**STEP 1: Introduction of the Concept** When sending data over a network, the data is divided into units called *datagrams*. Every network has a Maximum Transmission Unit (MTU), which is the largest size a datagram can be for transmission. If a datagram is larger than the MTU, it must be split into smaller pieces called *fragments* to be transmitted and later reassembled. --- **STEP 2: Answering Part (a)** - **What is MTU?** - MTU (Maximum Transmission Unit) is the largest size (in bytes) of a packet or frame that can be sent in a single network transaction on a specific layer (usually data link layer). - **Difference between datagram and fragments:** - A *datagram* is the original, complete packet of data to be sent. - *Fragments* are smaller parts of the datagram, created when the datagram exceeds the MTU and needs to be split for transmission. Each fragment carries part of the original data and has its own header, including information for reassembly. --- **STEP 3: Answering Part (b) – Offset Calculation** - **Given:** - Original datagram size = 4000 bytes - MTU = 1500 bytes - Header size = 20 bytes (implied from standard IP fragmentation, since data field = 1480 bytes in a 1500-byte frame) - Data per fragment (except last) = 1480 bytes - **First Fragment:** - Length = 1500 bytes (1480 data + 20 header) - Offset = 0 - **Second Fragment:** - Length = 1500 bytes (1480 data + 20 header) - Offset = Previous data offset + (data size / 8) = 1480 / 8 = 185 - **Third Fragment:** - Remaining bytes = 4000 - 1480 - 1480 = 1040 bytes (data left) - Length = 1040 bytes (assuming header is included, but usually it's 1040 data + 20 header = 1060 total, but let's follow the diagram) - Offset = Previous offset + previous data size / 8 = 185 + 1480 / 8 = 185 + 185 = 370 So, the offsets (in 8-byte blocks) will be: - First fragment: **0** - Second fragment: **185** - Third fragment: **370** --- **STEP 4: Final Short Answer** MTU is the largest size of data that can be sent in one frame. Datagrams are the original packets, and fragments are smaller pieces split for transmission due to MTU limits. For the given fragmentation, the offsets should be 0, 185, and 370 for the three fragments. --- **STEP 5: What We Did in Each Step** - We introduced network fragmentation and MTU. - We defined MTU, datagram, and fragment. - We calculated how the datagram is divided and determined the offset values for each fragment. - We summarized the final answers concisely.