AN ACTIVE PROGRAMMABLE HARNESS FOR MEASURMENT OF COMPOSITE NETWORK STATES

Transcription

1 IEEE Inernaional Conference on Neworking, ICN 1, Colmer, France, June 1, pp AN ACTIVE PROGRAMMABLE HARNESS FOR MEASURMENT OF COMPOSITE NETWORK STATES Javed I. Khan and Asrar U. Haque Inerneworking and Media Communicaions Research Laboraories Deparmen of Mah & Compuer Science, Ken Sae Universiy 33 MSB, Ken, OH Absrac In his paper we presen he acive harness, a scalable and versaile means for deep probing of nework local saes. The approach makes a clear separaion beween he communicaion from he informaion par of he probing process. The composiion of he informaion componen is handled by means of nework embedded harness plug-ins. I can faciliae no only a new generaion of nework aware applicaions bu also nework problems. 1.Inroducion Measuremen and exchange of sae informaion inside a nework is a mea service. The abiliy o consruc any global opimizaion service, wheher in nework layer or above, depends on how well he decision sysems are aware of and up-o-dae on he relevan local saes in perinen nework elemens. For example, local link sae informaion is he building block for rouing services and BGP, OSPF, or MPLS [] all require sophisicaed cos meric from local nodes following complex propagaion paerns. There are also hos of oher advanced nework services (such as dynamic QoS provisioning, mobile IP forwarding), and new generaion of applicaions (such as disribued server, proxy prefech) all requiring exchange of such nework sae informaion. A prerequisie o any QoS provisioning, wheher by dynamic resource allocaion or by reservaion, is he knowledge abou he resources. Disribued caching requires informaion such as curren congesion and curren delay o assign bes mirror server o a reques. Clearly, wih he complexiy of he Inerne and he push for opimized services and applicaions i is becoming increasingly more imporan o find he means for monioring and propagaing various complex nework sae measuremens. In his paper we presen he concep of acive harness designed for provisioning his crucial mea inerne service. Before presening he proposed sysem below a brief accoun of he curren sae of he Inerne probing echnologies is given Relaed Work Simple Nework Managemen Proocol (SNMP), designed in 199 and (RFC 1157 and RFC 1155) laes updaed in 1995 was he firs o provide a simple bu sysemaic way of monioring he Inerne saes. I s curren version SNMPv [,11] now provides a simple poin-o-poin measuremen framework. I defines a se of imporan variables ino a daabase called managemen informaion base organized ino 1 caegories of informaion (Curren version MIB-II) and allows nodes o send simple poin-o-poin UDP based queries. SNMP has been very successful in providing he required sandardized organizaion, synax and represenaion (ASN.1) for a base se of criical

2 IEEE Inernaional Conference on Neworking, ICN 1, Colmer, France, June 1, pp sae informaion. However, is communicaion model is sill poin-o-poin. Consequenly, composie measuremens canno be made easily using SNMP. Because of he difficuly in is scalabiliy, SNMP has been used more successfully in nework managemen and monioring han in dynamic run-ime querying. Opimizing sysems ha need nework wide informaion propagaion herefore generally build heir own cusom mechanism. Rouing informaion propagaion in IGP, OSPF, BGP all are classical examples of his siuaion. Video mulicas group managemen and synchronizaion require racking of jier and round rip delay. RTP and RTCP [1] have been proposed o collec cusom ime relaed saisics over a mulicas ree. Similarly, pahchar [7], cprobe, bprobe, [1,9], woodpecker [3], and hos disance esimaion ool [5] have been proposed argeing various specific measuremens. In his conex, his research proposes a novel sysem ha can address wo emergen issues in nework probing-- scalabiliy and versailiy, and hese are illusraed below. 