Transcript Network Components

Module 4.0: Network Components
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Repeater
Hub
NIC
Bridges
Switches
Routers
VLANs
K. Salah
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Hardware Components
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Repeater
– Layer 1 device that provides physical and electrical
connections.
– It receives signals from one cable segment, regenerates,
retimes, and amplifies them, and then transmits these
“revitalized” signals to another cable segment.
– Transmits in both directions
– Joins two segments of cable
– No buffering
– No logical isolation of segments
Hub
– Used to describe a repeater
– Can be “repeater hub”, “switching hub”, bridging hub”.
NIC
– Network Interface Card
– Performs layer-2 functions: framing, error detection, and
flow control.
– Performs layer-1 functions by converting the bits into
electrical signals using appropriate coding scheme.
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Bridges
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Layer 2 devices
Interconnects two or more individual LANs or LAN segments.
Desirable for separating traffic among segments. A segment is part of a LAN in which traffic is
common to all nodes, i.e. it is a single continuous conductor, though it may include repeaters.
Can be used to connect different speeds/physical layer types of networks together (10BaseT to
100Base F)
Split the segment with bridges/switches, if link utilization is more than 30%.
Store-and-forward devices. They capture the entire frame before deciding whether to filter or
forward it. Frames with bad CRC are not forwarded.
Minimal buffering to meet peak demand
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Switches
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Switches can operate at different layers: layer 2, 3, 4, and 7..
Basically a switch is hardware based, not software based.
Three types of layer 2 switches:
– Store-and-Forward Switch
 Similar to store-and-forward bridge. Store entire frame, check for errors,
and then switch to the other ports, based on the destination MAC
address.
– Cut-Through Switch
 The transmission of frame begins as soon as it reads the destination
MAC address. Two switch fabric/matrix designs:
 Crossbar
 Backplane with bus speed > aggregate port speeds
– Hybrid Switch
 Reliability: store-and-forward. Turn ON when errors are high.
 Low latency: cut-through. Turn ON when errors are low.
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Routers vs. Switches
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The primary difference is one semantics. Switches historically infer
CO links; routers use CL links. Traditionally, routers have performed
router table lookups and packet forwarding in software.
Layer-2 Switches start having routing functionality, and Layer-3 routers
start having ASIC (Application Specific Integrated Circuit) switching
technology for packets.
Layers 2 and 3 are merging and it is becoming difficult to distinguish
between switches and routers.
Layer 3 or IP switching: routing IP packets in ASIC, e.g, MPLS.
Layer 4/7 switching is a new and emerging area, called information
content switching.
– Layer 4: direct all traffic based on TCP destination port.
 All traffic with destination TCP port 80, is directed to a switch
port where a web cache resides.
– Layer 7: direct traffic based on information used in the payload.
 Examine URL GET request. If request for image, direct it
request to an optimized image server port.
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VLANs
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VLAN is a logical grouping of nodes
using Ethernet switches. Nodes don’t
need to be connected physically to the
same switch. A broadcast frame will be
heard by all nodes within VLAN.
Benefits:
– Isolates broadcasts
– Frees up network from physical
locations
– Easily shares resources. A server
can be part of multiple VLANs.
– Performance. Easily can be
enhanced by creating new VLANs.
– Security. By containing who can
listen to broadcast.
VLAN Membership (implicit tagging)
– Port-based
– MAC-based
– Layer 3/IP
– Combination of the above
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