Sem 2 Networking Programming 5-2 Ethernet Switching

Ethernet Switching

• When an error is detected in a frame, the switch discards the frame to reduce bandwidth consumption by corrupt data.
• Store-and-forward switching is required for quality of service (QoS) analysis on converged networks, where frame classification for traffic prioritization is necessary.

Cut-Through Switching

• In cut-through switching, the switch acts upon the data as soon as it is received, even if the transmission is not complete.
• The switch buffers just enough of the frame to read the destination MAC address and determine to which port it should forward the data.
• Cut-through switching has two variants: fast-forward switching and fragment-free switching.

Fast-Forward Switching

• Fast-forward switching offers the lowest level of latency by immediately forwarding a packet after reading the destination address.
• Because fast-forward switching starts forwarding before the entire packet has been received, there may be times when packets are relayed with errors.
• The destination NIC discards the faulty packet upon receipt.

Fragment-Free Switching

• Fragment-free switching is a compromise between the high latency and high integrity of store-and-forward switching and the low latency and reduced integrity of fast-forward switching.
• The switch stores and performs an error check on the first 64 bytes of the frame before forwarding.

Memory Buffering on Switches

• An Ethernet switch may use a buffering technique to store frames before forwarding them or when the destination port is busy due to congestion.
• There are two methods of memory buffering: port-based memory and shared memory.

Port-Based Memory

• Frames are stored in queues that are linked to specific incoming and outgoing ports.
• A frame is transmitted to the outgoing port only when all the frames ahead in the queue have been successfully transmitted.

Shared Memory

• Deposits all frames into a common memory buffer shared by all switch ports.
• The amount of buffer memory required by a port is dynamically allocated.

Ethernet Frames

• Ethernet operates in the data link layer and the physical layer.
• It is a family of networking technologies defined in the IEEE802.2 and 802.3 standards.

Data Link Sublayers

• The 802 LAN/MAN standards, including Ethernet, use two separate sublayers of the data link layer to operate: LLC sublayer and MAC sublayer.

LLC Sublayer

• The LLC sublayer places information in the frame to identify which network layer protocol is used for the frame.

MAC Sublayer

• The MAC sublayer is responsible for data encapsulation and media access control.
• It provides data link layer addressing.

Data Encapsulation

• IEEE 802.3 data encapsulation includes the following:
  • Ethernet frame
  • Ethernet addressing
  • Ethernet error detection

Ethernet Addressing

• The Ethernet frame includes both a source and destination MAC address to deliver the Ethernet frame from Ethernet NIC to Ethernet NIC on the same LAN.

Ethernet Error Detection

• The Ethernet frame includes a frame check sequence (FCS) trailer used for error detection.

Media Access

• The IEEE 802.3 MAC sublayer includes specifications for different Ethernet communications standards over various types of media, including copper and fiber.

Duplex and Speed Settings

• Two of the most basic settings on a switch are the bandwidth ("speed") and duplex settings for each individual switch port.
• It is critical that the duplex and bandwidth settings match between the switch port and the connected devices.
• There are two types of duplex settings used for communications on an Ethernet network: full-duplex and half-duplex.

Autonegotiation

• Autonegotiation is an optional function found on most Ethernet switches and NICs.
• It enables two devices to automatically negotiate the best speed and duplex capabilities.

Broadcast MAC Address

• An Ethernet broadcast frame is received and processed by every device on the Ethernet LAN.
• It has a destination MAC address of FF-FF-FF-FF-FF-FF in hexadecimal (48 ones in binary).
• It is flooded out all Ethernet switch ports except the incoming port.
• It is not forwarded by a router.

Multicast MAC Address

• An Ethernet multicast frame is received and processed by a group of devices that belong to the same multicast group.
• It has a destination MAC address of 01-00-5E when the encapsulated data is an IPv4 multicast packet and a destination MAC address of 33-33 when the encapsulated data is an IPv6 multicast packet.

Learn about the differences between cut-through switching and store-forward switching in networking. Understand how they handle error detection and quality of service (QoS) analysis.