1.. Scalabiliy Poin-o-poin mode of communicaion ofen severely limis scalabiliy in a large nework. For example, for measuremen of pah saisics he requesing node is required o send individual SNMP messages o all inermediae nodes. Consequenly, redundan informaion flows inside he nework increasing he overhead, severely reducing he ransparency of he measuremen process. Disseminaion/aggregaion of informaion wih only a poin-o-poin communicaion means creaes excessive raffic on he nework severely limiing he scalabiliy. I seems much of he limiaions arises because SNMP canno exrac any inelligence from he inermediae nodes. Since here is no means for in nework composiion, all composiions mus be done a he endpoins, only afer polling all sae informaion here Versailiy On he oher hand, he specific probing kis provide greaer scalabiliy bu hardly can be reused for oher measuremens. Neverheless, he rend suggess ha versailiy of he informaion is becoming equally imporan. Exacly, wha measuremen is useful depends on he opimizaion objecive. For example, in a video server scenario, wheher he jier or he hard delay is more imporan is dependen on he specific video repair algorihm. In a differen scenario, a server before sending daa may wan o poll informaion abou he speed of only he las link o he home user s compuers. In some oher scenario he min/max of he pah downsream delays and jiers from various juncion nodes can help in sraegically placing jier-absorbing buffers in a mulimedia sreaming virual privae nework ree. Emerging ele-ineracion applicaions (such as ele-surgery, remoe insrumen conrol) will require handle on he delay incurred a he video frame level, which is exacly no he same as he packe delay. The rend suggess ha as more advanced, and complex necenric applicaions are being envisioned more versaile nework sae informaion would have o be exchanged. 1.. Our Approach Can scalabiliy and versailiy boh be reained simulaneously? Apparenly, here may no be any efficien answer in an end-o-end paradigm. In he general case, a nework can choke wih polynomial messaging a he end-poins. However, he recen adven of Acive Nework echnology seems o offer an innovaive way ou from his dichoomy

3 IEEE Inernaional Conference on Neworking, ICN 1, Colmer, France, June 1, pp * : Updae Generaor ^ : Updae Aggregaor Reques S + # ^ + : Reques Generaor x : Reply Generaor # : Reply Aggregaor A +x # * ^ +x # * ^ C Updae D + x * # + x * # E + x * # H Reply I + x * # J K L M O P Q R x x x x x x x x Fig-1 Componens of Acive Harness [13,1,8]. Acive nework allows programmable modules o be embedded inside nework juncions. In his research we propose an experimenal dynamic mechanism for sae informaion polling and propagaion inside nework wih similar embedded informaion synhesizers, which seems o be boh scalable and versaile. The approach firs makes a clear separaion beween he communicaion from he informaion of he sae exchange and propagaion process. Communicaion is handled by he componen called harness. Harness propagaes all informaion via coordinaed messaging. On he oher hand he informaion componen of he process is conrolled by a se of sof programmable plug-ins. These plug-ins decide he conen of he messages propagaed by he harness. In his paper in secion 3 firs presens he archiecure of he proposed sysem. Secion hen illusraes he operaion of he harness for a ypical applicaion. Finally, in secion 5 we share boh analyical and empirical resuls depicing he performance of he proposed harness sysem..harness Archiecure The harness is responsible for iniiaing, propagaing and responding o a series of wellcoordinaed messages beween he nodes in a nework. The harness once insalled in nework nodes, can ac in hree roles-- iniiaor, sae synhesizer, and erminals. The iniiaor acs as he communicaion agen in he nework layer for he applicaion ha acually requires he informaion. The synhesizer propagaes he sae