Transmission Media

Communication Media or Transmission Media is the means through which information in the form of signals usually move from one network device to another. There are different types but they can be categorized into one of two categories:

  1. Guided Transmission Media (Cables)
  2. Unguided Transmission Media (Wireless)


Unshielded Twisted Pair (UTP)

This consists of two copper wires covered with a thin plastic coating twisted together. The twist in the wires act as a means of reducing electrical interference from the wires and radiation of radio frequencies. UTP is broken down into five categories:


Category 1 (CAT 1): – Voice Only (telephone wire)

Category 2 (CAT 2):- Data to 4Mbps

Category 3 (CAT 3):- Data to 10Mbps (Ethernet)

Category 4 (CAT 4):- Data to 20Mbps (16Mbps Token Ring)

Category 5 (CAT 5):- Data to 100Mbps (Fast Ethernet)

Shielded Twisted Pair (STP)

Similar to the UTP with the addition of a sheet of aluminium foil shielding each wire pair. The shield is grounded and prevents interference and signal radiation.


This cable consists of a central conductor surrounded by a shield. Coaxial cables are highly resistant to interference and are able to support wide bandwidths. This cable carries signals farther than 500m.

Optical Fibre

Optical Fibres use pulses of light, rather than pulses of electricity, to send data. It is made of glass or plastic fibres. It consists of a small fibre core encased in a thin, light absorbent plastic or glass jacket referred to as its cladding. The cladding is enclosed by a thick plastic or Teflon. Optical Fibre comes in many forms:

  1. Multi-mode Fibre (Step index) – light is introduced at several angles. At some angles, the light escapes and is absorbed by the cladding. At other angles it is reflected down the length of the fibre.
  2. Multi-mode Graded Index Fibre – uses a glass fibre in which the index of refraction varies. Instead of reflecting signals, multi-mode fibre bends the signal as they approach the cladding.
  3. Single Mode Fibre – the diameter of the core is reduced so that only one coherent light signal will be transmitted.
  4. Breakout Cable – has several fibres (often 4), each with its own cladding and its own jacket bound together with a larger jacket.
  5. Distribution Cable – Breakout cable with a larger jacket.
  6. Loose Cable –  1-12 fibres float inside a loose tube filled with get

Unguided/Wireless Transmission Media

Unguided media transport electromagnetic waves without using a physical conductor. This type of communication is often called wireless communication. Signals are normally broadcast through free space and thus are available to anyone who has a device capable of receiving them.


TCP/IP Suite

Transmission Control Protocol (TCP) / Internet Protocol (IP)

TCP/IP is a suite of protocols that performs the transfer of data between two computers or groups of dissimilar computers.

TCP is responsible for verifying the correct delivery of data from client to server. TCP also adds support to detect errors or lost data and to trigger retransmission until the data is correctly and completely received.

IP is responsible for moving packets of data from node to node. IP forwards packets based on a four byte destination address (IP number).

Application Layer

A TCP/IP application is any network process that occurs above the Transport Layer. This includes all the processes that users directly interact with, as well as other processes that users are not aware of.


Transport Layer

The transport layer corresponds to the Session and Transport Layer of the OSI model. It establishes a secure session between two machines and breaks down packets or datagrams.


  • Transmission Control Protocol (TCP) – ensures that the user gets data exactly as it was sent
  • User Datagram Protocol (UDP) – this protocol does not perform end-to-end reliability checks

Internet Layer

This is equivalent to the Network layer of the OSI model. It is concerned with how packets are routed and solving congestion problems. This layer uses Internet Protocol (IP), which is a connectionless protocol and Internet Control Message Protocol (ICMP).

Network Interface/Access Layer

The Network Access layer is equivalent to the Data Link and Physical layers of the OSI model. It ensures that data transmitted between sender and receiver is correct. This layer also provides guidelines on how to move data bits between modems.

Communication between Nodes

When connection-oriented services such as HTTP, FTP and pure IP are used, a connection must be established between the source and destination. This connection is called a handshake. The handshake has three steps. For argument sake, lets call the device that initiated the handshake Device A, and the target or destination Device B.

Step 1: – Device A sends its TCP sequence number and maximum segment size to Device B.

Step 2:- Device B responds by sending its sequence number and maximum segment size to Device A.

Step 3:- Device A acknowledges receipt of the sequence number and segment size information. Device A begins transmission.

A normal connection between a user (Alice) and...

A normal connection between a user (Alice) and a server. The three-way handshake is correctly performed. (Photo credit: Wikipedia)