2-11 ATM Interfaces

  • ATM interfaces use a default MTU of 4470 bytes, a maximum of 2048 virtual circuits (VCs), and 1024 Virtual Circuit Identifiers (VCIs) per Virtual Path Identifier (VPI).

  • ATM cells are 53 bytes in length.

  • Available Bit Rate (ABR). QoS is used for best-effort service. No guarantees of cell delay or loss are made. Transmission rates are adjusted dynamically based on congestion control messages.

  • ILMI (Integrated Local Management Interface) management. PVC can be monitored using the ILMI communication between the router and the ATM switch.

  • OAM (operation, administration, and maintenance) management. OAM loopback cells are used to monitor and manage VCs. With management, protocols in use can become aware of VC status in order to reroute packets quickly.

  • Classical IP over ATM (ClIP) emulates a logical IP subnet over SVCs. One ATM device acts as an ATM ARP server, receiving requests from ATM ARP clients (every other ClIP device) to resolve ATM NSAP addresses. Every ATM ARP client keeps an open connection to the server so that the server can keep a table of IP-to-NSAP addresses.

  • Classical IP over ATM can also use PVCs. However, PVCs inherently support ATM inverse ARP for address resolution. Therefore, no ClIP clients and servers are necessary.

  • Inverse Multiplexing over ATM (IMA) provides a means to carry a single high-speed data stream over multiple lower-speed "bundled" physical connections. As more bandwidth is needed, additional low-speed connections can be added to the bundle.

Configuration

  1. Select an ATM interface.

    1. Use a major interface:

       (global)  interface atm   slot  /   (or  slot  /  port-adapter  /   ) 
    2. Use a subinterface:

       (global)  interface atm   slot  /0.  subinterface  {  point-to-point   multipoint  } 

      The subinterface must be defined as either a point-to-point or point-to-multipoint ( multipoint ) interface.

  2. Configure a PVC.

    1. Use PVC discovery.

      • Enable ILMI:

         (interface)  pvc  [  name  ]  0/16 ilmi  

        A PVC is created with VPI/VCI pair 0/16 for ILMI communication. PVCs are discovered from ILMI information sent from an adjacent ATM switch.

      • Enable PVC discovery:

         (interface)  atm ilmi-pvc-discovery  {  subinterface  } 

        PVCs are discovered and assigned to the major ATM interface. The subinterface keyword causes the PVCs to be assigned to individual ATM subinterfaces, where the PVC VPI number becomes the subinterface number.

      • Assign a protocol address to the interface.

        Any protocol addresses should be configured on the interface or subinterface. As soon as a PVC is discovered, it is assigned to the appropriate interface and receives the protocol address.

        -OR-

    2. Manually configure a PVC on an interface:

       (interface)  pvc  [  name  ]  vpi/vci  

      The PVC can have a name assigned (a text string of up to 16 characters ). The virtual path identifier (vpi) and the virtual channel identifier (vci) must be given.

  3. Configure an SVC.

    1. Configure the ILMI PVC.

      • Select the major ATM interface:

         (global)  interface atm   slot/  

        ILMI can be configured only on the major ATM interface, not on a subinterface.

      • Define the ILMI PVC:

         (interface)  pvc  [  name  ]  0/16 ilmi  

        ILMI communication with an ATM switch always occurs on VPI/VCI 0/16. This PVC can be named if desired.

      • (Optional) Set the ILMI keepalive interval:

         (interface)  atm ilmi-keepalive  [  seconds  ] 

        ILMI keepalives are disabled by default. If enabled, keepalives are sent to the ATM switch at seconds intervals (the default is 3 seconds).

    2. Define the call setup PVC:

       (interface)  pvc  [  name  ]  vpi/vci   qsaal  

      SVC call setup signaling uses QSAAL and operates over the VPI/VCI pair that is configured on the local ATM switch (usually 0/5).