requess and processes he reurning saes from he erminals. The harness conrols he communicaion paern and hus deals wih he efficiency of messaging. Harness sysem acceps a se of plug-ins, which deermines he conen of hese messages, and how hey are propagaed and aggregaed a he juncion poins..1. Messaging The harness sysem has been designed o operae wih a novel reques-reply-updae messaging scheme. I has hree ypes of messages reques, reply and updae. A reques message conains fields indicaing wha informaion i needs, and dicaing how far down he nework he probing session should propagae, i.e. level, and any informaion needed by he receiver o compue required daa, e.g. o compue he jier a receiver needs o know he ime samp of sending successive daa. The reques iniiaor decides how ofen a reques is generaed. The reques messages are sen o he erminals if hey are immediaely conneced, or o synhesizers for furher downsream propagaion. A synhesizer upon receiving a reques propagaes he query by generaing a new reques message o he down-sream nodes. However, a he same ime i migh also generae

4 IEEE Inernaional Conference on Neworking, ICN 1, Colmer, France, June 1, pp an immediae reply for he requesor. The replies from synhesizers may conain curren local sae and/or pas remoe saes. The erminal nodes send replies o heir respecive requesors. The erminal reply conains locally rerieved curren saes. In he reurn rip of informaion, he synhesizer nodes aggregae he informaion and a each sage generae updae messages for heir requesors. Once a node receives all or specific number of updae messages from is immediae down-sream nodes or on imeou, i updaes he nework local sae variables and generaes a new updae message. The updae message conains a synhesized summary of informaion calculaed from all is immediae downsream nodes. This hree-par reques-reply-updae communicaion model, if needed, allows he informaion o be colleced wihou working in locksep. Even if a node downsream is delayed or silen, i does no hold he enire sysem; he esimaion process can proceed for remaining nodes. The updae phase is furher equipped wih opional and configurable imers o avoid updae lockup. In essence, he reques-reply phase allows collecion of local immediae saes. The reply mechanism allows immediae probing ino curren local saes and pas synhesized remoe saes, while he updae message rerieves laes remoe saes... Sae Composiion Harness sysem acceps a se of five plug-ins which are called reques generaor, reply generaor, reply aggregaor, updae generaor, and updae aggregaor. These modules ogeher deermine he conen of hese messages, and how hey are aggregaed a he juncion poins. They work via a virual slae. A copy of which is mainained in each of he nodes. The slae works as he local absrac daa srucures. The slae is programmable and is defined a he session iniiaion phase. The reques generaor specifies he reques message describing he fields i wans from he slae of is downsream node. A individual nodes he model suppors MIB-II and hus acs as a superse of SNMP. The erminal nodes can read/copy MIB variables (or heir processed combinaion) exising in he local slae ino variables marked for reply. The harness hen invokes he reply messages wih he designaed slae variables. Reply aggregaor (or updae aggregaors) in a similar fashion is invoked each ime a reply (or updae) is received by he harness. They perform domain specific processing of he reply message fields and similarly updae heir own slae variables. The updae generaor is invoked when a special rigger variable becomes rue. The rigger variable is a se of condiions such as all, any, or a specified number of down-sream nodes have updaed/replied, or a imer fires. The updae generaor sends he slae variables synhesized by he updae aggregaors o he upsream node. Fig-1 describes he archiecure of he proposed harness sysem. I shows he roles, he ypical locaions of he plug-in modules and he direcion of he messages. A he hear of he composiion abiliy is he ransfer funcions of he inermediae synhesizers. The reques and updae phase can be represened by equaions: S S j j i = Φ( Ε( Q ), M, S ), j, k j j = Ψ( F( P ), M, S ), and Q = F( S ) = E( S ), j, j j, j, k 1 and, i, j,_ 1 P.(1).()

