Transit Networking in ATM/B-ISDN based on Service Category

Transcription

1 Transt Networkng n ATM/B-ISDN based on Servce Category Young-Tak Km Dept. of Informaton and Communcaton Engneerng, College of Engneerng, YeungNam Unv. E-mal : ytkm@ynucc.yeungnam.ac.kr ABSTRACT The ATM Forum and ITU-T specfy multple servce categores of B-ISDN, such as (constant bt rate), RT-VBR (realtme - varable bt rate), NRT-VBR-COD/CLD (non-realtme - varable bt rate - connecton-orented data/connectonless data), ABR (avalable bt rate), and UBR (unspecfed bt rate). Each servce category specfes dfferent traffc parameters and QoS parameters : bandwdth, end-to-end transfer delay, cell transfer delay varance, bt error rate, and cell loss rate. In ths paper, we propose a transt networkng scheme n ATM/B-ISDN based on the servce category. In the proposed scheme the end-to-end vrtual channel/vrtual path connectons are routed accordng to the requred traffc characterstcs, dfferently. The major purpose of the servce category-based transt networkng s to provde the requred QoS to end users effcently, whle mantanng the network utlzaton level hgh. We also propose a restoraton strategy wth 5 restoraton classes. In the proposed restoraton strategy the user selects a restoraton class for hs specfc applcaton at the connecton setup phase. 1. B-ISDN servce categores ATM Forum defnes 5 B-ISDN servce categores [1]: (constant bt rate), RT-VBR (realtme - varable bt rate), NRT-VBR (non-realtme - varable bt rate), ABR (avalable bt rate), and UBR (unspecfed bt rate). The examples of servce are plan old telephone servce (POTS), crcut emulaton for DS1 (1.544/2.048 Mbps) and DS3 (45 Mbps), and -Vdeo. servce requres constant transfer rate that s specfed by ts end-to-end cell transfer delay (CTD) and peak cell rate (PCR). The examples of RT-VBR servce nclude the packetvdeo and audo n teleconferencng and n multmeda applcatons. In RT-VBR servces, the data transfer rate vares accordng to the amount of nformaton that s usually specfed by the source codng scheme. Thus the RT-VBR traffc s defned by the set of traffc/qos parameters, such as end-to-end CTD, PCR, sustanable cell rate (SCR) wth maxmum burst sze (MBS). The NRT-VBR servce category s ntended for nonreal-tme applcatons whch have bursty traffc characterstcs. NRT-VBR-COD (connecton-orented data) s defned for the connecton-orented data servces, such as X.25 PSDN or Frame relay. NRT-VBR-CLD (connectonless data) s defned for the connectonless data servces, such as IP datagram servce and SMDS (swtched mult-megabt data servce). For NRT-VBR- CLD, the transport network provdes several connectonless servce functon (CLSF) nodes n order to provde the store-and-forward data servce. Both NRT- VBR-COD and NRT-VBR-CLD do not specfy the tmng requrements, such as end-to-end CTD and CDV tolerance. ABR servce category s defned for the Internetnterconnecton servce through ATM/B-ISDN. The ABR traffc defnes the requred bandwdth by MCR (mnmum cell rate) that s the mnmum bandwdth that the transport network must guarantee. UBR servce category does not specfy any traffc/qos parameter. It only uses the currently avalable bandwdth of the transport network. The example traffc/qos parameters for each servce are as shown n the table. In the 64 kbps voce telephony servce, the end-to-end cell transfer delay should be kept below 300 ms for most lve conversatonal type applcaton [1-2]. The DS1/DS3 crcut emulaton requres the cell transfer delay 33

