Da Communic an ta ation d EmaNetwor sonvq@hcmut il: edu.vn king Telecomm Dept DCN2013 Cont  Chapter 5: ent Telecom Networks 802.x standard IP Addressing: an VLS Ethernet, Token Pass, Token Classless d M Ring Switc an Routi Network devices hing Telecomm Dept d ng DCN2013 Local Area A local area network (LAN) is a computer network that Network school, laborat o offi buildi usi netw  interconnects computers in a limited computer ory, r ce ng ng ork  area mediasuch as a home, Medium:  Coaxial cable  Twisted-pair line Telecomm Dept DCN2013 Wide Area A wide area network (WAN) is a network that covers a broad Network metropolitan, regional, bounda usi priv  o netw transp area (i.e., any telecommunications orpub national ries) ng ate rnetwork lic orkthatorts links across Telecomm Dept DCN2013 Topology Bus Ring Star Telecomm Dept Physical Extended Star Hierarchical Mesh DCN2013   Project IEEE 802 refers to a family of IEEE standards dealing with local 802 area networks and metropolitan area networks Control (LLC)and andprotocols Cont (MA s th th The services specified in thi layers can be Media Access IEEE 802 map to the rol C), o at e listed lower like two layerss:(Data Link and Physical) Data link layer of the seven-layer • LLC Phys lay reference model In fact, OSI networking Sublayer: ical IEEE 802 er splits the Telecomm DCN6 Dept.• MAC 2013    Modules in Project 802 LLC: based on HDLC protocol  Multiplexing protocols transmitted over the MAC layer (when transmitting) and decoding them Telecomm (when Dept Project 802 DCN2013  LLC PDU: formats LLC Frame DSAP: Destination Service SSAP: Servi Access Point Source ce  Access fiel Contr Pointd: ol format HDLC Telecomm Dept DCN2013 Ether  Topology: bus, star, ring  Media Access Control: net Deterministic, Non-deterministic  Addressing: Every computer has a unique way of identifying itself : MAC address or physical address The physical address is located on the Network Interface Card (NIC) MAC addresses have no structure, and are considered flat address spaces MAC addresses are sometimes referred to as burned-in addresses (BIAs) because they are burned Telecomm DCN9 Dept 2013 IEEE 802.3: frame Preamble: 10101010 (7 bytes) The Start Frame field (10101011) tells other format devices on the network that a       frame is coming down the wire The Address field stores the source and destination MAC addresses  Source address is unicast, Destination address can be unicast, multicast or broadcast The Type/Length field is an optional field  Exact length of frame, or Layer protocol making the sending request, or Not used The Data field is the actual information being Telecomm DCNsent by the upper layer Dept 2013   Router receives packets and forwards them to  the Check the header destination (based  of IP  on packet  Look up the destination IP) routing How doestable router Determine the work? output port Forward the packet to the Telecomm output port Dept Routing Control Plane Forwarding Table Next Hop + Port Routing Packets Output Packets Packet Classif cation i Input Packets Header Queuing Schedule rules and Output Queue payload User Plane DCN2013 Routing  Each router routi proto t update the its tab needs running a ng col o routing le  Delay of packets Queuing delay Propag del Processing delay ation Telecomm Dept ay DCN2013 Routing Protocols: Global or decentralized information? Classification  Global:   •• router all routers have complete knows physically-connected • topology, link cost info • link costs to neighbors neighbors, • iterative “link state” algorithms Static or dynamic? process of computation, exchange   Decentralized: Static: of info with neighbors •• “distance routes change vector” algorithms routes change more •slowly over time • quickly  Dynamic: periodic update Telecomm DCNin response to link Dept 2013 Routing Algorithms: Dijkstra’s Notati net topology, link algorithm on: Link State to y; = ∞ if not costs   c(x,y): link cost from node x known to all nodes   accomplished via “link state broadcast”  all nodes have same info computes least cost paths from one node (‘source”) to  all other nodes  gives forwarding tabletfork know co pat that node least after st khiterations, o iterative: Telecomm dest.’s Dept  direct neighbors  D(v): current value of cost of path from source to dest v  p(v): predecessor node along path from source to v N': set of nodes whose least DCNcost path