Ethernet – Ethernet is the most widely used local area network (LAN) technology. Ethernet is a link layer protocol in the TCP/IP stack, It was first implemented by a group called DIX (Digital, Intel, and Xerox). They created and implemented the first Ethernet LAN specification, IEEE 802.3 committee came. This was a 10Mbps network that ran on coax and then twisted-pair and then fiber media. The IEEE extended the 802.3 committee to two new committees known as 802.3u (Fast Ethernet) and 802.3ab (Gigabit Ethernet on category 5) and then finally 802.3ae (10Gbps over fiber and coax).

Preamble – An alternating 1,0 pattern provides a 5MHz clock at the start of each packet, which allows the receiving devices to lock the incoming bit stream.

Start Frame Delimiter (SFD)/Synch – The preamble is seven octets and the SFD is one octet (synch). The SFD is 10101011.

Destination address – It can be an individual address or a broadcast or multicast MAC address.

Length or Type – 802.3 uses a Length field, but the Ethernet_II frame uses a Type field to identify the Network layer protocol. 802.3 cannot identify the upper-layer protocol.

Frame Check Sequence (FCS)- At the end of the frame that’s used to store the cyclic redundancy check (CRC) answer. When a receiving host receives the frame and runs the CRC, the answer should be the same. If not, the frame is discarded, assume that errors have occurred.

This is the beauty of the Ethernet_II frame. Because of the Type field.

The EIA/TIA (which stands for the Electronic Industries Association and the newer Telecommunications Industry Alliance) is the standards body that creates the Physical layer specifications for Ethernet. The EIA/TIA specifies that Ethernet use a registered jack (RJ) connector on unshielded twisted-pair (UTP) cabling (RJ45). However, the industry is moving toward calling this just an 8-pin modular connector. EIA/TIA 232 speed upto 64 kbps, support unbalanced circuits and closely resembled to V.24 specification. EIA/TIA 449 known as RS-449 and speed upto 2 Mbps.

ITU-T make V,X,G specification. V.24 same as RS-232 and speed upto 64 kbps. V.35 used for synchronous comm. and speed upto 48 kbps. X.21 is also used for synchronous comm. and used in Europe and japan.

G.703/G.704 BNC used between DTE and DCE connector. E1(2 Mbps) to E3(45Mbps) used in india. T1(1.544Mbps) to T3(44.736Mbps) used in USA.

Each Ethernet cable type that is specified by the EIA/TIA has inherent attenuation, which is defined as the loss of signal strength as it travels the length of a cable and is measured in decibels (dB). The cabling used in corporate and home markets is measured in categories. A higher-quality cable will have a higher-rated category and lower attenuation. For example, category 5 is better than category 3 because category 5 cables have more wire twists per foot and therefore less crosstalk. Crosstalk is the unwanted signal interference from adjacent pairs in the cable.

100Base-TX (IEEE 802.3u)- It most commonly known as Fast Ethernet, uses EIA/TIA category 5, 5E, or 6 UTP two-pair wiring.

100Base-FX (IEEE 802.3u)- Uses fiber cabling 62.5/125-micron multimode fiber. Point-to-point topology; up to 412 meters long. It uses ST and SC connectors, which are media-interface connectors.

1000Base-CX (IEEE 802.3z)- Copper twisted-pair called twinax (a balanced coaxial pair) that can run only up to 25 meters and uses a special 9-pin connector known as the High Speed Serial Data Connector (HSSDC).

1000Base-T (IEEE 802.3ab) -Category 5, four-pair UTP wiring up to 100 meters long and up to 1Gbps.

1000Base-SX (IEEE 802.3z)- The implementation of 1 Gigabit Ethernet running over multimode fiber-optic cable (instead of copper twisted-pair cable) and using short wavelength laser. Multimode fiber (MMF) using 62.5- and 50-micron core; uses an 850 nanometer (nm) laser and can go up to 220 meters with 62.5-micron, 550 meters with 50-micron.

1000Base-LX (IEEE 802.3z)- Single-mode fiber that uses a 9-micron core and 1300 nm laser and can go from 3 kilometers up to 10 kilometers.

1000BASE-ZX (Cisco standard)- 1000BaseZX (or 1000Base-ZX) is a Cisco specified standard for gigabit Ethernet communication. It operates on ordinary single-mode fiber-optic link with spans up to 70 km).

10GBase-T – It is a standard proposed by the IEEE 802.3an committee to provide 10Gbps connections over conventional UTP cables (category 5e, 6, or 7 cables).