2 B-ISDN Servce Category RT-VBR NRT- VBR- COD NRT- VBR- CLD ABR UBR Servce Examples POTS, Crcut Emulaton, -Vdeo Packet-Vdeo & Audo n teleconferencng, multmeda applcatons Connecton orented data servce (X.25,Frame-Relay) Connectonless data servces (IP-over-ATM,SMDS) Connecton orented data servce (LAN-nterconnecton) Connectonless data servces (LAN-nterconnecton, nternet) Traffc / QoS Parameters PCR, End-to-End CTD, Peak-to-Peak CDV, BER, CLR PCR, SCR/MBS, Endto-End CTD, Peak-to-Peak CDV, BER, CLR PCR, SCR/MBS, BER, CLR PCR, SCR/MBS, BER, CLR PCR, MCR Table 1: Servce categores n ATM/B-ISDN less than 150 µs, and the cell delay varance less than 250 µs at each swtchng node [3]. The servce for PVC Cell Relay requres the end-to-end CTD as 4 ms wth addtonal 2 ms for each 100 mles [5]. The VBR servces for mage/vdeo data transfer requres the cell transfer delay of 0.8 ms ~ 5 ms and the peak-to-peak cell delay varance of 1 ms ~ 6.5 ms. These two QoS parameters are tghter than those of traffc. The VBR traffc requres the bt error rate (BER) of 6 x 10-7 ~ 2.5 x 10-6 and the cell loss rato (CLR) of 8 x 10-7 ~ 9.5 x 10-6, when there s the error handlng mechansm n AAL. The data applcatons n general are ntolerant of errors, and data ntegrty between communcaton end ponts s requred [4]. When human nteracton s nvolved, data applcatons are ntolerant of large delays (for example, 3 seconds), whereas servces between machnes can tolerate moderately large delay. A user accessng a teller machne to do a bankng transacton demands a response tme of a few seconds, whereas account updates that take place between dfferent nformaton centers of a bank do not mpose a strct delay constrants. Delay jtter s not a bg concern n data servces, snce no synchronzaton or constant play-out rates are requred at the recever. The NRT-VBR-COD traffc for connecton-orented Frame Relay servce requres the end-to-end cell transfer delay of 27 ms ~ sec and the cell loss rato of 10-7 [6]. The NRT- VBR-CLD traffc for connectonless data servce such as SMDS requres smlar characterstcs for the VCC/VPC between the CLSFs. The LAN emulaton and IP-over- ATM traffc can be supported ether by ABR servce or UBR servce. In the case of ABR servce, mnmum cell rate (MCR) and cell loss rato (CLR) are guaranteed; whle the transport network guarantee nothng for the UBR servce. 2. Multple vrtual transt networks of servce categores In order to maxmze the network utlzaton whle guaranteeng the QoS requrements of each servce, the network should select the most approprate route for each VP/VC connecton establshment request. The ATM transport network mantan the lnk status data for each transmsson lnk between the swtchng nodes, and the node status data for each swtchng node. The lnk status data nclude nstalled capacty (LC j ), currently allocated bandwdth (AB j ), avalable bandwdth (AVB j ), utlzaton, current load ( ρ j ), resdual error rate (ε j ), and lnk transfer delay (τ j). The node status data nclude nstalled swtchng capacty (SC k ), currently allocated swtchng capacty (SAB k ), resdual error rate (ε k ), utlzaton, current load (ρ k ), swtchng delay (τ k ), and Cell Delay Varance (CDV k ). For the connecton establshment of a servce, the network selects an end-to-end VP/VC connecton route of shortest path that can guarantee the requred PCR, end-to-end CTD, peak-to-peak CDV. The connecton establshment of RT-VBR servces, the network selects an end-to-end VP/VC connecton route of shortest path that can guarantee the requred SCR & MBS, end-to-end CTD, peak-to-peak CDV. The connecton establshment of NRT-VBR servces fnds an end-to-end VP/VC connecton route whch can support the requred SCR & MBS or MCR, and CLR. For the ABR servces, the end-to-end VP/VC connecton route that can support the requred MCR s selected. In the case of UBR, there s no specfed traffc/qos restrctons. 34

