Site Outline

This information is lists the topics that will be covered. The information here provides a detailed description of the subjects which the site covers.

A road-map provides an easy way to access the on-line information about general topics.

The course will cover the following terms and concepts.

Note: Items in square brackets [] are not currently examinable.

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Open Systems Interconnection Reference Model
1. Definition of a Communications Network
   Concept of a node; Nodes connected by links to form networks; Names & Addresses; the idea of "address resolution"
2. Types of Network
   Understanding of operation and examples of use.
   • Point-to-point Circuits
     Fixed configuration; dedicated capacity
   • Circuit-switched Networks
     Circuit setup; reserved capacity; (e.g. telephony)
   • Message-switched Networks
     Circuit set-up; store and forward; message headers; (e.g., telex, SMS, MMS, Fax)
   • Packet-switched Networks
     Packet headers; pipelining; datagram networks; (e.g., Internet)
3. Types of Equipment
   • End Systems (ES) (e.g. client or server)
   • Intermediate Systems (IS) (e.g. router, bridge)
4. Types of Packet-Switched Network
   • Wide Area Networks (WANs)
   • Internet Service Providers (ISPs)
   • Local Area Networks (LANs)
     
5. Types of Communication
   • Client and Server Communication (e.g. DNS, arp, ping)
   • Broadcast, Unicast and Multicast modes of tranamission
   • Simplex, Duplex and Half-Duplex information flow
6. Open System Interconnection
   Definition of OSI; Reasons for using the Reference Model
   • Protocol Layers
     • The Seven Layers of the OSI Reference Model
       Knowledge of the seven layers and their BASIC functions, particularly of the four lowest layers.
     • TCP/IP stack
   • Communications between layers
     • Protocols
     • Peer to Peer Communication between Remote Layers
     • Service Access Points
     • [Service Primitives and Communication Between Adjacent Layers]
   • Encapsulation of PDUs
     Addition of headers on transmission; Removal on reception
   • Segmentation & reassembly by protocol layers

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Physical Layer
1. Properties of the Physical Layer
   Movement of bits
2. Transmission Media
   Open Wire; Twisted Pair; Coaxial Cable; Optical Fibre.
3. Synchronous Transmission
   • Bit Timing
     Clock Encoding; Need for DPLL.
   • Shift Register, Bit Order
   • Principles of Clock Encoding
     • NRZ Encoding
       Operation; Bandwidth; Use with synchronous and asynchronous circuits.
     • Manchester Encoding
       Operation; Bandwidth; Use in Ethernet.

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Link Layer
1. Role of the data link layer.

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Local Area Networks
1. Definition of a Local Area Network
   • Ethernet
   • Network Interface Card
2. Medium Access Control Layer
   • Medium Access Control Frame Format
     Format of the address field in MAC; Size of MAC header.
   • Source Address
   • Destination Address; Broadcast, Multicast, and Unicast Addresses
   • CRC-32; Discard of frames with invalid CRC; Invalid Length
   • Normal and Promiscuous modes
   • Calculation of Utilisation and Throughput
3. Access to the Shared Medium (Cable)
   • Transceiver
   • Preamble
     To ensure DPLL locks-up prior to first byte of frame.
   • Start of Frame Delimiter (at end of preamble)
   • Carrier Sense
     Checking for other users; Possible contention.
   • Collision Detection (CD)
     • Ethernet Transceiver (detection of current)
     • Jam Signal
     • Exponential Back-off
     • Need to avoid congestion
     • Slot Time
     • Capture
4. Cabling (media)
   
   • 10B5 Thick Ethernet (low loss co-axial cable)
   • 10B2 Thin Ethernet (low cost co-axial cable)
   • 10BT Unshielded Twisted Pair (unshielded twisted pair cable, UTP CAT-5)
   • 10BF Fibre Optic Links (point to point fibre link)
   • Higher bandwidth twisted pair cable (CAT-5e, CAT-6, CAT-7, STP)
5. Higher Speed Communciation
   • Fast Ethernet100 Mbps
   • Gigabit Ethernet 1 Gbps
   • 10 Gbps, and higher
6. Wireless Etherbnet (WiFi)
   • 11 Mbps Wireless Ethernet
   • Access Points (AP)
   • The "Hidden Node" problem in Wireless Ethernet, CSMA/CA
   • Need to avoid Capture by an AP
   • [Higher speed WiFi]

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LAN Interconnection
1. Repeaters
   Operation at the physical layer; Regeneration of timing; Ethernet Repeaters; 10BT Hub.
2. Bridges and Switches
   Operation at the data link layer; Operation of a bridge; Packet forwarding; Internal queuing of packets.
   • Address Tables
     • Learning local addresses (by observing source address in promiscuous mode)
     • Forwarding to correct port (by observing destination address)
     • Flooding of broadcast, multicast and unknown destination address
   • Use of timer to discard unwanted addresses from the tables (ageing).
   • Filtering And Security
     • Virtual LANs (VLANs)
     • [Over-riding the normal learning of local addresses]
     • [Network Maagement]
3. Routers, and Operation of Routers
   • Packet Forwarding
     • Difference between routing and bridging
     • Decision whether to send directly or use a router
     • Network-layer fields updated during routing: Time To Live field
   • Routing Tables
     
