CPEG 514 Lecture 11 Asynchronous Transfer Mode (ATM) 2

Outline ATM Introduction Virtual Circuit Setup – PVC vs. SVC Quality of Service and Congestion Control IP over ATM ATM and Frame Relay interworking CPEG 514

ATM Network (integrated voice, video, and data services) Private Carrier to carrier Is not really common Integrated via IP CPEG 514

ATM Standards ITU-T, ATM Forum, IETF User-to-Network Interface (UNI) 2.0 UNI 3.0, UNI 3.1, UNI 4.0 Network-to-Network Interface (NNI) PNNI Private NNI Public-Network Node Interface RFC 2684 (Multiprotocol encapsulation over ATM) LAN Emulation (LANE) Multiprotocol over ATM (MPoA) CPEG 514

Synchronous vs. Asynchronous ATM- cell switching technology (asynchronous) NO clock synch between xmt/rcv TDM – circuit switching technology (synchronous) clock synch between xmt/rcv ATM is more efficient than TDM. (why?) TDM: dedicated time slots. ATM: time slots are available on demand with information identifying the destination address of the transmission contained in the header of each ATM cell. CPEG 514

ATM Network Components If i/f is not ATM, the switch would have to do the interworking function CPEG 514

ATM PCI NIC (ATM to the desktop) Network ATM OC-3c OC-3 155Mbps Price: $605 (cf. how much is Gigabit-E NIC?) http://www.techstore.com/Item.aspx?sku=227610TD&sgd=330d316d317d314d315 Should remember OC-3 speed Number of T1 on OC-3, 28 T1s Q: is there still a market for ATM to the desktop? why? Ethernet is cheaper even at the Gbps, 1Gb Ethernet = $30, 100 BaseT = $7-10 CPEG 514

ATM UNI, PNNI, and NNI NNI? PNNI Is there a public ATM? Is there a public Frame Relay? Private NNI (PNNI): connecting two private networks through a public one. or Inside the same carrier’s network CPEG 514

ATM Cell Format CPEG 514

ATM Cell Format Generic Flow Control (GFC) – typically not used. Virtual Path Identifier (VPI) – 8 (UNI) or 12 (NNI) bits Virtual Channel Identifier (VCI) – 16 bits Payload Type (PT)— 3 bits first bit: user data (0) or control data (1) second bit: Congestion Indicator 0 = no congestion, 1 = congestion), Set to 1 if pkt encountered congestion third bit: whether the cell is the last cell (1) in a series of AAL5 frame Cell Loss Priority (CLP)—Indicates whether the cell should be discarded (1) if it encounters extreme congestion as it moves through the network. Similar to - DE (Discard Eligibility in Frame Relay) Header Error Control (HEC)—checksum on the first 4 bytes of the header. CPEG 514

ATM PVC and SVC PVC (permanent virtual circuit ) allows direct connectivity between sites, and is similar to a leased line. +++ guarantees availability of a connection +++ does not require call setup procedures between switches. --- requires manual setup between the source and the destination. --- no network resiliency/Flexibility is available with PVC. SVC (Switched virtual circuits) is created and released dynamically and remains in use only as long as data is being transferred. In this sense, it is similar to a telephone call. Dynamic call control requires a signaling protocol between the ATM endpoint and the ATM switch. +++ connection flexibility +++ call setup that can be handled automatically by a networking device. --- the extra time and overhead required to set up the connection. --- network management and trouble shooting due to dynamic nature of SVC CPEG 514

ATM Virtual Connections ATM switching is based on VPI/VCI However, VPI+VPI is not called ATM address. VPI/VCI has local significance only at the port level of the ATM switch. NSAP is ATM’s address CPEG 514

ATM Physical Layer Up 8 T1s as one link using IMA ATM over T1 ATM over multiple T1 - Inverse Multiplexing over ATM (IMA) Up 8 T1s as one link using IMA ATM over DS3, OC-3, OC-12, OC-48, and OC-192 http://www.nwfusion.com/edge/news/2002/1002marconi.html Note: Marconi bought Fore Switch in 2000. Q; What is the max speed for Frame Relay? Up to 30Mbps CPEG 514