    3. Define the NSAP source address.

      • Use the NSAP prefix from the ATM switch:

         (interface)  atm esi-address   esi.   selector  

        The NSAP prefix (26 hexadecimal digits) is provided by the ATM switch via ILMI. The local router must then add the ESI ( esi, 12 hexadecimal digits) and the selector ( selector, two hexadecimal digits).

        -OR-

      • Define the complete NSAP address:

         (interface)  atm nsap-address   nsap-address  

        The complete source nsap-address is given as a 40-digit hexadecimal string. The address should be in the dotted format pp.pppp.pp.pppppp.pppp.pppp.pppp.eeee.eeee.eeee.ss, where p is an NSAP prefix digit, e is an ESI digit, and s is a selector digit.

    4. Define an SVC:

       (interface)  svc  [  name  ]  nsap   nsap-address  

      The NSAP destination address for the far end of the SVC is defined as nsap-address. The SVC can also be named with a text string (up to 16 characters).

  4. (Optional) Configure VC parameters (PVC or SVC).

    1. (Optional) Create a VC class to use as a template:

       (global)  vc-class atm   class-name  

      If you have several virtual circuits to define with common parameters, you can use a VC class to act as a template. The VC class receives the parameter definitions and is then applied to an ATM interface, a PVC, or an SVC.

      NOTE

      Steps b through g define specific parameters for a virtual circuit. These commands can be applied to a PVC (with the pvc command in Step 2b), an SVC (with the svc command in Step 3d), or a VC class template (with the vc-class atm command in Step 4a). For simplicity, these commands are all shown in atm-vc configuration mode.

    2. Assign a protocol address to a VC:

       (atm-vc)  protocol   protocol  {  address   inarp  } [[  no  ]  broadcast  ] 

      A static mapping is created for the VC and a protocol address. Available protocol names include aarp (AppleTalk ARP), apollo, appletalk, arp (IP ARP), bridge, bstun (Block Serial Tunnel), cdp, clns, clns_es (ISO CLNS end system), clns_is (ISO CLNS intermediate system), compressedtcp, decnet, dlsw (Data Link Switching), ip, ipx, llc2 (Logical Link Control 2), qllc (Qualified Logical Link Control), rsrb (Remote Source Route Bridging), snapshot (snapshot routing), stun (Serial Tunnel), vines, and xns. A protocol address can be given to create a static mapping. For IP and IPX, however, the inarp keyword can be used instead of an address. Inverse ARP will be enabled and used on the VC to resolve protocol addresses.

      The broadcast keyword can be used to cause broadcasts for the configured protocol to be forwarded out the VC.

    3. Set the AAL and encapsulation type:

       (atm-vc)  encapsulation  {  aal5mux   protocol   aal5snap  } 

      The aal5mux keyword is used as a multiplex VC to support a single protocol over a VC. Available protocol values for aal5mux are apollo, appletalk, decnet, frame (Frame Relay-ATM), ip, ipx, vines, voice (voice over ATM), and xns.

      The aal5snap keyword (the default) is used to multiplex more than one protocol over a single VC. Logical Link Control/Subnetwork Access Protocol (LLC/SNAP) is used to encode multiple protocols.

    4. Enable broadcast replication:

       (atm-vc)  broadcast  

      Broadcast replication and forwarding are disabled by default. Broadcast forwarding can be configured on a per-protocol basis with the protocol command (in Step 4b) or for all protocols on a VC with the broadcast command.

    5. Manage VC connectivity (PVCs and SVCs).

      • (PVCs and SVCs) Use end-to-end OAM loopback cells:

         (atm-vc) {  oam-pvc   oam-svc  } [  manage  ] [  frequency  ] 

        End-to-end F5 OAM loopback cells are sent on a VC and are expected to be received from the far end. By default, loopback cells are not generated but are looped back if they are received. The oam-pvc keyword is used for PVCs, and oam-svc is used for SVCs. The manage keyword is used to enable OAM management. When the router sends loopback cells and doesn't receive a reply, the VC is declared down (PVC) or is torn down (SVC). The frequency that loopback cells are sent can be set in seconds (0 to 600; the default is 10 seconds).

