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Module 4.0: Network Components • • • • • • • Repeater Hub NIC Bridges Switches Routers VLANs K. Salah 1 Hardware Components • • • 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. K. Salah 2 Bridges • • • • • • • 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 K. Salah 3 Switches • • • 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. K. Salah 4 Routers vs. Switches • • • • • 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. K. Salah 5 VLANs • • • 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 K. Salah 6