Network Layer

Services and Protocols

  • Transport segment from sending to receiving host

    • Sender - encapsulates segments into datagrams, passes to link layer

    • Receiver - delivers segments to transport layer protocol

  • Network layer protocols in every Internet device: hosts, routers

  • Routers

    • Examines header fields in all IP datagrams passing through it

    • Moves datagrams from input ports to output ports to transfer datagrams along end-end path

2 Key Functions

  • Forwarding - move packets from a router’s input link to appropriate router output link

  • Routing - determine route taken from source to destination by packets from source to destination

    • Routing algorithms

Data Plane

  • Local, per-router function

  • Determines how datagram arriving on router input port is forwarded to router output port

Control Plane

  • Network-wide logic

  • Determines how datagram is routed among routers along end-end path from source host to destination host

  • Two control-plane approaches:

    • Traditional routing algorithms - implemented in routers

    • Software-defined networking (SDN) - implemented in (remote) servers

Per-Router Control Plane

Individual routing algorithm components in each and every router interact in the control plane

Internet's Network-Layer Service Model

What service model for “channel” transporting datagrams from sender to receiver?

  • Example services for individual datagrams:

    • Guaranteed delivery

    • Guaranteed delivery with less than 40 msec delay

  • Example services for a flow of datagrams:

    • In-order datagram delivery

    • Guaranteed minimum bandwidth to flow

    • Restrictions on changes in interpacket spacing



Quality of Service (QoS) Guarantees?

->

->

->

Network Architecture

Service Model

Bandwidth

Loss

Order

Timing

Internet

Best effort

None

No

No

No

ATM

Constant bit rate

Constant rate

Yes

Yes

Yes

ATM

Available bit rate

Guaranteed min

No

Yes

No

Internet

Intserv Guaranteed (RFC 1633)

Yes

Yes

Yes

Yes

Internet

Diffserv (RFC 2475)

Possible

Possibly

Possibly

No

Internet “Best Effort” Service Model

No guarantees on:

  • Successful datagram delivery to destination

  • Timing or order of delivery

  • Bandwidth available to end-end flow

Reflections

  • Simplicity of mechanism has allowed Internet to be widely deployed adopted

  • Sufficient provisioning of bandwidth allows performance of real-time applications (e.g., interactive voice, video) to be “good enough” for “most of the time”

  • Replicated, application-layer distributed services (datacenters, content distribution networks) connecting close to clients’ networks, allow services to be provided from multiple locations

  • Congestion control of “elastic” services helps