5 IEEE Inernaional Conference on Neworking, ICN 1, Colmer, France, June 1, pp Here S j is he local slae sae a even ime a node j, E is he reques receiving filer (RRF), M is he local nework sae (such as MIB variable), F is he reques forwarding filer (RFF). Q i,j,- is he arrived reques from paren i, o node j and Q -,j,k is he propagaed requess o children k. E is he updae forwarding filer (UFF), F is he updae receiving filer (URF). P -,j,k is he arrived updae from child k, and P i,j,- is he propagaed updae o paren i. While, he filers deermined he informaion propagaion rules, composiion funcions Φ() and Ψ() ogeher deermine he message conen. While, in principle each of hese componens for each of he individual harness sies can be programmed differenly, however he associaed managemen will be inracable. In his harness we divide he nework nodes ino subses based on heir role in he opology. Nodes in he opological subses hen inheri uniform programmed behavior. Thus, we need only five disinc programmed modules (plug-ins) o be supplied by he harness programmer. 3.Harness Execuion Model The harness operaes hrough 8 saes. Fig- shows he sae ransiion diagram. The oval shaped boxes describe aciviies and he square boxes indicae plug-in modules used for hose aciviies. The iniiaor have saes if i generaes a reques of level 1 and if reply is expeced, oherwise if level is 1 and reply is no expeced hen i has saes If he iniiaor generaes a reques message of level more han one, and reply and updae is expeced, hen i has saes The erminal nodes have saes Parens of erminal nodes (if boh reply and updae is expeced) have saes Oher synhesizers (if boh reply and updae is expeced) have saes As fig- suggess, oher combinaions are possible depending on wheher reply and/or updae is no expeced. Generae Reply Reply Generaor On Recving a Reques Generae Reply 1 If iniiaor If child = Nil Is he iniiaor Is no iniiaor Gen Updae Reply 8 Generaor Reply Expeced Gen Reques Wai for Reply Process Reply 3 5 Reques Reply Generaor Aggregaor Reply No Expeced Is no iniiaor Updae No Expeced Is no iniiaor On n Updae or Timeou Fig- Sae Transiion Diagram of Acive Harness Reply Recvd On n Reply or Timeou Updae Ex peced Process Updae 7 Updae Aggregaor Wai for Updae 6 On Recving Updae

6 IEEE Inernaional Conference on Neworking, ICN 1, Colmer, France, June 1, pp example Probing: Transcoder Sep Compuaion Below we presen an example of cusom harness service ha helps in configuring an embedded video ranscoding ree nework. In a mulicas disribuion ree a video ranscoder [15] sis in he juncion nodes and seps down he video rae o mach he downsream pah capaciies. The rae of he individual links however canno be deermined jus wih node or link local informaion. The sep-down parameers are quasi-global sae dependen. The opimum rae assignmen is a funcion of he S 5 9 a 9 k 7 8 c 5 k 5 5 k 6 7 e g h 3 k k 1 k 3 k b 1 d 7 f i 8 g Fig-3 Transcoder Auo Sabilizaion using Acive Harness upsream and downsream pahs, requiremens of he sinks as well as he delivery capaciy of he source. Below we show how he harness sysem can be programmed o configure he ranscoding nework in a wo-phase reques/updae cycle. Le us consider he ranscoding nework of Fig-3. Each ranscoder juncion node has o know he amoun of video i is geing from is paren via up-link and he maximum possible amoun of video ha can flow hrough all is down-links. The values have o be deermined opimally so ha i does no receive more han wha i can deliver or wha is required down he sream. We map he iniiaor a he video source and he erminals a he video sinks and he