8-4 Cisco BPX 8600 Series Reference
BPX Switch and ESP Interfaces
BPX Switch and ESP Interfaces
The BPX switch supports the UNI and NNI interfaces for SVC operations as described in the
following:
• UNI, that is the User Network Interface, is the interface for either ATM or Frame Relay customer
premise equipment (CPE) to the BPX switch. The UNI is defined as any interface between a user
device and an ATM network (i.e., an ATM switch). The UNI defines the signaling method which
the CPE must use to request and setup SVCs through the wide-area ATM network. In addition,
the UNI is used to send messages from the network to the CPE (i.e., user device) on the status of
the circuit and rate control information to prevent network congestion.
For ATM SVCs, the UNI supports either the ATM Forum 3.0 or 3.1 signaling standards as well
as traditional ATM PVCs. (Remember the BPX switch also supports high-speed ATM UNI
ports.)
For Frame Relay, the UNI supports Frame Relay Forum Frame Relay User-to-Network SVC
Implementation Agreement (FRF.4), which specifies the Frame Relay SVC signaling protocols.
BPX switch Frame Relay UNIs (FRSMs) also support traditional Frame Relay PVCs.
• Network-to-Network Interface (NNI). The NNI is the interface to other BPX switch or foreign
ATM Switches. The BPX switch supports Interim Inter-switch Protocol (IISP) 3.0 /3.1 or the
Private Network to Network Interface (PNNI). These NNI interfaces provide the switching and
routing functions between Cisco StrataCom wide-area networks and other networks. Information
passing across a NNI is related to circuit routing and status of the circuit in the adjacent network.
(Note that NNI could refer to both a connection between a BPX switch with ESP, and a
connection between a BPX switch with ESP and a foreign switch.)
Interim Inter-switch Protocol Routing
Interim Inter-switch Protocol (IISP) is an interim static routing protocol defined by the ATM Forum
to provide base level capability until the Private Network to Network Interface (PNNI) was specified.
The IISP provides users with some level of multi-vendor switch interoperability based on the
existing ATM Forum UNI 3.1 specifications. IISP assumes no exchange of routing information
between switching systems. It uses a a fixed routing algorithm with static routes. Routing is done on
a hop-by-hop basis by making a best match of the destination address in the call setup with address
entries in the next hop routing table at a given switching system. Entries in the next hop routing table
are configured by the user.
PNNI
The Private Network to Network Interface standards essentially define two protocols:
• Topology
The Private Network to Network Interface (PNNI) defines a protocol for distributing topology
information between switches and clusters of switches. This information is used to compute
paths through the network. A key feature of the PNNI mechanism is its ability to automatically
configure itself in networks in which the address structure reflects the topology. PNNI topology
and routing are based on the well-known link-state routing technique.
• Signaling
PNNI also defines a second protocol for signaling, that is message flows used to establish
point-to-point connections across the ATM network. This protocol is based on the ATM Forum
UNI signaling, with mechanisms added to support source routing, crankback, and alternate
routing of call setup requests in case of connection setup failure.
