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Boris
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## Lecture 1 (12:00)
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### Flow Control
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If sender sends data faster than recipient can consume it, the recipient must store the data in a buffer until it is ready - in RAM or storage.
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If this happens for a sustained period, the buffer gets full, and any excess data is discarded.
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Flow Control is the mechanism that ensures the sender stops transmitting before the buffer is full to prevent wasted bandwidth.
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- Full Duplex (Two way negotiation)
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- Destination has received all frames sent so far
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- Destination is ready to receive more data.
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- Data and control info can flow simultaneously
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- Simplex (one way) transmission system, we cant have two-way negotiation
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### Packets
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- Frame / Packet is a chunk of data with a fixed or max size.
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- May stand alone or be fragments of larger items
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- Dividing data gives us chance to send management info between frames.
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- Extra overhead = Slight loss of efficiency.
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- Propagation Time vs Transmission Time
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- Propagation Time is the amount of time it takes for one particular signal to get from one point to another.
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- Transmission Time is the total amount of data that can be sent from one place to another in a given period of time.
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#### Sliding Windows Flow Control
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- Every packet is numbered in sequence.
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- **Window Size** defines the number of packets that can be sent by the sender without needing an acknowledgement from the recipient
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- Amount of space recipient reserves for buffer space to be used for conversations with this particular sender.
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- Recipient will periodically tell the sender the start of the window
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- This way , the sender can send packets up to (windowStart + windowSize - 1)
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- Used in the TCP protocol on the internet.
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### Error Correction
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- Fix the Error (FEC)
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- Ask for the frame containing the error to be re-transmitted - Automatic Repeat ReQuest / Query (ARQ)
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- Throw away the frame containing the error
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- Usual, and ARQ requires it
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- Ignore the error
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- Useful for low quality streaming multimedia data
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- Dangerous in networking, as it often matters where the error is.
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#### Forward Error Correction (FEC)
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- Represent something using more bits than needed. An error results in an invalid value that can be rounded to the nearest valid one.
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- The more extra bits, the better redundancy gained.
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- Simple ex.
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- Majority Voting:
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- Transmit each bit 3+ times (000, 111)
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- For the recipient, 001/010/100 are rounded to 0
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- 110/101/011 are rounded to 1
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#### Re-transmission
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- If we cannot fix the error, ask for retransmission
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- We need a return channel to ask, so we cannot do this over simplex channels ( ex. TV )
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- Must be unicast ( cannot be performed over broadcast / multicast data )
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- Data must be time independent ( cannot be used for realtime data such as multimedia )
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#### Go-Back-N ARQ
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- Pairs with Sliding Windows Flow Control.
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- Recipient discards a packet if it contains an error
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- You notice you have discarded the packet when you receive the next packet with an out of sequence number.
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- When noticed, discard packet and request sender to backpedal to last correct packet.
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- Sender re-transmits all packets started from missing packet.
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- Sender polls for a response if no acknowledgement is received (assumed lost)
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- Recipient re-sends last acknowledgement.