3 Servce Example Voce telephony Crcut Emulaton PVC cell relay - Vdeo Phone Vdeo conference TV dstrbuton Bt rate End-to-End cell transfer delay (CTD) Peak-topeak cell delay varance (CDV) wthout error handlng n AAL BER wth error handlng n AAL wthout error handlng n AAL 64 kbps 300 ms 10 ms DS1 : 1.5 Mbps DS3 : 45 Mbps 64 kbps ~ 45 Mbps 64 kbps ~ 384 kbps 150 µs 1) 250 µs 1) ms ms per 100 mles CLR wth error handlng n AAL ) 1.7 x ms ms 130 ms x x x Mbps VBR 5 ms 6.5 ms x Mbps VBR 5 ms 6.5 ms x x x ~ 25 Mbps VBR 0.8 ms 1 ms 3 x x x 10-7 MPEG 1 core 1.5 Mbps VBR 5 ms 6.5 ms 4 x x x 10-6 MPEG 2 core 10 Mbps VBR 0.8 ms 1 ms 6 x x x x 10-6 Frame Relay SMDS LAN Emulaton 64 kbps ~ 2 Mbps 64 kbps ~ 45 Mbps 27ms ~ sec 2) 5 x ~ 10 Mbps - - IP-over-ATM ~ 70 Mbps - - 1) per swtchng node, 2) 1600 ~ 4096 octets frame 5 ms 1) 10-7 Table 2: Traffc parameters and QoS parameters of B-ISDN servce examples When there are multple canddates wth same condton, the routng algorthm selects the route that maxmze the network utlzaton. As we have shown n the prevous secton, the B- ISDN servce categores requre dfferent traffc characterstcs. As a result, the connecton management functon should select an end-to-end VP/VC connecton path based on the dfferent route selecton crtera of each servce category. For the realtme servces of and RT-VBR, the most mportant route selecton crtera are the requred bandwdth of PCR or SCR, end-to-end CTD, and CDV. For the NRT-VBR COD/CLD servces, the end-toend CTD and CDV are not crtcal crtera, so the routng algorthm may not fnd a shortest path. Instead, the routng algorthm wll select a path that can maxmze the network utlzaton, whle supportng the requred SCR or MCR, and CLR. The ABR servces requre only the guaranteed MCR wth tmng specfcaton. For the UBR servces, the network does not guarantee any traffc/qos parameter. CLSF Node B CLSF Node A Fg. 1: Multple transt routes 35

4 Servce Category 1 () Servce Category 2 (RT-VBR) Servce Category 3 (NRT-VBR-COD/CLD) Servce Category 4 (ABR) Servce Category 5 (UBR) Fg. 2: Separated vrtual networks based on servce category Snce the multmeda termnals connected to a Local Exchange (LEX) node requre multple connectons of varous servce categores to other LEX nodes, t s more effcent to confgure n advance the separated vrtual transt VP route for each LEX-to-LEX par, based on the estmated traffc amounts of each servce category, and allocate dynamcally the VC bandwdth for each connecton setup request. By ths pre-planned vrtual transt VP networks, the network can be confgured to keep the maxmzed utlzaton level accordng to the estmated traffc amount. The vrtual transt VP network s perodcally reconfgured to reflect the current traffc requrements and network load condtons. 3. Bandwdth allocatons n servce categorybase4d Networkng In order to guarantee the requred QoS level to users and mantan the network utlzaton n best condton, the transport network must perform the bandwdth allocaton and the route selecton accordng to the servce category. For the servce, the bandwdth must be allocated for the requred PCR (peak cell rate), and the end-to-end CTD must be guaranteed. The route selecton for the traffc s fndng a route wth mnmum end-to-end CTD that can allocate the requred bandwdth, peak-to-peak CDV (cell delay varance) and CLR (cell loss rato). In RT-VBR servce, the bandwdth s allocated for the requred SCR (sustanable cell rate) that s defned as the upper bound on the conformng average rate of an ATM connecton. For the RT-VBR servces, the transport network guarantee the SCR wth assocated MBS (maxmum burst sze), end-to-end cell transfer delay tmng, and peak-to-peak CDV. The route selecton crtera for the RT-VBR traffc are same as the servce. In NRT-VBR-COD/CLD servces, the requested bandwdth s allocated ether by SCR or MCR. The transport network must guarantee the SCR/MCR, mean CDV. The route selecton crtera are CLR and maxmzed network utlzaton. In