definitively known 2013 Dijkstra’s St N D(v),p D(w),p D(x),p D(y), algorithm: example (w) p(y) ep1 4, (x) 2, ux' (v) 2, 02 uxyu uxyv uxyv w uxyv wz Telecomm Dept 2, u u 2, u 1, 5,u x u 3, y 3, w v y2 u x y ∞ x z D(z), p(z) ∞ ∞ 4, y 4, y 4, y DCN2013 Dijkstra’s Result shortest- fro u w ing path tree example m v: algorithm: u Resulting tab i u destina lin forwarding tion v k(u, le n : x y w z Telecomm Dept x y z v) (u,x) (u,x) (u,x) (u, x) DCN2013 Dijkstra’s algorithm,  Algorithm complexity: n discussion nodes each iteration: need to check all nodes, w, not in N n(n+1)/2 comparisons: O(n2) e.g., costimplementations = carripossible: traf O(nlogn) more efficient A 1+ amount link  1Oscillations possible: 2+ A of D 0e B D B 1+ e e 0 C eC 1 e … initi Telecomm ally Dept recompu te ed A 2+ fic D 0e B C 1+ e … recompu 2+ A D e 1+ e B eC … recompu DCN6 2013 te Distance Vector  Bellman-Ford Equation Algorithm (dynamic programming) dx(y) := cost of least- xt y Define: Th cost path from en dx(y) = {c(x,v) o + dv(y) } whe mi i tak ov al neighb vo x re n s en er l ors Telecomm Dept f DCN2013 Bellman-Ford Clearly, d (z) = 5, example d (z) = 3, d (z) v w =3 v u x 2 x 1 y z w B-F equation says: du(z) = { c(u,v) + c(u,w) ++ } dv(z), c(u,x) dx(z), d w(z) 1+3 = + 5, , =4 5+{2 No th achie minim is path hop in de at ves umforwar nexttab } ➜ ding le shortest Telecomm DCNDept 2013 Distance Vector  Dx(y) = estimate of least y Algorithm  Node cost fromx xknows to cost to v each neighbor  Node distance c(x,v) x Dx = [Dx(y): y є N ] maintains vector  Node x also maintains its For each neighbors’ xmaint Dv = yєN] neighbor v, ains [Dv(y): Telecomm Dept : dista vect nce ors DCN2013 Distance Vector  Basic idea: Algorithm From time-to-time, each node sends its own distance vector estimate to neighbors Asynchronous When a node x receives new DV estimate from neighbor, updates its own DV using B-F equation: for each Dx(y) ← i t node y ∊ N minv{c(x,v) + Under minor, natural D x( Dv(y)}t th actu lea co dx( conve conditions, the estimate y) rge o e al st st y) Telecomm Dept DCN2013 Distance Vector eac Iterative, Each asynchronous: h node: Algorithm wait for (change local iteration caused by:  local link cost change  DV update message from neighbor Distributed:  each node notifies neighbors only when its DV changes  neighbors then notify their Telecomm neighbors if necessary Dept in local link cost or msg from recompute neighbor) estimates if DV to any dest has changed, notify neighbors DCN2013 Dx(z) = min{c(x,y) + Dy(z), c(x,z) + Dz(z)} = min{2+1 , 7+0} = Dx(y) = min{c(x,y) + Dy(y), c(x,z) + Dz(y)} node x cost , 7+1} = = min{2+0 table cost x0 y7 z x y z x to x to x fro m ∞∞ node y ∞ t table costx yo z x ∞ ∞ ∞ y z node z cost table ∞ ∞ x∞ ∞y ∞ z x to ∞ y z fro m fro m y ∞∞ ∞ z fro m y ∞∞ ∞ z Telecomm Dept Network Layer tim e y DCN2013 z Dept x y z fro m fro m fro m cost xto y z y z cost xto y z x z x y z 3 11 fro m fro m node z cost table ∞ ∞ x∞ ∞y ∞ z x to ∞ y z ∞ ∞ ∞ Telecomm y z fro m fro m y z fro m fro m Dx(z) = Dx(y) = min{c(x,y) + Dy(y), min{c(x,y) + c(x,z) + Dz(y)} node x Dy(z), c(x,z) cost , 7+1} = cost = min{2+0 table cost + Dz(z)} x0 y7 z x0 y3 z x y z to x to x to x = min{2+1 , y ∞∞ ∞ y y z z z 7+0} = ∞∞ node y ∞ cost cost table xto y z y x0 y7 z x y z cost to x ∞ ∞ ∞ x to x 0tim e DCN2013 Distance Vector: link Link cost changes: cost changes y node detects local link cost change  updates routing info, recalculates distance vector  z changes, notify At time t0, y detects the link-cost change, neighbors updates its DV, and informs its neighbors if DV “go od new s Telecomm trav Dept  x At time t1, z receives the update from y and updates its table At time t2, y receives z’s update and Ity’s computes a new least costdoes to x not and least costs not updates its distance table sends neighbors changeitsand hence yits DV send any message to z DCN2013 ... Project IEEE 802 refers to a family of IEEE standards dealing with local 802 area networks and metropolitan area networks Control (LLC)and andprotocols Cont (MA s th th The services specified in... 14; Dept 2013 Subnetting  Network administrators sometimes need to divide networks, especially large ones, into smaller networks: Reduce the size of a Ibroadcast network But wantdomain netwo se...Cont  Chapter 5: ent Telecom Networks 802.x standard IP Addressing: an VLS Ethernet, Token Pass, Token Classless d M Ring