Lecture 11 Asynchronous Transfer Mode ()
Outline Introduction Virtual Circuit Setup PVC vs. SVC Quality of Service and Congestion Control IP over and Frame Relay interworking
Network (integrated voice, video, and data services) Private Carrier to carrier Is not really common Integrated via IP
Standards ITU-T, 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 ) LAN Emulation (LANE) Multiprotocol over (MPoA)
Synchronous vs. Asynchronous - cell switching technology (asynchronous) NO clock synch between xmt/rcv TDM circuit switching technology (synchronous) clock synch between xmt/rcv is more efficient than TDM. (why?) TDM: dedicated time slots. : time slots are available on demand with information identifying the destination address of the transmission contained in the header of each cell.
Network Components? Network If i/f is not, the switch would have to do the interworking function
PCI NIC ( to the desktop) OC-3c OC-3 155Mbps Network Price: $605 (cf. how much is Gigabit-E NIC?) http://www.techstore.com/item.aspx?sku=227610td&sgd= 330d316d317d314d315 Q: is there still a market for to the desktop? why? Ethernet is cheaper even at the Gbps, 1Gb Ethernet = $30, 100 BaseT = $7-10
UNI, PNNI, and NNI PNNI NNI? Is there a public? Is there a public Frame Relay? Private NNI (PNNI): connecting two private networks through a public one. or Inside the same carrier s network
Cell Format
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.
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 endpoint and the 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
Virtual Connections switching is based on VPI/VCI However, VPI+VPI is not called address. VPI/VCI has local significance only at the port level of the switch.
Physical Layer over T1 over multiple T1 - Inverse Multiplexing over (IMA) Up 8 T1s as one link using IMA 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
video data audio data Switching 10 20 P1 P3 P4 10 P2 P5 30 11 21 12 30 IN/port VPI/VCI OUT/port VPI/VCI P1 0/10 P3 0/11 P1 0/20 P4 0/21 P2 0/10 P4 0/12 P2 0/30 P5 0/30 For PVC, table done Manually SVC, table is done dynamically/ondemand
Reference Model AAL
Protocol Layers Applications Adaptive Layer (AAL) Layer Physical Layer Layer Physical Layer Applications Adaptive Layer (AAL) Layer Physical Layer End Station Switch End Station
Adaptation Layer 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: AAL Physical Designed for data application Unspecified Bit Rate (UBR)
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?
AAL5 CPCS-PDU Payload Padding (0-47) up to 2 16-1 Carries upper other Protocols inside CPCS payload (i.e. tcp/ip, ethernet why do we need padding? 8 byte trailer CPCS-UU (1) CPI (1) Length (2) CRC (4) Trailer alignment to 32 bit CPCS Payload Not including PAD CPCS: Common Part Convergence Sublayer PDU: Protocol Data Unit UU: User-to-user interface information CPI: Common Part Indicator 48 bytes (0..47) Cell payload To make the Full PDU Divisible by 48 Bytes And divide it Evenly into 48 byte segments
Segmentation and Reassembly (SAR) H:5-bytes H Cell 1 H Cell 2 H Cell n AAL5 Frame
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. NNI: same issue with Frame Relay. NSAP: Network Service Access Point based on E.164 (phone #) 20 bytes
Connection Establishment A B Goal: setup VPI/VCI between any two devices
UNI Signaling (Q.2931) - SVC End Device SETUP PROCEEDING ALERT Switch SETUP PROCEEDING ALERT Switch SETUP ALERT CONNECT End Device VPI/VCI Will be Setup For each Direction CONNECT CONNECT Why do we need this signaling protocol? Connection Established, control, mgmt, Does it look familiar (Q.931)?
Signaling VCI (VPI=0) (UNI) e.g. VPI =0, VCI for connection establishment signaling Q; What is the VPI/VCI in the Q.2931 SETUP message? VPI= 0 VCI = 5
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 attached devices to operate correctly.
PVC or SVC 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)
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 Service Bit Rate CBR PCR SCR VBR UBR
QoS 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.
IP over Protocol (RFC 2684) 192.168.1.10/24 192.168.1.11/24 IP Both and Ethernet Switching IP 802.3 802.3 802.3 802.3 802.3 802.3 PHY PHY RFC 2684 RFC 2684 PHY PHY AAL5 PHY AAL5 PHY Same Subnet Then we are Using switches 802.3: IEEE Media Access Control layer (also know as Ethernet)
Frame Relay and Interworking Frame Relay is an access technology, and it is rarely used on the carrier backbone (core). The backbone is usually the network, slowly migrating to IP/MPLS backbone. How is Frame Relay carried over the network?
/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?
/FR Network Interworking (FRF.5) p1r1 FR (T1) OC-3 FR (T1) p1r3 FRF.5 Convert FR frames to cells Core Network FRF.5 Convert cells to FR frames
/FR Network Interworking (FRF.5) FR-SSCS: Frame Relay Service Specific Convergence Sublayer IWF: Interworking Function p1r1 Core p1r3 /FR IWF /FR IWF ULP FR PHY FR PHY FR-SSCS AAL5 PHY FR-SSCS AAL5 PHY FR PHY ULP FR PHY
/FR Network Interworking (FRF.8) FR-SSCS: Frame Relay Service Specific Convergence Sublayer IWF: Interworking Function Core p1r1 FR p1r3 /FR IWF IP RFC2427 IP FR FR FR-SSCS (FRF.8) RFC2684 PHY PHY AAL5 AAL5 PHY PHY PHY