Advance Computer Networks Lecture#11& 12 Instructor: Engr. Muhammad Mateen Yaqoob

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wide area network Mateen Yaqoob Department of Computer Science Mobility: vocabulary home network: permanent “home” of mobile (e.g., /24) permanent address: address in home network, can always be used to reach mobile e.g., home agent: entity that will perform mobility functions on behalf of mobile, when mobile is remote

Transcript of Advance Computer Networks Lecture#11& 12 Instructor: Engr. Muhammad Mateen Yaqoob

Advance Computer Networks Lecture#11& 12 Instructor: Engr. Muhammad Mateen Yaqoob Mateen Yaqoob Department of Computer Science What is mobility? spectrum of mobility, from the network perspective: no mobility high mobility mobile wireless user, using same access point mobile user, passing through multiple access point while maintaining ongoing connections ( like cell phone) mobile user, connecting/ disconnecting from network using DHCP. wide area network Mateen Yaqoob Department of Computer Science Mobility: vocabulary home network: permanent home of mobile (e.g., /24) permanent address: address in home network, can always be used to reach mobile e.g., home agent: entity that will perform mobility functions on behalf of mobile, when mobile is remote Mateen Yaqoob Department of Computer Science Mobility: more vocabulary wide area network care-of-address: address in visited network. (e.g., 79, ) visited network: network in which mobile currently resides (e.g., /24) permanent address: remains constant ( e.g., ) foreign agent: entity in visited network that performs mobility functions on behalf of mobile. correspondent: wants to communicate with mobile Mateen Yaqoob Department of Computer Science Mobility: approaches let routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange. routing tables indicate where each mobile located no changes to end-systems let end-systems handle it: indirect routing: communication from correspondent to mobile goes through home agent, then forwarded to remote direct routing: correspondent gets foreign address of mobile, sends directly to mobile Mateen Yaqoob Department of Computer Science let routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange. routing tables indicate where each mobile located no changes to end-systems let end-systems handle it: indirect routing: communication from correspondent to mobile goes through home agent, then forwarded to remote direct routing: correspondent gets foreign address of mobile, sends directly to mobile not scalable to millions of mobiles Mobility: approaches wide area network Mateen Yaqoob Department of Computer Science Mobility: registration end result: foreign agent knows about mobile home agent knows location of mobile home network visited network 1 mobile contacts foreign agent on entering visited network 2 foreign agent contacts home agent home: this mobile is resident in my network Mateen Yaqoob Department of Computer Science Mobility via indirect routing wide area network home network visited network correspondent addresses packets using home address of mobile home agent intercepts packets, forwards to foreign agent foreign agent receives packets, forwards to mobile mobile replies directly to correspondent Mateen Yaqoob Department of Computer Science Indirect Routing: comments mobile uses two addresses: permanent address: used by correspondent (hence mobile location is transparent to correspondent) care-of-address: used by home agent to forward datagrams to mobile foreign agent functions may be done by mobile itself triangle routing: correspondent-home-network- mobile inefficient when correspondent, mobile are in same network Mateen Yaqoob Department of Computer Science Indirect routing: moving between networks suppose mobile user moves to another network registers with new foreign agent new foreign agent registers with home agent home agent update care-of-address for mobile packets continue to be forwarded to mobile (but with new care-of-address) mobility, changing foreign networks transparent: on going connections can be maintained! Mateen Yaqoob Department of Computer Science Mobility via direct routing home network visited network correspondent requests, receives foreign address of mobile correspondent forwards to foreign agent foreign agent receives packets, forwards to mobile mobile replies directly to correspondent Mateen Yaqoob Department of Computer Science Mobility via direct routing: comments overcome triangle routing problem non-transparent to correspondent: correspondent must get care-of-address from home agent what if mobile changes visited network? Mateen Yaqoob Department of Computer Science wide area network 1 foreign net visited at session start anchor foreign agent 2 4 new foreign agent 3 correspondent agent correspondent new foreign network Accommodating mobility with direct routing anchor foreign agent: FA in first visited network data always routed first to anchor FA when mobile moves: new FA arranges to have data forwarded from old FA (chaining) 5 Mateen Yaqoob Department of Computer Science Wireless, mobility: impact