Voice Solution Architecture

As shown in Figure 11, the two main components of the voice solution are the packet gateway controller (PGC) and the packet gateway (PG) feature on JUNOS routing platforms. The PGC and the PG communicate over the Packet Gateway Control Protocol (PGCP).

Packet Gateway Controller

The PGC is an external device that controls the PG on the router. The PGC requests media services and resource allocation from the PG, and it uses those services and resources for VoIP call signaling setup. The PGC maintains awareness and control over the network's transport resource using PGCP connections with all of the PGs in the network.

Packet Gateway on the JUNOS Routing Platform

The packet gateway feature on the router provides Interconnect-BGF transport services for VoIP sessions. The packet gateway feature consists of:

• Virtual packet gateways (VPGs)—A VPG consists of a packet gateway configuration on the Routing Engine. VPGs are controlled by a PGC. A VPG receives instructions from the PGC and instructs the MultiServices PIC how to treat voice traffic.

  You can configure two VPGs in a router. Each VPG appears to the PGC as a separate network entity, and is connected to a PGC over its own PGCP connection. One VPG can connect to one PGC and one PIC at the same time.

• pgcpd—The packet gateway has a process called pgcpd running in the Routing Engine. The pgcpd process decodes PGCP messages that VPGs receive from the PGC and translates the PGCP messages to IPC messages.
• IPC—The VPGs and the MultiServices PIC communicate by exchanging Inter-Process Communication (IPC) messages over a TCP connection.
• MultiServices PIC—A MultiServices PIC controls voice traffic based on instructions it receives from the VPG.

PGCP

The PG and the PGC communicate over a Packet Gateway Control Protocol (PGCP) connection. PGCP is an H.248 v3 protocol with Juniper Networks extensions.