synhesizers in each of he inermediae nodes. The slae, messages and he five plug-in modules are shown in Fig- (a)-(c). The process begins from he source. I sends a reques, which conains is maximum delivery capaciy. Each of he synhesizers regeneraes a new downward reques, which shows he maximum deliverable video rae, recompued by he reques generaor plug-in modified by is local downward link. 3 AppxChildBW [ ] : floa, UsableChildBW [ ] : floa, TreeLevel : in, MaxDownLinkTreeBW : floa, UpLinkBW : floa, SinkOrSourceCapaciy : floa (All are iniialized o 1) Fig-(a) Slae RequesMsg: MsgType:HarnessVariable, DeliverableRae: floa, Level: in ReplyMsg: MsgType: HarnessVariable, Recvable: floa UpdaeMsg: MsgType: HarnessVariable, MaxRecvable:floa Fig-(b) Message Definiions

7 IEEE Inernaional Conference on Neworking, ICN 1, Colmer, France, June 1, pp Reques Generaor Module { if (i is a source) UpLinkBW= SinkOrSourceCapaciy; for each child I { RequesMsg.DeliverableRae = min (UpLinkBW, AppxChildBW[I]); >> Send RequesMsg o child [I]; << Reply Generaor Module { UpLinkBW=RequesMsg.DeliverableRae; if (Terminal Node) ReplyMsg.Recvable = min (UpLinkBW, SinkOrSourceCapaciy); >> Send Reply Message; << Reply Aggregaor Module { if (i paren of erminal I){ MaxDownLinkTreeBW = max (MaxDownLinkTreeBW, ReplyMsg.Recvable); UsableChildBW[I] = ReplyMsg.Recvable; Updae Generaor Module { UpdaeMsg.MaxRecvable = MaxDownLinkTreeBW; >> Send Updae Message; << Updae Aggregaor Module { MaxDownLinkTreeBW = max (UpdaeMsg.MaxRecvable,MaxDownLinkTreeBW); UsableChildBW[I] = UpdaeMsg.MaxRecvable; (Noe: The messages enclosed by << and >> are send by he harness) Fig-(c) Relevan Pseudocode of Modules capaciy. When, he erminal receives he reques i hen compares he value wih is sink capaciy, and deermines he bandwidh receivable based on he deliverable and is sink capaciy. The synhesizers above he erminals collec he bandwidh receivable values and compue heir own bandwidh receivable based on he maximum demand and pas value of bandwidh deliverable. The informaion evenually propagaes upward o he source. In his example (fig-3) here is a source S, a, b, ec. are inermediae nodes, and k 1, k, ec are video sinks. The numbers beside he edges denoe bandwidh of ha link. For example, he bandwidh of link ac is 9 Mbps. The source, S, can generae video a a maximum rae of 1 Mbps and he capaciy of sink k 1 is 3 Mbps. The numbers in recangles indicae bandwidh deliverable ha he paren sends o respecive child in he reques message. The numbers inside he circles indicae he bandwidh receivable ha can be absorbed by down-links and are carried by he updae messages. The updae messages propagae from he sink owards he source carrying he maximum unis ha can be absorbed. Before a reques is generaed, he concerned nodes approximae he bandwidh of all he children using SNMP. Each node mainains wo liss. The lis AppxChildBW iniially sores he approximaed bandwidh of respecive child and he oher lis UsableChildBW finally has he maximum bandwidh ha respecive child should receive. MaxDownLinkTreeBW sores maximum bandwidh up o level of TreeLevel. UpLinkBW sores he bandwidh of he link connecing i o is paren. SinkOrSourceCapaciy sores he amoun produced or absorbed by i if i is a source or a sink respecively. Here we have demonsraed an insance how an applicaion can benefi from he harness in deep probing. The harness sysem can also faciliae collecion of oher common forms of global informaion such as jier, and end-o-end delay. I can also

