1 K. Salah Module 4.0: Network Components Repeater Hub NIC Bridges Switches Routers VLANs

2 K. Salah 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.

3 K. Salah 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

4 K. Salah 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.

5 K. Salah 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.

6 K. Salah 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