Telecommunication Protocols Laboratory Course

Transcription

1 Telecmmunicatin Prtcls Labratry Curse Lecture 2 March 11,

2 Last time We examined sme key terms: prtcl, service, layer, netwrk architecture We examined sme reference mdels fr netwrk architecture OSI/ISO and TCP/IP We delimited a certain netwrk architecture t be fllwed March 11,

3 Netwrk architecture March 11,

4 Service and Prtcls March 11,

5 Assignments Each netwrk layer has specific prtcls Each team will chse ne prtcl frm each layer and ffer a simulatin fr it The simulatin has t emphasize the prtcl features crrespnding t its layer it des nt need t be cmplicated Each assignment is dcumented and lgged The prgrams are sent t vpretea@ab.fi (the curse assistant Virel Preteasa) The dcuments are sent t lpetre@ab.fi March 11,

6 Timetable We will cver five (sub)layers: DLL, MAC, NL, TL, AL First assignment: 25.3 DLL prtcl 18.3 grups frmed, lg and dcumentatin started, DLL prtcl chsen Lectures: 18.3, 25.3, 1.4, 8.4 Remaining time: feedback n request, slving assignments time Grading each prtcl will be detailed later, same with final grade Tday we study data link layer (DLL) prtcls March 11,

7 The Data Link Layer Studies algrithms fr achieving reliable and efficient cmmunicatin between 2 adjacent machines at DLL Adjacent machines: cnnected by a wire-like cmmunicatin channel Bits delivered in exactly the same rder in which they are sent Prblems t be handled Errrs made by cmmunicatin circuits Finite data rate f cmmunicatin circuits Nn-zer prpagatin delay March 11,

8 Functins f the Data Link Layer Prvide service interface t the netwrk layer Dealing with transmissin errrs Regulating data flw Slw receivers nt swamped by fast senders March 11,

9 Functins f the Data Link Layer (2) Relatinship between packets and frames. March 11,

10 Data Link Layer Design Issues Services Prvided t the Netwrk Layer Framing Errr Cntrl Flw Cntrl March 11,

11 Services Prvided t Netwrk Layer (a) Virtual cmmunicatin. (b) Actual cmmunicatin. March 11,

12 DLL services Unacknwledged cnnectinless service Acknwledged cnnectinless service Acknwledged cnnectin-riented service March 11,

13 Framing idea T prvide service t NL, DLL uses service f PL PL accepts a bit stream and delivers it t destinatin Bit stream nt guaranteed t be errr-free It is up t DLL t detect and, if necessary, t crrect errrs DLL breaks the bit stream int discrete frames and cmputes sme checksum C fr each frame At destinatin the checksum f the received frames recmputed in C If C C DLL knws an errr ccurred Framing = breaking the bit stream int frames March 11,

14 Framing methds Character cunt Flag bytes with byte stuffing Starting and ending flags with bit stuffing PL cding vilatins March 11,

15 Framing A character stream. (a) Withut errrs. (b) With ne errr. March 11,

16 Framing (2) (a) A frame delimited by flag bytes. (b) Fur examples f byte sequences befre and after stuffing. March 11,

17 Framing (3) Bit stuffing (a) The riginal data. (b) The data as they appear n the line. (c) The data as they are stred in receiver s memry after destuffing. March 11,

18 Errr cntrl DLL has t ensure that all frames are delivered t NL at destinatin in right rder and nly nce Tls Acknwledgements Timers Sequence numbers March 11,

19 Flw cntrl Occurs in DLL and at higher layers What t d with fast senders that eventually swamp slw receivers 2 methds Feedback-based flw cntrl Rate-based flw cntrl (never used at DLL) March 11,

20 Errr Detectin and Crrectin Errrs are cmmn n twisted cpper pairs and in wireless cmmunicatin On reliable channels Errr-Detecting Cdes On prne-t-errr channels Errr-Crrecting Cdes March 11,

21 Elementary Data Link Prtcls 1. An Unrestricted Simplex Prtcl 2. A Simplex Stp-and-Wait Prtcl 3. A Simplex Prtcl fr a Nisy Channel Reliable, cnnectin-riented service One directin, later bth Infinite supply f data frm NL, later nt March 11,

22 Prtcl Definitins Cntinued Sme definitins needed in the prtcls t fllw. March 11,

23 Prtcl Definitins (ctd.) Sme definitins needed in the prtcls t fllw.

24 Unrestricted simplex prtcl Data transmitted in ne directin nly Bth transmitting and receiving layers always ready Prcessing time ignred Infinite buffer space available Cmmunicatin channel never lses/damages frames March 11,

25 Unrestricted Simplex Prtcl

26 A simplex stp-and-wait prtcl Infinite buffer nt any lnger Slutin: receiver sends acknwledgement frame (just a dummy frame) t sender, which gives the latter permissin t transmit the next frame Exp f flw cntrl March 11,

27 Simplex Stp-and- Wait Prtcl

28 A simplex prtcl fr a nisy channel Errrs are nw pssible Slutin: timers and sequence numbers March 11,

29 A Simplex Prtcl fr a Nisy Channel A psitive acknwledgement with retransmissin prtcl. Cntinued

30 A Simplex Prtcl fr a Nisy Channel (ctd.) A psitive acknwledgement with retransmissin prtcl.

31 Sliding Windw Prtcls Need t transmit data in bth directins Idea Fr this, piggybacking used Sender maintains a a set f sequence numbers, fr frames it is permitted t send => sending windw Receiver maintains a receiving windw, fr frames it is permitted t accept => receiving windw Buffers needed Receiver windw keeps its size March 11,

32 Sliding Windw Prtcls (2) A sliding windw f size 1. (a) Initially. (b) After the first frame has been sent. (c) After the first frame has been received. (d) After the first acknwledgement has been received. March 11,

33 A One-Bit Sliding Windw Prtcl Cntinued

34 A One-Bit Sliding Windw Prtcl (ctd.) March 11,

35 A One-Bit Sliding Windw Prtcl (2) Tw scenaris fr prtcl 4. (a) Nrmal case. (b) Abnrmal case. The ntatin is (seq, ack, packet number). An asterisk indicates where a netwrk layer accepts a packet. March 11,

36 Other prtcls Assumptin: prcessing time nt ignred With sender waiting ack befre transmitting next frame, bad efficiency is achieved Slutin: the sender transmits up t w frames befre blcking fr ack => sliding windw f length w With an unreliable channel, 2 slutins G back N Selective repeat March 11,

37 G Back N and Selective Repeat

38 Prtcl Verificatin Finite State Machined Mdels Petri Net Mdels March 11,

39 Finite State Machined Mdels (a) State diagram fr prtcl 3. (b) Transitins. March 11,

40 Petri Net Mdels A Petri net with tw places and tw transitins. March 11,

41 Petri Net Mdels (2) A Petri net mdel fr prtcl 3.

42 Example Data Link Prtcls HDLC High-Level Data Link Cntrl Bit stuffing fr framing Sliding windw fr flw cntrl Acknwledgements als fr cntrl frames PPP Pint-t-pint prtcl Multi-prtcl framing mechanism Byte stuffing fr framing Sliding windw fr flw cntrl Handles errrs detectin Allws IP addresses t be negtiated at cnnectin time Permits authenticatin March 11,

43 The Data Link Layer in the Internet A hme persnal cmputer acting as an internet hst. March 11,