8 IEEE Inernaional Conference on Neworking, ICN 1, Colmer, France, June 1, pp probe variey of precise and deail pseudo-global and local nework saes which are no easily accessible oday, such as end-poins of he mos consrained link in a pah, jier across he m-h hop down-seam, aggregae of ougoing bandwidh from a arge node ec. All i needs are differen composiion rules. 5.Performance Below we provide esimaes of he impac on he links and on he nodes due o he harness operaion respecively for one execuion/propagaion wave. Here L and B sand for a probing deph level and branching facor of he conex nework ree respecively. The sizes of he Reques, Reply, and Updae are of r, p, and u byes respecively and compuaional impac due o reques generaor, reply generaor, reply aggregaor, updae generaor and updae aggregaor are rg, pg, pa, ug, and ua respecively. Table- 1 shows he nework wide raffic, message per link and he bye densiy. The erminals do no generae updaes hence erminal links do no carry updae messages. Table- shows he compuaional impac on he nework nodes due o he plug-in. A paricular sae probing session may be launched wih a subse of capabiliies (such as no reply, bu updae). The design objecive is o provide he leas impac communicaion for he given applicaion scenario. Table-1 Link Traffic Impac Type Bye Max Msg Msg/link Byes/link Reques r B L 1 r Reply p B L+1 1 p Updae u B L 1 u Table- Node Processing Impac Node Reques Reply Updae Generaor Generaor Aggregaor Generaor Aggregaor Iniiaor θ(b,rg) θ(b,pa) θ(b,ua) Synhesizer θ(b,rg) θ(b,pg) θ(b,pa) θ(b,ug) θ(b,ua) Terminal θ(b,pg) We have also performed saisical simulaion o projec he performance of he harness sysem under various consrains. The performance depends on he characerisics of he programmable componens (complexiy of he plug-ins, message size ec.) as well as on he nework (such as bandwidh, opology, probing deph ec.) and plaform characerisics (scheduling delay, messaging delay, ec). Fig-5(a) shows how one reques/response cycle ime varies for various plug-in execuion ime (x-axis) of he updae for hree orders of message sizes (1K, 1 byes, and 1 byes). In cyclic mode his also represens wors case bound on he informaion recency. Fig-5(b) shows he updae delay wih respec o he ranspor layer messaging delay. Anoher imporan meric from he nework poin of view is he background raffic ha he harness operaion creaes for informaion collecion. Fig-5(c) compares he scalabiliy of he harness sysem as compared o a poin-o-poin mechanism. I plos he nework hum (he background raffic generaed by he probing process) for various deph and

9 IEEE Inernaional Conference on Neworking, ICN 1, Colmer, France, June 1, pp UPDATE CYCLE VS. HARNESS PROPERTIS 7 6 DELAY (sec) UPDATE AGGREGATION TIME (sec) UPDATE CYCLE VS. MSG. PROPERTIES 35 3 DELAY (sec) TRANSPORT LATENCY (sec) MSG=1B MSG=5 B Fig-5(a) MSG=1B branching facor of he opology. I plos nine cases. The firs hree curves shows how he ho-spo hum (y-axis) near he probing roo grows in he case of poin-o-poin mechanism wih he increase in he deph of probing (x-axis) for hree branching facors (BF=,,8). The second se of hree curves shows he average hum for he same hree cases, which is somewha lesser bu sill grows rapidly wih he probing deph. The average hum provides a measure ha how much raffic on he average will be conribued by random sponaneous probing processes appearing a various nework locaions. On he oher hand, he ho-spo hum indicaes he change ha he applicaion rying o probe, iself has, o be chocked wih excessive surrounding probing raffic. The las hree plos show he hum due o harness process (for hree message sizes) (righ y-axis). The dramaic scalabiliy of he harness probing is quie apparen. As, can be seen ha he hum in harness scheme is no only low bu also fla. The resul is no unexpeced. The nework embedded synhesis removes raffic informaion redundancy. 1.E+1 BACKGROUND TRAFFIC 6.Conclusions 1.E+1 1.E+1 1.E+1 1.E+1 The key o he sysem s 1.E+8 1.E+8 scalabiliy and versailiy are 1.E+6 1.E+6 1.E+ he embedded aggregaors. 