Network Layer Characteristics

Explain how the network layer uses IP protocols for reliable communications.

The Network Layer

• Provides services to allow end devices to exchange data
• IP version 4 (IPv4) and IP version 6 (IPv6) are the principle network layer communication protocols.
• The network layer performs four basic operations:
• • Addressing end devices
  • Encapsulation
  • Routing
  • De-encapsulation

IP Encapsulation

• IP encapsulates the transport layer segment.
• IP can use either an IPv4 or IPv6 packet and not impact the layer 4 segment.
• IP packet will be examined by all layer 3 devices as it traverses the network.
• The IP addressing does not change from source to destination.

Note: NAT will change addressing, but will be discussed in a later module.

Characteristics of IP

IP is meant to have low overhead and may be described as:

• Connectionless
• Best Effort
• Media Independent

Connectionless

IP is Connectionless

• IP does not establish a connection with the destination before sending the packet.
• There is no control information needed (synchronizations, acknowledgments, etc.).
• The destination will receive the packet when it arrives, but no pre-notifications are sent by IP.
• If there is a need for connection-oriented traffic, then another protocol will handle this (typically TCP at the transport layer).

Best Effort

IP is Best Effort

• IP will not guarantee delivery of the packet.
• IP has reduced overhead since there is no mechanism to resend data that is not received.
• IP does not expect acknowledgments.
• IP does not know if the other device is operational or if it received the packet.

IP is unreliable:

• It cannot manage or fix undelivered or corrupt packets.
• IP cannot retransmit after an error.
• IP cannot realign out of sequence packets.
• IP must rely on other protocols for these functions.

Media Independent

IP is media Independent:

• IP does not concern itself with the type of frame required at the data link layer or the media type at the physical layer.
• IP can be sent over any media type: copper, fiber, or wireless.

The network layer will establish the Maximum Transmission Unit (MTU).

• Network layer receives this from control information sent by the data link layer.
• The network then establishes the MTU size.

Fragmentation is when Layer 3 splits the IPv4 packet into smaller units.

• Fragmenting causes latency.
• IPv6 does not fragment packets.
• Example: Router goes from Ethernet to a slow WAN with a smaller MTU

Other related topics

Other useful information

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