Explain the 6LoWPAN packet structure
Answer:-
6LoWPAN Packet Structure
The packet structure contains the following fields:
- Length, Version (VER), Traffic Class, and Payload Length
- Flow Label: Used for packet flow identification.
- Next Header: Indicates the next header type.
- Source and Destination Addresses (128 bits each)
- Hop Limit: Specifies the maximum number of hops for the packet.
Components of the 6LoWPAN Stack
1. PHY and MAC Layers:
- PHY Layer: Comprises 27 wireless channels, each having a distinct frequency band and varying data rates.
- MAC Layer: Defines the access methods for these channels. The MAC layer in 6LoWPAN supports:
- Beaconing tasks for device identification, including beacon generation and synchronization.
- Channel access control using CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance).
- PAN membership control for associating and dissociating devices within a Personal Area Network (PAN).
The packet structure at this layer includes:
- IEEE 802.15.4 Header Fields:
- Pan ID
- Destination ID (64 bits)
- Source ID (64 bits)
- DSN (Data Sequence Number)
2. Adaptation Layer:
The adaptation layer compresses and retrofits IPv6 packets to the IEEE 802.15.4 packet format. This layer addresses the challenges posed by the differing packet sizes:
- IPv6 requires a minimum packet size of 1280 octets.
- IEEE 802.15.4 supports a maximum of 127 bytes (including headers).
This discrepancy is resolved using:
- Header Compression: Reduces IPv6 headers to fit into the limited payload size.
- Packet Fragmentation: Breaks large IPv6 packets into smaller fragments.
- Packet Forwarding: Ensures proper routing of packets across constrained networks.
3. Address Format
The address format in 6LoWPAN comprises two parts:
- Short Address (16 bits):
- PAN-specific and used for device identification within a local PAN.
- Scope is restricted to the local network.
- Extended Address (64 bits):
- Globally unique, allowing identification of devices beyond the local network.