NRT-VBR-COD servce, a route s establshed between end-users; whle n the NRT-VBR-CLD servces, routes are establshed between connectonless servce functon (CLSF) such as IP-routers. In ABR servces, the transport network guarantees the MCR (mnmum cell rate) of the requested bandwdth and the CLR. The route selecton crteron s the maxmzed network utlzaton. In UBR servces, the transport network guarantees no specfc traffc/qos parameters for the servces. Thus, the route selecton crteron s just the maxmzed network utlzaton. B-ISDN Servce Category RT-VBR Bandwdth allocaton PCR SCR Route selecton Guarantee Other selecton crtera PCR, end-to-end CDV mn end-to-end CTD, peak-to-peak CDV, CLR SCR, end-to-end CTD, P- mn end-to-end CTD, peak-to-peak to-p CDV CDV, CLR NRT-VBR-COD SCR, MCR SCR, MCR, mean CTD CLR, max utlzaton NRT-VBR-CLD SCR, MCR SCR, MCR CLR, max utlzaton ABR MCR MCR, CLR max utlzaton UBR None None max utlzaton Table 3: Bandwdth allocaton and route selecton crtera 36

5 At each swtchng node, the bandwdth allocaton s performed accordng to the prorty of servce category. The swtchng node determnes the acceptance of the connecton establshment request by the connecton admsson control (CAC) wth the buffer allocaton (BA) strategy. The servce traffc has the hghest prorty n the bandwdth allocaton. The network guarantees the peak cell rate (PCR) and the end-to-end cell transfer delay (CTD) of each servce. Also, the swtchng node should guarantee the cell delay varance (CDV) by allocatng enough buffer sze. The RT-VBR servce traffc has the second prorty n the bandwdth allocaton. The network guarantees the sustanable cell rate (SCR), the end-to-end CTD and the CDV of each RT-VBR servce. Node A Node B Avalable bandwdth for ABR & UBR traffc Reserved bandwdth for ABR traffc = Reserved bandwdth for RT-VBR traffc = Guaranteed bandwdth for traffc = MCR Reserved bandwdth for NRT-VBR-COD/CLD traffc = SCR PCR Fg. 3: Bandwdth management at ATM swtchng node The NRT-VBR-COD and NRT-VBR-CLD servces specfy the requred bandwdth by SCR or MCR. The network must guarantee the SCR or the MCR of each NRT-VBR-COD/CLD servce as specfed n the connecton setup request. There s no tmng requrement of end-to-end CTD and peak-to-peak CDV n NRT- VBR-COD/CLD servce. For some specfc applcatons, the mean end-to-end CTD may be specfed n the NRT- VBR-COD traffc/qos parameters. For the ABR servce traffc, the ATM transport network guarantees the mnmum cell rate (MCR). There s no tmng requrement n the ABR servce. The remanng bandwdth can be allocated to ABR and UBR servce. For the UBR servce traffc, nothng s guaranteed by the transport network. SCR 4. based on servce categores To provde fault tolerant communcaton servces, the ATM transport network must reserve backup path for each actve end-to-end connecton wth approprate bandwdth, so as to reroute the end-to-end VC path n the case of fault occurrence. The bandwdth allocaton for the backup path s determned accordng to the restoraton strategy. In ths paper, we propose a restoraton strategy wth 5 restoraton classes. class 1 provdes the guaranteed backup bandwdth for 100 % of the PCR. In ths case, the actve end-to-end VP/VC connecton has a backup path that can restore the whole traffc when there s a lnk or node falure. The restoraton class 1 can be used for the servce of hgher prorty that requres relable nformaton transfer servces. In restoraton class 2, the backup route s allocated wth 100 % of the SCR of the actve path, whle 100 % of the MCR of the actve path s allocated n restoraton class 3. The restoraton class 2 and class 3 can be used n the RT-VBR servce and NRT-VBR-COD servce, respectvely. In restoraton class 4, a backup path s shared by multple actve connectons. The backup path has