQ Protocol

• Automatic Repeat Request (ARQ) protocol is used for error detection and correction
• Classification chart:
  • Stop-and-Wait ARQ
  • Go-Back-N ARQ
  • Selective Repeat ARQ

MAC and LLC Sublayers

• Medium Access Control (MAC) sublayer resolves collisions and manages network access
• Logical Link Control (LLC) sublayer provides flow control, error detection, and correction
• Static MAC: permanently assigned MAC addresses
• Dynamic MAC: dynamically assigned MAC addresses

ALOHA

• ALOHA is a protocol for managing access to a shared network channel
• Pure ALOHA: sends data packets without checking for collisions
• Slotted ALOHA: divides time into slots and sends data packets in slots

Multiple Access Control

• CSMA (Carrier Sense Multiple Access) protocol: listens for collisions before transmitting data
• CSMA/CD (Collision Detection): carrier sense and collision detection
• CSMA/CA (Collision Avoidance): carrier sense and collision avoidance
• IEEE 802.11 wireless LAN standards: managing wireless network access

Network Layer

• Provides services to Transport layer such as routing, addressing, and congestion control
• Functions: routing, addressing, congestion control, and fragmentation

Routing

• Shortest path routing algorithm: finds the shortest path between source and destination
• Flow-based routing: forwards packets based on flow information
• OSPF (Open Shortest Path First): link-state routing protocol
• IP address classes: Class A, B, C, D, and E

Border Gateway Protocol (BGP)

• BGP is a routing protocol used for exchanging routing information between networks
• How BGP works: advertises routes, selects best path, and updates routing tables

Other Concepts

• Crash recovery: recovering from a network failure
• Choke packets: used to control congestion in networks
• Jitter control: managing packet delay variation in networks