ATM Switching video data audio data For PVC, table done Manually 10 11 P1 data 20 P3 21 P4 P2 audio 10 12 P5 data 30 30 IN/port VPI/VCI OUT/port P1 0/10 P3 0/11 0/20 P4 0/21 P2 0/12 0/30 P5 For PVC, table done Manually SVC, table is done dynamically/on-demand Audio and Video having the same VPI, that is OK and does not need to be. VPI/VCI have local significance at the port level. CPEG 514

ATM Reference Model AAL CPEG 514

ATM Protocol Layers ATM Switch ATM Applications ATM Applications ATM Adaptive Layer (AAL) ATM Adaptive Layer (AAL) ATM Layer ATM Layer ATM Layer Physical Layer Physical Layer Physical Layer ATM Switch ATM End Station ATM End Station CPEG 514

ATM Adaptation Layer AAL1: AAL5: AAL ATM Physical Function: Add control information and break Protocol Data Unit (PDU) into cells Segmentation and Reassembly (SAR) AAL1: Designed for voice application Constant Bit Rate (CBR) Circuit Emulation Service (CES) (emulates TDM circuit) AAL2 (Not covered in this class) Variable Bit Rate (VBR) VBR-rt (voice) VBR-nrt (data) AAL5: Designed for data application Unspecified Bit Rate (UBR) AAL ATM Physical CPEG 514

AAL1 Convergence Sublayer Sends 47 bytes to SAR Which adds 1 byte of SAR hdr SAR Hdr Payload = 47 SN: Sequence Number 1 bit Convergence Sublayer Indicator (Clock recovery) + 3 bit Sequence Count (for entire PDU from convergence sublayer) SNP: Sequence Number Protection: 3 bit CRC for the SN + Last bit, parity check for the previous 7 bits (SN and CRC) Q: How much overhead in an AAL1 cell? A cell has 47bytes * 8 bits/byte = 376 bits G.7111 DS0 at 64kbps 64000bits/sec 20ms has 64000/20 = 1280bits which needs 1280/376 = 4 cells CPEG 514

AAL5 CPCS-PDU Payload Padding (0-47) CPCS-UU (1) CPI (1) Length (2) Carries upper other Protocols inside CPCS payload (i.e. tcp/ip, ethernet CPCS-PDU Payload up to 216 -1 Padding (0-47) why do we need padding? 8 byte trailer CPCS-UU (1) CPI (1) Trailer alignment to 32 bit Length (2) CPCS Payload Not including PAD 48 bytes (0..47) Cell payload To make the Full PDU Divisible by 48 Bytes And divide it Evenly into 48 byte segments CRC (4) CPCS: Common Part Convergence Sublayer PDU: Protocol Data Unit UU: User-to-user interface information CPI: Common Part Indicator CPEG 514

ATM Segmentation and Reassembly (SAR) H:5-bytes H Cell1 H Cell2 H Celln AAL5 Frame CPEG 514

ATM NSAP Address This is required for NNI, but it is rarely used. Note NSAP has global significance while VPI/VCI is an addressing scheme that has local significance only. ATM NNI: same issue with Frame Relay. NSAP: Network Service Access Point based on E.164 (phone #) 20 bytes CPEG 514

ATM Connection Establishment Goal: setup VPI/VCI between any two ATM devices CPEG 514

ATM UNI Signaling (Q.2931) - SVC End Device ATM Switch ATM Switch ATM End Device SETUP SETUP SETUP VPI/VCI Will be Setup For each Direction PROCEEDING PROCEEDING ALERT ALERT CONNECT ALERT CONNECT CONNECT Why do we need this signaling protocol? Connection Established, control, mgmt, Does it look familiar (Q.931)? CPEG 514

Signaling VCI (VPI=0) (UNI) e.g. VPI =0, VCI for connection establishment signaling Q; What is the VPI/VCI in the ATM Q.2931 SETUP message? VPI= 0 VCI = 5 CPEG 514