a reserved bandwdth of 100 % of the largest PCR of the actve connectons that uses t. When there are multple lnk/node falures concurrently, only one connecton can be rerouted to the backup path, and all other connectons must be restored by dynamc end-toend connecton establshment mechansms. In restoraton class 5, no backup bandwdth s allocated, but the most approprate backup route s preplanned. When a lnk/node falure s occurred n the actve path, the connecton management functon tres to allocate the bandwdth along the backup route. If the bandwdth allocaton s not successful, the reroutng must fnd a new end-to-end connecton for restoraton by the dynamc connecton establshment mechansm. The user selects a specfc restoraton for hs applcaton at the connecton setup phase. The usage costs of the restoraton classes are dfferent accordng to the bandwdth allocaton for both the actve connecton and the backup path. 37

6 class class 1 class 2 class 3 class 4 class 5 Strategy Guaranteed backup bandwdth for 100 % PCR Guaranteed backup bandwdth for 100 % SCR Guaranteed backup bandwdth for 100 % MCR N : 1 shared backup bandwdth 0 backup bandwdth wth just pre-routng for the canddate route Table 4: classes In general, the hghly relable servce wll select the restoraton class 1 whch guarantees a backup path wth 100 % of PCR. For fault tolerant servce provson, the RT-VBR servce wll select restoraton class 2 whch guarantees a backup path 100 % of SCR. In the same manner, the relable NRT-VBR-COD/CLD servces wll select the restoraton class 3 whch guarantees a backup path wth 100 % of MCR. For the same servce category, however, dfferent restoraton class can be chosen accordng to the specfc applcaton and the requested level of relablty of the servce. For example the NRT-VBR-COD servce for the money transfer between dfferent banks may requre restoraton class 3, whle the NRT-VBR-COD servce for the transfer of log data between nformaton centers may requre restoraton class 5, because of the dfference of the urgency. 5. Perodc Re-balancng of Vrtual Transt Networks For the maxmum network utlzaton, the connecton management functon of the ATM/B-ISDN must pre-plan the separated vrtual transt network for each servce category. The connecton management functon setups the ATM VPCs for transt networkng accordng to the predcted usage between the ATM LEX par. In ths transt route desgn, several VPCs are establshed for each of the B-ISDN servce classes n order to satsfy the multple QoS class requrements. Also, for the VPC restoraton at falure occurrence, backup bandwdth must be prepared for the workng connectons. The bandwdth allocatons for the backup routes are determned by the estmated restoraton strategy of the users. The transt route desgn algorthm must establsh the transt routes for the maxmze network avalablty. It also has to desgn the transt route to guarantee the performance requrements of the predcted ATM VC connectons. The result of the transt route desgn s nformed to the subnetwork management systems and the swtchng nodes. At each swtchng node, the route selecton parameters (such as nstalled lnk capacty, lnk usage cost and prorty) are specfed by the connecton management functon. The user plane s VP/VC lnks are establshed by the sgnalng of the control plane, along the pre-planned transt VP route for each servce category, based on the route selecton parameters. In order to reflect the actual fluctuatons around the predctons, we need a load balancng procedure that analyzes the short-term/long-term network usage, and reflects the results on the routng decsons. The load balancng functons updates the route selecton parameters (selecton prorty, lnk cost, etc.) that are used by the route selecton algorthm (RSA) of the control plane