      • Tune OAM management operation:

         (atm-vc)  oam retry   up-count down-count retry-freq  

        OAM management flags a PVC as up if up-count loopback cell replies are received (the default is 3). A PVC is declared down or an SVC is torn down if down-count loopback replies are missed (the default is 5). If a loopback reply is missed, OAM management sends loopback cells at intervals of retry-freq (the default is 1 second) to verify the VC state.

      • (PVCs only) Use ILMI management:

         (atm-vc)  ilmi manage  
    6. Set the SVC idle timeout (SVC only):

       (atm-vc)  idle-timeout   seconds  [  minimum-rate  ] 

      If an SVC is idle (no traffic is sent or received) for seconds (the default is 300 seconds), it is torn down. The SVC can also be considered idle if the minimum-rate is configured and the traffic flow falls below that rate (the default is 0 kbps, or no minimum rate).

    7. Define an ATM quality of service (QoS).

      By default, UBR QoS is used at the maximum interface line rate.

      • Use Available Bit Rate QoS (ABR; PVC only):

         (atm-vc)  abr   output-pcr output-mcr  

        The peak cell rate (PCR) can be set to output-pcr (kbps), the maximum allowed cell rate (ACR). The minimum cell rate (MCR) can be set to output-mcr (kbps), the minimum ACR.

      • Use Unspecified Bit Rate QoS (UBR):

         (atm-vc)  ubr   output-pcr  [  input-pcr  ] 

        The output PCR can be set to output-pcr (kbps). For SVCs, the input PCR can be set to input-pcr (kbps).

      • Set the UBR and peak and minimum cell rates:

         (atm-vc)  ubr+   output-pcr output-mcr  [  input-pcr  ] [  input-mcr  ] 

        UBR is enabled, and the peak and minimum cell rates can be given as output-pcr and output-mcr (kbps). For SVCs, the input PCR and MCR can also be set to input-pcr and input-mcr (kbps).

      • Set the Variable Bit Rate-Non Real Time (VBR-NRT):

         (atm-vc)  vbr-nrt   output-pcr output-scr output-mbs  [  input-pcr  ]   [  input-scr  ] [  input-mbs  ] 

        VBR-NRT QoS is enabled. The output peak cell rate (PCR), sustainable cell rate (SCR), and maximum burst cell size (MBS) are set to output-pcr (kbps), output-scr (kbps), and output-mbs (number of cells). For SVCs, the input PCR, SCR, and MBS can also be set.

    8. Apply the VC class to a PVC or SVC:

       (atm-vc)  class   vc-class-name  

      Any parameters that were set for the VC class are inherited by the interface or VC.

  5. (Optional) Use Classical IP and ARP over ATM:

     (interface)  atm arp-server  {  self  [  time-out   minutes  ]  nsap   server-nsap  } 

    The major interface's NSAP address must already be defined. To become an ATM ARP server, the self keyword is used. ARP entries are kept in the server's table for minutes (the default is 20 minutes) before they are verified again or aged out. To become an ATM ARP client, the nsap keyword is used. The NSAP address of the ATM ARP server must be specified as server-nsap.

  6. (Optional) Use Inverse Multiplexing over ATM (IMA).

    1. Configure the individual ATM links.

      • Select an ATM T1/E1 interface:

         (global)  interface atm   slot/port  
      • (Optional) Specify the clock source:

         (controller)  clock source  {  line   internal   loop-timed  } 

        The clock source can be set to the network ( line ), to the free-running internal clock ( internal ), or from the line but decoupled from the system clock ( loop-timed ).

      • (Optional) Set the line build-out (T1 only):

         (interface)  lbo long   dbgain dbloss  

        -OR-

         (interface)  lbo short   length  

        The cable characteristics and line build-out can be set using the long keyword for cables that are longer than 655 feet from the router to the CSU/DSU. The receiver gain, dbgain, is given as gain26 (the default) or gain36 dB. The transmit signal decrease, dbloss, is given as -22.5db, -15db, -7.5db, or 0db (the default).