1.E+ 1.E+ Since local sae dependen 1.E+ 1.E+ aggregaion is performed 1.E E+ PROBING DEPTH (d) inside a nework, i reduces communicaion and hus PP,BF= PP,BF= PP,BF=8 PP,Avg Bye/Level PP,Avg Bye/Level PP,Avg Bye/Level enhances he sysem s H,MS=1,BF= H,MS=1K,BF= H,MS=1K,BF=8 scalabiliy. Aggregaors also Fig-5(c) provide he abiliy o compue nework relaive deep composie saisics, over he elemenary MIB-II variables, hus enhancing he versailiy of is abiliy o collec nework saes. MAX/AVG LINK LOAD (bps) d=.1s d=.5s d=.1s Fig-5(b) 1.E+1 The scope of his paper does no permi discussion on implemenaion. I is non-rivial neverheless can be realized a user space as deamons. Embedded implemenaion can cu down some overhead and will be criical for sub-second range probing cycles. Implemenaion on some form of acive plaform [8,13,1] can furher faciliae maers such as remoe deploymen, and seamless secured execuion of he plug-ins. The harness plug-ins require very limied form of programmabiliy compared o general LINK LOAD (bps)

10 IEEE Inernaional Conference on Neworking, ICN 1, Colmer, France, June 1, pp acive ne proposal. Also, he read-wrie suggesions are hrough local slae variables only. These characerisics assuage many of he securiy concerns. The proposed harness is perhaps one of hose cases where provisioning even very low-grade programmabiliy can be highly rewarding. The harness increases sae visibiliy of nework. In effec i faciliaes high pay off smar opimizaions for numerous applicaions, which are no possible oday due o he black box naure of curren nework. Ineresingly, such a nework layer uiliy is no only crucial for building a new generaion of nework aware applicaions bu i is also vial for many of he curren problems inerne is grappling wih. Ineresingly many of which are arguably arifacs of he opaciy of curren nework design. Currenly, we are exploring is acive nework based simulaion. The work is being suppored by he DARPA acive nework Research Gran F References 1. Carer, Rober L., Mark E. Crovella. Measuring Boleneck Link Speed in Packe-Swiched Neworks. Performance Evaluaion 7 & 8 (1996), Comer D. E., Inerneworking wih TCP/IP, Principles, Proocols, and Archiecures, h Ed, Preice Hall, New Jersey, USA, ISBN , 3. Dong, Yingfeng, Yiwei Thomas Hou, Zhi-Li Zhang, Tomohiko Taniguchi. A server-based noninrusive measuremen Infrasrucure for Enerprise Neworks. Performance Evaluaion (1-), 1999, Downey Allen B., Using Pahchar o Esimae Inerne Link Characerisics. hp://ee.lbl.gov/nrgalks.hml, April Francis, P., Sugih Jamin, Vern Paxson, Lixia Zhang, Daniel F. Gryniewicz, Yixin Jin. An Archiecure for a Global Inerne Hos Disance Esimaion Service. Proceedings IEEE INFOCOM New York, Jacobson, V., Traceroue, [URL: fp://fp.ee.ibl.gov/raceroue.ar.z,] Jacobson, V, Pahchar- a ool o infer characerisics of Inerne pahs, [URL: hp://ee.ibl.gov/nrgalks.hml ], April Javed I. Khan, S. S. Yang, Mediane Acive Swich Archiecure, Technical Repor: -1-, Ken Sae Universiy, [available a URL hp://mediane.ken. edu/ echnicalrepors.hml, also mirrored a hp:// brisi.facne.mcs.ken.edu/mediane] 9. Ma Mahis, Jamshid Mahdavi. Diagnosing Inerne Congesion wih a Transpor Layer Performance Tool. Proceedings INET, 1996, Monreal Canada. 1. Paxson, V., Jamshid Mahdavi, Andrew Adams and Ma Mahis. An Archiecure for Large-Scale Inerne Measuremen. IEEE Communicaion Magazine, Augus 1998, Rose, M.T., & McCloghrie, K. How o manage your Nework Using SNMP, Englewood Cliffs, NJ, Preice Hall, Schulzrinne, H., S. Casner, R. Frederick, and V. Jacobson. RTP: A Traspor Proocol for Real Time Applicaions, RFC 1889, Tennenhouse, D. L., J. Smih, D. Sincoskie, D. Weherall & G. Minden.. A Survey of Acive Nework Research. IEEE Communicaions Magazine, Vol. 35, No. 1, Jan 97, pp Weherall, Guag, Tennenhouse. ANTS: A Tool ki for Building and Dynamically Deploying Nework Proocols. IEEE OPENARCH'98, San Francisco, April Available a: hp:// 15. Javed I. Khan & S. S. Yang. Resource Adapive Nomadic Transcoding on Acive Nework, Applied Informaics. AI 1, February 19-, 1, Insbruck, Ausria, [available a URL hp://mediane.ken.edu/, also mirrored a hp:// brisi.facne.mcs.ken.edu/mediane] (in press).