ATM ILMI (mgmt plain) Integrated Local Management Interface (ILMI) enables devices to determine status of components at the other end of a physical link and to negotiate a common set of operational parameters to ensure interoperability. ILMI operates over a reserved VCC of VPI = X, VCI = 16. Administrators may enable or disable ILMI at will, but it is highly recommended to enable it. Doing so allows the devices to determine the highest UNI interface level to operate (3.0, 3.1, 4.0), UNI vs. NNI, as well as numerous other items. Furthermore, ILMI allows devices to share information such as NSAP addresses, peer interface names, and IP addresses. Without ILMI, many of these parameters must be manually configured for the ATM attached devices to operate correctly. CPEG 514

PVC or SVC Core (SVC) vs. Access (PVC) Q1: What is the purpose of PVC and SVC? Q2: What are differences between PVC and SVC? Q3: For data services, is it better to use PVC or SVC? Core (SVC) vs. Access (PVC) Using the dynamic setup in the core would be easier Q4: For voice services, is it better to use PVC or SVC? Core (PVC – trunks are already there) vs. Access (SVC) CPEG 514

ATM Quality of Service (QoS) CBR: Constant Bit Rate Guaranteed transmission rate EMULATING TDM circuit VBR: Variable Bit Rate (Requires QoS attention) rtVBR and nrtVBR (rt = real time) Peak Cell Rate (PCR) – MAX allowed data rate The maximum cell rate at which the user will transmit Sustained Cell Rate (SCR) – allowable cell rate over time Max Burst Size (MBR) Minimum Cell Rate (MCR) UBR: Unspecified Bit Rate No guarantee, best effort CBR Service Bit Rate PCR VBR SCR UBR CPEG 514

ATM QoS ABR: Available Bit Rate How does a carrier ensure that QOS can be met? Connection Admission Control (CAC) Procedure for determining whether each new SETUP request should be granted or denied based on current network conditions Usage Parameter Control (UPC) Procedure for verifying whether customer is conforming to their contractual Traffic Parameters. PER the SLA Resource Management (RM) Procedure for notifying ABR users when they should slow down ABR: Available Bit Rate Selective Cell Discard (SCD) Procedure for discarding cells (CLP=1)during congestion. CPEG 514

IP over ATM Protocol (RFC 2684) 192.168.1.11/24 192.168.1.10/24 ATM Both ATM and Ethernet Switching IP IP 802.3 802.3 802.3 802.3 802.3 802.3 PHY PHY RFC 2684 RFC 2684 PHY PHY AAL5 AAL5 Same Subnet Then we are Using switches Need to remember protocol stack ATM ATM PHY PHY 802.3: IEEE Media Access Control layer (also know as Ethernet) CPEG 514

Frame Relay and ATM Interworking Frame Relay is an access technology, and it is rarely used on the carrier backbone (core). The backbone is usually the ATM network, slowly migrating to IP/MPLS backbone. How is Frame Relay carried over the ATM network? CPEG 514

ATM/FR IWF Frame Relay Service Specific Convergence Sublayer (FR-SSCS) uses the same PDU format as Frame Relay (Q.922) minus the FCS and FLAG. FR traffic parameters (FECN, BECN, and DI) are maintained in FR-SSCS PDU. FRF.5 supports both one-to-one (one DLCI to one VPI/VCI) and many-to-one (many DLCIs to one VPI/VCI) mappings. Q: is DLCI in FR-SSCS used for addressing? CPEG 514

ATM/FR Network Interworking (FRF.5) p1r1 p1r3 FR (T1) FR (T1) OC-3 ATM Core Network FRF.5 Convert FR frames to ATM cells FRF.5 Convert ATM cells to FR frames CPEG 514

ATM/FR Network Interworking (FRF.5) FR-SSCS: Frame Relay Service Specific Convergence Sublayer IWF: Interworking Function ATM Core p1r1 p1r3 ATM/FR IWF ATM/FR IWF ULP ULP FR FR FR FR-SSCS FR-SSCS FR PHY PHY PHY AAL5 AAL5 PHY ATM ATM PHY PHY CPEG 514

ATM/FR Network Interworking (FRF.8) FR-SSCS: Frame Relay Service Specific Convergence Sublayer IWF: Interworking Function ATM Core p1r1 p1r3 FR ATM ATM ATM/FR IWF IP IP RFC2427 (FRF .8) FR FR FR-SSCS RFC2684 PHY PHY AAL5 AAL5 ATM ATM ATM PHY PHY PHY CPEG 514