        For cable lengths shorter than 655 feet, use the short keyword, along with the closest match length in feet: 133, 266, 399, 533, or 655.

      • (Optional) Set the line impedance (E1 only):

         (interface)  line-termination  {  75-ohm   120-ohm  } 

        The E1 impedance can be set to either 75 ohms or 120 ohms (the default), depending on the dongle cable that is attached to the IMA interface.

    2. Assign the individual links to an IMA group :

       (interface)  ima-group   ima-group  

      The T1/E1 interface is assigned or bundled into an IMA group numbered ima-group (0 to 3).

    3. Configure the IMA group.

      • Select the IMA group:

         (global)  interface atm   slot  /  ima   ima-group  

        The IMA group is treated as a logical interface (such as atm 0/ima2). Any ATM- related parameters should be assigned to the IMA group interface: PVCs, SVCs, IP addresses, QoS types, and so forth.

      • Set the IMA clock mode:

         (interface)  ima clock-mode  {  common  [  port  ]  independent  } 

        The transmit clock can be set to the same source for all IMA ports ( common, where port is the port where the clock is derived), or to different sources on the various IMA ports ( independent ). If independent clock sources are used, the clock source must be configured for each individual ATM interface.

      • Set the maximum latency in an IMA group:

         (interface)  ima differential-delay-maximum   milliseconds  

        The maximum latency for the slowest link in the IMA group can be set such that the slowest link can still participate in the group. The latency is given as milliseconds (T1: 25 to 250 msec; the default is 250; E1: 25 to 190 msec; the default is 190).

      • Set the minimum number of active links:

         (interface)  ima active-links-minimum   links  

        An IMA group must have a minimum number of links in operation in order for the IMA interface to stay up. Individual links can drop out of service while the group stays up. The minimum number of links is given as links (1 to 8; the default is 1).

Example

The ATM 7/0 interface is configured with an ILMI PVC so that other PVCs can be discovered automatically from the ATM switch. Each discovered PVC is assigned to a subinterface that is numbered according to the PVC's VPI number. VPI numbers 1 and 2 are preconfigured as subinterfaces atm 7/0.1 and 7/0.2 with IP addresses. As soon as they are discovered, the IP addresses are bound to the active subinterfaces.

Interface ATM 8/0 is configured with a PVC definition for a remote site. The IP address of the interface (192.168.4.1), along with the IP address of the far-end device (192.168.4.2), are given. AAL5mux encapsulation is used to transport only the IP protocol.

Interfaces ATM 9/0, 9/1, and 9/2 are all configured as a single IMA group for inverse multiplexing. A minimum of one link must be up in order for the IMA group to be up. The IMA group is given an IP address and a mapping for the IP address of a far-end router on the PVC. Figure 2-6 shows a network diagram.

Figure 2-6. Network Diagram for the ATM Interface Example

graphics/02fig06.gif

  interface atm 7/0   pvc ILMI 0/16 ilmi   atm ilmi-pvc-discovery subinterface   interface atm 7/0.1   ip address 192.168.17.1 255.255.255.0   interface atm 7/0.2   ip address 192.168.18.1 255.255.255.0   interface atm 8/0   ip address 192.168.4.1 255.255.255.0   pvc RemoteSite 0/27   protocol ip 192.168.4.2 broadcast   encapsulation aal5mux ip   interface atm 9/0   no ip address   ima-group 1   interface atm 9/1   no ip address   ima-group 1   interface atm 9/2   no ip address   ima-group 1   interface atm 9/ima1   ip address 172.16.74.1 255.255.255.0   ima clock-mode common 0   ima active-links-minimum 1   pvc HotsiteA 0/33   protocol ip 172.16.74.67 255.255.255.0  


Cisco Field Manual[c] Router Configuration
Cisco Field Manual[c] Router Configuration
ISBN: 1587050242
EAN: N/A
Year: 2005
Pages: 185

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