IEEE standards

IEEE 802.1     — LAN/MAN, Mac                             IEEE 802.16 — Wimax

IEEE 802.3     — Ethernet                                          IEEE 829      — Software test

IEEE 802.11   — WLAN, wifi                                      IEEE 1003    — Unix

IEEE 802.15   — wireless PAN                                  IEEE 1076    — VLSI

IEEE 802.15.1— Bluetooth                                        IEEE 1284    — Parallel port

IEEE 802.1 Standard

IEEE 802.1D  —  STP                                                   IEEE 802.1AB — LLDP

IEEE 802.1q   —  Virtual LAN                                    IEEE 802.1AX — Link aggregation

IEEE 802.1s   —  Multiple spanning tree                 IEEE 802.1BA — auto video bridging

IEEE 802.3 Standard (Ethernet)

IEEE 802.3a  —  10Base-2(thin)                                IEEE 802.3z   — 1000Base-X

IEEE 802.3c  —  10Mbps repeater                            IEEE 802.3ab — 1000Base-T

IEEE 802.3d  —  Fiber                                                  IEEE 802.3ac —  Vlan tag

IEEE 802.3i   —  10Base-T                                          IEEE 802.3ad — Parallel link (link aggregation/ether)

IEEE 802.3j   —  10Base-F                                           IEEE 802.3ae —  10G ethernet

IEEE 802.3u  —  10Base-T                                           IEEE 802.3as —  frame expansion

IEEE 802.3x  —   Full duplex                                        IEEE 802.3at —  POE plus

IEEE 802.11 Standard (CSMA/CA)

IEEE 802.11  – 2.4 Ghz, 1-2Mbps, 20 feet                  IEEE 802.11g – 2.4 Ghz, upto 54Mbps, upto 150 feet

IEEE 802.11a- 5 Ghz, upto 54Mbps, 20-75 feet       IEEE 802.11n – 2.4 Ghz, upto 600Mbps, upto175+

IEEE 802.11b- 2.4 Ghz, upto 11Mbps, upto 150 feet

Carrier Sense Multiple Access with Collision Detection (CSMA/CD) -Protocol that helps devices share the bandwidth evenly without having two devices transmit at the same time on the network medium.When a host wants to transmit over the network, it first checks presence of a digital signal on the wire. If all clear then host will proceed transmission. But it doesn’t stop there. The transmitting host constantly monitors the wire to make sure no other hosts begin transmitting. If the host detects another signal on the wire, it sends out an extended jam signal that causes all nodes on the segment to stop sending data (think busy signal).Full-duplex Ethernet uses two pairs of wires at the same time instead of one wire pair like half duplex.

MAC address – Every device have physical address of 48 bit long. The high-order bit is the Individual/Group (I/G) bit. When it has a value of 0, we can assume that the address is source portion of the MAC header. When it is a 1, we can assume that the address represents either a broadcast or multicast address in Ethernet or a broadcast or functional address in Token Ring and FDDI. The next bit is the global/local bit, or just G/L bit (also known as U/L, where U means universal). When set to 0, this bit represents a globally administered address (as by the IEEE). When the bit is a 1, it represents a locally governed and administered address. Error detection from a cyclic redundancy check (CRC). But remember—this is error detection, not error correction.


Rolled cable – It isn’t used to connect any Ethernet connections together, you can use a rolled Ethernet cable to connect a host EIA-TIA 232 interface to a router console serial communication (COM) port.

Data De-encapsulation – Devices reconstruct the frames, run a CRC, and then check their answer against the answer in the frame’s FCS field. If it matches, the packet is pulled from the frame and what’s left of the frame is discarded. This process is called de-encapsulation.

The Cisco Three-Layer Hierarchical Model

Core layer – User data is processed at the distribution layer, which forwards the requests to the core .

If there is a failure in the core, every single user can be affected. Therefore, fault tolerance at this layer is an issue. The core is likely to see large volumes of traffic.

  • Don’t do anything to slow down traffic. This includes using access lists, routing between virtual local area networks (VLANs), and implementing packet filtering.
  • Don’t support workgroup access here.
  • Avoid expanding the core (i.e., adding routers) when the internetwork grows. If performance becomes an issue in the core, give preference to upgrades over expansion.

Now, there are a few things that we want to do as we design the core:

  • Design the core for high reliability. Consider data-link technologies that facilitate both speed and redundancy, such as Gigabit Ethernet (with redundant links), or even 10Gigabit Ethernet.
  • Design with speed in mind. The core should have very little latency.
  • Select routing protocols with lower convergence times.

Distribution layer– It is sometimes referred to as the workgroup layer. The primary functions of the distribution layer are to provide routing, filtering, and WAN access and to determine how packets can access the core. The distribution layer must determine the fastest way that network service requests are handled—e.g. how a file request is forwarded to a server. After the distribution layer determines the best path, it forwards the request to the core layer if necessary. The core layer then quickly transports the request to the correct service.

  • Routing
  • Implementing tools (such as access lists), packet filtering, and queuing.
  • Implementing security and network policies, including address translation and firewalls.
  • Redistributing between routing protocols, including static routing
  • Routing between VLANs and other workgroup support functions.
  • Defining broadcast and multicast domains.

Access layer – Controls user and workgroup access to internetwork resources. The access layer is sometimes referred to as the desktop layer.


Some Questions related to this topic:-

Q.1. Hub to switch which cable used ?

Ans. Crossover cable.

Q.2. What is the function of FCS ?

Ans. Error detection.

Q.3. Contention method used by Ethernet is called_______ ?


Q.4 When I/G bit in MAC address is set to 1 the transmission is ________ ?

Ans. Broadcast and multicast.

Q.5 _________ on the Ethernet network is the retransmission delay that enforced when collision occurs.

Ans. Backoff.        (when collision occurs then random backoff algorithm come)

Q.6 Socket comprise of ________ ?

Ans. IP address and port number.

Q.7 What is the full form of ARPA.

Ans. Advanced Research Projects Agency.