n the on-demand VCC setup process. Long term Predcted usage Short term Network load (Network-wde traffc condton) Traffc montorng Fg. 4: Perodc load balancng and transt route management 6. Conclusons Network topology update Transt Route Desgn Multple transt VP trals based on servce category Routes update Load Balancng RSA ATM EX RSA ATM EX VC Connecton setup by sgnalng In ths paper, we proposed a transt networkng scheme based on servce category n ATM/B-ISDN. In the proposed transt networkng scheme the end-to-end ATM VP/VC connectons are routed accordng to the requred traffc characterstcs, dfferently. The major purpose of the servce category-based connecton management s to provde the requred QoS to end users effcently, whle mantanng the network utlzaton level at maxmum. RSA ATM EX Management plane Route selecton parameter (prorty, lnk cost) update Control plane Swtchng node and Lnk 38

7 We frst analyzed the traffc characterstcs of the 5 B-ISDN servce categores :, RT-VBR, NRT-VBR- COD/CLD, ABR, and UBR. And we defned the bandwdth allocaton strategy and the route selecton crtera. We then proposed a separated vrtual transt networkng for the servce categores. The vrtual transt network s pre-planned accordng to the estmated traffc amount between each local exchange (LEX) node pars. To accommodate the traffc load fluctuaton, the vrtual transt network s re-balanced perodcally based on the short-term usage and the long-term usage. We also proposed a restoraton strategy wth 5 restoraton classes. The restoraton class s selected by the user at the connecton setup request. In restoraton class 1, 2, 3, the network reserves backup bandwdth of 100 % of PCR, SCR, and MCR, respectvely. In restoraton class 4, one backup route s shared by N actve VCCs/VPCs. In restoraton class 5, no backup bandwdth s reserved, but the route s pre-planned to allocate the bandwdth n the case of lnk/node falure n best-effort. Each restoraton class has dfferent cost accordng to the bandwdth usage for both actve and backup paths. Currently, we are developng a smulaton software of the proposed transt networkng archtecture, on the OPNET smulaton platform [9]. We wll evaluate the performance of the connecton management archtecture wth a realstc network confguraton of Korean Informaton Infrastructure (KII). Generc Requrements for Exchange Access Frame Relay PVC servce, Issue 1, May [7] ATM Forum, Crcut Emulaton Servce - Interoperablty specfcaton Ver. 2.0, Jan [8] ATM Forum, Voce and Telephony over ATM to the desktop specfcaton, May [9] OPNET Ver 3.0 Manual Young-Tak Km graduated Yeung-Nam Unv. n Feb. 1984, and receved Master Degree and Ph.D. from KAIST (Korea Advanced Insttute of Scence and Technology) n 1986 and 1990, respectvely. He joned Korea Telecom (KT) n March 1990, where he researched and developed the ATM Metropoltan Area Network (MAN) Swtchng System, and the networkng of ATM Hghway for Informaton Infrastructure. He transferred to Yeung-Nam Unv. n September 1994 as an assstant professor. Hs research nterest feld s ATM/B-ISDN Transt Networkng Technology based on the IN (Intellgent Network), TINA (Telecommuncatons Informaton Networkng), TMN (Telecommuncatons Management Network), and Next Generaton Internet (NGI). [References] [1] ATM Forum, Traffc management specfcaton, ver. 4.0, Aprl [2] ATM Transport and Network Integrty, Tsong-Ho Wu and Norak Yoshka, Academc Press, [3] Bellcore, Techncal Advsory TA-NWT , Broadband ISDN Swtchng System Generc Requrements, Issue 2, August [4] Asynchronous Transfer Mode Networks : Performance Issues, 2nd Ed., Raf O. Onvural, Artech House, [5] Bellcore Techncal Advsory, TA-TSV , Generc Requrements for Exchange PVC Cell Relay Servce, Issue 1, August [6] Bellcore Techncal Reference, TR-TSV , 39