     • [Routing Protocols]

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The Internet
1. The Internet
   A collection of inter-connected networks
2. The Internet Protocol
3. Names and Addresses
   • Difference between a Name and an Address
   • Flat and Hierarchical Structures
4. The Internet Protocol
   • IP Header Fields
     Important header fields: Source Address, Destination Address, Size, Checksum, Protocol Type.
   • Datagrams
     Best Effort Service; Difference between packets (network layer) and frames (link layer); Need for destination address to identify recipient; Need for source address to identify sender.
   • Network Address
     IP Netmask; Broadcast & Multicast.
5. IP over Ethernet
   Encapsulation; Protocol headers added on transmission
   • Hardware Address (i.e. MAC address)
     Difference between network address and link layer hardware address
   • Address Resolution (arp)
     • arp server and client
     • Broadcast address for request
     • Unicast reply
     • Information exchanged by arp request and reply
     • Need to cache results for later packets
   • Maximum Transfer Unit
     • 1500 B MTU size for Ethernet
     • [IP Segmentation (Also known as Fragmentation)
       Segmentation based on MTU; Network layer header in each segment; Reassembly at final destination; Path-MTU; Path-MTU-Discovery]
6. ICMP
   Error reporting; Network testing using ICMP echo request and echo reply.
   • Error Reporting
   • The "ping" Program, and Round Trip Time
     • Practical familiarity with using "ping"
     • Use to see if a computer is operating (alive)
     • Use to measure round trip response time

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Transport Protocols and Applications
1. Functions of the Transport Service
   Definition of services provided; Encapsulation by network layer.
2. Best Effort Transport Service
3. User Datagram Protocol
• Source and Destination Port
• Transport checksum
• Demultiplexing to the application
1. Reliable Transport Service
   • Definition of Reliability
   • Acknowledgment
   • Error Recovery
     • The Trivial File Transfer Protocol (TFTP)
     • [Stop and Wait (Idle) Error Recovery]
     • The need for timers; frame transition diagram for recovery of packet loss
   • Transmission Control Protocol) Port ID; Data ;
     • Use to provide reliability; congestion control.
     • [Use for WWW, telnet, ftp, etc.]

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Performance of Protocols and Applications

• Drawing Frame Transition Diagrams
  Time Axis; Effect of data rate; Effect of propagation delay
• Calculating Utilisation
  Size of frame headers; Transmission delay
• Calculating Throughput

COURSE INFORMATION PAGE

1. Synchronous Transmission
   • Bit Timing
     Clock Encoding; Need for DPLL.
   • Principles of Clock Encoding
     • NRZ Encoding
       Operation; Use with synchronous and asynchronous circuits.
     • Manchester Encoding
       Operation; Bandwidth; Use in Ethernet.
     • AMI Encoding
       Operation; Bandwidth; Use in older telephony systems; Not transparent timing.
     • HDB3 Encoding
       Operation; Bandwidth; Use in modern telephony systems; Transparent timing.
2. Comparison of Asynchronous Character Framing with Synchronous Transmission

Link Layer

1. High-Level Link Control Protocol
   Bit transparent synchronous frame protocol standardised by ISO.
   • Flags
     The flag pattern (0111 1110) and it use to delimit (separate) frames.
   • Bit Transparency
     The need for transparency; the 0-bit insertion procedure; the flag, abort and idle sequence.
   • Address Field
   • CRC
     The use of a CRC for error detection; The CRC-16.
2. Connection-Less Services
   The non-reliable service; Connection-less frame header (UI).
3. Connection-Oriented Services
   • Other Frame Formats (e.g. I, RR, REJ)
   • Link Management
   • Definition of Reliability
   • Acknowledgment
   • Error Recovery
     • Stop and Wait (Idle) Error Recovery
       The need for timers; frame transition diagram.
     • The Sliding Window and sequence numbers
       The send sequence number, N(S); the receive sequence number, N(R); modulo numbering; the transmission window, k.
     • Checkpoint Recovery (Polling) Error Recovery
       Need for timer; The use of the poll/final bit; Wind-back of V(S).
     • Go-Back-N (REJ) Error Recovery
       Detection of error; Transmission of REJ(N(R)); Wind-back of N(S).
   • Timers
     The T1 timer in HDLC
4. Performance of Link Protocols
   • Drawing Frame Transition Diagrams
     Time Axis; Effect of data rate; Effect of propagation delay.
   • Calculating Utilisation
     Size of frame headers; Transmission delay.
   • Calculating Throughput
     Frame transition diagrams; Window Size; Propagation Delay, T1 timer.
5. Connection-Less Services
   The non-reliable service; Connection-less frame header (UI).