TECHNOLOGY DESCRIPTION

Technology overview

Ethernet General Ethernet framing Common topologies Virtual LANs VLANs in VLANs Layer 2 QoS Congestion avoidance RSTP Port aggregation Performances

IP General

Ethernet

General LAN protocol (high-speed data network covering a small, geographic area) Supports 10/100/1000 Mbps speeds Layer 2 of the OSI (data link layer):

o It splits data into frames for sending on the physical layer o It performs error checking and retransmits frames if an error is detected

Ethernet

Ethernet framing Frame sizes are from 64 to 1518 bytes Frame structure is:

How does an Ethernet switch work? o Source MAC addresses are learnt o Frames are forwarded by Ethernet switches based on destination MAC address

Unicast (0x00XXXX-XXXXXX) Multicast (0x01XXXX-XXXXXX) Broadcast (0xFFFFFF-FFFFFF)

o Unicast frames are switched to the port where the destination MAC address has been learnt o Multicast and broadcast frames are flooded

Source MAC

address

(6 bytes)

Destination

MAC address

(6 bytes)

Type

(2 bytes)

Information field

(46-1500 bytes)

Frame Check

Sequence

(4 bytes)

Header Payload CRC

Ethernet

Common topologies Point to Point (to connect 2 remote LANs)

Star (to connect multiple LANs)

Ring (redundancy in case of 1 failure)

Full-meshed (redundancy in case of multiple failures)

Ethernet

switch

Any physical

connection type

Long distance

capable physical

connection type

Ethernet

Virtual LANs Frames are forwarded by Ethernet switches based on destination MAC address AND VLAN Id (i.e. 1 to 4095) Frame sizes are from 64 to 1522 bytes

Used to split physical Ethernet networks for performance and/or security purposes

Source

address

(6 bytes)

Destination

address

(6 bytes)

Type

(2 bytes)

VLAN

(4 bytes)

Information field

(42-1500 bytes)

Frame Check

Sequence

(4 bytes)

Header Payload CRC

VLAN 1:

Administration

VLAN 2:

Sales

VLAN 3:

Engineering

Branch office Headquarter

1

2

3

1

2

3

4 4

Clients Servers

Ethernet

VLANs in VLANs Frames are forwarded by Ethernet switches based on destination MAC address AND 2 VLAN Ids Frame sizes are from 64 to 1526 bytes

Allows an operator network to switch traffic based on first VLAN layer, second VLAN layer remaining for private uses

Source

address

(6 bytes)

Destination

address

(6 bytes)

Type

(2 bytes)

First

VLAN

(4 bytes)

Second

VLAN

(4 bytes)

Information field

(38-1500 bytes)

Frame Check

Sequence

(4 bytes)

Header Payload CRC

Customer 1 Operator

network

Customer 2

First VLAN 1:

Customer 1

First VLAN 2:

Customer 2

Ethernet

Layer 2 QoS Applicable in case of congestion

Objective is to protect sensible applications 3 steps process: classification & mapping, scheduling, re-marking

1 Gbps 100 Mbps

Egress Ingress

Ethernet

Congestion avoidance Applicable in case of bottleneck

Objective is to prevent congestions Just before congestion happens, the ingress port sends an Ethernet packet to ask the transmitter to stop transmitting for X milliseconds.

1 Gbps 100 Mbps

Egress Ingress

Ethernet

Rapid STP Prevents switching loops Used to support link redundancy In the example below link A is first disabled by the protocol to prevent traffic to be looped forever ; in the case one link fails, say link B, link A is re-enabled to ensure all devices keep communicating together

X

Link A

Link D

Link B Link C

Link A

Link D

Link B Link C

Ethernet

Port aggregation Creates a virtual port from multiple physical ports to increase capacity Traffic is load balanced between the physical ports:

o Source MAC address o Destination MAC address o Source & destination MAC address o Source and destination IP address

Traffic is switched over the other physical ports in case of failure

2 x 1000 Mbps

Ethernet

Performances Switching is performed at a hardware level Maximum throughputs with 64 bytes packets

o 14,880 pps at 10 Mbps o 148,800 pps at 100 Mbps o 1,488,000 pps at 1000 Mbps

Low latencies Maximum number of MAC addresses learnt limited

IP

General Layer 3 of the OSI (network link layer):

o Moves frames across an internetwork from a source to a destination o Frames are forwarded by routers based on destination IP address Source

address

(6 bytes)

Destination

address

(6 bytes)

Type

(2

bytes)

IP information

(20 bytes)

Information

field

(66-1480

bytes)

Frame Check

Sequence

(4 bytes)

Ethernet

Header

Payload CRC IP

Header