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## Lecture 2 (15:00)
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### Sliding Windows Flow Control
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#### Parameters of Communication
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- **A** will send 8 packets to **B**
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- Transmission time (time to put on network) for a packet is 1 "time unit"
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- Transmission time for acknowledgement is 0 "time units"
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- Propagation Time (time to travel through network) is 2 "time units"
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- **B**'s packet processing time is 1 "time unit" (then acknowledges)
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- Initial **Window Size** is 3
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#### Legend
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- Thick border (yellow bg) = Sliding Window
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- Black number = in process of send
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- Red number = sent but no acknowledge
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- Green number = sent and acknowledged
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@@ -0,0 +1,175 @@
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Arman Arshad:cc1
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Mark De Souza:cc1
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Mihai Raul Blaga:cc1
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Michalis Kefalas:cc1
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Alweh Almohsin:cc1
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Naser Alrashidi:cc1
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Timea Kereszturi:cc1
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Santiago Vassoler:cc1
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Arif Khan:cc1
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Babacar Ba:cc1
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Akram Alsaleh:cn1
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William Coulson:cc1
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Abdullah Ali:cc1
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Michael Campbell:cn1
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Joshua Cherian:cn1
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Harry Page:wd1
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Mohemmed Sitab:cn1
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David Davies:cc1
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Mohammed Ntambiye:cc1
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Alex Chrisham:cn1
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Ruby Miller-Lawson:wd1
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Josephine Mullally:cc1
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Emma Cudworth:cn1
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Ilsan-Ul-Haq Khan:cn1
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Adal Khan:cn1
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Salman Shah:wd1
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Sara Nejad:wd1
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Qaiser Hussain:cn1
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Deming Meng:cc1
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Ayubalayefa Fitzgerald Ebieritei:cc1
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Liam Croft:cc1
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Robert Dobson:cc1
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Matthew Hargraves:cn1
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Nabeel Iqbal:cc1
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Dean McAndrew:cc1
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Liam Middleton:wd1
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Georgios Pilavas:cc1
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Ussama Qadir:cn1
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Marc Reed:cc1
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Matthew Smith:cc1
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Nathan Thornton:cc1
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Robert Adams:cc1
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Nadeem Ahmed:cc1
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Dan Brown:cc1
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James Burgess:cc1
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Dylan Eckersall:cc1
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Jindrich Gorner:cc1
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George Jemison-Bates:cc1
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Akab Khan:cn1
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Darren Maguire:cc1
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Michael Manville:cc1
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Lee Moore:cc1
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Zabir Patel:cn1
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Umar Raees:cn1
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Daniel Rutherford:cc1
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Ivan Totev:cc1
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Umar Adam:cc1
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Ryan Bailey:cc1
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Cameron Campbell:cc1
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Dilli Chhetri:cn1
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Tony Deverill:cc1
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Joseph Fleet:cc1
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Andrew Gilluley:cc1
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Timothy Hilditch:cc1
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Joshua Kisler:cc1
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Jack Latham:cn1
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Will Lound:cc1
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Liam Maguire:cn1
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Sam May:cc1
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Matthew McDermott:cc1
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Muminur Rahman:cn1
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Harry Richardson:cn1
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Zaafir Salam:cc1
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Reagan Turner:cn1
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Robert Woolvin:cc1
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Saman Abbas:cn1
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Ityaab Ahmed:cn1
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Joshua Cobb:cn1
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Jarred Cranfield:cn1
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Conor Glascoe:cn1
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Jack Harris:cn1
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Preston Leigh:cn1
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Stanislav Miloradov:cn1
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Adam Montgomery:wd1
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Ali Nadeem:cc1
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Jack Ormrod:cc1
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Marcin Poneta:cn1
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Georgia Rey:cn1
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Lukasz Romerowicz:cc1
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David Stubbs:cc1
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Donatos Tassis:cc1
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Matthew Wragg:cc1
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Mohsin Akujee:cn1
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Obaid Amiri:cn1
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Sulaymaan Babar:cc1
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Jarryd Bethune:wd1
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Ellis Delaney:wd1
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Jack Fielding:cn1
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Igor Filipek:wd1
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Tyler Kelly:cc1
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Adam Lawson:cc1
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Ben Monaghan:cc1