on higher layer protocols logically, impact should be minimal best effort service model remains unchanged TCP and UDP can (and do) run over wireless, mobile but performance-wise: packet loss/delay due to bit-errors (discarded packets, delays for link-layer retransmissions), and handoff TCP interprets loss as congestion, will decrease congestion window un-necessarily delay impairments for real-time traffic limited bandwidth of wireless links Multimedia: audio Mateen Yaqoob Department of Computer Science analog audio signal sampled at constant rate telephone: 8,000 samples/sec CD music: 44,100 samples/sec each sample quantized, i.e., rounded e.g., 2 8 =256 possible quantized values each quantized value represented by bits, e.g., 8 bits for 256 values time audio signal amplitude analog signal quantized value of analog value quantization error sampling rate (N sample/sec) Multimedia: audio Mateen Yaqoob Department of Computer Science example: 8,000 samples/sec, 256 quantized values: 64,000 bps receiver converts bits back to analog signal: some quality reduction example rates CD: Mbps MP3: 96, 128, 160 kbps Internet telephony: 5.3 kbps and up time audio signal amplitude analog signal quantized value of analog value quantization error sampling rate (N sample/sec) video: sequence of images displayed at constant rate e.g. 24 images/sec digital image: array of pixels each pixel represented by bits coding: use redundancy within and between images to decrease # bits used to encode image spatial (within image) temporal (from one image to next) Mateen Yaqoob Department of Computer Science Multimedia: video ... spatial coding example: instead of sending N values of same color (all purple), send only two values: color value (purple) and number of repeated values (N) ... frame i frame i+1 temporal coding example: instead of sending complete frame at i+1, send only differences from frame i Mateen Yaqoob Department of Computer Science Multimedia: video ... spatial coding example: instead of sending N values of same color (all purple), send only two values: color value (purple) and number of repeated values (N) ... frame i frame i+1 temporal coding example: instead of sending complete frame at i+1, send only differences from frame i CBR: (constant bit rate): video encoding rate fixed VBR: (variable bit rate): video encoding rate changes as amount of spatial, temporal coding changes examples: MPEG 1 (CD-ROM) 1.5 Mbps MPEG2 (DVD) 3-6 Mbps MPEG4 (often used in Internet, < 1 Mbps) Multimedia networking: 3 application types Mateen Yaqoob Department of Computer Science streaming, stored audio, video streaming: can begin playout before downloading entire file stored (at server): can transmit faster than audio/video will be rendered (implies storing/buffering at client) e.g., YouTube, Netflix, Hulu conversational voice/video over IP interactive nature of human-to-human conversation limits delay tolerance e.g., Skype streaming live audio, video e.g., live sporting event (futbol) Streaming stored video: 1.video recorded (e.g., 30 frames/sec) 2. video sent Cumulative data streaming: at this time, client playing out early part of video, while server still sending later part of video network delay (fixed in this example) time Mateen Yaqoob Department of Computer Science 3. video received, played out at client (30 frames/sec) Streaming stored video: challenges continuous playout constraint: once client playout begins, playback must match original timing but network delays are variable (jitter), so will need client-side buffer to match playout requirements other challenges: client interactivity: pause, fast-forward, rewind, jump through video video packets may be lost, retransmitted Mateen Yaqoob Department of Computer Science Voice-over-IP (VoIP) Mateen Yaqoob Department of Computer Science VoIP end-end-delay requirement: needed to maintain conversational aspect higher delays noticeable, impair interactivity < 150 msec: good > 400 msec bad includes application-level (packetization,playout), network delays session initialization: how does callee advertise IP address, port number, encoding algorithms? value-added services: call forwarding, screening, recording emergency services: 911 VoIP characteristics speaker s audio: alternating talk spurts, silent periods. 64 kbps during talk spurt pkts generated only during talk spurts 20 msec chunks at 8 Kbytes/sec: 160 bytes of data application-layer header added to each chunk chunk+header encapsulated into UDP or TCP segment application sends segment into socket every 20 msec during talkspurt Mateen Yaqoob Department of Computer Science VoIP: packet loss, delay network loss: IP datagram lost due to network congestion (router buffer overflow) delay loss: IP datagram arrives too late for playout at receiver delays: processing, queueing in network; end-system (sender, receiver) delays typical maximum tolerable delay: 400 ms loss tolerance: depending on voice encoding, loss concealment, packet loss rates between 1% and 10% can be tolerated Mateen Yaqoob Department of Computer Science constant bit rate transmission Cumulative data time variable network delay (j