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Jake Ramsden-Finnegan:cc1
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Ollie Steer:cc1
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Ryan Wallace:cc1
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Brad Cantel:cc1
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Shannon Beswick:cc1
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Mohammed Shah:cn1
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Kris Gibson:cc1
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Yazn Achtar:cc1
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Mahir Ahmed:cc1
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Pedrom Ameli-Savehchi:cn1
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Georgina Beckett:cc1
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Stephen Carr:cn1
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Mark Chaffer:cc1
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Ben Evans:cc1
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Roberto Graham:cc1
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Ksistof Grunt:wd1
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John Jackson:cn1
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Martin McCourt:cc1
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Jamie Orchison:cc1
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Fizan Saddique:cn1
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Michael Sutton:cc1
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Alex Hopkinson:cc1
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Konstantinos Papa:cn1
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Ali Shah:cc1
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Milad Yahya:cn1
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Josh Catterson-Reid:cc1
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Isavella Chrysanthou:cc1
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Jill Dacanay:wd1
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Shelton Madire:cn1
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Hussein Mohammed:cc1
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Kane Stephens:cc1
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Ahmad Wali:cc1
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Shakeal Mahmood:cn1
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Daniella Middleton:wd1
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Nawal Saheb:cc1
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Charles Packman:cn1
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Noman Ghous:cc1
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Reece Matthews:cc1
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Jayed Miah:cc1
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Mohammed Zakariya Kalang:cc1
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Hani Samir:cc1
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Ryan Davis:cc1
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Mohamed Shehata:cc1
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Omar Aljewari:cc1
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Mohammed Ullah:cn1
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Atif Hassan:cn1
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Ryan Sharkey:cc1
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Irfan Jamil:cn1
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Aroba Waheed:cc1
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Safwana Mohammed:cc1
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Edward Robertson:cc1
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Mohamed Ibrahim:wd1
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Helly Liking:cn1
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Azham Syed:cc1
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Daniel Turrell:cc1
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Connor Scott:cc1
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Alexander Dawson:cc1
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Sajid Jan:cc1
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Adebanjo Adegboye:cn1
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Navin Bajgai:cc1
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Ansoumane Konde:cc1
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Justyna Rodzevic:wd1
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Karl Sparham:wd1
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Hassan Buyondo:cn1
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Minhaj Patel:cc1
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Leonel Dos Santos Muzobo:cn1
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Matthew Spafford:cc1
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Mushir Faisal:cc1
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Arslaan Qadus:cc1
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Amit Budhathoki:cn1
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Umar Ali:cn1
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Hamdraza Rana:wd1
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Adam Ulanowski:cc1
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@@ -0,0 +1,6 @@
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* David_Beckham_(1996-2009),_115_Caps
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* Bobby_Charlton_(1958-1970),_106_Caps
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* Steven_Gerrard_(2000-2012),_100_Caps
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* Bobby_Moore_(1962-1973),_108_Caps
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* Peter_Shilton_(1970-1990),_125_Caps
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* Billy_Wright_(1946-1959),_105_Caps
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@@ -0,0 +1,25 @@
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#!/bin/bash
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if test -d completed/; then
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rm -f completed/*
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else
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mkdir completed
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fi
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cat level1.txt | while read LINE; do
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name=$(echo $LINE | cut -d : -f 1)
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course=$(echo $LINE | cut -d : -f 2)
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firstname=$(echo $name | cut -d " " -f 1)
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familyname=$(echo $name | cut -d " " -f 2-)
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outputfile="$course-$familyname.txt"
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if test -e completed/"$outputfile"; then
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outputfile="$course-$familyname $firstname.txt"
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fi
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cat template | sed -r -e "s/^NAME/$firstname/" \
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-e "s/COURSE$/\U$course/" \
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-e "/:/!p" \
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-e "/^.*($course|everyone).*:/!d; s///" \
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> completed/"$outputfile"
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done
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Binary file not shown.
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NAME
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Assessment dates
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================
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This is to remind you of upcoming assssesssssment dates for COURSE
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cc1: CSIL – around 14th December 2015
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cc1,wd1,cn1: Databases - some time 11th-22nd January 2016
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everyone: PD&P - some time 11th-22nd January 2016
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cc1: Java - some time 11th-22nd January 2016
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wd1,cn1: Invented module - Invented date 2016
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Please don't ask if you don't have any questions
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Programme Leader
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